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Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
Since the joule thief is very good boosting the voltages even lower than 1V (as voltages got from fuel cells) and it is essentielly a self oscillating boost-converter, cannot it be used to step voltages at higher powers (around 1-2 watts). Using a high speed BJT, a big base resistor, a bigger core and a schottky barrier diode. THe purpose is to step up lower voltages got from an eolic alternator (3-6V at 1.6Ohm) to 13V to charge a small SLA (1AH). The normal control circuits cannot go under 6V for driving converters, and i don't need regulation (the battery regulates itself). Any suggestions. Using a gapped core should be ok in this type of designs or not?
Registered Member #162
Joined: Mon Feb 13 2006, 10:25AM
Location: United Kingdom
Posts: 3140
First I'd have a look inside the generator, IF it's an alternator with rectifiers it may be better to use the ac direct from the alternator via a step-up transformer.
If it's a dc permanent magnet type with commutator then some kind of invertor is definitely required. I'd imagine a boost converter based on something like an LM2588 'simple switcher' would be quite good.
Registered Member #505
Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329
You could use a Joule thief to provide the power supply rail for a simple low power boost converter IC and have the actual input to the boost from your alternator.
Registered Member #14
Joined: Thu Feb 02 2006, 01:04PM
Location: Prato/italy
Posts: 383
It is a single phase alternator. Stepping up the voltage using a transformer needs a bigger transformer that would be at that power rating (the frequency is in the 25-40Hz range), but it would work. The idea is to use the joule thief to power a control circuit or a pair of mosfets in a royer type circuit. What type of core can i use?
Registered Member #573
Joined: Fri Mar 09 2007, 11:26AM
Location: Russia
Posts: 14
Since you dont need high voltage out, you can use simple boost converter ICs, like mc34063 or something. MAXIM provides a lot of them.
In the case you want to use exact "joule thief" circuit, try it with small E transformer, it should give 1-2watts but efficency will be low, until you find some text book about "blocking oscillator" and calculate one for your needs.
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Scaling up the joule thief
