Chapter: Linear Integrated Ciruits - Application of ICs

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IC 723 - General Purpose Regulator

The simplified functional block diagram can be divided in to 4 blocks. 1. Reference generating block 2. Error Amplifier 3. Series Pass transistor 4. Circuitry to limit the current

IC 723 - GENERAL PURPOSE REGULATOR

 

Disadvantages of fixed voltage regulator:

 

1.        Do not have the shot circuit protection

 

2.        Output voltage is not adjustable These limitations can be overcomes in IC723.

 

Features of IC723:

 

1.        Unregulated dc supply voltage at the input between 9.5V & 40V

 

2.        Adjustable regulated output voltage between 2 to 3V.

 

3.        Maximum load current of 150 mA (ILmax = 150mA).

 

4.        With the additional transistor used, ILmaxupto 10A is obtainable.

 

5.        Positive or Negative supply operation

 

6.        Internal Power dissipation of 800mW.

 

7.        Built in short circuit protection.

 

8.        Very low temperature drift.

 

9.        High ripple rejection.

 

The simplified functional block diagram can be divided in to 4 blocks.

 

 

1.        Reference generating block

 

2.        Error Amplifier

 

3.        Series Pass transistor

 

4.        Circuitry to limit the current

 

 

1.        Reference Generating block:

 

The temperature compensated Zener diode, constant current source & voltage reference amplifier together from the reference generating block. The Zener diode is used to generate a fixed reference voltage internally. Constant current source will make the Zener diode to operate at affixed point & it is applied to the Non – inverting terminal of error amplifier. The Unregulated input voltage ±Vcc is applied to the voltage reference amplifier as well as error amplifier.

 

 

 

2.   Error Amplifier:

 

 

Error amplifier is a high gain differential amplifier with 2 input (inverting & Non-inverting). The Non-inverting terminal is connected to the internally generated reference voltage. The Inverting terminal is connected to the full regulated output voltage.

 


 

3.   Series Pass Transistor:

 

 

Q1 is the internal series pass transistor which is driven by the error amplifier. This transistor actually acts as a variable resistor & regulates the output voltage. The collector of transistor Q1 is connected to the Un-regulated power supply. The maximum collector voltage of Q1 is limited to 36Volts. The maximum current which can be supplied by Q1 is 150mA.

 

 

4.   Circuitry to limit the current:

 

 

The internal transistor Q2 is used for current sensing & limiting. Q2 is normally OFF transistor. It turns ON when the IL exceeds a predetermined limit.

 

·           Low voltage, Low current is capable of supplying load voltage which is equal to or between 2 to 7Volts.

 

Vload = 2 to 7V

Iload = 150mA

 

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