**Experiment No.:** 3

**Experiment Name:**

Study of Fully Controlled Full Wave Rectifier using SCR

**Objective:**

To study Fully Controlled Full Wave Rectifier using SCR

**Theory:**

The ac input voltage is fed to the input of a power transformer T_{R} which has centre-tapped secondary. Thus, the voltage V_{i1} and V_{i2} developed across the two halves of the secondary are equal in magnitude but opposite in phase. These are fed to two identical SCRs with identical gate control circuit. the current of each SCR flows through the load resistor R_{L} in the same direction. Hence one SCR conduct during the positive half cycles of the ac input voltage while the other conducts during the negative halves. Hence, the fullwave output voltage is obtained across R_{L}. Figure 2 shows the output voltage waveform. Here also a filter may be placed between the rectifier and the load resistor R_{L} to remove the ripple voltages.

**Circuit Diagram:**

**Working of Single Phase Full Wave Controlled Rectifier using SCR:**

During the positive half cycle of voltage V_{i1}, SCR_{1} conducts during the period α to π radians where α is the firing angle. The negative half of V_{i1}, corresponds to the positive half of V_{i2}. During this positive half of V_{i2}, SCR_{2} conducts during the interval α and π radians. The two outputs get added. The resultant output voltage V_{0} has the shape shown in figure 2. The output is obtained during the shaded portion. The firing angle α may be changed by changing the gate current by varying the resistor R in the gate control circuit.

**Magnitude of Output Volatge and Current:**

Let the input voltage V_{i1} be a sinusoidal voltage of amplitude V_{m} and frequency f Hz and let it be given by,

………..(1)

Where ω is the angular frequency in radians/second and equals 2πf.

Let, α be the firing angle during the positive half cycle. Then SCR_{1} conducts during angle α to π radians during the positive half cycle. Hence the average output voltage V_{av1} contributed by SCR_{1} is given by,

………(2)

Similarly, the average voltage contributed by SCR_{2} due to input voltage V_{i2} is equal to V_{av1}. Hence, the total value of average output voltage V_{av} is given by,

……..(3)

…….(4)

### Average output current is,

………(5)

We thus, find that fullwave SCR rectifier produces average output voltage and average output current twice those in half wave SCR rectifier. Further, removal of ripple voltage by filter circuit is more effective in full wave SCR rectifier.

Shizue DeroosIt’s hard to come by well-informed people about this subject, however, you sound like you know what you’re talking about! Thanks