Well at the surface this is not too hard to understand but you do have to be able to calculate the voltage on both sides of the switch.
On the left side we have the DC input so that's not too hard to figure out, it's the battery voltage.
On the right side however we have to be able to calculate the wave shape using circuit analysis techniques.
Once we have the voltage on both sides of the switch vLeft and vRight, we can subtract to get the wave across the switch in time:
vSwitch=vLeft-vRight
but you should be able to do vRight=vLeft also. They will both be functions of time but of course the battery voltage is just a constant assuming zero internal resistance.
Next you apply the integral for the average voltage and that givers you the average DC voltage across the switch.

There may be a shortcut here but we are probably better off doing it this way as this applies to any circuit no matter how it is hooked up.

wow thank you so much. i was definitely overthinking it. this was extremely helpful, thank you!

 

Hi, I’m not quite understanding this piece. Is Vright the voltage across the inductor?

 

Hi, I’m not quite understanding this piece. Is Vright the voltage across the inductor?

vLeft is the node at the left side of the switch.
vRight is the node at the right side of the switch.
So yes, vRight ends up being the voltage across the inductor.
vLeft happens to be the input power supply voltage.

 

Hi
Can I ask you, how did you do number 11? I am making IL_max = IQ is it right?

Hi all,

First time posting in this thread, hoping I can get help on a homework I'm stuck with.

View attachment 182599
Working on a homework on buck-boost, given the following :

• Vin = 12V
• Vout = -5V
• R load = 2.5 ohm
• Fsw = 20kHz
• Assume ideal, at CCM

I have calculated more values based on some of the questions it asked:

1. Duty cycle = 0.2941
2. Inductor current = 2.833A
3. Inductor value (assuming delta IL = 15% of IL) = 20.76uH
4. Capacitor value (assuming delta Vc = 25mV) = 58.82uF

I am having trouble answering the last 2 questions of this HW:
View attachment 182596

My understanding is that the Vq is the switching voltage. Which means that the waveform should look something like this:
View attachment 182598

Assuming that, for question 12, the peak voltage should be equal to Vin = 12V. Furthermore, for #13, my guess is the DC component of this waveform should be Vin * D = 2.99V. Of course I got both questions wrong and thus I'm here looking for advice. Not sure how else to go about this logic at the moment. Any help is appreciated, thanks!

 

Hi
Can I ask you, how did you do number 11? I am making IL_max = IQ is it right?

Hi,

Sorry i dont see number 11 can you repeat that here please? I'll take a look.
In any of these however i would do an analysis using state vector differential equations and solve for different things mostly those that are repetitive.

 

I can't help thinking that it's going to be tricky to find a gate driver to make this circuit with an N-channel MOSFET.