Electronics > Beginners
MC34063 high voltage dc-dc boost converter
T3sl4co1l:
Correct! ;D
Tim
dazz:
--- Quote from: T3sl4co1l on January 02, 2020, 04:55:07 am ---Correct! ;D
Tim
--- End quote ---
Bah, I just noticed I misread you too. Anyway, all clear now. :-+
I'm getting some mixed results in the simulation now. Interestingly, the active pull down on the gate that Jack suggested worked great in the boost (no transformer) version, boosting the efficiency to a very nice 92%. OTOH I just can't seem to get the flyback version anywhere near as efficient. The active pull down doesn't work unless I reduce the current limiting resistor, which in turn increases the power dissipation in the mosfet, and the efficiency tanks as a result. Just to be sure, does the IRFZ44N look like a proper choice for this application?
MagicSmoker:
--- Quote from: dazz on January 02, 2020, 01:35:28 pm ---I'm getting some mixed results in the simulation now. Interestingly, the active pull down on the gate that Jack suggested worked great in the boost (no transformer) version, boosting the efficiency to a very nice 92%. OTOH I just can't seem to get the flyback version anywhere near as efficient. The active pull down doesn't work unless I reduce the current limiting resistor, which in turn increases the power dissipation in the mosfet, and the efficiency tanks as a result. Just to be sure, does the IRFZ44N look like a proper choice for this application?
--- End quote ---
The IRFZ44N is a very old MOSFET so, no, not a good choice for anything these days.
The isolated flyback is somewhat tricky to design. Post your LTSpice .asc file here if you want some help with tuning it, but as I already warned, SMPS transformer design is an art unto itself, so expect a lot of pain and escaping magic smoke.
dazz:
--- Quote from: MagicSmoker on January 02, 2020, 01:46:49 pm ---
--- Quote from: dazz on January 02, 2020, 01:35:28 pm ---I'm getting some mixed results in the simulation now. Interestingly, the active pull down on the gate that Jack suggested worked great in the boost (no transformer) version, boosting the efficiency to a very nice 92%. OTOH I just can't seem to get the flyback version anywhere near as efficient. The active pull down doesn't work unless I reduce the current limiting resistor, which in turn increases the power dissipation in the mosfet, and the efficiency tanks as a result. Just to be sure, does the IRFZ44N look like a proper choice for this application?
--- End quote ---
The IRFZ44N is a very old MOSFET so, no, not a good choice for anything these days.
The isolated flyback is somewhat tricky to design. Post your LTSpice .asc file here if you want some help with tuning it, but as I already warned, SMPS transformer design is an art unto itself, so expect a lot of pain and escaping magic smoke.
--- End quote ---
Yeah, I'm not going to build the flyback smps anytime soon. I'll make sure I do proper research before I do that.
The asc is attached, thanks
MagicSmoker:
--- Quote from: dazz on January 01, 2020, 06:02:40 pm ---Something's amiss here. I used the calculator for a flyback converter that you suggested yesterday: http://schmidt-walter-schaltnetzteile.de/smps_e/spw_smps_e.html
With 24V input, 300V and 200mA output, the calculator suggests 120uH in the primary and a turn ratio of 80...
--- End quote ---
Hey, that website is one I often recommend to SMPS beginners but it is giving me a "bad request" error on most (but not all) of the sections. Is it just me, or is it broken for others?
--- Quote from: dazz on January 02, 2020, 02:00:28 pm ---Yeah, I'm not going to build the flyback smps anytime soon. I'll make sure I do proper research before I do that.
The asc is attached, thanks
--- End quote ---
Right, a bunch of things wrong just at first glance. The transformer phasing is wrong - for a flyback the dot ends are inverted w/r/t each other - and you don't include the H when specifying the inductance, so the primary should just be 120u, not 120uH (you did specify the secondary correctly).
Next big issue is there is no RCD or Zener clamp across the primary; switch destruction is guaranteed in the real world, but LTSpice apparently doesn't care... :P
You also need to specify a diode on the secondary with an appropriate voltage rating; a 40V or whatever Schottky ain't gonna cut it with a 300V output.
The pot isn't a standard LTSpice component and simulating 3 seconds is about 2.99 seconds too much (quite literally: 10ms should be enough here). I like to set the simulation time to capture 100 to 1000 switching cycles, or 4-10 AC mains cycles, whichever applies.
Probably some other things but this should be enough to make your brain hurt for awhile.
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