McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Electronics Principles & Applications Seventh Edition Chapter 4 Power Supplies (student version) Charles A. Schuler McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. The System Half-Wave Rectification Full-Wave Rectification RMS to Average Filters Multipliers Ripple and Regulation Zener Regulator INTRODUCTION
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Dear Student: This presentation is arranged in segments. Each segment is preceded by a Concept Preview slide and is followed by a Concept Review slide. When you reach a Concept Review slide, you can return to the beginning of that segment by clicking on the Repeat Segment button. This will allow you to view that segment again, if you want to.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview The power supply energizes the system. Rectifiers change ac to dc. A half-wave rectifier conducts for half of the ac input cycle. The cathode end of the load circuit is positive. A full-wave rectifier conducts for the entire ac input cycle. Full-wave rectifiers use two diodes and a center tapped transformer. A bridge rectifier uses four diodes and provides full-wave performance without a transformer.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Power Supply Circuit A Circuit B Circuit C The power supply energizes the other circuits in a system. Thus, a power supply defect will affect the other circuits.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. ac Power Supply Circuit A Circuit B Circuit C dc Most line operated supplies change ac to dc.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved ac A series rectifier diode changes ac to dc. Half-wave pulsating dc The cathode makes this the positive end of the load.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Full-wave pulsating dc ac Two diodes and a transformer provide full-wave rectification. The cathodes make this the positive end of the load.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V LOAD is equal to one-half the total secondary voltage. C.T. Only half of the transformer secondary conducts at a time. ½ V TOTAL V TOTAL
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Full-wave pulsating dc ac The bridge circuit eliminates the need for a transformer.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Full-wave pulsating dc ac Reversing the diodes produces a negative power supply.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Power supply basics quiz Most line-operated power supplies change ac to ________. dc A single diode achieves ________ -wave rectification. half Two diodes and a center-tapped transformer provide ________ -wave rectification. full A bridge rectifier uses ________ diodes. four The positive end of the load is the end in contact with the diode ________. cathodes
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review The power supply energizes the system. Rectifiers change ac to dc. A half-wave rectifier conducts for half of the ac input cycle. The cathode end of the load circuit is positive. A full-wave rectifier conducts for the entire ac input cycle. Full-wave rectifiers use two diodes and a center tapped transformer. A bridge rectifier uses four diodes and provides full-wave performance without a transformer. Repeat Segment
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview When a meter is connected to the output of a rectifier, it will respond to the average value of the pulsating dc waveform. The average dc load voltage is 45% of the rms input voltage for half-wave rectifiers. The average dc load voltage is 90% of the rms input voltage for full-wave rectifiers. The average dc load voltage is 135% of the rms input voltage for full-wave rectifiers.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Vac Vdc ac V ac V dc Ignoring diode loss, the average dc is 45% of the ac input for half-wave. V ac V dc Converting rms to average
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc ac V ac V dc Ignoring diode loss, the average dc is 90% of the ac input for full-wave.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. 0 V -200 V +200 V 20 ms40 ms 0 ms 3 120 V 60 Hz Three-phase rectification is used in commercial, industrial and vehicular applications. Full-wave, 3 bridge V dc = 1.35 x V rms = 162 V
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Time in milliseconds Volts Three-phase rectifier output V dc = 1.35 x V rms = 162 V
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Average dc quiz The average dc voltage with half-wave is equal to ______ of the ac voltage. 45% The effective ac voltage in a two-diode, full-wave rectifier is _______ of the secondary voltage. half The average dc voltage with a full-wave rectifier is _________ of the effective ac voltage. 90% The average dc voltage with a bridge rectifier is equal to ________ of the ac voltage. 90% The average dc voltage with a 3 bridge rectifier is equal to ________ of the ac voltage. 135%
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review When a meter is connected to the output of a rectifier, it will respond to the average value of the pulsating dc waveform. The average dc load voltage is 45% of the rms input voltage for half-wave rectifiers. The average dc load voltage is 90% of the rms input voltage for full-wave rectifiers. The average dc load voltage is 135% of the rms input voltage for full-wave rectifiers. Repeat Segment
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview A filter capacitor will charge to the peak value of the ac input. The peak value of the ac input is 141% of the rms value. The peak value is 141% for both half-wave and full-wave circuits. Voltage doublers produce a peak value that is 282% of the rms input value.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Filter capacitor Charge Discharge VPVP A relatively large filter capacitor will maintain the load voltage near the peak value of the waveform. ac
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. ac Discharge time is less. Full-wave is easier to filter since the discharge time is shorter than it is for half-wave rectifiers. VPVP
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Adding a filter capacitor increases the dc output voltage. V ac V dc ac V ac V dc Ignoring diode loss and assuming a large filter, the dc output is equal to the peak value for both half-wave and full-wave.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc V ac V dc ac Ignoring diode loss and assuming a large filter, the dc output is equal to the peak value for both half-wave and full-wave.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. ac V ac V dc Full-wave doubler V ac V dc Ignoring diode loss and assuming large filters, the dc output is twice the peak ac input.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. C 1 is charged. C1C1 ac Half-wave voltage doubler C2C2 The charge on C 1 adds to the ac line voltage and C 2 is charged to twice the peak line value.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Capacitive filter dc output quiz (Ignore diode loss and assume a light load for this quiz.) The dc output in a well-filtered half-wave supply is _____ of the ac input. 141% The dc output in a well-filtered full-wave supply is _____ of the ac input. 141% The dc output in a well-filtered half-wave doubler is _____ of the ac input. 282% The dc output in a well-filtered full-wave doubler is _____ of the ac input. 282%
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review A filter capacitor will charge to the peak value of the ac input. The peak value of the ac input is 141% of the rms value. The peak value is 141% for both half-wave and full-wave circuits. Voltage doublers produce a peak value that is 282% of the rms input value. Repeat Segment
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Preview The ideal dc power supply has no ac ripple. The percentage of ac ripple is a measure of how closely a real power supply approaches the ideal. The dc output voltage of an ideal supply never changes.. The percentage of voltage regulation is a measure of how closely a real power supply approaches the ideal. Zener diodes are used as voltage regulators. The voltage drop across a zener diode remains almost constant, if it is conducting.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc V ac V dc An ideal dc power supply has no ac ripple. ac ripple = 0%
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc V ac V dc ac ac ripple = 12 V dc 1.32 V ac x 100% = 11 % Real power supplies have some ac ripple.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc An ideal power supply has perfect voltage regulation. The voltage does not change.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. V ac V dc V ac V dc ac The output of a real supply drops under load. Voltage Regulation = VV V FL x 100 % = 12 V 1 V x 100 % = 8.33 %
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved Reverse bias in Volts Reverse current in mA I V V rev The voltage across a conducting zener is relatively constant
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. ac V ac V dc A shunt zener diode can be used to regulate voltage. V ac V dc V ac V dc If the zener stops conducting, the regulation is lost.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Power supply quality quiz The voltage regulation of an ideal power supply is ___________. 0% The ac ripple output of an ideal power supply is ___________. 0% small The ac component of an ideal dc power supply should be as ________ as is feasible. small A device that is commonly used to regulate voltage is the ________ diode. zener V in a real power supply should be as ___________ as is feasible.
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. Concept Review The ideal dc power supply has no ac ripple. The percentage of ac ripple is a measure of how closely a real power supply approaches the ideal. The dc output voltage of an ideal supply never changes.. The percentage of voltage regulation is a measure of how closely a real power supply approaches the ideal. Zener diodes are used as voltage regulators. The voltage drop across a zener diode remains almost constant, if it is conducting. Repeat Segment
McGraw-Hill © 2008 The McGraw-Hill Companies Inc. All rights reserved. REVIEW The System Half-Wave Rectification Full-Wave Rectification RMS to Average Filters Multipliers Ripple and Regulation Zener Regulator