TC620/TC621
4.2
Temperature Controlled Fan
4.0
4.1
TYPICAL APPLICATIONS
In the application in Figure 4-2, a high and a low tem-
perature is selected by two R and R . The TC620
Dual Speed Temperature Control
L
H
monitors the ambient temperature and turns the FET
switch on when the temperature exceeds the HIGH
TEMP set point. The fan remains on until the tempera-
ture decreases to the LOW TEMP set point. This
provides the hysteresis. In this application, the fan
turns on only when required.
In Figure 4-1, the Dual Speed Temperature Control
uses a TC620 and a TC4469 quad driver. Two of the
drivers of the TC4469 are configured in a simple oscil-
lator. When the temperature is below the LOW TEMP
set point, the output of the driver is OFF. When the tem-
perature exceeds the LOW TEMP set point, the
TC4469 gates the oscillator signal to the outputs of the
driver. This square wave signal modulates the remain-
ing outputs and drives the motor at a low speed. If this
speed cannot keep the temperature below the HIGH
TEMP set point, then the driver turns on continuously
which increases the fan speed to high. The TC620 will
monitor the temperature and only allow the fan to oper-
ate when needed and at the required speed to maintain
the desired temperature. A higher power option can be
designed by adding a resistor and a power MOSFET.
The TC621 uses an external thermistor to monitor the
ambient temperature. This adds one part, but allows
more flexibility with the location of the temperature
sensor.
FIGURE 4-1:
DUAL SPEED TEMPERATURE CONTROL
+12V
V
MOTOR
0.1µF
10µF
1M
Fan Motor
8
Low Temp
14
˚
30 C
1N4148
1N4148
100k
13
4
High
Limit
2
3
1
5
6
7
2
1
3
5
8
MOSFET
50Ω
TC620
50pF
6
High Temp.
TC4469
˚
9
50 C
Low
Limit
Higher Power Option
Fan Motor
10
11
12
4
Temperature Scale
˚
˚
0 C – 30 C (Fan Off)
7
1µF
10k
˚
˚
30 C – 50 C (Fan Low)
˚
50 C – UP (Fan High)
FIGURE 4-2:
TEMPERATURE CONTROLLED FAN
+12V
+12V
Thermistor
(NTC)
Fan Motor
8
Fan Motor
MTP3055E
Low Temp.
1
2
3
4
High
Temp.
1
2
3
4
8
7
6
5
R
L
7
TC620
TC621
R
H
6
MTP3055E
Low Temp.
R
H
R
L
5
High Temp.
2002 Microchip Technology Inc.
DS21439B-page 7
MICROCHIP [ MICROCHIP ]
