My analysis of the AMC7135 Driver

There really isn't much to say except it works, and works very nicely. For use with an open can diode it is good to go as is. The driver will supply 340ma's all the way down to 3.3 volts before it begins to drop off. So for use with an open can diode, all you need to do is put a capacitor across the diode like Daedal does in his circuit.

In order to use this driver with the group buy diode, you need to put a resistor in parallel with the laser diode, along with the capacitor. The resistor will absorb the excess current we do not want to go to the laser diode. I found by placing a 33 ohm 1/2 watt resistor in parallel with the LD, the LD was drawing 240ma's of current.

Thankfully, this is a common resistor available at Radio Shack. I do not recommend anything less than a 1/2 watt resistor as the resistor does feel warm, but not hot. The results of my testing using the resistor were the same....the driver began to drop off at 3.3 volts and this was to be expected.

To supply the driver with the correct voltage without having to heatsink it, I do not recommend any more than 4.5 volts. The driver will work perfectly with 3 nimh or alkaline batteries..thus it is perfect for use with the Dorcy Metal Gear since it takes three AAA batteries.

Any good li-ion battery will also work well but I do strongly recommend using a protected li-ion battery to prevent over discharging it, and of course they are safer.

There is a diode on the driver board that provides for polarity protection. I do recommend leaving it in place and it is the only diode you need.

I was actually very impressed with the regulation of the AMC7135. I did all of my testing with a GB diode, and ran it for as long as 5 minutes. I was able to light a non-sharpied match instantly at about 2 feet, and a white headed paper match instantly at about a foot.

http://www.dealextreme.com/details.dx/sku.3160

One drawback to using this driver is the laser module must be electrically isolated from the rest of the flashlight body, if the case is being used for the ground side. The reason is the ground wire coming from the 7135 is not the same as battery ground.

Awesome Gazoo. Would you mind drawing a schematic?

So would a few ohms in series dissipate the same amt of heat as 33 ohms in parallel? i.e. I guess we have to waste 300mw no matter what? (dropping from 350 to 250ma at about 3V)
I've had a batch of these on order for a week - can't wait to experiment with them.

I tried putting resistors and silicon diodes in sereis with the LD, and the same amount of current went to the LD...the full 340ma's.

You would only be "wasting" 100ma's. There is no way around it. And if using an open can diode the waste would be negligible...the voltage drop is measured in millivolts. 100ma's of wasted current is a small amount...the 7135 is very efficient.. I am sure you will like them.

Nice to know it works that well... ordering complete boards for only the component seems silly, but its probably the cheapest way to get them anyhow.

As for the efficiency: it's definetely a loss, but if you're tight on voltage this option can be attractive: should be possible to run an LD on either a single 3.7V rechargeable lithium, or on 3 AA(A) NiMH's using this setup. It might be required to remove the (series) protection diode though, i'm not sure if reverse voltage will actually kill the chip... it saves you 0.7v drop for the whole thing.

For the best deal on the chip, get this one:
http://www.dealextreme.com/details.dx/sku.1886

It provides 40 (!) of these chips for $17.50 shipped.

so this would replace the need for me to make that circuit that has all those components to stop the LD from burning out?

stock as it is, it's putting out 350ma which for the GB diodes is a bit much without heatsinking. I've burned out quite a few even with heatsinking at 350,ma 380ma, and 390ma. So unless you added the resistors this really isn't a "ready to go solution"

Nah, it remains a bit of a hack. The same company does make a chip (AMC7124) that can deliver 180 or 240 mA with zero external components though:
http://www.addmtek.com/Datasheet/DD029-AMC712X_B(LF).pdf

Unfortunately, i have no idea how to order those or any boards that contain them.

BTW, I did try with and without the diode...the regulator began to drop out at 3.2 volts either way. It did seem to provide a bit more output after it dropped out without the diode. But I still feel it's best to leave it in place.

I realize AMC makes these regulators in all flavors, but where do we get them? The DX solution is a winner for now because as far as I am concerned it is a much better and more efficient solution than the LM317T, even with the added resistor. Like I posted before, 100ma's is not a big waste compared to what is wasted with the LM317.

And for those that don't know, DX sells different versions of these, for example a driver board just like the one I posted the link to but capable of supplying 1400 ma's. And these boards can be easily modified to supply 350, 700, or 1050 ma's.

It's too bad that these components are often difficult to actually order - usually the smallest thing available is a reel of a few 1000 chips.

The DX solution is a winner for now because as far as I am concerned it is a much better and more efficient solution than the LM317T, even with the added resistor. Like I posted before, 100ma's is not a big waste compared to what is wasted with the LM317.

Click to expand...

That really depends though. If you have voltage to spare, such as running in a body with 2 CR123's, the LM317 solution is superior - it draws only the current for the diode, and the drop is no problem.

But with anything that can be configured to hold batteries at lower voltage (3 or 4 AA(A), 1 lithium), your approach is definitely better. Another interesting possibility is to use a 2 CR123 body, and put in a single 18650 rechargeable lithium.

But the LM317 doesn't draw just the output current - AFAIK it dissipates all the voltage that it drops as heat.
So if you use a higher supply voltage to hold off the point where you start losing output current, your regulator gets that much hotter.

hey gazoo i found one here https://www.kaidomain.com/WEBUI/ProductDetail.aspx?TranID=3215

its current is adjustable from 980ma 300ma 120ma

Benm said:

It's too bad that these components are often difficult to actually order - usually the smallest thing available is a reel of a few 1000 chips.

The DX solution is a winner for now because as far as I am concerned it is a much better and more efficient solution than the LM317T, even with the added resistor. Like I posted before, 100ma's is not a big waste compared to what is wasted with the LM317.

Click to expand...

That really depends though. If you have voltage to spare, such as running in a body with 2 CR123's, the LM317 solution is superior - it draws only the current for the diode, and the drop is no problem.

But with anything that can be configured to hold batteries at lower voltage (3 or 4 AA(A), 1 lithium), your approach is definitely better. Another interesting possibility is to use a 2 CR123 body, and put in a single 18650 rechargeable lithium.

Click to expand...

The LM317 doesn't run that well on 2 CR123 batteries. As soon as the voltage begins to sag, the regulator drops out.

But the LM317 doesn't draw just the output current - AFAIK it dissipates all the voltage that it drops as heat.
So if you use a higher supply voltage to hold off the point where you start losing output current, your regulator gets that much hotter.

Click to expand...

The LM317 will dissipate any excess voltage, but so will the 1735. The difference is that the 1735 is factory set for 350 mA, so it will burn more current in the same application, and get hotter too.

The LM317 doesn't run that well on 2 CR123 batteries. As soon as the voltage begins to sag, the regulator drops out.

Click to expand...

That depends on the make too.. it can by specification require 4.25 volts drop to do its trick, but most do a bit better than that.

Neither solution is ideal, and both have its useful applications in specific circumstances. Both the 317 and 1735 are components you would choose for simplicity of the circuit, not for optimum performance.

Given the choice for a "fixed current" regulator, I would take the 7135 over the 317 in a heartbeat for all of the reasons I have already stated. For a current adjustable circuit, then obviously the 317 would be more ideal. It would also depend on the batteries I was going to use, but I would not use 2 CR123's with the 317 or the 7135 unless the 7135 was heatsinked.

I totally agree that neither solution is the perfect one with the exception the 7135 is perfect for open can diodes.. IMO.

The problem, once again, is getting the 7135 in it's different flavors...AMC makes the same chip designed to regulate at 250ma's. How do we get it?

What I was hoping in accomplishing with sending this off to gazoo to test in the first place is to find a driver that was current regulated to run off 1 14500 and a dummy battery to work in this host:





Now, I've not got the time to "build" a driver to get the exact current I need.  Nor do I wanna throw in something that is put together by me.  I want something I can buy, throw it in, hook it up and go!  This isn't the ideal choice as it's putting out 350ma instead of like 250ma-300ma like I would like to see but it does do the job and considering I've put together a total of 9 Dorcy Jr.'s and they are putting out 350ma this should be exactly the same as the dorcy Jr.  To bad the host is using a luxeon rebel and not a normal luxeon 1 watt led.

Considering that the 14500 is AA sized, puts out 3.6v and is rechargable I figured it was a perfect solution.  As soon as I get my latest shipment from Dx I will be testing this out to see if it works.

http://www.dealextreme.com/details.dx/sku.6240