Circuit Modeling

[BlackMelon]

Hello all,

The problem statement is on the attachment named "part 1". I am modeling this DC to DC converter circuit. There are two states as shown in the files. So I model each state one-by-one. However, after I have finished the modeling, I could not see the term Vin (DC input), since it has been eliminated by dVin/dt. My question is:

Did I make it correct?
If so, how can a DC-DC converter operate without caring its input?

Thank You
BlackMelon

 

[Harald Kapp]

Why did you remove Vin from state1? Why should D4 be off in this state? Where would current through S1 and S2 come from with D4 off?

 

[BlackMelon]

Why did you remove Vin from state1? Why should D4 be off in this state? Where would current through S1 and S2 come from with D4 off?

Please find the attached research paper (pdf file) below. The circuit of state 1 and state 2 are on Fig 5.

I understand what you are thinking. I guess what you mean is to charge the inductors using Vin in the state 1. The paper's notation is quite confusing here, but the story is like this:

>>The circuit begins with the state 2 first. Vin supplies energy through D4 to C1 and C2. As you can see in Fig 4, the voltages of the two capacitors rise in state 2.

>>The circuit is now at its state 1. Even with the absence of Vin, C1 and C2 supply energy to the inductors. Hence the inductor currents rise, and the voltages of the two capacitors fall. (Fig 4)

>>Now we are back at the state 2 again. What we have more than the first time is the inductors are connected in series with Vin. This will sum up all of the back EMF from inductors and Vin, sending out a higher voltage to the output.

So to answer your question,
1. D4 is in the off state because it is the two caps, not Vin, who charge the inductors and causing the current to flow through S1 and S2.
2. And the two caps get their energy from state 2 at the very very first time we operate this circuit

If I am wrong, please correct me. This is based on my understanding from reading the paper

So, my question, still, is why Vin is absent from my model?