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11-27-2008, 12:54 PM #17
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Benm
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Re: possible 3\$ boost circuit

Are you measuring voltage and current at the same time, or unloaded voltage first, and short-circuit current after that?

11-27-2008, 01:45 PM #18
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hydrogenman15
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Re: possible 3\$ boost circuit

This looks promising. If its true then making lasers could get a whole lot cheaper.

--hydro15

11-27-2008, 06:11 PM #19
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iccy
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Re: possible 3\$ boost circuit

Quote:
 Originally Posted by Benm Are you measuring voltage and current at the same time, or unloaded voltage first, and short-circuit current after that?
I'm not sure if I get what your saying, I measured the voltage off of each battery, and then measured it after the circuit. After that I measured current.

I tried to make my previous post more clear, hope that helps.

11-27-2008, 07:21 PM #20
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Re: possible 3\$ boost circuit

What he's asking is important. It is a boost circuit, but how much current can it put out with a 3V load? My guess is much less than 400mA. Give it a shot with 4 regular silicon diodes in series as a dummy load and hook your multimeter in series with that and see what current you get.
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11-28-2008, 12:13 AM #21
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Benm
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Re: possible 3\$ boost circuit

As drlava says above - in needs to be feeding a voltage to something and still maintain the current.

Otherwise, if you just put a ampmeter over the output, the results mean nothing. In the typical boost configuration that actually shorts the battery over an inductor and a diode, so the current obtained depends mostly on the ohmic resistance of that inductor.

For example, see this circuit: http://www.nomad.ee/micros/mc34063a/index.shtml

That's not one for 1.5v power, but general concept and topology might very well be similar.

11-28-2008, 12:16 AM #22
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iccy
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Re: possible 3\$ boost circuit

[s]If the current was lets say 100mA, does that mean that it is giving 100mA to the laser diode? I thought that it would always be putting out the 400mA (like I measured) to whatever it is hooked up to. :-? [/s]
- EDIT Benm explained it
Quote:
 Originally Posted by drlava What he's asking is important. *It is a boost circuit, but how much current can it put out with a 3V load? *My guess is much less than 400mA. *Give it a shot with 4 regular silicon diodes in series as a dummy load and hook your multimeter in series with that and see what current you get.
Alright, it makes sense now.

I have rkcstr's test load and it says to measure in mV, should I measure it in mA?

I hope it works out, but I have a bad feeling

Anyways, Ill test it asap.

11-28-2008, 01:49 AM #23
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digital_blue
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Re: possible 3\$ boost circuit

Oh, I recognize those circuits! They are a revamped version of the &quot;joule thief&quot; circuit. Just an inductor/transformer circuit that drives a transistor. They are meant to drive LEDs...

http://www.elecfree.com/electronic/w...ed-flasher.jpg

11-28-2008, 04:14 AM #24
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jonrobertd
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Re: possible 3\$ boost circuit

With the test load on mine I got 3.1 volts @98ma.
I have been messing with one of these for a month now, trying to get it to work alone, but figure it might work with a Flexdrive.?
With the original LED in place it reads 3.41v 78ma.

11-28-2008, 04:28 AM #25
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iccy
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Re: possible 3\$ boost circuit

With resistor removed?

EDIT: I tested mine but I'm only getting 50mA? *I'm not getting how you got 98mA?

11-28-2008, 05:28 AM #26
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jonrobertd
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Re: possible 3\$ boost circuit

Thats nothing, the ones I killed went up to 142ma and as low as 51ma.
No modifications done yet though.
I have been through 7 and have 3 more

11-29-2008, 03:06 PM #27
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chimo
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Re: possible 3\$ boost circuit

It's a simple boost circuit. I see an inductor, a schottky diode, a capacitor and a switcher chip. It's unlikely that this will boost to 400mA.

11-29-2008, 03:38 PM #28
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Benm
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Re: possible 3\$ boost circuit

It seems unlikely that inductor and chip will provide 3V/400mA. At 1.5 volt supply and accounting for switching and diode losses, it would have to drive that coil at well over 1 amp.

But boosting from a single AA(A) cell is always tricky - i'd recommend against it except for simple applications like driving a small led on a keychain. An interesting low-cost light that delivers quite some power from a single AA cell is this one: http://www.dealextreme.com/details.dx/sku.1120

The circuitry is a fair bit bigger than what is used in the light in this thread, and it can provide a few 100 mA to the led with good batteries. It's not regulated well enough to drive a laser though.

11-29-2008, 03:54 PM #29
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jonrobertd
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Re: possible 3\$ boost circuit

Agreed, but what about driving a flexdrive, or is there still not enough mAs?
Seems not likely because as far as I understand there has to be the required mAs for the flexdrive, but I still don't know what that is. (800ma 200ma 100ma)

11-29-2008, 05:55 PM #30
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Benm
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Re: possible 3\$ boost circuit

You mean putting another regulator after the boost circuit?

That is entirely possible if the boost circuit provides enough current at the required voltage (for laser plus secondary driver), but it would be less efficient (and more complex) than driving it properly in one step.

12-02-2008, 07:53 AM #31
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Kage
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Re: possible 3\$ boost circuit

Quote:
 Originally Posted by Benm It seems unlikely that inductor and chip will provide 3V/400mA. At 1.5 volt supply and accounting for switching and diode losses, it would have to drive that coil at well over 1 amp. But boosting from a single AA(A) cell is always tricky - i'd recommend against it except for simple applications like driving a small led on a keychain. An interesting low-cost light that delivers quite some power from a single AA cell is this one: http://www.dealextreme.com/details.dx/sku.1120 The circuitry is a fair bit bigger than what is used in the light in this thread, and it can provide a few 100 mA to the led with good batteries. It's not regulated well enough to drive a laser though.
Exactly. And because of the current requirement (1Amp+), a 1.5V AAA battery would simply not hold up long enough for this to be practical.

Don't forget they do make a AAA size LI-Ion 3.6-4.2V battery. You could combine one of these with one of Drlava's drivers and actually make this work, but still only for a very few minutes at a time!

I just tried connecting a Ultrafire 10440 to one of my own boost regulators and get 200mW out of a DX200 diode. It draws around 550mA even from this battery, but proves it can be done.
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