Electronics > Beginners
MC34063 high voltage dc-dc boost converter
dazz:
--- Quote from: MagicSmoker on December 31, 2019, 09:10:32 pm ---
--- Quote from: dazz on December 31, 2019, 08:45:46 pm ---Oh, OK. I think I see what you mean now. The internal switches are not necessarily mosfets. So for example in the MC34063 the internal switch is that darlington pair at the SWC & SWE outputs, right?
--- End quote ---
Right, the switch in a switching power supply can be a MOSFET, BJT, SCR... heck, even a relay (see the "vibrator" type power supply used in early car radios). In this case, you are mostly correct - the actual switch in the MC34063 is Q1 while the driver for it is Q2. Note that the collector for driver Q2 is brought out to a separate pin to allow for more flexibility in driving Q1; most of the time you'll just connect the collectors together in a straight Darlington configuration, though.
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Doh! True, it's not a Darlington pair. And the fact that they're BJT's is an issue because it has higher output impedance and loads what's connected to it more than say, fets? Is that right?
Also, I just tried TI's Webench and performed a parametrical search. Apparently the boost topology is the simplest one (obviously), push-pull is the most efficient and flyback is a compromise between the two... well I really need to read the relevant chapter in The Art of Electronics to understand how those topologies work.
But one of the suggested IC's in webench looks like it could be a good option for my next design: the UC3844A. It's also one of the ones that Tim recomends in that imgur post. It's cheap, through hole and readily available
dazz:
But I can't seem to find a spice model for that UC3844A... dunno, maybe I've become too reliant on the simulation
T3sl4co1l:
https://forums.ni.com/t5/Multisim-and-Ultiboard/model-for-UC2842-or-UC3842/td-p/524298?profile.language=en
Don't worry about 44, it's the half duty cycle version, aimed at forward converters.
Do however use the 43; set the UVLO thresholds to say 5 and 6V in that case.
--- Code: ---vlow vlow1 0 dc 5
vhigh vhigh1 0 dc 5.5
--- End code ---
Tim
dazz:
--- Quote from: T3sl4co1l on January 01, 2020, 12:38:51 am ---https://forums.ni.com/t5/Multisim-and-Ultiboard/model-for-UC2842-or-UC3842/td-p/524298?profile.language=en
Don't worry about 44, it's the half duty cycle version, aimed at forward converters.
Do however use the 43; set the UVLO thresholds to say 5 and 6V in that case.
--- Code: ---vlow vlow1 0 dc 5
vhigh vhigh1 0 dc 5.5
--- End code ---
Tim
--- End quote ---
Dude, you're awesome. Thanks so much
dazz:
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?
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