EEVblog Electronics Community Forum
Electronics => Beginners => Topic started by: JJalling on February 20, 2022, 02:50:24 pm
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Hello, I'm trying to make a boost converter (5V -> ~180V).
I have made a small board with the attached circuit, but I cannot get it to work. I'm only getting ~3V out, and the transformer gets hot.
Am I doing something obviously wrong?
BR Jonas
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Checking the datasheet again, I have now added C1 (22pF) to the circuit, but without any change.
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Its telling that the LMR62014 (https://www.ti.com/lit/ds/symlink/lmr62014.pdf) datasheet doesn't show a single flyback application. SW (pin 1) is rated for abs. max. 22V and you didn't even give it a snubber! You should probably also have connected the secondary in series with the primary to make a tapped inductor boost converter.
Also ATB3325-nnnnnCT (https://product.tdk.com/en/system/files?file=dam/doc/product/rf/rf/balun/catalog/rf_balun_atb3225_en.pdf) is a range of RF baluns with a minimum operating frequency of 5MHzm not intended for power applications. If that's what you are using as it doesn't even specify a DC resistance and the LMR62014 max. frequency is a fraction of its min. frequency, its saturating and you are S.O.L. I *HOPE* you've got the so-called 'ATB3225' step-up transformer: ATB3225nn-110 (https://media.digikey.com/pdf/Data%20Sheets/TDK%20PDFs/ATB322515-(15,24)_DS.pdf)!
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Assuming part with 1:10 turns ratio, 180V on the output would theoretically reflect 5V+18V on the input with perfect snubbing or no leakage inductance; this already exceeds the absolute maximum Vsw rating significantly. There is no way this could ever work, not even close.
Pick a part with higher Vsw rating and provide an RCD snubber typical to flybacks (google for typical flyback schematics to get the idea).
Feedback path / loop compensation with boost and flyback is also a bit finicky because of the Right Half Plane Zero.
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Hi Ian,
Thanks for your reply, but I'm a bit puzzled why you are bringing ATB3325 into the thread. Can you elaborate on that. The schematics I showed, states ATB3225.
BR Jonas
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Assuming part with 1:10 turns ratio, 180V on the output would theoretically reflect 5V+18V on the input with perfect snubbing or no leakage inductance; this already exceeds the absolute maximum Vsw rating significantly. There is no way this could ever work, not even close.
Pick a part with higher Vsw rating and provide an RCD snubber typical to flybacks (google for typical flyback schematics to get the idea).
Feedback path / loop compensation with boost and flyback is also a bit finicky because of the Right Half Plane Zero.
Thanks, that's good info. I'll dig further in my part drawers and see what I can find!
BR Jonas
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AAgh!! I made a typo searching google and didn't notice then copy/pasted the bad part number and result. :palm: Please *IGNORE* my stupidity.
Siwastaja has nailed it. I'm surprised its even outputting 3V as I would expect overvoltage to blow the LMR62014's output transistor, dead short to ground. Ground /SHDN and see if the SW pin is lower than Vin or if the transformer is getting hot.
The LMR62014 may still be viable if you can find a higher ratio pulse transformer. Maybe one with a center tap on the low turns count side?
Another option, keeping the ATB3225 would be to use a voltage doubling rectifier so the LMR62014 only 'sees' 5V+90V/10 (=14V) reflected peak at SW, but you still get 180V out.
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Thanks Ian for your feedback!
BR Jonas