Friends,
I am designing an LED driver, along with other associated circuitry - like charge controller and deep discharge protection. In a sense, this gives you an idea of my application.
As mentioned above I use a LM317T in the standard CC (Constant Current) mode. I use it to drive two parallel channels, each comprising of 1W HB LED. I use the variation given in the application note AND8109/D of ON Semiconductors. The app note is attached.
My component values are R-sense = 4.3R and the base drive is 1K Ohms. The transistors I have tried are 2N 5551 and 2N 2222.
I notice that the LED drive currents in both arm vary, rather significantly. For eg., the battery current drawn is 420 mA while the two arm draw currents of 140 mA and 180 mA each. I have tried changing the LEDs and the transistors, the other component values are quite closely matched or almost equal.
Can you please help explain the discrepancy or a way of working around this issue? This is causing a difference in illumination levels of the two LEDs, hence the question.
Any help is greatly appreciated.
Regards
AM
I am designing an LED driver, along with other associated circuitry - like charge controller and deep discharge protection. In a sense, this gives you an idea of my application.
As mentioned above I use a LM317T in the standard CC (Constant Current) mode. I use it to drive two parallel channels, each comprising of 1W HB LED. I use the variation given in the application note AND8109/D of ON Semiconductors. The app note is attached.
My component values are R-sense = 4.3R and the base drive is 1K Ohms. The transistors I have tried are 2N 5551 and 2N 2222.
I notice that the LED drive currents in both arm vary, rather significantly. For eg., the battery current drawn is 420 mA while the two arm draw currents of 140 mA and 180 mA each. I have tried changing the LEDs and the transistors, the other component values are quite closely matched or almost equal.
Can you please help explain the discrepancy or a way of working around this issue? This is causing a difference in illumination levels of the two LEDs, hence the question.
Any help is greatly appreciated.
Regards
AM
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