Experiment 2: Ideal & Practical Switch Implementation Objectives: • Understand the differences between ideal and non-ideal (practical) switch • Gain an understanding of the non-ideal characteristics of a practical switch such as: • Rise time • Fall time Delay time • Voltage drop • Leakage Current • Limited speed • Distinguish between switching and conduction losses and compute each in a switching cycle • Compute the switch average power loss Compare between different power semiconductor switching devices and select the right device for a specific application/nIdeal switch 2.1 Consider the switching circuit shown in Fig. P2.1 with a resistive load. Assume the switch is ideal and operating at a duty ratio of 50%. (a) Sketch the waveforms for isw and Vsw. (b) Determine the average output voltage. (c) Determine the average output power delivered to the load. (d) Determine the average output power supplied by the de source. (e) Determine the efficiency of the circuit. 100 V Fig. P2.1 i sw + Vsw- +81 www 592 On 0.5T Off T On Assume: fsw = 100 kHz D = 0.5 Vswon = 0 Isw, off = 0/nPractical Switch • For the previous circuit, repeat the simulation and answer the questions if: tdelay = 0.1 µs trise = tfall = 0.5 µs Rsw,on = 0.10 Rsw,off = 10 k Repeat for fsw = 50, 200 and 500 kHz Questions • Show the simulation results (waveforms) for the current, voltage and power loss for one switching cycle for the ideal and practical switch. For the practical switch (support your answers with simulation verification): • How does the switching loss change when the frequency increases? • How does the conduction loss change when the frequency increases?/n• What is the effect of the rise, fall and delay times on the efficiency? • What is the effect of the voltage drop and leakage current on the efficiency? • Which power loss is dominant at low frequencies, switching or conduction loss? Which is dominant at high frequencies? Hint • You can use an ideal switch model and add non idealities to it. • See the model below in LTSpice./n3.2m Vou This shows an example of suppling a model statement as a SPICE directive directly on the schematic to define a voltage controlled switch. IN VI PULSE (0 10.5m. 5m 01m) OUT RI SI IK MYSW .tran im model MYSW SW(Ron=1 Roff=1Meg Vt=5 Vh=-4) V2 3.3 4.3m 0f

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