On Mon, Oct 08, 2001 at 11:19:43AM +0200, Wojciech Zabolotny wrote:
>
> Probably, when the relay gets switched off the spike of high voltage is
> generated on the NPNs collector, which then breaks down the CB junction and
> further propagates to the PIC's output (BTW what is the resistor between PIC
> output and the NPNs base?).
> Add the diode parallelly to the relay's coil (anode to the NPNs collector,
> cathode to the Vcc), it should fix the problem.

Ooops... sorry I've sent the message before I thought carefully. The effect
described above should not lead to PIC destruction, because the high voltage
spike will be shorted to the GND by BE junction :-(. But anyway you need the
protection diodes to avoid NPN destruction.
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                              Wojciech M. Zabolotny
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