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Transcript
Clipper & Clamper Circuits Clippers • Clipping circuit: A wave shaping circuit which controls the shape of the output waveform by removing or clipping a portion of the applied wave. • Half wave rectifier is the simplest example. (It clips negative half cycle). • Also referred as voltage limiters/ amplitude selectors/ slicers. • Applications: - In radio receivers for communication circuits. - In radars, digital computers and other electronic systems. - Generation for different waveforms such as trapezoidal, or square waves. - Helps in processing the picture signals in television transmitters. - In television receivers for separating the synchronising signals from composite picture signals Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Types of clippers • According to non- linear devices used: - Diode clippers and Transistor clippers • According to biasing - Biased clippers and Unbiased clippers. • According to level of clipping - Positive clippers, Negative clippers and combination clippers Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. THUMB RULE Action of biasing on diode • When diode is forward biased, it acts as a closed switch ( ON state). • When diode is reverse biased, it acts as a open switch ( OFF state). Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Series Diode Configurations Reverse Bias Diodes ideally behave as open circuits Analysis • VD = E • VR = 0 V • ID = 0 A Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 5 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Parallel Configurations V 0.7 V D V V V 0.7 V D1 D2 O V 9.3 V R EV 10 V .7 V D I 28 mA R R .33kΩ I D1 I D2 28 mA 14 mA 2 Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 6 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Diode Clippers The diode in a series clipper “clips” any voltage that does not forward bias it: • •A reverse-biasing polarity •A forward-biasing polarity less than 0.7 V (for a silicon diode) Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 7 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Biased Clippers Adding a DC source in series with the clipping diode changes the effective forward bias of the diode. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 8 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Parallel Clippers The diode in a parallel clipper circuit “clips” any voltage that forward bias it. DC biasing can be added in series with the diode to change the clipping level. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 9 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Summary of Clipper Circuits more… Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 10 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Summary of Clipper Circuits Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 11 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Drawbacks • Series Diode Clipper When diode is “OFF”, there should be no transmission of input signal to output. But in case of high frequency, signal transmission occurs through diode capacitance which is undesirable. • Shunt Diode clippers When diode is “OFF”, transmission of input signal to output should take place. But in case of high frequency input signals, diode capacitance affects the circuit operation and signal gets attenuated. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Clampers A diode and capacitor can be combined to “clamp” an AC signal to a specific DC level. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 13 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Note: • Start the analysis of clamping network, by considering that part of the input signal that will forward bias the diode. • During the period that the diode is in the “ON” state, assume that capacitor will charge up instantaneously to a voltage level determined by the network. • Assume that during the perod when the diode is in “OFF” state, capacitor will hold on its established voltage level. • Keep in mind the general rule, that Total swing of total output = Swing of input signal Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Biased Clamper Circuits The input signal can be any type of waveform such as sine, square, and triangle waves. The DC source lets you adjust the DC clamping level. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 15 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. For t1-t2 cycle Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Summary of Clamper Circuits Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 17 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Zener Diodes The Zener is a diode operated in reverse bias at the Zener Voltage (Vz). • When Vi VZ – The Zener is on – Voltage across the Zener is VZ – Zener current: IZ = IR – IRL – The Zener Power: PZ = VZIZ • When Vi < VZ – The Zener is off – The Zener acts as an open circuit Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 18 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Zener Resistor Values If R is too large, the Zener diode cannot conduct because the available amount of current is less than the minimum current rating, IZK. The minimum current is given by: I Lmin I R I ZK The maximum value of resistance is: RLmax VZ I Lmin If R is too small, the Zener current exceeds the maximum current rating, IZM . The maximum current for the circuit is given by: VL V Z RL RL min The minimum value of resistance is: I L max RL min RVZ Vi VZ Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 19 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved. Practical Applications • Rectifier Circuits – Conversions of AC to DC for DC operated circuits – Battery Charging Circuits • Simple Diode Circuits – Protective Circuits against – Overcurrent – Polarity Reversal – Currents caused by an inductive kick in a relay circuit • Zener Circuits – Overvoltage Protection – Setting Reference Voltages Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 20 Copyright ©2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 • All rights reserved.