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Fundamentals of Power Supplies

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Rectifier Filter Regulator

AC Input

AC Rectified

(Pulsating DC)

Smoothed DC

Smoothed & Regulated DC

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Basic Diode Circuits

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Capacitive Filtering

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Finite Charge/Discharge times of RC circuit smooths out pulsating DC from the Rectifying

circuit

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•The effect of a single diode rectifying circuit - called a half-wave rectifier - produces the 60 Hz pulsating DC signal that must be smoothed by the filter circuit.

•The action of this circuit removes 1/2 of the AC component from the Power Supply input and increases the difficulty of smoothing.

•The full-wave rectifier saves both halves of the AC input and makes the signal easier to smooth by the filter circuit

Types of Rectifiers

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Full-Wave Rectifier

AC Input

Diode B

Diode A

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Output waveform from Diode A - half wave rectified + cycle

Output waveform from Diode B - half wave rectified - cycle

Combined waveform from both + & - cycles

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The full-wave rectifier circuit requires a center tapped transformer in order to function.

Transformers are usually the most expensive part of a power supply; with center tapped transformers more expensive than single transformers.

For these reasons, an alternate full-wave circuit is usually used, called a full-wave bridge rectifier.

Full-Wave Rectifiers

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Full-Wave Bridge Rectifier

+

-+

-

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Full-Wave Rectifier and Filter Circuit

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Full-Wave Bridge Rectifier and Filter Circuit

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The operation of all of these circuits is based on the rectifying property of semiconductor diodes.

We saw these effects in the Workbench exercise done earlier.

A plot of diode voltage versus diode current is shown on the next slide.

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Scale is mA

Scale is A

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