# Power Supply

Topics: Diode, Rectifier, Direct current Pages: 6 (898 words) Published: September 24, 2010
EXPERIMENT NO. 1

AIM: - Study of power supply, Function generator and multimeter.

DESCRIPTION: -

Power supply: - A power supply is a vital part of all electronic systems. It consists of transformer whose output is then applied to the bridge rectifier which converts sinusoidal input into full wave rectified output. The filter capacitors at the output of bridge rectifier are charged to peak voltage values of the rectified output voltage, whenever the diodes are forward biased. since the diodes are not forward biased during the entire positive and negative half cycles of the input waveform, the voltage across filter capacitor is pulsating dc i.e. combination of dc and ripple voltage. From a pulsating de voltage regulator circuit extracts a regulated ac voltage.

BLOCK DIAGRAM OF POWER SUPPLY: -

[pic]

Function generator:- A function generator is capable of producing simultaneous sine, square and triangular waves. Output frequency may range from as low as 0.01 hertz to as high as 300 kHz since wave distortion may be trimmed. The unit has provision for variable cycle and swept frequency operation.

Front panel of a signal generator: -
The instrument consists of following arrangements:-
i. Frequency selector: - It selects frequency range from 10 Hz to 1 MHz. ii. Variable amplitude: - it attenuates sine wave amplifier continuously. iii. Symmetry: - It varies symmetry of square waveform from 30% to 70%. iv. Amplitude: - It attenuates square wave or square wave output. v. Power ON: - It energies the instrument ON position.

vi. Neon lamp: - It glows when instrument is in ON position. vii. Output: - This provides sine or square wave.

BLOCK DIAGRAM OF FUNCTION GENERATOR: -

[pic]

Multimeter: -

A Multimeter is used to measure many electrical quantities: it can measure voltages (ac and dc), currents (ac and dc) and resistances. A multimeter is a voltmeter, milliammeter and ohmmeter combined together. In addition it has various ranges of voltage, current and resistance measurement, a selector switch is provided to set up required circuit for a desired measurement. A multimeter is normally used to measure ac and dc voltage from 0 to 3000v.ac and dc currents from 0 to 3 amps and resistance from 0 to 20 mega ohms. In ac ranges, the measurements are possible from 40Hz to 10 k Hz. It is calibrated for pure sine wave signal when used as a voltmeter, the resistance of the meter is determined by its sensitivity in expressed in ohm/volt and full scale voltages. While measuring resistance, never connect the meter terminals to energize the circuits. To select mode of measurement, a function switch is matched to fix a range of measurement. It is useful to start with highest range and then switch down to lower ones until a correct range.

EXPERIMENT NO.2

Aim:- To study the V-I characteristics of the p-n junction diode.

APPARATUS REQUIRED:
P-n junction diode, multimeter, connecting wires, breadboard, power supply, resistor,etc.

THEORY :

FORWARD CHARACTERSTICS:
When the positive terminal of the supply is connected to the anode of the diode and the negative terminal of the supply to the cathode of the diode, diode is said to be forward biased. During the forward biasing there is no diode current till the threshold or knee voltage is reached. Threshold voltage for silicon is 0.7V and for germanium, 0.3V.However, after the threshold voltage the current rises exponentially.

REVERSE CHARACTERSTICS:
When the applied reverse voltage is below a certain voltage known as the Breakdown voltage, the diode current is small and remains constant. This value of current is called reverse saturation current. It is in the order of nanoamperes for silicon diode and microamperes for germanium diode.

V-I CHARACTERSTICS:
It is the graph between the voltage applied across the terminals of the diode and the current that flows through it. The complete graph can be divided into two parts namely...