Auxiliary Power Supply for Welder

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GeorgesWelding

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I needed two 15V isolated auxiliary power supplies for the SMPS Welder I'm currently trying to design/build. This is the simplest design I could come up with. This power supply will fit on a 1 7/8" x 2 3/4" board. One of these will be powering a TL494, a few LM324 Op-Amps, and a couple UHS Opto-couplers(5mA each) and the second one of these supplies will be powering two IR2110 gate driver ICs each driving 2 IGBTs.

It's using a TL431 instead of a zener diode so that the output is slightly adjustable. The simulation of the opto-coupler and the TL431 works fine, but will this all work properly in the real power supply?

Here is the schematic: View attachment 15V Adjustable Supply (Schematic).pdf
 

No no, I need two separate +15V supplies that are not only isolated from each other but isolated from the mains as well and they needed to be regulated. These supplies are super simple and I harvested the ICs, transformer cores, and the diodes from PC PSUs that I had laying around. I was just curious as to whether using the TL431 in the way I did would work in practice the same way it works in simulation. I assume it does, but sometimes Multisim does things that don't work in the real world. The datasheet for the TNY266 mentions using the TL431 instead of a zener but provides no example.
 

The TL431 will work the way you have it hooked up. I just tried it with hardware and a variable supply.

I find it's a good idea to install a safety resistor inline with the led. In your schematic I would start by making R4 470 ohms.

You will have to adjust values, in order to find a range where led brightness changes sufficiently to affect the photosensor inside the optocoupler.
 

You're right, in simulation the current draw through the diode was over the 80mA max rating in the datasheet when using the 100R resistor. I stepped it up to 470R and that dropped the diode voltage down to 1.227V@21.8mA which was still plenty to trigger the photosensor in Multisim. If it isn't enough in practice, I also have 390R & 330R resistors I can try which will give more brightness while still being within the operating limits of the LED. Thank you for catching that. That's why I post these things here before I go building them. Still learning.

-Brad George
 

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