ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Topic: Triacs

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Triacs Prepared by: Abe Clements Dept. of Electrical and Computer Engineering Utah State University 3/7/2008

2. Outline • Reference list • To Explore Further • Major Applications • What is a Triac • Triac Construction and Symbol • Dimmer Switch • Basic Working Principal • Switching Inductive Loads • Digital Dimmer Switch • Key Parameters • Selection Guidelines • Common Packaging • Limitations • Components Commonly Used With Triacs • Variations of Standard Triacs • Cost • Where to Buy ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • http://home.howstuffworks.com/dimmer-switch3.htm • http://www.fairchildsemi.com/an/AN/AN-3003.pdf • http://www.mouser.com/Search/Refine.aspx?N=1491683+4294689442 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further • http://www.epanorama.net/circuits/semiconductor_relays.html • http://www.allaboutcircuits.com/vol_3/chpt_7/6.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • AC switching • Dimmer Switches • AC motor controllers • Solid State Relays ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. What is a Triac • A Triac is two Silcon Controlled Rectifiers (SCR) placed back to back. • An SCR controls current though it, by the current applied to the gate. When current is applied to the gate then current will flow though the device. • When the current is removed from the gate current will continue to flow though the SCR until the current falls below a treshold. For current to flow the SCR after this the gate has to be retriggered • An SCR only allow current to flow one way though it. A triac behaves in the same manner but allows current to flow in both ways ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

7. Triac Construction and Symbol When current flow between the bottom terminal and the gate a cascading effect between the n and p layers is created. This allows current to flow though the triac. The triac will remain in the conductive state until the current is removed regardless of the current between the gate and bottom terminal Image from http://home.howstuffworks.com/dimmer-switch3.htm ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Basic Working Principals • Applying voltage (VGT) between T1 and G is induces a current between the gate and T1. This current triggers the device. The device remains conductive until current between T2 and T1 is removed. • Triacs allow current to flow in either direction • VGT is usually created by a phase difference between T1 and G • If T1 and G are in Phase the Triac will remain off ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Dimmer Switch • By chopping the voltage across a load the energy dissipated can be controlled ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Typical Dimmer Circuit ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Design Considerations • Switching on an AC signal at any point other than zero crossings creates high frequency noise. • Filtering is often required with the use of Triacs when used for AC chopping (dimming) . L1 and C2 provide this filtering in the above circuit. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Switching Inductive Loads • In inductive loads the current and voltage are not in phase. If the triac tries to turn of when the voltage is high. It appears as a large increase in volatage to the traic. If this voltage increase exceed the (dv/dt)C value of the triac the triac will remain on. • Snubbing circuits are required in these cases to control the maximum rate at which the voltage increases. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Digital Dimmer Switch Circuit ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Digital Dimmer Switch • When a microcontroller detects a zero counter a can be used to delay the firing of OFF(ON). • By pulsing the OFF(ON) line twice per cycle the percent of the cycle that the light is on can be controlled by varying the time from a zero crossing to a pulse. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. Key Parameters ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. General Selection Guidelines ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Common Packaging RD91 SOT-223 SOT-428 TO-220 SOT-54 SOT-78 SOT-82 DPAK TO-92 TOP3 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. Limitations • Triacs commonly fire unsymmetrically • Can’t Switch DC • Once turned on they would remain on ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Components Commonly Used With Triacs • Optical Couplers (Optical Triacs) • Used to allow to digital components or DC components to control gate of triacs. • Often Connected in Darlington configuration to allow switching of large currents • AC line monitors • Allows detection of zero crossings of AC signals • Diacs • Commonly referred to as AC Diodes • Conduct current after a threshold voltage is reached typically 20V • Commonly connected to gate of triacs to allow voltage control of gate. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Variations of Standard Triac • Zero Crossing Triacs • employ circuitry to detect zero crossing and only turn on at zero crossings • Snubberless Triacs • do not require snubber circuits to switch inductive loads. • Triac and Diac packaged together • Optical Triacs • Allow DC or digital control of gate on triac • Usually have small IT values ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Cost • Varies from 10 cents to 80 dollars • Depends mostly on IGM • VGM =600V IGM =30A ~ $1 • VGM =600V IGM =315A ~ $10 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. Where to Buy • www.digikey.com • www.mouser.com ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators