[hpsdr] How to fry.....

[John Miles]

> -----Original Message-----
> From: hpsdr-bounces at lists.hpsdr.org
> [mailto:hpsdr-bounces at lists.hpsdr.org]On Behalf Of stoskopf at tri.net
> Sent: Wednesday, June 11, 2008 11:33 AM
> To: hpsdr at lists.hpsdr.org
> Subject: Re: [hpsdr] How to fry.....
>
>
> ***** High Performance Software Defined Radio Discussion List *****
>
> In my experience, the little three terminal regulators tend to fail full
> on and in a buddies case, popped all of the caps off his MMICs on a
> DownEast board.

This tends to happen when you have a lot of capacitance on the output side
of the regulator compared to what's on the input side.  At power-down the
part ends up reverse-biased, and the series pass transistor shorts out.

A diode across the regulator's input and output pins can save a lot of
more-expensive parts downstream.  Why the 78xx regulator manufacturers
didn't do that is a real head-scratcher.

-- john, KE5FX



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