Lecture No# 3 Prepared by: Engr. Qurban Ali Memon Incharge of Project Lab.

LAB EXPERIMENT NO # 03 Rectifier: To understand the operation of half wave rectification by using (a) Kit (b) Breadboard. Components: 1. Kit 2. diode 3. A.C supply 4. Load resistor (180Ω) 5. Oscilloscope 6. Few connecting leads Rectifier: A rectifier is a circuit that converts pulsating ac into pulsating dc. There are three basic types of rectifier circuits: the half wave, full wave (center tapped) and bridge rectifiers.

Full wave bridge Half wave Full wave center tapped Input ac cycle Input AC Output of full wave bridge Output of half wave Output of full wave

1. Half wave Rectifier Half wave rectification is a process, which converts an ac sinusoidal input voltage into a pulsating dc voltage with the output pulse occurring for each input cycle. In half rectifier current flows only during the positive half cycle. In half rectifier blocks the flow of current during the negative half cycle. The half wave rectifier is made up of a single diode and a resistor (load). Therefore current always flow in one direction (i.e. d.c) through the load after every half cycle. Input of half wave rectification Circuit of half wave rectification Output of half wave rectification

Positive Half Cycle: In the positive half cycles when the input AC power is given to diode. The diode will allow current flowing in clock wise direction from anode to cathode in the forward bias (diode conduction will take place in forward bias) which will generate only the positive half cycle of the AC. The diode will eliminate the variations in the supply and give the pulsating DC voltage to the load resistance RL. We can get the pulsating DC at the Load resistance.

Negative Half Cycle: In the negative half cycle the current will flow in the anti- clockwise direction and the diode will go in to the reverse bias. In the reverse bias the diode will not conduct so, no current in flown from anode to cathode, and we cannot get any power at the load resistance. Only small amount of reverse current is flown from the diode but this current is almost negligible. And voltage across the load resistance is also zero.

Ripple Factor (r) The ratio of r.m.s value of ac component over a dc component is called ripple factor.

Ripple Factor (r) The ratio of r.m.s value of ac component over a dc component is called ripple factor. Next, one can connect a capacitor across the resistor in the circuit of half wave rectifier to obtain a smoother DC output. Here the capacitor charges through the diode D during the positive pulse of the input while it discharges through the load resistor RL when the input pulse will be negative. Thus the output waveform of such a rectifier will have ripples in it as shown in the figure.

Input and output wave form with ripple factor

Oscilloscope: An CRO is an abbreviation Cathode ray Oscilloscope (CRO). The oscilloscope is a versatile instrument. The main function of Oscilloscope is used to measure the dc/ac voltage, dc/ac current and also we can check two or more waveforms on the screen. We can observe the input and output on Oscilloscope Oscilloscope:

Peak Inverse Voltage During negative half-cycle of the input voltage, the diode is reversed biased, no current flows through the load resistance. RL and so causes no voltage drop across load resistance RL and consequently the whole of the input voltage appears across the diode. Thus the maximum voltage, that appears across the diode, is equal to the peak value of the secondary voltage i.e. VSM. Thus for a half-wave rectifier PIV = VSM /

Ripple factor: