how to flip a relay by digital signal

Discussion in 'Electronic Basics' started by saurabh9, Jul 10, 2008.

1. saurabh9Guest

Hi,
What would be an easy way to turn on a relay by a digital signal. The
relay would be hooked to a 220 V AC device.

2. neon

1,325
0
Oct 21, 2006
flip flop changes states but for relay to change states all you need is remove power and re-apply power like a switch douple pole double throw 240v humm are you sure your relay is rated for that voltage and current i say that because of your question.

3. Rich GriseGuest

Drive the coil with a suitable transistor. Don't forget the catch diode!

Cheers!
Rich

4. Bill BowdenGuest

Actually, the catch diode might not be needed. There's lots of
capacitance in the windings of the relay coil which charges up when
the transistor switches off and limits the voltage to whatever the
capacitance is combined with the energy put into it. A 1 millihenry
coil at 12 volts and 120 ohms will store 1/2 L* I^2 = 5 microjoules.
If the winding capacitance is say 2000pF, the voltage will be 1/2
CE^2= .000005 = 70 volts.

Did I do that right?

-Bill