Tl494 laboratory power supply. Scheme of a switching laboratory power supply on TL494

Most modern switching power supplies are made on chips like TL494, which is a pulse PWM controller. The power part is made from powerful elements, such as transistors. The connection circuit of the TL494 is simple, a minimum of additional radio components is required, it is described in detail in the datasheet.

Modification options: TL494CN, TL494CD, TL494IN, TL494C, TL494CI.

I also wrote reviews of other popular ICs.

• 1. Characteristics and functionality
• 2. Analogues
• 3. Typical connection diagrams for power supply on TL494
• 4. Power supply diagrams
• 5. Converting an ATX power supply into a laboratory one
• 6.Datasheet
• 7. Electrical characteristics graphs
• 8. Microcircuit functionality

Characteristics and functionality

The TL494 chip is designed as a PWM controller for switching power supplies, with a fixed operating frequency. To set the operating frequency, two additional external elements are required: a resistor and a capacitor. The chip has a source reference voltage at 5V, the error of which is 5%.

Scope of application specified by the manufacturer:

1. power supplies with a capacity of more than 90W AC-DC with PFC;
2. microwaves;
3. boost converters from 12V to 220V;
4. power supplies for servers;
5. inverters for solar panels;
6. electric bicycles and motorcycles;
7. buck converters;
8. smoke detectors;
9. desktop computers.

Analogs

The most famous analogues of the TL494 chip are the domestic KA7500B, KR1114EU4 from Fairchild, Sharp IR3M02, UA494, Fujitsu MB3759. The connection diagram is similar, the pinout may be different.

The new TL594 is an analogue of the TL494 with increased comparator accuracy. TL598 is an analogue of TL594 with a repeater at the output.

Typical connection diagrams for power supply on TL494

The basic circuits for switching on the TL494 are collected from datasheets from various manufacturers. They can serve as the basis for the development of similar devices with similar functionality.

Power supply circuits

Complex circuits I will not consider TL494 switching power supplies. They require a lot of parts and time, so making them yourself is not rational. It’s easier to buy a ready-made similar module from the Chinese for 300-500 rubles.

When assembling boost voltage converters, pay special attention to cooling the output power transistors. For 200W the output current will be about 1A, relatively not much. Testing for stability of operation should be carried out with the maximum permissible load. It is best to form the required load from 220 volt incandescent lamps with a power of 20w, 40w, 60w, 100w. Do not overheat the transistors by more than 100 degrees. Follow safety precautions when working with high voltage. Try it on seven times, turn it on once.

The boost converter on the TL494 requires virtually no adjustment and is highly repeatable. Before assembly, check the resistor and capacitor values. The smaller the deviation, the more stable the inverter will operate from 12 to 220 volts.

It is better to control the temperature of transistors using a thermocouple. If the radiator is too small, it is easier to install a fan so as not to install a new radiator.

I had to make a power supply for the TL494 with my own hands for a subwoofer amplifier in a car. At that time, 12V to 220V car inverters were not sold, and the Chinese did not have Aliexpress. As ULF amplifier used a microcircuit TDA series at 80W.

Over the past 5 years, interest in electrically driven technology has increased. This was facilitated by the Chinese who started mass production electric bicycles, modern wheel-motor with high efficiency. I consider two-wheeled and one-wheeled hoverboards to be the best implementation. In 2015, the Chinese company Ninebot bought the American Segway and began producing 50 types of Segway-type electric scooters.

A good control controller is required to control a powerful low voltage motor.

Converting an ATX power supply into a laboratory one

Every radio amateur has a powerful unit ATX power supply from a computer that produces 5V and 12V. Its power ranges from 200W to 500W. Knowing the parameters of the control controller, you can change the parameters of the ATX source. For example, increase the voltage from 12 to 30V. There are 2 popular methods, one from Italian radio amateurs.

Let's consider the Italian method, which is as simple as possible and does not require rewinding transformers. The ATX output is completely removed and modified according to the circuit. A huge number of radio amateurs have repeated this scheme due to its simplicity. Output voltage from 1V to 30V, current up to 10A.

Datasheet

The chip is so popular that it is produced by several manufacturers; offhand I found 5 different datasheets, from Motorola, Texas Instruments and other lesser known ones. The most complete datasheet TL494 is from Motorola, which I will publish.

All datasheets, you can download each one:

• Motorola;
• Texas Instruments - the best datasheet;
• Contek

Switching power supplies are often used by radio amateurs in homemade designs. With relatively small dimensions they can provide high output power. Using pulse circuit It became possible to obtain output power from several hundred to several thousand watts. Moreover, the dimensions of the pulse transformer itself are no larger than a matchbox.

Switching power supplies - operating principle and features

The main feature of pulsed power supplies is their increased operating frequency, which is hundreds of times higher than the network frequency of 50 Hz. At high frequencies with a minimum number of turns in the windings, high voltage can be obtained. For example, to obtain 12 Volts of output voltage at a current of 1 Ampere (in the case of a mains transformer), you need to wind 5 turns of wire with a cross-section of approximately 0.6–0.7 mm.

If we talk about a pulse transformer, the master circuit of which operates at a frequency of 65 kHz, then to obtain 12 Volts with a current of 1A, it is enough to wind only 3 turns with a wire of 0.25–0.3 mm. This is why many electronics manufacturers use pulse block nutrition.

However, despite the fact that such units are much cheaper, more compact, have high power and low weight, they have electronic filling, and therefore are less reliable when compared with a network transformer. It is very simple to prove their unreliability - take any switching power supply without protection and short-circuit the output terminals. At best, the unit will fail, at worst, it will explode and no fuse will save the unit.

Practice shows that the fuse in a switching power supply burns out last, first of all the power switches and the master oscillator fly out, then all parts of the circuit one by one.

Switching power supplies have a number of protections both at the input and output, but they do not always save. In order to limit the current surge when starting the circuit, almost all SMPS with a power of more than 50 Watts use a thermistor, which is located at the input of the circuits.

Let's now look at the TOP 3 best schemes switching power supplies that you can assemble with your own hands.

Simple DIY switching power supply

Let's look at how to make the simplest miniature switching power supply. Any novice radio amateur can create a device according to the presented scheme. It is not only compact, but also operates over a wide range of supply voltages.

A homemade switching power supply has a relatively low power, within 2 Watts, but it is literally indestructible and is not afraid of even long-term short circuits.

Circuit diagram of a simple switching power supply

Transformer of a simple switching power supply

First we wind the primary winding, which consists of 200 turns, the wire cross-section is from 0.08 to 0.1 mm. Then we put insulation and use the same wire to wind the base winding, which contains from 5 to 10 turns.

We wind the output winding on top, the number of turns depends on what voltage is needed. On average, it turns out to be about 1 Volt per turn.

Video about testing this power supply:

Do-it-yourself stabilized switching power supply on SG3525

Let's take a step-by-step look at how to make a stabilized power supply using the SG3525 chip. Let's immediately talk about the advantages of this scheme. The first and most important thing is stabilization of the output voltage. There is also a soft start, protection against short circuit and self-recording.

Don't think that this will make the scheme more complicated. On the contrary, everything becomes simpler, safer and cheaper. For example, if you install a driver at the output of a microcircuit, then it needs a harness.

We calculate the resistance of the resistor:

R = U squared/P
R = 24 squared/1
R = 576/1 = 560 Ohm.

Calculation of voltage stabilization:

U out = 2 + U stab1 + U stab2
U out = 2 + 11 + 11 = 24V
Possible error +- 0.5 V.

You may ask, why not increase the fee and make everything normal? The answer is as follows: this was done so that it would be cheaper to order the board in production, since boards larger than 100 square meters. mm are much more expensive.

Well, now it’s time to assemble the circuit. Everything is standard here. We solder without any problems. We wind the transformer and install it.

Check the output voltage. If it is present, then you can already connect it to the network.

Now let's check the most important thing - stabilization. To do this, take a 24V lamp with a power of 100W and connect it to the load.

Video about this switching power supply:

The TL494 microcircuit implements the functionality of a PWM controller and therefore is very often used to build switching push-pull power supplies (this is the microcircuit most often found in computer power supplies).

Switching power supplies compare favorably with transformer ones by increased efficiency, reduced weight and dimensions, and stable output parameters. However, at the same time, they are sources of RF interference and have special requirements for the minimum load (without it, the power supply may not start).

The block diagram of TL494 is as follows.

Rice. 1. Block diagram of TL494

The assignment of the TL494 pins in relation to the case looks like this.

Rice. 2. TL494 pin assignment

Rice. 3. Appearance in the DIP case

There may be other versions.

As modern analogues we can consider:

1. Improved versions of the original chip - TL594 and TL598 (accuracy optimized and input repeater added, respectively);

2. Direct analogues Russian production- K1006EU4, KR1114EU4.

So, as can be seen from the above, the microcircuit is still not outdated and can be actively used in modern power supplies as a node element.

One of the options for a switching power supply based on TL494

The power supply diagram is below.

Rice. 4. Power supply circuit

Here, two field-effect transistors (necessarily attached to the heat sink) are responsible for equalizing the current. They must be powered from a separate source direct current. Suitable, for example, modular DC-DC converter, such as TEN 12-2413 or equivalent.

About 34 V should come from the output windings of the transformer (several can be combined).

Rice. 5. Second version of power supply

This circuit implements a power supply with an adjustable output voltage (up to 30V) and a current threshold (up to 5A).

A step-down transformer acts as a galvanic isolation. The output of the secondary winding (or a set of connected secondary windings) should be about 40V.

L1 – toroidal throttle. VD1 is a Schottky diode, installed on the radiator, since it is involved in the rectification circuit.

Pairs of resistors R9 and 10, as well as R3 and 4, are used to fine-tune the voltage and current, respectively.

In addition to the VD1 diode, the following should be placed on the radiator:

1.Diode bridge(for example, KBPC 3510 is suitable);

2. Transistor (KT827A was used in the circuit, analogues are possible);

3.Shunt (indicated R12 in the diagram);

4.Choke (coil L1).

It is best to blow the heat sink by force using a fan (for example, a 12 cm cooler from a PC).

Current and voltage indicators can be digital (it is best to take ready-made ones) or analog (scale calibration will be required).

Third option

Rice. 6. Third version of power supply

Final implementation option.

Rice. 7. Appearance of the device

Due to the fact that the TL494 has low power built-in key elements, transistors T3 and 4 were used to help control the main transformer TR2, which in turn are powered by the control transformer TR1 (which is controlled by transistors T1 and 2). It turns out to be a kind of double control cascade.

The L5 choke was wound by hand on a yellow ring (50 turns with 1.5 mm copper wire).
The hottest elements are transistors T3 and 4, as well as diode D15. They should be mounted on heat sinks (preferably with airflow).

Choke L2 is used in the circuit to suppress RF interference in a household network.
Due to the fact that the TL494 cannot operate at high voltages, a separate transformer is used to power it (Tr3 is BV EI 382 1189, the output of which is 9 V, 500 mA).

With such a number of elements, the assembled circuit easily fits into the Z4A case, although the latter needs to be slightly modified to ensure airflow (the fan is placed on top).

A complete list of elements is given below.

PSU connects to the network alternating current and provides power with a constant voltage in the range of 0-30V and a current of more than 15A. Current and voltage limitation are conveniently adjustable.

Publication date: 22.01.2018

Readers' opinions

• Alexander / 04/04/2019 - 08:25
  Would you mind sharing the signet file? Possible by email [email protected]

This project is one of the longest I have done. One person ordered a power supply for a power amplifier.
Previously, I had never had the opportunity to make such powerful pulse generators of a stabilized type, although I have experience in assembling IIP quite big. There were many problems during assembly. Initially, I want to say that the scheme is often found on the Internet, or more precisely, on the website, an interval, but.... the scheme is initially not ideal, has errors and most likely will not work if you assemble it exactly according to the scheme from the site.

In particular, I changed the generator connection diagram and took the diagram from the datasheet. I redid the power supply unit of the control circuit, instead of parallel-connected 2-watt resistors, I used a separate 15 Volt 2 Ampere SMPS, which made it possible to get rid of a lot of hassle.
I replaced some components to suit my convenience and launched everything in parts, configuring each node separately.
A few words about the design of the power supply. This is a powerful switching network power supply based on a bridge topology, has output voltage stabilization, short-circuit and overload protection, all these functions are adjustable.
The power in my case is 2000 watts, but the circuit can easily remove up to 4000 watts if you replace the keys, the bridge and fill it with 4000 uF of electrolytes. Regarding electrolytes, the capacity is selected based on the calculation of 1 watt - 1 µF.
Diode bridge - 30 Ampere 1000 Volt - ready-made assembly, has its own separate airflow (cooler)
Mains fuse 25-30 Ampere.
Transistors - IRFP460, try to select transistors with a voltage of 450-700 Volts, with the lowest gate capacitance and the lowest resistance of the open channel of the switch. In my case, these keys were the only option, although in a bridge circuit they can provide the given power. They are installed on a common heat sink; they must be isolated from each other; the heat sink requires intensive cooling.
Soft Start Mode Relay - 30 Amp with 12 Volt Coil. Initially, when the unit is connected to a 220 Volt network, the starting current is so high that it can burn the bridge and much more, so a soft start mode is necessary for power supplies of this rank. When connected to the network through a limiting resistor (a chain of series-connected resistors 3x22Ohm 5 Watt in my case), the electrolytes are charged. When the voltage on them is high enough, the control circuit power supply (15 Volt 2 Ampere) is activated, which closes the relay and through the latter the main (power) power is supplied to the circuit.
Transformer - in my case, on 4 rings 45x28x8 2000NM, the core is not critical and everything connected with it will have to be calculated using specialized programs, the same with output chokes of group stabilization.

My unit has 3 windings, all of them provide bipolar voltage. The first (main, power) winding is +/-45 Volts with a current of 20 Amps - for powering the main output stages (current amplifier) ​​of the UMZCH, the second +/-55 Volts 1.5 Amps - for powering the diff stages of the amplifier, the third +/- 15 for powering the filter unit.

The generator is built on TL494, tuned to 80 kHz, beyond the driver IR2110 to manage keys.
The current transformer is wound on a 2000NM 20x12x6 ring - the secondary winding is wound with 0.3mm MGTF wire and consists of 2x45 turns.
In the output part, everything is standard; a bridge of KD2997 diodes is used as a rectifier for the main power winding - with a current of 30 amperes. The bridge for the 55 volt winding is UF5408 diodes, and for the low-power 15 volt winding - UF4007. Use only fast or ultra-fast diodes, although you can use regular pulse diodes with a reverse voltage of at least 150-200 Volts (the voltage and current of the diodes depends on the winding parameters).
The capacitors after the rectifier cost 100 Volts (with a margin), the capacity is 1000 μF, but of course there will be more on the amplifier board itself.

Troubleshooting the initial circuit.
I will not give my diagram, since it is not much different from the one indicated. I will only say that in circuit 15 we unhook the TL pin from 16 and solder it to pins 13/14. Next, we remove resistors R16/19/20/22 2 watts, and power the control unit with a separate power supply of 16-18 Volts 1-2 amperes.
We replace resistor R29 with 6.8-10 kOhm. We exclude the SA3/SA4 buttons from the circuit (under no circumstances short them! There will be a boom!). We replace R8/R9 - they will burn out the first time they are connected, so we replace them with a 5-watt 47-68 Ohm resistor; you can use several series-connected resistors with the specified power.
R42 - replace it with a zener diode with the required stabilization voltage. I highly recommend using all variable resistors in the circuit of the multi-turn type for the most accurate settings.
The minimum limit for voltage stabilization is 18-25 Volts, then the generation will fail.

SWITCH POWER SUPPLY FOR TL494 AND IR2110

Most automotive and network voltage converters are based on a specialized TL494 controller, and since it is the main one, it would be unfair not to briefly talk about the principle of its operation.
The TL494 controller is a plastic DIP16 package (there are also options in a planar package, but it is not used in these designs). Functional diagram controller is shown in Fig. 1.

Figure 1 - Block diagram of the TL494 chip.

As can be seen from the figure, the TL494 microcircuit has very developed control circuits, which makes it possible to build converters on its basis to suit almost any requirements, but first a few words about the functional units of the controller.
ION circuits and protection against undervoltage. The circuit turns on when the power reaches the threshold of 5.5..7.0 V (typical value 6.4V). Until this moment, the internal control buses prohibit the operation of the generator and the logical part of the circuit. Current idle move at supply voltage +15V (output transistors are disabled) no more than 10 mA. ION +5V (+4.75..+5.25 V, output stabilization no worse than +/- 25mV) provides a flowing current of up to 10 mA. The ION can only be boosted using an NPN emitter follower (see TI pp. 19-20), but the voltage at the output of such a “stabilizer” will greatly depend on the load current.
Generator generates a sawtooth voltage of 0..+3.0V (the amplitude is set by the ION) on the timing capacitor Ct (pin 5) for the TL494 Texas Instruments and 0...+2.8V for the TL494 Motorola (what can we expect from others?), respectively, for TI F =1.0/(RtCt), for Motorola F=1.1/(RtCt).
Allowable operating frequencies from 1 to 300 kHz, with the recommended range Rt = 1...500 kOhm, Ct = 470pF...10 μF. In this case, the typical temperature drift of frequency is (of course, without taking into account the drift of attached components) +/-3%, and the frequency drift depending on the supply voltage is within 0.1% over the entire permissible range.
For remote shutdown generator, you can use an external key to short-circuit the Rt input (6) to the ION output, or short-circuit Ct to ground. Of course, the leakage resistance of the open switch must be taken into account when selecting Rt, Ct.
Rest phase control input (duty factor) through the rest phase comparator sets the required minimum pause between pulses in the arms of the circuit. This is necessary both to prevent through current in the power stages outside the IC, and for stable operation of the trigger - the switching time of the digital part of the TL494 is 200 ns. The output signal is enabled when the saw exceeds the voltage at control input 4 (DT) by Ct. At clock frequencies up to 150 kHz with zero control voltage, the resting phase = 3% of the period (equivalent bias of the control signal 100..120 mV), at high frequencies the built-in correction expands the resting phase to 200..300 ns.
Using the DT input circuit, you can set a fixed rest phase (R-R divider), soft start mode (R-C), remote shutdown (key), and also use DT as a linear control input.
The input circuit is assembled using PNP transistors, so the input current (up to 1.0 μA) flows out of the IC rather than into it. The current is quite large, so high-resistance resistors (no more than 100 kOhm) should be avoided. See TI, page 23 for an example of surge protection using a TL430 (431) 3-lead zener diode. Error Amplifiers
- in fact, operational amplifiers with Ku = 70..95 dB at constant voltage (60 dB for early series), Ku = 1 at 350 kHz. The input circuits are assembled using PNP transistors, so the input current (up to 1.0 μA) flows out of the IC rather than into it. The current is quite large for the op-amp, the bias voltage is also high (up to 10 mV), so high-resistance resistors in the control circuits (no more than 100 kOhm) should be avoided. But thanks to the use of pnp inputs, the input voltage range is from -0.3V to Vsupply-2V
When using an RC frequency-dependent OS, you should remember that the output of the amplifiers is actually single-ended (series diode!), so it will charge the capacitance (upward) and will take a long time to discharge downward. The voltage at this output is within 0..+3.5V (slightly more than the generator swing), then the voltage coefficient drops sharply and at approximately 4.5V at the output the amplifiers are saturated. Likewise, low-resistance resistors in the amplifier output circuit (feedback loop) should be avoided.
Amplifiers are not designed to operate within one clock cycle of the operating frequency. With a signal propagation delay inside the amplifier of 400 ns, they are too slow for this, and the trigger control logic does not allow it (side pulses would appear at the output). In real PN circuits, the cutoff frequency of the OS circuit is selected on the order of 200-10000 Hz. Trigger and output control logic
- With a supply voltage of at least 7V, if the saw voltage at the generator is greater than at the DT control input, and if the saw voltage is greater than at any of the error amplifiers (taking into account the built-in thresholds and offsets) - the circuit output is allowed. When the generator is reset from maximum to zero, the outputs are switched off. A trigger with paraphase output divides the frequency in half. With logical 0 at input 13 (output mode), the trigger phases are combined by OR and supplied simultaneously to both outputs; with logical 1, they are supplied in phase to each output separately. - npn Darlingtons with built-in thermal protection (but without current protection). Thus, the minimum voltage drop between the collector (usually closed to the positive bus) and the emitter (at the load) is 1.5 V (typical at 200 mA), and in a circuit with a common emitter it is a little better, 1.1 V typical. The maximum output current (with one open transistor) is limited to 500 mA, the maximum power for the entire chip is 1 W.
Switching power supplies are gradually replacing their traditional relatives in audio engineering, since they look noticeably more attractive both economically and in size.
The same factor that switching power supplies contribute significantly to the distortion of the amplifier, namely the appearance of additional overtones, is no longer relevant mainly for two reasons - the modern element base makes it possible to design converters with a conversion frequency significantly higher than 40 kHz, therefore the power modulation introduced by the power supply will already be in ultrasound. In addition, a higher power supply frequency is much easier to filter, and the use of two L-shaped LC filters along the power supply circuits already sufficiently smoothes out the ripples at these frequencies. Of course, there is a fly in the ointment in this barrel of honey - the difference in price between a typical power supply for a power amplifier and a pulsed one becomes more noticeable as the power of this unit increases, i.e. how more powerful block
nutrition, the more profitable it is in relation to its standard counterpart.
And that is not all. When using switching power supplies, it is necessary to adhere to the rules for installing high-frequency devices, namely the use of additional screens, feeding the power part of the common wire to the heat sinks, as well as correct ground wiring and connection of shielding braids and conductors.

After a short lyrical digression about the features of switching power supplies for power amplifiers, the actual circuit diagram of a 400W power supply: Picture 1. Schematic diagram
switching power supply for power amplifiers up to 400 W

The control controller in this power supply is TL494. Of course, there are more modern chips to perform this task, but we use this particular controller for two reasons - it is VERY easy to purchase.
For quite a long time, TL494 from Texas Instruments was used in the manufactured power supplies; no quality problems were found. The error amplifier is covered by OOS, which makes it possible to achieve a fairly large coefficient. stabilization (ratio of resistors R4 and R6).
After the TL494 controller there is an IR2110 half-bridge driver, which actually controls the gates of the power transistors. The use of the driver made it possible to abandon the matching transformer, which is widely used in computer power supplies. The IR2110 driver is loaded onto the gates through the R24-VD4 and R25-VD5 chains that accelerate the closing of the field gates. Power switches VT2 and VT3 operate on the primary winding of the power transformer. Midpoint required to obtain AC voltage V
primary winding
The transformer is formed by elements R30-C26 and R31-C27.
A few words about the operating algorithm of the switching power supply on the TL494:
During a soft start, the duration of the pulses that open the power transistors increases gradually, thereby gradually charging the secondary power capacitors and limiting the current through the rectifier diodes. The duration increases until the secondary supply is sufficient to open the LED of optocoupler IC1.

As soon as the brightness of the optocoupler LED becomes sufficient to open the transistor, the pulse duration will stop increasing (Figure 2).

Figure 2. Soft start mode. It should be noted here that the duration of the soft start is limited, since the current passing through resistors R16, R18, R20, R22 is not enough to power the TL494 controller, the IR2110 driver and the switched-on relay winding - the supply voltage of these microcircuits will begin to decrease and will soon decrease to a value at which TL494 will stop generating control pulses. And it is up to this moment that the soft start mode must be completed and the converter must return to normal operating mode
, since the TL494 controller and IR2110 driver receive their main power from a power transformer (VD9, VD10 - midpoint rectifier, R23-C1-C3 - RC filter, IC3 - 15 V stabilizer) and that is why capacitors C1, C3, C6, C19 have such large ratings - they must maintain the controller’s power supply until it returns to normal operation. The TL494 stabilizes the output voltage by changing the duration of control pulses of power transistors at a constant frequency - Pulse-Width Modulation - PWM

. This is only possible if the value of the secondary voltage of the power transformer is higher than that required at the output of the stabilizer by at least 30%, but not more than 60%.

Figure 3. Operating principle of a PWM stabilizer. trimmer resistor R26.
It should be noted that the TL494 controller does not regulate the duration of each pulse depending on the output voltage, but only the average value, i.e. the measuring part has some inertia. However, even with capacitors installed in the secondary power supply with a capacity of 2200 μF, power failures at peak short-term loads do not exceed 5%, which is quite acceptable for HI-FI class equipment. We usually install capacitors in the secondary power supply of 4700 uF, which gives a confident margin for peak values, and the use of a group stabilization choke allows us to control all 4 output power voltages.
This switching power supply is equipped with overload protection, the measuring element of which is the current transformer TV1. As soon as the current reaches a critical value, thyristor VS1 opens and bypasses the power supply to the final stage of the controller.
The control pulses disappear and the power supply goes into standby mode, which it can remain in for quite a long time, since the thyristor VS2 continues to remain open - the current flowing through resistors R16, R18, R20 and R22 is enough to keep it in the open state. How to calculate a current transformer.
To exit the power supply from standby mode, you must press the SA3 button, which will bypass the thyristor VS2 with its contacts, the current will stop flowing through it and it will close.
As soon as the contacts SA3 open, the transistor VT1 closes itself, removing power from the controller and driver. Thus, the control circuit will switch to minimum consumption mode - thyristor VS2 is closed, therefore relay K1 is turned off, transistor VT1 is closed, therefore the controller and driver are de-energized.
When assembling more powerful options, you should pay attention to the capacitors of the primary power supply smoothing filters C15 and C16. The total capacitance of these capacitors must be proportional to the power of the power supply and correspond to the proportion 1 W of the output power of the voltage converter corresponds to 1 µF of the capacitance of the primary power filter capacitor. In other words, if the power of the power supply is 400 W, then 2 capacitors of 220 μF should be used, if the power is 1000 W, then 2 capacitors of 470 μF or two of 680 μF must be installed.
This requirement has two purposes. Firstly, the ripple of the primary supply voltage is reduced, which makes it easier to stabilize the output voltage. Secondly, using two capacitors instead of one facilitates the operation of the capacitor itself, since electrolytic capacitors of the TK series are much easier to obtain, and they are not entirely intended for use in high-frequency power supplies - the internal resistance is too high and at high frequencies these capacitors will heat up. Using two pieces is reduced internal resistance, and the resulting heating is divided between two capacitors.
When used as power transistors IRF740, IRF840, STP10NK60 and similar ones (for more information about the transistors most commonly used in network converters, see the table at the bottom of the page), diodes VD4 and VD5 can be abandoned altogether, and the values ​​of resistors R24 and R25 can be reduced to 22 Ohms - power The IR2110 driver is quite enough to control these transistors. If a more powerful switching power supply is being assembled, then more powerful transistors. Attention should be paid to both the maximum current of the transistor and its dissipation power - switching stabilized power supplies are very sensitive to the correct installation of the snubber and without it, the power transistors heat up more because currents formed due to self-induction begin to flow through the diodes installed in the transistors. Read more about choosing a snubber.
Also, the closing time that increases without a snubber makes a significant contribution to heating - the transistor stays in linear mode longer.
Quite often they forget about one more feature field effect transistors- with increasing temperature, their maximum current decreases, and quite strongly. Based on this, when choosing power transistors for switching power supplies, you should have at least a twofold margin of maximum current for power supplies of power amplifiers and threefold for devices operating on a large, unchanging load, for example, an induction melter or decorative lighting, powering low-voltage power tools.
The output voltage is stabilized using the group stabilization choke L1 (GLS). You should pay attention to the direction of the windings of this inductor. The number of turns must be proportional to the output voltages. Of course, there are formulas for calculating this winding unit, but experience has shown that the overall power of the core for a DGS should be 20-25% of the overall power of the power transformer. You can wind until the window is filled by about 2/3, not forgetting that if the output voltages are different, then the winding with a higher voltage should be proportionally larger, for example, you need two bipolar voltages, one at ±35 V, and the second to power the subwoofer with voltage ±50 V.
We wind the DGS into four wires at once until 2/3 of the window is filled, counting the turns. The diameter is calculated based on a current intensity of 3-4 A/mm2. Let's say we got 22 turns, let's make up the proportion:
22 turns / 35 V = X turns / 50 V.
X turns = 22 × 50 / 35 = 31.4 ≈ 31 turns
Next, I’ll cut two wires for ±35 V and wind up another 9 turns for a voltage of ±50.
ATTENTION! Remember that the quality of stabilization directly depends on how quickly the voltage changes to which the optocoupler diode is connected. To improve the stabilization coefficient, it makes sense to connect an additional load to each voltage in the form of 2 W resistors with a resistance of 3.3 kOhm. The load resistor connected to the voltage controlled by the optocoupler should be 1.7...2.2 times less.

The circuit data for network switching power supplies on ferrite rings with a permeability of 2000 Nm are summarized in Table 1.

However, it is not always possible to recognize the brand of ferrite, especially if it is ferrite from horizontal transformers of televisions. You can get out of the situation by finding out the number of turns experimentally. More details about this in the video:

Using the above circuitry of a switching power supply, several submodifications were developed and tested, designed to solve a particular problem at various powers. The printed circuit board drawings for these power supplies are shown below.
Printed circuit board for a switching stabilized power supply with power up to 1200...1500 W. Board size 269x130 mm. In fact, this is a more advanced version of the previous printed circuit board. It is distinguished by the presence of a group stabilization choke, which allows you to control the magnitude of all power voltages, as well as an additional LC filter. Has fan control and overload protection. The output voltages consist of two bipolar power sources and one bipolar low-current source, designed to power the preliminary stages.

External view of the printed circuit board for a power supply up to 1500 W. DOWNLOAD IN LAY FORMAT

A stabilized switching network power supply with a power of up to 1500...1800 W can be made on a printed circuit board measuring 272x100 mm. The power supply is designed for a power transformer made on K45 rings and located horizontally.

It has two bipolar power sources, which can be combined into one source to power an amplifier with two-level power supply and one bipolar low-current source for preliminary stages.

Printed circuit board of a switching power supply up to 1800 W. DOWNLOAD IN LAY FORMAT This power supply can be used to power automotive equipment. high power

, for example, powerful car amplifiers, car air conditioners.

The power supply up to 2000 W is made on two boards measuring 275x99, located one above the other. The voltage is controlled by one voltage. Has overload protection.

The file contains several options for the “second floor” for two bipolar voltages, for two unipolar voltages, for the voltages required for two and three level voltages.

The power transformer is located horizontally and is made on K45 rings.

Appearance of a “two-story” power supply DOWNLOAD IN LAY FORMAT

A power supply with two bipolar voltages or one for a two-level amplifier is made on a board measuring 277x154. Has a group stabilization choke and overload protection.

Appearance of a “two-story” power supply DOWNLOAD IN LAY FORMAT

The power transformer is on K45 rings and is located horizontally.

Appearance of a “two-story” power supply DOWNLOAD IN LAY FORMAT

Power up to 2000 W.

External view of the printed circuit board DOWNLOAD IN LAY FORMAT

Almost the same power supply as above, but has one bipolar output voltage.

The switching power supply has two power bipolar stabilized voltages and one bipolar low current.

Equipped with fan control and overload protection. It has a group stabilization choke and additional LC filters.

The switching power supply has two power bipolar stabilized voltages and one bipolar low current.

There is much more space for ferrites on boards than there could be. The fact is that it is not always necessary to go beyond the sound range. Therefore, additional areas are provided on the boards. Just in case, a small selection of reference data on power transistors and links to where I would buy them. By the way, I have ordered both TL494 and IR2110 more than once, and of course power transistors. It’s true that I didn’t take the entire assortment, but so far I haven’t come across any defects.