Re: [SI-LIST] : Zener used to clamp Vcc?

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From: Vinu Arumugham ([email protected])
Date: Fri Feb 25 2000 - 14:56:31 PST


I have used such Zener diodes to protect the 5V devices against damage should an accidental short occur between 5V and a higher voltage supply during lab debug.

In one instance, we discovered that a lab DC supply was producing 12V spikes on its 5V output. After a few power cycles, the Zener diode would smoke. The 5V devices on the board were unharmed.

Vinu

Chris Bobek wrote:

> Hi,
>
> I was instructed to use a 5.6V Zener diode on the 5V Vcc plane of our
> board to clamp the voltage in the case of voltage spikes on the power
> supply. The Zener diode they chose is a 400mW diode. In your
> experience, is this the best way to handle power supply spikes? Is
> 400mW enough to accomplish anything? Our power supply is a 500W supply,
> I believe. The board typically draws 2A.
>
> I'm not sure what power supply spikes they are referring to. When I
> look at Vcc on a scope, the rising edge is a nice, quick, R-C charging
> curve. There's a lot of capacitance on our board and supply that
> dampens this response.
>
> Thanks for your help,
>
> Chris
>
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