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role of 1N4007 and reverse current

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kangyunmei

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Do you know the role of 1N4007 in this circuit? And do I need to consider reverse current?
image.png
 

When the relays are switching OFF the voltage jumps up between those terminals for a moment. This voltage can be quite high positive value at the collector, so a diode is added in parallel with the relay to handle the spike voltage and protect the more sensitive switching transistor.
 

It is to ground the reverse current. 1N4007 will be sufficient for almost all relays. For fast switching relays i use a BA159.
 

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