Voltage and Current Conductions (Problem 19.4)

I'm familiar with the traditional H-bridge in the text with parallel diodes across the transistor. But the homework problem (19.4) I'm having trouble visualizing what is conducting (as far as voltage is concerned) to get the sinusoidal nature.

Let's take below resonance (vc(t) leads Ig(t)] for example. In the first interval, Q1, Q4, D1, D4 must conduct to get positive Ig. This interval can be broken up into 2 subintervals......when Ig is positive and vc(t) is positive......and when Ig is positive but vc(t) is negative. What devices conduct voltage for each of these two subintervals?

Peak transistor current P19.1 e & g

Do we have to give a numerical value for this or its a waveform only?

HW2 P19.1 part d.

I am getting F as a complex number when I try to solve the radical!! What might I be doing wrong here. Anyone else having this problem.

Problem 19.3: Transfer Function

As we have been discussing, we can simply use Figure 19.22 for our analysis. However, the tank network is a parallel L and C. This will lead into a Transfer function problem of H(s) = 1........since all voltages are in parallel........which should not be the case.

Am I misinterpreting something?

19.3: Resonant Tank

Is the resonant tank, all though a dual of the series resonator, acting with the characteristics of a parallel resonant tank? I think this is what dual implies........the dual of series network is a parallel network.....

HW2 Problem 19.1 Part a

I am having trouble visualizing the current ig. I think it would be similar to Figure 19.8, but since it is a half bridge, vs will not go negative, and therefore ig cannot go negative. Also, when vs is zero, ig would also be zero.

Is the current through Cb and L like a sin wave (positive and negative)?

If ig is zero for more than half the period, how does this correlate to the model derived in class? Do I need to determine an equation for the fundamental component, then integrate to get the average ig?

How do you find the value of the phase shift?

Calculating ||H(jw)||

Hey everyone, I need a sanity check. Can someone tell me how to go about calculating the magnitude of a transfer function?

M (conversion ratio) of resonant converters

Can anyone help me with a doubt I have......we've learnt in class that for resonant converters the conversion ratio M evaluates as H(jw_s) and hence we concluded that to change the output voltage we vary the frequency rather than D as in hard-switched or PWM converters. That said, do we then operate these converters always with a duty cycle of D=0.5? Or does it matter if we operate at any other D?

Hw 2 Pb 19.3

Hello All,
I've trouble understanding how the circuit should work in this pb.
Can I have a hint please ?
Thanks,

HW1, Prob 2

Please forgive my lack of recall with respect to DE's. It's been a few years.

For parts b and c I understand that we take the derivative and set it equal to zero to find a max but I'm not sure what we solve for at that point. I assume it's t. I think that would give us the time at which v is at max. Am I correct in this approach?

HW1 Problem 3 Part c

Will the diode current waveform throughout the reverse recovery time look the same as it did in parts a and b? Or do I need to use Qr? How does Qr help me?

I think the intent of the circuit is to turn on Ms to store the energy from the diode D reverse recovery in the inductor Ls. Then at the end of the reverse recovery time, turn on M (zero voltage switching) and shortly after turn off Ms. The energy stored in Ls will then be dumped back to the load via diode Ds. I think we need to equate the energy stored in Ls to the energy that would be lost due to diode reverse recovery. However I don’t know where to start. Any hints?

Switching loss

I am getting this in order of hundreds of Watts. This doesn't sound right.

HW1 Problem 3 Waveform Questions

The diode current waveform shown, along with the description of the voltage waveform in the problem, indicate that the diode current goes negative before the voltage across the diode is affected. How is this possible? Because L and C are large, the fet voltage would start to decrease at the same time the diode voltage starts to increase. Why does the voltage across the fet remain constant until after time interval ta? I would think that the voltage across the fet would start to rise as soon as it starts to conduct current.

If there is a constant 5A through the inductor, it would go directly to the load when the diode is conducting. With a 400V output, 5A * 400V = 2,000 watts. (The problem says 500W.)

Is part b asking what are the switching losses in M, the switching losses in D, and the two added together?

HW1 Prob3 Questions

1) Could someone give me a sanity check on the switching loss of M1 w/o the aux circuit? I'm getting around 30W. Is that in the ballpark?

2) In ECEN 5807 there normally was no switching loss in the diode. The switching loss showed up in the primary switch. In this case, during time tb, there is an increasing voltage across the diode as there is still current decaying to zero. It looks like there must be some power loss in the diode during time tb. Am I correct?

HW1 pb3 D=?

Referred to fig1 (problem3):

Assuming the converter is lossless:

Pin=Pout=500W, Vin=500W/5A=100V

- Volt second balance: D’=Vin/Vout=100V/400V=0.25; D=0.75

- Charge balance: D’*I=Iout=Pout/Vout=500W/400A=1.25A

D’=Iout/I=1.25A/5A=0.25; D=0.75

 

Is D=0.5?

 

Thank you,

Hw1 Pb3

Hello All,

On Pb 3c (the boost conv with aux circuit), can I get a hint
how the aux circuit should work ?

I wonder if the secondary diode will share load current
with first diode when M is off ?

Thanks

Submitting Homework

For off campus students --- Does anyone know who we should submit the homework too? Whose email? Is their a TA for this course? There's one point in Lecture 1 where it could have been mentioned (in introductory comments) where the sound faded out dramatically.

Thanks.

HW1 Problem 2 - Q?

Do we need to consider Q? This would affect the answer for max value of Z.

Hw1, Pb1 Time domain analysis

Hello,

I am not sure if I'm doing it right.
I get the solution for current as:
I(t) = I + (Io-I) * cos(t/sqrt(L*C))

Assuming the result is correct,
peak current for I(t) will depend on value of Io.
If Io > I, then Ipeak = Io, @ cos(t/sqrt(L*C)) = 1
If Io < I, then Ipeak = I, @ cos(t/sqrt(L*C)) = 0

Thanks,
Tanto

Trying to understand the zero loss in M1 during turn-off transition.

From lectures 1 & 2, during the M1 turn-off transition, the energy loss in M1 was said to be zero. However the plot of v_s(t) was shown as a sloping line as it drops from Vdc towards 0. But inductor current must continue flowing with +ve polarity. That means it flows through C1 during the period marked X? I wasnt; sure I understood this very well.

Problem viewing the first lecture.

Is anyone else having problems watching the first class online? For me, it keeps buffering too often and the slides are not following the professor's lectures. Sometimes slide just goes blank.
Thanks

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