3v leds x 20, leds paralel, 3v in, led calc says use 1 ohm each resistor, can I skip that since 3v led and 3v input v?
I am building a led array light bulb.
3v leds x 20, leds parallel, 3v in, led calc says use 1 ohm each resistor, can I skip that since 3v led and 3v input v?
Led calc also says 0 ohm / use the next standard resistor 1ohm..
does 1 ohm x 20 really needed for a 3.0- 3.2v white led with a 3v 2000ma source>
thanks in advance..
3v leds x 20, leds parallel, 3v in, led calc says use 1 ohm each resistor, can I skip that since 3v led and 3v input v?
Led calc also says 0 ohm / use the next standard resistor 1ohm..
does 1 ohm x 20 really needed for a 3.0- 3.2v white led with a 3v 2000ma source>
thanks in advance..
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You need SOMEthing to current limit. As you say, you're so close to "3Volts" it doesn't seem necessary, but as the temperature of the dies change, so does the current curve for the LED and it WILL start to draw more current tthan it can handle. You really would be better running them as multiple parallel chains with either sensible resistors, dropping ~three volts, or use a decent constant current driver.
Jul 28, 2010. 11:09 AMWillard2.0
says:
I would use the 1ohm resistors. Without them, any slight surge in the power supply goes directly to the LEDs, likely killing them. A resistor will suppress some small surges and keep the current to the LEDs limited to a safe level.
Jul 31, 2010. 7:37 PMalboz (author)
says:
Thanks for answering my question, I will use resistors.
Jul 28, 2010. 2:20 PMRe-design
says:
I don't think a 1 ohm resistor is going to suppress enough current to help.
Indeed.
If your power supply is 3V and they are 3V LED's then you do not need any resistor.
I don't see why anyone thinks a 1ohm resistor would suppress anything?
Dynamic resistance of the LED when operating at full intensity is something like 150ohms.
(3V/0.02A)
If the supply voltage would raise 1V, with no resistor, you'll get 4V over your LED, killing it instantly.
If the supply voltage raises 1V, with a 1ohm resistor, you'll get 3.97V over the LED and 26.49mV over the 1ohm resistor.
3.97V over the LED would still kill it.
Now it doesn't really look like a 1ohm resistor would 'protect' your LED right?
If your power supply is 3V and they are 3V LED's then you do not need any resistor.
I don't see why anyone thinks a 1ohm resistor would suppress anything?
Dynamic resistance of the LED when operating at full intensity is something like 150ohms.
(3V/0.02A)
If the supply voltage would raise 1V, with no resistor, you'll get 4V over your LED, killing it instantly.
If the supply voltage raises 1V, with a 1ohm resistor, you'll get 3.97V over the LED and 26.49mV over the 1ohm resistor.
3.97V over the LED would still kill it.
Now it doesn't really look like a 1ohm resistor would 'protect' your LED right?
If you're using a 3V supply, I'll guess you're on AAs?
Bump it up to 9V at least, run some in series.
It's easy to double-up 9V batteries to 18V - so you might run 5 in series with a resistor, 4 times.
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