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unexpected behaviour - 405nm driver - solved

dbrown2k

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So i've been building a driver based on the iC-Haus, iC-HKB, driver chip [LINK].

I've run a test using a laser diode test load which gave me expected curves of current vs control voltage as below;



This shows the current output versus control voltage for a range of control resistances (0ohm to 22Ohm)

Then when i ran the same tests with the actual diode (Sony SDL3232VF 50mW 405nm) I got the following output current (photo diode voltage also logged);



I expected the LED zone then the ramp up at threshold, but did not expect the platau with little change in current and monitor voltage. Is this something that others have come accross?

The biggest difference is that I needed to use the 0 ohm setting, which when running the dumb test load and the data sheet for the driver should be passing maximum 150mA at a control voltage of 2.5V. Using the actual diode i was barely getting 50mA at 4.0V control voltage. All the tests were run with a 5.3V regulated supply voltage
 

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diachi

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Re: unexpected behaviour - 405nm driver

What's the voltage at the output...? Vf at Iop (55mA) is 5.3VDC according to the datasheet for the diode. If you're only supplying the regulator with 5.3VDC then you won't be able to reach the Vf specified in the datasheet of the diode, and as such won't even be able to reach the Iop specified. You need to account for the dropout voltage of the regulator.
 
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dbrown2k

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Re: unexpected behaviour - 405nm driver

The supply voltage at the diode is 5.2V and the drain voltage is 0.66V. For a control voltage of 1.40V with current through the diode of ~31mA.

So if the difference over the diode should be 5.3V then I would need to add an additional 0.66V to the supply voltage?
 

diachi

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Re: unexpected behaviour - 405nm driver

The supply voltage at the diode is 5.2V and the drain voltage is 0.66V. For a control voltage of 1.40V with current through the diode of ~31mA.

So if the difference over the diode should be 5.3V then I would need to add an additional 0.66V to the supply voltage?
That's 5.2V referenced to ground right? What's the voltage drop across the LD? If I'm understanding the IC and your numbers correctly that'd result in a voltage across the LD of 4.54V (5.2V - 0.66V drop across the regulator). Assuming you're getting that 0.66V number by measuring the voltage across LDK and ground.

In which case you need to increase the supply voltage to account for the drop across the IC.

Is there a specific reason you've used this IC rather than a more simple linear regulator such as an LM317?

Can you post pictures of your complete schematic and circuit?
 

dbrown2k

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Re: unexpected behaviour - 405nm driver

During operation;
from LD anode to ground was 5.26V
from common / cathode to ground was 0.66V
across the diode is 4.60V
current through is ~32mA (measured off 0.2ohm current sense resitor)

This is for a project to design a UV light exposer where I will have several 10's of diodes fiber coupled, one for each pixel and control the brightness (limited) and the pulse duration (likely sub 1ms to 13ms). So this chip is low cost with low support component count, but specifically designed for pulse operation and has simple voltage control over the current sink.

i've attached the schematic of the testing board
 

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dbrown2k

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Re: unexpected behaviour - 405nm driver

Yes it looks like you are correct, the system is starved (under volts) if i bring the voltage up to 5V across the diode then output current is as expected ~50mA

I will run some more experiments.

Thank you for your input, another set of eyes is always good.

If you want more information about the project, some of the stuff is on hackaday - https://hackaday.io/projects/hacker/116541
 
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paul1598419

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From where I am, I get too late a start to be involved in any of these. I see now why you used that IC. A Vcc of +6 VDC should give you the headroom you need to get to 50 mW.
 

CynicalBrad

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I took a look at your projects on hack-a-day and have to say that I am impressed. Seems that uv photo resist printer could be perfect for diy pcb's or even as a way to cure a photo resist for electroplating patterns on metal or even etching them. Nice to see a project where it actually makes sense to use lasers for a change. Will rep when on my pc.
 
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diachi

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I took a look at your projects on hack-a-day and have to say that I am impressed. Seems that uv photo resist printer could be perfect for diy pcb's or even as a way to cure a photo resist for electroplating patterns on metal or even etching them. Nice to see a project where it actually makes sense to use lasers for a change. Will rep when on my pc.

Take a look at this if you're interested in photo resist exposers for PCBs.

Laser PCBs with LDGraphy | Hackaday

Sounds like a similar project?
 

dbrown2k

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I took a look at your projects on hack-a-day and have to say that I am impressed. Seems that uv photo resist printer could be perfect for diy pcb's or even as a way to cure a photo resist for electroplating patterns on metal or even etching them. Nice to see a project where it actually makes sense to use lasers for a change. Will rep when on my pc.
It would certainly work for them but as pointed out there are other projects that would be better suited for binary nature of exposed/unexposed for etching / resist applications.

Where this differs is in having control over essentially the numbers of photons that hit the pixel area. Exactly the same as if you take a photo, but unlike other methods there is the ability to have zero in one pixel, even if you need a long exposure in another, so any pixel can have an arbitary exposure length.
 
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