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Ulrich Schweitzer wrote:
> On Wednesday 15 September 2004 19:20, Jon Gilchrist wrote:
>
>
>
> > I tested every
> > ps I could find in my house (probably 20 or more) and *none* of them
> > put out the stated voltage. A typical 9v was putting out somewhere
> > between 12 and 15.
> >
> >
>
> It is nearly impossible to build a power supply that puts out the rated
> voltage when there is no load.
Not nearly impossible. It just requires a little more intelligence be
put into the power supply. All the regulated power supplies my company
produces contain a circuit called a down programmer. This circuits job
is to discharge the filter capacitors and maintain the rated voltage
under no-load conditions. It's essentially a fet or transistor run as a
load across the output, but to the user, the output of our supplies is
very, very stable. I'm pretty sure that if you found a good quality
wall wart (oxymoron? Is there such a beast?) it would contain a similar
circuit. Otherwise, just cheat and use a power resistor selected to
draw about 10% of the power supplies rated current. This should provide
decent load regulation at the expense of efficiency.
Rob
> Most will put out too high a voltage (like
> you have seen), some just shut down.
> To meassure the voltage of a PS, shorten it with a 1000 Ohm resistor or
> something like that and meassure the voltage at the resistor.
>
> Ulrich
>
>
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Message has 1 Reply:
 | | Re: RCX 2.0 Power Supply
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| (...) Sure it can be done, but it is very uncommon. I seriously doubt that any wall-wart (even very good ones) do it. I have a very high quality wall-wart. It puts out 2A at 3 to 24V, is very stable at the whole range from very little to full load (...) (20 years ago, 16-Sep-04, to lugnet.robotics, lugnet.trains)
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Message is in Reply To:
| | Re: RCX 2.0 Power Supply
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| (...) It is nearly impossible to build a power supply that puts out the rated voltage when there is no load. Most will put out too high a voltage (like you have seen), some just shut down. To meassure the voltage of a PS, shorten it with a 1000 Ohm (...) (20 years ago, 15-Sep-04, to lugnet.robotics, lugnet.trains)
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