LM3911 Temperature Controller
June 1994
LM3911 Temperature Controller
General Description
The LM3911 is a highly accurate temperature measurement
and or control system for use over a
b
25 C to
a
85 C tem-
perature range Fabricated on a single monolithic chip it
includes a temperature sensor a stable voltage reference
and an operational amplifier
The output voltage of the LM3911 is directly proportional to
temperature in degrees Kelvin at 10 mV K Using the inter-
nal op amp with external resistors any temperature scale
factor is easily obtained By connecting the op amp as a
comparator the output will switch as the temperature trans-
verses the set-point making the device useful as an on-off
temperature controller
An active shunt regulator is connected across the power
leads of the LM3911 to provide a stable 6 8V voltage refer-
ence for the sensing system This allows the use of any
power supply voltage with suitable external resistors
The input bias current is low and relatively constant with
temperature ensuring high accuracy when high source im-
pedance is used Further the output collector can be re-
turned to a voltage higher than 6 8V allowing the LM3911 to
drive lamps and relays up to a 35V supply
The LM3911 uses the difference in emitter-base voltage of
transistors operating at different current densities as the ba-
sic temperature sensitive element Since this output de-
pends only on transistor matching the same reliability and
stability as present op amps can be expected
The LM3911 is available in two package styles a metal can
TO-46 and an 8-lead epoxy mini-DIP In the epoxy package
all electrical connections are made on one side of the de-
vice allowing the other 4 leads to be used for attaching the
LM3911 to the temperature souce The LM3911 is rated for
operation over a
b
25 C to
a
85 C temperature range
Features
Y
Y
Y
Y
Y
Y
Y
Uncalibrated accuracy
g
10 C
Internal op amp with frequency compensation
Linear output of 10 mV K (10 mV C)
Can be calibrated in degrees Kelvin Celsius or
Fahrenheit
Output can drive loads up to 35V
Internal stable voltage reference
Low cost
Block Diagram
Typical Applications
Ground Referred
Centigrade Thermometer
Basic Temperature Controller
Proportioning Temperature
Controller
Output goes negative on
temperature increase
Trims out initial zener tolerance
Set output to read C
R
S
e
(V
a
b
6 8V) kX
Note 1
C1 determines proportioning frequency f
Note 2
R10
e
TL H 5701 鈥?1
1
2R4 C1
l
V
a
l
a
l
V
b
l
b
7V
0 0015A
Note 3
Either V
b
or V
a
can be ground
C
1995 National Semiconductor Corporation
TL H 5701
RRD-B30M115 Printed in U S A
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