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guitar_joe 8th May 2007 02:31 PM

SG3525 switchmode psu
I'm having a crack at rod elliots car supply and built the controller circuitry. I hooked the outputs up to a scope to see if it was working and i noticed some pretty nasty ringing on the switching square waves. Is this normal??

luka 8th May 2007 03:07 PM


Where did you look at this ringings? At output from SG?

ifrythings 8th May 2007 07:29 PM

Do you have the 0.1uF cap across pins 12 and 13 of the IC (as close to the IC as posible?)

Is this just the SG3525 by it's self or do you have a transformer hooked up?

If you have poor grounding on your scope probe you'll get the same thing.

guitar_joe 8th May 2007 10:25 PM

I took these measurements at the out puts of the sg3525. No output devices were connected. I already tried a capacitor it made no difference. I measured it with the probe grounded and then floating and it made no difference.
Cheers, steve

ifrythings 8th May 2007 10:45 PM

Can you post an image of what your getting, it will help us help you out better.

BTW which schematic are you using? Sergio's (first schematic?) or Rod Elliott's (second schematic?)


I measured it with the probe grounded and then floating and it made no difference
You should get a different wave form (mostly ringing) when the ground is removed. If you get no difference with or with out, then I would say you have a grounding issuse with either your scope or your current setup.

Perry Babin 9th May 2007 03:03 AM

Can you post a photo of the waveform?

sachserjuris 16th May 2007 08:58 PM

rod elliott smps is great!!
Hi SMPS builders

I Build many smps rod elliott project. Itīs working very good. I have a SG3525 + 12 FTP50N06 mosfet + 2 inches toroidal transformer/ input 12VDC- output +63/-63VDC. I can post pics for you, ok?
I build other SMPS with 115/230VAC and +80/-80VDC for my power amp. Itīs very good the performance.

Thank you very much.


bawang 17th May 2007 12:41 AM

Hi Sach..... Please do, and if possible, the PCB layout too. I am trying to build one to power all my power amps for my car......

luka 17th May 2007 06:11 AM


And the one for 230Vac

guitar_joe 22nd May 2007 12:34 PM

Getting there!!!
I filtered out the noise with some capacitors.
Built the mosfet power side of the circuit and wound a small toroidal transformer.
I havent got the high speed rectifier diodes but i still ran a few tests.
I hooked up the supply to a 13.8v 30a bench supply and loaded it down with a 16 ohm dummy load across the whole secondary.
I get around 70v p-p with it loaded down.
When loaded it sucks around 10A from the bench supply

I'm pretty happy with this so im gonna design a pcb for this and post it when its complete.

I'll post pics soon of my prototype... 10 amps of current through a veroboard....

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