Electronic load for split/bipolar supply testing

[Beakman]

Hello All,

Researching here and on the wider web I've seen dozens of designs for programmable electronic loads, but none! for testing both positive and negative currents simultaneously as necessary for testing split or bipolar power supplies. 

Can someone point me towards an existing design or comment on how to modify a normal "positive" load for use in with negative voltages.  This assumes that the positive and negative voltages share a common ground.

Thanks!

[OM222O]

It's literally called a class A amplifier (or AB). Instead of using 1 fet connected to a shunt which goes to ground, you use 2 fets in common source configuration (AB) or pre bias the fet (A). I personally recommend AB since it's easier to implement.

Do some research on that topic and let me know if you have any questions regarding that.

[Howardlong]

Hello All,

Researching here and on the wider web I've seen dozens of designs for programmable electronic loads, but none! for testing both positive and negative currents simultaneously as necessary for testing split or bipolar power supplies. 

Can someone point me towards an existing design or comment on how to modify a normal "positive" load for use in with negative voltages.  This assumes that the positive and negative voltages share a common ground.

Thanks!

What current and voltage ranges?

[Beakman]

Funny, I had just begun contemplating the similarities of what I want  to do to the way power amplifiers draw current from their power supplies.

In my work power supplies are normally +/-15 to 18V, up to 10A per rail.  If I was going to build something I would want it to handle +/-24V at 10A.

Programmability is a requirement, voltage and current readouts a nice luxury.

[Beakman]

These are cheap and have nice heatsinking:

https://www.ebay.com/itm/250W-Electronic-Load-Battery-Capacity-Tester-Testing-Module-Discharge-Board-E6V9/254649147899?hash=item3b4a45a1fb:g:3vIAAOSwKrJfBwbX

Using two of these loads in tandem would be quick and easy but I don't know if it would be possible to get a schematic for them with an eye to modifying one for use on the negative rail.

[Jay_Diddy_B]

Hi,

Here are two options:

1) Using two 'positive' loads.

Assuming the load terminals are floating, you can connect two loads in series, and connect the center tap of the loads to the center tap of the power supplies. Each load is connected with the correct polarity.



2) Make a 'negative' load:



This is the normal load circuit. The N. Channel MOSFET has been replaced by a P Channel MOSFET. The reference polarity is inverted.

This has the advantage that the current monitor and reference are with respect to ground.

Jay_Diddy_B

[David Hess]

Electronic loads with multiple channels are available.

[Beakman]

Thanks, Jay.  It looks like it should be simple enough to graft your suggestion onto your "standard" uni-polar load.

[eblc1388]

If the current rating of both the power supplies are equal, then you can test them as a single supply. Just connect the electronic load to the +pos and -neg terminals, ignoring the common terminal.

e.g. a +12V 3A and -5V 3A supply can be tested to full load as a 17V 3A supply.

[Beakman]

That's a good idea in a lot of situations if everything is operating as specified, but if one rail is not up to snuff, say, sagging under a heavy load before the other rail, I need to be able to see that.  Voltage and current monitoring for each rail are necessary for me.

[2N3055]

For single output bipolar supply you can use unipolar load, diode bridge and auxiliary 3-4 V 10A supply to achieve zero dropout for load...

[eevcandies]

you could get one of these cheep
https://www.ebay.com/itm/Electronic-Measurements-Inc-The-BOS-S-Bipolar-Operational-Source-Sink/184372807091?hash=item2aed79c5b3:g:m7EAAOSwODZfGD07

details

https://us.lambda.tdk.com/products/legacy-products/pdf/bos-s.pdf

[Howardlong]

you could get one of these cheep
https://www.ebay.com/itm/Electronic-Measurements-Inc-The-BOS-S-Bipolar-Operational-Source-Sink/184372807091?hash=item2aed79c5b3:g:m7EAAOSwODZfGD07

details

https://us.lambda.tdk.com/products/legacy-products/pdf/bos-s.pdf

That’s a pretty useful bit of test gear, four quadrant 20A/20V for $95. Sadly for me not shipping to the UK.