Question

1. In a high-frequency converter, the non-linear junction capacitance of diodes and transistors often forms part of a turn-off snubber. Consider the buck converter shown below and the capacitor Cs is nonlinear. Specifically, its incremental capacitance is: Cs = dQ/dv = Co * sqrt(VIN / vc(t)) where Q is the charge in the capacitor, and Co is the value of Cs when the voltage across the capacitor (vc) equals VIN. Assume that VIN = 400 V, IL = 50 A, and Co = 0.1 uF. Also, assume that when the transistor turns off at t = 0, its current drops linearly to zero at tf = 0.25 uS. (a) Find the voltage across Q, vq(t): (i) 0 <= t <= tf (ii) t >= tf. (b) What is the value of yv = vq(tf)/VIN? (c) Calculate the energy stored in Cs when vq = VIN. (d) If the capacitor is linear, what is the energy stored in Cs when vq = VIN?

          1. In a high-frequency converter, the non-linear junction capacitance of diodes and transistors often forms part of a turn-off snubber. Consider the buck converter shown below and the capacitor Cs is nonlinear.
Specifically, its incremental capacitance is:
Cs = dQ/dv = Co * sqrt(VIN / vc(t))
where Q is the charge in the capacitor, and Co is the value of Cs when the voltage across the capacitor (vc) equals VIN. Assume that VIN = 400 V, IL = 50 A, and Co = 0.1 uF. Also, assume that when the transistor turns off at t = 0, its current drops linearly to zero at tf = 0.25 uS.
(a) Find the voltage across Q, vq(t):
(i) 0 <= t <= tf
(ii) t >= tf.
(b) What is the value of yv = vq(tf)/VIN?
(c) Calculate the energy stored in Cs when vq = VIN.
(d) If the capacitor is linear, what is the energy stored in Cs when vq = VIN?

1. In a high-frequency converter, the non-linear junction capacitance of diodes and transistors often forms part of a turn-off snubber. Consider the buck converter shown below and the capacitor Cs is nonlinear.
Specifically, its incremental capacitance is:
Cs = dQ/dv = Co * sqrt(VIN / vc(t))
where Q is the charge in the capacitor, and Co is the value of Cs when the voltage across the capacitor (vc) equals VIN. Assume that VIN = 400 V, IL = 50 A, and Co = 0.1 uF. Also, assume that when the transistor turns off at t = 0, its current drops linearly to zero at tf = 0.25 uS.
(a) Find the voltage across Q, vq(t):
(i) 0 <= t <= tf
(ii) t >= tf.
(b) What is the value of yv = vq(tf)/VIN?
(c) Calculate the energy stored in Cs when vq = VIN.
(d) If the capacitor is linear, what is the energy stored in Cs when vq = VIN?

Added by Barbara W.

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