TC620/TC621
4.0
4.1
TYPICAL APPLICATIONS
Dual Speed Temperature Control
4.2
Temperature Controlled Fan
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.
In the application in Figure 4-2, a high and a low tem-
perature is selected by two R
L
and R
H
. The TC620
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.
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
0.1µF
10µF
14
2
1
3
5
8
13
4
6
9
10
11
12
100k
50
Ω
50pF
Higher Power Option
MOSFET
VMOTOR
1M
Low Temp
30˚C
2
3
High Temp. 1
5
50˚C
8
High 6 1N4148
Limit
Fan Motor
TC620
Low 7
Limit
4
1µF
1N4148
TC4469
Temperature Scale
0˚C – 30˚ C (Fan Off)
30˚C – 50˚ C (Fan Low)
50˚C – UP (Fan High)
10k
7
Fan Motor
FIGURE 4-2:
TEMPERATURE CONTROLLED FAN
+12V
Thermistor
(NTC)
+12V
Low Temp. 1
R
L
2
3
R
H
4
High Temp.
8
Fan Motor
TC620
7
6
5
MTP3055E
High
Temp.
R
H
Low Temp. R
L
1
2
3
4
8
Fan Motor
TC621
7
6
5
MTP3055E
2002 Microchip Technology Inc.
DS21439B-page 7
©
MICROCHIP [ MICROCHIP TECHNOLOGY ]
