>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>Sent: 25 May 2006 12:28
>To: Microcontroller discussion list - Public.
>Subject: Re: SMPSU component selection (was [PIC]: Info on PWM 
>PSUs andPIDwith PICs?)
>
>
>Phil,
>
>On Mon, 22 May 2006 21:39:32 +0100, Philip Pemberton wrote:
>
>>...
>> > > What I'm getting is a spike of about 10V,
>> > 
>> > This is when a large load is suddenly removed?
>> 
>> No, it's a startup spike. When the circuit first gets 
>powered up, Vout 
>> jumps to 10V, then settles down at 5V after a few seconds.
>
>I believe you're doing this with no load?  Regardless of your 
>control algorithm, you'll be very lucky to get 
>an SMPS to work reliably without something for it to control 
>against.  A lot of PC PSUs have a minimum load 
>specified on the +5V line, and it's often a significant current...

This is primarily because only one of the rails is actualy regulated, the others are just extra windings on the transformer.  Under the minimum load conditions those rails can fall well out of spec, and the the PSU will usualy shut down.

Regards

Mike

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