Newbie's bench power supply design: build on top of existing units?

[technix]

The M103v2 and M103v3 boards were both busts.  Back to the drawing boards.

I have an old Dell laptop power supply with a busted ID chip: it works properly otherwise, but the laptop won't properly recognize it any more. It outputs 65W maximum at 19.5V. Since my output power cap is 50W anyway, maybe I can build my bench power supply from this? Maybe I should use a modular design with hot plugging in mind.

On the same note, another piece of equipment I may reuse is an old ATX computer power supply. What is the best way to repurpose it into a bench power supply with adjustable output voltages? And how to disable the minimum load requirement of the power supply, preferably without using a power resistor and burn away a few watts at all times? Is it a good idea to build the ATX-based adjustable power supply in some kind of standard form factor (like mini-ITX, 170mm-by-170mm board with four screw holes at specific locations) and put the build into a standard small form-factor computer case?

[Mechatrommer]

another piece of equipment I may reuse is an old ATX computer power supply. What is the best way to repurpose it into a bench power supply with adjustable output voltages?

put adjustable LM317 on the ATX PSU output

And how to disable the minimum load requirement of the power supply, preferably without using a power resistor and burn away a few watts at all times?

minimum load means energy you should waste for better regulation. use constant current circuit...

[technix]

another piece of equipment I may reuse is an old ATX computer power supply. What is the best way to repurpose it into a bench power supply with adjustable output voltages?

put adjustable LM317 on the ATX PSU output[//quote]
Not acceptable. Should the ATX power supply being used I will shoot for as high the maximum output power as possible, so a switcher is a must-go.

And how to disable the minimum load requirement of the power supply, preferably without using a power resistor and burn away a few watts at all times?

minimum load means energy you should waste for better regulation. use constant current circuit...

This is no better than a power resistor.

[David Hess]

If you use a 317, then the output divider normally also provides the minimum load current.