JSJ type transistor time relay circuit

 The entire circuit is divided into main power supply, auxiliary power supply, bistable trigger and auxiliary circuits.
    Its working principle is as follows: when the power is turned on, VT1 is driven by the wind and the wind, the relay coil K obtains a bias current and is in the conductive state, and VT2 is in
the cut-off state. At this time, although there is current passing through the relay coil K, the current is too small, so it cannot action. After the main power supply and auxiliary power supply voltage are superimposed, they pass through
the potentiometer RP and the variable resistor R. The normally
closed contacts of K charge the capacitor Ch. During the charging process
, the potential at point a gradually increases until
the potential at point a is higher than the potential at point b. The diode
VD3 is turned on, causing the positive voltage of the auxiliary power supply
to be added to the base of the transistor VT1, and VT1
changes from on to off. ． VT2 obtains the bias current from Ri
and is turned on, so the relay K acts and
sends out the corresponding on or off control
signal through the contact. After that, the capacitor bar passes through R and is discharged
, ready for the next work. Potentiometer
RP is used to set the delay time.