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The relay needs to use the condition of the flyback diode.

Hardware design
January 29, 2021 by Davia 1088

Assuming a low-power signal relay, 3V, 140mW coil, driven by a 2N3904 NPN transistor, do I need a flyback diode? If necessary, what parameters determine it?

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Rainy Posted on January 29, 2021

Have you ever used LTspice? I tried it without a diode and the peak value is 11kV.

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Tino Posted on January 29, 2021

What should be considered is the energy that will damage the transistor, similar to an electrostatic pulse.

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Doyle Posted on January 29, 2021

The flyback diode is selected according to the voltage and current. For example, your coil voltage is 3V and the power is 140mW, so the current=0.14/3=0.046A, then you can choose the diode, you can choose 1N4007, because this is very cheap Of it.

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