On Friday, Apr 16, 2004, at 08:25 US/Pacific, Michael Rigby-Jones wrote:

>> On the other hand, a bench supply in constant voltage mode
>> simply adjusts current to keep the voltage level approximately
>> stationary.  I think this is more the point that he is missing.
>>
>
> No it does not.  In constant voltage mode, the only thing that can
> adjust the current flowing is the resistance connected.  A PSU cannot
> magicaly alter current into a fixed resiatnce without changing it's
> voltage.
>
Well, yes, but that's just Ohms law.  The transistors in your power
supply are current-controlling devices.  To achieve constant voltage,
the change the amount of current they're willing to provide.  This is
effectively done by changing the internal resistance between a
pseudo-ideal voltage source and the load resistance.  Of course.

The point is that it's no more valid to think of a constant-current
supply as adjusting the voltage to meet the load than to think of a
constant-voltage supply as adjusting the current to meet the load...

BillW

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