Time-adjustable delay power socket circuit diagram

The time-adjustable delay power socket is suitable for rice cookers, electric lighting equipment and other electrical equipment.

1. This power socket circuit consists of a power circuit (see Figure 1) and a delay circuit (see Figure 2). Here's how it works.

The input alternating current is stepped down by capacitor C0, rectified by D1 and D2, stepped down by R1, and filtered by C1 to obtain a stable DC voltage V0 at both ends of R2, which provides voltage for the delay circuit. The input voltage is 200°C and 220°C, and the suitable V0 is 20~23. The LED lights up, indicating that there is AC voltage input. R3 is the current limiting resistor, and R0 is the discharge resistor of C0.

The delay circuit uses the charging characteristics of the capacitor to achieve delay. When the potential of the positive electrode of capacitor C2 is lower than the potential of IC2 pin, the IC1 pin working in the comparator state outputs a low level of about 2V, which cannot saturate Tr and conduct, the relay J is in the released state, and the socket is not charged. When the potential of the positive electrode of C2 is slightly higher than the potential of IC2 pin, IC1 pin outputs a high level of about 22V, which makes Tr saturated and conductive, the relay is in the pull-in state, the socket is charged, and the electrical appliance is connected. Due to the negative feedback effect of R7, the potential of IC2 pin decreases, pin1 maintains a stable high level, and the relay reliably closes. D3 is the discharge diode of C2, RV1 is the delay potentiometer (the resistance is linearly related to the angle), R4 is the delay resistor, S is the delay time switch, R5 and R6 provide the reference potential for IC2 pin, R8 and R9 It is the current limiting resistor, Tr is the driving transistor, LED2 is the socket live indicator light, D4 is the freewheeling diode, used to protect the transistor Tr.

2. Calculation of circuit-related data

2.1 The potential of IC pin 2 U2=V0R6/(R5+R6)=(2)/(3)V0

2.2 The charging time when the initial voltage of C2 is 0 and the positive potential of C2 reaches (2)/(3)V0.

a When S1 is closed, t=1.1RV1*C2, and the delay time is 0 to 22 hours. When C2 is fixed, t∝RV1. When RV1 is the same, a larger C2 can make the time adjustable range wider, but the adjustment accuracy decreases; a smaller C2 will cause the opposite.

b When S1 is disconnected, t=1.1(RV1+R4)*C2, the delay time is 3 to 5.2 hours.
2.3 Calculation of discharge time of capacitor C2　

When the relay is released, the voltage stored in C2 is discharged to ground through D3 and R2, and the discharge time is 5R2C2. At this time, the voltage across C2 is only 0.007V.
T=5×1.3×103×3300×10-6=22 (seconds)
To ensure timing accuracy, the CT can be used again after unplugging it from the power source for 22 seconds.
3 The key relay in the circuit design
should have two sets of normally open and normally closed contacts. When the socket is not powered, the normally closed contacts of J-2 are connected to provide voltage V for the delay circuit. When the relay is closed, the normally closed contact of J-2 is disconnected and the normally open contact is connected. At the same time, the normally open contact of J-1 is connected to electrify the socket. The purpose of using two sets of normally open and normally closed relays is: at the end of the delay time, J is provided with the pull-in voltage by R2; the reed connected to the moving contact maintains the pull-in voltage during the swing process by C1; the normally open contact When the head is closed, the pull-in voltage is provided by the coil DC resistance of J (the coil DC resistance is about 1.2K), so V0 remains basically unchanged.