Adjustable voltage regulated power supply circuit

Adjustable voltage regulated power supply circuit

The figure shows an adjustable voltage stabilized power supply with voltage of 1.5-9V and current of 0.2A. It is composed of diodes VD1-VD4 for rectification, transistors VT2 and VT3 for compound adjustment, transistor VT4 for comparison and amplification, voltage stabilizer tube VD7 for reference voltage source, voltage stabilizer tube VD5 for constant current source, resistors R1, R2, R3, transistor VT4 for current limiting protection and detection resistor R0.

If the output voltage changes due to some reason (input voltage changes or load current changes), the comparison and amplifier part amplifies the change signal and sends it to the adjustment part, causing it to produce an opposite change to offset the change in the output voltage.

Potentiometer RP and resistor R6 sample the output voltage and send it to the comparison amplifier of transistor vT4 to compare with the reference voltage of voltage regulator VD7. In the circuit, voltage regulator VD5 and resistors R1, R2, and R3 form a bias circuit, which makes the collector current Ic through transistor VT1 change very little and can be basically considered constant, so this part of the circuit is generally called a constant current source load.

The transistor vT5 and the detection resistor R0 in the circuit form an overload and short-circuit protection circuit. When the load current exceeds the set value or short-circuits, the voltage drop on the detection resistor Ro will be greater than the conduction voltage (0.5V) of VT5, causing VT5 to conduct, and most of the current sent by the constant current source flows into VT5, reducing the base current Ib of the adjustment tube and thus limiting the output current of the adjustment tube.