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Unformatted text preview: Problems Section 4.1 4.1 Starting with the currentvoltage characteristic for a capacitor C , show that for the case of fullwave rectification and RC filtering v ripple ≈ i Load 2 fC , where i Load is the load current and f is the frequency of the ac input. 4.2 Show that Eq. 4.12 cos φ = 1 v ripple v max applies to both halfwave and fullwave rectification. 4.3 The circuit of Fig. P4.3 features an ideal diode and 0.6V output ripple. The ac power source ( V s ) produces 18 V rms at 200 Hz. (a) Determine the maximum instantaneous load current (through R ). (b) Determine the time duration of the intervals of forward diode bias. (c) Find the maximum instantaneous diode current. (d) Find the diode peak reverse voltage. v out R 500 C V s + + Ω Figure P4.3 4.4 A particular circuit with RC filtering rectifies a 50Hz voltage waveform. Two conditions are known: • The capacitor value is 10 mF. • The current to the parallel RC combination has the time dependence shown in Fig. P4.4. (a) Does the circuit feature halfwave or fullwave rectification? (b) Determine the ripple voltage. (c) Find the maximum instantaneous load current. i (A) 10 10 20 t (ms) 0.5 ms Figure P4.4 4.5 Design a capacitively filtered halfwave rectifier circuit to deliver 50 mA to a 400Ω load resistance with 2% ripple voltage. Specify the diode ratings. Assume a 60Hz 115V (rms) power source. 4.6 Repeat Problem 4.5 with fullwave rectification. 4.7 Design a capacitively filtered halfwave rectifier circuit to deliver 100 mA to a 100Ω load resistance with 5% ripple voltage. Specify the diode ratings. Assume a 60Hz 115V (rms) power source. 4.8 Repeat Problem 4.7 with fullwave rectification. 4.9 The 4.7mF (electrolytic) capacitor selected for the RCfiltered power supply of Example 4.1 has a parasitic equivalent series resistance (ESR) of 75 mΩ. Estimate the power dissipated in the capacitor when R L = 200 Ω (minimum load resistance). c 2010 Edward W. Maby All Rights Reserved 4.10 This problem features a diode as a detector . In a simple amplitude modulation (AM) process, a received radio signal has the form v r ( t ) = ˜ v m (1 + m sin ω m t )sin ω c t , where ω c is the “carrier” angular frequency (to which the radio is tuned), ω m is the “modulating” angular frequency of the signal with information content, and constant m is the modulation index (0 ≤ m ≤ 1). In what follows, let ω c and ω m correspond to 10kHz and 1kHz frequencies, respectively. In practice, ω c is significantly larger, and ω m is part of a spectrum with particular ˜ v m weightings. (a) Use SPICE to plot v r ( t ) over two ω m periods. Assume that the signal is applied to a 1kΩ load, and let m = 1....
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 Fall '10
 Maarek
 Fig, Switchedmode power supply, Edward W. Maby

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