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.
- posted
15 years ago
how to flip a relay by digital signal
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- posted
15 years ago
Drive the coil with a suitable transistor. Don't forget the catch diode!
Cheers! Rich
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- posted
15 years ago
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