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Currently, microcircuits (domestic and imported) are widely represented on the market, which implement a different set of PWM control functions for switching power supplies. Among microcircuits of this type, KR1114EU4 (manufacturer: Kremniy-Marketing JSC, Russia) is quite popular. Its imported analogue is TL494CN (Texas Instrument). In addition, it is produced by a number of companies under different names. For example, (Japan) produces the IR3M02 microcircuit, (Korea) - KA7500, f. Fujitsu (Japan) МВ3759.
The KR1114EU4 (TL494) chip is a PWM controller for a switching power supply operating at a fixed frequency. The structure of the microcircuit is shown in Fig. 1.
Based on this microcircuit, it is possible to develop control circuits for push-pull and single-cycle switching power supplies. The microcircuit implements a full set of PWM control functions: generation of a reference voltage, amplification of an error signal, generation of a sawtooth voltage, PWM modulation, generation of a 2-cycle output, protection against through currents, etc. It is produced in a 16-pin package, the pinout is shown in Fig. 2.
The built-in ramp voltage generator requires only two external components to set the frequency - Rt and Ct. The frequency of the generator is determined by the formula:
For remote shutdown generator, you can use an external key to close the RT input (pin 6) to the ION output (pin 14) or close the ST input (pin 5) to the common wire.
The chip has a built-in reference voltage source (Uref = 5.0 V), capable of providing a current flow of up to 10 mA to bias the external components of the circuit. The reference voltage has an error of 5% in the operating temperature range from 0 to +70°C.
The block diagram of a pulsed step-down stabilizer is shown in Fig. 3.
The regulating element RE converts the input DC voltage UBX into a sequence of pulses of a certain duration and frequency, and the smoothing filter (inductor L1 and capacitor C1 converts them again into an output constant voltage. Diode VD1 closes the current circuit through the inductor when the RE is turned off. With the help feedback The control circuit of the control system controls the regulating element in such a way that the desired stability of the output voltage Un is ultimately obtained.
Stabilizers, depending on the stabilization method, can be relay, pulse-frequency modulated (PFM) and pulse-width modulated (PWM). In stabilizers with PWM, the pulse frequency (period) is a constant value, and their duration is inversely proportional to the value of the output voltage. Figure 4 shows pulses with different duty cycles Ks.
PWM stabilizers have the following advantages compared to other types of stabilizers:
The conversion frequency is optimal (in terms of efficiency), determined by the internal oscillator of the control circuit and does not depend on any other factors; the pulsation frequency at the load is a constant value, which is convenient for constructing suppression filters; synchronization of conversion frequencies of an unlimited number of stabilizers is possible, which eliminates the occurrence of beats when several stabilizers are powered from a common primary source direct current.
The only thing is that the circuits with PWM differ comparatively complex circuit management. But the development of integrated circuits of the KR1114EU4 type, containing inside most of the control units with PWM, makes it possible to significantly simplify pulse stabilizers.
The circuit of a pulsed step-down stabilizer based on KR1114EU4 is shown in Fig. 5.
The maximum input voltage of the stabilizer is 30 V, it is limited by the maximum permissible drain-source voltage of the p-channel field-effect transistor VT1 (RFP60P03). Resistor R3 and capacitor C5 set the frequency of the sawtooth voltage generator, which is determined by formula (1). From the reference voltage source (pin 14) D1, through a resistive divider R6-R7, part of the reference voltage is supplied to the inverting input of the first error amplifier (pin 2). The feedback signal through the divider R8-R9 is fed to the non-inverting input of the first error amplifier (pin 1) of the microcircuit. The output voltage is regulated by resistor R7. Resistor R5 and capacitor C6 carry out frequency correction of the first amplifier.
It should be noted that the independent output drivers of the microcircuit ensure operation of the output stage in both push-pull and single-cycle modes. In the stabilizer, the output driver of the microcircuit is switched on in single-cycle mode. To do this, pin 13 is connected to the common wire. Two output transistors (their collectors are pins 8, 11, emitters are pins 9, 10) are connected according to a common emitter circuit and operate in parallel. In this case, the output frequency is equal to the generator frequency. The output stage of the microcircuit through a resistive divider
R1-R2 controls the regulator regulator element - field-effect transistor VT1. For more stable operation of the stabilizer on the power supply of the microcircuit (pin 12), the LC filter L1-C2-C3 is included. As can be seen from the diagram, when using KR1114EU4 a relatively small number of external elements. It was possible to reduce switching losses and increase the efficiency of the stabilizer thanks to the use of a Schottky diode (VD2) KD2998B (Unp=0.54 V, Uarb=30 V, lpr=30 A, fmax=200 kHz).
To protect the stabilizer from overcurrent, a self-restoring fuse FU1 MF-R400 is used. The operating principle of such fuses is based on the property of sharply increasing their resistance under the influence of certain value current or temperature environment and automatically restore its properties when these causes are eliminated.
The stabilizer has maximum efficiency (about 90%) at a frequency of 12 kHz, and the efficiency at output power up to 10 W (Uout = 10 V) reaches 93%.
Details and design. Fixed resistors are type S2-ZZN, variable resistors are SP5-3 or SP5-2VA. Capacitors C1 C3, C5-K50-35; C4, C6, C7 -K10-17. Diode VD2 can be replaced with any other Schottky diode with parameters no worse than the above, for example, 20TQ045. The KR1114EU4 chip is replaced by TL494LN or TL494CN. Choke L1 - DM-0.1-80 (0.1 A, 80 µH). Inductor L2 with an inductance of about 220 μH is made on two ring magnetic cores folded together. MP-140 K24x13x6.5 and contains 45 turns of 01.1 mm PETV-2 wire, laid evenly in two layers around the entire perimeter of the ring. Between the layers there are two layers of varnished fabric. LShMS-105-0.06 GOST 2214-78. Self-resetting fuse type MF-RXXX can be selected for each specific case.
The stabilizer is made on a breadboard measuring 55x55 mm. The transistor is installed on a radiator with an area of at least 110 cm2. During installation, it is advisable to separate the common wire of the power part and the common wire of the microcircuit, as well as to minimize the length of the conductors (especially the power part). The stabilizer does not require adjustment if installed correctly.
The total cost of purchased stabilizer radio elements was about $10, and the cost of the VT1 transistor was $3...4. To reduce the cost, instead of the RFP60P03 transistor, you can use the cheaper RFP10P03, but, of course, this will make things worse specifications stabilizer.
The block diagram of a boost-type pulse parallel stabilizer is shown in Fig. 6.
In this stabilizer, the regulating element RE, operating in pulse mode, is connected in parallel with the load Rh. When the RE is open, current from the input source (Ubx) flows through inductor L1, storing energy in it. At the same time, diode VD1 cuts off the load and does not allow capacitor C1 to discharge through the open RE. The current to the load during this period of time comes only from capacitor C1. At the next moment, when the RE is closed, the self-induction emf of inductor L1 is summed with the input voltage, and the energy of the inductor is transferred to the load. In this case, the output voltage will be greater than the input voltage. Unlike the step-down stabilizer (Fig. 1), here the inductor is not a filter element, and the output voltage becomes greater than the input voltage by an amount that is determined by the inductance of the inductor L1 and the duty cycle of the control element RE.
The schematic diagram of a pulse boost stabilizer is shown in Fig. 7.
It uses basically the same electronic components as in the step-down stabilizer circuit (Fig. 5).
Ripple can be reduced by increasing the capacitance of the output filter. For a “softer” start, capacitor C9 is connected between the common wire and the non-inverting input of the first error amplifier (pin 1).
Fixed resistors - S2-ZZN, variable resistors - SP5-3 or SP5-2VA.
Capacitors C1 C3, C5, C6, C9 - K50-35; C4, C7, C8 - K10-17. Transistor VT1 - IRF540 (n-channel field-effect transistor with Uс=100 V, lc=28 A, Rс=0.077 Ohm) - installed on a radiator with an effective surface area of at least 100 cm2. Throttle L2 is the same as in the previous circuit.
It is better to turn on the stabilizer for the first time with a small load (0.1...0.2 A) and a minimum output voltage. Then slowly increase the output voltage and load current to maximum values.
If the step-up and step-down stabilizers operate from the same input voltage Uin, then their conversion frequency can be synchronized. To do this (if the buck stabilizer is the master and the step-up stabilizer is the slave) in the step-up stabilizer you need to remove resistor R3 and capacitor C7, close pins 6 and 14 of the D1 chip, and connect pin 5 of D1 to pin 5 of the D1 chip of the step-down stabilizer.
In a boost-type stabilizer, inductor L2 does not participate in smoothing out the ripple of the output DC voltage, therefore, for high-quality filtering of the output voltage, it is necessary to use filters with sufficiently large values of L and C. This, accordingly, leads to an increase in the weight and dimensions of the filter and the device as a whole. Therefore, the power density of a step-down stabilizer is greater than that of a step-up stabilizer.
I needed to make a speed controller for the propeller. To blow away the smoke from the soldering iron and ventilate the face. Well, just for fun, pack everything into a minimum price. The easiest way to regulate a low-power DC motor, of course, is with a variable resistor, but to find a motor for such a small nominal value, and even the required power, it takes a lot of effort, and it obviously won’t cost ten rubles. Therefore, our choice is PWM + MOSFET.
I took the key IRF630. Why this one MOSFET? Yes, I just got about ten of them from somewhere. So I use it, so I can install something smaller and low-power. Because the current here is unlikely to be more than an ampere, but IRF630 capable of pulling through itself under 9A. But it will be possible to make a whole cascade of fans by connecting them to one fan - enough power :)
Now it's time to think about what we will do PWM. The thought immediately suggests itself - a microcontroller. Take some Tiny12 and do it on it. I threw this thought aside instantly.
- I feel bad about spending such a valuable and expensive part on some kind of fan. I'll find a more interesting task for the microcontroller
- Writing more software for this is doubly frustrating.
- The supply voltage there is 12 volts, lowering it to power the MK to 5 volts is generally lazy
- IRF630 will not open from 5 volts, so you would also have to install a transistor here so that it supplies a high potential to the field gate. Fuck it.
Op amps can be discarded outright. The fact is that the op-amp general purpose already after 8-10 kHz, as a rule, output voltage limit it begins to collapse sharply, and we need to jerk the fieldman. Moreover, at a supersonic frequency, so as not to squeak.
Op-amps without such a drawback cost so much that with this money you can buy a dozen of the coolest microcontrollers. Into the furnace!
What remains are comparators; they do not have the ability of an op-amp to smoothly change the output voltage; they can only compare two voltages and close the output transistor based on the results of the comparison, but they do it quickly and without blocking the characteristics. I rummaged through the bottom of the barrel and couldn’t find any comparators. Ambush! More precisely it was LM339, but it was in a large case, and religion does not allow me to solder a microcircuit for more than 8 legs for such a simple task. It was also a shame to drag myself to the storehouse. What to do?
And then I remembered such a wonderful thing as analog timer - NE555. It is a kind of generator where you can set the frequency, as well as the pulse and pause duration, using a combination of resistors and a capacitor. How much different crap has been done on this timer over its more than thirty-year history... Until now, this microcircuit, despite its venerable age, is printed in millions of copies and is available in almost every warehouse for a price of a few rubles. For example, in our country it costs about 5 rubles. I rummaged through the bottom of the barrel and found a couple of pieces. ABOUT! Let's stir things up right now.
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How it works
If you don’t delve deeply into the structure of the 555 timer, it’s not difficult. Roughly speaking, the timer monitors the voltage on capacitor C1, which it removes from the output THR(THRESHOLD - threshold). As soon as it reaches the maximum (the capacitor is charged), the internal transistor opens. Which closes the output DIS(DISCHARGE - discharge) to ground. At the same time, at the exit OUT a logical zero appears. The capacitor begins to discharge through DIS and when the voltage on it becomes zero (full discharge), the system will switch to the opposite state - at output 1, the transistor is closed. The capacitor begins to charge again and everything repeats again.
The charge of capacitor C1 follows the path: “ R4->upper shoulder R1 ->D2", and the discharge along the way: D1 -> lower shoulder R1 -> DIS. When we turn the variable resistor R1, we change the ratio of the resistances of the upper and lower arms. Which, accordingly, changes the ratio of the pulse length to the pause.
The frequency is set mainly by capacitor C1 and also depends slightly on the value of resistance R1.
Resistor R3 provides a pull-up of the output to high level- so there is an open collector output. Which is not able to independently set a high level.
You can install any diodes, the conductors are approximately the same value, deviations within one order of magnitude do not particularly affect the quality of work. At 4.7 nanofarads set in C1, for example, the frequency drops to 18 kHz, but it is almost inaudible, apparently my hearing is no longer perfect :(
I dug into the bins, which itself calculates the operating parameters of the NE555 timer and assembled a circuit from there, for astable mode with a fill factor of less than 50%, and screwed in a variable resistor instead of R1 and R2, with which I changed the duty cycle of the output signal. You just need to pay attention to the fact that the DIS output (DISCHARGE) is via the internal timer key connected to ground, so it could not be connected directly to the potentiometer, because when twisting the regulator to its extreme position, this pin would land on Vcc. And when the transistor opens, there will be a natural short circuit and the timer with a beautiful zilch will emit magic smoke, on which, as you know, all electronics work. As soon as the smoke leaves the chip, it stops working. That's it. Therefore, we take and add another resistor for one kilo-ohm. It won’t make a difference in regulation, but it will protect against burnout.
No sooner said than done. I etched the board and soldered the components:
Everything is simple from below.
Here I am attaching a signet, in the native Sprint Layout -
And this is the voltage on the engine. A small transition process is visible. You need to put the conduit in parallel at half a microfarad and it will smooth it out.
As you can see, the frequency floats - this is understandable, because in our case the operating frequency depends on the resistors and capacitor, and since they change, the frequency floats away, but this does not matter. Throughout the entire control range, it never enters the audible range. And the entire structure cost 35 rubles, not counting the body. So - Profit!
When working with many different technologies, the question is often: how to manage the power that is available? What to do if it needs to be lowered or raised? The answer to these questions is a PWM regulator. What is he? Where is it used? And how to assemble such a device yourself?
What is pulse width modulation?
Without clarifying the meaning of this term, it makes no sense to continue. So, pulse-width modulation is the process of controlling the power that is supplied to the load, carried out by modifying the duty cycle of the pulses, which is done at a constant frequency. There are several types of pulse width modulation:
1. Analog.
2. Digital.
3. Binary (two-level).
4. Trinity (three-level).
What is a PWM regulator?
Now that we know what pulse width modulation is, we can talk about the main topic of the article. A PWM regulator is used to regulate the supply voltage and to prevent powerful inertial loads in automobiles and motorcycles. This may sound complicated and is best explained with an example. Let’s say you need to make the interior lighting lamps change their brightness not immediately, but gradually. The same applies to side lights, car headlights or fans. This desire can be realized by installing a transistor voltage regulator (parametric or compensation). But when high current it will generate extremely high power and will require the installation of additional large radiators or an addition in the form of a forced cooling system using a small fan removed from the computer device. As you can see, this path entails many consequences that will need to be overcome.
The real salvation from this situation was the PWM controller, which works on powerful field power transistors. They can switch high currents (up to 160 Amps) with only 12-15V gate voltage. It should be noted that the resistance of an open transistor is quite low, and thanks to this, the level of power dissipation can be significantly reduced. To create your own PWM regulator, you will need a control circuit that can provide a voltage difference between the source and gate within the range of 12-15V. If this cannot be achieved, the channel resistance will greatly increase and the power dissipation will increase significantly. And this, in turn, can cause the transistor to overheat and fail.
A whole range of microcircuits for PWM regulators are produced that can withstand an increase in input voltage to a level of 25-30V, despite the fact that the power supply will be only 7-14V. This will allow the output transistor to be turned on in the circuit along with the common drain. This, in turn, is necessary to connect a load with a common minus. Examples include the following samples: L9610, L9611, U6080B ... U6084B. Most loads do not draw more than 10 amps of current, so they cannot cause voltage sags. And as a result, you can use simple circuits without modification in the form of an additional unit that will increase the voltage. And it is precisely these samples of PWM regulators that will be discussed in the article. They can be built on the basis of an asymmetrical or standby multivibrator. It’s worth talking about the PWM engine speed controller. More on this later.
Scheme No. 1
This PWM controller circuit was assembled using CMOS chip inverters. It is a rectangular pulse generator that operates on 2 logic elements. Thanks to the diodes, the time constant of discharge and charge of the frequency-setting capacitor changes separately here. This allows you to change the duty cycle of the output pulses, and as a result, the value of the effective voltage that is present at the load. In this circuit, it is possible to use any inverting CMOS elements, as well as NOR and AND. Examples include K176PU2, K561LN1, K561LA7, K561LE5. You can use other types, but before that you will have to think carefully about how to correctly group their inputs so that they can perform the assigned functionality. The advantages of the scheme are the accessibility and simplicity of the elements. Disadvantages are the difficulty (almost impossibility) of modification and imperfection regarding changing the output voltage range.
Scheme No. 2
Possesses best characteristics than the first sample, but more difficult to implement. Can regulate the effective load voltage in the range of 0-12V, to which it changes from an initial value of 8-12V. The maximum current depends on the type of field-effect transistor and can reach significant values. Given that the output voltage is proportional to the control input, this circuit can be used as part of a control system (to maintain the temperature level).
Reasons for the spread
What attracts car enthusiasts to a PWM controller? It should be noted that there is a desire to increase efficiency when constructing secondary electronic equipment. Thanks to this property this technology can also be found in manufacturing computer monitors, displays in phones, laptops, tablets and similar equipment, and not just in cars. It should also be noted that the this technology when used. Also, if you decide not to buy, but to assemble a PWM controller yourself, you can save money when improving your own car.
Conclusion
Well, you now know what a PWM power regulator is, how it works, and you can even assemble similar devices yourself. Therefore, if you want to experiment with the capabilities of your car, there is only one thing to say about this - do it. Moreover, you can not only use the diagrams presented here, but also significantly modify them if you have the appropriate knowledge and experience. But even if everything doesn’t work out the first time, you can gain a very valuable thing - experience. Who knows where it might come in handy next and how important its presence will be.
Over the past 10-20 years, the number of consumer electronics has increased manifold. A huge variety of electronic components and ready-made modules has appeared. Power requirements have also increased; many require stabilized voltage or stable current.
The driver is most often used as a current stabilizer for LEDs and charging car batteries. Such a source now exists in every LED spotlight, lamp or luminaire. Let's consider all stabilization options, ranging from old and simple to the most effective and modern. They are also called led drivers.
- 1. Types of stabilizers
- 2. Popular models
- 3. Stabilizer for LEDs
- 4. 220V driver
- 5. Current stabilizer, circuit
- 6.LM317
- 7. Adjustable current stabilizer
- 8. Prices in China
Types of stabilizers
Pulse adjustable DC
15 years ago, in my first year, I took tests in the subject “Power Sources” for electronic equipment. From then until today, the LM317 microcircuit and its analogues, which belong to the class of linear stabilizers, remain the most popular and popular.
On this moment There are several types of voltage and current stabilizers:
- linear up to 10A and input voltage up to 40V;
- pulsed with high input voltage, step-down;
- pulse with low input voltage, boost.
On a pulse PWM controller, the characteristics are usually from 3 to 7 amperes. In reality, it depends on the cooling system and efficiency in a particular mode. Boosting a low input voltage makes the output higher. This option is used for power supplies with a low number of volts. For example, in a car, when you need to make 19V or 45V from 12V. With a lowering one it is easier, the high is reduced to the desired level.
Read about all the ways to power LEDs in the article “12 and 220V”. Connection diagrams are described separately, from the simplest ones for 20 rubles to full-fledged units with good functionality.
Based on functionality, they are divided into specialized and universal. Universal modules usually have 2 variable resistances to adjust the Volt and Ampere output. Specialized ones most often do not have building elements and the output values are fixed. Among the specialized ones, current stabilizers for LEDs are common; circuit diagrams are available in large quantities on the Internet.
Popular models
Lm2596
The LM2596 has become popular among pulsed ones, but by modern standards it has low efficiency. If more than 1 amp, then a radiator is required. A small list of similar ones:
- LM317
- LM2576
- LM2577
- LM2596
- MC34063
I’ll add a modern Chinese assortment, which has good characteristics, but is much less common. On Aliexpress, searching by marking helps. The list is compiled by online stores:
- MP2307DN
- XL4015
- MP1584EN
- XL6009
- XL6019
- XL4016
- XL4005
- L7986A
Also suitable for Chinese daytime running lights DRL. Due to their low cost, LEDs are connected through a resistor to a car battery or car network. But the voltage jumps up to 30 volts in pulses. Low-quality LEDs cannot withstand such surges and begin to die. Most likely, you have seen flashing DRLs or running lights where some of the LEDs do not work.
Assembling a circuit with your own hands using these elements will be simple. These are mainly voltage stabilizers, which are switched on in current stabilization mode.
Do not confuse the maximum voltage of the entire block and the maximum voltage of the PWM controller. Low-voltage 20V capacitors can be installed on the block when the pulse microcircuit has an input of up to 35V.
Stabilizer for LEDs
The easiest way to make a current stabilizer for LEDs with your own hands is using LM317; you just need to calculate the resistor for the LED using an online calculator. Food can be used at hand, for example:
- laptop power supply 19V;
- from the printer at 24V and 32V;
- from consumer electronics at 12 volts, 9V.
The advantages of such a converter are low price, easy to buy, minimum parts, high reliability. If the current stabilizer circuit is more complex, then assembling it with your own hands becomes irrational. If you are not a radio amateur, then a pulse current stabilizer is easier and faster to buy. In the future it can be modified to required parameters. You can find out more in the “Ready-made modules” section.
220 V driver
If you are interested in a driver for a 220V LED, then it is better to order or buy it. They have an average manufacturing complexity, but setup will take more time and will require setup experience.
The 220 LED driver can be removed from faulty LED lamps, lamps and spotlights that have a faulty circuit with LEDs. In addition, almost any existing driver can be modified. To do this, find out the model of the PWM controller on which the converter is assembled. Typically, the output parameters are set by a resistor or several. Using the datasheet, look at what the resistance should be to get the required Amps.
If you install an adjustable resistor of the calculated value, then the number of Amperes at the output will be adjustable. Just do not exceed the rated power that was indicated.
Current stabilizer, circuit
I often have to look through the assortment on Aliexpress in search of inexpensive but high-quality modules. The difference in cost can be 2-3 times, time is spent searching minimum price. But thanks to this, I order 2-3 pieces for testing. I buy for reviews and consultations with manufacturers who buy components in China.
In June 2016 optimal choice became universal module on XL4015, the price of which is 110 rubles per free shipping. Its characteristics are suitable for connection powerful LEDs up to 100 watts.
Circuit in driver mode.
IN standard version The XL4015 case is soldered to the board, which serves as a heatsink. To improve cooling, you need to install a radiator on the XL4015 case. Most people put it on top, but the efficiency of such an installation is low. Better system Place cooling at the bottom of the board, opposite the place where the microcircuit is soldered. Ideally, it is better to unsolder it and place it on a full-fledged radiator using thermal paste. The legs will most likely have to be extended with wires. If the controller requires such serious cooling, then the Schottky diode will also need it. It will also have to be placed on the radiator. This modification will significantly increase the reliability of the entire circuit.
In general, the modules do not have protection against incorrect power supply. This instantly disables them, be careful.
LM317
The application (rolling) does not even require any skills or knowledge of electronics. The number of external elements in the circuits is minimal, so this is an affordable option for anyone. Its price is very low, its capabilities and applications have been tested and verified many times. Only she demands good cooling, this is its main drawback. The only thing you should be wary of is low-quality Chinese LM317 microcircuits, which have worse parameters.
Due to the absence of excess noise at the output, linear stabilization microcircuits were used to power high-quality Hi-Fi and Hi-End DACs. For DACs, cleanliness of power plays a huge role, so some use batteries for this.
The maximum power for the LM317 is 1.5 Amps. To increase the number of amperes, you can add a field-effect transistor or a regular one to the circuit. At the output it will be possible to get up to 10A, set by low-resistance resistance. In this diagram, the main load is taken by the KT825 transistor.
Another way is to install an analogue with higher technical characteristics on a larger cooling system.
Adjustable current stabilizer
As a radio amateur with 20 years of experience, I am pleased with the range of ready-made blocks and modules sold. Now you can assemble any device from ready-made blocks in a minimum amount of time.
I began to lose confidence in Chinese products after I saw in “Tank Biathlon” how the wheel of the best Chinese tank fell off.
Chinese online stores have become the leaders in the range of power supplies, DC-DC current converters, and drivers. They have almost any modules available for free sale; if you look harder, you can also find very highly specialized ones. For example, for 10,000 thousand rubles you can assemble a spectrometer worth 100,000 rubles. Where 90% of the price is a markup for the brand and slightly modified Chinese software.
The price starts from 35 rubles. for a DC-DC voltage converter, the driver is more expensive and has two or three trimming resistors instead of one.
For more versatile use, an adjustable driver is better. The main difference is the installation of a variable resistor in the circuit that sets the output amperes. These characteristics can be specified in standard schemes inclusions in the specifications for the microcircuit, datasheet, datasheet.
The weak points of such drivers are the heating of the inductor and the Schottky diode. Depending on the PWM controller model, they can withstand 1A to 3A without additional cooling of the chip. If above 3A, then cooling of the PWM and a powerful Schottky diode is required. The choke is rewound with a thicker wire or replaced with a suitable one.
The efficiency depends on the operating mode and the voltage difference between the input and output. The higher the efficiency, the lower the heating of the stabilizer.
Prices in China
The cost is very low, considering that delivery is included in the price. I used to think that because of a product that costs 30-50 rubles, the Chinese wouldn’t even get dirty; it’s a lot of work for a low income. But as practice has shown, I was wrong. They pack up any cheap nonsense and send it out. It arrives in 98% of cases, and I have been purchasing on Aliexpress for more than 7 years and for large sums, probably already about 1 million rubles.
Therefore, I place an order in advance, usually 2-3 pieces of the same name. I sell what I don’t need on the local forum or Avito, everything sells like hot cakes.
Currently, microcircuits (domestic and imported) are widely represented on the market, which implement a different set of PWM control functions for switching power supplies. Among microcircuits of this type, KR1114EU4 (manufacturer: Kremniy-Marketing JSC, Russia) is quite popular. Its imported analogue is TL494CN (Texas Instrument). In addition, it is produced by a number of companies under different names. For example, (Japan) produces the IR3M02 microcircuit, (Korea) - KA7500, f. Fujitsu (Japan) МВ3759.
The KR1114EU4 (TL494) chip is a PWM controller for a switching power supply operating at a fixed frequency. The structure of the microcircuit is shown in Fig. 1.
Based on this microcircuit, it is possible to develop control circuits for push-pull and single-cycle switching power supplies. The microcircuit implements a full set of PWM control functions: generation of a reference voltage, amplification of an error signal, generation of a sawtooth voltage, PWM modulation, generation of a 2-cycle output, protection against through currents, etc. It is produced in a 16-pin package, the pinout is shown in Fig. 2.
The built-in ramp voltage generator requires only two external components to set the frequency - Rt and Ct. The frequency of the generator is determined by the formula:
To turn off the generator remotely, you can use an external key to short-circuit the RT input (pin 6) to the ION output (pin 14) or short-circuit the ST input (pin 5) to the common wire.
The chip has a built-in reference voltage source (Uref = 5.0 V), capable of providing a current flow of up to 10 mA to bias the external components of the circuit. The reference voltage has an error of 5% in the operating temperature range from 0 to +70°C.
The block diagram of a pulsed step-down stabilizer is shown in Fig. 3.
The regulating element RE converts the input DC voltage UBX into a sequence of pulses of a certain duration and frequency, and the smoothing filter (choke L1 and capacitor C1 converts them again into an output constant voltage. Diode VD1 closes the current circuit through the inductor when the RE is turned off. Using feedback, the control circuit of the control system controls the regulating element in such a way that the resulting stability of the output voltage Un is obtained.
Stabilizers, depending on the stabilization method, can be relay, pulse-frequency modulated (PFM) and pulse-width modulated (PWM). In stabilizers with PWM, the pulse frequency (period) is a constant value, and their duration is inversely proportional to the value of the output voltage. Figure 4 shows pulses with different duty cycles Ks.
PWM stabilizers have the following advantages compared to other types of stabilizers:
- the conversion frequency is optimal (from the point of view of efficiency), determined by the internal oscillator of the control circuit and does not depend on any other factors;
- the pulsation frequency at the load is a constant value, which is convenient for constructing suppression filters;
- It is possible to synchronize the conversion frequencies of an unlimited number of stabilizers, which eliminates the occurrence of beats when several stabilizers are powered from a common primary DC source.
The only difference is that PWM circuits have a relatively complex control circuit. But the development of integrated circuits of the KR1114EU4 type, containing inside most of the control units with PWM, makes it possible to significantly simplify pulse stabilizers.
The circuit of a pulsed step-down stabilizer based on KR1114EU4 is shown in Fig. 5.
The maximum input voltage of the stabilizer is 30 V, it is limited by the maximum permissible drain-source voltage of the p-channel field-effect transistor VT1 (RFP60P03). Resistor R3 and capacitor C5 set the frequency of the sawtooth voltage generator, which is determined by formula (1). From the reference voltage source (pin 14) D1, through a resistive divider R6-R7, part of the reference voltage is supplied to the inverting input of the first error amplifier (pin 2). The feedback signal through the divider R8-R9 is fed to the non-inverting input of the first error amplifier (pin 1) of the microcircuit. The output voltage is regulated by resistor R7. Resistor R5 and capacitor C6 carry out frequency correction of the first amplifier.
It should be noted that the independent output drivers of the microcircuit ensure operation of the output stage in both push-pull and single-cycle modes. In the stabilizer, the output driver of the microcircuit is switched on in single-cycle mode. To do this, pin 13 is connected to the common wire. Two output transistors (their collectors are pins 8, 11, emitters are pins 9, 10) are connected according to a common emitter circuit and operate in parallel. In this case, the output frequency is equal to the generator frequency. The output stage of the microcircuit through a resistive divider
R1-R2 controls the regulator regulator element - field-effect transistor VT1. For more stable operation of the stabilizer on the power supply of the microcircuit (pin 12), the LC filter L1-C2-C3 is included. As can be seen from the diagram, when using KR1114EU4 a relatively small number of external elements is required. It was possible to reduce switching losses and increase the efficiency of the stabilizer thanks to the use of a Schottky diode (VD2) KD2998B (Unp=0.54 V, Uarb=30 V, lpr=30 A, fmax=200 kHz).
To protect the stabilizer from overcurrent, a self-restoring fuse FU1 MF-R400 is used. The operating principle of such fuses is based on the property of sharply increasing their resistance under the influence of a certain current value or ambient temperature and automatically restoring their properties when these causes are eliminated.
The stabilizer has maximum efficiency (about 90%) at a frequency of 12 kHz, and the efficiency at output power up to 10 W (Uout = 10 V) reaches 93%.
Details and design. Fixed resistors are type S2-ZZN, variable resistors are SP5-3 or SP5-2VA. Capacitors C1 C3, C5-K50-35; C4, C6, C7 -K10-17. Diode VD2 can be replaced with any other Schottky diode with parameters no worse than the above, for example, 20TQ045. The KR1114EU4 chip is replaced by TL494LN or TL494CN. Choke L1 - DM-0.1-80 (0.1 A, 80 µH). Inductor L2 with an inductance of about 220 μH is made on two ring magnetic cores folded together. MP-140 K24x13x6.5 and contains 45 turns of 01.1 mm PETV-2 wire, laid evenly in two layers around the entire perimeter of the ring. Between the layers there are two layers of varnished fabric. LShMS-105-0.06 GOST 2214-78. Self-resetting fuse type MF-RXXX can be selected for each specific case.
The stabilizer is made on a breadboard measuring 55x55 mm. The transistor is installed on a radiator with an area of at least 110 cm2. During installation, it is advisable to separate the common wire of the power part and the common wire of the microcircuit, as well as to minimize the length of the conductors (especially the power part). The stabilizer does not require adjustment if installed correctly.
The total cost of purchased stabilizer radio elements was about $10, and the cost of the VT1 transistor was $3...4. To reduce the cost, instead of the RFP60P03 transistor, you can use the cheaper RFP10P03, but, of course, this will somewhat worsen the technical characteristics of the stabilizer.
The block diagram of a boost-type pulse parallel stabilizer is shown in Fig. 6.
In this stabilizer, the regulating element RE, operating in pulse mode, is connected in parallel with the load Rh. When the RE is open, current from the input source (Ubx) flows through inductor L1, storing energy in it. At the same time, diode VD1 cuts off the load and does not allow capacitor C1 to discharge through the open RE. The current to the load during this period of time comes only from capacitor C1. At the next moment, when the RE is closed, the self-induction emf of inductor L1 is summed with the input voltage, and the energy of the inductor is transferred to the load. In this case, the output voltage will be greater than the input voltage. Unlike the step-down stabilizer (Fig. 1), here the inductor is not a filter element, and the output voltage becomes greater than the input voltage by an amount that is determined by the inductance of the inductor L1 and the duty cycle of the control element RE.
The schematic diagram of a pulse boost stabilizer is shown in Fig. 7.
It uses basically the same electronic components as in the step-down stabilizer circuit (Fig. 5).
Ripple can be reduced by increasing the capacitance of the output filter. For a “softer” start, capacitor C9 is connected between the common wire and the non-inverting input of the first error amplifier (pin 1).
Fixed resistors - S2-ZZN, variable resistors - SP5-3 or SP5-2VA.
Capacitors C1 C3, C5, C6, C9 - K50-35; C4, C7, C8 - K10-17. Transistor VT1 - IRF540 (n-channel field-effect transistor with Uсi=100 V, lc=28 A, Rсi=0.077 Ohm) - is installed on a radiator with an effective surface area of at least 100 cm2. Throttle L2 is the same as in the previous circuit.
It is better to turn on the stabilizer for the first time with a small load (0.1...0.2 A) and a minimum output voltage. Then slowly increase the output voltage and load current to maximum values.
If the step-up and step-down stabilizers operate from the same input voltage Uin, then their conversion frequency can be synchronized. To do this (if the buck stabilizer is the master and the step-up stabilizer is the slave) in the step-up stabilizer you need to remove resistor R3 and capacitor C7, close pins 6 and 14 of the D1 chip, and connect pin 5 of D1 to pin 5 of the D1 chip of the step-down stabilizer.
In a boost-type stabilizer, inductor L2 does not participate in smoothing out the ripple of the output DC voltage, therefore, for high-quality filtering of the output voltage, it is necessary to use filters with sufficiently large values of L and C. This, accordingly, leads to an increase in the weight and dimensions of the filter and the device as a whole. Therefore, the power density of a step-down stabilizer is greater than that of a step-up stabilizer.
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