[sdiy] Update! Re: 78xx regulator gives negative output half the time

[Harry Bissell]

Few points...

You might have a batch of counterfit components that made their way to market,
or some bad batch bought as surplus and re-sold

It might be that the regulator is unstable, check to see that you have
proper decoupling per the manufacturer's recommendation.

I had some SGS regulators that would not function correctly with inputs from
8V - 13V.  Motorola parts were fine. Of course I got rid of the manufacturer
that caused me trouble. That was years ago and I have since forgiven them...

H^) harry



----- Original Message -----
From: Tom Wiltshire <tom at electricdruid.net>
To: Dave Kendall <davekendall at ntlworld.com>
Cc: sdiy DIY <synth-diy at dropmix.xs4all.nl>
Sent: Fri, 29 Oct 2010 10:47:46 -0400 (EDT)
Subject: Re: [sdiy] Update! Re: 78xx regulator gives negative output half	the time

Seriously? What the hell happened to their QA?
Surely that kind of thing isn't good for business?

T.

On 29 Oct 2010, at 14:58, Dave Kendall wrote:

> This rings a bell.
> 
> There was a bad batch of LM7812s a while back - I forget where this was discussed - either here, or on electromusic.com, or possibly on the 9090 forum. I seem to remember they were outputting +21V.... not exactly what you want.....I can't remember whether national semi or fairchild parts were the culprits.
> 
> 
> cheers,
> Dave
> 
> On Oct 29, 2010, at 14:39, Karl Ekdahl wrote:
> 
>> Hi List
>> 
>> I have once again gotten this weird problem; unit does not start once plugged in but if you immediately unplug it and plug it back in it starts up. The cuplrit is again a 7809 regulator.
>> 
>> Now this time the back-to-back diode network did *not* work to my big horror. I do however think i've found the problem; seems like the Fairchild LM7809ACT does not work, though the LM7809CT does! The only difference i can find inbetween the two is that the latter has a wider temperature range and slightly less awesome line/load regulation.
>> 
>> So before i order 50 of the LM7809CT as replacements i've got three questions:
>> 
>> 1. Does this seem right? Can anyone refute my findings?
>> 
>> 2. Do you think this is a manufacturing error on the part / a bad bath or just different behavior?
>> 
>> 3. If this is not a bad batch of parts, how the hell can one make sure that you don't get the sensitive / weird parts if (like now) the part that first worked isn't in stock? There are literally 100's of 78xx/79xx regulators and i guess some work and some don't. The first time i had this problem (Re: this e-mail) i was working with some 7812 regulators - perhaps there's a 7812 regulator that will work?
>> 
>> Oh btw. i'll get back to y'all on this once i know all the hard facts, maybe it's time to watch out for any ACT regulators...
>> 
>> Thanks!
>> 
>> Karl
>> 
>> --- Den tors 2010-04-29 skrev Ian Fritz <ijfritz at comcast.net>:
>> 
>>> Från: Ian Fritz <ijfritz at comcast.net>
>>> Ämne: Re: [sdiy] 78xx regulator gives negative output half the time
>>> Till: "Karl Ekdahl" <elektrodwarf at yahoo.se>, synth-diy at dropmix.xs4all.nl
>>> Datum: torsdag 29 april 2010 02:13
>>> At 05:42 PM 4/28/2010, Karl Ekdahl
>>> wrote:
>>>> However i'm still not entirely sure i understand why
>>> this is happening in the first place, JH suggested he's seen
>>> it while doing circuits with unevens loads - but i've built
>>> literally 100s of circuits using this very same PSU scheme -
>>> that definitely have uneven loads - and i've never had this
>>> happen before.
>>> 
>>> Different manufacturers?  There's been trouble with
>>> this reported in the past.
>>> 
>>> Ian
>>> 
>> 
>> 
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>> 
> 
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-- 
Harry Bissell & Nora Abdullah 4eva