solution Diode reverse recovery in a boost converter

Solution Diode - ECEN5817 Diode reverse recovery in a boost converter solution – D i t M i d i L = I V v ds g L C Figure 1 Figure 2 Initially

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Diode reverse recovery in a boost converter: solution + D i t M i d i L = I + V _ + v ds _ g L C Figure 1 Figure 2 Initially, diode D is on and i d = i L = I = 5 A. Transistor voltage is v ds = V = 400 V. Upon turn-on, MOSFET M current i t increases at the rate d i t /d t = 90 A/ s, as stated in the problem. Since i L = I = 5 A = i t + i d at all times, diode current i d decreases at the rate of 90 A/ s. At time t 1 = 5 A/(90 A/ s) = 56 ns, i d = 0, i t = I , and reverse recovery of the diode begins. See Textbook Section 4.2.1 for a brief summary of power diode physics, and Textbook Section 4.3.2 for a brief discussion of the diode reverse recovery. Due to the excess minority-carrier charge in the lightly-doped n - region of the p + -n - -n + structure, the p + -n - junction initially remains forward biased even as diode current reverses polarity. As long as the junction is forward biased, the diode forward voltage drop remains close to zero, and the transistor voltage remains equal to v ds = V . According to the problem statement, the junction remains forward biased throughout the interval t a . At the end of interval t a , diode current reaches the maximum negative value – I RM , and at the same time the excess charge is depleted so that the junction becomes reverse biased, allowing diode reverse-bias voltage to ramp up during interval t b . During t b , the junction depletion region increases to support increasing reverse-biased voltage. Diode current, in the process of charging up the depletion region capacitance, decays to zero (approximately at the end of t b ). At the end of t b , as stated in the problem, diode reverse-bias voltage increases to V = 400 V, which means that the MOSFET voltage v ds drops to zero. (a)

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This note was uploaded on 10/02/2010 for the course ECEN 5817 taught by Professor Maksimovic during the Spring '10 term at University of Colombo.

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Solution Diode - ECEN5817 Diode reverse recovery in a boost converter solution – D i t M i d i L = I V v ds g L C Figure 1 Figure 2 Initially

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