Modding Bench Power Supply

[veryevil]

Hey, guys.

It looks like I'm gonna be getting a bench power supply for my birthday next month which should be really nice.

The one I'm looking at is the Circuit Specialists Triple Output DC Bench Power Supply 0-30V/0-3A w/Large LCD Display (CSI3003X3) (See: http://www.circuitspecialists.com/prod.itml/icOid/3506)

First off is this any good for £135 GBP?

Second they also do a 5A version for £175 but provide the schematics for both versions on their American website.

3 AMP Version http://www.circuitspecialists.com/pdf/3003X-III_schematic.pdf

5 AMP Version http://www.circuitspecialists.com/pdf/3005X-III_schematic.pdf

Now looking over the schematics it looks like the only difference is the extra two transistors and resistors per channel on the Adjust boards and R50 next to the digital pot (X9C103) on the control boards which are used to set the output current.

I'm guessing both will use the same circuit board so it should be a matter of putting in the missing parts and changing that resistor value to mod the 3A version to the 5A version.

What do you guys think? Also spot any other improvements or any other differences?

Cheers Steven

[david77]

Looks like quite a classic design for a power supply. I was surprised to see ICL7106's as panel meter drivers.

The one thing that might be different is obviously the transformer. That's the most expensive part of a power supply and so it makes sense for the manufacturer to use different types in differently specified units.
I would guess that the 3A unit has a 4A and the 5A unit maybe a 6A transformer in it.
That is something you have to look out for, otherwise you might fry the transformer when hacking the 3A psu to give 5A output current!
I would leave it as it is, to be honest. When do you need so much power realisticly? 3A is plenty and if you need more you can always parallel both supplys to give 6A current. Just my 2ct.

[veryevil]

I think you might be right. Looking at the schematics again it looks like the 5 Amp version has a separate transformer for each channel and the 3 Amp version has only a single transformer.

Also why is the panel meter driver a surprise?

[david77]

It's just a very old component that's been around since 1978 or so. I'd have thought they'd use some micro nowadays.