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Topic: 555 timer beginner circuit help (Read 9116 times) previous topic - next topic

afremont


http://electronics.stackexchange.com/questions/22291/why-exactly-cant-a-single-resistor-be-used-for-many-parallel-leds



This is a little different situation isn't it?  The LEDs might be in parallel, but they are never on at the same time since they are reversed, so this wouldn't apply, right?
Experience, it's what you get when you were expecting something else.

nickgammon


When I connect up the 2nd led in the backwards direction  ...


I assumed he meant he flipped one of the two LEDs so now they are both in parallel.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

EVP

So with a 5v supply maybe 12 at a push what is the best way to power 256 ir led's? all with the same signal a pwm signal. After much head scratching and taking apart a 60 led torch to find all led in parallel and one resistor, i decided on a constant currant led driver and to put them in groups of around 700ma(what the driver is rated at). Now the led are rated at 20ma maybe more for pulsing, i have them running at around 10ma. My thought was an i think i'm wrong now was that at that currant there would be no heating and no thermal runaway.

How else could i  power them?

nickgammon


Interesting....
When I connect up the 2nd led in the backwards direction with the resistor going to GND. the whole circuit turns off. I thought that those two resistors might just be shorting out the whole circuit.

Is that whats going on?


If you moved the top 220R resistor to go to Gnd, then there is no power reaching pins 2 and 6.
Please post technical questions on the forum, not by personal message. Thanks!

More info: http://www.gammon.com.au/electronics

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