EE 330 Lecture 23 - Iowa State University

EE 330 Lecture 23

•Thyristor Wrap-up •Area Comparison between MOS and Bipolar Circuits •Operating Point Characterization

Bi-directional switching with the Triac

G

MT2

p

pn

n

n

MT1

nn

• Has two cross-coupled SCRs !

• Manufactured by diffusions

• Single Gate Control

MT1

MT2

G

Review from Last Lecture

The Basic Triac Circuit Assume ideal Triac

IT

VTR

IG=0

IH

BGF V

BGF -V

AC

L

VR

AC V

AC -V

AC

L

VR

−

CC T L TRV = I R +VLoad Line:

The solution of these two equations is at the intersection of the load line and the device characteristics

Analysis: AC T L TRV = I R +V

( ),FI TR GT1I = f V V

IT

VTR

IG=0

IH

BGF V

BGF -V

AC

L

VR

AC V

AC -V

AC

L

VR

−

Two stable operating points for both positive and negative VAC

VAC

VGT1

RL

VTRIT

Review from Last Lecture

IT

VTR

IG4>IG3>IG2>IG1=0

MT1

MT2

G

The Actual Triac Review from Last Lecture

MT1

MT2

G

IT

VM21

VGT1

IGIT

VM21

IG4>IG3>IG2>IG1=0

VM21

VGT1

Quadrant 1Quadrant 2

Quadrant 3 Quadrant 4

Quadrants of Operation Defined in VM21-VGT1 plane (not in the IT-VM21 plane)

But for any specific circuit, can map quadrants from the VM21-VGT1 plane to IT-VM21 plane

MT1

MT2

G

IT

VM21

VGT1

IG

VM21

VGT1



Identification of Quadrants of Operation in IT -VM21 plane

MT1

MT2

G

IT

VM21

VGT1

IG

VM21

VGT1



Identification of Quadrants of Operation in IT-VM21 plane

Curves may not be symmetric between Q1 and Q3 in the IT-VM21 plane Turn on current may be large and variable in Q4 (of the VM21-VGT1 )

Generally avoid operation in Q4 (of the VM21-VGT1 plane)

Most common to operate in Q2-Q3 quadrants or Q1-Q3 quadrants (of the VM21-VGT1 plane)

Some Basic Triac Application Circuits

VAC

RL

VTRIT

MT1

VGG

VAC

RL

VTRIT

MT1

VGG

VM21

VGT1



Quad 1 : Quad 4

(not attractive because of Quad 4)

(VGG often from logic/control circuit) (VGG often from logic/control circuit)

Quad 2 : Quad 3

Some Basic Triac Application Circuits VAC

RL

VTRIT

MT1

VGG

VM21

VGT1



Quad 2 : Quad 3

Limitations ?

If VAC is the standard 120VAC line voltage, where do we get the dc power supply?

120VAC

1K

10KVOUT

CFILTER

Direct digital control of trigger voltage/current with dedicated IC


VAC

RL

VTRIT

MT1

VAC

RL

VTRIT

MT1

VAC

RL

VTRIT

MT1

Quad 1 : Quad 3

VM21

VGT1



Quad 1 : Quad 3 Quad 1 : Quad 3


VAC

RL

VTR

IT

MT1

VM21

VGT1



Quad 1/ Quad 2 : Quad 3/Quad 4

Not real popular

Thyristor Types

• SCR • Triac • Bidirectional Phase-controlled thyristors (BCT) • LASCR (Light activated SCR) • Gate Turn-off thyristors (GTO) • FET-controlled thyristors(FET-CTH) • MOS Turn-off thyristors (MTO) • MOS-controlled thyristors (MCT)

Some of the more major types:

Thyristor Applications

Thyristors are available for working at very low current levels in electronic circuits to moderate current levels such is in incandescent light dimmers to very high current levels

ITRIAC from under 1mA to 10000A

Applications most prevalent for moderate to high current thyristors

SCR, rated about 100 amperes, 1200 volts, 1/2 inch stud, photographed by C J Cowie. Uploaded on 4 April 2006.

Thanks to Prof. Ajjarapu for providing the following slides:

From ABB Web Site

Diameter = 140mm

1988 Paper


2008 Paper



Control Circuit

Thyristor

Stud- Mounted SCR 110 Amp RMS Rating

Stud Anode

Cathode Lead

Gate Lead (White)

Auxiliary Cathode Lead (Red) Extends cathode potential to the control circuit.


Cross-section of a BCT wafer showing the antiparallel arrangement of the A and B component thyristors. The arrows indicate the convention of forward blocking for A and B.


Thyristor Valve - 12 Pulse Converter ( 6.5Kv, 1568 Amp, Water cooled)


Thyristor Observations

Many different structures used to build thyristors Range from low power devices to extremely high power devices Often single-wafer solutions for high power applications Usually formed by diffusions Widely used throughout society but little visibility Applications somewhat restricted

Thyristors

The good

SCRs Triacs

The bad Parasitic Device that can destroy integrated circuits

The Thyristor

S G D GS DConsider a Bulk-CMOS Process

A bipolar device in CMOS Processes

If this parasitic SCR turns on, either circuit will latch up or destroy itself

Guard rings must be included to prevent latchup Design rules generally include provisions for guard rings

MOS and Bipolar Area Comparisions

How does the area required to realize a MOSFET compare to that required to realize a BJT?

Will consider a minimum-sized device in both processes

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55

Consider Initially the Emitter in the BJT surrounded by a base region

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From design rules (left to right) 4.3, 5.1, 5.4, 5.6, 5.5

3λ

4λ

2λ2λ

2λ

19λ

12λ

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23λ

2λ

Add n+ buried for collector

From design rule 1.2

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23λ

14λ 14λ

51λ

14λ 14λ

Add n-epi region from design rules 2.3 and 3.3

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3λ 2λ

23λ

14λ

51λ

14λ

4λ

Add contact to n-epi region from design rules 2.3 and 3.3

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14λ

61λ

14λ

4λ 6λ

12λ

2λ 2λ

NOT TO SCALE

Note: 26λ required Between p-base and isolation diffusion

19λ

But, there are some rather strict rules relating to the epi contact

from (left to right) rules 4.4, 5.4, 4.6

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26λ

71λ

6λ

12λ

2λ

2λ


Note: Not to vertical Scale

44λ

19λ

14λ

Consider a structure with a collector contact on both sides of epi

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26λ

71λ

6λ

12λ

2λ



44λ

4λ

19λ

26λ

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15

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71λ


44λ

75λ

48λ

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75λ

48λ

Bounding Area = 3600λ2

Major contributor to large size of BJT is the isolation diffusion which diffuses laterally a large distance beyond the drawn edges of the isolation mask

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16λ

13λ


Comparison with Area for n-channel MOSFET in Bulk CMOS

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14λ

12λ


Active Area = 6λ2

Minimum-Sized MOSFET

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75λ

48λ

MOSFET BJT

Area Comparison between BJT and MOSFET

• BJT Area = 3600 λ2

• n-channel MOSFET Area = 168 λ2 • Area Ratio = 21:1

Operating Point of Electronic Circuits Often interested in circuits where a small signal input is to be amplified The electrical port variables where the small signal goes to 0 is termed the Operating Point, the Bias Point, the Quiescent Point, or simply the Q-Point By setting the small signal to 0, it means replacing small voltage inputs with short circuits and small current inputs with open circuits When analyzing small-signal amplifiers, it is necessary to obtain the Q-point When designing small-signal amplifiers, establishing of the desired Q-point is termed “biasing” Capacitors become open circuits (and inductors short circuits) when determining Q-points Simplified dc models of the MOSFET (saturation region) or BJT (forward active region) are usually adequate for determining the Q-point in practical amplifier circuits

End of Lecture 23

EE 330 Lecture 23 - Iowa State University

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