COLECTOR
I am using a relay; 12v@15mA, it is located between the power supply (12v) and the colector of a transistor (BC337 hFE = 100).

BASE
At the base there is a resistor of about 2.2 kohm to turn on and off the transistor.

EMMITER
So at the emmiter is the ground.

When I apply 5 volts (from a microcontroller pin) the relay works, is ON, when no signal is on the pin, the relay is OFF.

My question is, which component offers me a better protection a DIODE 1N4148 = 1N914 or a TVS DIODE, with a stand-off voltage of 13v and a Vbr of 14.4v. if this is the right choice, it should be uni or bidirectional.

The diode of course is located between the power supply (12V line) and the Colector of the transistor.

Does anyone knows where I can find application notes about ESD, lightning surge and electrical fast transients

Thanks in advanced.

 

A simple diode is all that's required, no point fitting anything else as that's all that's needed.

__________________
PIC programmer software, and PIC Tutorials at:
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In your example, the diode is used to protect the
transistor from reverse EMF generated by the
relay. In general, a 1N4001 would probably be a
better choice, although a signal diode will suffice
it the relay coil is small, or the switching speed
is not abrupt.
As for the app notes, google will bring you more
than you want to read on all the subjects you
mentioned.
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