Objectives: Lab 4: Triode for Alternating Current (TRIAC) Operation 1. To verify the operation of TRIAC using DC triggering. 2. To demonstrate the phase control operation of TRIAC using AC triggering. Procedures: Part I: TRIAC Operation - DC Triggering 1. Construct the circuit as shown in the figure 1 using multisim. VCC 12V t -12.0V VEE VCC 12V S1 \Key = Space Basic >> Switch >> SPST S2 RA X1 12V_10W ⇒ Indicators >> Lamp >> 12V 10W ww 2.2ΚΩ Key = Space S3 D1 RB ww 10ΚΩ Key = Space 2N6073BG → Diodes >> TRIAC >> 2N6073BG S4 RC w 2.2ΚΩ Key = Space Figure 1: TRIAC Operation with positive voltage at MT2 2. Remember the TRIAC is a bi-directional device unlike SCR, which is unidirectional. a. It means we can have current flowing from MT2 to MT1 or MT1 to MT2. b. In the above circuit, we have current flowing from MT2 to MT1, since MT2 side held at VCC (using conventional current direction). 3. TRIAC can be ON with both positive and negative voltages at the gate. If you close switch, a. S2, positive voltage is applied to the gate. b. S3, OV is applied to the gate and c. S4, negative voltage is applied to the gate 4. Place the voltage probes at Gate and MT2 of the TRIAC to measure the DC voltage. 5. Change the position of the switches in order as listed under table 1 and record voltage at the gate, MT2 and TRIAC/Lamp condition either ON or OFF. Do not stop the simulation until you complete the table. Switch S1 Position Gate Switch Position Gate Voltage (VG) Voltage across TRIAC TRIAC/Lamp Gate condition Switch (VMT2-MT1) (On/Off) Position Close S1 Close S3 Open S3 Close S1 Close S2 Close S1 Open S2 Open S1 Close S1 Close S4 Close S1 Open S4 Open S1 Close S2 Table 1: Voltage values and condition of TRIAC 6. Modify the above circuit as shown in figure 2 below. Observe the switch S1 is connected to VEE. As mentioned in step 2, in this case the current will flow from MT1 to MT2. VCC 12V -12.0V VEE -12.0V S1 \Key = Space ⇒ Basic >> Switch >> SPST S2 RA w 2.2ΚΩ X1 12V 10W ➤ Indicators >> Lamp >> 12V 10W Key = Space S3 D1 RB w 10ΚΩ Key = Space 2N6073BG Diodes >> TRIAC >> 2N6073BG S4 RC w 2.2ΚΩ Key = Space VEE Figure 2: TRIAC Operation with negative voltage at MT2 7. Place the voltage probes at Gate and MT2 of the TRIAC to measure the DC voltage. 8. Change the position of the switches in order as listed under table 2 and record voltage at the gate, MT2 and TRIAC/Lamp condition either ON or OFF. Do not stop the simulation until you complete the table. Switch S1 Position Gate Switch Position Gate Voltage (VG) Voltage across TRIAC (VMT2-MT1) TRIAC/Lamp condition Gate Switch (On/Off) Position Close S1 Close S3 Open S3 Close S1 Close S2 Close S1 Open S2 Open S1 Close S1 Close S4 Close S1 Open S4 Open S1 Close S2 Table 2: Voltage values and condition of TRIAC Part II: TRIAC Phase control - AC Triggering 9. Modify the previous circuit as shown below. + กับ V1 10Vrms 60Hz 0° X1 ㄡˋ 12V 10W R1 3.3ΚΩ Key=A 0% R2 3.3ΚΩ C1 = 0.1μF MT1 MT2 D1 2N6073BG Figure 3: TRIAC Phase control - AC Triggering XSC1 B Ext Trig 10. Connect the channel A of the oscilloscope across the lamp and channel B across the TRIAC as shown above. 11. Change the color of the channel B wire by right clicking on the wire >> segment color >> blue. This way we can easily identify red color waveform is across the lamp and blue one is across the TRIAC. 12. Turn the potentiometer to 0%. 13. Run the simulation. Insert the voltage waveform across the lamp and across TRIAC below (use snipping tool. You need to separate both the waveforms using Y-pos. (Div) on the scope). 14. When the potentiometer at 0%, total voltage dropped across the TRIAC is the entire source voltage (where you will see full sinewave) and OV across the lamp (so lamp will be OFF). 15. Turn the potentiometer to 10%, while observing the voltage waveforms. 16. Insert the voltage waveform across the lamp and across TRIAC below. 17. Observe the waveform across the lamp (red waveform), it has the negative side as well, which implies the TRIAC is bidirectional. Therefore, the power will be delivered during positive and negative cycles as well unlike in SCR, where the power will be delivered during positive cycle only. 18. By increasing the potentiometer setting, TRIAC will be firing angle will be decreased and more power will be delivered to the lamp, means it will be more brighter. 19. Change the potentiometer in steps of 25%, take the screenshot of the oscilloscope image (use snipping tool), and insert below. Potentiometer @ 25%: Potentiometer @ 50%: Potentiometer @ 75%: Potentiometer @ 100%: Experiment Questions: 1. Before firing, the voltage across the TRIAC is a. OV b. Approximately Equal to power supply. 2. Once the TRIAC is turned on, it can only be turned off by. a. Removing gate voltage. b. Reducing the current flowing through TRAIC below the holding current value. C. Both a and b. 3. The TRIAC can be triggered on by applying. voltage. a. A positive at the gate b. A negative at the gate c. both a & b 4. How TRIAC is different from SCR? State your observations below.