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

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