Adjustable voltage regulator circuit that needs manual recovery

(1) Circuit Description

The manual recovery voltage regulator circuit is shown in the figure. The current of the reference voltage power supply flowing through the voltage zener diodes VD3 and VD4 is stabilized by the bulb H, thereby improving the stability. The bulb also serves as an overload indicator. By adjusting the potentiometer RP2, the output voltage of the voltage regulator can be adjusted within the range of 0.2 to 15V, and the maximum load current (which can play a protective role under this current) can be determined by adjusting the fine-tuning resistor RP1. When the VT5 is equipped with a heat sink and the output voltage is 15V, the voltage regulator can pass a current of 1A for a long time, or a current of 2 to 3A within 30 to 40 minutes (determined by the air convection conditions of the adjustment tube heat sink). The circuit adopts two measures: electronic protection and electromagnetic protection.

(2) Electronic protection circuit

The electronic protection circuit is composed of transistor VT1 and thyristor V. When overloaded or short-circuited, the voltage drop on the detection resistor R0 increases, and the transistor VT1 and thyristor V are triggered and turned on. Since it short-circuits the reference voltage power supply, the transistors VT3 and VT4 are cut off, and the base of the adjustment tube VT5 is cut off without bias, achieving the purpose of overcurrent protection.

When the overload or short circuit fault is eliminated, if you want the power supply to return to the initial state, just press the reset button SB. After pressing the button, the anode-cathode of the thyristor V is short-circuited, and the control electrode has no bias, so the thyristor is cut off.

The purpose of introducing an electronic lock composed of transistor VT1 in the voltage regulator is to reduce the output impedance of the voltage regulator, but this is not necessarily necessary.
(3) Electromagnetic protection circuit

The use of an additional electromagnetic protection circuit consisting of transistor VT2 and relay KA is based on the following reasons: when the voltage stabilizer has been operating at a current close to the maximum value for a long time, without electromagnetic protection, when the load is slightly overloaded, although the electronic protection is activated, the adjustment tube VT5 is not completely cut off, and a large current continues to pass through it, which is likely to burn it out.

With electromagnetic protection, when the load is slightly overloaded or short-circuited, it can act quickly. That is, when the thyristor V is turned on, the base of the transistor VT2 is added to the positive polarity end of the voltage-stabilizing diode through the resistor R2, VT2 is turned on, the relay KA is attracted, and its normally open contact 1 is closed, connecting the base of the adjustment tube VT5 to the positive polarity end, VT5 is turned off, and the load circuit is cut off.

(4) Production instructions

The high-power tube 3AD56 is a device with high power consumption. In addition to the standard high-power triode shell package, it must also be equipped with sufficient heat sinks. The heat sink can be installed on the circuit board during production. The indicator light H and button SB are installed on the front panel for display and operation; the input and output terminals are installed on the back panel for easy wiring. 2CW72 are two ordinary voltage regulator diodes with a voltage regulation value of 7.0~8.8V.