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 R_L 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 R_L and through the diode D₁. In both cases, the current passes through the R_L 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 R_L, 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. R_L is 1kΩ resistor. The rectified output is obtained across R_L.

 

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

r = V_ac/V_dc

ac output voltage = V_ac = ........V

dc output voltage = V_dc = ........V

Ripple Factor, r = V_ac/V_dc = .........

 

(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 = V_ac = ........V

dc output voltage = V_dc = ........V

Ripple Factor, r = V_ac/V_dc = .........

 

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 R_L; and a graph with r and R_L may be drawn.