100A time delay relay circuit

Figure 1 is a monostable delay relay composed of a double D flip-flop CD4013. After S1 is turned on, pin 1 of CD4013 is low level in steady state, and relay K does not act. Press button S2, pin 3 of the CP terminal of the IC is triggered by the rising edge of the positive pulse, and the high level of pin D of the data terminal is sent to the output terminal Q. The potential of pin 1 of the IC becomes high, and the circuit enters a monostable state. At this time, the transistor VT1 is saturated and conductive, the relay coil is electrically activated, its contacts are closed, and a large DC current is output. When the potential of pin 1 of the IC becomes high, the capacitor C is charged through the resistor R2 and the potentiometer RP. When the voltage at both ends of C is charged to the clear O threshold level of the 4th pin of CD4013, the pin 1 of the IC returns to low potential, and the monostable state ends. . The relay is released, and the high-current power supply is disconnected from the external circuit. The time that the IC is in the monostable state is approximately t=0 7(R2+RP)C. This circuit can adjust the timing time within the range of about 15s-30s, which can meet the timing requirements of the laboratory. For other applications, the timing time can be changed by selecting the parameters of R2, RP and capacitor C. After the monostable state ends, pin 1 of the IC changes to low level, and the capacitor C is quickly discharged through the diode D2 and the resistor R4, preparing for the next trigger.

Figure 2 is a monostable time relay composed of a time base circuit NE555. When the switch S1 is closed, the circuit enters a stable state. Pins 3 and 7 of the IC are both low level. At this time, the capacitor C cannot be charged; the transistor VT1 is cut off. Relay K does not operate. Press the start button S2, pin 2 of the IC is triggered by a pulse from high to low, pin 3 of the IC becomes high, pin 7 is left floating, and the circuit enters a monostable state. At this time, the transistor VT1 is saturated and conducts, and the relay coil is energized. Action, its contacts are closed, and large DC current is output. At the same time, the capacitor C is charged through the resistor R2 and the potentiometer RP. When the voltage across the capacitor C reaches 2/3VCC, the monostable state ends, pin 3 of the IC becomes low, the relay loses power and is released, and the DC large current stops outputting. After the circuit returns to steady state, the capacitor C is discharged through pin 7 of the IC and waits for the next trigger. The monostable duration t, that is, the length of the DC high current output time, is determined by the parameters of the monostable circuit's timing element resistor R2, potentiometer RP, and capacitor C. It can be estimated by the following formula: t=1.1(R2+RP )C, after adjusting RP, it can meet the delay time requirement of 20±2 seconds.

Relay K in the above two circuits uses HG4119 ultra-small electromagnetic relay, and the other components can be selected according to the parameters marked in the figure. If you want to transplant it to applications that require accurate timing, you can choose tantalum capacitors, metal film resistors, multi-turn potentiometers or digital potentiometers as timing components, which can meet the accuracy requirements in most electronic production.