Microelectronics: Chapter 2 - Diode Circuits - Prof. Aurangzeb Khan, Assignments of Electrical and Electronics Engineering

Download Microelectronics: Chapter 2 - Diode Circuits - Prof. Aurangzeb Khan and more Assignments Electrical and Electronics Engineering in PDF only on Docsity! 1 Microelectronics Circuit Analysis and Design Donald A. Neamen Chapter 2 Diode Circuits In this chapter, we will: • Determine the operation and characteristics of diode rectifier circuits, which is the first stage of the process of converting an ac signal into a dc signal in the electronic power supply. • Apply the characteristics of the Zener diode to a Zener diode voltage regulator circuit. • Apply the nonlinear characteristics of diodes to create wave shaping circuits known as clippers and clampers. • Examine the techniques used to analyze circuits that contain more than one diode. Rectifier Circuits • A basic rectifier converts an ac voltage to a pulsating dc voltage. • A filter then eliminates ac components of the waveform to produce a nearly constant dc voltage output. • Rectifier circuits are used in virtually all electronic devices to convert the 120-V 60-Hz ac power line source to the dc voltages required for operation of electronic devices. • In rectifier circuits, the diode state changes with time and a given piecewise linear model is valid only for a certain time interval. Chap 3 -4 2 Half Wave Rectification If rf is zero, when diode is on, vo = vs-vγ PIV = Vs+Vγ Figure 2.6 Full-wave rectifier: (a) circuit with center-tapped transformer, (b) voltage transfer characteristics, and (c) input and output waveforms Full-Wave Rectifiers Full-wave rectifiers cut capacitor discharge time in half and require half the filter capacitance to achieve a given ripple voltage. All specifications are the same as for half-wave rectifiers. Reversing polarity of the diodes gives a full- wave rectifier with negative output voltage. 5 A capacitive filter added to the output of a full-wave bridge rectifier is shown at the left. One drawback of a half-wave rectifier is the higher level of ripple voltage after filtering. Full-wave rectification reduces this ripple voltage. Power Supply Applications Full-wave Rectifier with Filter Smoothening the Output Voltage of a Rectifier Add a Capacitor across Load Power Supply Circuits Filters and Regulators A capacitor-input filter will charge and discharge such that it fills in the “gaps” between each peak. This reduces variations of voltage. This voltage variation is called ripple voltage. Power Supply Circuits Filters and Regulators The advantage of a full-wave rectifier over a half-wave is quite clear. The capacitor can more effectively reduce the ripple when the time between peaks is shorter. Power Supply Circuits Filters and Regulators Vripple 6 Power Supply Applications Half-wave Rectifier with Filter Full-wave rectifier with filter design Output voltage of a full-wave rectifier with an RC filter Design of Filter Capacitor Power Supply Circuits RCf VV Mripple 2 = RCt M t Mo eVeVtv '')( −− == τ Voltage across the capacitor: RCT ML eVV '−= Minimum out voltage: T’: discharge time ( )RCTMLMripple eVVVV '1 −−=−= Ripple voltage: T’ << RC      ≈ RC TVV Mripple ' T’ ≅ TP     ≈ RC TVV PMripple PT f 2 1 = Assume capacitor takes negligible time to charge Output voltage of a full-wave rectifier with an RC filter time 7 Root Mean Square V V 2 0.707VRMS M M= = Mean value of sinusoidal over one period signal is zero Example 2.3 Design a full-wave rectifier to meet particular specification. A full-wave rectifier is to be designed to procedure a peak output voltage of 12 V, deliver 120 mA to the load, and produce an output with a ripple of not more than 5.0 %. An input line voltage of 120 V (rms), 60 Hz is available. P61 “Full-wave rectifier design” Variation on Problem 1.62H W # 2 Variation con’t For -0.7V < VI < 0.7V, II = 0 The device under test (DUT) acts like an open and can be modeled as such over this voltage range. Variation con’t When VI ≥ 0.7V, II changes linearly with voltage VVk mA VVrf 7.0 and 35.22 7.05 =Ω= − = γ 10 Sizing Series Resistance L i zps Z LZ zps i IR VV I Or II VV R − − = + − = Case 1: Vz > Vzo Vps = min, Iz = min, IL = max Case 2: Pz ≤ rated diode dissipation Vps = max, Iz = max, Il = min Sizing Series Resistance Case 1: Case 2: (max)I(min)I V(min)V R LZ zps i + − ≤ (min)I(max)I V(max)V R LZ zps i + − ≥ Power Supply Applications Input ZPS i I VVR −= Assume the Zener resistance is zero for ideal diode Load i ZPS Z IR VVI −−=→ Load Z Load R VI = 1. The IZ(min) when ILoad(max) and VPS(min). 2. The IZ(max) when ILoad(min) and VPS(max). For proper operation, the diode must remain in the breakdown region and power dissipation in diode must not exceed its rated value. In other words, (min)(max) (max) (max)(min) (min) LoadZ ZPS i LoadZ ZPS i II VVR II VVR + − = + − = [ ] [ ] [ ] [ ](max)(min)(max)(min)(max)(min) LoadZZPSLoadZZPS IIVVIIVV +⋅−=+⋅− If minimum requirement is IZ(min)= 0.1×IZ(max), [ ] [ ] (max)1.09.0(min) (min)(min)(max)(max)(max) PSZPS ZPSLoadZPSLoad Z VVV VVIVVII −− −−−⋅ = iR Zener Voltage Regulator Circuit Current-limiting resistor LoadZInput III += = 11 Voltage Regulation where: VL(nom) = the nominal output voltage Voltage regulation is the measure of circuit ability to maintain a constant output even when input voltage or load current varies %regulation is used to measure how well the regulator is performing its function 100x )nom(V (min)V(max)Vregulation% L LL −= Example 2.5 P68 In the Circuit given in Fig, the resistance R = 1 kΩ, VL = 10 V at 1 mA, and rZ = 30 Ω. Given that Vin changes from 11 V to 20 V, calculate the Zener current change and the output voltage change. Demonstration of Zener diode as a voltage regulator When Vin = 11 V Example rzIzVz Solution: Three-Terminal IC Voltage Regulators • Regulators use feedback with high-gain amplifiers to reduce ripple voltage at the output. Bypass capacitors provide low-impedance paths for high- frequency signals to ensure proper operation of the regulator. • Regulators provide excellent line and load regulation, maintaining constant voltage even if the output current changes by many orders of magnitude. 12 Voltage triplers and quadruplers utilize three and four diode-capacitor arrangements respectively. Voltage Multipliers Homework solution (page 108)