Discharge time relay circuit

Discharge time relay circuit

This timer uses a field effect
transistor, so it has the characteristics of high timing accuracy and long timing time.
When R3-IOOOMfl, and C-200VF, the delay time
reaches 8h.
    Press button SB, transistor VTi conducts, VT3 conducts
, relay KA closes, and the delay starts. When the capacitor C discharges
to a certain value, VT2 changes from cut-off to conduction, VT3 cuts off, and
KA is released.
    The delay time is determined by R3, RP and C.