Hello. I am designing/building a pwm using a 555 then taking the triangle wave ( 20KHz) from the cap in the RC filter to the inverting pin of an open loop op amp and varying the duty cycle by varying resistance from the non inverting pin to + and - of the dual rail supply. Then output to RC filter to give a dc out.
This is all well and good but.... I just don't get how Frequency remains at 20KHz if the on/off time is changing. How does the RC filter maintain roll of at a given frequency. If this is to much typing or theory to explain, might someone have a link that could enlighten me? I have the math, I can now put the circuits together but what good is running numbers and knowing targets if I don't really understand how it really works? Surely pretty soon I will come unstuck. Thanks for taking time to read my post.
This is all well and good but.... I just don't get how Frequency remains at 20KHz if the on/off time is changing. How does the RC filter maintain roll of at a given frequency. If this is to much typing or theory to explain, might someone have a link that could enlighten me? I have the math, I can now put the circuits together but what good is running numbers and knowing targets if I don't really understand how it really works? Surely pretty soon I will come unstuck. Thanks for taking time to read my post.