EE231: Electronics-1
Lecture: 10-12
Zener Diodes
• The analysis is quite similar to the
ones done for a normal diode
previously
• First of all state of diode must be
determine
– Whether ON or OFF
• Secondly an appropriate model
must be substituted
• After this, the unknown quantities
Approximate equivalent circuits
should be determined for Zener diode in the three
• Occasionally an application might possible regions of application
use Zener diode in the forward bias
region
Zener Diode as a Regulator
• Regulator is a combination of circuit elements
designed to ensure that the output voltage of
a supply remains fairly constant
• Zener diode can be used to establish reference
voltages and act as a protection device
• Network for maintaining +20 volts during positive portion of input
signal and 0 V during negative portion of input signal
vi > 20.7 V vi < 20.7 V
Zener Regulator & its Conditions
• Zener regulator can be analyzed under three
conditions
– Vi and RL fixed
– Fixed Vi and variable RL
– Fixed RL and variable Vi
Example 2.26, Pg: 96
Vi and RL Fixed
• (a) Determine VL, VR, IZ and PZ
• (b) Repeat (a) with RL = 3 kΩ
Example 2.27, Pg: 98
Fixed Vi & variable RL
a) Determine the range of RL and IL that will
result in VRL being maintained at 10 V
b) Determine the maximum wattage rating of
the diode
Example 2.28, Pg: 99
Fixed RL and Variable Vi
• Determine the range of values of Vi that will
maintain Zener diode in the ON state
Voltage Multiplier Circuits
• The relatively low peak secondary voltage of a
transformer can be stepped up to two, three,
four or more times the peak rectified voltage
• These circuits use a combination of diodes
and capacitors to step up the output voltage
of rectifier circuits
• The output voltage is in multiples of the peak
value of the secondary voltage of the
transformer
Half Wave Doubler
• Positive half cycle
– D1 conducts
– D2 is switched off
– C1 charges to Vm
• Negative half cycle
– D2 conducts
– D1 is switched off
– Voltage across C2 can be found by applying
KVL during negative half cycle
Full Wave Doubler
• During positive half cycle
– D1 conducts
– D2 is switched off
– C1 charges to Vm
• During the negative half-cycle
– D2 conducts
– D1 is switched off
– C2 charges to Vm
• The output voltage taken
across the two capacitors is
2Vm
Voltage Tripler & Quadrupler
3. Next +ve half cycle
1. +ve half cycle • D1 and D 3 conduct
• D1 conducts • C3 charges to 2Vm
Voltage across C1 and C3
• C1 charges to Vm is 3Vm
Hence we get a voltage
2. -ve half cycle Tripler
• D2 conducts 4. Next -ve half cycle
• D2 and D4 conduct
• C2 charges to • C4 charges to 2Vm
2Vm Voltage across C2 and C4
is 4Vm
Hence, we get a voltage
quadrupler
