UC3842A, UC3843A, UC2842A, UC2843A
V
CC
V
V
in
CC
V
in
7(12)
7(12)
+
5.0V
+
ref
−
5.0V
+
ref
−
+
−
+
−
+
−
+
−
+
7(11)
6(10)
5(8)
7(11)
6(10)
5(8)
R
g
−
Q1
−
Q1
S
R
S
R
Q
−
Q
−
+
+
Comp/Latch
R
Comp/Latch
3(5)
3(5)
R
S
C
R
S
Series gate resistor R will damp any high frequency parasitic oscillations
g
caused by the MOSFET input capacitance and any series wiring inductance
in the gate−source circuit.
The addition of the RC filter will eliminate instability caused by the leading
edge spike on the current waveform.
Figure 27. Current Waveform Spike Suppression
Figure 28. MOSFET Parasitic Oscillations
I
B
V
in
+
V
V
in
CC
7(12)
0
Base
Charge
Removal
+
Isolation
Boundary
−
5.0V
ref
−
+
C
1
−
+
V
Waveforms
GS
−
Q1
+
7(11)
6(1)
5(8)
Q1
+
0
−
+
0
−
−
6(1)
5(8)
50% DC
25% DC
S
R
V
− 1.4
N
N
(pin 1)
P
Q
−
I
=
pk
+
S
3 R
S
R
Comp/Latch
3(5)
R
S
3(5)
C
N
S
R
S
N
p
The totem−pole output can furnish negative base current for enhanced
transistor turn−off, with the addition of capacitor C .
1
Figure 29. Bipolar Transistor Drive
Figure 30. Isolated MOSFET Drive
From V
O
2.5V
+
R
1.0mA
2R
i
2(3)
+
−
8(14)
4(7)
R
R
EA
R
d
C
I
Bias
R
f
R
1(1)
Osc
5(9)
+
1.0mA
2R
Error Amp compensation circuit for stabilizing any current−mode topology except
for boost and flyback converters operating with continuous inductor current.
+
−
EA
2(3)
1(1)
R
From V
O
2.5V
+
1.0mA
2R
R
p
2N
3905
2(3)
5(9)
MCR
101
R
i
+
−
EA
2N
3903
C
I
R
R
f
d
R
C
p
1(1)
5(9)
The MCR101 SCR must be selected for a holding of less than 0.5 mA at T
The simple two transistor circuit can be used in place of the SCR as shown. All
resistors are 10 k.
.
A(min)
Error Amp compensation circuit for stabilizing current−mode boost and flyback
topologies operating with continuous inductor current.
Figure 31. Latched Shutdown
Figure 32. Error Amplifier Compensation
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