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Old 01-25-2012, 03:35 AM #1
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Post True Adjustable Test Load...

Hey guys...

I was contemplating an idea.

Would you be interested in buying a test load, with a 5% or lower tolerance 1 ohm resistor, and a truly variable voltage drop so you can actually match your diodes? (aka instead of just going with .7 volt increments, you can actually change it in real time to match your diodes drop!)

It'll have a voltmeter on it and a switch, so you can flip between the voltage drop and the voltage across the resistor.

The voltmeter however, would need a separate supply; probably a 9 volt battery.

Would it change your minds if it was on protoboard as opposed to PCB? I would hand solder all of them too.

It would cost around $22 for protoboard ones, and around $28 for the PCB ones...

Thoughts?


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Old 01-25-2012, 03:39 AM #2
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Default Re: True Adjustable Test Load...

Quote:
Originally Posted by Le Quack View Post
Hey guys...

I was contemplating an idea.

Would you be interested in buying a test load, with a 5% or lower tolerance 1 ohm resistor, and a truly variable voltage drop so you can actually match your diodes? (aka instead of just going with .7 volt increments, you can actually change it in real time to match your diodes drop!)

It'll have a voltmeter on it and a switch, so you can flip between the voltage drop and the voltage across the resistor.

The voltmeter however, would need a separate supply; probably a 9 volt battery.

Would it change your minds if it was on protoboard as opposed to PCB? I would hand solder all of them too.

It would cost around $22 for protoboard ones, and around $28 for the PCB ones...

Thoughts?
Hmmm it's a really cool idea. Maybe you could come up with a prototype to show us? A picture is worth a thousand words! I really like the idea the voltage draw changing to truly mimic a diode!

You have officially piqued my interest!
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Old 01-25-2012, 03:52 AM #3
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Default Re: True Adjustable Test Load...

Great Idea, Thats something i would really like.. I find the good old test loads to be outdated and inaccurate sometimes..
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Old 01-25-2012, 04:54 AM #4
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Default Re: True Adjustable Test Load...

Okay, I'm working out some things here...

Trying to find a voltmeter that would work for this but I can't!

The voltage difference between the v-drop and the measurement across the resistor is too great. It wouldn't be able to accurately measure both.

There's gotta be something else I can do.... hrm.



EDIT

Maybe instead of getting derpy with the resistor, why not just measure it with an amp meter? It would help simplify the construction too, removing one of the more expensive parts.


Lemme ask this, which would you rather have on the test load? An amp meter, to measure the current flow, or a volt meter, to measure the V-drop across the transistor?

If an amp meter is on the test load, I could include some sort of loops (test points) or something so you can measure the v-drop with your DMM. Then the amp meter does the rest!

Last edited by Hiemal; 01-25-2012 at 05:08 AM.
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Old 01-25-2012, 12:51 PM #5
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Default Re: True Adjustable Test Load...

Quote:
Originally Posted by Le Quack View Post
Hey guys...

I was contemplating an idea.
The voltmeter however, would need a separate supply; probably a 9 volt battery.
Would it change your minds if it was on protoboard as opposed to PCB? I would hand solder all of them too.
It would cost around $22 for protoboard ones, and around $28 for the PCB ones...

Thoughts?
Quote:
Originally Posted by Le Quack View Post
Okay, I'm working out some things here...

Trying to find a voltmeter that would work for this but I can't!

The voltage difference between the v-drop and the measurement across the resistor is too great. It wouldn't be able to accurately measure both.

There's gotta be something else I can do.... hrm.
I find it strange that you can quote a price and don't even
have the Voltmeter you speak of...

You seem to be putting the horse before the cart.

I would suggest you build a working prototype to know the
actual parts and labor costs before quoting production item
pricing...



Jerry
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Old 01-25-2012, 01:30 PM #6
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Default Re: True Adjustable Test Load...

The problem is that you're not really setting voltage for your load, but rather the voltage drop for your load. A voltage drop is a function of Ohm's law, and implies that in order to produce a voltage- and current-accurate "smart" load, you need to have a load that exactly mimics the current-voltage curves of your diode, which is no small feat. If you don't match those characteristics, the voltage drop you see may induce current-passing characteristics that could be harmful if applied to your laser diode.

We allow dummy loads to be less accurate in voltage, compared to current, because laser diodes are more sensitive to current changes than voltage changes. Also, most of our drivers are capable of dropping excess voltage as needed. The voltage drop you build into your dummy load is just to get the dummy load within the "range" of the voltage regulation you need so that the excess voltage drop doesn't have much effect. As a rule: don't sacrifice accuracy for your critical parameters for secondary parameters.

Instead of trying to match voltage, why don't you work on the accuracy of other parts of your dummy load? For example, I noticed you mentioned using a 5% tolerance resistor. I wouldn't use anything less than 1%; high-tolerance resistors are not that expensive. That way your current reading isn't +/- 5%, which can be quite a bit at higher power levels. With a high-tolerance resistor like this you've increased your measurement accuracy by an order of magnitude.

You can also use different resistors that produce different voltage drops at different current ratings. In that manner you can help match the voltage drop you need for an expected current. It'll take more calculations, of course.

Last edited by Bionic-Badger; 01-25-2012 at 01:34 PM.
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