Re: Using zener diode to protect test circuit?

On Sun, 24 Apr 2005 04:24:07 GMT, snovotill@xxxxxxxxxxx wrote:

>On Sat, 23 Apr 2005 15:56:05 +0100, "Andrew" <ajhuk@xxxxxxxxxxx>
>wrote:
>
>>I am designing a test instrument that will be powered from the circuit under
>>test. Consequently there is a high probability of the incorrect voltage or
>>polarity being supplied to my circuit. I cannot protect against reverse
>>polarity by using a series diode as this will drop the supply voltage too
>>much.
>>
>How about a PNP in common base:
>
>IN -----+ +----------OUT
> | |
> V |
> ------- 2N3906
> |
> |
> /
> \
> / 560 ohm
> \
> /
> |
> |
>GND-------+------------GND
>
>The emitter will not break down with only 5.1V reverse.
>Am I dreaming? ...or is it really this simple?
>
>Stepan

That _might_ work if the reverse voltage doesn't ever go above 6V, but
you're playing it awfully close to Absolute Maximum specification.

Now how about the over voltage requirement?

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.
.

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