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Topic: Automotive and Arduino (Read 3127 times) previous topic - next topic

dephwyggl

Here's a correction to the correction: D1 isn't a reverse-polarity protection diode. It is a transient undervoltage clipping diode. It clips all negative voltage spikes to -0.7V or so, keeping them from damaging the circuits from negative voltage spikes coming from the alternator on the 12V battery feed. As shown, the circuit in discussion doesn't have a reverse-polarity protection diode. Leave D1 as it is, but add a reverse-polarity diode in series too.

Notice that D1 and D2 (the zener) work together. They each clip negative voltages to ~-0.7V, but the 15V Zener also clips positive voltage spikes down to only 15V. I wonder if D1 is needed at all actually, on second thought, since D2 will clip negative voltages down to -0.7V or so by itself anyway. See the "Zener Diode Clipping" section of the link below, for instance.
Sounds to me like you talked yourself into having D1 be re-positioned to provide reverse polarity protection. (I don't see the need for 2 diodes clipping the -.7V stuff either.)

Cheers!
Dirk

panther3001

Agreed. Sounds good to me.
Visit my RC aircraft, electronics, & Arduino website at http://www.electricrcaircraftguy.com

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