Possible driver substitute?

[Ginge]

Hello, Internet

I am new to the laser community and my research on this forum has raised a question about the possibility of substituting a driver with only a resistor and a protected battery. I looked for an answer but I couldn't find anything, so I'm sorry if this is a repeat...

I read a thread that said a protected (nice rhyming eh?) battery stops the jump in voltage that the battery can give off when first turned on after a period of time. ( I'm sure different protected batteries do different things, but that's the basic idea i got from it. Correct me if I'm wrong...)

Moreover, a drivers purpose is both to buck off excess current from the battery during a spike, as well as too feed the laser a steady voltage (since they are power hungry and will draw as much as they can. Again correct my shortcomings)

So in detail my question is:

With the battery's circuit board protecting from spikes in current, could you just attach a resistor to the diode to keep the voltage at a constant rate, thereby supplying the diode in the same way as a driver?

It seems something so simple would be used more often which is why I'm pretty sure that I'm wrong. Teach me, laser superiors...

 

[jander6442]

Howdy IE <waves hand>

 

[PersonGuyDude]

No way in hell I would trust a 25 cent chinese battery protection circuit with a $45 diode.

 

[Cyparagon]

The protection board doesn't regulate current, it just disconnects the battery if the current gets too high.

 

[tsteele93]

Hello, Internet

I am new to the laser community and my research on this forum has raised a question about the possibility of substituting a driver with only a resistor and a protected battery. I looked for an answer but I couldn't find anything, so I'm sorry if this is a repeat...

I read a thread that said a protected (nice rhyming eh?) battery stops the jump in voltage that the battery can give off when first turned on after a period of time. ( I'm sure different protected batteries do different things, but that's the basic idea i got from it. Correct me if I'm wrong...)

Moreover, a drivers purpose is both to buck off excess current from the battery during a spike, as well as too feed the laser a steady voltage (since they are power hungry and will draw as much as they can. Again correct my shortcomings)

So in detail my question is:

With the battery's circuit board protecting from spikes in current, could you just attach a resistor to the diode to keep the voltage at a constant rate, thereby supplying the diode in the same way as a driver?

It seems something so simple would be used more often which is why I'm pretty sure that I'm wrong. Teach me, laser superiors...

Some people do this with some red diodes as they tend to be more robust and more able to survive that kind of abuse, but generally speaking there are a good number of inexpensive constant current drivers that are available for $5-$20 so it just doesn't make much sense to try and risk a laser diode that way.

Especially not an expensive diode!

 

[Sigurthr]

There is a distinction that the OP is missing. The protection circuit does not regulate (that means to keep constant) the voltage nor the current of the cell. It only prevents too much voltage from being applied to the cell when charging or too much current being drawn when using the battery.

You can run any laser diode off of a Constant VOLTAGE power source in series with a current limiting resistor. If the voltage is never allowed to change, the current through a fixed value of resistance can also never change. Batteries are not CV sources though, as they discharge their voltage drops (called sagging). So yes, if your diode's Vf is less than your fully charged cell's Voc you can put a precision resistance in series with it and the diode and it will run perfectly fine, but the diode will dim as the battery gets used.

 

[Cyparagon]

You can run any laser diode off of a Constant VOLTAGE power source in series with a current limiting resistor. If the voltage is never allowed to change, the current through a fixed value of resistance can also never change.

Nope. The forward voltage of the diode goes down as it heats up which leads to a (albeit slight) current increase.

 

[Sigurthr]

Nope. The forward voltage of the diode goes down as it heats up which leads to a (albeit slight) current increase.

I disagree;

If your diode has a Vf of 3.0V and an If of 100mA you use a 30R resistor and set the CV source to 3.0V. Now if the diode heats up and drops it's Vf to 2.8V only 93mA will flow through the diode, but the resistor will still restrict the flow to no more than 100mA. The diode would dim, but be fine.

If the Vf increases on the diode instead of decreases the resistor will still restrict current flow in the load to only 100mA, but now the CV source is not supplying enough voltage to fully forward bias the diode, so it may not draw the full 100mA as it is not fully on, the equivalent of a linear region (thought it isn't actually linear). The diode will dim but be fine.

 

[Cyparagon]

The current across the resistor is (Vin-Vout)/resistance. In your case you get zero current because the voltage at either end of the resistor is the same.

To get 100mA you need a higher voltage than the Vf of the diode. 5V for example would need:

(5-3)/R=0.1
R=20Ω

If you assemble the circuit as such and the Vf drops to 2.8, you get:

(5-2.8)/20=110mA

 

[Ginge]

Thanks to all for the info. I guess ill just get a cheap diode to tinker with and try this stuff out myself. I've noticed that IR diodes are very cheap, even very powerful ones. Are they more robust than the reds?

 

[tsteele93]

Thanks to all for the info. I guess ill just get a cheap diode to tinker with and try this stuff out myself. I've noticed that IR diodes are very cheap, even very powerful ones. Are they more robust than the reds?

Unless you are experienced with lasers, I would highly recommend NOT starting with IR or even high power reds.

Start with something low power and cheap and learn.

 

[Ginge]

Indeed, tsteele, safety is key. I won't play with anything I am not sure i can handle. I'm starting with a PHR-803T build, but that is just to work my way up to a more powerful laser. So, are the IR diodes able to take more of a beating than reds?

 

[tsteele93]

Indeed, tsteele, safety is key. I won't play with anything I am not sure i can handle. I'm starting with a PHR-803T build, but that is just to work my way up to a more powerful laser. So, are the IR diodes able to take more of a beating than reds?

I honestly don't know. I haven't come up with a good reason to mess with IR. I just haven't figured out a use for an IR laser pointer.

Maybe someone else can chime in here - not sure what you would do with it.

There is a group buy on a new red diode that is >400mW going on right now and the diodes are $17.

And you can go to DTR's store here on the forum (and modwerx and others) and get LPC-826's that are 660nm red that will do >250mW pretty reliably.

 

[Ginge]

The only reason I would be interested in IR is because its cost to power ratio. I want to make a laser that is a powerful burner at some point, and i found some >1W diodes for dirt cheap. That probably means that they are pieces of crap, idk. I haven't researched them much because it will be a while before i start trying to mess with anything over a watt. I still need to finish my first one, but the idea of a very powerful laser is enticing...

 

[tsteele93]

The only reason I would be interested in IR is because its cost to power ratio. I want to make a laser that is a powerful burner at some point, and i found some >1W diodes for dirt cheap. That probably means that they are pieces of crap, idk. I haven't researched them much because it will be a while before i start trying to mess with anything over a watt. I still need to finish my first one, but the idea of a very powerful laser is enticing...

What are you looking to burn? You can get a 2 watt 445 for around $45 and cheap drivers for them. There are people on here who melt solder with them...

There are starting to be some high powered 405nm diodes too, that really pack a nice punch.

 

[Ginge]

Hmmm my future goal is world domination... but for now I dont have anything in particular I'd like to burn. Pretty much if it burns, then i want to burn it. I guess if im going to make a very powerful laser I'll hold out till i can afford a much cooler 445 rather than waste a bunch of effort on an IR. What's the most impressive thing you guys have burned or heard about being burned with one of these? I know that there are IR laser engravers at >3W. Can anyone make a mark in some steel?