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Electronic Circuits POWER SUPPLIES

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**INTRODUCTION Electronic Circuits The System Half-Wave Rectification**

Full-Wave Rectification RMS to Average Filters Multipliers Ripple and Regulation Zener Regulator

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Electronic Circuits 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.

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**Electronic Circuits Most line operated supplies change ac to dc. dc**

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

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**the positive end of the load.**

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

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**the positive end of the load.**

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

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**Electronic Circuits VLOAD is equal to one-half the total secondary**

Only half of the transformer secondary conducts at a time. VLOAD is equal to one-half the total secondary voltage. C.T. VTOTAL ½ VTOTAL

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

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**Reversing the diodes produces a negative power supply.**

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

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**Electronic Circuits Power Supply Review dc half full four cathodes**

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

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**Vac Vdc Vac Vdc Vac Vdc Ignoring diode loss, the average dc is 45%**

of the ac input for half-wave. Vac Vdc ac Converting rms to average

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**Vac Vdc Vac Vdc Ignoring diode loss, the average dc is 90%**

of the ac input for full-wave. ac Vac Vdc

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**Three-phase rectification is used in commercial, **

industrial and vehicular applications. Full-wave, 3 f bridge 3 f 120 V 60 Hz Vdc = x Vrms = 162 V 0 V -200 V +200 V 20 ms 40 ms 0 ms

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**Three-phase rectifier output**

200 160 120 Vdc = x Vrms = 162 V Volts 80 40 10 20 30 40 Time in milliseconds

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**Review Electronic Circuits 45% half 90% 90% 135%**

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 f bridge rectifier is equal to ________ of the ac voltage. 135%

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**Electronic Circuits VP Filter Discharge capacitor + ac Charge -**

A relatively large filter capacitor will maintain the load voltage near the peak value of the waveform. + Charge ac -

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**Electronic Circuits VP Discharge time is less. + ac -**

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

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**Adding a filter capacitor increases the dc output**

Vac Vdc Ignoring diode loss and assuming a large filter, the dc output is equal to the peak value for both half-wave and full-wave. Adding a filter capacitor increases the dc output voltage. Vac Vdc ac

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**Vac Vdc Vac Vdc 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 Vac Vdc

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**Vac Vdc Vac Full-wave doubler Vdc Ignoring diode loss and**

assuming large filters, the dc output is twice the peak ac input. ac Vac Vdc Full-wave doubler

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**Electronic Circuits Half-wave voltage doubler**

The charge on C1 adds to the ac line voltage and C2 is charged to twice the peak line value. C1 is charged. C1 ac Half-wave voltage doubler

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**(Ignore diode loss and assume a light load for this quiz.)**

Electronic Circuits Review (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%

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**Electronic Circuits Vac Vdc An ideal dc power supply has no ac ripple.**

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**Electronic Circuits Vac Vdc 1.32 Vac 12 Vdc Vac Vdc ac x 100%**

ac ripple = x 100% = 11 % Real power supplies have some ac ripple. Vac Vdc

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Electronic Circuits An ideal power supply has perfect voltage regulation. The voltage does not change. Vac Vdc

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**Electronic Circuits Vac Vdc Vac Vdc DV x 100 % Voltage Regulation =**

VFL = 12 V 1 V x 100 % Vac Vdc ac = % The output of a real supply drops under load. Vac Vdc

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**The voltage across a conducting zener is relatively constant.**

Electronic Circuits Reverse Bias in Volts 12 10 8 6 4 2 5 I 10 Reverse Current in mA 15 Vrev 20 25 30 35 The voltage across a conducting zener is relatively constant. V

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**be used to regulate voltage.**

Vac Vdc If the zener stops conducting, the regulation is lost. Vac Vdc Electronic Circuits Vac A shunt zener diode can be used to regulate voltage. Vdc ac

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**Review Electronic Circuits 0% 0% small small zener**

The voltage regulation of an ideal power supply is ___________. 0% The ac ripple output of an ideal power supply is ___________. 0% V in a real power supply should be as ___________ as is feasible. 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

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