(BUCK BOOST)variable duty cycle pulse generator ....help!!!

[pisaac001]

am designing a Buck boost converter on simulink ... as u know with a buckboost... the set output does not change even if the input changes....
aslo the duty cycle needs to be changed with input voltage in order to have the desired output (-vout/-vout-vin)=dutycycle
i have attachd the circuit..
basically i want a duty cycle that changes as the input voltage changes..
is there away to get variable duty cycle on simulink
if not how do i build one ..
pls look at the circuit help me plsssss lol am ready to listen to ideas
am not sure if i explained the problem right if u dnt understnd wat i mean plss ask

 

[crutschow]

The basic way to built a duty-cycle modulator is to generate a sawtooth waveform and connect it to one input of a voltage comparator. A variable voltage at the other comparator input will cause the duty-cycle of the output to vary with the voltage. See this.

 

[RCinFLA]

That is not a buck-boost circuit topology. It will generate a negative output voltage.

If you are looking for a buck-boost, look up 'SEPIC converter'.

 

[indulis]

It is a buck boost converter... they are inverting.

 

[pisaac001]

Yh u are right indulis it is a buck boost..though the output is inverted
RCinFLA i am also looking at the 'SEPIC converter' converter thanks
Am very greatfull crutschow...am going to go through the pdf..and then give it ago...i will let u know how it goes..