TC642 Просмотр технического описания (PDF) - Microchip Technology

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TC642

PWM Fan Speed Controller with FanSense™ Technology

Microchip Technology 

Some applications require the fan to be powered from

the negative 12V supply to keep motor noise out of the

positive voltage power supplies. As is shown in

Figure 5-8, zener diode D1 offsets the -12V power sup-

ply voltage, holding transistor Q1 off when VOUT is low.

VDD

TC642

When VOUT is high, the voltage at the anode of D1

increases by VOUT, causing Q1 to turn on. Operation is

otherwise consistent with the case of fan operation

from +12V.

VDD

VDD

Fan

Fan

Fan

RBASE

RBASE

VOUT

Q1

VOUT

Q1

VOUT

Q1

Q2

RSENSE

RSENSE

RSENSE

GND

a) Single Bipolar Transistor

GND

b) Darlington Transistor Pair

FIGURE 5-7:

Output Drive Transistor Circuit Topologies.

+5V

GND

c) N-Channel MOSFET

VDD

R2*

2.2 kΩ

VOUT

Fan

TC642

D1

12.0V

Zener

Q1*

GND

R4*

10 kΩ

R3*

2.2Ω

FIGURE 5-8:

-12V

*Note: Value depends on the specific application and is shown for example only.

Powering the Fan From a -12V Supply.

 2002 Microchip Technology Inc.

DS21444C-page 13

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