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Thursday, October 13, 2011



Aim:   To design a low voltage Regulator using IC 723.


1.      Voltage Regulator trainer kit
2.      Oscilloscope
3.      Digital multimeter
4.      Connecting patch chords

Circuit description:

The IC 723 is a monolithic integrated circuit voltage regulator featuring high ripple rejection, excellent input and load regulation, excellent temperature stability etc.,

It consists of a temperature compensating reference voltage amplifier, an error amplifier, 150mA output transistor and an adjustable output current limiter.
The basic low voltage regulator type 723 circuit is shown in fig (1). The unregulated input voltage is 24V and the regulated output voltage is from 0.2V to 7.3V by varying POTR. RSC (R1) is connected across current sense (CS) and current limit (CL) terminals to limit the accidental short circuit current.

A stabilizing capacitor (C1) of 100 pF is connected between frequency compensation terminal and inverting (INV) terminal. External NPN pass transistor is added to the basic 723-regulator circuit to increase its load current capability.

The output voltage can be regulated from 7 to 37 Volts for an input voltage range from 9.5 to 40Volts. For intermediate output voltages the following formula can be used

The resistor values  are calculated from potential divider network® .


1.      Switch ON the experimental board by connecting the power card to the ac mains.
2.     Make sure that the potentiometer are in minimum position.
3.     Connect the 8V AC tapping of the transformer secondary to the bridge rectifier input and short Raw DC +ve voltage point and pin 12 of 723.
4.     Measure the output voltage with a DMM and also measure the output with the 10KΩ potentiometer with its maximum position.
5.     Now disconnect the 8V AC tapping and connect 10V AC tapping and note down the minimum and maximum output voltages with 10KΩ minimum and maximum positions.
6.     Repeat the same procedure for 12V, 16V , and 18V AC transformer secondary tapping and tabulate these values.
7.     Now, again connect 8V AC to the bridge rectifier input, set the output DC voltage at 5V with 10KΩ potentiometer.
8.     Connect the load resistor with(0-50mA) milliammeter and vary the load resistor and note down the readings of the output voltage and output current with different load resistor. 

Load regulation:

9.     Calculate and tabulate the load regulation at each load current.
% Regulation  = (VNL-VFL) * 100/ VFL
                                      Where VNL= DC output voltage at no load
                                    VFL = DC output voltage at full load
10.                        Draw a graph between load current Idc and load                          voltage Vdc regulation


% of load regulation

Circuit Diagram Filter:



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