JS20 single junction transistor time relay circuit

The circuit consists of five parts: delay link, amplitude detector, output circuit, power supply and indicator light.
    The voltage stabilizing part of the power supply consists of the resistor R and the voltage stabilizing tube VS, which supplies power to the delay link. The thyristor VTH and relay KA in the output circuit
are directly powered by the half-wave rectifier circuit.
    The working principle of the circuit is as follows: when the power is turned on, after rectification by diode VD1, filtering by capacitor cl, and voltage stabilization by RJ and VS,
capacitor G is charged through RP1 and R4. The voltage on the capacitor
G gradually increases exponentially. When this voltage
is greater than the peak voltage of the single-junction transistor VT, the single
-junction transistor is turned on, G
is discharged through the eb1 pole of VT and the wind, and a pulse voltage is output on the wind, triggering the fan. The gate
tube VTH is turned on, causing the relay KA to close.
The contacts of KA short-circuit C3 at the same time, causing it to discharge rapidly.
The voltage between ebl of the single-junction transistor drops rapidly. When it drops
to Vr. When the valley point voltage is reached, Vr is turned off. At the same time,
the LED indicator lights up. When the power is cut off, the relay
KA is released and the circuit returns to its original state, waiting for the next
action. By adjusting RP. The delay time can be adjusted.