At 03:05 PM 3/8/2009, solarwind wrote:
>Let's say  I have a voltage source at 10 V lighting up an LED. At this
>voltage, the LED has a brightness factor of 100.
>
>Now let's say that I use PWM at 50% duty cycle at 10 V lighting the
>same LED. Let's say that humans will now perceive the LED to have a
>brightness factor of 50.
>
>1. If I put a very sensitive light intensity sensor and measure the
>peak intensity, will it be 100 or only 50 while using the PWM signal?

Only if the sensor is slow enough to average out the variations.

>2. People say that PWM "averages" the voltages out depending on the
>duty cycle. But if I have a semiconductor rated at a maximum of 6 V
>and I use a 10 V source with PWM to average it out to 5 V, will the
>semiconductor blow? How does the voltage "averaging" work exactly?

In this case the output of the PWM needs to be filtered to produce DC 
at the average value. Otherwise the 10V peaks will destroy the 6V 
semiconductor. PWM generates a rectangular waveform that has an on to 
off ratio which varies, the peak value remains the same.

JD


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