Voltage Control For Buck Converter

[Jeff Demmer]

Wondering if anyone can help me out with the control of a Buck converter.
Right now I have my ref voltage and output voltage being fed into a summing
amp that will give me the error between the two, this error is being fed
into a PI control, the PI control is being fed into another summer and then
this summer is being fed into a comparator and am comparing this to a saw
tooth wave form that will be the switching frequency,

Does anyone have a schematic of this control circuit so that I can compare
what I am doing to something that has been tested and works,

Thanks
Jeff Demmer