Sound and light alarm DC regulated power supply circuit

This circuit has two DC regulated power supplies , of which the main power supply outputs 1.530V continuously adjustable, and the other auxiliary power supply outputs a 5V fixed voltage
DC power supply for short circuit protection and audible and visual alarms. If the output terminal of the main circuit is short-circuited, the 30V AC circuit on the secondary side of the transformer will be immediately cut off
for full protection, and an audible and visual alarm will sound to remind the user. After the fault is eliminated, the fork returns to normal. This circuit has
the characteristics of stability, reliability and rapid response, and can solve the problem of unprotected DC power supply and frequent component burnout.
    (1) Circuit working principle
    1) Main power supply circuit principle: As shown in the figure, AC 220v is transformed through transformer T, VD1 ~ VD4 bridge rectifier, capacitor Ci
filter, LM317 three-terminal voltage regulator, adjust the potentiometer RP to make DC The output voltage is 1.5~30V. Watch the voltmeter reading. Among them, EL is the AC
indicator light, Jl is the normally closed contact of the relay, capacitor C2 improves ripple and suppresses over-voltage, and G improves the transient response of the load.
    2) Short-circuit protection and audible and visual alarm circuit: The short-circuit protection circuit uses an optical coupler 4N25. The output terminal has no feedback effect on the input terminal, and the signal
can only be transmitted in one direction, realizing light transmission control. Optocouplers consist of light-emitting diodes and phototransistors. Day, ruler. , 4N25 constitutes
a signal control circuit, controls VT1, VTZ, K and Y form an audio oscillation circuit. When the circuit is normal, the DC output passes through R,, R. When added to
pins 1 and 2 of 4N25, the light-emitting diode emits light, turning on pins 5 and 4. The base of VT1 is biased and cut off, and the audio oscillator does not work. When the DC output is short
-circuited, the voltage is zero and the LED does not work. The phototransistor is turned off and divides the voltage with Rs to provide a forward bias current to the base of VT1 to turn it on.
When the VT2 amplifier tube is working, the relay K coil on the collector is energized, the normally closed contact on the secondary side of the Ti series is disconnected, the AC power supply is cut off, and the green indicator
light goes out, fully protecting the circuit. The KZ normally open contact is closed, the LED is flashing, the music piece circuit is working, playing a beautiful piece
of music, and the sound and light alarm are completed simultaneously to remind the user. After checking and troubleshooting, the circuit returns to normal.
    3) Auxiliary regulated power supply: The auxiliary power supply is only used for protection and sound and light alarm circuits. When there is no short circuit in the main circuit, the auxiliary power supply is in "standby" state
, and the circuit principle is omitted. Reset button S2, during circuit troubleshooting, in order to relieve the audible and visual alarm, set it to "reset". After troubleshooting,
set S2 to "protect" state.