Page 33 - Electrician - TT (Volume 2)

ELECTRICIAN - CITS

Fig 4

Fig 5

DC output: Fig 6 shows the input AC and the output pulsating DC wave-form of a bridge rectifier.
This wave-form is similar to that of the full wave rectifier using a centre-tap transformer. Hence, the average DC
value of the output is,
V = 0,636 V
dc s(peak)
or V = 0.9 V s(rms)
dc
where, Vs(rms) is the full secondary AC rms voltage.
NOTE: In a two -diode full wave rectifier V s(rms) refers to only half for the total secondary voltage
whereas in a bridge rectifier V refers to full secondary voltage.
s(rms)
Example: In Fig 5, if the transformer secondary voltage V s(rms) is 24 volts, the rectified DC voltage V across the
dc
load RL will be,
From equation ....2, V for a bridge rectifier is given by, Vdc = 0.9 V s(rms)
dc
In the given example, V = 24 volts
s(rms)
Therefore, V = 0.9 x 24 = 21.6 volts
dc
NOTE: Using the same transformer, a two-diode full wave rectifier would have given only 10.8 volts
which is half of that of bridge rectifier output.
Ripple frequency - Bridge rectifier: The pulsating DC output of a bridge is similar to the two diode full wave.
Hence as in a two diode fullwave rectifier, the output ripple frequency of the bridge rectifier is also twice the input
AC frequency.

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CITS : Power - Electrician & Wireman - Lesson 60-69