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DIY diode test load circuit

rkcstr

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So, most of you probably have soldered together some standard diodes (like the 1N400x series) with a 1 ohm resistor to measure current and make sure your driver is operating properly.  Well, me too.  Except, I do it A LOT with making my drivers, so I decided to make it easy on myself and make a board I can quickly solder to the driver and test and remove again, but also be able to test at blu-ray voltages and red voltages, so here's what I made:



You can switch between Red and Violet loads by bridging the correct setting pads (shown as 3.3V and 4.7V on the above board).  You hook up the positive input of the board to the positive output of the driver and same for the negative, power up the driver and measure the voltage across the resistor; 1mV = 1mA.

The link below is the PCB layout, slightly modified from the one above and ready to print (should be 2.286 x 0.63 inches).  If you're ambitious enough to etch your own boards, feel free to use it.  You only need to use the side with the components, the other side really just has instructions and name, so you can use a single-sided board.

Right-click and Save As, the file is about 500Kb:
http://i13.photobucket.com/albums/a272/skimaniac3/lasers/testload-1.jpg

Parts list:
6x Surface mount diodes (standard 1A rectifier, DO-214AC or SMA sized):
http://www.mouser.com/Search/ProductDetail.aspx?qs=ZpPixqFcBtwZcQeNkRuA9A==

1x 1ohm 1W resistor (metal oxide, can be multi-watt as well, the board's big enough to fit up to 5W, I think):
http://www.mouser.com/Search/Produc...R0Jvirtualkey66000000virtualkey660-MOSX1C1R0J

The total parts cost for one is all of $.90, but you'll be paying about $7 in shipping costs :(

If you want, I can send you the ExpressPCB file and you can modify it to fit standard diodes, then you can just buy the 1N400x diodes and the 1ohm 10W resistor from Radioshack, but the board will have to be bigger to fit the large 10W resistor.

Also, the settings are about 2.8V and 4.2V worth of diodes, but the resistor makes it around 2.8-3.6V for Red or 4.2-5.0V for Violet, depending on the current output.
 



drlava

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Nicely executed! these ARE a big help in testing, I have used diode stacks before too.
PM!
 

Benm

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It's a nice test circuit. Another idea is to mount a LED with a series resistor as well to get some optical feedback for when you're tweaking drivers. I usually just use a high power led (luxeon-3 or similar) as a dummy, but those are overkill in terms of light output.
 

rkcstr

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So I'll be selling this item shortly along with my new adjustable driver. But, I just had a few considerations that I'm deciding on before I start production, and I was hoping to get some opinion on preferences for the output voltage settings.

So, the diode I'm using is a S1B-E3/51T, basic 1A diode with ~0.6-1V Vf. The problem becomes that as the current increases, so does Vf as well as the voltage across the resistor (adding to the total voltage for the test load).

The different configurations I'm considering are:

1. For red ranges (~150-430mA), having 3 series diodes with 1ohm resistor, giving about 2.5V to 2.8V over the range). Blue range (~30mA to 150mA) would be 6 diodes to give an output somewhere around 4.2V to 5V over the range.

2. Red range having 4 series diodes and 1ohm resistor gives about 3V to 3.5V over the range. Blue remains the same (6 diodes).

For the red ranges, there's no in between the above voltage differences with increasing current output, so I didn't know whether to overshoot or undershoot. Just wondering what people would prefer, though it's probably not a huge deal since this is mainly to test that the driver's putting out the right current anyway.
 

sooraj

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Hi,

I am doing a project on free space laser communication so i need to operate my 650nm laser pointer in pulsed mode... can anyone suggest me a driver so that laser can be operated in safe range...

Thank you.
 




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