# JEE Main & Advanced Physics Semiconducting Devices P-N Junction Diode as a Rectifier

P-N Junction Diode as a Rectifier

Category : JEE Main & Advanced

Rectifier is a circuit which converts ac to unidirectional pulsating output. In other words it converts ac to dc. It is of following two types

(1) Half wave rectifier :  When the P-N junction diode rectifies half of the ac wave, it is called half wave rectifier (i) During positive half cycle

Diode $\xrightarrow{{}}$ forward biased

Output signal $\xrightarrow{{}}$ obtained

(ii) During negative half cycle

Diode $\xrightarrow{{}}$ reverse biased

Output signal $\xrightarrow{{}}$ not obtained

(iii) Output voltage is obtained across the load resistance ${{R}_{L}}$. It is not constant but pulsating (mixture of ac and dc) in nature .

(iv) Average output in one cycle

${{I}_{dc}}=\frac{{{I}_{0}}}{\pi }$ and ${{V}_{dc}}=\frac{{{V}_{0}}}{\pi };\,\,{{I}_{0}}=\frac{{{V}_{0}}}{{{r}_{f}}+{{R}_{L}}}$

(${{r}_{f}}=$forward biased resistance)

(v) r.m.s. output  :  ${{I}_{rms}}=\frac{{{I}_{0}}}{2},\,{{V}_{rms}}=\frac{{{V}_{0}}}{2}$

(vi) The ratio of the effective alternating component of the output voltage or current to the dc component is known as ripple factor.

$r=\frac{{{I}_{ac}}}{{{I}_{dc}}}={{\left[ {{\left( \frac{{{I}_{rms}}}{{{I}_{dc}}} \right)}^{2}}-1 \right]}^{1/2}}=1.21$

(vii) Peak inverse voltage (PIV) : The maximum reverse biased voltage that can be applied before commoncement of Zener region is called the PIV. When diode is not conducting PIV across it $={{V}_{0}}$

(viii) Efficiency : If ${{R}_{L}}>>{{r}_{f}}$ then $\eta =40.6%$

If ${{R}_{L}}={{r}_{f}}$ then $\eta =20.3%$

(ix) Form factor = $\frac{{{I}_{rms}}}{{{I}_{dc}}}=\frac{\pi }{2}=1.57$

(x) The ripple frequency $(\omega )$ for half wave rectifier is same as that of ac.

(2) Full wave rectifier : It rectifies both halves of ac input signal. (i) During positive half cycle

Diode : ${{D}_{1}}$ $\xrightarrow{\,\,\,\,\,\,\,}$ forward biased

${{D}_{2}}$  $\xrightarrow{\,\,\,\,\,\,\,}$ reverse biased

Output signal $\xrightarrow{\,\,\,\,\,\,\,}$obtained due to ${{D}_{1}}$ only

(ii) During negative half cycle

Diode : ${{D}_{1}}$ $\xrightarrow{\,\,\,\,\,\,\,}$ reverse biased

${{D}_{2}}$ $\xrightarrow{\,\,\,\,\,\,\,}$ forward biased

Output signal $\xrightarrow{\,\,\,\,\,\,\,}$ obtained due to ${{D}_{2}}$ only

(iii) Fluctuating dc constant dc.

(iv) Output voltage is obtained across the load resistance RL. It is not constant but pulsating in nature.

(v) Average output : ${{V}_{av}}=\frac{2{{V}_{0}}}{\pi },\,{{I}_{av}}=\frac{2{{I}_{0}}}{\pi }$

(vi) r.m.s. output  : ${{V}_{rms}}=\frac{{{V}_{0}}}{\sqrt{2}},\,{{I}_{rms}}=\frac{{{I}_{0}}}{\sqrt{2}}$

(vii) Ripple factor : $r=0.48=48%$

(viii) Ripple frequency : The ripple frequency of full wave rectifier = 2 $\times$ (Frequency of input ac)

(ix) Peak inverse voltage (PIV) : It's value is $2{{V}_{0}}$

(x)  Efficiency : for ${{r}_{ff}}<<{{R}_{L}},\,\,\eta =81.2%$

(3) Full wave bridge rectifier : Four diodes ${{D}_{1}},\,\,{{D}_{2,\,\,}}{{D}_{3}}$  and ${{D}_{4}}$ are used in the circuit.

During positive half cycle ${{D}_{1}}$ and ${{D}_{3}}$ are forward biased and D2 and D4 are reverse biased

During negative half cycle ${{D}_{2}}$ and ${{D}_{4}}$ are forward biased and ${{D}_{1}}$ and ${{D}_{3}}$ are reverse biased #### Other Topics

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