Hi,
In a PWM LED controller system, I need to calculate the power dissipation in the LED's. It should be straight forward to calculate power as the product of current and voltage, but I have become unsure, which method is the right one
Currently Duty cycle (D) is 66%.
1. With a digital multimeter, I made a DC current measurement. Voltage is also measured in DC with the meter. Both values should be average values. Power is calculated as:
Pavg = Uavg * Iavg
2. In an alternative setup, I measured the peak voltage with an oscilloscope. Peak current is measured as the voltage drop over a small series resistor with the oscilloscope.
I calculate Peak power by :
Ppeak = Upeak * Ipeak
then, I multiply by dutycycle:
Pavg = Ppeak * D
In method 2, I only get 66% of method 1.
I assume my assumptions; Uavg = Upeak * D, Iavg = Ipeak*D and Pavg = Ppeak * D are wrong
Which approach is the right?
I'd appreciate some advise
/GLEMU
In a PWM LED controller system, I need to calculate the power dissipation in the LED's. It should be straight forward to calculate power as the product of current and voltage, but I have become unsure, which method is the right one
Currently Duty cycle (D) is 66%.
1. With a digital multimeter, I made a DC current measurement. Voltage is also measured in DC with the meter. Both values should be average values. Power is calculated as:
Pavg = Uavg * Iavg
2. In an alternative setup, I measured the peak voltage with an oscilloscope. Peak current is measured as the voltage drop over a small series resistor with the oscilloscope.
I calculate Peak power by :
Ppeak = Upeak * Ipeak
then, I multiply by dutycycle:
Pavg = Ppeak * D
In method 2, I only get 66% of method 1.
I assume my assumptions; Uavg = Upeak * D, Iavg = Ipeak*D and Pavg = Ppeak * D are wrong
Which approach is the right?
I'd appreciate some advise
/GLEMU