Isolated Power Supplies

Shop deals on ebay
Advertise with us
shop deals on amazon
GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
Rochey

Rochey

Well-known member
White Market Member
Joined
Jul 2, 2004
Messages
2,697
Location
Dallas, TX - Formerly UK
Gents,

a dumb Q, but this is always a good place to ask both Dumb Q's and smart ones!

I'm building a programmable load to test a DC-DC power supply I'm building. The control circuitry needs to be isolated, so that it can float with the negative rail of the power supply under test. I initially thought using a 9V battery would be safest, but I'm now wondering if I can use an off the shelf 9VDC power supply.

Maybe I've misunderstood, but most of the AC/DC switching supplies all have isolated outputs?
What throws me is there's often a Y-class capacitor that bridges the primary and secondary. doesn't that defeat the isolation?

Cheers

R
 
Make a box with a BNC connector on one end and banana jacks on the other. BNC goes to voltage divider and gate of p-channel mosfet. Source and drain of mosfet connect directly to bananas. Put the load on the banana jacks and drive the BNC input with a function generator like one of the old protek ones with a DC control. Make your voltage divider so that the max voltage of the fn generator makes the mosfet 100% on. Now to test you just adjust the DC and if you want to see what the load regulation looks like play with the fn generator frequency / amplitude. No batteries. If the SMPS is isolated (if it's not I wouldn't use it) then you don't need isolation. But if you want further isolation you could add an opto isolator in front of the mosfet. Depending on how long and how much power your test is going to be for, use a die cast aluminum box and mount the mosfet through it to a heatsink. And maybe add a 10 ohm resistor to the source for safety / reduce temp effects / make DC adjust smoother.

Just thinkin' out loud of course.
 
squarewave said:
Make a box with a BNC connector on one end and banana jacks on the other. BNC goes to voltage divider and gate of p-channel mosfet. Source and drain of mosfet connect directly to bananas. Put the load on the banana jacks and drive the BNC input with a function generator like one of the old protek ones with a DC control. Make your voltage divider so that the max voltage of the fn generator makes the mosfet 100% on. Now to test you just adjust the DC and if you want to see what the load regulation looks like play with the fn generator frequency / amplitude. No batteries. If the SMPS is isolated (if it's not I wouldn't use it) then you don't need isolation. But if you want further isolation you could add an opto isolator in front of the mosfet. Depending on how long and how much power your test is going to be for, use a die cast aluminum box and mount the mosfet through it to a heatsink. And maybe add a 10 ohm resistor to the source for safety / reduce temp effects / make DC adjust smoother.

Just thinkin' out loud of course.
Click to expand...

Interesting. You don't have any feedback then to keep the current steady. The circuit you describe, if I read it correctly, is completely open loop?
 
Rochey said:
Interesting. You don't have any feedback then to keep the current steady. The circuit you describe, if I read it correctly, is completely open loop?
Click to expand...
True. Linearizing would be better. But even small source resistor will linearize quite a bit. To make it more linear you would require a few more parts but for basic load testing I'm not sure if it's really necessary.
 

Similar threads

mihaelbele
Troubleshooting PC audio noise
Replies
13
Views
652
mihaelbele
mihaelbele
kato
  • Locked
Isolated stompbox power supplies sharing a board, share the ground plane? Or fully isolate?
2 3
Replies
45
Views
4K
JohnRoberts
JohnRoberts
R
THAT1512 Pre. DIY, reasonable replacement for Cheap Preamp Art?
Replies
8
Views
1K
ricardo
R
S
C12 with Moby's V2545
2
Replies
35
Views
5K
soapfoot
S
calaverasgrande
Regulated pedal power, in a car.
2
Replies
23
Views
3K
calaverasgrande
calaverasgrande

Latest posts

Back
Top