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Go Back   Laser Pointer Forums - Discuss Laser Pointers > Lasers > Drivers, Test-load, Power Supply, & Batteries



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Old 05-12-2012, 04:55 PM #1
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Default Home brew test load

Hi all,

I thought I'd share my effort at a test load, well two actually.

The biggie has a 1% 20W SMT sense resistor and 8A diodes.
You can select the number of diodes by moving the 2mm "banana" jump lead, the sockets are just a 5mm brass rod with a 2mm hole drilled in the centre and soldered to the board.

The small version is for blue diodes only (no jumpers) - the resistor is 1% 5W and 1.5 A diodes, but they get hot at 0.5A so I might need to heat sink them somehow.

I've mades some simple linear LD1085 driver boards that just need soldering up...those 10uf 10v caps are tiny !!!


I was thinking, what is the effect of the forward voltage spec' of the diodes, how much difference does that make when setting the current of the driver - I guess not much???? (experts please jump in )

ATB
MM


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Old 05-12-2012, 06:22 PM #2
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Default Re: Home brew test load

That's great, i bet those would handle the 1.8~2.5A we commonly use all day long..

You should consider the 3A ones like 1n539x through hole.. They have a 1V voltage drop afaik..
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Old 05-12-2012, 08:27 PM #3
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Default Re: Home brew test load

Quote:
Originally Posted by sinner View Post
That's great, i bet those would handle the 1.8~2.5A we commonly use all day long..
You should consider the 3A ones like 1n539x through hole.. They have a 1V voltage drop afaik..
Hi Siner,

Hopefully I've used a high current diode with a Vf as close as I could to the standard 1n4001.
At 1A the 1n4001 Vf is about 0.9v and the bigger diode is about the same maybe 0.85v from the graphs.

I'm trying to understand the effect of the slightly lower Vf of the bigger diode at say 2A on the set current using the test load to set the laser driver and when its exchanged for the laser diode...

As far as I can tell, the current will be as the desired set point (it should as its a current driver) but just needs a higher supply voltage to push the current to the set value.

I'm just wanting to make sure that when I set the driver using either of the test loads, the laser diode will see the correct current.

Here's the forward voltage drop graphs.

ATB
MM

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