# Buck boost inverter design with current mode

As a project, I should design inverting buck boost converter without using IC. I designed somehow the converter but not optimized it yet since I have no proper drive.

I am planning to set output of PI controller then use comparator and flip flop to feed MOSFET.

First of all, I have not much information especially about control diagram therefore I am kindly requesting your help. Questions are:

1. How much should I reduce to voltage to make PI controller circuit work properly I tried like 5V Vref?

2. For the output of the opamp what should I expect to see since I will compare this with shunt resistor current at the source of MOSFET ?

3. I created somehow transfer equations but can not calculate the proper capasitor and resistance so I tried it first without capasitor to experience opamp bit. I supplied almost 4.6V and Vref is 5V as far as I tried like that 5-4.6 = 0.4 V * 5 = 2V should be output of the op amp but I see at output 7V. Is there something I did wrong ?

I just simulate the output of the converter to play over it with following values.

Vref3 = 400VDC

Vref = 5V

Transfer function V(in) = 200V V(out) = 400V

V(s) / E(s) = Kp + Ki /s

Kp = Rf/Ri Ki = 1 /C*Ri

Some points might be defined wrongly so let me know please.

• I'm confused. What PI controller, exactly? I don't see one. Is the schematic shown your way of supporting your #2 point? If so, why not just say so in writing, too, to make sure no one has to work hard to decide that? I see no transfer function, but you say you calculated one and can't work out how to implement it. So it would help your question if you allowed us to see that transfer function. Wouldn't it? I kind of see a vague connection of dots here. But you may need to write substantially more than you have. But some people have better crystal balls than I do. So it may just be me.
– jonk
May 19, 2021 at 20:11
• Welcome to EE.SE! 2 and 3 are not questions. To get along well with fellow EEs, please draw schematics with inputs to the left and outputs to the right with negative voltages pointing down and positive up. May 19, 2021 at 20:32
• Thank you for replies , I added the circuit diagram which I want to build up. I found equations of transfer function but could not conclude it. Input will be 200V and output is -400V. I can clarify if there is still something needed
– Srtc
May 19, 2021 at 22:36