Just as a note of completeness. When using the circuit of the previous post the driving frequency for the PWM intensity control was 55.7922 Hz. Note that the IMP803 chip is normally turned on and off via the RSW pin. When ON the chip runs the voltage booster circuit at the frequency determined by the resistance from +5V to the RSW pin. (750K ohms in the example). The usage of the PWM is to actually turn the driver chip on and off at the 55.7 Hz rate.

We found that the persistance of the EL strip made the 55.7 Hz frequency usable over the intensity range we wanted to achieve. Do not however that different EL strips may have a different characteristic and as such it may be possible that the 55.7 Hz rate may be too slow and lead to flickering of the EL strip. Also note that the PWM frequency must be chosen carefully becasuse it should be a frequency that is slower than the switching frequency of the voltage booster or the EL output switching rate (Which is about 350 Hz with the 2M ohm tied to the REL pin.

Michael Karas

PS.....Note that the 55.7 Hz was no magic number. That happened to be the frequency that I got when setting up the PWM timer channel for full count span of 65535.
MJK