DC stabilized power supply works

In the circuit, D5, D6 and C1 form a full-wave rectification and filtering circuit, which converts the input AC power into DC power; Q1 and Q2 form a Darlington injection circuit, Q1 is called an adjustment tube, and Q2 is called a push tube. Power supply; Q3, D8, R2, R3, RW1 together constitute the output voltage sampling negative feedback circuit, Q3 is called the sampling amplifier tube, D8 is called the reference voltage regulator tube, this part is used to stabilize the output voltage; Q4, R5 constitute the output current sampling The circuit provides overcurrent protection for the output; C5 is the output filter capacitor. Since the regulating tube and the load are connected in series with respect to the input, this power source is called a series-type DC regulated power supply.

Figure 1 DC stabilized power supply schematic

After the 220V AC power is stepped down to low-voltage AC power, the full-wave rectification and filtering circuit composed of D5, D6, and C1 is rectified and filtered to become DC power, which is sent to the Darlington injection circuit, and finally the DC voltage is supplied to the load by the injection-related circuit. VO, the magnitude of this voltage VO is determined by the reference voltage VREF and the voltage division ratio of the sampling branch. When the output voltage VO rises instantaneously for some reason, the collector current of Q3 of the output voltage sampling circuit increases, causing the base current of the emitter to fall, the internal resistance of the adjustment tube increases, and the tube pressure drop increases. The output voltage VO is lowered; when the output voltage VO is instantaneously decreased, the collector current of the output voltage sampling circuit Q3 is decreased, the base current of the injection circuit is increased, and the tube voltage drop is reduced, thereby making the output voltage VO also rises; the above process stabilizes the output voltage at a certain voltage value, thereby achieving regulation. By adjusting RW1, you can change the value of the output voltage value.

When the load current exceeds the rated output current, the voltage drop across R5 will turn Q4 on, forcing the bias voltage of the shoot-in circuit to decrease, the internal resistance to increase, and the tube voltage drop to increase, the output current of the shooter is limited. The output voltage is also reduced, thereby providing overcurrent protection. This structure belongs to the current limiting protection circuit.

The input 220V AC voltage is stepped down by the transformer, and the output is pulsating DC voltage after rectification by the rectifier diode. It has a large voltage ripple. After the smooth filtering of the capacitors C1, C2 and C3, the output voltage is relatively stable, and then input to the voltage regulator. The circuit can get a stable DC voltage regulated power supply with small voltage ripple at the output.