Question

The maximum efficiency of full wave rectifier is

• A. $100\%$
• B. $25.20\%$
• C. $40.6\%$
• D. $81.2\%$

Answer 1

Answer: (D)

Efficiency of a rectifier is given by
$\eta =\frac{DC\text{ power output }}{AC\text{ power input }}$
For full wave rectifier $DC$ power output
$=I_{DC}^2\times R_L=\left(\frac{2I_0}{\pi }\right)\times R_L$
AC input power $=I_{rms}^2\left(r_f+R_L\right)$
$={\left(\frac{I_0}{\sqrt{2}}\right)}^2\left(r_f+R_L\right)$
$\therefore$ Rectifier efficiency
$\eta =\frac{{\left(\frac{2I_0}{\pi }\right)}^2{R}_L}{{\left(\frac{I_0}{\sqrt{2}}\right)}^2\left(r_f+R_L\right)}$
$=\frac{0.812R_L}{r_f+R_L}\eta$
will be maximum, if $r_f$ is negligible as compared to $R_L$
$\therefore$ Maximum rectified efficiency $=81.2\%$