what is purpose of using diode across relay coil? - Electronic Circuits Projects Diagrams Free

samina · 21st October 2009, 04:38 PM

what is purpose of using diode across relay coil?

Mike2545 · 21st October 2009, 04:42 PM

It suppresses the fly back when the coil is de-energized.

audioguru · 21st October 2009, 08:59 PM

Take a relay and a battery.
Hold one hand (not two hands) across the relay coil.
Connect the relay coil to the battery then disconnect it.
Your hand will feel the hundreds of volts caused when the current in the inductance of the relay coil suddenly collapses which induces the very high voltage (the flyback voltage).
The hundreds of volts will destroy a transistor that drives the relay coil unless the coil has a reverse-connected diode across it which reduces the voltage spike to 0.7V more than the supply voltage.

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21st October 2009, 04:38 PM	#1
samina	what is purpose of using diode across relay coil? what is purpose of using diode across relay coil?

21st October 2009, 04:42 PM	#2
Mike2545	It suppresses the fly back when the coil is de-energized. __________________ Mike2545

21st October 2009, 08:59 PM	#3
audioguru	Take a relay and a battery. Hold one hand (not two hands) across the relay coil. Connect the relay coil to the battery then disconnect it. Your hand will feel the hundreds of volts caused when the current in the inductance of the relay coil suddenly collapses which induces the very high voltage (the flyback voltage). The hundreds of volts will destroy a transistor that drives the relay coil unless the coil has a reverse-connected diode across it which reduces the voltage spike to 0.7V more than the supply voltage. __________________ Uncle $crooge