CR iy Department of Electrical and Electronic Engineering Experiment Number: 03 Experiment Name: Study of Single-phase Half-wave Controlled Rectifier Cireuit with Resistive Load Objective: To observe the output wave shape and measure the output voltage (d.c) of the single- phase half-wave controlled rectifier circuit. Theory: SCR are very useful in a.c circuits where they may serve as rectifiers whose output current can be controlled by controlling the gate current. An example of this type of application is the use of SCRs to operate and control de motors or de load from an ac supply. The SCR is a unidirectional conduction device. When the SCR is reverse-biased by a negative anode- to- cathode voltage, it is turned off and no current can flow. When the SCR is forward-biased by a positive anode-cathode voltage but below the forward break over value, it is turned off until a positive gate signal with respect to cathode is applied. Once the positive gate signal is applied, the SCR is turned on and the current can flow from anode to cathode. Figure 3: Input-output voltage waveform of half-wave controlled rectifier Circuit Diagram: Resistance trigger circuits are the simplest and most economical method. During the positive half cycle of the input voltage, SCR become forward biased but it will not conduct until its gate current exceeds gate threshold (V,.). Diode D1 allows the flow of current during positive half cycle only. RI is the variable resistance and is used to limit the current through the circuit (I,) and to vary the gate voltage and thus the firing angle. During the positive half cycle current I, flows. I, increases and when V, = Vj = IpniaR the SCR turns ON .The firing angle can be varied from 0 to 90° by varying the resistance R1. Capacitor, C1 charges and discharges with a phase shift. When the capacitor voltage is equal to the gate threshold voltage (V,), SCR get triggered. Page 10 of 27Department of Electrical and Electronic Engincering ale ; Laue fe © pe bu — C1 = , *e4tenur Apparatus: BRNS mexnau SCR, BT1S1 Resistor, R1= 10k, POT Capacitor, C1= 0.1F,100V Diode, 1N4007 Transformer, 220/12V, 3A Lamp, (Incandescent), 12V (21W) Digital Multimeter Trainer Board Oscilloscope 0. Connecting Wires Procedure: 5, Olpe Olpe Olpe Olpe Olpe Olpe Olpe Olpe Olpe As necessary Complete the connections as per the circuit diagram, Keep the potentiometer RI in minimum position (maximum resistanc circuit), in the Turn on the power switch and vary R1 potentiometer Observe the output voltage waveform, SCR voltage and gate signals for various firing angle. Observe the range of firing angle control and record the output voltages. Report: 1 2. What are the differences between controlled and uncontrolled rectifier circuit? Explain the UJT relaxation oscillator circuit for SCR gate triggering, 3. Draw a graph delay angle vs output voltage. Page 11 of 27CR iy Department of Electrical and Electronic Engincering Experiment Number: 05 Experiment Name: Study of Single-phase Full-wave AC Voltage Controller Objective: To observe the output wave shape and measure the output voltage (a.c) of the single- phase full-wave controlled ac to ac converter circuit, Theory: DIAC and TRIAC are used AC power control circuit. The firing of a TRIAC can be phase controlled. Since the exercised in both directions the power in the load can be varied from full value to almost zero. Figure 5.1 shows a RC phase shift circuit applied as control signal to the gate. The DIAC in the circuit gives a wide range of summetrical firing of the TRIAC. The resistance R; control the Gate current by controlling the voltage across C. Here the voltage across C first turns on the DIAC which in turns applies enough voltage to the Gate to turn on the TRIAC. By property matching the DIAC to the TRIAC symmetrical triggering of the TRIAC in both the positive and negative alternations is accomplished, Moreover, the range of firing control is much wider so that a turn on delay of almost 180° is possible in each alternation. @- 27 “Ny | Figure 5.1: AC to AC voltage controller Circuit Diagram: Lawpt Lamp2 TRI Rn " 77 a zavac el “ ioe TW Ne SZ ut Bac (as; zaonz012V,90m0mA a T tos 0.14F 1000 Figure 5.2: Complete experimental setup (Light dimmer circuit) Page 14 of 27CR iy Department of Electrical and Electronic Engineering Apparatus: 1, TRIAC, BT136 Olpe 2. Resistor, RI = 100k, POT Olpe 3. Capacitor, C1 = 0.11F,100V Olpe 4. DIAC, DB3 Olpe 5. Transformer 220/12V, 3A Olpe 6. Lamp (Incandescent), 12V (21W) O2pes 7. Digital Multimeter Olpe 8. Trainer Board Olpe 9. Oscilloscope Olpe 10. Connecting Wires As necessary Procedure: Complete the connections as per the circuit diagram, Keep the potentiometer RI in minimum position (maximum resistance in the circuit) 3. Tum on the power switch and vary the R1 potentiometer. 4. Observe the output voltage waveform, TRIAC voltage and gate signals for various firing angle. 5. Record the output voltages and observe the range of firing angle control. Report: 1. Draw a graph delay angle vs output voltage. 2. How Does the DIAC conduct equally during the positive & negative alterations? 3. What is the main function of TRIAC? 4. How is a TRIAC equivalent to two antieparallel SCRs? Is it exact anti-parallel? maw How do you get the phase controlled ac output voltage in this experiment? Explain why a TRIAC can replace a SCR but a SCR cannot replace a TRIAC? ‘Why do not we use UST relaxation oscillator instead of DIAC? Page 15 of 27