[quote]…First you must be sure of the power supply on the PIC controller.
You can measure this between pin 1 & 14. (must be around 5V).[/quote] Yes, the voltage between pin 1 & 14 is 5V.
Now I have found out that the real problem is the too small dynamic range, which results from the control voltage of 0-4,7V at Pin 9 (PIC).
To switch the lamp to 0%, the voltage at Pin 9 must be less than 2,46V.
To turn it on 98%, the voltage at Pin 9 must be min. 4,32V.
This results in a required minimum range at Pin 9 of 2,46-4,32V (difference: 1,86V).
With a control voltage of 0-4,7V this area is not completely covered.
The range that results from this control voltage is, depending on the potentiometer settings, 2,89-4,32V or 2,46-3,91V (difference: only 1,43V !!!)
Therefore the brightness can not be controlled over the full range!
Now the question is, how can I achieve the minimum range at pin 9 with the control voltage of 0-4,7V?
I think the combination of the resistors R18 and R19 must be another. But I am not sure.
Or maybe other values for R11 and R12??