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

[Mike Beauchamp]

I just realized I made another mistake. The 10uF capacitor that I
removed to successfully remove the HF oscillation was actually on the
ADJ pin going to ground. According to the datasheet I followed
(National's) "The 10 μF capacitors are optional to improve ripple
rejection".

Brain is getting farty lately, apologies guys.

Mike


On Wed, Sep 21, 2011 at 2:42 PM, Mike Beauchamp <mikebeauchamp at gmail.com> wrote:
> 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]
>



-- 
[mike]