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?
Erin ポストする October 27, 2020
Have you used LTspice, I tried it without a diode, the peak value is 11kV
Cody ポストする October 27, 2020
I tried adding 1N4148, and I can get the peak value to +4V (though I did not consider the dissipation)
Nolan ポストする October 27, 2020
What should be considered is the energy that will damage the transistor, similar to an electrostatic pulse
Brody ポストする October 27, 2020
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.
