TRIAC Working

TRIAC Working

• 1.
  TRIode for AlternatingCurrent “Triacs are semiconductor devices that are widely used for switching medium power AC - their advantage is that they can switch both halves of alternating cycle” 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 1
• 2.
  TRIAC Symbol It hasthree terminals 1. Main Terminal 1 (MT1), 2. Main Terminal 2 (MT2) and 3. Gate (G). 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 2
• 3.
  TRIAC Equivalent usingSCR A TRIACs can be formed by connecting two equivalent SCRs in inverse parallel to one another and the gates of the two SCR are connected together to form a single gate. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 3
• 4.
  TRIAC Construction Gate It isa four-layer device that consists of six doping regions. The gate terminal is designed in a way to have ohmic contact with both N and P regions, which helps the device to get triggered with both positive and negative polarities. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 4
• 5.
  TRIAC Working Principleand Operation  TRIAC can go to conduction state if the applied voltage is equal to the breakdown voltage, but the most preferred way of turning on a TRIAC is by providing a gate pulse, either positive or negative. If the gate current is high, a very small amount of voltage is enough to turn on the TRIAC.  As the TRIAC is bidirectional and has an ability to get turned on with both the polarities to the gate pulse it can operate in four different types of modes of operation 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 5
• 6.
  Modes of operation 1.MT2 is positive with respect to MT1 with a gate polarity positive with respect to MT1. 2. MT2 is positive with respect to MT1 with a gate polarity negative with respect to MT1. 3. MT2 is negative with respect to MT1 with a gate polarity negative with respect to MT1. 4. MT2 is negative with respect to MT1 with a gate polarity positive with respect to MT1 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 6
• 7.
  1st Mode: MT2is positive with respect to MT1 with a gate polarity positive with respect to MT1 When the terminal MT2 is positive with respect to the Terminal MT1 the current will be flowing in the path of P1-N1-P2-N2. During this operation, the junction between the layers P1-N1 and P2-N2 are forward biased whereas the Junction between N1-P2 is reverse biased. When the positive signal is applied to the gate the junction between P2-N2 is forward biased and breakdown occurs 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 7
• 8.
  2nd Mode: MT2is positive with respect to MT1 with a gate polarity negative with respect to MT1 When the MT2 is positive and the gate pulse is negative, the current flow will be in the same path as the first mode which is P1-N1-P2-N2, but here the junction between the P2-N2 is forward biased and the current carriers are injected into the P2 layer. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 8
• 9.
  3rd Mode: MT2is negative with respect to MT1 with a gate polarity negative with respect to MT1 When the terminal MT2 is positive and negative pulse is provided to the gate terminal the current will be flowing in the path of P2-N1-P2-N2. During the operation the junction between the layers P2-N1 and P1-N4 are forward biased whereas the junction between the layers N1-P1 is reverse biased, hence the TRIAC is said to operate in the negatively biased region. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 9
• 10.
  4th Mode: MT2is negative with respect to MT1 with a gate polarity positive with respect to MT1 When the terminal MT2 is negative and the gate is triggered with a positive pulse the junction between P2-N2 is forward biased and the current carriers are injected, hence the TRIAC is turned on. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 10
• 11.
  Which mode isused in TRIAC?  The TRIAC doesn’t usually operate in mode 4 because it carries a disadvantage that it should not be used for circuits with high di/dt. The sensitivity of triggering of TRIAC with mode 2 and 3 is high and negative gate pulse is used in case of a marginal triggering capability. The triggering of mode 1 is even more sensitive than mode 2 and 3 triggering but it requires a positive gate pulse for triggering. In most of the cases, the triggering mode 2 and 3 are preferred. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 11
• 12.
  V-I characteristics ofTRIAC 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 12
• 13.
  TRIAC Characteristics  Sincethe TRIAC is a bidirectional device it’s the VI characteristics curve of TRIAC will be on the first and third quadrant of the graph, which is similar to the VI characteristics of a Thyristor (SCR). When the terminal MT2 is set to be positive with respect to the terminal MT1 the TRIAC will be operating in the forward blocking mode. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 13
• 14.
   During theinitial stage due to the resistance of the TRIAC, there will be a small leakage current flowing through the device as the applied voltage is less than the breakdown voltage. When the voltage is increased and it reaches the breakdown voltage the TRIAC is turned on and high current starts flowing through the device 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 14
• 15.
   Apart fromincreasing the voltage of the device the TRIAC can be turned ON by applying the gate pulse, even if the applied voltage is less than the breakdown voltage.  The same operation can be carried out in the negative direction of the TRIAC which can leave us with a mirror image of the same curve on the negative quadrant.  The supply voltage at which the TRIAC starts conduction will depend on the gate current applied to the TRIAC. If the gate current is higher, then the voltage required to turn ON the TRIAC can be less. 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 15
• 16.
  TRIAC Application  TRIACsare commonly used to switch AC voltages.  Control circuits like electric fan speed control and smaller motor controls  High Power lamp switching and light dimmers  AC power control domestic appliances 21-04-2020 Electronic Devices - V Unit ECE Department - RMK College of Engineering and Technology 16
• 17.
  Thank You 21-04-2020 Electronic Devices- V Unit ECE Department - RMK College of Engineering and Technology 17