Diacs are often used in conjunction with triacs to provide symmetrical

Diacs are often used in conjunction with triacs to

This preview shows page 53 - 71 out of 107 pages.

Diacs are often used in conjunction with triacs to provide symmetrical triggering.
Image of page 53
Diac Figure 21 Figure 21 (a) shows the schematic symbol of a diac , and Figure 21 (b) shows the bidirectional symbol.
Image of page 54
Diac Constructions Figure 22 Shows the diac internal constructions.
Image of page 55
Diac Construction Neither terminal is referred to as cathode Contain 2 anodes, anode 1(electrode 1) and anode 2(electrode 2) When anode 1 is positive, the applicable layers are p 1 n 2 p 2 and n 3 When anode 2 is positive, the applicable layers are p 2 n 2 p 1 and n 1
Image of page 56
Diac Figure 23 Shows the diac characteristic curve.
Image of page 57
Diac Basic Operation From A1 to A2 Q1 & Q2 forward-biased Q3 & Q4 reverse-biased Operate on the upper right portion of the characteristic curve.
Image of page 58
Diac Basic Operation From A2 to A1 Q3 & Q4 forward-biased Q1 & Q2 reverse-biased Operate on the lower left portion of the characteristic curve.
Image of page 59
Diac Applications Trigger circuit for the Triac Proximity sensor circuit
Image of page 60
Triac A triac is a bi-directional thyristor used to control the power in ac circuits. It is like a diac with a gate control or equivalent to two SCRs in parallel. A triac has two leads designated M T1 , and M T2 or A 1 and A 2 . It can conduct current in either direction when it is trigger ON (depending on polarity of voltage across it terminal A 1 and A 2 ). A triac has a gate lead which is used to control its conduction,which can be turned on by a pulse of gate current and does not require the breakover voltage to initiate conduction.
Image of page 61
Triac Figure 24 The schematic symbol for a triac is shown in Figure 24 (a). There are two anode terminals, A 2 and A 1 , and a gate lead. The triac is the equivalent of two SCRs connected in parallel, as shown in Figure 24 (b).
Image of page 62
Triac Figure 25 A 2 Gate Mode + + 1 + 2 + 3 4 Figure 25 shows the four operating modes for a triac. When the anode 2 (A 2 ) terminal is positive, the triac can be turned on with either a positive or negative gate voltage. When the anode 2 (A 2 ) terminal is negative, the triac can be turned on with either a positive or negative gate voltage.
Image of page 63
Triac Figure 26 Figure 26 shows a very effective way to provide a wide range of control over load current. R 1 -C 1 and R 2 -C 2 provide the required phase shift necessary for full control of the load current.
Image of page 64
Triac Construction Neither terminal is referred to as cathode Contain 2 anodes, anode 1(electrode 1) and anode 2(electrode 2) & 1 gate terminal.
Image of page 65
Triac Characteristic Curve
Image of page 66
Current in direction depending on the polarity across the terminal. It turn OFF when the current drop sufficient low level. Breakover potential decrease as the gate current increase. Triac Characteristic Curve
Image of page 67
Triac Basic Operation Terminal A1 is biased positive with respect to A2
Image of page 68
Triac Basic Operation Terminal A2 is biased positive with respect to A1.
Image of page 69
Triac Typical Packages and Pin
Image of page 70
Image of page 71

You've reached the end of your free preview.

Want to read all 107 pages?

  • Fall '15
  • Engr.Vergara
  • SCR, SCRs, basic operation

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

  • Left Quote Icon

    Student Picture

Stuck? We have tutors online 24/7 who can help you get unstuck.
A+ icon
Ask Expert Tutors You can ask You can ask You can ask (will expire )
Answers in as fast as 15 minutes