Laser diode driver circuit

[Electro132]

Hi,

Trying to make a Laser Diode Driver circuit. Can you help? I have the LM317, 2x 10 ohm resistors, 1n4001 diode, 10 uf 16 v cap and 100 ohm variable resistor.

I have attached a pic of the PCB i've been working on.

Thanks

 

[(*steve*)]

Aside from the funkyness of your drawing, it is mostly correct.

I would remove the capacitor from the output as it will cause you huge problems if the photodiode's connection ever becomes intermittent (you will cook the photodiode).

 

[Electro132]

Aside from the funkyness of your drawing, it is mostly correct.

I would remove the capacitor from the output as it will cause you huge problems if the photodiode's connection ever becomes intermittent (you will cook the photodiode).

Thanks, although i tried this on a copper tracking and only got heat flowing through but the LD didn't work. not sure what went wrong. I'll have to do it again and see just to make sure. My doubts are on the copper tracking.

Also for the 100 ohm variable, there are 2 pins connected on the same copper tracking. Just wanted to know if that is connected to the 2nd pin and that the copper tracking is connected to that 2nd pin?

 

[(*steve*)]

What was getting hot?

 

[Harald Kapp]

Looks like you swapped output and adjust pins. Input is right, output is center, adjust is left (seen from top). See datasheet, page 1. Output needs to go to the Laser/LED.

 

[(*steve*)]

Output needs to go to the Laser/LED.

No, this is a current regulator.

ADJ goes to the load and resistance designed to drop 1.25V at the desired current goes between the output and adj.

I've noticed that the diode in the original image is superfluous too. Remove that and the capacitor.

A good test is to replace the load (the laser diode) with an ammeter and measure the current. This should be variable using the pot.

I am rather concerned that your trimpot won't be up to the current. What current do you want to use -- it would be easier to just use fixed resistors.

 

[Harald Kapp]

Oops, of course steve's right.

 

[Electro132]

No, this is a current regulator.

ADJ goes to the load and resistance designed to drop 1.25V at the desired current goes between the output and adj.

I've noticed that the diode in the original image is superfluous too. Remove that and the capacitor.

A good test is to replace the load (the laser diode) with an ammeter and measure the current. This should be variable using the pot.

I am rather concerned that your trimpot won't be up to the current. What current do you want to use -- it would be easier to just use fixed resistors.

Thanks for the replies. Are you saying that the diode and cap don't do anything? I thought they helped regulate the current flow to the + of the LD? If i took it out, the LD might go bust and it's worth alot to me.

I've tested the leads going to the LD with a multi meter and the voltage is variable but nothing is coming out.

If i use fixed resistors i won't be able to drive the current from low to high and vice versa. I'm thinking of just using 100 mA - 150 mA. But i was told that the LD could handle up to 300 mA or even more since it came from a DVD drive. Just want to be safe so i'll go with 100 - 150 mA i guess.

My first objective is to make at least a red light come out of it but so far only current has been flowing so i'm baffled whether i placed the wrong components or something.

 

[(*steve*)]

Using 20 ohms (both resistors in series) will give you 62mA.

Using one of these resistors (10 ohms) will give you 125mA

Using two 10 ohm resistors in parallel will give you 250mA

Start with 62mA

remove the diode and cap -- the cap just puts the laser diode at risk (I've said that earlier).

Don't hook up the laser diode, just place an ammeter in its place and measure the current. It should be within a few percent of the calculated figure.

Tell us what you get.

 

[Electro132]

Using 20 ohms (both resistors in series) will give you 62mA.

Using one of these resistors (10 ohms) will give you 125mA

Using two 10 ohm resistors in parallel will give you 250mA

Start with 62mA

remove the diode and cap -- the cap just puts the laser diode at risk (I've said that earlier).

Don't hook up the laser diode, just place an ammeter in its place and measure the current. It should be within a few percent of the calculated figure.

Tell us what you get.

What if i use a 100 ohm variable resistor instead of the 10 ohm resistors in series or parallel? That would still work won't it?

I've attached the diagram. (LD driver 1)

Also i've noticed that with this driver circuit my LD goes from dim to bright when i turn the dial. Now if i wanted it to go beyond, let's say, the surface of the first piece of wood and onto the second piece of wood behind it what would i need to do?

I've attached a picture of what i mean. (LD Penetration)

 

[(*steve*)]

The problem with a variable resistor in this position is that it has to handle the full load current.

If you're not careful you'll burn it up.

Use fixed resistors to set the maximum current, then if you want, add a variable resistor in series to allow you to reduce the current.

The power rating of the variable resistor is given by:

I^2R, where I is the maximum current in amps, and R is the resistance of the pot in ohms.

So, if you have the two 10 ohm resistors in parallel (giving you a max current of 250mA) and a 100 ohm pot in series with them, it's power rating needs to be 0.25*0.25*100 = 16 Watts.. It may not be practical, or if practical, it will be expensive.

 

[Electro132]

So, if you have the two 10 ohm resistors in parallel (giving you a max current of 250mA) and a 100 ohm pot in series with them, it's power rating needs to be 0.25*0.25*100 = 16 Watts.. It may not be practical, or if practical, it will be expensive.

Thanks man, good news - it worked. But the light is not enough for some reason, i got the red dot appearing when i turned the dial on the variable resistor the light got brighter and brighter but it was still dim even at max peak. My power supply was 7.2 v from rechargeable batts. I would of thought it was enough but i'll try placing the 2x 10 ohm resisters in parallel and see if that does something.

When i did your calculation I got 6.25 not 16 watts. Just wanted to know if you converted it from something.

Also i was wondering what if i just applied 2x 2 pairs of darlington pairs to multiply the input power to make up for the power amount needed (e.i. 16 watts) ? The LM317 VR can go up to 35V.

 

[(*steve*)]

When i did your calculation I got 6.25 not 16 watts. Just wanted to know if you converted it from something.

Which is why I try to give the working. I calculated 1/4 * 1/4 = 1/16 then had a brain fart that 1/16*100 = 16!

Also i was wondering what if i just applied 2x 2 pairs of darlington pairs to multiply the input power to make up for the power amount needed (e.i. 16 watts) ? The LM317 VR can go up to 35V.

I'm not sure exactly what you mean, but the answer I think is No.

 

[Electro132]

Which is why I try to give the working. I calculated 1/4 * 1/4 = 1/16 then had a brain fart that 1/16*100 = 16!

I'm not sure exactly what you mean, but the answer I think is No.

Ah i see. Ok well, i'll try it with the 2x 10 ohms R in parallel. But at least the 100 ohm Var Res works.

The Darlington pair works with the E of one Transistor connected to the B of the other transistor which causes the current to multiply its amount when it comes out of the E on the 2nd transistor. Not sure why that happens but that's what happens apparently.

I was reading that you could input some power at one end and it can be converted to a higher amount when it comes out the other end.

 

[Electro132]

Which is why I try to give the working. I calculated 1/4 * 1/4 = 1/16 then had a brain fart that 1/16*100 = 16!

I'm not sure exactly what you mean, but the answer I think is No.

Hey it works with 2x 10 ohm res in parallel. great stuff. I'll probably upload a vid when i get time.

Btw, was thinking of doing a pulse type as an add-on but wasn't sure if a 555 IC could do it with a driver attached. Also looking at gamma to add into the mix with the driver.

 

[Electro132]

Using 20 ohms (both resistors in series) will give you 62mA.

Using one of these resistors (10 ohms) will give you 125mA

Using two 10 ohm resistors in parallel will give you 250mA

Start with 62mA

remove the diode and cap -- the cap just puts the laser diode at risk (I've said that earlier).

Don't hook up the laser diode, just place an ammeter in its place and measure the current. It should be within a few percent of the calculated figure.

Tell us what you get.

Hey steve, it worked. YIppeee!! I'll load it up and give you guys a link. In the meanwhile, just wanted to know, is it possible to go beyond 250 mA on a red LD? I was thinking of maybe using 5 ohms Res or even 1 ohm Res but was afraid that it might destroy the diode.

 

[(*steve*)]

Hey steve, it worked. YIppeee!! I'll load it up and give you guys a link.

Cool!

In the meanwhile, just wanted to know, is it possible to go beyond 250 mA on a red LD? I was thinking of maybe using 5 ohms Res or even 1 ohm Res but was afraid that it might destroy the diode.

Who knows? (hint -- the manufacturer, and that's why they have datasheets)

Quite often you will find a graph that shows maximum current vs duty cycle (or pulse length)

 

[Electro132]

Cool!Who knows? (hint -- the manufacturer, and that's why they have datasheets)

Quite often you will find a graph that shows maximum current vs duty cycle (or pulse length)

Ok, since this is from a dvd burner, i'm assuming it will take 480 mA max or 430 mA at least? Just out of my head since it is no ordinary LD.

Also would you happen to know what type of lens and material the Aixiz Housing Cylinder is made out of?

It's abit difficult trying to get one here. I found one around $8 aud, but i also have to pay P &H of another $8 which is $16 altogether just for one.

 

[(*steve*)]

Ok, since this is from a dvd burner, i'm assuming it will take 480 mA max or 430 mA at least? Just out of my head since it is no ordinary LD.

I have no way of knowing if that's true or not.

Also would you happen to know what type of lens and material the Aixiz Housing Cylinder is made out of?

No

It's abit difficult trying to get one here. I found one around $8 aud, but i also have to pay P &H of another $8 which is $16 altogether just for one.

OK. But even of you know what it's made of, you don't think you're going to be able grind a lens yourself do you?

 

[CDRIVE]

I was reading that you could input some power at one end and it can be converted to a higher amount when it comes out the other end.

As usual that is a vague, if not ambiguous statement.

Chris