Electronics > Beginners

MC34063 high voltage dc-dc boost converter

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MagicSmoker:

--- Quote from: dazz on January 01, 2020, 12:14:33 pm ---I'm having a look at the UC3843 datasheet. Apparently it's maximum supply voltage is 30V and the maximum output current is 1A. Does that mean this IC can't do more than 30W output?

--- End quote ---

No, that (very rough estimate) only applies to *internal switch* regulator ICs, not *external switch* controller ICs. Note the distinctive terminology used, which applies when searching for parts on the usual distributors, btw.

dazz:

--- Quote from: MagicSmoker on January 01, 2020, 12:28:11 pm ---
--- Quote from: dazz on January 01, 2020, 12:14:33 pm ---I'm having a look at the UC3843 datasheet. Apparently it's maximum supply voltage is 30V and the maximum output current is 1A. Does that mean this IC can't do more than 30W output?

--- End quote ---

No, that (very rough estimate) only applies to *internal switch* regulator ICs, not *external switch* controller ICs. Note the distinctive terminology used, which applies when searching for parts on the usual distributors, btw.

--- End quote ---

I see, thanks MS. Hopefully one day I'll be capable of building a full blown AC-DC SMPS with this chip, as I reckon that would provide the best efficiency. Baby steps though

dazz:
I'm a bit baffled by this. I'm simulating the flyback version of the MC34063 converter at the moment, and surprisingly it seems to be slightly less efficient (82%)
I swapped the mosfet for a IRFZ44N with Id=49A & Vds=55V that I think should be suitable for this application, but it's dissipating a whopping 10W and killing the efficiency of the converter. Is it spending too much time in the linear zone or something? (attached screenshot)

JackJones:
Try adding active pull down on the gate. For example see the third image on this page: https://threeneurons.wordpress.com/nixie-power-supply/

dazz:

--- Quote from: JackJones on January 01, 2020, 04:35:54 pm ---Try adding active pull down on the gate. For example see the third image on this page: https://threeneurons.wordpress.com/nixie-power-supply/



--- End quote ---

Great, thanks Jack. That's a really cool trick to speed up the switching of the mosfet. According to the datasheet the IRFZ44N has a fall time of 45ns, almost twice as much as the IRF740 I was using in the boost configuration, so that might explain the increased power dissipation in the mosfet, correct?

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