The role of adjustable control of AVR voltage regulated power supply

The AVR voltage regulator can be controlled by a three-terminal adjustable voltage regulator block LM317T, which is output after current expansion by an external high-power transistor 2N3055. The output voltage is continuously adjustable within 0.8V to 24V. The overload and short-circuit protection current is 1.4A (measured value), and the protection circuit is composed of R1~R4, V1, V2, C2, unidirectional thyristor VS and relays.

1. When the output terminal is overloaded or short-circuited, and the current on the sampling resistor R1 reaches 1.4A, the relay is closed, the output switch K is connected to point B, the output current is cut off, and maintenance is achieved. LED1 lights up, the buzzer H sounds, and an audible and visual alarm is issued. After the overload and short circuit are eliminated, press the reset switch S, V2 is turned on, VS is turned off, and the relay is released. Switch K is connected to point A, and the output returns to normal, and maintenance is exempted.

2. Telephone tester The telephone tester in this circuit has three test functions: ringing, dialing, and sending. Select the required test function through the function selection switch SK. When testing ringing, dial SK to the K1 position, and the 30V AC voltage is input into the telephone through R10 to complete the ringing. When testing dialing and sending, dial SK to the K2 position. When picking up the phone or in the hands-free state, each time a number key is pressed, LED3 lights up once. When redialing, LED3 will flash continuously, and the number of flashes is the same as the number of digits entered in the redial number. When testing sending, the operator speaks or blows into the microphone, and LED3 will be lit, indicating that the sending function is normal.

3. Remote control tester. As for the remote control tester, there was an article in "Electronics News" that introduced it, so I won't elaborate on it here.

4. Component selection. The transformer is a 100W, dual 26V plus dual 15V toroidal transformer. For AC 26V, select one of the dual 26Vs. For AC 30V, connect the dual 15Vs in series. The transistor is 2N3055, which has severe heat generation and needs a large enough heat sink. If necessary, a fan can be installed for heat dissipation.