DIY Homemade laser diode driver

[woop]

it depends how long you use it for. do it and see.

 

[IgorT]

I was just wanting confirm that you do put the caps in series, and not in parallel, or vice versa.

If you put a cap in series, it will prevent the current from flowing.

 

[IgorT]

SO....I need a heat-sink!

The circuit will give out the same current and voltage, no matter what voltage you apply to it, as long as it is OVER 6V..

This means the 317 has to dissipate the power difference in heat, so the higher the imput voltage, the more power it will have to dissipate in heat..

I don't think you would need a heatsink at 7.2V (actually 8.4 when battery full), but it definatelly can't hurt if you use one..

Besides the 317 has thermal protection, so it would shut down if it would overheat..

 

[Daedal]

Besides the 317 has thermal protection, so it would shut down if it would overheat..

Exactly

--DDL

 

[yuip]

Another round of quick questions!

I worked on a circuit between yesterday and today and finally thought I had finished it. When I went to test the circuit, I found that I had miswired/fried both the LM317 and the 1N4001! The output voltage was nearly as high as the input voltage, so I knew something was wrong. ;D

I did have the iron to them a little longer than I probably should have, but the pot seemed to work for the most part.

So, my three questions for today are:

How static sensitive are the components in the circuit (besides the LD)?

What do you recommend to interconnect components? I used 30 gauge wire, and I think some of my connections may be bad. :

If you are adding a capacitor before the LM317, does the LM317 go in parallel with it?

Thanks in advance, and please pardon my ignorance!  :'(

 

[a_pyro_is]

First, re-read the thread. (especially the bits about how to test your driver. Search the thread for ’dummy load’)
Next, check your wiring, that you understand which pin is which on the 317, and all connections.
Finally, now that you’ve got it working post lots of pics in the Multimedia Board. ;D

 

[yuip]

First, re-read the thread. (especially the bits about how to test your driver. Search the thread for ’dummy load’)
Next, check your wiring, that you understand which pin is which on the 317, and all connections.
Finally, now that you’ve got it working post lots of pics in the Multimedia Board.  ;D

Thanks for the tips and encouragement! I'll recheck the connections and pinouts. Hopefully I can get it working.

If I can't get it working, I'll just try to build it again.

 

[a_pyro_is]

I'm certain you'll work it out.
But if it's somehow still giving you trouble, start a thread in the Help Board with pics of your circuit and one way or another we'll get you glowing red.

 

[wooooooolazer]

Since it doesnt regulate voltage i think the voltage will change, mine outputted like 6.5v with no load with a 7.2v battery.


....lazer.... ;D ;D ;D

 

[yuip]

I'm certain you'll work it out.
But if it's somehow still giving you trouble, start a thread in the Help Board with pics of your circuit and one way or another we'll get you glowing red.

Good news! I had it wired correctly the whole time. I tested it out on an old Rohm diode that I thought I had fried, only to find out that it worked after all.

I think that I may have fried the 1N4001, though. When I input ~12.9 volts in I get ~12.9 volts out with no load. I assume that the LM317 does not begin to regulate until it has an acceptable load, but I thought the diode would always take about 0.7 volts from the output.

Even if I did fry it, it's okay. I have 2-3 more circuits to make later today. Then it will be on to extracting the precious Blu-Ray diode.

Thanks so much!

 

[IgorT]

Good news! I had it wired correctly the whole time. I tested it out on an old Rohm diode that I thought I had fried, only to find out that it worked after all.

I think that I may have fried the 1N4001, though. When I input ~12.9 volts in I get ~12.9 volts out with no load. I assume that the LM317 does not begin to regulate until it has an acceptable load, but I thought the diode would always take about 0.7 volts from the output.

Even if I did fry it, it's okay. I have 2-3 more circuits to make later today. Then it will be on to extracting the precious Blu-Ray diode.

Thanks so much!

Look, there's probably nothing wrong with your circuit. You're testing the output WITHOUT a load. In this case you would get the maximum output voltage possible..

If you give it a load, the circuit will regulate the voltage, to achieve the desired current..

Test it with a LED or an array of them in parallel.

This was explained at least 4 times in the last few pages..

And it's unlikely to kill a diode (4001).


EDIT: If the diode was in SERIES it would drop the voltage by 0.7V. Here it is in parallel and in reverse, to protect the LD from wrong polarity, by creating a short in this case. If the polarity is right, the diode does not do anything, and if the polarity is wrong, it makes the current flow through itself instead of letting it kill the LD.

 

[IgorT]

Since it doesnt regulate voltage i think the voltage will change, mine outputted like 6.5v with no load with a 7.2v battery.


....lazer.... ;D ;D ;D

It DOES regulate the voltage.

But it is set up in a way, that the voltage is dependant on the current.

Basically it regulates the current by regulating the voltage - it gives the load just enough voltage to achieve the desired current..


As long as the input voltage is ABOVE 6V the current AND the voltage WILL stay the same!



There will be small variations in the voltage tho, because as the LD heats up, it's resistance goes down.. The circuit then tries to keep the current constant, so it drops the voltage a little.


You don't have to worry about voltage, as long as the circuit is regulating the current properly.


You also can't test the circuit without a load. It needs a load to regulate the current, otherwise it will try to reach the set current, but since it can't flow, it will raise the voltage to the max, and it will still not flow. This is why you get weird readings..

There is nothing wrong with it. Use a few LEDs in parallel to simulate the load, and you will see that the current AND the voltage stay the same from 6V up to 35V. (at higher voltages it needs a heatsink, since it has to dissipate more power)


EDIT: If the circuit was set up to regulate the voltage, you could test it without a load. If it's set up to regulate the current, the current must be able to flow, or else no regulation is possible.

 

[Zarniwoop]

Nicely spelled-out Igor - a lot of people still don't get this.

Makes me think we need a sticky about how current regulation works, or maybe also some basic electronics like Ohm's law, how to measure current going to the LD, etc.

But then a lot of people don't seem to read the stickies we already have.

 

[wooooooolazer]

Igor thanks i dont really now to much about electricty only how to make circuits, Im gona test it out with leds now thanks.


....lazer.... ;D ;D ;D

 

[yuip]

Look, there's probably nothing wrong with your circuit. You're testing the output WITHOUT a load. In this case you would get the maximum output voltage possible..

If you give it a load, the circuit will regulate the voltage, to achieve the desired current..

Test it with a LED or an array of them in parallel.

This was explained at least 4 times in the last few pages..

And it's unlikely to kill a diode (4001).


EDIT: If the diode was in SERIES it would drop the voltage by 0.7V. Here it is in parallel and in reverse, to protect the LD from wrong polarity, by creating a short in this case. If the polarity is right, the diode does not do anything, and if the polarity is wrong, it makes the current flow through itself instead of letting it kill the LD.

IgorT, thanks for the reassurance. Yesterday afternoon I discovered that I did test the circuit with the load in parallel to the 1N4001. I looked at the circuit diagram and discovered that it should be in series with load, as you said.

I think my circuit is fine for now.

Thanks again!

 

[IgorT]

IgorT, thanks for the reassurance. Yesterday afternoon I discovered that I did test the circuit with the load in parallel to the 1N4001. I looked at the circuit diagram and discovered that it should be in series with load, as you said.

I think my circuit is fine for now.

Thanks again!

No, no, no!

The circuit shows the diode in PARALLEL with the load, but in reverse! That is not in series..

Do the circuit exactly like its drawn, only make sure you get the pins of the 317 right. I think (not sure) they are drawn in the wrong order (compared to where they really are). There is another pic with the elements pictures, and there it should be right.. Check the datasheet for the correct pinout!



About the diode..
Usually they are placed BEFORE a circuit, in series, to protect from reverse polarity.. But when the polarity is right, they drop the voltage, so you need a higher imput voltage..

In order for this circuit to work from 6V up, the diode was put in parallel with the load but in reverse, which is a "dirty" solution to the problem, as it shorts the battery when the polarity is wrong, but at least it doesn't  drop the voltage, when the polarity is right.

This means the diode does NOTHING when the polarity is right.. It's just there to protect the LD from accidents.


EDIT: If you're not sure, TEST THE CIRCUIT WITH SOME LEDs! They are cheap and hard to kill. Then power the circuit down, SHORT the capacitor (if it's not yet on the LD) and then connect the LD, with the current set to minimum (pot - max resistance), and slowly turn the pot to achieve the desired current..

You also need a way to measure the current. A 1 Ohm resistor in series with the LD is great for this, as you don't have to disconnect anything - less chance of killing the LD and it doesn't affect the circuit (the LD will still get the same current, only the imput voltage needs to be slightly higher, but it's hardly noticable). We discussed this a couple of pages ago. Measure the voltage drop across the 1 Ohm resistor, then mV = mA..


EDIT EDIT: Ground yourself, then ground youself, and when youre done grounding yourself, ground yourself! Then, before you touch the LD, ground yourself! Then ground yourself some more!