PWM frequency change?

[embedded1988]

Hi Everyone,

I tried to generate 2 PWM signals 180 degree out of phase for my dc-dc converter with blanking pulse introduced, the problem I see at the moment is that when I introduce blanking time(Dead Time) the frequency of the PWM signal changes(otherwise not when dead time is 0)  when the Pulae length(duty cycle ticks) are close to 90% and above of the Pulse period(PWM period). I could not figure out how to overcome this problem. The PNG of FPGA VI is attached.

Any help in this regard is really appreciated. OR is there any other way to generate same signals?

Regards,

azy

[GerdW]

Hi azy,

yes, adding another deadtime will change your PWM signal.

Maybe you should rethink your math behind all those time values?

Can you provide formulas for all time parameters?

[embedded1988]

Hi GerdW,

Thanks for quick reply, the Loop timer 14 and Wait 12 is 16bits(Ticks), while the both dead times are 8bits(Ticks) and i use FPGA base 40MHz clock. when i do not add dead time the pwm signal freq is accurate but with addition it is changed.

I wanted PWM signal independent of each Freq,duty cycle,blanking time.

i attach a PNG's of signal i wanted to generate to have better understanding.

best regards,

ayz

[GerdW]

Hi azy,

you need to provide correct formulas for each timing parameter - and then you need to apply those formulas to your settings!

When you add deadtime you surely increase the overall waiting time - and now you wonder why the frequency changes…

Do your homework and get the math done!