Hey, all. I've got a project that I need to do for work, but I'm not sure where to start. I need to design and build a box that will run on and put out 24 VDC, but also be able to put out +/- 10 VDC. It will also need to have test points to monitor the signals on the pins of a 12 pin connector. It's a breakout box combined with a power supply and control function, I guess. My main problem is the power supply. How do I pull +/- 10 VDC from +24VDC?

 

How do I pull +/- 10 VDC from +24VDC?

Just reverse the leads.. We use a +48VDC supply at work and just by reversing the leads you get +48 or -48VDC.

So a 24 V isolated supply plus a 10V regulator circuit.
What current level do you need for the -/+10V?

 

Never more than 2 amps. I had a problem with this circuit before where there seemed to be a grounding issue. I could not get the circuit to work properly and I was getting some strange voltages where they shouldn't be. This was using a 12V regulator and a switch to reverse the leads.

 

I remember that thread. Here: http://forum.allaboutcircuits.com/showthread.php?t=58057

If you must power the +/-10v supplies with 24VDC, you will need to use switching regulators that have galvanically isolated outputs; something like this:
http://search.digikey.com/us/en/products/PTB78560CAH/296-20363-ND/789181

If you have anywhere from 100VAC to 240VAC available, you could probably use a pair of these:
http://www.mpja.com/12VDC-2A-Regulated-Plug-Supply-Jasper/productinfo/18776+PS/
12v, 2A regulated switching plug supplies.

 

Thank you, SgtWookie. And thank you for your previous help. I'll look at the links you sent me.

 

So just plugging an isolated DC/DC converter in between the control circuit and the power circuit should work? I've found one here http://www.milelectronics.com/products/series-p.htm
Will this work? It meets the specs that I am looking for. +24VDC input with a +12V output and 150V isolation between the two.

Edit: Found a dual converter here, too. http://products.cui.com/CUI_VASD1-S24-D12-SIP_Datasheet.pdf?fileID=2862

 

Well, with 24v in, the PD412 model will give you ±12v @ 40mA maximum; is that going to be sufficient? (better stay at 80% or less of that maximum rating; so <=32mA)

 

The current draw on the control circuit is negligible. 2 or 3mA maximum. 40mA should be more than enough, not to mention a heck of a lot cheaper.

 

Note that you need to maintain a minimum load on those supplies.
Use a 2.4k resistor from each out ±12v terminal to the output common terminal.

 

Ah, yes, I see that. I'll be sure to do that.

 

The isolated converter works like a dream. Thanks for all the help!

 

Cool beans! Glad you finally got it working.