UC3845 데이터 시트보기 (PDF) - ON Semiconductor
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UC3845 Datasheet PDF : 16 Pages
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UC3844, UC3845, UC2844, UC2845
VCC
7(12)
Vin
5.0Vref
+ +−
−
+− +
−
T
S
−
+
Q
R
Comp/Latch
7(11)
Rg
Q1
6(10)
5(8)
3(5)
RS
Series gate resistor Rg will damp any high frequency parasitic oscillations
caused by the MOSFET input capacitance and any series wiring inductance
in the gate−source circuit.
Figure 25. MOSFET Parasitic Oscillations
IB
Vin
+
0
Base
−
Charge
Removal
C1
Q1
6(1)
5(8)
3(5)
RS
The totem−pole output can furnish negative base current for enhanced
transistor turn−off, with the addition of capacitor C1.
Figure 26. Bipolar Transistor Drive
8(14)
R
Bias
R
5.0Vref
+−
+ +−
−
T
S
−+ RQ
Comp/Latch
7(12)
+
−
VCC
Vin
Isolation
Boundary
7(11)
6(10)
5(8)
R
Q1
ÉÉ É +
0
ÉÉ ÉÉ −
VGS Waveforms
+
0
−
50% DC
25% DC
Ipk =
V(pin 1) − 1.4
3 RS
NP
NS
3(5) C
RS
NS
Np
MCR
2N
101
3905
4(7)
2(3)
1(1)
2N
3903
OSC
+
+−
EA
1.0mA
2R
R
5(9)
The MCR101 SCR must be selected for a holding of less than 0.5 mA at TA(min).
The simple two transistor circuit can be used in place of the SCR as shown. All
resistors are 10 k.
Figure 27. Isolated MOSFET Drive
Figure 28. Latched Shutdown
From VO
Ri
Rd CI
Rf ≥ 8.8 k
2.5V +
2(3)
+−
1.0mA
Rf
EA
2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing any current−mode topology except
for boost and flyback converters operating with continuous inductor current.
From VO
Rp Ri
Cp
Rd CI
2.5V +
2(3)
+
1.0mA
Rf
−
EA
2R
R
1(1)
5(9)
Error Amp compensation circuit for stabilizing current−mode boost and flyback
topologies operating with continuous inductor current.
Figure 29. Error Amplifier Compensation
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