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TMP01GBC

Low Power, Programmable Temperature Controller

Analog Devices 

TMP01

Switching Loads With The Open-Collector Outputs

In many temperature sensing and control applications some type

of switching is required. Whether it be to turn on a heater when

the temperature goes below a minimum value or to turn off a

motor that is overheating, the open-collector outputs Over and

Under can be used. For the majority of applications, the switches

used need to handle large currents on the order of 1 amp and

above. Because the TMP01 is accurately measuring tempera-

ture, the open-collector outputs should handle less than 20 mA

of current to minimize self-heating. Clearly, the Over-temp and

Under-temp outputs should not drive the equipment directly.

Instead, an external switching device is required to handle the

large currents. Some examples of these are relays, power

MOSFETs, thyristors, IGBTs, and Darlingtons.

Figure 15 shows a variety of circuits where the TMP01 controls

a switch. The main consideration in these circuits, such as the

relay in Figure 15a, is the current required to activate the

switch.

+12V

1

VREF

TEMPERATURE

SENSOR &

VOLTAGE

VPTAT

8

IN4001

R1

REFERENCE

OR EQUIV.

MOTOR

SHUTDOWN

2

7

R2

WINDOW

COMPARATOR

3

6

2604-12-311

COTO

R3

4

HYSTERESIS

5

GENERATOR

TMP01

Figure 15a. Reed Relay Drive

It is important to check the particular relay you choose to ensure

that the current needed to activate the coil does not exceed the

TMP01’s recommended output current of 20 mA. This is easily

determined by dividing the relay coil voltage by the specified

coil resistance. Keep in mind that the inductance of the relay

will create large voltage spikes that can damage the TMP01 out-

put unless protected by a commutation diode across the coil, as

shown. The relay shown has a contact rating of 10 watts maxi-

mum. If a relay capable of handling more power is desired, the

larger contacts will probably require a commensurately larger

coil, with lower coil resistance and thus higher trigger current.

As the contact power handling capability increases, so does the

current needed for the coil. In some cases an external driving

transistor should be used to remove the current load on the

TMP01 as explained in the next section.

Power FETs are popular for handling a variety of high current

DC loads. Figure 15b shows the TMP01 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 15c shows a similar circuit

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

to source voltage is positive. Because of this reason an external

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

turn on when the “Under Temp” output pulls down.

R1

VREF

1

TEMPERATURE

SENSOR &

VOLTAGE

VPTAT

8

V+

REFERENCE

2.4kΩ (12V)

1.2kΩ (6V)

2

7 NC 5%

IRFR9024

R2

WINDOW

OR EQUIV.

COMPARATOR

3

6

R3

HEATING

ELEMENT

4

HYSTERESIS

5 NC

GENERATOR

TMP01

NC = NO CONNECT

Figure 15b. Driving a P-Channel MOSFET

VREF

1

TEMPERATURE

SENSOR &

VPTAT

VOLTAGE

8

V+

R1

REFERENCE

4.7kΩ 4.7kΩ

2

7 NC

HEATING

ELEMENT

R2

WINDOW

COMPARATOR

3

6

2N1711

IRF130

R3

4

HYSTERESIS

5 NC

GENERATOR

TMP01

NC = NO CONNECT

Figure 15c. Driving a N-Channel MOSFET

Isolated Gate Bipolar Transistors (IGBT) 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 15d. The turn on voltage

for the IGBT shown (IRGBC40S) 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.

VREF

1

TEMPERATURE

SENSOR &

VOLTAGE

VPTAT

8

V+

R1

REFERENCE

4.7kΩ 4.7kΩ

2

7 NC

R2

WINDOW

COMPARATOR

3

6

2N1711

R3

4

HYSTERESIS

5 NC

GENERATOR

TMP01

NC = NO CONNECT

Figure 15d. Driving an IGBT

MOTOR

CONTROL

IRGBC40S

–10–

REV. C

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