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Relay back emf protection

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markjsunil

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The circuit below says diode is connected to protect the transistor from back emf. What about other devices like ICs connected to +V. Will they not get damaged due to back emf as diode provides the path for back emf to pass through the diode up to +V and to other devices connected to +V.

Relay.jpg

-Thanks
mark
 

in that figure i.e.relay....generally relays dealt with high voltages and currents when compared with ic's which consumes current in milli amps,thats why here we have free wheeling diode to protect from back emf's
 

Electro Builder said:
in that figure i.e.relay....generally relays dealt with high voltages and currents when compared with ic's which consumes current in milli amps,thats why here we have free wheeling diode to protect from back emf's
Click to expand...

Thanks. For ex, +V is at 6V for 6V relays. If there are other ICs connected to this 6V rail and there is a back emf from the relay coil will this back emf not pass through the free wheeling diode and through the 6V rail and damage ICs conected to the 6V rail?
 

The back EMF is the opposite polarity to that used to energise the relay. When the transitor turns off, the polarity across the relay coil is positive at the bottom (transistor end) and negative at the top so the diode conducts and clamps the voltage to no more than about 0.7V. The clamp current flows only through the relay coil and diode, no other components are affected.

Brian.
 
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