SG1844 查看數據表（PDF） - Microsemi Corporation
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SG1844 Datasheet PDF : 12 Pages
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PRODUCT DATABOOK 1996/1997
SG1844/SG1845 Series
CURRENT-MODE PWM CONTROLLER
PRODUCTION DATA SHEET
TYPICAL APPLICATION CIRCUITS
Pin numbers referenced are for 8-pin package and pin numbers in parenthesis are for 14-pin package.
VCC
VIN
VCC
VIN
7 (12)
7 (12)
7 (11)
Q1
6 (10)
SG1844/45
5 (8)
R
3 (5)
C
RS
IPK
IPK(MAX)
=
1.0V
RS
7 (11)
R1
Q1
SG1844/45 6 (10)
5 (8)
RS
3 (5)
FIGURE 14. — CURRENT SENSE SPIKE SUPPRESSION
The RC low-pass filter will eliminate the leading edge current spike
caused by parasitics of Power MOSFET.
FIGURE 15. — MOSFET PARASITIC OSCILLATIONS
A resistor (R1) in series with the MOSFET gate reduce overshoot and
ringing caused by the MOSFET input capacitance and any inductance
in series with the gate drive. (Note: It is very important to have a
low inductance ground path to insure correct operation of the I.C.
This can be done by making the ground paths as short and as wide
as possible.)
IB
VC +
» R2
VC1
» R1||R2 _
VC
SG1844/45
VC1
7 (11)
R2
C1
6 (10)
R1
VIN
Q1
5 (8)
VCC
7 (12)
Isolation
Boundary
7 (11)
6 (10)
SG1844/45
5 (8)
R
3 (5)
C
RS
VIN
Q1
VGS Waveforms
+
0_
50% DC
+
0_
NS
NP
25% DC
3 (5)
RS
FIGURE 16. — BIPOLAR TRANSISTOR DRIVE
The 1844/45 output stage can provide negative base current to
remove base charge of power transistor (Q1) for faster turn off. This
is accomplished by adding a capacitor (C ) in parallel with a resistor
1
(R1). The resistor (R1) is to limit the base current during turn on.
V (PIN 1) - 1.4
IPK =
3RS
NP
NS
FIGURE 17. — ISOLATED MOSFET DRIVE
Current transformers can be used where isolation is required
between PWM and Primary ground. A drive transformer is then
necessary to interface the PWM output with the MOSFET.
Copyright © 2000
Rev. 1.4 4/00
11
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