Demonstration Model IC Regulated Dc Power Supply

Demonstration Model IC Regulated Dc Power Supply

1.In all the electronic circuits solid state devices are employed. For the operation of these devices constant voltage DC power is required. Although, DC batteries fulfill this requirement but they are rarely employed because of their heavy cost. Therefore, in practices DC power for electronic circuits is obtained from commercial AC lines by using transformer rectifier and filter. This combination of transformer-rectifier-filter is called an ordinary power supply.

2.The DC voltage obtained from an ordinary power supply is seldom constant, it may vary when AC mains voltage changes or when the load on it changes. This variation in the DC supply voltage may affect the performance of the electronic circuits, therefore, a voltage regulating device is employed with the ordinary power supply to keep the DC voltage at fairly constant value. We shall focus our attention on some of the important voltage regulating circuits commonly used to obtain regulated power supply.

3.These variations in DC output may affect the performance of electronic circuits. For instance, the frequency of oscillations will change in an oscillator and in transmitters the output may be distorted. Thus, it is concluded that ordinary power supply is not suitable for some of the electronic circuits, with such circuits we have to employ a regulated power supply which gives fixed output voltage.

4.A power supply that maintains the output voltage constant irrespective of AC mains fluctuations or load variations is known as a Regulated Power Supply.

(i) Transformer: - usually, DC voltage required for the operation of various electronic equipment is 12V to 15V. This is quite small than the AC mains voltage. Therefore, before rectification a step-down transformer is employed to decrease the voltage to the required level.

(ii) Rectifier: - It converts AC into pulsating DC. The rectifier may be half-wave or full-wave. Mostly full wave rectifier is preferred because of its unchallenging merits.

(iii) Filter: - It removes the ripples from the output of rectifier and smoothes it out. The DC output received from the filter is constant till the mains voltage and load is kept constant. However, if either of the two is varied, DC voltage received at this point changes. Therefore, a regulator is employed at the output stage.

(iv) Voltage Regulator:- It is a circuit that keeps the output DC voltage constant even if the AC mains voltage or load varies. A classic voltage regulator IC LM317 is a three terminal voltage regulator IC from National Semi-Conductor. The IC is capable of delivery upto 1A of output current. Input voltage can be up to 15V and output voltage can be adjusted from 1.2V to 10V.

C1 is the input capacitor filter and C2 is the output capacitor filter. In this IC-Regulated DC Power Supply, the two resistor used to set the output voltage from the LM317 are called R1 and R2. In this IC Regulated DC Power Supply R1 is fixed at 330 Ohms, and R2 is a 4.7K potentiometer which means that R2 has a range of 0-4700 Ohms which can be selected by rotating the potentiometer. Output voltage can be seen with the help of moving coil voltmeter