buck converter duty cycle control in hspice

[baltzois]

hi,
i have a buck converter and the switch is controlled by a pulse source. I have designed it in hspice . What i want to do is to control the pulse source with variable pulse width but hspice doesn;t give me that option. Can anybody tell me how to change pulse width in time ,and having the Vpp constant??
thank you

 

[FvM]

You have to design the behavioural model of a PWM controller, e.g. from a ramp generator and a comparator.

Or use the simulation model of any real PWM controller of your choice.

 

[baltzois]

well maybe i put it in a wrong way...i want to run one transient analysis where the duty cycle changes from 5 to 90% ...will the ramp generator help me??
thank you for your help!