Time relay two

The time relay introduced in this example uses a 555 time base integrated circuit to replace the JSKl series of transistor time relays.
Circuit Operation Principle The time relay circuit consists of a power supply circuit, a monostable circuit, and a relay control circuit, as shown in Figure 8-136.

The power circuit is composed of a power transformer T, a rectifier diode VD1, a VD2, a three-terminal voltage regulator integrated circuit ICl, and filter capacitors Cl and C2.
The monostable circuit consists of potentiometer RP, diode VD3, capacitors C3, C4, time base integrated circuit IC2 and normally closed contacts of relay K1.
The relay control circuit is composed of resistors R1, R2, relays K1, K2, diodes VD4 and light-emitting diodes VL.
AC 220V (or AC 380V) voltage through T step-down, VDl and VD2 rectification, Cl filter, ICl voltage regulation, generate +l2V voltage at both ends of C2, as the working power of IC2. The +l2V voltage is also applied to both ends of Kl via Rl, so that Kl is energized and pulled, its normally closed contact is disconnected, and C3 is slowly charged through the RP.
When the power is turned on, the 2nd and 6th pins of IC2 are low, the 3rd pin outputs a high level, K2 does not operate, and VL does not emit light. When the voltage across C3 is charged to 8V or more, the circuit in IC2 is turned over, the 3 pin becomes low level, K2 is energized, its normally open contact is turned on, and VL is lit.
Changing the resistance of RP and the capacity of C3 can change the delay time of the relay (when the resistance of RP is l5Mn, the capacity of C3 is 33μF, the delay is 9min; the resistance of RP is lOMn, When the capacity of C3 is 33pF, the delay time is 6MΩ; when the resistance of RP is 1.5MΩ, and the capacity of C3 is 22μF, the delay time is 1-30s).
Component selection
Rl selects 1/2W metal film resistor for use; 1/4W metal film resistor is used for saturation.
RP uses organic solid variable resistors.
Cl uses aluminum electrolytic capacitors with a withstand voltage of 5 OV; C2 and C3 select aluminum electrolytic capacitors with a withstand voltage of 13V; C4 uses monolithic capacitors or polyester capacitors.
VDl-VD4 selects 1N4007 silicon rectifier diode for use.
VL selects high brightness LED of φ3mm.
ICl selects LM7812 type three-terminal integrated voltage regulator; IC2 selects NE penalty type 5 time base integrated circuit.
T selects 3-5W secondary voltage for 24V (with center tap, 380V/24V or 220V/24V) power transformer.
Kl and K2 use JRX-l3F or JM-4 type 12V DC relay.