I know the 10nF at the top and the 47Kohm, center left, set the frequency (about 470 hz) but, what is the formula and suggestions for varying them. This is being used to speed control relatively high current, iron core 3 pole, 12volt brushed motors. (1/24 scale slot car motors) I want to experiment with frequencies around 1-20 khz. Im using a SUP 90P06 pfet for the output. I'll post the data sheet next time.