Switching power supply for a stereo amplifier, 220/2x15 volts 2x2 amps. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Power Supplies

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When creating a stereo amplifier for an audio center or, as they say now, a home theater, on a modern integrated element base, I want the power supply to keep up with progress. In addition, a switching power supply is not only interesting from the point of view of progress, but also from a practical point of view. After all, finding a suitable power transformer, or just a core with a frame, is now difficult, and if there is a suitable item, it will be very cumbersome and heavy.

I searched a little on the Internet, looked through datasheets and service manuals on TVs, and this is what happened - the diagram is shown in the figure.

(click to enlarge)

The circuit is a flyback switching power supply based on the UC3842 PWM chip. The circuit is almost typical, almost the same as recommended by the manufacturer of this IC.

The voltage from the mains through the choke filter C10-L1-C11 is fed to a bridge rectifier on diodes VD1-VD4. Resistor R10 limits the inrush current pulse to charge capacitor C9. The DC voltage at the output of this rectifier is about 300 V.

Power is supplied to the A1 chip in two ways. Start power via R1. After starting the generator, power begins to flow from winding 2 of the transformer T1 through a rectifier on the VD6 diode. The same voltage is also the control voltage for the voltage stabilization circuit (the control voltage is supplied to the stabilization circuit through R3-R5-C2).

The generated pulses come from pin 6 A1 to the gate of the field-effect transistor VT1. The primary winding of the pulse transformer T1 is included in its drain circuit. In the source circuit, there is a resistor R9, which serves as a protection circuit for this transistor against overcurrent. When the permissible current is exceeded, the voltage across this resistor increases and enters the control input A1 (pin 3). If the voltage at this output exceeds the threshold value, the output stage is turned off (pulses cease to flow to VT1).

The secondary voltage of ±25 V is formed by two independent secondary windings 3 and 4, and respectively rectifiers on diodes VD6 and VD7. Then, already in direct current, they are connected in series. If the amplifier circuit requires separate sources that are not connected to the GND point, then they can be disconnected.

Output voltages 2x15 V, at load current 2x2 A.

Despite the presence of stabilization in the primary circuits, the secondary voltages are unstable. Rather, their value does not change when the mains voltage changes over a wide range, but is subject to some changes depending on the load. Almost the same as depending on the load, the voltage at the output of the rectifier, fed from a conventional low-frequency power transformer, changes.

A stereo amplifier with TDA2030 microcircuits (without additional transistor "amplifiers") in the PA circuit works from this power source, with an output power of 2x15 watts.

As a core and a frame for a pulse transformer, a frame and a core from a 3-USCT TV pulse transformer are used. The primary winding of the transformer T1 (1) contains 60 turns of PEV wire 0,61. Winding 2-10 turns of wire PEV 0,43 windings 3 and 4 each with 10 turns of wire PEV 0,61. The windings of all coils must be carried out according to the instructions on the diagram (the beginnings of the windings are marked with bold dots), the direction of all windings is the same.

Inductor L1 is a ready-made surge protector from the same TV. Inductors L2 and L3 are wound on ferrite rings with an outer diameter of about 20 mm, it contains 20 turns of PEV 0,61 wire.

The transistor needs a heatsink.

During the adjustment process, it may become clear that the output voltages differ from the calculated ones. Then they can be slightly adjusted to the required value by selecting the resistance R4. Replace this resistor only after turning off the source from the mains. An increase in R4 leads to an increase in voltage, and a decrease causes a decrease in the output voltage.

Author: Sadovnikov P.F.

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