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Thread: New to forum and SMPS.... first far.

  1. #1

    Red face New to forum and SMPS.... first far.

    I build a stereo amplifier module and found myself in need of a power supply. For this project I did not want to use a big piece of iron to power it so the next option is SMPS. I decided I would start simple with a push pull step up circuit, 12VDC to +/-30VDC. The toroid cores I ordered were slightly too small as the plan was to stack two as one transformer. It turned out that I need to get the 1.5cm high cores instead of the 1cm size. So, more just for fun, I made 3 transformers equal and connected them in series.. To my surprise it seems to work well. Also a quick sketch of circuit. The plan is to model the PWR supply out, tested, before doing the PCB with the CAD program. Most certainly there is room for improvement, my skills at SMPS is rather novice tho. Although, it did work first time it was connected so maybe just luck..6
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    Last edited by Chris_C; 02-02-2018 at 01:22 AM.

  2. #2
    So 12DC is convenient for a car but not for a home supplied with 120VAC. Next project I cobbled together from a bunch of junk lying around is an offline half bridge converter. The core came from some POS car inverter, one of those you plug into cigarette lighter for 120VAC . I think it was one transistor forward or flyback. Anyway, I am pretty sure It is ETD, but smaller than 29. Exactly 20g, I estimated Ae at about 65mmSq. I like to start small. You tend to get smaller explosions when you start small and foul up. .

    I used small toroid for current transfo, and inrush limit inductor. I figured the poor coupling on the current transformer this way will help with voltage spikes on the secondary when loaded with a resistor Also, for gate drive (temporarily until E-cores arrive) it works tho. I have not tried the on off switch circuit yet, may opt for small PCB transformer. I have not yet connected the circuit directly to the mains, it is hooked up to isolation transformer (that huge toroid on the bench) for safety obviously but it seems to be working, as in the amp cranks and the devices and transformers seem to be operating at a reasonable temperature. I think I can power the scope with the isolation transformer so that the GND reference of scope is floating. This should allow me to use scope on offline connected circuit, or am I missing something? Have avoided spectacular fireworks so far, hope to continue that trend.
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    Last edited by Chris_C; 02-02-2018 at 02:10 AM.

  3. #3

    What is being powered.

    Stereo module, more detail later. There is alot of detail....

    This is my first 4-layer PCB project and to my great surprise not too many errors. At least no real show stoppers. About 100W X 2 @4R. Logic and volume control is all included. It works great and the new changes have been made to PCB drawing in CAD. BTW I use Eagle. Once the Power supplies are worked out, so that both a 12VDC or 120VAC supply source can be used, I can proceed to the next phase. Not there yet, still learning.
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