Adjustable regulated power supply with overload and short circuit protection

The characteristics of this regulated power supply are: 1. The circuit is simple, the voltage stabilization accuracy is high, and the output voltage remains unchanged after adding the rated load. 2. It has overload and output short circuit protection and alarm functions. When overload occurs, the voltage drop on resistor R8 increases. When the voltage drop reaches 0.6V, the silicon controlled thyristor SCR is turned on, causing the base potential of Q1 to drop to about 1V. Therefore, tube Q1 and adjustment tubes Q2 and Q3 are all cut off, and the protection The adjustment tube is protected from burnout. After Q2 and Q3 are cut off, the output voltage is zero, the electronic switch Q4 is cut off, and Q5 is turned on, causing the multivibrator composed of Q6 and Q7 to start oscillating (tens of Hertz), and the light-emitting tube LED2 flashes to indicate an alarm. When the output terminal is short-circuited (maximum overload), the voltage drop on R8 is much greater than 0.6V, the thyristor is turned on immediately, and the regulated output is also cut off. After the short circuit fault is eliminated, just press the reset button AN to "reset" the thyristor, and the regulated power supply will immediately work as usual. At this time, Q4 is normally turned on, Q5 is cut off, and Q6 and Q7 stop vibrating and go out. This power supply is easy to make, and the amplification factors of Q2 and Q3 should be close to the same. Resistors R2, R4, R5, R6, R17 are selected as 1/2W, and the rest are 1/4W. Resistor R8 is made of 6 constantan wires with a diameter of 0.25mm and a length of 18Cm connected in parallel. If there is no constantan wire, you can also use 8 1/4W2.2O European color ring resistors connected in parallel. This resistor only affects the protection current setting value and has nothing to do with the voltage stabilization accuracy. The adjusting tube radiator adopts a commercially available special aluminum alloy radiator and is installed outside the iron shell.