Experiment No: 9
Experiment Name: Single Phase Half Controlled Bridge Rectifier .
Aim: To study the working of single phase half controlled bridge rectifier.
Apparatus Required:
1.
2.
3.
4.
5.
SPHB102 Single Phase SCR Half Bridge Converter.
2mm Patch cords.
Cathode Ray Oscilloscope.
CRO probes.
Multimeter.
Circuit Diagram:
1. Single phase SCR connected Half Bridge Converter circuit
2. Firing Circuit
CVA
Model Waveforms:
1. Input Voltage(VS)
2. Output Voltage(V0) with R load
3. Output Voltage(V0) with RL load
Theory:
Rectifier is a device which converts ac supply to dc. In half bridge rectifier, each leg will have a
thyristor connected with a diode. During positive half cycle thyristor T 1 and diode D2 conduct and
in negative half cycle thyristor T2 and diode D1 conduct. As the conduction is through diode, the
output voltage wave during R load will not extend in the negative direction as shown in the
figure. But, in the case of RL load, the output voltage wave will extend in the negative portion as
shown in the figure. The average output voltage value will be V0 
2Vm

(1  cos  ) ; where Vm is
the maximum value of the ac wave, α is the firing angle.
Observation Table:
Input voltage= ____ Volt.
Average Output Voltage (V0) Volt
Firing angle (α)
Theoretical
Graphical
Procedure:
1.
2.
3.
4.
5.
CVA
Connect the circuit as per the connection diagram for the half bridge rectifier.
By keeping a particular value of control voltage, generate a firing pulse.
Apply the firing pulses to the SCR's.
Note the output voltage waveform, by connecting CRO across the output.
Determine the average output voltage by using a multimeter.
6. Obtain the firing angle both theoretically and graphically.
7. Vary the control voltage to some other value and repeat the steps 2-6.
Precautions:
1.
2.
3.
4.
Check the firing pulses before applying them to the thyristors.
The connections are to be proper and tight.
The settings in the CRO are to be proper.
Avoid double connections if possible.
Result:
The working of single phase SCR half bridge converter is studied along with the waveforms.
Conclusion:
The firing angle of the thyristors for the waveforms shown are ____ and ____.
CVA