Determine the limit of its output voltage using LM 317 Regulator Experiment

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LM 317 Regulator

 Aim :

To construct an adjustable dc voltage source using LM 317, determine the limit of its output voltage and study the load regulator characteristics for a selected value of the output voltage.

Apparatus :

Unregulated power supply, IC LM 317, three resistance boxes, DC ammeter (0-500mA), DMM etc.

LM 317 Regulator as a variable voltage source - Experiment

 

Formula :

LM 317 Regulator as a variable voltage source - Experiment

 

Circuit Diagram :

LM 317 Regulator as a variable voltage source - Experiment

 

Procedure :

Credit – Afrotechmods

  1. Switch on unregulated DC power supply and measure the input voltage Vin.
  2. Design the circuit of the voltage regulator for the maximum output Vo(max)= (Vin- 3V).
  3. Calculate R1 using formula.
  4. Make necessary connection. Measure the minimum (for R2 = 0) and maximum (for R2 = R2max) values of Vo and compare it with expected values. 
  5. To design the circuit for Vo = 10V, calculate R2 such that the minimum current (Imin) through it is atleast 50 times Iadj.
  6. Study the load regulation characteristic of the voltage regulator.
  7. Plot a graph of VL against IL with the maximum load current IFL lying between 200mA to 300mA hence determine percentage load regulation at IFL. 8) Measure the input ripple Vir(p-p) at IFL using CRO.

Observation :

 

Viva Question and Answers [FAQ] :

1. What is the Aim of the experiment? 

Ans : Determine the limit of its output voltage and study the load regulator characteristics for a selected value of the output voltage.

2. What is LM317?

Ans : LM317 is a popular adjustable positive linear voltage regulator. It has line regulation of 0.01% and load regulation of 0.1%.

3. What is the apparatus of the experiment? 

Ans : Unregulated power supply, IC LM 317, three resistance boxes, DC ammeter (0-500mA), DMM etc.

4. How many pins are there in LM317 and mention pin name? 

Ans : In LM317 three pins are there. Adjust pin, output pin and input pin.

5. Who invented LM317? 

Ans : Robert C. Dobkin and Robert J. Wilder

6. What is characteristic of LM317? 

Ans : It is a three terminal positive voltage regulator. It requires only 2 external resistors to set the output voltage. LM317 is capable of providing current of 1.5 A.

7. What is Duty cycle? 

Ans : It operates intermittently rather than continuously. Time occupied as the percentage of available time.

8. What is the relationship between ripple voltage amplitude and output load current? 

Ans : Input ripple voltage amplitude is directly proportional to the output load current.

9. Define Load regulation? 

Ans : Is to maintain constant output voltage. Percentage load regulation of power supply should be idealy zero and practically small.

10. What is the use of voltage regulator? 

Ans : Voltage regulator are used for the purpose of voltage regulation i.e to maintain a constant voltage or maintain voltage level within acceptable range.

11. What is the name of two main kinds of regulator? 

Ans : a. Fixed voltage regulator
          b. Variable voltage regulator
 

12. What is the use of Bandgap reference voltage? 

And : Bandgap reference voltage is used to generate constant output voltage irrespective of the chages in supply power.

13. How LM317 can be used as precision current regulator? 

Ans : By connecting a fixed resistor between output and adjustable of LM317 regulator.

14. What is the use of LM317? 

Ans : LM317 can be used as current regulator and voltage regulator.

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