Need help with DC to DC current buck boost converter

[tanky321]

DC to DC Buck Boost

Im trying to design a simple DC-DC current controlled buck boost converter, and im having a tough time. I calculated the inductor value by using this eq. L=Vin^2/(10f*Iout*Vout)
Where Vin= 12V Vout= 6-18V (used 18.) Iout= 1Amax f=200kHz

I can get the converter to boost just fine, up to 28V or so. But i cant get it to buck what so ever. No matter what the pulse width.

Here's the schematic, does anything stick out?

Thanks,

Andrew

 

[FvM]

DC to DC Buck Boost

If you intend the voltage across R1 to be the output voltage of your circuit, you should use a differential voltage probe. You are measuring V1 + Vout now.

 

[tanky321]

Re: DC to DC Buck Boost

Thank you, I will try that!