Question

In a full wave junction diode rectifier the input ac has rms value of $20\, V$. The transformer used is a step up transformer having primary and secondary turn ratio $1 : 2$. The dc voltage in the rectified output is

• A. $12\, V$
• B. $24 \,V$
• C. $36\, V$
• D. $42\, V$

Answer 1

Answer: (C)

Here, input $V_{rms} = 20\, V$
Peak value of input voltage
$V_{0} = \sqrt{2} V_{rms} $
$ = \sqrt{2} \times 20 $
$ = 28.28 \,V$
Since the transformer is a step up transformer having transformer ratio $1 : 2$, the maximum value of output voltage of the transformer applied to the diode will be
$V_{0}' = 2 \times V_{0} $
$= 2\times 28.28 \,V$
$\therefore $ dc voltage $= \frac{2V_{0}'}{\pi} $
$ = \frac{2\times 2\times 28.28}{22/7} $
$ = 36 \,V$