Electronics Principles & Applications Fifth Edition Chapter 4 Power Supplies ©1999 Glencoe/McGraw-Hill Charles A. Schuler

The System Half-Wave Rectification Full-Wave Rectification RMS to Average Filters Multipliers Ripple and Regulation Zener Regulator INTRODUCTION

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.

ac Power Supply Circuit A Circuit B Circuit C dc Most line operated supplies change ac to dc.

ac A series rectifier diode changes ac to dc. Half-wave pulsating dc The cathode makes this the positive end of the load.

+ - 0 Full-wave pulsating dc ac Two diodes and a transformer provide full-wave performance. The cathodes make this the positive end of the load.

V LOAD is equal to one-half the total secondary voltage. C.T. One-half of the transformer secondary conducts at a time.  V TOTAL V TOTAL

+ - 0 Full-wave pulsating dc ac The bridge circuit eliminates the need for a transformer.

+ - 0 Full-wave pulsating dc ac Reversing the diodes produces a negative power supply.

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

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

V ac V dc ac V ac V dc Ignoring diode loss, the average dc is 90% of the ac input for full-wave.

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%

Filter capacitor Charge Discharge VPVP A relatively large filter capacitor will maintain the load voltage near the peak value of the waveform. ac

+ - 0 Discharge time Full-wave is easier to filter since the discharge time is shorter than it is for half-wave rectifiers. VPVP

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.

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.

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.

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 value.

Capacitive filter dc output quiz (assume a very 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%

V ac V dc V ac V dc An ideal dc power supply has no ac ripple. ac ripple = 0%

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.

V ac V dc An ideal power supply has perfect voltage regulation. The voltage does not change.

V ac V dc V ac V dc ac The output of a real supply drops under load. Voltage Regulation = VV V FL x 100 % = 12 V 1 V x 100 % = 8.33 %

ac V ac V dc A zener diode can regulate voltage. V ac V dc V ac V dc But, if the zener stops conducting, the regulation is lost.

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.

REVIEW The System Half-Wave Rectification Full-Wave Rectification RMS to Average Filters Multipliers Ripple and Regulation Zener Regulator