A very high gain relay can be very useful on the project bench. The circuit we describe can trigger relays from signals with 10, 100 or 1000 times less intensity than the needed in a normal application.
It is a gain super-amplifier which depends on R1 and R2 according to the table in the figure, using a source according to the relay. The source must be symmetric.
The circuit is designed for sensitive relays but can work with other types which have a maximum coil current of 100 mA.
In Figure 1, we have the complete diagram of this electronic relay which can be built on a breadboard or printed circuit board.
Material list
CI-1 -741 - integrated circuit
Q1- BC548 - NPN general purpose transistor
D1- 1N4148 - general purpose diode
K1- 6 V or 12 V - Sensitive relay
R1- see table
R2 - see table
R3 - equal to R1
R4 - 1k ohm x 1/8 W- resistor - brown, black, red
Miscellaneous:
Printed circuit board, symmetrical power supply according to the relay voltage, wires, welding, etc.
