Cheap diode drivers.

[Voldy356]

Are cheap eBay laser diode drivers such as https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/262878776688 safe/good to use? If not, why?

 

[Alaskan]

I don't know about those particular drivers because I've never used them, but I don't think there is anything wrong with them, if the size is right for what you want to use them for. They are however power limited to what, 800 milliamps? The specs say good for 300-700 mw laser diodes. I'd feel comfortable at the lower rating, but not sure for the upper. However, the price is right, give it a try with a laser diode test load at 800 mA and see if the active device gets too hot, if it does, heat sink it some and see if it is better.

That all said, 800 mA isn't a whole lot of current, you will have a limited choice of red laser diodes to use with it. Red laser diodes operate from about 1.5 to 2.2 volts, perhaps this unit has a limited amount of voltage input (under 4.2 VDC?) and or a limited range for the operating voltage.

 

[Voldy356]

I don't know about those particular drivers because I've never used them, but I don't think there is anything wrong with them, if the size is right for what you want to use them for. They are however power limited to what, 800 milliamps? The specs say good for 300-700 mw laser diodes. I'd feel comfortable at the lower rating, but not sure for the upper. However, the price is right, give it a try with a laser diode test load at 800 mA and see if the active device gets too hot, if it does, heat sink it some and see if it is better.

That all said, 800 mA isn't a whole lot of current, you will have a limited choice of red laser diodes to use with it. Red laser diodes operate from about 1.5 to 2.2 volts, perhaps this unit has a limited amount of voltage input (under 4.2 VDC?) and or a limited range for the operating voltage.

Bought it. The diode I want to drive is a Mitsubishi 500mw 638, which usually operates on around 750ma. I asked the seller and he said the output voltage was 2.2v, which is ideal for my diode. About the dummy load, does it matter how many diodes I connect in series? I already made a dummy load with five 1n4001 diodes and a 1 ohm resistor. Also, the diode is multi-mode, if it matters.

 

[Alaskan]

Multimode is just a propagation characteristic within the laser diode dye, it produces a higher divergence wider beam which can be improved with a cylinder pair to correct the wide rectangle shape it makes into more of a square shape, and the higher divergence of multimode diodes can be reduced using either a longer focal length larger diameter collimation lens, or a beam expander after collimation with a short focal length, small diameter lens.

As long as the total series voltage drop of the diodes you are using in that test setup are close to the forward or operating voltage of that diode, I suppose, that's what you need.

 

[Cyparagon]

You didn't have the patience to read through any of the laser building tutorial threads? You don't know the difference between constant current and constant voltage, don't know how to calculate voltage drop of PN junctions in series, don't know how to apply ohm's law, and you're building a laser from scratch?

You, sir, are about to learn the hard way. That's fine, we all do it on some projects, just be aware.

 

[Voldy356]

You didn't have the patience to read through any of the laser building tutorial threads? You don't know the difference between constant current and constant voltage, don't know how to calculate voltage drop of PN junctions in series, don't know how to apply ohm's law, and you're building a laser from scratch?

You, sir, are about to learn the hard way. That's fine, we all do it on some projects, just be aware.

I actually do know these things. I go to an electrical engineering school. I just wanted to be sure. What made you conclude I don't?

 

[Alaskan]

I was reading your post and wondering why he had that impression too.

 

[paul1598419]

I haven't seen one of these drivers in a long time. They are very cheap linear drivers and I had some, but only tried them out as the switching drivers work much better for the ML501P73 diodes. I think I still have at least one left in my stock somewhere.

 

[Cyparagon]

What made you conclude I don't?

Well it's just going to make you look even more silly if I outline these step by step, but if you insist.

I asked the seller and he said the output voltage was 2.2v, which is ideal for my diode.

This suggests you don't know the difference between supplying constant current and constant voltage.

This is also covered in many build tutorials, which suggests you haven't read them.

I already made a dummy load with five 1n4001...

This demonstrates your inability to calculate the voltage drop of PN junctions in series. In what world does this add up to 2.2 Vf?

This is also covered extensively in many build tutorials, which suggests you haven't read them.

...and a 1 ohm resistor.

This, as above, demonstrates your inability to utilize ohm's law to calculate voltage drop on a shunt. In what world does this and the diodes above add up to 2.2 Vf?

I was reading your post and wondering why he had that impression too.

This demonstrates either that you haven't read this thread, haven't read tutorial stickies, or lack an ability to compare and contrast them here.

 

[Alaskan]

Cyp., you have been silent for far too long.

 

[Voldy356]

Well it's just going to make you look even more silly if I outline these step by step, but if you insist.



This suggests you don't know the difference between supplying constant current and constant voltage.

This is also covered in many build tutorials, which suggests you haven't read them.



This demonstrates your inability to calculate the voltage drop of PN junctions in series. In what world does this add up to 2.2 Vf?

This is also covered extensively in many build tutorials, which suggests you haven't read them.



This, as above, demonstrates your inability to utilize ohm's law to calculate voltage drop on a shunt. In what world does this and the diodes above add up to 2.2 Vf?



This demonstrates either that you haven't read this thread, haven't read tutorial stickies, or lack an ability to compare and contrast them here.

Yes, I messed up, but now I got it figured out. Since 1n4001's voltage drop is 0.7v, and I calculated the resistor's voltage drop to be around the same (0.8v) I need two 1n4001 diodes. I might be wrong, I'm just a beginner.

 

[paul1598419]

If you are planning on setting the driver for 800 milliamperes that will give you a forward voltage of ~2.2 volts. Seems good enough for most red diodes.

 

[Voldy356]

Yup, It works. Turns out I didn't even need a dummy load. I was, for some reason, completely obvious to the fact the driver's MAX output is 800mA, so the only thing I had to do Is crank that thing up all the way, and it works. And let me tell you, the divergence is absolutely terrible. But that's not a big problem since I ordered a proper lens. Overall, I'm happy with this diode.

 

[paul1598419]

Unless you measure the output of the driver you can't know what it is set to do. But, it will likely not do more than 800 mA. For the MIts, ML501P73 that should be fine as they have been driven over 1000 mA without problems.

 

[Voldy356]

Unless you measure the output of the driver you can't know what it is set to do. But, it will likely not do more than 800 mA. For the MIts, ML501P73 that should be fine as they have been driven over 1000 mA without problems.

Yeah. I'm irresponsible like that.

 

[reloader45]

Hello,

what is wrong with a 1Ohm dummy load resistor?
Have a look at the DTR thread: https://laserpointerforums.com/threads/dummy-load-batteries-for-m140.87938/

I use 0,1 Ohm and 1 ohm resistors, it depends on the maximum current.


best regards


Edgar