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> Another Seven Transistor Special, Boost Converter
Sch3mat1c
Posted: May 09, 2017 11:27 am
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Enjoy wink.gif

Interesting features:
- Q6 can be pretty much any stupid transistor. I've tried everything from the slow TIP31C to a blazing fast 2SC4821 (2GHz!). The slower ones switch more slowly of course, but they do switch.
- Even Darlingtons work. They go fast, too -- about 1/3 the rated switching time!
- Also works with MOSFETs. Needs logic level type (notice 5V supply, as shown), and remove D4 and R11 (and all the spooky junk -- C1, C3, L3, R6-R8).
- Topology is common ground, so it can be used for boost or buck configurations with little change (main downside to buck: the whole thing is floating and needs a bootstrap supply).
- Output power is varied by two currents: one shown (I1, more current --> shorter off time --> higher frequency --> more power), the other into Q7 base (node IS2), which puts an offset I * R12 in series, thus reducing the turn-off peak current threshold (this is a peak current mode controller).
- Supply operating range is designed for 5V, but it should be pretty flexible, give or take what ends up happening with the voltages and currents around R2-R4.

Calling it "Seven Transistors" is kind of a lie, because you'll need two more transistors -- for those current sources -- and one more for voltage error amp (preferably a TL431, an "ideal transistor", nevermind what's inside it wink.gif ), to make a proper regulated voltage supply.

Tim


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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
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Jimthecopierwrench
Posted: August 23, 2017 02:19 am
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QUOTE
Calling it "Seven Transistors" is kind of a lie, because you'll need two more transistors


Hadn't thought about that before now .. 7 IIRC was a common number in late 70's AC/DC portable sets, no? What else if anything? Minimum number to perform some task? Is it (the number in the name) relevant? Just assumed like many Inc. names it might have been arbitrary, or not necessarily have much to with production .. ie. a lucky number, aesthetic phonetics, number of some one's siblings.

Yeah I'm in the cups .. nice jug of hooch for watching the boss man's pooch while they went to Disney. laugh.gif


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Sch3mat1c
Posted: August 23, 2017 02:20 am
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QUOTE (Jimthecopierwrench @ August 22, 2017 08:19 pm)
QUOTE
Calling it "Seven Transistors" is kind of a lie, because you'll need two more transistors


Hadn't thought about that before now .. 7 IIRC was a common number in late 70's AC/DC portable sets, no? What else if anything? Minimum number to perform some task? Is it (the number in the name) relevant? Just assumed like many Inc. names it might have been arbitrary, or not necessarily have much to with production .. ie. a lucky number, aesthetic phonetics, number of some one's siblings.

Yeah I'm in the cups .. nice jug of hooch for watching the boss man's pooch while they went to Disney. laugh.gif


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Answering questions is a tricky subject to practice. Not due to the difficulty of formulating or locating answers, but due to the human inability of asking the right questions; a skill that, were one to possess, would put them in the "answering" category.
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