voltage regulator

Dec 24, 2011 4 Replies

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Michael Robinson 14 years ago

This is an idea for a voltage regulator for an antique six-volt vehicle. It has an old-school generator with pole shoes. The aim is to PWM the field at a frequency on the order of 1kHz, or a few hundred Hz, to avoid the heat sink that linear regulation would require. I built such a voltage regulator for a modern 12 volt vehicle a while back, using a voltage reference, an op amp and a vco. That worked great, still in service. But I would like to cut down on the parts count this time. The drawing below is not complete, but it shows the heart of the design I am considering. View in Courier or other fixed font. The positive feedback from the cap is meant to ensure solid switching, preventing the comparator from lapsing into high frequency oscillation. Assu-me-ing this circuit works, what I'm trying to figure out is fast it would switch. I can't simulate it because the generator, as part of the feedback loop, plays a role in the behavior of the circuit.

battery positive | +-------------------, | | | | 470k | field | 1k | | 1n | | \ ,---||---1meg--|-----+ / | | | 50k \ | |\ | | /------+--||_ 1.2v | | / nmos| ref--|--------|+/ | | |/LM393 | 100k /// | ///

The cap and resistors have a timing constant, obviously. But would that put an upper or lower limit on the switching frequency?

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NT 14 years ago

=A0It

t put

I'm probably wrong here. I thought the usual thing was a PM dynamo plus a low frequency mechanical switch mode controller, which monitored battery voltage and current load to estimate mark-space ratio for best charge. What you're discussing sounds more like a modern alternator, and what you're proposing sounds like a modern control scheme. If so, why?

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Michael Robinson 14 years ago

I'm probably wrong here. I thought the usual thing was a PM dynamo

--I've worked on vehicles as old as 1952 and never seen a permanent magnet generator.

--There may be some few vehicles that use permanent magnets (late model Sportsters come to mind); not my concern here.

--I am working on a classic generator that has an armature with a segmented commutator and pole shoes screwed into the case.

plus a low frequency mechanical switch mode controller, which monitored battery voltage and current load to estimate mark-space ratio for best charge. What you're discussing sounds more like a modern alternator,

-- No, it's a generator from the nineteen fifties.

and what you're proposing sounds like a modern control scheme. If so, why?

--Solid state regulators outperform mechanical ones. I hope that's explanation enough.

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NT 14 years ago

Everything modern about cars outperforms the old stuff. But I wouldnt replace it. Then again, the 50s is not an era I like much.

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omg 14 years ago

I'd join in the conversation if you could be bothered to follow quoting convetions, it's not hard to 'speak' clearly, unambiguously.

Grant.

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