Sanity check on boost converter

[JJalling]

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

[JJalling]

Checking the datasheet again, I have now added C1 (22pF) to the circuit, but without any change.

[Ian.M]

Its telling that the LMR62014 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 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!

[Siwastaja]

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.

[JJalling]

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

[JJalling]

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

[Ian.M]

AAgh!! I made a typo searching google and didn't notice then copy/pasted the bad part number and result.    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.

[JJalling]

Thanks Ian for your feedback!

BR Jonas