UC3844B, UC3845B, UC2844B, UC2845B
V
CC
7(12)
Isolation
Boundary
5.0V Ref
+
−
+
−
T
S
Q
R
Comp/Latch
3(5)
C
R
R
S
N
S
7(11)
Q1
+
0
−
6(10)
5(8)
50% DC
V
GS
Waveforms
+
0
−
25% DC
V
in
I
pk
=
V
(Pin 1)
− 1.4
3 R
S
NS
Np
N
P
Figure 27. Isolated MOSFET Drive
8(14)
R
Bias
R
Osc
4(7)
+
1.0 mA
2(3)
2R
R
EA
1(1)
MCR
101
2N
3905
2N
3903
5(9)
The MCR101 SCR must be selected for a holding of < 0.5 mA @ T
A(min)
. The
simple two transistor circuit can be used in place of the SCR as shown. All
resistors are 10 k.
Figure 28. Latched Shutdown
From V
O
R
i
C
f
2.5V
+
1.0mA
2(3)
R
f
1(1)
EA
2R
R
From V
O
R
p
C
p
2.5V
+
1.0mA 2R
EA
R
R
i
R
d
C
f
2(3)
R
f
1(1)
R
d
R
f
≥
8.8k
5(9)
5(9)
Error Amp compensation circuit for stabilizing any current mode topology except
for boost and flyback converters operating with continuous inductor current.
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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