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Thread: 9mm 445 diode peaks at ~1.4W and then drops as current increased

  1. #1
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    Default 9mm 445 diode peaks at ~1.4W and then drops as current increased

    I have a dual module with a 9mm 445 and a 462 diode, and I'm just tuning the power levels.

    The 445 diode gets to about 1.4W and then once I turn the drive current further, it drops in output at about the same rate as when i turn the current down.

    I know these things have some protection built in, does this sound like its protecting itself, or could it be a bad diode?
    The 462 next to it (speculation just a binned 445 diode) is easily making 1.5W and goes higher as I increase current.

    I have an identical module in another projector so I'll pop that open in a bit and see what that does too for comparison.
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  2. #2
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    Hello Norty,

    Maybe your problem comes from a poor thermal conduction between the diode and the mount ? The amount of heat which must be dissipated over 1.4W decreases prematurely the output power. This phenomenon is usually visible when 9mm 445nm diodes are pushed around 3 watts and could be shifted at 1.4 watts in your case.

    Did you try to swap the driver channels ? This is the best way to see if it's the driver who is limiting the current, or if it is a defect diode.

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  3. #3
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    I agree that you have to do a little investigation. You need to confirm that the driver is actually increasing the current as you increase the modulation voltage. This was a problem I saw with a couple of the Badpip drivers. Exchanging the 462 and the 445 driver circuits might be useful, but it wont actually give you any numbers, such as current, to compare. I don't suspect your meter because you are measuring "normal" behavior from the 462 and that's less than 20nm away. I don't think it is a thermal runaway problem unless the diode is held so loosely in its mount that you are unlikely to see a well aligned/focused beam. But, you should probably check the retention screws on this off chance. I don't suspect the lens. If the module is driving the 445 so hard (the current will show this) that the output is beginning to round over and less than 1/2 is getting out then the beam should look bad and the housing should be generating a lot of diffuse glow.

    1.4W from a 9mm 445 is way to low to be acceptable. If the drive current is rising appropriately then it probably is a bad diode and that's pretty easy to fix.

  4. #4
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    You need to confirm that the driver is actually increasing the current as you increase the modulation voltage.
    No, this is with 5V applied and as I increase the current on the driver itself and measure the output. It's one of Dave's drivers.

    The only other thing it might be is the waveplate on the 445 might not be at the optimum angle, so it being driven really hard, but not all the light is getting through the cube due to poor polarisation.

    Can i measure the current across the driver outputs with the diode connected safely?
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  5. #5
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    Can i measure the current across the driver outputs with the diode connected safely?
    No. You could do a very rough measurement/calculation by metering the driver INPUT current and voltage and measure the driver output voltage all while running the diode. These drivers are probably somewhere in the 80-100% efficient conversion range and probably closer to 100%. Now calculate the input watts and subtract the differential of the input voltage from the drive voltage, multiply by the driver input current to give a "dumped" watts. Input watts minus dumped watts gives a diode watts. Diode watts divided by diode drive voltage gives diode drive amps. Now re-read this several times. This should be accurate enough to differentiate a bad from a good diode.

    The problem still derives from your uncertainty about the current drive to the diode. If you KNOW that the diode is getting 2-3A then it is either defective or the light is being absorbed. I don't think you will miss this absorption. 1.5 watts of 445 failing to get through a lens or being dumped within a PBS due to a poor wave plate will make a lot of spurious glow as well as a lot of heat.

  6. #6
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    No. You could do a very rough measurement/calculation by metering the driver INPUT current and voltage and measure the driver output voltage all while running the diode. These drivers are probably somewhere in the 80-100% efficient conversion range and probably closer to 100%. Now calculate the input watts and subtract the differential of the input voltage from the drive voltage, multiply by the driver input current to give a "dumped" watts. Input watts minus dumped watts gives a diode watts. Diode watts divided by diode drive voltage gives diode drive amps. Now re-read this several times.
    Hmmmm...... don't fancy my chances much!

    Could I just put my current meter in series with the +ve supply line from the SMPS to the driver? Thats easy enough to do with some mini croc leads
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  7. #7
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    Yes, you can. If you are able to disconnect the diode and insert the meter then this will work. I made the assumption (maybe dumb) that you couldn't disconnect the diode.

  8. #8
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    Right, well I contacted Dave and he explained there's a current sense resistor next to the FETs, which reads 100mV per amp, so I just took a measurement there and got 200mV = 2A of drive current.

    So, compared to Jordan's test pics, I'm getting the output that he got with only 1A.

    I have checked the 'sister' module to this one and the 445 on that is now running at 2W, so no issues with that one.

    Planters, if the waveplate is incorrectly aligned, will i see a lot of spill in the cube? Would I be right in thinking I'll be getting the rest spill out the other side, which should be measurable?

    P.S. I did also confirm that the current was actually going up at the point I started to see the power going down again. At 2.3A I was down to 1.2W
    Last edited by norty303; 07-27-2014 at 03:26.
    Frikkin Lasers
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    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

  9. #9
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    Hmm, I didnt think the diodes were that efficient. From memory, I was seeing ~1.5w at 1.5A, but they were knifed. It sort of sounds like a thermal issue, or perhaps is there a possibility the diode is loosing its polarisation as the current is increased?


    Quote Originally Posted by norty303 View Post
    Right, well I contacted Dave and he explained there's a current sense resistor next to the FETs, which reads 100mV per amp, so I just took a measurement there and got 200mV = 2A of drive current.

    So, compared to Jordan's test pics, I'm getting the output that he got with only 1A.

    I have checked the 'sister' module to this one and the 445 on that is now running at 2W, so no issues with that one.

    Planters, if the waveplate is incorrectly aligned, will i see a lot of spill in the cube? Would I be right in thinking I'll be getting the rest spill out the other side, which should be measurable?

    P.S. I did also confirm that the current was actually going up at the point I started to see the power going down again. At 2.3A I was down to 1.2W
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  10. #10
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    Hmm, I didnt think the diodes were that efficient. From memory, I was seeing ~1.5w at 1.5A, but they were knifed.
    I'm just going by the pics here. Note these are the 9mm diodes, not the M140.

    https://sites.google.com/site/dtrlpf...odes/9mm-445nm

    At 2A, Jordan's test diode was doing 2.7W!

    Given that its got a 462 right next to it doing ok, and I've got another identical module with both diodes running as expected, I'm suspecting either waveplate or bad diode. These are in really big lumps of ally so I wouldn't have thought it was thermal. Part of the design brief for these was that they needed to be really well passively cooled.
    Frikkin Lasers
    http://www.frikkinlasers.co.uk

    You are using Bonetti's defense against me, ah?

    I thought it fitting, considering the rocky terrain.

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