Exp2 voltage regulator

Integrated Circuits Lab

1. Experiment:2 Dt:
VOLTAGE REGULATOR IC 723
AIM: To study the voltage regulation characteristics and plot the response curve for
line regulation and load regulation using 723 IC.
APPARATUS REQUIRED:
S.No Equipment/Component Name Specifications/Value Quantity
1 IC LM723 1
2 Regulated Power Supply (0-30V), 1 A 1
3 Resistors 1KΩ, 2.7KΩ, 4.7KΩ, 6.8KΩ 1 No. Each
4 Capacitors 100 pF 1
5 Voltmeter 0-20V 1
6 Ammeter 0-20mA 1
7 Bread board & Connecting wires

THEORY:
A voltage regulator is one of the most widely used electronic circuitry in any device. A
regulated voltage (without fluctuations & noise levels) is very important for the smooth
functioning of many digital electronic devices. A common case is with micro
controllers, where a smooth regulated input voltage must be supplied for the micro
controller to function smoothly.
Voltage regulators are of different types. An example of IC based voltage regulator
available in market is the popular 7805 IC which regulates the output voltage at 5 volts.
An IC voltage regulator is an integrated circuit whose basic purpose is to regulate the
unregulated input voltage (definitely over a predefined range) and provide with a
constant, regulated output voltage.
An IC based voltage regulator can be classified in different ways. A common type of
classification is 3 terminal voltage regulator and 5 or multi terminal voltage regulator.
Another popular way of classifying IC voltage regulators is by identifying them as
linear voltage regulator & switching voltage regulator. There is a third set of
classification as 1) Fixed voltage regulators (positive & negative) 2) Adjustable voltage
regulators (positive & negative) and finally 3) Switching regulators. In the third
classification, fixed & adjustable regulators are basically versions of linear voltage
regulators.

2. Functional diagram of the voltage regulator . It consists of a voltage reference source
(Pin 6), an error amplifier with its inverting input on pin 4 and non-inverting input on
pin 5, a series pass transistor (pins 10 and 11), and a current limiting transistor on pins 2
and 3. The device can be set to work as both positive and negative voltage regulators
with an output voltage ranging from 2 V to 37 V, and output current levels up to 150
mA. The maximum supply voltage is 40 V, and the line and load regulations are each
specified as 0.01%.

The output voltage can be set to any desired positive voltage between (7-37) volts. 7
volts is the reference starting voltage. All these variations are brought with the change
of values in resistors R1 and R2 with the help of a potentiometer. A darlington
connection is made by the transistor to Q1 to handle large load current. The broken
lines in the image indicate the internal connections for current limiting. Even foldback
current limiting is possible in this IC. A regulator output voltage less than the 7 V
reference level can be obtained by using a voltage divider across the reference source.
The potentially divided reference voltage is then connected to terminal 5.


PROCEDURE:

3. LINE REGULATION
1. Connections are made as per the circuit diagram.
2. RPS is connected as Vi.
3. A fixed load of 1KΩ is kept at the output.
4. Input Vi is varied from 15V to 25V in steps of 2V and Output voltage is measured.
5. Graph is drawn between the input voltage and output voltage.

LOAD REGULATION
1. Connections are made as per the circuit diagram.
2. RPS is connected as Vi.
3. Output voltage is measured by varying the load (Potentiometer), in steps of 1mA
4. Graph is drawn between the output voltage and output current (load).




OBSERVATIONS:

Line regulation:
Line voltage(Vin) Output voltage(Vout)





Line regulation = (ΔVout / ΔVin) X 100%

Load regulation:
Regulated output Load current Load resistance Load

4. regulation







%Regulation: (Vnoload-Vfullload)/Vfullload X 100

Model Graph: line regulation
Vo



Vi
Load regulation:
Vo




Load resistance
RESULT: The load regulations and line regulations are observed by the IC 723.
Outcome: After conducting this experiment students are able to use IC 723 as voltage
regulator and understand its operation.
Discussion Questions:
1. Which is not considered as a linear voltage regulator 1) Fixed output voltage
regulator 2) Adjustable output voltage regulator 3) Switching regulator 4)
Special regulator why
2. What is the dropout voltage in a three terminal IC regulator?
3. What is provided with to get a maximum output current

5. 4. Which type of regulator is considered more efficient?
5. What is called the change in output voltage for the corresponding change in load
current in a 7805 IC regulator?