TMP01

REV. C

–11–

The last class of high power devices discussed here are Thyris-

tors, which includes SCRs and Triacs. Triacs are a useful alter-

native to relays for switching ac line voltages. The 2N6073A

shown in Figure 15e is rated to handle 4A (rms). The

optoisolated MOC3011. Triac shown features excellent electri-

cal isolation from the noisy ac line and complete control over

the high power Triac with only a few additional components.

NC = NO CONNECT

NC

NC

V+ = 5V

R1

R2

R3

300

Ω

150

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

MOC3011

1

2

34

5

6

LOAD

AC

2N6073A

Figure 15e. Controlling the 2N6073A Triac

High Current Switching

As mentioned above, internal dissipation due to large loads on

the TMP01 outputs will cause some temperature error due to

self-heating. External transistors remove the load from the

TMP01, so that virtually no power is dissipated in the internal

transistors and no self-heating occurs. Figure 16 shows a few ex-

amples using external transistors. The simplest case, using a

single transistor on the output to invert the output signal is

shown in Figure 16a. When the open-collector of the TMP01

turns “ON” and pulls the output down, the external transistor

Q1’s base will be pulled low, turning off the transistor. Another

transistor can be added to reinvert the signal as shown in Figure

16b. Now, when the output of the TMP01 is pulled down, the

first transistor, Q1, turns off and its collector goes high, which

turns Q2 on, pulling its collector low. Thus, the output taken

from the collector of Q2 is identical to the output of the

TMP01. By picking a transistor that can accommodate large

amounts of current, many high power devices can be switched.

2N1711

V+

R1

R2

R3

4.7k

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

I

C

Q1

Figure 16a. An External Resistor Minimizes Self-Heating

Q1

Q2

2N1711

V+

R1

R2

R3

4.7k

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

I

C

4.7k

Ω

2N1711

Figure 16b. Second Transistor Maintains Polarity of

TMP01 Output

An example of a higher power transistor is a standard Darling-

ton configuration as shown in Figure 16c. The part chosen,

TIP-110, can handle 2A continuous which is more than enough

to control many high power relays. In fact the Darlington itself

can be used as the switch, similar to MOSFETs and IGBTs.

MOTOR

SWITCH

RELAY

+12V

2N1711

V+

R1

R2

R3

4.7k

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

1

2

3

4

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

TMP01

VPTAT

VREF

7

8

5

6

I

C

4.7k

Ω

TIP-110

Figure 16c. Darlington Transistor Can Handle Large Currents