A bridge rectifier using four P-N junction diodes can also be used as a full rectifier. Fig. 1.3 Voltage regulation by zener diode Voltage across the load resistance R L be V z = V L -Let I be the current drawn from the input voltage, I z be the current through the zener diode and I L be the current through the load resistance R L as shown in Fig. 1.3 By Kirchhoff’s law, I = I z + I L V = RI + I z R z V L = I L R L = I z Rz. …….1.3a Where R z is the d.c. resistance of zener diode. V = R ( I z + I L ) +I L R L = RI z + I L (R+R L ) = RI z + V L /R L (R + R L ) = RI z + V L [ 1+ (R/R L )] or I z = - V L /R [1+ (R/R L )]+ V/R …….1.3b 1.2 Voltage regulation by zener diode
A bridgerectifierusingfourP-Njunctiondiodescanalsobeused as a
full rectifier.
Fig. 1.3 Voltage regulation by zener
diodeVoltageacrosstheloadresistanceRLbeVzVL-Let !bethecurrent dra"n
fro# the in$ut %oltage& !zbe the current throughthe zener diode
and !L be the current through the load resistanceRL as sho"n in
Fig. 1.3 'y (irchhoff)s la"& ! !z * !LVR! * !z RzVL!L
RL!zRz.++.1.3a,here Rz is the d.c. resistance of zener diode. VR -
!z * !L. * !L RL R!z* !L -R*RL. R!z* VL/RL -R * RL. R!z* VL 0 1*
-R/RL.1 or !z - VL /R 01* -R/RL.1*V/R++.1.3b 1.2 Voltage regulation
by zener diode 3he abo%e e4n. -1.3b. related the current in zener
diode !zand %oltagedro$ across the zener diode VL A gra$h $lotted
for !z %s VL is a straight line "hichis called the load line. Figl.
1.3 sho"s the characteristic cor%eof the zener diode"ith load line
A' on it ha%ing the interce$ts V/R at$oint A on the !z 5 a6is
for"hich VL 7 and V/0 1*-R/RL.1 at $oint 'on the VL- a6is for "hich
!z7. 3he$oint $ at "hich the load line intersect the zener
characteristic& is the o$erating$oint.
