This is a Simple Relay Driver Circuit Diagram. This device is used to switch inductive loads such as relays, solenoids incandescent lamps, and small DC motors without the need of a free-wheeling diode.The relay operates a certain time, td, after power is applied to it, and then it operates for a length of time, tc. The SCR fires when the voltage on Ci reaches VA.
Simple Relay Driver Circuit Diagram
This operates the relay, which stays activated until the current charging C2 drops below the dropout current. To keep the relay in its activated position indefinitely (tc =00), eliminate C2 and choose R2 just large enough to keep the relay coil current within its related limits.
Typical component values
td = 30 seconds and tc = 2 seconds
are
Rl = 1.5 megohms,
R2 = 10 k ohms,
R3 = 3 k ohms,
Cl = 47 µ¥, and
C2 = 100 µ¥.
The SCR is a 2N1877 and the relay is a Potter Brumfield PW-5374. A value of 12 Vdc is assumed for V~.
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