VOLTAGE SHUNT REGULATOR

Date :

Experiment No. : 5

AIM :
1. To design a voltage shunt regulator for the given specifications.
2. To obtain and plot the regulation characteristics and transfer characteristics.
APPARATUS
S.No.
Name of the Component
Specifications
Quantity
1.
Transistor
(BC 107)
VC max = 100mA
PD = 300mW
VCEO = 45V
VBEO = 50V
1
2.
Resistor
(designed values)
RS = 48.9 K
RL = 202.5 K
1
1
3.
Zener Diode
BZ 7.5
1
4.
Ammeter
(0-100)mA
1
5.
Voltmeter
(0-10)V
1
6.
Regulated Power Supply
(0-30V), 1A
1












Design a Voltage Shunt Regulator to operate from a supply of 15V and to provide on output of 8.1V with load current 40mA

CIRCUIT DIAGRAM
Fig : Voltage Shunt Regulator


MODEL GRAPH

Fig : Load Regulation Characteristics Fig : Transfer Characteristics



DESIGN EQUATIONS :
Given data
Vi = 15V, V0 = VL = 8.1V, IL = 40mA
Choose hfe = 100
1) The load resistance

RL = 202.5
2) Applying KCL at node ‘1’
IS = IZ + IC + IL
From the circuit IZ = IB
Choose IZ = 1mA
We have IC = hfeIB
IC = 100 x 10-3
IC = 100mA
IS = 1m + 100m + 40m
IS = 141mA
3) Choose the zener voltage less than regulated output voltage.
From the fig VZ + VBE = V0
VZ = V0 - VBE
VZ = 8.1 – 0.7
VZ = 7.4V
4) Apply KVL around base section of the transistor Vi = ISRS + VZ + VBE
15 = 141 x 10-3 x RS + 8.1

RS = 48.9




TABULAR FORM :
LOAD REGULATION CHARACTERISTICS :
Input Voltage = 15V
S.No.
Load Resistance ( )
Output Voltage V0 (V)





























TRANSFER CHARACTERISTICS :
Load Resistance RL = 202.5
S.No.
Input Voltage Vi (V)
Output Voltage V0 (V)






























THEORY :
Most electronic circuits require low voltage, high current power supplies with output variations of less than 1mV. Since it is difficult to get such power supplies with zener regulator. We need some other circuitry to satisfy the required junction. The circuit is a simple transistor shunt regulator which is often employed to reduce ripple to as low as 1mV. This regulator is called as shunt regulator because the transistor is connected in shunt.
If the load increases, the output voltage reduces slightly. So the forward bias produced by the RB and RS voltage divider network decreases and hence the collector decreases and hence decrease in the collector current allows the same amount of decrease in the collector current allows the same amount of decrease in the load current. Thus the output voltage is stabilized against the variations in the load.
Thus there appears no variation in the load current and hence the output voltage is regulated against in the variations in the applied input voltage also.

PROCEDURE :
1. Connect the circuit as shown in figure.
2. For the given specifications calculate the component values.
3. To obtain load regulation characteristics
a) Apply a constant input voltage of 15V from RPS.
b) Vary the load resistance and note down the output voltage values from the corresponding meters.
c) Plot the graph between V0 VS RL and IL VS RL
4. To obtain transfer characteristics.
a) Keep the load resistance constant as 202.5 .
b) Vary the input voltage in steps of 1 Volt and note down output voltage readings.

PRECAUTIONS :
Ø Connections must be made carefully.
Ø Readings should be noted without any parallax error.
Ø The applied voltage should not exceed the maximum rating of the given transistor.

RESULT :
The load regulation characteristics and transfer characteristics of shunt voltage regulator are observed.