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constant current circuit

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yoosefheidari

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Hi

i need a circuit to drive 9 power led(1watt)
my source is a 13.5volt battey.
led's are 3 string in parallel.it means there is 3 led in each string so i have 3 string and strings are in parallel.

so each string need 330ma current and about 9.6volt.
so i need a circuit with 990ma constant current output and about 9.6volt to drive 9 led's.
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i need a simple switching or linear circuit with with STABLE output under load with battery.
please help me
 

could you please draw schematic for your requirement that case i would be able to help you. with voltage controlled current source or constant current source. or other way is : to do so just calculate simple resistor value to allow 330mA for each string. you need a resistor of around 29 ohms.
 
LEDs in parallel must be matched or the string with the lowest forward voltage uses most of the current and blows up, then the string with the next lowest forward voltage gets most of the current and blows up. Then you have only one string remaining using all the current for three strings so it blows up.

You could be like a Chinese LED flashlight factory and gather a few thousand LEDs, measure them all then sort them into matched groups. Or you can add resistors in series with each string to help match the strings.
 
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