Basic Relay or Solenoid Driver
The above is a standard way of driving Small Power
Relays from Control Signals generated by Logic or
and Automation - 02
C2 and R5 form a snubber which improves the life
of the metal contacts, the contacts can erode due
to sparking when switching inductive or even big
loads. reduces EMI_RFI.
of Switches in Electronics
The Electromagnetic Solenoid Coil is rated by
Volts and Ohms. If you choose 12V ensure a stable
12V is provided, more voltage will heat coil, less
voltage will cause sparking or will drop out the
magnetic holding. A high coil resistance is better
as the heat will be less and power consumption of
your design is low.
Q2 is any 500mA-50V-NPN device. For a relay drawing
100mA-12V use a 200mA-50V device or better. D1 is a
freewheeling diode, inductive kickback diode or
snubber or something that stops the coil from
zapping the Q2. Q1 and Q2 form a Darlington pair to
amplify the low current drive of some CMOS gates.
Phase AC SSR for 1 HP Motor
Chattering and Sparking
R2 and R1 is to hold the bases to ground and avoid
floating or else they will pick up noise and relay
will chatter..... the contacts will spark .......
the motor or heater will fail to work well.........
and your product will get rejected ........... the
payments will be held up ...... the customer may
even ........................... stop that right
Types of Relays
R3 and C1 is a dampener for the signal so that quick
relay operations can be avoided, this is important
if your relay is driving a three phase contactor
which runs a huge Motor. C1 can be increased if
required. When huge loads are switched on-off in a
factory, lots of spikes and drop outs will reset
timer and logic circuits, this will turn on off
above relay ... leading to the load switched by this
circuit going on-off. This may even lead to a
Oscillation with the spikes as feedback which can
cause great trouble during the troubleshooting
process. R4 limits current.