Using a DC/DC converter to power the laser

Saturn400K · Nov 25, 2007

Here is a prototype that I got working. It's the VPack voltage booster that I ordered from sparkfun electronics in combination with a really simple LM317 setup. First thing I did was modify the voltage booster by replacing the resistor at RF1 with a 200K pot, then I replaced the cap at the output end with a larger cap. This setup works better than I could imagine, It can kick out up to 9.7V from a single 1.5V battery

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I've been testing out a 3 watt luxeon star LED and It's powerful. I've even been using incandescents on it to see what kind of load it can take. The best part is that everything is adjustable through 2 pots. "voltage and current"

.

The LM317 circuit that I'm using has been simplified to my needs. I eliminated the diode and 4 ohm resistor from Daedals design.

timelord · Nov 25, 2007

9volt

nice work man

Saturn400K · Nov 25, 2007

Here's another picture of it powering my 3 watt luxeon LED with one AA. I measured about 3.15V @ 250mA at output. It works best with 2 cells. When I power it up with one, It takes about 5-7 seconds to charge up to full brightness and you can feel the battery get warm.

IgorT · Feb 3, 2008

Nice work, Saturn!

I see there was a lot going on, while i was away...
Could you please tell me which step up IC this VPack is using?

Anyway...
I have a couple of MAX756 and MAX1674 & 1675 left over from an old project..

MAX756, data sheet: http://www.ortodoxism.ro/datasheets/maxim/MAX756-MAX757.pdf

MAX756 is capable of producing a stable 3.3V or 5V output (depending on the setup) from a single AA or AAA battery, down to 0.7V.
I don't know if the voltage can be changed, like in your circuit. Probably not.

But as a 5V constant voltage source, it could be used to power a Blue Ray, since some people are using a LM7805 and a resistor...

And at 3.3V it could be used for a DVD burner with a simple resistor. Again, not as good as a current source, since the current would go up, as the LD would heat up, but at least the output wouldn't be dropping together with the battery voltage...

Still, a constant current source would be better, but i would need 9V for that..

MAX1674 & 6 datasheet: http://datasheets.maxim-ic.com/en/ds/MAX1674-MAX1676.pdf

These two have an adjustable output from 2 - 5V, again working from a single 1.5V cell, down to 0.7V.

Again, the same drawbacks remain, but since the Vo is adjustable, would it be possible to reference it to the current, to get a current regulated step up converter?

Chimo, do you know if this is possible?

I mean, i hate 9V batteries, and the size of the box they require..
I've seen you do a Blue Ray from the Charge2Go circuit. I think it's a great idea.

But is your circuit adjustable at all? What are it's max ratings?

Any ideas welcome!

Thanks!

P.S. In my country, some of the components are hard to come by, except in huge quantities, and buying online often has a shipping price higher than the stuff i want to order..

So i'm trying to make do with what i already have... Finding the right inductors might be a big enough problems anyway...

IgorT · Feb 4, 2008

Another thing i was thinking about would be the use of tiny transformers, that are found in disposable cameras to charge up the flash capacitor to a high voltage from a single AA cell.

If i were to rewire the secondary winding and rectify the output, and then use the LM317, the solution would be very small and would work from a single AA cell.

I have a bunch of these around, from when i convinced a few photo developing shops not to throw the disposables away, but give them to me instead..
I got a lot of free parts this way, that would cost quite a lot if i were to buy them.

Is this doable?

chimo · Feb 4, 2008

IgorT said:
Nice work, Saturn!

I see there was a lot going on, while i was away...
Could you please tell me which step up IC this VPack is using?

Anyway...
I have a couple of MAX756 and MAX1674 & 1675 left over from an old project..

MAX756, data sheet: http://www.ortodoxism.ro/datasheets/maxim/MAX756-MAX757.pdf

MAX756 is capable of producing a stable 3.3V or 5V output (depending on the setup) from a single AA or AAA battery, down to 0.7V.
I don't know if the voltage can be changed, like in your circuit. Probably not.

But as a 5V constant voltage source, it could be used to power a Blue Ray, since some people are using a LM7805 and a resistor...

And at 3.3V it could be used for a DVD burner with a simple resistor. Again, not as good as a current source, since the current would go up, as the LD would heat up, but at least the output wouldn't be dropping together with the battery voltage...

Still, a constant current source would be better, but i would need 9V for that..

MAX1674 & 6 datasheet: http://datasheets.maxim-ic.com/en/ds/MAX1674-MAX1676.pdf

These two have an adjustable output from 2 - 5V, again working from a single 1.5V cell, down to 0.7V.

Again, the same drawbacks remain, but since the Vo is adjustable, would it be possible to reference it to the current, to get a current regulated step up converter?

Chimo, do you know if this is possible?

I mean, i hate 9V batteries, and the size of the box they require..
I've seen you do a Blue Ray from the Charge2Go circuit. I think it's a great idea.

But is your circuit adjustable at all? What are it's max ratings?

Any ideas welcome!

Thanks!

P.S. In my country, some of the components are hard to come by, except in huge quantities, and buying online often has a shipping price higher than the stuff i want to order..

So i'm trying to make do with what i already have... Finding the right inductors might be a big enough problems anyway...

They could be used but the feedback reference voltages are fairly high. You would be wasting a fair bit of power across your sense resistor or you could add another comparitor stage to provide the feedback voltage. Of course, this would require prototyping to ensure stability.

Pretty well any voltage converter can be converted to a current source. The desired output current has to be converted to the feedback voltage.

Heres an example:

If the desired output current is 30mA and the chip's feedback voltage is 300mV, a 10 ohm resistor would be required to provide the required snese feedback voltage. The sense voltages for the chips you list is around 1.3V - that means for a simple sense resistor feedback the circuit will have to boost 1.25V more than the load voltage.

Paul

IgorT · Feb 5, 2008

chimo said:
If the desired output current is 30mA and the chip's feedback voltage is 300mV, a 10 ohm resistor would be required to provide the required snese feedback voltage. The sense voltages for the chips you list is around 1.3V - that means for a simple sense resistor feedback the circuit will have to boost 1.25V more than the load voltage.

Thanks for the explanation!

I'm not that obsessed with efficiency, i just want it to work and be as small as possible.

Anyway, i found those inductors, so at least i will be able to power the next two Blue Rays from a single AA with these ICs at 5V + a precision trimmer...

But for the burners, i'll have to find something better, i guess... I think i'll stop complicating, and go for two small LiPo rechargables in series and the LM317.

Thanks, Chimo!

IgorT · Feb 6, 2008

I just ffinished building the MAX756 step up circuit, and it works!

I used some resistor like inductors, since it's gonna be a few more days, before i get the good power inductors, but this was still good enough for testing.

It puts out a stable 5V, so it's gonna be perfect for driving my next Blue Rays off a single AA or even AAA Ni-Mh cell, right down to 0.7V!

If only i could squeeze one more volt out of it, to power a burner through a 317... Oh well...

woop · Feb 10, 2008

I found this nice little switching chip for use with led's. it has a feedback voltage of less than 300mV so it can be used with a shunt. and i think there are free samples.
it has intergrated 1.5A transistor so it will only require a diode, inductor, some resistors and capacitors to function. however it requires 3v to operate, but this means we can use a single lithium cell. or possibly a 1.5V cell with a switch to start it up and power for the chip coming from the output
http://www.onsemi.com/PowerSolutions/product.do?id=NCP3065PG

woop · Feb 10, 2008

and here is another shot from the datasheet showing an over complecated boost configuration.

IgorT · Feb 10, 2008

woop said:
and here is another shot from the datasheet showing an over complecated boost configuration.

Why did they have to make it that complicated? That's very strange.

But thanks for bringing it up. I'll try to order some samples.

It would be nice to have the possibility of powering a DVD burner with an adjustable constant current from a single LiPo and at a high efficiency.

phenol · Feb 10, 2008

hm, i have MC34063 which are more readily available where i am. the ref voltage is 1.25V but i guess it would work in a configuration similar to the above chip. if not, it should still be possible to use it as a boost dc/dc converter with min input voltage of 3V. im going to give it a try these days.

laserrod · Feb 10, 2008

Here's more goodies.
http://www.future-mag.com/0611/061101.asp

Too many components needed for IR chips for me. But U might like em.
I'm testing TI sync rect. boost drivers now but they are tiny bastards to solder.
Will post cool pics. latter.

DGM

drlava · Feb 10, 2008

chimo said:
Here are some current regulator schematics to stir your thought process.

great circuits, especially the first one is interesting. Can you specify which lights those came out of?

Hemlock_Mike · Feb 10, 2008

Lava -- Where'd you put that PG circuit again ?
Mike

chimo · Feb 10, 2008

drlava said:
[quote author=chimo link=1194375801/45#45 date=1195101532]Here are some current regulator schematics to stir your thought process.

great circuits, especially the first one is interesting. Can you specify which lights those came out of? [/quote]

ArcLS (grey market board)
BadBoy NexGen (Shoppe)
VIP (TaskLED)

Using a DC/DC converter to power the laser

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