Assessing the characteristics of a particular charger is difficult without understanding how an exemplary charge of a li-ion battery should actually proceed. Therefore, before moving directly to the diagrams, let's remember a little theory.
What are lithium batteries?
Depending on what material the positive electrode of a lithium battery is made of, there are several varieties:
- with lithium cobaltate cathode;
- with a cathode based on lithiated iron phosphate;
- based on nickel-cobalt-aluminium;
- based on nickel-cobalt-manganese.
All of these batteries have their own characteristics, but since these nuances are not of fundamental importance for the general consumer, they will not be considered in this article.
Also, all li-ion batteries are produced in various sizes and form factors. They can be either cased (for example, the popular 18650 today) or laminated or prismatic (gel-polymer batteries). The latter are hermetically sealed bags made of a special film, which contain electrodes and electrode mass.
The most common sizes of li-ion batteries are shown in the table below (all of them have a nominal voltage of 3.7 volts):
| Designation | Standard size | Similar size |
|---|---|---|
| XXYY0, Where XX- indication of diameter in mm, YY- length value in mm, 0 - reflects the design in the form of a cylinder |
10180 | 2/5 AAA |
| 10220 | 1/2 AAA (Ø corresponds to AAA, but half the length) | |
| 10280 | ||
| 10430 | AAA | |
| 10440 | AAA | |
| 14250 | 1/2 AA | |
| 14270 | Ø AA, length CR2 | |
| 14430 | Ø 14 mm (same as AA), but shorter length | |
| 14500 | AA | |
| 14670 | ||
| 15266, 15270 | CR2 | |
| 16340 | CR123 | |
| 17500 | 150S/300S | |
| 17670 | 2xCR123 (or 168S/600S) | |
| 18350 | ||
| 18490 | ||
| 18500 | 2xCR123 (or 150A/300P) | |
| 18650 | 2xCR123 (or 168A/600P) | |
| 18700 | ||
| 22650 | ||
| 25500 | ||
| 26500 | WITH | |
| 26650 | ||
| 32650 | ||
| 33600 | D | |
| 42120 |
Internal electrochemical processes proceed in the same way and do not depend on the form factor and design of the battery, so everything said below applies equally to all lithium batteries.
How to properly charge lithium-ion batteries
The most correct way to charge lithium batteries is a charge in two stages. This is the method Sony uses in all of its chargers. Despite a more complex charge controller, this ensures a more complete charge of li-ion batteries without reducing their service life.
Here we are talking about a two-stage charge profile for lithium batteries, abbreviated as CC/CV (constant current, constant voltage). There are also options with pulse and step currents, but they are not discussed in this article. You can read more about charging with pulsed current.
So, let's look at both stages of charging in more detail.
1. At the first stage A constant charging current must be ensured. The current value is 0.2-0.5C. For accelerated charging, it is allowed to increase the current to 0.5-1.0C (where C is the battery capacity).
For example, for a battery with a capacity of 3000 mAh, the nominal charge current at the first stage is 600-1500 mA, and the accelerated charge current can be in the range of 1.5-3A.
To ensure a constant charging current of a given value, the charger circuit must be able to increase the voltage at the battery terminals. In fact, at the first stage the charger works as a classic current stabilizer.
Important: If you plan to charge batteries with a built-in protection board (PCB), then when designing the charger circuit you need to make sure that the open circuit voltage of the circuit can never exceed 6-7 volts. Otherwise, the protection board may be damaged.
At the moment when the voltage on the battery rises to 4.2 volts, the battery will gain approximately 70-80% of its capacity (the specific capacity value will depend on the charging current: with accelerated charging it will be a little less, with a nominal charge - a little more). This moment marks the end of the first stage of charging and serves as a signal for the transition to the second (and final) stage.
2. Second charge stage- this is charging the battery with a constant voltage, but a gradually decreasing (falling) current.
At this stage, the charger maintains a voltage of 4.15-4.25 volts on the battery and controls the current value.
As the capacity increases, the charging current will decrease. As soon as its value decreases to 0.05-0.01C, the charging process is considered complete.
An important nuance of the correct charger operation is its complete disconnection from the battery after charging is complete. This is due to the fact that for lithium batteries it is extremely undesirable for them to remain under increased voltage, which usually provides the charger (i.e. 4.18-4.24 volts). This leads to accelerated degradation of the chemical composition of the battery and, as a consequence, a decrease in its capacity. Long-term stay means tens of hours or more.
During the second stage of charging, the battery manages to gain approximately 0.1-0.15 more of its capacity. The total battery charge thus reaches 90-95%, which is an excellent indicator.
We looked at two main stages of charging. However, coverage of the issue of charging lithium batteries would be incomplete if another charging stage were not mentioned - the so-called. precharge.
Preliminary charge stage (precharge)- this stage is used only for deeply discharged batteries (below 2.5 V) to bring them to normal operating mode.
At this stage, the charge is provided with a reduced constant current until the battery voltage reaches 2.8 V.
The preliminary stage is necessary to prevent swelling and depressurization (or even explosion with fire) of damaged batteries that have, for example, an internal short circuit between the electrodes. If a large charge current is immediately passed through such a battery, this will inevitably lead to its heating, and then it depends.
Another benefit of precharging is pre-warming the battery, which is important when charging at low temperatures environment(in an unheated room during the cold season).
Intelligent charging must be able to monitor the voltage on the battery during the preliminary charging phase and, in case the voltage for a long time does not rise, conclude that the battery is faulty.
All charge stages lithium ion battery(including the precharge stage) are schematically depicted in this graph: 
Exceeding the rated charging voltage by 0.15V can reduce the battery life by half. Lowering the charge voltage by 0.1 volt reduces the capacity of a charged battery by about 10%, but significantly extends its service life. The voltage of a fully charged battery after removing it from the charger is 4.1-4.15 volts.
Let me summarize the above and outline the main points:
1. What current should I use to charge a li-ion battery (for example, 18650 or any other)?
The current will depend on how quickly you would like to charge it and can range from 0.2C to 1C.
For example, for a battery size 18650 with a capacity of 3400 mAh, the minimum charge current is 680 mA, and the maximum is 3400 mA.
2. How long does it take to charge, for example, the same rechargeable batteries 18650?
The charging time directly depends on the charging current and is calculated using the formula:
T = C / I charge.
For example, the charging time of our 3400 mAh battery with a current of 1A will be about 3.5 hours.
3. How to properly charge a lithium polymer battery?
All lithium batteries charge the same way. It doesn't matter whether it is lithium polymer or lithium ion. For us, consumers, there is no difference.
What is a protection board?
The protection board (or PCB - power control board) is designed to protect against short circuit, overcharge and overdischarge of the lithium battery. As a rule, overheating protection is also built into the protection modules.
For safety reasons, it is prohibited to use lithium batteries in household appliances unless they have a built-in protection board. That's why all cell phone batteries always have a PCB board. The battery output terminals are located directly on the board: 
These boards use a six-legged charge controller on a specialized device (JW01, JW11, K091, G2J, G3J, S8210, S8261, NE57600 and other analogues). The task of this controller is to disconnect the battery from the load when the battery is completely discharged and disconnect the battery from charging when it reaches 4.25V.
Here, for example, is a diagram of the BP-6M battery protection board that was supplied with old Nokia phones: 
If we talk about 18650, they can be produced either with or without a protection board. The protection module is located near the negative terminal of the battery. 
The board increases the length of the battery by 2-3 mm. 
Batteries without a PCB module are usually included in batteries that come with their own protection circuits.
Any battery with protection can easily turn into a battery without protection; you just need to gut it. 
Today, the maximum capacity of the 18650 battery is 3400 mAh. Batteries with protection must have a corresponding designation on the case ("Protected"). 
Do not confuse the PCB board with the PCM module (PCM - power charge module). If the former serve only the purpose of protecting the battery, then the latter are intended to control the charging process - they limit the charge current by given level, control the temperature and, in general, ensure the entire process. The PCM board is what we call a charge controller.
I hope now there are no questions left, how to charge an 18650 battery or any other lithium battery? Then we move on to a small selection of ready-made circuit solutions for chargers (the same charge controllers).
Charging schemes for li-ion batteries
All circuits are suitable for charging any lithium battery; all that remains is to decide on the charging current and the element base.
LM317
Diagram of a simple charger based on the LM317 chip with a charge indicator: 
The circuit is the simplest, the whole setup comes down to setting the output voltage to 4.2 volts using trimming resistor R8 (without a connected battery!) and setting the charging current by selecting resistors R4, R6. The power of resistor R1 is at least 1 Watt.
As soon as the LED goes out, the charging process can be considered completed (the charging current will never decrease to zero). It is not recommended to keep the battery on this charge for a long time after it is fully charged.
The lm317 microcircuit is widely used in various voltage and current stabilizers (depending on the connection circuit). It is sold on every corner and costs pennies (you can take 10 pieces for only 55 rubles).
LM317 comes in different housings: 
Pin assignment (pinout): 
Analogues of the LM317 chip are: GL317, SG31, SG317, UC317T, ECG1900, LM31MDT, SP900, KR142EN12, KR1157EN1 (the last two are domestically produced).
The charging current can be increased to 3A if you take LM350 instead of LM317. It will, however, be more expensive - 11 rubles/piece.
The printed circuit board and circuit assembly are shown below: 
The old Soviet transistor KT361 can be replaced with similar to p-n-p transistor (for example, KT3107, KT3108 or bourgeois 2N5086, 2SA733, BC308A). It can be removed altogether if the charge indicator is not needed.
Disadvantage of the circuit: the supply voltage must be in the range of 8-12V. This is due to the fact that for normal operation of the LM317 chip, the difference between the battery voltage and the supply voltage must be at least 4.25 Volts. Thus, it will not be possible to power it from the USB port.
MAX1555 or MAX1551
MAX1551/MAX1555 are specialized chargers for Li+ batteries, capable of operating from USB or from a separate power adapter (for example, a phone charger).
The only difference between these microcircuits is that MAX1555 produces a signal to indicate the charging process, and MAX1551 produces a signal that the power is on. Those. 1555 is still preferable in most cases, so 1551 is now difficult to find on sale.
A detailed description of these microcircuits from the manufacturer is.
The maximum input voltage from the DC adapter is 7 V, when powered by USB - 6 V. When the supply voltage drops to 3.52 V, the microcircuit turns off and charging stops.
The microcircuit itself detects at which input the supply voltage is present and connects to it. If the power is supplied via the USB bus, then the maximum charging current is limited to 100 mA - this allows you to plug the charger into the USB port of any computer without fear of burning the south bridge.
When powered by a separate power supply, the typical charging current is 280 mA.
The chips have built-in overheating protection. But even in this case, the circuit continues to operate, reducing the charge current by 17 mA for each degree above 110 ° C.
There is a pre-charge function (see above): as long as the battery voltage is below 3V, the microcircuit limits the charge current to 40 mA.
The microcircuit has 5 pins. Here is a typical connection diagram: 
If there is a guarantee that the voltage at the output of your adapter cannot under any circumstances exceed 7 volts, then you can do without the 7805 stabilizer.
The USB charging option can be assembled, for example, on this one. 
The microcircuit does not require either external diodes or external transistors. In general, of course, gorgeous little things! Only they are too small and inconvenient to solder. And they are also expensive ().
LP2951
The LP2951 stabilizer is manufactured by National Semiconductors (). It provides the implementation of a built-in current limiting function and allows you to generate a stable charge voltage level for a lithium-ion battery at the output of the circuit.
The charge voltage is 4.08 - 4.26 volts and is set by resistor R3 when the battery is disconnected. The voltage is kept very accurately.
The charge current is 150 - 300mA, this value is limited by the internal circuits of the LP2951 chip (depending on the manufacturer).
Use the diode with a small reverse current. For example, it can be any of the 1N400X series that you can purchase. The diode is used as a blocking diode to prevent reverse current from the battery into the LP2951 chip when the input voltage is turned off. 
This charger produces a fairly low charging current, so any 18650 battery can charge overnight.
The microcircuit can be purchased both in a DIP package and in a SOIC package (costs about 10 rubles per piece).
MCP73831
The chip allows you to create the right chargers, and it’s also cheaper than the much-hyped MAX1555. 
A typical connection diagram is taken from: 
An important advantage of the circuit is the absence of low-resistance powerful resistors that limit the charge current. Here the current is set by a resistor connected to the 5th pin of the microcircuit. Its resistance should be in the range of 2-10 kOhm.
The assembled charger looks like this: 
The microcircuit heats up quite well during operation, but this does not seem to bother it. It fulfills its function.
Here is another PCB option with smd led and micro USB connector: 
LTC4054 (STC4054)
Very simple circuit, great option! Allows charging with current up to 800 mA (see). True, it tends to get very hot, but in this case the built-in overheating protection reduces the current. 
The circuit can be significantly simplified by throwing out one or even both LEDs with a transistor. Then it will look like this (you must admit, it couldn’t be simpler: a couple of resistors and one condenser): 
One of the printed circuit board options is available at . The board is designed for elements of standard size 0805.
I=1000/R. You shouldn’t set a high current right away; first see how hot the microcircuit gets. For my purposes, I took a 2.7 kOhm resistor, and the charge current turned out to be about 360 mA.
It is unlikely that it will be possible to adapt a radiator to this microcircuit, and it is not a fact that it will be effective due to the high thermal resistance of the crystal-case junction. The manufacturer recommends making the heat sink “through the leads” - making the traces as thick as possible and leaving the foil under the chip body. In general, the more “earth” foil left, the better.
By the way, most of the heat is dissipated through the 3rd leg, so you can make this trace very wide and thick (fill it with excess solder). 
The LTC4054 chip package may be labeled LTH7 or LTADY.
LTH7 differs from LTADY in that the first can lift a very low battery (on which the voltage is less than 2.9 volts), while the second cannot (you need to swing it separately).
The chip turned out to be very successful, so it has a bunch of analogues: STC4054, MCP73831, TB4054, QX4054, TP4054, SGM4054, ACE4054, LP4054, U4054, BL4054, WPM4054, IT4504, Y1880, PT6102, PT6181, VS6102 , HX6001, LC6000, LN5060, CX9058, EC49016, CYT5026, Q7051. Before using any of the analogues, check the datasheets.
TP4056
The microcircuit is made in a SOP-8 housing (see), it has a metal heat sink on its belly that is not connected to the contacts, which allows for more efficient heat removal. Allows you to charge the battery with a current of up to 1A (the current depends on the current-setting resistor). 
The connection diagram requires the bare minimum of hanging elements: 
The circuit implements the classical charging process - first charging with a constant current, then with a constant voltage and a falling current. Everything is scientific. If you look at charging step by step, you can distinguish several stages:
- Monitoring the voltage of the connected battery (this happens all the time).
- Precharge phase (if the battery is discharged below 2.9 V). Charge with a current of 1/10 from the one programmed by the resistor R prog (100 mA at R prog = 1.2 kOhm) to a level of 2.9 V.
- Charging with a maximum constant current (1000 mA at R prog = 1.2 kOhm);
- When the battery reaches 4.2 V, the voltage on the battery is fixed at this level. A gradual decrease in the charging current begins.
- When the current reaches 1/10 of the one programmed by the resistor R prog (100 mA at R prog = 1.2 kOhm) Charger turns off.
- After charging is complete, the controller continues monitoring the battery voltage (see point 1). The current consumed by the monitoring circuit is 2-3 µA. After the voltage drops to 4.0V, charging starts again. And so on in a circle.
The charge current (in amperes) is calculated by the formula I=1200/R prog. The permissible maximum is 1000 mA.
A real charging test with a 3400 mAh 18650 battery is shown in the graph: 
The advantage of the microcircuit is that the charge current is set by just one resistor. Powerful low-resistance resistors are not required. Plus there is an indicator of the charging process, as well as an indication of the end of charging. When the battery is not connected, the indicator blinks every few seconds.
The supply voltage of the circuit should be within 4.5...8 volts. The closer to 4.5V, the better (so the chip heats up less).
The first leg is used to connect a temperature sensor built into the lithium-ion battery (usually the middle terminal of a cell phone battery). If the output voltage is below 45% or above 80% of the supply voltage, charging is suspended. If you don't need temperature control, just plant that foot on the ground.
Attention! This circuit has one significant drawback: the absence of a battery reverse polarity protection circuit. In this case, the controller is guaranteed to burn out due to exceeding the maximum current. In this case, the supply voltage of the circuit directly goes to the battery, which is very dangerous.
The signet is simple and can be done in an hour on your knee. If time is of the essence, you can order ready-made modules. Some manufacturers of ready-made modules add protection against overcurrent and overdischarge (for example, you can choose which board you need - with or without protection, and with which connector). 
You can also find ready-made boards with a contact for a temperature sensor. Or even a charging module with several parallel TP4056 microcircuits to increase the charging current and with reverse polarity protection (example).
LTC1734
Also a very simple scheme. The charging current is set by resistor R prog (for example, if you install a 3 kOhm resistor, the current will be 500 mA).
Microcircuits are usually marked on the case: LTRG (they can often be found in old Samsung phones). 
A transistor will do just fine any p-n-p, the main thing is that it is designed for a given charging current.
There is no charge indicator on the indicated diagram, but on the LTC1734 it is said that pin “4” (Prog) has two functions - setting the current and monitoring the end of the battery charge. For example, a circuit with control of the end of charge using the LT1716 comparator is shown. 
The LT1716 comparator in this case can be replaced with a cheap LM358.
TL431 + transistor
It is probably difficult to come up with a circuit using more affordable components. The hardest part here is finding the TL431 reference voltage source. But they are so common that they are found almost everywhere (rarely does a power source do without this microcircuit). 
Well, the TIP41 transistor can be replaced with any other one with a suitable collector current. Even the old Soviet KT819, KT805 (or less powerful KT815, KT817) will do.
Setting up the circuit comes down to setting the output voltage (without a battery!!!) using a trim resistor at 4.2 volts. Resistor R1 sets the maximum value of the charging current.
This circuit fully implements the two-stage process of charging lithium batteries - first charging with direct current, then moving to the voltage stabilization phase and smoothly reducing the current to almost zero. The only drawback is the poor repeatability of the circuit (it is capricious in setup and demanding on the components used).
MCP73812
There is another undeservedly neglected microcircuit from Microchip - MCP73812 (see). Based on it, a very budget charging option is obtained (and inexpensive!). The whole body kit is just one resistor!
By the way, the microcircuit is made in a solder-friendly package - SOT23-5. 
The only negative is that it gets very hot and there is no charge indication. It also somehow doesn’t work very reliably if you have a low-power power source (which causes a voltage drop). 
In general, if the charge indication is not important for you, and a current of 500 mA suits you, then the MCP73812 is a very good option.
NCP1835
A fully integrated solution is offered - NCP1835B, providing high stability of the charging voltage (4.2 ±0.05 V).
Perhaps the only drawback of this microcircuit is its too miniature size (DFN-10 case, size 3x3 mm). Not everyone can provide high-quality soldering of such miniature elements. 
Among the undeniable advantages I would like to note the following:
- Minimum number of body parts.
- Possibility of charging a completely discharged battery (precharge current 30 mA);
- Determining the end of charging.
- Programmable charging current - up to 1000 mA.
- Charge and error indication (capable of detecting non-chargeable batteries and signaling this).
- Protection against long-term charging (by changing the capacitance of the capacitor C t, you can set the maximum charging time from 6.6 to 784 minutes).
The cost of the microcircuit is not exactly cheap, but also not so high (~$1) that you can refuse to use it. If you are comfortable with a soldering iron, I would recommend choosing this option.
More detailed description is in .
Can I charge a lithium-ion battery without a controller?
Yes, you can. However, this will require close control of the charging current and voltage.
In general, it will not be possible to charge a battery, for example, our 18650, without a charger. You still need to somehow limit the maximum charge current, so at least the most primitive memory will still be required.
The simplest charger for any lithium battery is a resistor connected in series with the battery: 
The resistance and power dissipation of the resistor depend on the voltage of the power source that will be used for charging.
As an example, let's calculate a resistor for a 5 Volt power supply. We will charge an 18650 battery with a capacity of 2400 mAh.
So, at the very beginning of charging, the voltage drop across the resistor will be:
U r = 5 - 2.8 = 2.2 Volts
Let's say our 5V power supply is rated for a maximum current of 1A. The circuit will consume the highest current at the very beginning of the charge, when the voltage on the battery is minimal and amounts to 2.7-2.8 Volts.
Attention: these calculations do not take into account the possibility that the battery may be very deeply discharged and the voltage on it may be much lower, even to zero.
Thus, the resistor resistance required to limit the current at the very beginning of the charge at 1 Ampere should be:
R = U / I = 2.2 / 1 = 2.2 Ohm
Resistor power dissipation:
P r = I 2 R = 1*1*2.2 = 2.2 W
At the very end of the battery charge, when the voltage on it approaches 4.2 V, the charge current will be:
I charge = (U ip - 4.2) / R = (5 - 4.2) / 2.2 = 0.3 A
That is, as we see, all values do not go beyond the permissible limits for of this battery: the initial current does not exceed the maximum permissible current charge for a given battery (2.4 A), and the final current exceeds the current at which the battery no longer gains capacity (0.24 A).
The main disadvantage of such charging is the need to constantly monitor the voltage on the battery. And manually turn off the charge as soon as the voltage reaches 4.2 Volts. The fact is that lithium batteries tolerate even short-term overvoltage very poorly - the electrode masses begin to quickly degrade, which inevitably leads to loss of capacity. At the same time, all the prerequisites for overheating and depressurization are created.
If your battery has a built-in protection board, which was discussed just above, then everything becomes simpler. When a certain voltage is reached on the battery, the board itself will disconnect it from the charger. However, this charging method has significant disadvantages, which we discussed in.
The protection built into the battery will not allow it to be overcharged under any circumstances. All you have to do is control the charge current so that it does not exceed the permissible values for a given battery (protection boards cannot limit the charge current, unfortunately).
Charging using a laboratory power supply
If you have a power supply with current protection (limitation), then you are saved! Such a power source is already a full-fledged charger that implements the correct charge profile, which we wrote about above (CC/CV).
All you need to do to charge li-ion is set the power supply to 4.2 volts and set the desired current limit. And you can connect the battery.
At first, when the battery is still discharged, laboratory block power supply will operate in current protection mode (i.e. it will stabilize the output current at a given level). Then, when the voltage on the bank rises to the set 4.2V, the power supply will switch to voltage stabilization mode, and the current will begin to drop.
When the current drops to 0.05-0.1C, the battery can be considered fully charged.
As you can see, the laboratory power supply is an almost ideal charger! The only thing it can’t do automatically is make a decision to fully charge the battery and turn off. But this is a small thing that you shouldn’t even pay attention to.
How to charge lithium batteries?
And if we are talking about a disposable battery that is not intended for recharging, then the correct (and only correct) answer to this question is NO.
The fact is that any lithium battery (for example, the common CR2032 in the form of a flat tablet) is characterized by the presence of an internal passivating layer that covers the lithium anode. This layer prevents a chemical reaction between the anode and the electrolyte. And the supply of external current destroys the above protective layer, leading to damage to the battery.
By the way, if we talk about the non-rechargeable CR2032 battery, then the LIR2032, which is very similar to it, is already a full-fledged battery. It can and should be charged. Only its voltage is not 3, but 3.6V.
How to charge lithium batteries (be it a phone battery, 18650 or any other li-ion battery) was discussed at the beginning of the article.
STMicroelectronics' line of ICs designed to build chargers for lithium batteries consists of only eight products, but these products cover the entire range of market needs for such products. The line includes battery charging microcircuits, battery status monitoring microcircuits and battery charge level indication.
In modern mobile electronic devices, even those designed with
Taking into account minimizing energy consumption, the use of non-renewable batteries is becoming a thing of the past. And from an economic point of view - already over a short period of time, the total cost of the required number of disposable batteries will quickly exceed the cost of one battery, and from the point of view of user convenience - it is easier to recharge the battery than to look for where to buy a new battery. Accordingly, battery chargers are becoming a commodity with guaranteed demand. It is not surprising that almost all manufacturers integrated circuits For power supply devices, attention is also paid to the “charging” direction.
Just five years ago, the discussion of microcircuits for charging batteries (Battery Chargers IC) began with a comparison of the main types of batteries - nickel and lithium. But at present, nickel batteries have practically ceased to be used and most manufacturers of charge chips have either completely stopped producing chips for nickel batteries or produce chips that are invariant to battery technology (the so-called Multi-Chemistry IC). The STMicroelectronics product range currently includes only microcircuits designed to work with lithium batteries.
Let us briefly recall the main features of lithium batteries.
Advantages:
. High specific electrical capacity. Typical values are 110...160 W*hour*kg, which is 1.5...2.0 times higher than the same parameter for nickel batteries. Accordingly, with equal dimensions, the capacity of a lithium battery is higher.
. Low self-discharge: approximately 10% per month. In nickel batteries this parameter is 20...30%.
. There is no “memory effect”, making this battery easy to maintain: there is no need to discharge the battery to a minimum before recharging.
Flaws lithium batteries:
. The need for current and voltage protection. In particular, it is necessary to exclude the possibility of short circuiting the battery terminals, supplying voltage with reverse polarity, or overcharging.
. The need for overheating protection: battery heating is higher certain value negatively affects its capacity and service life.
There are two industrial technologies for manufacturing lithium batteries: lithium-ion (Li-Ion) and lithium polymer (Li-Pol). However, since the charging algorithms for these batteries are the same, the charging chips do not separate lithium-ion and lithium-polymer technologies. For this reason, we will skip the discussion of the advantages and disadvantages of Li-Ion and Li-Pol batteries, referring to the literature.
Consider the algorithm for charging lithium batteries presented on Figure 1.
Rice. 1
First phase, the so-called pre-charge, is used only in cases where the battery is very discharged. If the battery voltage
below 2.8 V, then it cannot be immediately charged with the maximum possible current: this will have an extremely negative impact on the battery life. It is necessary to first “recharge” the battery with a low current to approximately 3.0 V, and only after that charging with a maximum current becomes permissible.
Second phase: charger as source direct current. At this stage, the maximum current for the given conditions flows through the battery. At the same time, the battery voltage gradually increases until it reaches a limit value of 4.2 V. Strictly speaking, upon completion of the second stage, the charge can be stopped, but it should be borne in mind that the battery is at this moment charged to approximately 70% of its capacity. Note that in many chargers the maximum current is not supplied immediately, but gradually increases to the maximum over several minutes - a “soft start” mechanism is used.
If it is desirable to charge the battery to capacity values close to 100%, then we move on to the third phase: the charger as a source of constant voltage. At this stage, a constant voltage of 4.2 V is applied to the battery, and the current flowing through the battery decreases from a maximum to some predetermined minimum value during charging. At the moment when the current value decreases to this limit, the battery charge is considered complete and the process ends.
Let us recall that one of the key parameters battery is its capacity (unit of measurement - A*hour). Thus, the typical capacity of a lithium-ion battery of AAA size is 750...1300 mAh. As a derivative of this parameter, the “current 1C” characteristic is used, this is the current value numerically equal to the rated capacity (in the example given - 750...1300 mA). The value of “current 1C” makes sense only as a determination of the maximum current value when charging the battery and the current value at which the charge is considered complete. It is generally accepted that the maximum current value should not exceed 1*1C, and the battery charge can be considered complete when the current decreases to 0.05...0.10*1C. But these are the parameters that can be considered optimal for a particular type of battery. In reality, the same charger can work with batteries various manufacturers and different capacities, while the capacity of a particular battery remains unknown to the charger. Consequently, charging a battery of any capacity will generally not occur in the optimal mode for the battery, but in the mode preset for the charger.
Let's move on to consider the line of charging microcircuits from STMicroelectronics.
Chips STBC08 and STC4054
These microcircuits are fairly simple products for charging lithium batteries. The microcircuits are made in miniature packages such as DFN6 and TSOT23-5L, respectively. This allows these components to be used in mobile devices ah with fairly stringent requirements for weight and size characteristics (for example, Cell Phones, MP3 players). Connection diagrams for STBC08 and STC4054 are presented at Figure 2.
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Despite the limitations imposed by the minimum number of external pins in the packages, the microcircuits have fairly broad functionality:
. There is no need for an external MOSFET, blocking diode or current resistor. As follows from figure 2, the external wiring is limited by a filter capacitor at the input, a programming resistor and two (for STC4054 - one) indicator LEDs.
. The maximum value of the charge current is programmed by the value of the external resistor and can reach a value of 800 mA. The fact of the end of the charge is determined at the moment when, in constant voltage mode, the value of the charging current drops to a value of 0.1*I BAT, that is, it is also set by the value of the external resistor. The maximum charge current is determined from the relationship:
I BAT = (V PROG /R PROG)*1000;
where I BAT is the charge current in Amperes, R PROG is the resistance of the resistor in Ohms, V PROG is the voltage at the output of P ROG equal to 1.0 Volts.
. In constant voltage mode, a stable voltage of 4.2 V is generated at the output with an accuracy of no worse than 1%.
. Charging of heavily discharged batteries automatically begins in pre-charge mode. Until the voltage at the battery output reaches 2.9 V, the charge is carried out with a weak current of 0.1 * I BAT. This method, as already noted, prevents a very likely failure when trying to charge heavily discharged batteries. in the usual way. In addition, the starting value of the charging current is forcibly limited, which also increases the service life of the batteries.
. An automatic trickle charging mode has been implemented - when the battery voltage drops to 4.05 V, the charge cycle will be restarted. This allows you to ensure a constant charge of the battery at a level not lower than 80% of its nominal capacity.
. Protection against overvoltage and overheating. If the input voltage exceeds a certain limit (in particular, 7.2 V) or if the case temperature exceeds 120 ° C, the charger turns off, protecting itself and the battery. Of course, low input voltage protection is also implemented - if the input voltage drops below a certain level (U VLO), the charger will also turn off.
. The ability to connect indication LEDs allows the user to have an idea of the current state of the battery charging process.
Battery charge chips L6924D and L6924U
These microcircuits are devices with greater capabilities compared to STBC08 and STC4054. On Figure 3 presented standard schemes inclusion of L6924D and L6924U chips.
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Let's consider those functional features of the L6924 chips that relate to setting the parameters of the battery charging process:
1. In both modifications it is possible to set the maximum duration of battery charge starting from the moment of switching to DC stabilization mode (the term “mode” is also used fast charging" - Fast charge phase). When entering this mode, a watchdog timer is started, programmed for a certain duration T PRG by the value of the capacitor connected to the T PRG pin. If before this timer is triggered, the battery charge is not stopped according to the standard algorithm (the current flowing through the battery decreases below the I END value), then after the timer is triggered, charging will be interrupted forcibly. Using the same capacitor, the maximum duration of the pre-charging mode is set: it is equal to 1/8 of the duration T PRG. Also, if during this time there is no transition to fast charging mode, the circuit turns off.
2. Pre-charge mode. If for the STBC08 device the current in this mode was set as a value equal to 10% of I BAT, and the switching voltage to DC mode was fixed, then in the L6924U modification this algorithm was preserved unchanged, but in the L6924D chip both of these parameters are set using external resistors connected to inputs I PRE and V PRE.
3. The sign of completion of charging in the third phase (DC voltage stabilization mode) in STBC08 and STC4054 devices was set as a value equal to 10% of I BAT. In L6924 microcircuits, this parameter is programmed by the value of an external resistor connected to the I END pin. In addition, for the L6924D chip, it is possible to reduce the voltage at the V OUT pin from the generally accepted value of 4.2 V to 4.1 V.
4. The value of the maximum charging current I PRG in these microcircuits is set in the traditional way - through the value of an external resistor.
As you can see, in simple “charging” STBC08 and STC4054, only one parameter was set using an external resistor - the charging current. All other parameters were either rigidly fixed or were a function of I BAT. The L6924 chips have the ability to fine-tune several more parameters and, in addition, provide “insurance” for the maximum duration of the battery charging process.
For both modifications of the L6924, two operating modes are provided if the input voltage is generated by the AC/DC network adapter. First - standard mode linear step-down regulator of output voltage. The second is the quasi-pulse regulator mode. In the first case, a current can be supplied to the load, the value of which is slightly less than the value of the input current taken from the adapter. In the DC stabilization mode (second phase - Fast charge phase), the difference between the input voltage and the voltage at the “plus” of the battery is dissipated as thermal energy, as a result of which the dissipated power in this charge phase is maximum. When operating in switching regulator mode, a current whose value is higher than the value of the input current can be supplied to the load. In this case, significantly less energy is lost into heat. This, firstly, reduces the temperature inside the case, and secondly, increases the efficiency of the device. But it should be borne in mind that the accuracy of current stabilization in linear mode equals approximately 1%, and in pulsed mode - about 7%.
The operation of L6924 microcircuits in linear and quasi-pulse modes is illustrated picture 4.
Rice. 4
The L6924U chip, in addition, can operate not from a network adapter, but from a USB port. In this case, the L6924U chip implements some technical solutions, which can further reduce power dissipation by increasing charging duration.
The L6924D and L6924U chips have an additional input for forced charge interruption (that is, load shutdown) SHDN.
In simple charging microcircuits, temperature protection consists of stopping the charge when the temperature inside the microcircuit case rises to 120°C. This, of course, is better than no protection at all, but the value of 120°C on the case is more than conditionally related to the temperature of the battery itself. The L6924 products provide the ability to connect a thermistor directly related to the battery temperature (resistor RT1 in Figure 3). In this case, it becomes possible to set the temperature range in which charging the battery will be possible. On the one hand, it is not recommended to charge lithium batteries at sub-zero temperatures, and on the other hand, it is also highly undesirable if the battery heats up to more than 50°C during charging. The use of a thermistor makes it possible to charge the battery only under favorable temperature conditions.
Naturally, the additional functionality of the L6924D and L6924U chips not only expands the capabilities of the designed device, but also leads to an increase in the area on the board occupied by both the chip body itself and external elements strapping.
Battery charging chips STBC21 and STw4102
This is a further improvement of the L6924 chip. On the one hand, approximately the same functional package is implemented:
. Linear and quasi-pulse mode.
. Thermistor connected to the battery as a key element of temperature protection.
. Ability to set quantitative parameters for all three phases of the charging process.
Some additional features, missing in L6924:
. Reverse polarity protection.
. Short circuit protection.
. A significant difference from the L6924 is the presence of a digital I 2 C interface for setting parameter values and other settings. As a result, more precise settings of the charging process become possible.
The recommended connection diagram for STBC21 is shown in Figure 5. Obviously, in this case, the question of saving board area and strict weight and size characteristics does not arise. But it is also obvious that the use of this microcircuit in small-sized voice recorders, players and mobile phones simple models not expected. Rather, these are batteries for laptops and similar devices, where replacing the battery is an infrequent procedure, but also not cheap.
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ICs STBC21 and STw4102 do not belong to the same family. Despite the fact that their main functionality similar in small details there is a significant amount of variation. The STw4102 chip, for example, provides greater opportunities for “fine” settings of almost all possible parameters; in addition, additional functions battery monitoring, it is possible to use an external MOSFET transistor. However, the target application of both chips is approximately the same.
Control/indication chips
The basis of the line of “battery microcircuits” of any manufacturer is precisely the battery charger microcircuits (Battery Chargers IC), which were discussed above. But many manufacturers supplement the range with “related” microcircuits, which include battery status monitoring microcircuits (Battery Status Monitor) and battery charge level indicating microcircuits (Battery Gas Gauge). In the STMicroelectronics nomenclature, both these roles are performed by the STC3100 and STC3105. The STC3105 connection diagram is shown in Figure 6. From a functional point of view, the microcircuit periodically measures the voltage values at the output of the microcircuit and the current flowing through it. The received and processed data is transmitted to the microcontroller via the I 2 C channel. These microcircuits, on the one hand, can be an effective addition to simple charging microcircuits in applications where there is no point in complicating the charging procedure itself, but it may be useful to expand the control functions over the process. On the other hand, the I 2 C interface assumes the presence of a microcontroller that must receive data and, as a result, make some decision based on it. But in this case, the decision begs to use smart chips STBC21 and STw4102, which already implement some monitoring functions.
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CC/CV controllers
In addition to functionally complete battery charging chips, STMicroelectronics offers a family of CC/CV controller chips, in particular the TSM101x series chips. These chips include a voltage reference and two operational amplifiers, usually with a combined output. On Figure 7 a fragment of a circuit diagram of a network charger for a lithium battery using a TSM1012 controller is presented. The first operational amplifier (CV - Constant Voltage) implements a stabilized direct voltage circuit, and the second (CC - Constant Current) implements a stabilized direct current circuit. The remaining components are typical wiring of a switching power supply and master circuits.
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Recall that the charge cycle of a lithium battery consists of two phases in which the device acts as a constant current source and one phase in which the device acts as a constant voltage source. Of course, designing a charger based on universal “bricks” is a more troublesome and time-consuming task than using specialized circuits. However, in this case it becomes possible to create devices in which some parameters are at a significantly different quality level. For example, the work presents a number of solutions that can significantly reduce the power consumption of a network charger in idle mode. Calculations are given according to which a typical solution provides a total power consumption value of 440 mW. Initial optimization of the circuit using the TMS1011 controller results in a value of 140 mW, and further optimization of the circuit using the TMS1012 controller provides a further reduction in power to 104 mW. Of course, in most cases you can get by and standard solutions, which do not give record, but quite acceptable indicators. However, it is worth keeping in mind the fact that the product line contains components that allow, if necessary, to develop a device with “elite” values of individual parameters.
DC/DC converters for solar panels
For most battery-powered mobile devices, the charger is designed as a stand-alone device for the household network alternating current. That is, in any case, an AC/DC converter is required to generate a DC input voltage for the battery charging microcircuit. STMicroelectronics offers a wide range of such converters, as well as proven design technology network adapters. However, network chargers - although the most common, are not the only ones Possible Solution. Solar energy stored in solar panels can be used as an energy source. The STMicroelectronics product range includes DC/DC converter microcircuits for solar panels using the MPPT (Maximum Power Point Tracking) algorithm maximum power). Without going into specific details, we note that today MPPT technology is the most advanced and efficient technology for solar charge controllers. Calculating the maximum charging efficiency point from a solar module allows you to increase the efficiency of solar energy generation by up to 25...30% compared to other types of controllers. IN currently STMicroelectronics produces two microcircuits - SPV1020 and SPV1040.
The first works with a chain of series-connected solar cells with an output voltage in the range of 6.5...40 V. The second, as a rule, with one battery with a voltage of up to 5.5 V. STMicroelectronics has also released a demo board STEVAL-ISV012V1, which includes itself MPPT DC/DC converter SPV1040 and charge chip L6924D.
Figure 8 shows a demo board.
The main problem when creating a portable device with an autonomous power source in the form of a battery is the charger, or more precisely, the element base that can be built into the device.
The main selection criteria are a minimum of body kit, 5V power supply, indication output, charging current within 500mA with the possibility of installation, low cost. It seems that the requirements are not so colossal, but each memory chip has its own disadvantages, which I will try to describe.
It all started with the BQ2057 chip (PDF). I do not provide a connection diagram, since there is a datasheet. First impressions - it works. The cost is not that high, but the presence of a large number of body parts (especially the current sensor) is scary.
| BQ2057 |
- The maximum charging current depends on the output transistor and shunt.
- There is a charge indication.
Minuses:
- The TSSOP-8 case is not very convenient for soldering.
- Lots of body parts.
Verdict - ideal for external chargers, or devices with large battery capacity for high current charge.
The next chip in this epic was NCP1835 (PDF).
For some time this chip was the ideal option for me. More than one design with this microcircuit was assembled until they ran out.
The characteristics and diagram can again be viewed in the datasheet.
 |
| NCP1835 |
- Availability of charge indication.
- Charging timer with error indication.
- Minimum body kit parts.
Minuses:
- The body is smaller than the previous one - DFN-10 (3x3mm).
Verdict - an ideal option for miniature devices, but it complicates board manufacturing and installation, and the price is not the lowest, but quite acceptable.
After this microcircuit, I became acquainted with the products of the Microchip company - MCP73812 (PDF). An excellent, inexpensive microcircuit with a resistor-shaped body kit, and the fly in the ointment is the lack of indication, and in my opinion it gets quite hot and I didn’t really like it.
 |
| MCP73812 |
- Minimum body kit parts.
- Select the charging current using an external resistor (not a shunt).
- Housing SOT23-5.
Minuses:
- Lack of indication.
- Not very stable operation during power loss.
Verdict - it exists, and is suitable for the simplest circuits where there is no need to indicate the charging process.
And now here’s where my search has stopped for now about the reason for satisfying all my requests (naturally in terms of memory) - a microcircuit from ST, a cheaper option with the same functionality as the LTC4054 - STC4054 (PDF).
At a price that differs 6 times from the original (up to $1), it meets all my needs and fits perfectly into all designs.
 |
| STC4054 |
 |
| LIR14500 |
Pros:
- Minimum body kit parts.
- Select the charging current using an external resistor (not a shunt).
- Housing SOT23-5.
- Availability of charge indication.
- Charge current up to 800mA.
Minuses:
- In my understanding, there are none.
Verdict - ideal ratio of price, functionality, size, simplicity of the circuit.
This chip was used to assemble the memory for the LIR14500 for my
I liked the small microcircuits for simple chargers. I bought them from our local offline store, but as luck would have it, they ran out there, they took a long time to be transported from somewhere else. Looking at this situation, I decided to order them in small bulk, since the microcircuits are quite good, and I liked the way they work.
Description and comparison under the cut.
It was not in vain that I wrote about comparison in the title, since during the journey the dog could have grown up. Microphones appeared in the store, I bought several pieces and decided to compare them.
The review will not have a lot of text, but quite a lot of photographs.
But I’ll start, as always, with how it came to me.
It came complete with other various parts, the mikruhi themselves were packed in a bag with a latch and a sticker with the name. 
This microcircuit is a charger microcircuit for lithium batteries with a charge end voltage of 4.2 Volts.
It can charge batteries with a current of up to 800mA.
The current value is set by changing the value of the external resistor.
It also supports the charge function with a small current if the battery is very discharged (voltage lower than 2.9 Volts).
When charging to a voltage of 4.2 Volts and the charging current drops below 1/10 of the set value, the microcircuit turns off the charge. If the voltage drops to 4.05 Volts, it will again go into charging mode.
There is also an output for connecting an indication LED.
More information can be found in, this microcircuit has a much cheaper one.
Moreover, it is cheaper here, on Ali it’s the other way around.
Actually, for comparison, I bought an analogue. 
But imagine my surprise when the LTC and STC microcircuits turned out to be completely identical in appearance, both were labeled LTC4054. 
Well, maybe it’s even more interesting.
As everyone understands, it’s not that easy to check a microcircuit; it also needs a harness from other radio components, preferably a board, etc.
And just then a friend asked me to repair (although in this context it would be more likely to remake) a charger for 18650 batteries.
The original one burned out, and the charging current was too low.
In general, for testing we must first assemble what we will test on.
I drew the board from the datasheet, even without a diagram, but I’ll give the diagram here for convenience. 
Well actually printed circuit board. There are no diodes VD1 and VD2 on the board; they were added after everything. 
All this was printed out and transferred to a piece of textolite.
To save money, I made another board using scraps; a review with its participation will follow later. 
Well, the printed circuit board was actually made and the necessary parts were selected. 
And I will remake such a charger, it is probably very well known to readers. 
There's a lot inside him complex circuit, consisting of a connector, LED, resistor and specially trained wires that allow you to equalize the charge on the batteries.
Just kidding, the charger is located in a block that is plugged into an outlet, but here there are simply 2 batteries connected in parallel and an LED constantly connected to the batteries.
We'll return to our original charger later. 
I soldered the scarf, picked out the original board with contacts, soldered the contacts themselves with the springs, they will still be useful. 
I drilled a couple of new holes, in the middle there will be an LED indicating the device is turned on, in the sides - the charging process. 
Soldered into new board contacts with springs, as well as LEDs.
It is convenient to first insert the LEDs into the board, then carefully install the board in its original place, and only after that solder it, then they will stand evenly and equally. 
The board is installed in place, the power cable is soldered.
The printed circuit board itself was developed for three power supply options.
2 options with a MiniUSB connector, but in installation options on different sides of the board and under the cable.
In this case, at first I didn’t know how long the cable would be needed, so I soldered a short one.
I also soldered the wires going to the positive contacts of the batteries.
Now they go through separate wires, one for each battery. 
Here's how it turned out from above. 
Well, now let's move on to testing
On the left side of the board I installed the mikruha bought on Ali, on the right I bought it offline.
Accordingly, they will be located mirrored on top.
First, mikruha with Ali.
Charge current. 
Now purchased offline. 
Short circuit current.
Likewise, first with Ali. 
Now from offline. 
There is complete identity of the microcircuits, which is good news :)
It was noticed that at 4.8 Volts the charge current is 600 mA, at 5 Volts it drops to 500, but this was checked after warming up, maybe this is how the overheating protection works, I haven’t figured it out yet, but the microcircuits behave approximately the same.
Well, now a little about the charging process and finalizing the rework (yes, even this happens).
From the very beginning I was thinking of just setting the LED to indicate the on state.
Everything seems simple and obvious.
But as always, I wanted more.
I decided that it would be better if it was extinguished during the charging process.
I soldered a couple of diodes (vd1 and vd2 on the diagram), but got a small bummer, the LED indicating the charging mode shines even when there is no battery.
Or rather, it doesn’t shine, but flickers quickly, I added a 47 µF capacitor in parallel to the battery terminals, after which it began to flash very briefly, almost imperceptibly.
This is exactly the hysteresis of switching on recharging if the voltage drops below 4.05 Volts.
In general, after this modification everything was fine.
The battery is charging, the red light is on, the green light is not on, and the LED does not light up where there is no battery. 
The battery is fully charged. 
When turned off, the microcircuit does not pass voltage to the power connector, and is not afraid of shorting this connector; therefore, it does not discharge the battery to its LED. 
Not without measuring the temperature.
I got just over 62 degrees after 15 minutes of charging. 
Well, this is what a fully finished device looks like.
External changes are minimal, unlike internal ones. A friend had a 5/Volt 2 Ampere power supply, and it was quite good.
The device provides a charge current of 600 mA per channel, the channels are independent. 
Well, this is what the original charger looked like. A friend wanted to ask me to increase the charging current in it. It couldn’t stand even its own, where else to raise it, slag. 
Summary.
In my opinion, for a chip that costs 7 cents it's very good.
The microcircuits are fully functional and are no different from those purchased offline.
I am very pleased, now I have a supply of mikrukhs and don’t have to wait for them to be in the store (they recently went out of sale again).
Of the minuses - This is not a ready-made device, so you will have to etch, solder, etc., but there is a plus: you can make a board for a specific application, rather than using what you have.
Well, in the end, getting a working product made by yourself is cheaper than ready-made boards, and even under your specific conditions.
I almost forgot, datasheet, diagram and trace -
The battery is a common power source for various mobile devices, gadgets, robots... Without it, class portable devices, probably would not exist or would not be recognizable. One of the most modern types of batteries can rightfully be considered lithium-ion and lithium-polymer. But the device has worked, the battery is exhausted, now you need to take advantage of its main difference from simple batteries - charge it.
The article will briefly talk about two common microcircuits (more precisely, about one common LTC4054 and its similar replacement STC4054) for charging single-can Li-ion batteries.
These microcircuits are identical, the only difference is in the manufacturer and price. Another huge plus is the small amount of wiring - only 2 passive components: an input 1 µF capacitor and a current-setting resistor. If desired, you can add an LED - an indicator of the charging process status; on - charging is in progress; off - charging is complete. Supply voltage 4.25-6.5 V, i.e. The charging is powered by the usual 5V, it’s not for nothing that most simple USB-powered chargers are built on the basis of these microcircuits. Charges up to 4.2V. Maximum current 800mA.
The board is based on an LTC4054 or STC4054 charging chip. Input capacitor with a capacity of 1 μF of standard size 0805. Current-setting resistor 0805, resistance is calculated below. And LED 0604 or 0805 with a current-limiting resistor of size 0805 at 680 Ohm.
The resistor (or charge current) is calculated using the following formulas:
Because Vprog=~1V, we get the following simplified formulas
Some calculation examples:
| I, mA | R, kOhm |
| 100 | 10 |
| 212 | 4,7 |
| 500 | 2 |
| 770 | 1,3 |
Finally, a couple of photos of the option homemade USB charging for lithium polymer batteries of a small helicopter.
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