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Re: [Amps] Series PC Power Supplies

To: "Jim Forsyth" <>, <>
Subject: Re: [Amps] Series PC Power Supplies
From: "Roger Glover" <>
Date: Fri, 2 Jun 2006 11:35:58 +0100
List-post: <>
Jim and group,

I shoudn't have replied at that time of night. Sorry.

----- Original Message ----- 
From: "Jim Forsyth" <>
To: <>
Sent: Friday, June 02, 2006 2:41 AM
Subject: Re: [Amps] Series PC Power Supplies

> Please explain that more clearly, especially the "opposite sense" part.

What I should have said was that the remaining load current of the system 
through the 'tripped' supply will cause the voltage on that power supply's 
output terminals to be reversed - possibly up to the sum of the voltage of 
the remaining working supplys.

> Are
> you suggesting that the current somehow flows in the opposite direction
> through the supply in current limit?

No. Instead of the supply working as a source, it operates as a sink and 
therefore the voltage polarity is reversed.

> Perhaps you meant to say the current may charge the output capacitor to a
> reverse voltage. That is where the diode could be helpful as I mentioned 
> in
> my previous email.

Yes Jim.
However, it's not just the output capacitor that's of concern.
The reason for my post was to try to highlight the reason and likely dire 
consequences when several 'unprotected' PSUs are used in series.

> Jim, AF6O
>> All is fine until that load current rises to the current limit of the
>> 'weakest' supply. When this limit is reached, that power supply will shut
>> down or limit. The remaiing load current is presented to that supply in
>> the opposite sense.


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