[sdiy] High Frequency ripple in PSU - no clue..

[Mike Beauchamp]

Hi Harry, I'm definitely going to try another manufacturer of the
LM337. I -think- this one may have come out of my parts bin, which
means it could have been a random one from futurlec or something.

The input voltage at the lowest point measures -18.5VDC.

Mike


On Wed, Sep 21, 2011 at 2:29 PM, Harry Bissell <harrybissell at wowway.com> wrote:
> Try another manufacturer for the chip. I had some wierd results years back with
> an ST brand regulator, and it took a long time to figure out that there was a specific
> chip issue.
>
> maybe I missed a previous post, what is the input voltage to the chip (lowest point
> including the ripple).
>
> H^) harry
>
>
> ----- Original Message -----
> From: Mike Beauchamp <mikebeauchamp at gmail.com>
> To: MrMcCrash <mrmccrash at gmail.com>
> Cc: sdiy DIY <synth-diy at dropmix.xs4all.nl>
> Sent: Wed, 21 Sep 2011 14:09:33 -0400 (EDT)
> Subject: Re: [sdiy] High Frequency ripple in PSU - no clue..
>
> Just an update on this..
>
> I initially had a 10uF electrolytic on the output of the LM337. This
> was according to the datasheet that shows "†C1 = 1 μF solid tantalum
> or 10 μF aluminum electrolytic required for stability" at the output.
>
> However, removing it completely stopped the high frequency ripple!
> Replacing it with a 1uF tant reintroduced the ripple though. Very
> strange.
>
> Even putting a .1uF cap across the output of the LM337 reintroduces
> the high frequency ripple, but only at .5V p-p.
>
> For now I'll just leave that capacitor off completely, but it feels
> weird leaving it like that. I also still don't know WHY it's acting
> this way.
>
> Mike
>
>
>
>
>
> On Wed, Sep 14, 2011 at 3:59 AM, MrMcCrash <mrmccrash at gmail.com> wrote:
>> The LM3x7's should have an .1uF ceramic on each input and output leg to
>> ground. Too much capacity (>10uF) on the Output will probably cause
>> oscillation and instability.
>>
>> cu
>
>
>
> --
> [mike]
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> --
> Harry Bissell & Nora Abdullah 4eva
>



-- 
[mike]