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Old 06-25-2010, 10:07 PM #1
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Default Do I need Resistors across each diode?

I'm going to be running two A-130s in series, off of an LM317 driver.

The current through the diodes will be monitored, and the Vf across each diode will be monitored as well.

I hear that it is good to put a high value resistor across each diode, to help compensate for PIV something or other.

And to do that, would kind of resistance are we talking about?

Will the resistors in place, affect the readings on the ammeter, and voltmeter?

Since I'm not too sure what the exact voltage drops across each diode will be a 1A, I'm not sure how large of a resistor I might look for. Would a 5W be alright?

Thanks guys!


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Old 06-26-2010, 01:18 AM #2
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Default Re: Do I need Resistors across each diode?

should affect voltmeters etc, V=IR
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Just starting off my collection. Currently have:
150mW 405nm from O-like *outputting 156mW quite stable*
Jayrob SS 18650 kit, A140 diode at 1A putting out 900mW
100mW 532nm from dealextreme *broke*
500mW 532nm from O-like *lense dmg? down to 150mW with scatter*

200mW waterproof 650nm from O-like *outputting 210mW quite stable*
Plan to have soon:
1W 455nm from wicked lasers (ofc)

01010000011000010111001101110100011000010010000001 10111000100000011100110110000101110101011000110110 01010011101000100000011010010111010001110011001000 00011000010110110101100010011010010110011101110101 01101111011101010111001100100001
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Old 06-26-2010, 04:45 AM #3
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Default Re: Do I need Resistors across each diode?

So... would a set of 100K Ohm resistors work alright? They might move the decimal point on the meters down a bit... how might I adjust that?
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Old 06-26-2010, 02:51 PM #4
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Default Re: Do I need Resistors across each diode?

cant say about any technical stuff, im more into the fundamental physics side, and even that not fully qualified yet
__________________
Just starting off my collection. Currently have:
150mW 405nm from O-like *outputting 156mW quite stable*
Jayrob SS 18650 kit, A140 diode at 1A putting out 900mW
100mW 532nm from dealextreme *broke*
500mW 532nm from O-like *lense dmg? down to 150mW with scatter*

200mW waterproof 650nm from O-like *outputting 210mW quite stable*
Plan to have soon:
1W 455nm from wicked lasers (ofc)

01010000011000010111001101110100011000010010000001 10111000100000011100110110000101110101011000110110 01010011101000100000011010010111010001110011001000 00011000010110110101100010011010010110011101110101 01101111011101010111001100100001
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Old 06-26-2010, 05:07 PM #5
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Default Re: Do I need Resistors across each diode?

I haven't heard of putting a resistor for compensation in such a circuit. Are you sure that even does anything? The only place I've heard of adding resistors is for temperature compensation, but the LM317 already has temperature compensation circuitry.

If you're adding resistors so you can more easily measure the voltages, I'd use as high a resistor value as you can so you don't sap away current from the diodes.

Last edited by Bionic-Badger; 06-26-2010 at 05:10 PM.
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Old 06-26-2010, 06:49 PM #6
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Default Re: Do I need Resistors across each diode?

if you are putting a very high value resistor in parallel with the diodes it should be fine. because the alternate (parallel) path will be of high resistance, very little current will go down it. voltmeters themselves for the most part are high resistance, if you were going to have the voltmeter in parallel with the diodes, I dont think putting a resistor in line with the voltmeter will cause much difference, although it might mess up your voltage values, best to leave it alone concerning that. a resistor in series with the diodes will reduce current through them and consume alot of voltage, making them very dim.
__________________
Just starting off my collection. Currently have:
150mW 405nm from O-like *outputting 156mW quite stable*
Jayrob SS 18650 kit, A140 diode at 1A putting out 900mW
100mW 532nm from dealextreme *broke*
500mW 532nm from O-like *lense dmg? down to 150mW with scatter*

200mW waterproof 650nm from O-like *outputting 210mW quite stable*
Plan to have soon:
1W 455nm from wicked lasers (ofc)

01010000011000010111001101110100011000010010000001 10111000100000011100110110000101110101011000110110 01010011101000100000011010010111010001110011001000 00011000010110110101100010011010010110011101110101 01101111011101010111001100100001
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