Adjustable SMPS Power Supply 0.2V-80V 0-10A TL494

 0.2V-80V Switching power supply based on TL494 IC is used in various devices, motors, batteries, battery charging processes, etc. Designed for. There is an additional SMPS circuit with TNY267 integrated circuit to power elements such as TL494, Fan, Relay. Like many circuit elements used in the SMPS Project, this material was supplied from PC power supplies.

Adjustable SMPS Circuit parameters: Input voltage: 210V – 265V, Power consumption and current: max. 860W / 4.5A, Output voltage: 0.2V-80V, Ripple: up to about 0.3V, Adjustable Output current: 0-10 Amp., Short circuit current limitation: 14 Amp.
The shunt resistor used for the ammeter is handmade. 7 parallel connected 40mm 0.56mm wires are soldered between two copper rectangles of 15x15x5mm. The wire gives a resistance of 1.761Ω per 1-meter length. The shunt used for the current detection of the SMPS Circuit is in the 0.1Ω 50W TO220 Transistor case.

80V 10A SMPS Power Supply Circuit Diagram

Components List

Parameters

• Input voltage: 210V to 265V~
• Power input and current taken from the network: max. 860W / 4.5A
• Output voltage: 0.2V – 80V
• Ripple: up to approx. 0.3V
• Output current: 0-10A.
• Short-circuit current limitation: >14A
• Dimensions (cabinet) W x D x H: 230 x 220 x 70mm

Feature

The mains voltage passes through the input filter formed by the toroidal choke TL1 and capacitors C2, C8. The voltage is supplied to the bridge rectifier through the resistor R16 which limits the current surge caused by the charging of the smoothing capacitors after the power is turned on. After the start of the auxiliary source, relay K1 bridges resistor R16 and disables it from the circuit. Behind the rectifier, the voltage is filtered by a pair of electrolytic capacitors C10, C11. Both the main and auxiliary sources are powered by this voltage. Resistor R20 ensures the discharge of capacitors after switching off the source.

The auxiliary source creates a supply voltage of 17V for the control circuit of the power source and 12V for the cooling fan. The basis of the auxiliary source is a proven integrated circuit from the TINYSWITCH-II family in a catalog connection. It is a blocking converter with a frequency of 132Khz and requires a minimum of external components. The supply voltage is supplied through resistor R22 and the primary winding of the transformer to pin 5 of IC2, which is the "Drain" of the switching transistor. The voltage is filtered by capacitor C13. Resistor R29 determines the starting threshold of the converter, the value of 4.7MΩ determines that the source starts to start when the input voltage reaches about 300V. Diodes D8, D9 protect the switching transistor from voltage peaks arising during the expansion of the inductive load. The damping element works as follows. When the transistor in IC5 is open and current flows through the primary winding, D8 is polarized in the closing direction and no current flows through the damping element. After opening the transistor, a voltage of the opposite polarity is induced on the primary winding, D8 is now biased in the forward direction and supplies a voltage to the cathode of transil D9. When the rising voltage reaches the opening threshold of the transil (200V), it opens and current starts flowing through the diodes. The voltage on the primary winding no longer increases. The damping element therefore limits the height of negative pulses to 200V. There must be an ultra-fast diode at position D8. C15 is a filter capacitor for the internal reference source. The secondary winding of the transformer has a 12V tap for powering relay K1 and for the cooling fan. The voltage from the secondary winding is rectified by the one-way rectifier D15 and filtered by the capacitor C18 (or D14, C19). Stabilization of the output voltage is realized by feedback through optocoupler OK1. Only the 17V branch of the source is stabilized. The twelve volt branch supplies only the fan and relay K1, therefore it does not need stabilization, its voltage is given by the transformer ratio. The stabilized voltage +17V is fed through the resistor R39 and the diode D16 to the LED diode of the optocoupler, if the voltage at the output reaches a voltage of 17V, the zener diode D16 opens and the current begins to flow through the LED diode in OK1. The diode lights up and partially opens the photo transistor which pulls the EN terminal of the control circuit to ground and blocks the pulses to the primary winding of transformer TR2. The moment the voltage drops, the pulses are restored. The value of the output voltage of the source 17V was chosen with regard to the control voltage of the IGBT transistors, at this voltage the transistors are already safely open.

 Main source

As the control circuit of the main source, the integrated circuit TL494 is used in single-action mode. I chose this circuit because it has two separate control amplifiers and the voltage at their inputs can vary from -0.4V to the supply voltage. It is therefore possible to regulate from scratch. Single-acting / double-acting mode is switched by connecting pin 13 of IC1 to ground or +5V. By connecting to ground, the circuit works as a single-acting source. The frequency of the sawtooth generator is determined by the capacity of the timing capacitor C9 and the resistance of the resistor R19. The frequency is set to 50Khz, calculated according to the formula [f = 1/(R*C)]. The output transistor in IC1 and transistor Q5 together form the driver of the decoupling transformer. The bidirectional transil D7 protects the power transistor from voltage peaks arising during the expansion of the inductive load. Transistor Q5 can be of type IRF540, IRF630, etc. A wound power transformer from a 350W PC source is used as the excitation transformer. I will give the winding prescription and details at the end of the article. The transformer is wound as permeable and the sense of the windings must be respected. When the transistor Q5 is open, a positive pulse is generated on the secondary windings of the transformer, which charges the gate capacity of the IGBT transistor Q9 through the diode D11 and the resistor R37. Resistor R37 limits max. peak current when charging the gate. R33 forms the minimum load of the excitation transformer TR1 and helps discharge the gate of the power transistor Q9. Zener diode D13 protects the gate against exceeding the maximum allowed voltage, which is usually 20V. Transistor Q7 is closed during the positive period, because due to the voltage drop on diode D11 (about 0.7V), the voltage at the base of the transistor is more positive than at the emitter. After the end of the excitation pulse, the energy accumulated in the magnetic field of the transformer core tries to maintain the direction of the current and the polarity of the voltage on the secondary windings is reversed. A negative signal period occurs. The charge accumulated on the gate capacitance of the power transistor Q9 maintains a positive voltage on the emitter of the transistor Q7. Diode D11 is now reverse biased and closed. The current from the excitation transformer now flows through resistor R28 to the base of Q7, which opens and avalanche discharges the charge accumulated on the gate capacitance of transistor Q9. Transistor Q9 closes. The above also applies to the driver of the second power transistor Q8. Power transistors Q8, Q9 and diodes D17, D21 form the final stage for driving the power transformer. The transistors must be fast IGBTs with a current of around 30A. The topology of the exciter with switching of both ends of the winding is chosen for the following reasons. A power transformer is sufficient with only two simple windings. Power transistors are not threatened by high voltage and cheaper types are sufficient. The function of the final stage is as follows. Both transistors Q8,Q9 are opened at the same time. The excitation current flows from the positive terminal of the filter capacitor through transistor Q9, the primary winding of the power transformer and transistor Q8 to the negative pole of the filter capacitor. The impulse current reaches up to 37 amperes. Through the passage of current, part of the energy accumulates in the magnetic field of the transformer and part flows to the secondary side.

After the end of the excitation pulse, transistors Q8, Q9 are closed. The accumulated energy in the core tries to maintain the direction of the current in the windings, part of the energy still flows through the secondary winding and part is induced back into the primary winding but with the opposite polarity. Since the return voltage is of the opposite polarity, the recovery diodes D17, D21 open and connect the winding in the correct polarity to the filter capacitor. The passing current back-charges the capacitors, returning part of the energy back to the input. This increases the efficiency of the source and effectively limits the voltage peak to the size of the voltage on the filter capacitors. Additional RDC cells protect the power transistors against too fast voltage rise on the "drains" when the load is switched off (dU/dT). Diodes D18 and D19 must be ultra-fast with a breakdown voltage of at least 800V. The RDC cells must be placed as close as possible to the terminals of the transistors. Capacitor C22 covers current peaks arising when switching transistor Q8 because it is located further from the filter capacitors. At first glance, the TR3 transformer is drawn strangely, but it is not a special part. It is a simple transformer with two windings, just to the end of the winding, between the body and the pins of the body, a toroidal ring of the current transformer is strung for measuring the peak current of the power transistors. The secondary winding of the current transformer is connected to the two outermost pins of the power transformer. From the point of view of the printed circuit board, both transformers form one component. The goal of this solution was to reduce the parasitic inductances of the transformer terminals and to simplify the circuit board. The power transformer is followed by a one-way rectifier formed by the upper half of the D22 diode. In the active period of the signal, when the positive polarity of the voltage at the upper end of the secondary winding, the upper half of the diode D22 is biased in the forward direction. The diode is open and current flows through it, which continues to flow through choke TL2 and charges smoothing capacitors C24, C25, C26, C27. Capacitors must have low series resistance (Low ESR). At the same time, the energy is stored in the choke TL2. In the inactive period, the upper half of D7 is closed, and the energy accumulated in TL2 is supplied to the load through the lower half of the diode D22. From the output filter, the voltage is already supplied through transistor Q11 to the output terminals of the source. The feedback control voltage is taken from the output of the source, through the resistor divider R2, R52, R51, R13. With an output voltage of 80V, there will be a voltage of about 4.75V at the non-inverting input, pin 16 of IC1. The voltage from the potentiometer for adjusting the voltage is applied to the inverting input of the control amplifier. By changing the pulse width, the control loop tries to match the output voltage and thus the voltage at the non-inverting input so that the voltage difference at the inputs of the control amplifier is zero.

The output voltage is measured only at the terminals of the source in order to compensate for all voltage drops that occur in the circuit. (decrease in resistance Q11, wire resistances, printed circuit resistance, etc.) Fineness of voltage regulation depends on the quality of the potentiometer, so I recommend using a higher-quality sealed, linear potentiometer with a larger diameter. Preferably double 5KΩ and connect both sections in parallel. The gain of the bias voltage amplifier is determined by the RC element C6, R10. Too high a gain results in oscillation of the source.
Current regulation works similarly. The current is sensed on resistor R44. The passage of current creates a voltage of negative polarity on R44. The non-inverting bias amplifier input, pin 1 of IC1 is connected to ground. Current limiting therefore occurs when the voltage at the inverting input, terminal 2 of IC1, reaches negative values, typically -2mV. The resistance divider, which consists of a current potentiometer, resistors R8, R43 and trimmer R53, is calculated so that with a maximum current of 10A at the output of the source (i.e. -1V at the upper end of R30) and the potentiometer fully turned to the maximum, there is exactly 0V at the inverting input . R11 and C7 determine the gain of the bias current amplifier. Diode D20 protects the inputs of the amplifiers from a negative voltage greater than –0.3V that can occur in case of a short circuit at the output of the source and it must be a Schottky diode with a very low voltage drop in the forward direction (parameter Uf < 0.3V). I couldn't find such diodes in terminal design, so I used STPS2L40U diodes in SMD design. Terminals must be soldered to the diodes and mounted on the board as a terminal component. Current regulation using a sensing resistor was chosen due to the smoothness of the regulation. Current regulation using a measuring current transformer is more of a step-by-step character because the saw-tooth voltage at its output tends to be noisy and variously wavy. In contrast, regulation using a sensing resistor is fine and accurate but slow. In the event of a short circuit at the output, it cannot react quickly enough, therefore the source also uses "cycle-by-cycle" protection, which checks the current in each switching cycle of the power transistors.
Operational amplifier IC3 realizes the current limit indication. When the voltage at the inverting input drops to about -2mV, the OZ flips over and a positive voltage of about 16V appears at the output, which lights up the current limiting LED. The LED lighting threshold is set with the trimmer R34. Resistors R35 and R40 introduce fine hysteresis into the circuit so that the transitions between the individual states of the indication are sharp.

The soft start of the source and the protection of power transistors against current overload are implemented by transistors Q1 to Q4 and several components around them. The principle description from the manufacturer is in the document "Designing Switching Voltage Regulators With the TL494". Both functions affect the width of the excitation pulse, using the DTC input pin 4 of IC1. The voltage at this input can range from 0 to 5V, while at about 3.3V the pulse width is 0% and at 0.1V it is 90%. The maximum pulse width is set by resistor divider R1, R26, in our case 45%. Components C1, R26, R1, D2 ensure a soft start of the source. After switching on the power supply, capacitor C1 is discharged and 5V voltage from the reference voltage source is supplied to the DTC input via diode D2. By passing the current through the resistor R26, the capacitor C1 starts charging. The voltage on the DTC starts to drop, the pulses gradually expand up to the value set by the divider R1, R26.
Current protection (cycle-by-cycle) works by prematurely closing the power transistors in case of excessive current and ending the current signal period. The current is sensed by the measuring current transformer and has a saw-tooth pattern. As the current flowing through the primary winding of the transformer increases, the amplitude of the sawtooth voltage on the secondary side of the current measuring transformer also increases. This voltage is fed through D6, R13 and trimmer R3 to the base of transistor Q1. Resistor R17 forms the load of the current measuring transformer, C3 removes disturbing voltage peaks from the saw-like pulse. Trimmer R3 sets the threshold at which the current is limited. If the voltage at the base of transistor Q1 reaches the opening limit, transistor Q1 opens and with its collector current opens transistor Q2, which brings a positive voltage of 5V to the DTC output of control circuit IC1. The circuit immediately reacts and terminates the current impulse. At the same time, current begins to flow through D1, R9 to the base of transistor Q3, which opens and with its collector current keeps transistor Q2 open even after the end of the pulse from the measuring current transformer. It thus creates a flip-flop circuit that keeps blocking the pulse until the end of the signal period. Transistor Q2 remains open until the discharge of capacitor C9, when the voltage at the output of CT IC1 drops to zero. The current flowing through the diode D5 opens the transistor Q4, which pulls the base of Q3 to ground and it closes. The circuit is ready for the next period. Diode D1 introduces hysteresis into the circuit so that the circuit flips reliably. Diode D4 reduces the positive voltage component to about 0.3V, which oscillates on diode D5. Because of this positive component, transistor Q4 is also used, without it, transistor Q3 would open spontaneously. Diode D2 separates the soft start circuit so that the capacitor C1 is not charged and the signal alternation is not affected when the current protection is applied. Diode D3 separates the current protection circuit from the DTC terminal which acts as a 0.1V voltage source and would affect the circuit's function. At the same time, the diode D2 protects the circuit from false triggering of the protection when the source starts up. By prematurely closing the power transistors, the excitation pulse to the primary of the transformer is narrowed and thus effectively limits the current through the primary winding of the transformer. This protection, as long as it is well set, will protect the final transistors from various short-circuits at the output and even from inter-turn short-circuits of the power transformer.

A short circuit at the output of such powerful sources is a serious matter, especially at the highest voltage, when the smoothing capacitors are fully charged. It melts the supply cables, creates an arc, splashes molten metal and there is a risk of injury to the operator as well as damage to the source. Therefore, the output of the source is protected against excessive short-circuit current. This protection ensures that in the event of a short circuit at the output, a current greater than 14A will not flow through the output terminals. The foundation is formed by transistor Q11, which is connected in series with the positive branch of the source. The transistor is held in the permanently open state under normal operating conditions by the +18V voltage supplied by resistors R48 and R49 to the control electrode of Q11. Since its on-state resistance is only 8mΩ, the voltage drop is negligible. Operating current can flow through the transistor without being limited and the transistor does not even heat up. When the output terminals are short-circuited, current will flow through resistor R44 and a voltage drop will occur. Transistor Q10 is biased against resistor R44 so that R44 acts as a positive voltage source for the base of transistor Q10. The base is connected through a 1:2.5 divider formed by resistors R46 and R47. When the voltage on the resistor R44 reaches about 1.4V (at a current of 14A), the transistor Q10 opens and the gate of the transistor Q11 is discharged through R49, it closes and the flowing current decreases. As long as the short-circuit current persists, transistor Q11 maintains the current flowing at 14A. Since resistor R44 is common to both short-circuit protection and current limiting, the excitation pulses to the terminal transistors will be blocked for the duration of the short-circuit current and the source will be shut down. Choke L1 and diode D7 form a voltage source for the "floating" transistor Q11. The voltage on the Q11 gate must always be +18V higher than the output voltage of the source. If the output voltage is below 17V, the voltage on the capacitor C37 is too low and the gate Q11 is powered through the diode D28 from the auxiliary source. When the output voltage of the source is above 17V, the voltage on C37 will increase so much that the diode D28 closes and the gate is powered via L1 and D27. The voltage on C37 can reach up to 150V at full power of the source, transistor Q10 must also be sized for this voltage. Diode D26 protects gate Q11 from exceeding the permitted voltage. Diodes D23, D24, D29 protect transistor Q11 against exceeding the maximum collector voltage.

The next and last part of the source is the resistive load. This is mainly needed to speed up the source's response to control changes. Without a load, when the voltage potentiometer is quickly turned from maximum to minimum, the voltage would only drop very slowly. With load, the source reacts to changes in the control elements faster. It also realizes the minimum resource load. At low consumption, it still switches to intermittent mode, which is manifested by a weak hum coming from the transformer. The source must not whistle, if it whistles something is wrong.

Construction and revival

I originally designed the wiring without trimmers using only fixed resistors. Compiling the required resistance value proved to be very difficult, time-consuming and inaccurate. That's why I ended up using precision, multi-turn trimmers. I recommend using them even if they are a bit more expensive. The voltage potentiometer is a double linear 2x5k, sections connected in parallel. The current sensing resistor R44 must be of good quality, preferably in a TO220 case. An ordinary wire resistor cannot be used because the ceramic in which it is embedded is not capable of dissipating the generated heat. The stability of the current limitation is directly dependent on the stability of the resistance under changing temperature. When I used a regular ceramic resistor and set the current limit to 10A, after a few minutes the current started to drop as the temperature of the resistor rose. After ten minutes, the source was already delivering only 6A.
An alternative would be to make your own resistor from resistance wire, e.g. from Constantan, but I haven't tried that. Another problem is the oscillation of the current loop when using a wire resistor. I didn't investigate further what causes the oscillation, since all problems disappeared by using a resistor in the TO220 case. The stability with this resistor is excellent, after an hour of operation the output current changed by only 8mA. I installed the source in an aluminum case type WK12703 from the former manufacturer Tesla. In the lower right corner of the printed circuit board, only low parts are installed, leaving a place for the 80x80mm fan. The cooler consists of a 3 mm thick duralumin enclosure. In the corners, it is attached to the circuit board using corner posts. There is a gap of 5 mm between the bottom edge of the enclosure and the flat surface, for air intake. In the back, there is still a finned cooler attached to the enclosure, originating from the PII processor. The air is sucked in at the back through the cooler, flows through the gap between the cooler and the board. It then flows between the components towards the fan. The aluminum cabinet itself also participates in cooling. The strongest cooling is needed by the rectifier bridge B1, D22 and R44, while the power transistors heat up only slightly. I used the TK1382 module to display voltage and current. It turned out that the module lives up to the "Chinese scoundrel" menu, the displayed current value floats when the shunt temperature changes, and the current loop's transient resistance is enormous (thin wires, connector transient resistance, etc...). At a current of 10A, for which the module is primarily intended, the shunt heats up so strongly that the tin dissolves over time and the shunt can even fall out. Current measurement around 10A is only possible for a short time, in a few seconds due to the heating of the shunt, the measured value starts to go away. After a while, the ammeter shows errors. That's why I had to modify the module. I threw out the shunt and connected the module via an external, high-quality shunt. This removed the transient resistances of the module and the ammeter stopped responding to temperature changes. The shunt must be made separately for each piece of the module, because each piece has an original shunt with a different resistance value. In some it is 10mV at 1A, in others it is 7mV at 1A. Another problem is that the module cannot be clicked into the hole, because the flexible pawls rest against the display inside. I had to disassemble and modify the module, otherwise it cannot be mounted. Furthermore, two of the four ordered pieces were defective. One had a cracked display and the other turns off after heating. Because I had already made labels, I decided to purchase three more displays. In this new "batch", one piece was defective again, it does not go from 79.9V to 80V but to 100V. Due to the mentioned problems, I recommend to use some other modules and avoid them. If we use other modules and for the power supply it will probably be necessary to use a DC/DC converter, the module connection diagram indicated on the printed circuit diagram.

Wires to terminals and potentiometers should be used as short as possible. The cross-section of the wires to the output terminals should be at least 4mm², so that the voltage drop is as low as possible. This needs to be fulfilled especially if we want the source to deliver a current of 10A to the load starting from 1V at the output. Potentiometers should be used preferably sealed or at least somehow protected against dust. Mains fuse around 6 to 8A. I make labels by printing the template with a laser printer in mirror image on a transparent film and pasting it with self-adhesive wallpaper of the desired color. I stick the label on the front panel with thin double-sided adhesive tape. I will leave possible modifications and improvements to the reader.
Prerequisites for construction are at least basic knowledge of resource construction and basic workshop equipment. To revive it, you will need a two-channel oscilloscope, a laboratory power supply, a multimeter, a separating transformer from 230V to 230V / 500W (or at least to separate the oscilloscope power supply), as a load, some car bulbs, etc.. Even before the production of the circuit board, it is best to collect all the parts and, if necessary modify the circuit board according to the component cases. The scheme and the flat are drawn in the design system EAGLE 7.2.0., to draw the polygons you need to press the "Ratsnest" button.

Preparation the Winding Parts

In order not to get entangled in winding directions, the good old lesson still applies: "twice a change is not a change". This means that if we flip the ends of the windings, we must wind all the windings in the same direction. Conversely, if we wind the individual windings in the opposite direction, then we must no longer swap the ends. The dots at the ends of the windings in the wiring diagram indicate the sense of the windings, while on the circuit board they indicate the actual beginnings of the windings. Therefore, we wind all transformer windings Tr1, Tr2, Tr3 in the same direction, and the dot tells us where to connect the beginning of the wire.

The core is a toroidal ferrite ring type T09/5/3.2 dark green color, Al = 2500. Obtained from a disassembled old PC power supply. The coil has 50 turns of lacquered wire with a diameter of 0.25 mm. The inductance of the coil is approx. 6.5mH. The length of the conductor is approx. 80 cm, even with a reserve.

Table 1 - Construction of the measuring current transformer

The choke core is toroid type T45 – 45/28/11 Lj T 4511 – CF139 Cosmo ferrites. Al – 2200nH, inductance is 2x5mH. Two windings are wound on the toroid, 2 x 48 turns of painted wire with a diameter of 1 mm, in the same direction, see the picture. The inductance of each winding is 5 mH. The winding must be wound so that all ends are on one side. An insulating gap must be left between the windings to prevent a short circuit.

Table 2 - Construction of the suppression choke 2x5mH, input network filter

Choke Type 203420 inductance 8.2mH. Raster 5/10, Core diameter 10mm, height 15mm, wire diameter 0.15mm. The choke comes from an old monitor, but you can easily buy it or wind it yourself.

Table 3 - Choke L1 for supplying protection against excessive short-circuit current

I made the shunt for the ammeter from two copper rectangles 15 x 15 x 5 mm. The wire is a constant diameter of 0.56mm with a resistance of 1.761Ω per 1 meter of length. For a resistance of 70mΩ the length of the shunt (from inner edge to inner edge) is 28mm 100mΩ the length of the shunt is 40mm According to the formula: lb [mm] = ((Rb/Rd) * 100) * n Where: lb – shunt length, Rb – shunt resistance, Rd – wire resistance, n – number of wires in parallel I made 7 notches in the lower edge of the copper rectangles with a saw, into which I soldered the individual wires. Eventually the shunt buckled due to dilation. It was not necessary to make an exact setting because the measuring module has a trimmer for fine-tuning the measured current. The number of wires is chosen so that warming is as small as possible. The permitted current value for the given diameter of the wire is 2.2A, I chose a current of less than 1.5A per wire.

Table 4 - Ammeter shunt

The transformer core is type E 65/27/20 material N27 Pramet Al = 7200 or N87 (3F3) Al = 7900 Cube for the core E65 horizontal assembly, 2 x 8 outlets, purchased at www.Ferity.cz The primary winding has 26 turns of twisted wire of 5 lacquered wires with a diameter of 0.5 mm, l = 3.7 m. The secondary winding has 20 turns of a cable composed of 10 lacquered wires with a diameter of 0.5 mm, l = 2.6 m. The beginnings and ends of the windings must be connected according to the markings on the printed circuit board. Both windings must be wound in the same direction. The secondary is wound first, in two layers of 10 turns. The primary is wound as the second, also in two layers of 13 and 13 turns. The individual layers are interlaced with an insulating film. In case of emergency, painter's tape can also be used. We varnish each turn of the tape. At least 8 layers must be placed between the primary and the secondary, or one turn of insulating film must be inserted. At the end of the primary winding, we thread a piece of heat-shrink tubing, onto which we thread the current measuring transformer. The secondary winding of the transf. connect the current to the two outer terminals on the chassis. You have to pay attention to the meaning of the windings. When folding the core, it is necessary to create an air gap of 0.2 mm in total. For example from the foil to the copier, which has a thickness of 0.1 mm. We can glue the core with a drop of PCB varnish. Finally, wrap the entire transformer with Cu foil and connect to GND, on the secondary side.

Table 5 - Power transformer design

Tlmivka sa skladá z dvoch paralelne zložených toroidných železo-prachových jadier, typu T157 40/24/14,5 žlto – biela farba materiál 26. Vinutie má 69 závitov, dvoma paralelne zloženými lakovanými drôtmi o priemere 1mm. (alebo 4×0.85mm, alebo 7×0,6mm …) Dĺžka vodiča je cca 7m. Indukčnosť je 940uH bez prúdu a 310uH pri prúde 10A. Závity treba dobre utiahnuť a klásť pekne jeden vedľa druhého, inak vinutie do jadier nevlezie.You can buy it here

Table 6 - Construction of smoothing choke TL2

The transformer comes from a 350W PC power supply, we can take it apart by boiling it in water and taking it apart while still hot. The core is type EE 22x30x6, the size of the middle column is 6x6 mm. The primary has 140 turns of lacquered wire with a diameter of 0.25 mm. The secondary has 16+7 turns of lacquered wire, diameter 0.35 mm. If we connect the beginnings of the windings according to the marks on the joint, all windings must be wound in the same direction. We glue the core with a drop of varnish on the printed circuit boards, without an air gap. The die has two sections, each winding has its own. We wind the secondary closer to the terminals. The individual layers of the primary winding must be interlaced with tape.

Table 7 - Construction of transformer TR2

The core is type EI 33x29x13mm. The size of the middle column is 13×9.5 mm. The transformer is permeable, all windings are wound in agreement. First, we wind the primary with 30 turns of 0.35 mm wire. Next comes 1 turn of copper foil, we connect it to the V- outlet. Finally, we wind the first and second secondary 30 + 30 turns with 0.35 mm wire. Each winding is a separate layer. The individual layers must be well insulated from each other, there is enough space on the skeleton, so the insulation can be thicker. We glue the core without a gap. The length of the wire is about 3x2m. For ETD core secondary 25+25 turns.

Table 8 - Construction of excitation transformer TR1

once we have finished all the winding parts, we need to collect the other parts and check the cases, or modify the design of the printed circuit board and make the printed circuit board. First we install the small parts, then the big ones and finally the transformers. We are not installing the TR3 transformer yet. We solder wire eyes to the marked jumpers. We will create measurement points as in the image to the right. We will connect potentiometers, LED current indicators, or an instrument meter for voltage and current. Turn the voltage potentiometer to the left to the minimum and the current potentiometer to about 10%. We will put some coolers on the transistors, small ones are enough, the transistors don't get particularly hot. Green hatched areas, "hacesoft" layer, need to be roughly tinned. For more details see Figure below

WARNING! In no case do not connect the source to the network without going through the recovery procedure!

Without TR3

• We turn all trimmers to the left to the minimum.
• Check for short circuits. We connect the laboratory power supply to the output terminals of the switching power supply and slowly raise the voltage to about 12v, the consumption must not exceed 30mA.
• Lab. we now connect the source to the GND measurement point and connect the positive pole to the cathode D14. Relay K1 will click and the consumption should be around 30mA. (without connected fan) Lab. switch the source to the 220V input, the consumption will be max. a few mA, we check both polarities. If the consumption is greater than about 100mA and R22 heats up, IC2 or D8, D9 is probably damaged.

• Signal Q8,Q9 Vertical 10V Div.

The owner of the updated project, @Niki31, commented on important edits. The translation is below. Thanks @Niki31

This power supply is very robust, it has been built 10 times. His results are excellent. All electronic components including the PCB plate, are available here on the site. For further details do not hesitate to contact us.