EE 330 Lecture 26. Thyristors SCR TRIAC

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1 EE 330 ecture 26 Thyristors SC TIAC

2 eview from ast ecture Area Comparison between BJT and MOSFET BJT Area = 3600 l 2 n-channel MOSFET Area = 168 l 2 Area atio = 21:1

3 eview from ast ecture The Thyristor A bipolar device in CMOS Processes Consider a Bulk-CMOS Process S G D S G D p n p n Have formed a lateral pnpn device! Will spend some time studying pnpn devices

4 eview from ast ecture The SC Silicon Controlled ectifier Widely used to switch large resistive or inductive loads Widely used in the power electronics field Widely used in consumer electronic to interface between logic and power Anode A Gate G C Cathode Usually made by diffusions in silicon p n p n A A A G G G C C C Symbols Consider first how this 4-layer 3-junction device operates

5 eview from ast ecture ariation of Current Gain (β) with Bias for BJT Note that current gain gets very small at low base current levels

6 eview from ast ecture Operation of the SC Consider a modified application by adding a load (depicted as ) G I G G A C p n p n F CC CC F I C1 Q 1 I B2 C A Q 2 I C2 I B1 G I G G I G All operation is as before, but now, after the triggering occurs, the voltage F will drop to approximately 0.8 and the voltage CC -.8 will appear across If CC is very large, the SC has effectively served as a switch putting CC across the load and after triggering occurs, I G can be removed! But, how can we turn it off? Will discuss that later

7 eview from ast ecture Operation of the SC A The Ideal SC I = f, F F G I G G C F G I H is very small I G1 is small (but not too small) I = f, F F G called the SC model As for MOSFET, Diode, and BJT, several models for SC can be developed

8 Operation of the SC Operation with the Ideal SC CC oad ine: CC = IF +F F Analysis: CC = IF +F I = f, F G G The solution of these two equations is at the intersection of the load line and the device characteristics I H CC I G =0 oad ine CC when I G =0 F Note three intersection points Two (upper and lower) are stable equilibrium points, one is not When operating at upper point, F =0 so CC appears across We say SC is ON When operating at lower point, approx 0 so no signal across We say SC is OFF When I G =0, will stay in whatever state it was in

9 Operation of the SC Operation with the Ideal SC A I = f, F G I G G G C F On State G1 F Off State

10 Operation of the SC Operation with the Ideal SC CC Now assume it was initially in the OFF state and then a gate current was applied F I H CC I G=0 oad ine CC F CC = IF +F I = f, F G G CC oad ine Now there is a single intersection point so a unique solution The SC is now ON I H I G =I G1 >0 CC F emoving the gate current will return to the previous solution (which has 3 intersection points) but it will remain in the ON state

11 Operation of the SC Operation with the Ideal SC CC Turning SC off when I G =0 CC oad ine G F I H I G =0 CC BGF0 F educe CC so that CC / goes below I H This will provide a single intersection point CC can then be increased again and SC will stay off Must not increase CC much above BGF0 else will turn on

12 Operation of the SC Operation with the Ideal SC CC Turning SC off when I G =0 F CC G oad ine I H I G =0 CC BGF0 F

13 Operation of the SC CC Operation with the Ideal SC Often CC is an AC signal (often 110) F SC will turn off whenever AC signal goes negative G CC oad ine I H I G =0 CC BGF0 F CC

14 Operation of the SC CC Operation with the Ideal SC Often CC is an AC signal (often 110) F SC will turn off whenever AC signal goes negative G CC oad ine I H I G =0 CC BGF0 F CC

15 Operation of the SC Operation with the Ideal SC CC Turning SC off when I G >0 F CC oad ine G I H I G =I G1 >0 CC F educe CC so that CC / goes below I H This will provide a single intersection point CC But when CC is then increased SC will again turn on Not practical to turn it off if I G is very large

16 Operation of the SC Operation with the Ideal SC Duty cycle control of AC AC F t G OAD I GATE

17 Operation of the SC Operation with the Ideal SC Duty cycle control of AC F OAD G I GATE OAD I GATE

18 Operation of the SC Operation with the Ideal SC Duty cycle control of AC AC F t G OAD I GATE

19 Operation of the SC Operation with the Ideal SC Duty cycle control of AC F OAD G I GATE OAD I GATE

20 Operation of the SC Operation with the actual SC I G G A C F Δ F G I G =0 B I H BF0 F

21 Operation of the SC Operation with the actual SC I G G A C F G B I H F BF0 I G4 >I G3 >I G2 >I G1 =0

22 Operation of the SC Operation with the actual SC CC CC Δ F I G =0 F BG I H CC BGF0 F G Still two stable equilibrium points and one unstable point

23 Operation of the SC Operation with the actual SC CC CC F G B I H CC F I G4 >I G3 >I G2 >I G1 =0 BGF0 To turn on, must make I G large enough to have single intersection point

24 SC Terminology CC CC G F I I G =0 B I H F BGF0 I H is the holding current I is the latching current (current immediately after turn-on) BGF0 is the forward break-over voltage B is the reverse break-down voltage I GT is the gate trigger current GT is the gate trigger voltage

25 SC Terminology CC Issues and Observations CC F I G =0 I B I H F G BGF0 Trigger parameters ( GT and I GT ) highly temperature dependent Want gate sensitive but not too sensitive (to avoid undesired triggering) SCs can switch very large currents but power dissipation is large Heat sinks widely used to manage power Trigger parameters affected by both environment and application Trigger parameters generally dependent upon F Exceeding B will usually destroy the device Exceeding BGF0 will destroy some devices ack of electronic turn-off unattractive in some applications Can be used in alarm circuits to attain forced reset Maximum 50% duty cycle in AC applications is often not attractive

26 Thyristors The good SCs Triacs The bad Parasitic Device that can destroy integrated circuits

27 imitations of the SC A I G G C F I G =0 G I H BGF0 F 1. Only conducts in one direction 2. Can t easily turn off (though not major problem in AC switching) I G =I G1 >0 I H F BGF1

28 Operation of the SC Performance imitations with the SC Assume CC is an AC signal (often 110) and G is static CC F AC t G CC oad ine CC F CC SC is always off

29 Operation of the SC Performance imitations with the SC Assume CC is an AC signal (often 110) and G is static CC F AC t G CC oad ine CC F CC SC is ON about 50% of the time

30 Operation of the SC CC Performance imitations with the SC Assume CC is an AC signal (often 110) and G is static F AC CC oad ine t G CC BGF0 F CC SC is ON less than 50% of the time (duty cycle depends upon G ) Often use electronic circuit to generate G

31 Alarm Application eset Switch (NC) S 1 Buzzer 6 DUT 1 2 S 2 NC Foil/ Widow Switch

32 Bi-directional switching MT 1 G 2 G 1 MT 2 Use two cross-coupled SCs imitations Size and cost overhead with this solution Inconvenient triggering since G 1 and G 2 WT different terminals

33 Bi-directional switching with the Triac MT 2 MT 2 n p n G n p n G MT 1 MT 1 Has two cross-coupled SCs! Manufactured by diffusions Single Gate Control

34 The Triac n Q4 MT 2 Q2 MT 2 G G I G Can define two cross-coupled transistor pairs in each side I C3 Q 3 G I B4 Q 4 Q 2 I B3 2 I C4 MT 2 I G3 MT 1 MT2 I G1 MT1 I C2 I B1 I B2 Q 1 Model for Quadrants 1 and 4 (n-diffusion for gate not shown) I C1 nn Q3 Q1 MT 1 As for SC, both circuits have regenerative feedback G MT 1 Can turn ON in either direction with either positive or negative current Defines 4 quadrants (in MT21 - G-MT1 plane) for operation > >0 Quadrant 1 MT2 MT1 G-MT1 > <0 Quadrant 2 MT2 MT1 G-MT1 < <0 Quadrant 3 MT2 MT1 G-MT1 < >0 Quadrant 4 MT2 MT1 G-MT1 Usually use only one G : MT for control p n p n Different voltage, duration strategies exist for triggering Can t have single G : MT control with two SCs

35 The ideal Triac The Triac MT 2 I G T - BGF I H I G =0 G GT1 MT 1 T BGF Consider the basic Triac circuit AC I G =I G1 <0 or I G =I G1 >0 T - BGF I H BGF1 BGF T GT1

36 Assume ideal Triac The Basic Triac Circuit AC AC oad ine: CC = IT +T T - BGF - AC I H I G =0 AC BGF T Analysis: AC = IT +T I = f, F GT1 GT1 AC The solution of these two equations is at the intersection of the load line and the device characteristics AC Two stable operating points for both positive and negative AC - BGF I G =0 - AC I H AC BGF T AC

37 Assume ideal Triac The Basic Triac Circuit AC AC oad ine: CC = IT +T - BGF - AC I H BGF1 I G =I G1 <0 or I G =I G1 >0 AC BGF T Analysis: AC = IT +T I = f, F GT2 GT1 T AC Single solution for both positive and negative AC AC Thus this state turns on the Triac for any input - BGF I G =I G1 <0 or I G =I G1 >0 - AC I H BGF1 AC BGF T AC

38 Assume ideal Triac The Basic Triac Circuit AC AC T GT1 - AC BGF1 AC T AC

39 The Actual Triac MT 2 G MT 1 T I G4 >I G3 >I G2 >I G1 =0

40 The Actual Triac in Basic Circuit AC AC Δ F T I G =0 BG - AC I HF T GT1 I H AC BGF0 AC Two stable operating points I G =0 State

41 The Actual Triac in Basic Circuit AC T GT1 AC AC - AC AC I G4 >I G3 >I G2 >I G1 =0 F - AC AC I G4 >I G3 >I G2 >I G1 =0 F AC AC Can turn on for either positive or negative AC with single gate signal

42 Phase controlled bidirectional switching with Triacs AC t OAD I GATE OAD I GATE OAD I GATE

43 Quadrants of Operation Defined in M21 - GT1 plane (not in the - M21 plane) I G MT 2 M21 M21 G GT1 MT 1 Quadrant 2 Quadrant 1 GT1 M21 I G4 >I G3 >I G2 >I G1 =0 Quadrant 3 Quadrant 4 But for any specific circuit, can map quadrants from the M21 - GT1 plane to - M21 plane

44 Identification of Quadrants of Operation in - M21 plane M21 MT 2 I G M21 Quadrant 2 Quadrant 1 G GT1 MT 1 GT1 Quadrant 3 Quadrant 4

45 Identification of Quadrants of Operation in - M21 plane M21 MT 2 I G M21 Quadrant 2 Quadrant 1 G GT1 MT 1 GT1 Quadrant 3 Quadrant 4 Curves may not be symmetric between Q 1 and Q 3 in the - M21 plane Turn on current may be large and variable in Q 4 (of the M21 - GT1 ) Generally avoid operation in Q 4 (of the M21 - GT1 plane) Most common to operate in Q2-Q3 quadrants or Q1-Q3 quadrants (of the M21 - GT1 plane)

46 Quadrants of Operation Defined in M21 - GT1 plane (not in the - M21 plane) I G MT 2 M21 M21 G GT1 MT 1 Quadrant 2 Quadrant 1 GT1 M21 I G4 >I G3 >I G2 >I G1 =0 Quadrant 3 Quadrant 4 But for any specific circuit, can map quadrants from the M21 - GT1 plane to - M21 plane

47 Identification of Quadrants of Operation in - M21 plane M21 MT 2 I G M21 Quadrant 2 Quadrant 1 G GT1 MT 1 GT1 Quadrant 3 Quadrant 4

48 Identification of Quadrants of Operation in - M21 plane M21 MT 2 I G M21 Quadrant 2 Quadrant 1 G GT1 MT 1 GT1 Quadrant 3 Quadrant 4 Curves may not be symmetric between Q 1 and Q 3 in the - M21 plane Turn on current may be large and variable in Q 4 (of the M21 - GT1 ) Generally avoid operation in Q 4 (of the M21 - GT1 plane) Most common to operate in Q2-Q3 quadrants or Q1-Q3 quadrants (of the M21 - GT1 plane)

49 Some Basic Triac Application Circuits Quadrant 2 M21 Quadrant 1 GT1 Quadrant 3 Quadrant 4 AC AC T T MT 1 MT 1 GG GG ( GG often from logic/control circuit) ( GG often from logic/control circuit) Quad 1 : Quad 4 Quad 2 : Quad 3 (not attractive because of Quad 4)

If AC is the standard 120AC line voltage, where do we get the dc power

50 Some Basic Triac Application Circuits AC Quadrant 2 M21 Quadrant 1 GT1 Quadrant 3 Quadrant 4 MT 1 T Quad 2 : Quad 3 GG imitations? If AC is the standard 120AC line voltage, where do we get the dc power supply? OUT 10K C FITE 1K 120AC Direct digital control of trigger voltage/current with dedicated IC

51 M21 Some Basic Triac Application Circuits Quadrant 2 Quadrant 1 GT1 AC Quadrant 3 Quadrant 4 AC AC T T MT 1 MT 1 T MT 1 Quad 1 : Quad 3 Quad 1 : Quad 3 Quad 1 : Quad 3

52 Some Basic Triac Application Circuits M21 Quadrant 2 Quadrant 1 GT1 AC Quadrant 3 Quadrant 4 T MT 1 Quad 1/ Quad 2 : Quad 3/Quad 4 Not real popular

53 End of ecture 26

EE 330 Lecture 30. Thyristors. SCR Basic circuits and limitations Triacs Other thyristor types

EE 330 Lecture 30. Thyristors. SCR Basic circuits and limitations Triacs Other thyristor types EE 330 ecture 30 Thyristors SC Basic circuits and limitations Triacs Other thyristor types Exam 3 Friday April 13 eview from ast ecture The Thyristor A bipolar device in CMOS Processes Consider a Bulk-CMOS