How to calculate PWM dimming current?

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danesh

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hi guys,
Hw do i calculate the dimming current, if im using pwm to dim the led circuit. asuming i connect the base of transistor to pwm source and drive the led which connected to collector and emitter is grounded on npn transistor?

thanks
 

Re: PWM dimming

First, calculate current without PWM ..
Normal stuff, [Vcc - Vled] / R - for the time being, forget about voltage drop across the BJT ..



Then, set the duty cycle equal to 50% ..
The average LED current will be 0.5 of the calculated value ..
Change the duty cycle in the range from 0 to 100% and the LED current will change accordingly ..

Regards,
IanP
 

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