# Investigatory Project on Bridge Rectifier

INVESTIGATORY PROJECT ON THE BRIDGE RECTIFIER

Aim: To construct a bridge rectifier using four identical diodes and to calculate its ripple factor with and without filtering.

Materials and Apparatus

(i) Four identical diodes

(ii) An electrolytic condenser 500µF or 1000 µF, a condenser 0.1 µF

(iii) Resistance 1000Ω

(iv) A step down transformer with 220 to 240 V primary and 6.3 V, 100mA secondary

(v) ac and dc voltmeters or a multimeter etc.

(vi) CRO

Working

During the positive half cycles of the secondary voltage in the circuit, the diodes D2 and D4 would conduct current and the diodes D1 and D3 would not conduct. Therefore, the current flows through the secondary winding of the transformer to the diode D2, then Load resistor RL and through the diode D4. During the negative half cycles in the circuit, the diodes D1 and D3 would conduct and the diodes D2 and D4 would not conduct. Therefore, current flows through the secondary winding of the transformer to the diode D3, then load resistor RL and through the diode D1. In both cases, the current passes through the RL in the same direction.

Procedure

1. Wire the Bridge rectifier circuit without capacitor after testing all the components.

2. Switch ON the mains supply to generate current. Observe the Secondary Voltage waveform from the transformer and and also the output voltage waveform across RL, simultaneously on CRO Screen. Note down peak values.

3. Calculate the ripple factor using the expression.

4. Connect the capacitor filter and observe the waveforms. Calculate the ripple factor using the expression.

5. Connections are made as shown in the figure. D1, D2, D3 and D4 are four identical diodes, C is a 500 µF or 1000 µF electrolytic condenser, C’ is a 0.1µF condenser. RL is 1kΩ resistor. The rectified output is obtained across RL.

(a) To find the ripple factor (r) with filter circuit

Specification of the diodes (from data book)

Type number of the diode: ............

Maximum forward current rating = ............mA

PIV rating = .........V

The ac output voltage Vac is measured by an ac voltmeter or by a multimeter across the points T3 and T4. The dc output voltage Vdc is measured between the point T1 and T2. The ripple factor is calculated by the equation,

r = Vac/Vdc

ac output voltage = Vac = ........V

dc output voltage = Vdc = ........V

Ripple Factor, r = Vac/Vdc = .........

(b) To find the ripple factor (r) without the filter circuit

The filter circuit is removed by disconnecting the condenser C from the above figure. The ripple factor is determined as explained above.

ac output voltage = Vac = ........V

dc output voltage = Vdc = ........V

Ripple Factor, r = Vac/Vdc = .........

Result:

The ripple factor of the bridge rectifier:

(a) with the filter circuit = ......

(b) without the filter circuit = ......

Note: Ripple factor r may be calculated for different loads RL; and a graph with r and RL may be drawn.