TMP12

REV. 0

–12–

Power FETs are popular for handling a variety of high current

dc loads. Figure 24 shows the TMP12 driving a P-channel

MOSFET transistor for a simple heater circuit. When the out-

put transistor turns on, the gate of the MOSFET is pulled down

to approximately 0.6 V, turning it on. For most MOSFETs a

gate-to-source voltage or Vgs on the order of -2 V to -5 V is suf-

ficient to turn the device on. Figure 25 shows a similar circuit

for turning on an N-channel MOSFET, except that now the

gate to source voltage is positive. For this reason an external

transistor must be used as an inverter so that the MOSFET will

turn on when the trip point pulls down.

NC

IRFR9024

OR EQUIV

HEATING

ELEMENT

2.4k

Ω (12V)

1.2k

Ω (6V)

5%

V+

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

+5V

TMP12

NC = NO CONNECT

Figure 24. Driving a P-Channel MOSFET

IRF130

NC

2N1711

HEATING

ELEMENT

V+

4.7k

Ω

4.7k

Ω

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

+5V

TMP12

Figure 25. Driving an N-Channel MOSFET

Isolated Gate Bipolar Transistors (IGBTs) combine many of the

benefits of power MOSFETs with bipolar transistors and are

used for a variety of high power applications. Because IGBTs

have a gate similar to MOSFETs, turning on and off the devices

is relatively simple as shown in Figure 26. The turn on voltage

for the IGBT shown (IRGB40S) is between 3.0 and 5.5 volts.

This part has a continuous collector current rating of 50 A and a

maximum collector to emitter voltage of 600 V, enabling it to

work in very demanding applications.

IRGBC40S

NC

2N1711

V+

4.7k

Ω

4.7k

Ω

MOTOR

CONTROL

+5V

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

TMP12

NC = NO CONNECT

Figure 26. Driving an IGBT

The last class of high power devices discussed here are Thyristors,

which include SCRs and Triacs. Triacs are a useful alternative to

relays for switching ac line voltages. The 2N6073A shown in Fig-

ure 27 is rated to handle 4 A (rms). The opto-isolated MOC3021

Triac shown features excellent electrical isolation from the noisy ac

line and complete control over the high power Triac with only a

few additional components.

NC

V+ = 5V

300

Ω

150

Ω

MOC3011

1

2

34

5

6

LOAD

AC

2N6073A

NC = NO CONNECT

TEMPERATURE

SENSOR &

VOLTAGE

REFERENCE

HYSTERESIS

GENERATOR

WINDOW

COMPARATOR

VPTAT

VREF

100

1

2

3

4

8

5

7

6

+5V

TMP12

Figure 27. Controlling the 2N6073A Triac