How do I calculate the resistor value needed in parallel with a relay coil to protect the switching transistor from the coil back EMF (I do not want to slow operation by using a flyback diode).
The relay is a SS-112D, coil resistance of 320Ω, 12V rated voltage, nowhere on the data sheet mentions coil inductance.
The switching transistor is a 2N3904, Absolute max rating Vce of 40V.
The relay is closing for ~100ms twice per minute, and I left it running over night. I woke up this morning realizing I’d forgotten to put ANY protection in for the transistor, expecting it to be blown, but everything was fine.
How come the transistor isn’t blown?
How do I calculate the resistor to be used to ensure back EMF doesn’t reach 40V?