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112 Basic Electronics Dr. Faraz Akram

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A rectifier is an electrical device that converts alternating

current (AC), to direct current (DC).

What is AC and DC? In direct current (DC), the current only flows in one direction.

In alternating current (AC), changes direction periodically.

Is house current AC or DC?

Name some devices that work on AC

Why we need to convert AC to DC?

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Rectifiers are found in all DC power supplies that operate from an AC voltage

source.

DC power supply converts the standard 220 V, 50Hz ac voltage into a constant

dc voltage

220V, 50Hz

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220V, 50Hz

In half wave rectification, the positive half of the ACwave is passed, while the other half is blocked.

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Note: The diode

is considered to

be ideal.

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Example: What is the average value of the half-wave rectified

voltage in Figure

= =

=

2

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In the previous discussion, the diode was considered ideal. When

the practical diode model is used with the barrier potential of 0.7V

taken into account, this is what happens.

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Draw the output voltages of each rectifier for the indicated

input voltages.

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Thepeak inverse voltage (PIV) equals the peak value of theinput voltage, and the diode must be capable of withstanding

this amount of repetitive reverse voltage.

= ()

A diode should be

rated at least 20%

higher than the

PIV.

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A transformer is often used to couple the ac input voltage from

the source to the rectifier, as shown in Figure

Transformer coupling provides two advantages. First, it allows the source voltage to be stepped down as needed.

Second, the ac source is electrically isolated from the rectifier, thus

preventing a shock hazard in the secondary circuit.

Half wave rectifier with transformer

coupled input voltage

=

= 0.7

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