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

[Harry Bissell]

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