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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Switching power supply with a voltage regulator 1 ... 32 volts with a power of 200 watts. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Power Supplies The presented power supply has the ability to change the voltage by turning the knob of the R9 resistor from 1 to 32 volts, it has overload protection and the necessary power for all amateur radio experiments. Load capacity on all ranges does not exceed 6 amperes. The power supply has voltage stabilization and galvanic isolation from the 220V network. This power supply was invented by me and my friend and tested in action. During assembly and configuration of the power supply (PSU), a dual-beam oscilloscope is required.
The alternating voltage is supplied to the unit for preventing an instantaneous surge of huge current when charging capacitors C5 and C6, consisting of resistors R1, R2, R3 relays, RES22, a transistor, a KS156A zener diode, capacitor C1 and a capacitor with a capacity of 0.33 microfarad 250V, a diode assembly on KD105B. When turned on, the capacitors C5 and C6 are charged through the resistor R3, the time-delay circuit of the relay operation provides the necessary time to charge the powerful capacitors C5 and C6, after the capacitors are charged, the relay closes the contacts and the current flows directly, thereby making it possible to load the power supply at full power. The next node is the noise protection node of the power supply to the AC mains and to the surrounding area. The power supply housing must be made of metal. It serves as a screen protecting against interference in the surrounding space and must be grounded. An interfering voltage is applied to the housing through capacitors C2 and C3; these interferences also go to the ground wire. The noise filter in the 220V network is made on the L1 coil and the C4 capacitor. The power rectifier is made on a powerful diode assembly KVRS1006, it is small in size and can withstand a direct current of 10A, and up to 50A in a pulse. A voltage divider by 5 is assembled on capacitors C6 and C3 and resistors R4 R2, thereby lowering the voltage in the region of 150 volts , this voltage is supplied to the power transformer T1 through the capacitor C7, which has a small capacitance and thereby decouples the powerful field-effect transistors in direct current during the switching of the transformer at a frequency of 50 kHz. Capacitor C7 prevents the breakdown of the IRF740 transistors in the event of a stop of the master pulse generator. The high-frequency diodes shunting the T1 transformer and the IRF740 transistors protect against high-voltage surges of the T1 transformer without breaking through the transistors with high voltage, although the transistors themselves have protection in this case, but the diodes work faster and more reliably. The choice of field effect transistors is due to the fact that they have faster rates than bipolar ones, this is of great importance because transistors experience more instantaneous power during the transition from off to open. The faster the open or close cycle of transistors, the greater their load capacity. The control of field-effect transistors is completely entrusted to the IR2113 microcircuit. Field-effect transistors have a parasitic gate-drain capacitance, therefore they have a braking effect during control, the IR 2113 microcircuit can develop a pulse current of up to 2 amperes during control, thereby ensuring fast saturation of power field-effect transistors, as well as output from saturation. Resistors included in the gates of the 10 ohm transistors prevent excessive current. Capacitor C18 and diode KD247D serve as a power source for the control unit of the IR2113 microcircuit, the upper one according to the IRF740 transistor circuit. The amplitude at the gates of the transistors should not exceed 18..20V and should not be lower than 11 volts. The control pulses of the IR2113 chip come from the TL494 pulse-width modulator. This microcircuit, by narrowing and expanding rectangular pulses, changes the power delivered to the power transformer, and thereby acts as a stabilizer and voltage regulator. The control pulses from the outputs 9 and 10 of the TL494 are fed to the control input of the upper transistor 10 IR2113 and the lower 12 IR2113. The outputs of the TL494 are loaded with two 1 kΩ resistors. The frequency of the master oscillator at which the power supply operates is determined by the capacitance of the capacitor connected to input 5 of TL494 and the trimmer connected to input 6 of TL494. The IRF740 control transistors must close between pulses during their operation, this is due to the fact that transistors cannot close instantly and thus a through current may appear when the upper transistor has not yet completely closed, and the lower one has already begun to open and therefore a direct current can go through two transistors at once and, thereby, disable them. To do this, a voltage is applied to input 4 of the TL494 that sets this minimum gap between pulses. Capacitor C14 and a trimming resistor of 15 kΩ create the same bias, allow you to adjust this gap, and capacitor C14 smoothly raises the voltage when the unit is connected to the network. When charging, it reduces the protective gap and increases the width of the control pulses of the transformer T1. What should be checked on an oscilloscope? The protective dead gap should not be lower than the pulse width by a quarter of its width. The pulse width from the TL494 outputs is adjustable depending on the voltage in the range from 0 ... 3 volts applied to input 3. This voltage is supplied from the voltage regulator of the TL494 microcircuit from outputs 14 and 13, it is equal to 5 V ± 5%. The optocoupler, which performs galvanic isolation, regulates this voltage applied to input 3 of the TL494 depending on the voltage of the power supply output. A 680 ohm resistor connected in series with the optocoupler and a 100 microfarad capacitor prevent excitation of the power supply, if this happens, the ratings of these parts must be increased. If excitation occurs, then in no case should the power supply be loaded, since the IRF740 power transistors may be overloaded while charging capacitors C8 C9 C10. During excitation, the power supply starts to squeal and the output voltage starts to jump. The rectifier of the secondary windings consists of two Schottky diodes; they have a speed of 100 kHz and a maximum current of up to 30 amperes, their type is KD2997A or they can be replaced by KD213 with any letter. First, smoothing occurs on capacitors C8 and C9, C8 at high frequencies C9 at low 50 Hz, then through a choke and another capacitor C10. Short circuit protection is assembled on a transistor, several resistors and an RS flip-flop, it has a high speed. The adjustment of the operation current is adjusted with a tuning resistor R8. The voltage-amplified signal from the transistor VT1 is fed to the trigger, which, when a voltage below 2 volts appears at input 4, turns on the PS2501 optocoupler through the transistor, which connects the 16th input of TL494 to +5 V, which leads to the termination of the supply of control pulses. From the optocoupler at the 16th input of the microcircuit, the voltage through a 10 kΩ resistor goes to the diode and capacitor, charging up to a diode saturation voltage of 0,5 volts. In this case, a silicon diode is required, for example KD103A, when the trigger control button is pressed, the optocoupler turns off and the power supply leaves the overload state. At input 16 TL494, the voltage gradually decreases, discharging to a resistor of 2 kΩ and 10 kΩ, and thus the pulse width begins to increase to the limit set by the variable resistor R9. Details should be the same as in the diagram. The T1 transformer is made of W-shaped ferrite MN2000 with a section of 12X14, a window height of 31mm and a width of 9mm. The primary winding has 32 turns of individual wires 0,3 mm PEV-2, the secondary winding has 8 turns of individual wires of 0,8 mm PEV-2, for the primary with a total cross section of all wires 1 mm, secondary 2 mm. The secondary can also be wound on another voltage at the rate of 4 volts per turn. The inductor in the output stage is made of the same ferrite and has 20 turns of PEV-2 1,2 mm. Transformer T2 has a power of 4 ... 10 watts. Power transistors need heatsinks with an area of 80 cm2, on the diodes of the output stage are the same for each. Author: Rodikov E.Yu.; Publication: N. Bolshakov, rf.atnn.ru
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