参数资料
型号: TC649VUATR
元件分类: 运动控制电子
英文描述: BRUSHLESS DC MOTOR CONTROLLER, PDSO8
封装: PLASTIC, MSOP-8
文件页数: 6/28页
文件大小: 478K
代理商: TC649VUATR
TC649
DS21449C-page 14
2002 Microchip Technology Inc.
A base-current limiting resistor is required with bipolar
transistors (Figure 5-7). The correct value for this
resistor can be determined as follows:
VOH
= VRSENSE + VBE(SAT) + VRBASE
VRSENSE
= IFAN x RSENSE
VRBASE
= RBASE x IBASE
IBASE
= IFAN / hFE
VOH is specified as 80% of VDD in Section 1.0,
“Electrical Characteristics”; VBE(SAT) is given in the cho-
sen transistor data sheet. It is now possible to solve for
RBASE.
EQUATION
Some applications benefit from the fan being powered
from a negative supply to keep motor noise out of the
positive supply rails. This can be accomplished as
shown in Figure 5-8, with zener diode D1 offsetting the
-12V power supply voltage, holding transistor Q1 off
when VOUT is low. When VOUT is high, the voltage at
the anode of D1 increases by VOUT, causing Q1 to turn
on. Operation is otherwise the same as in the case of
fan operation from +12V.
FIGURE 5-7:
Circuit For Determining
RBASE.
FIGURE 5-8:
Powering the Fan from a -12V Supply.
RBASE =
VOH - VBE(SAT) - VRSENSE
IBASE
Q1
GND
VDD
RSENSE
RBASE
VOH = 80% VDD
+ V
RBASE
VBE
(SAT)
+
VR
SENSE
Fan
+
GND
+5V
-12V
Q1*
VDD
VOUT
TC649
FAN
R2*
2.2 k
R3*
2.2
R4*
10 k
D1
12.0V
Zener
Note: * Value depends on the specific application and is shown for example only.
See Section 5.0, "Typical Applications", for more details.
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