UC3842B, UC3843B, UC2842B, UC2843B, NCV3843BV
V
CC
7(12)
+
5.0V Ref
+
−
+
−
7(11)
C1
R
g
6(10)
S
Q
R
Comp/Latch
3(5)
R
S
5(8)
5(8)
6(10)
Q1
Q1
0
−
Base Charge
Removal
V
in
I
B
V
in
3(5)
R
S
Series gate resistor R
g
will damp any high frequency parasitic oscillations
caused by the MOSFET input capacitance and any series wiring inductance in
the gate−source circuit.
The totem pole output can furnish negative base current for enhanced
transistor turn−off, with the addition of capacitor C
1
.
Figure 28. MOSFET Parasitic Oscillations
Figure 29. Bipolar Transistor Drive
V
CC
7(12)
Isolation
Boundary
5.0V Ref
+
−
+
−
7(11)
Q1
V
in
8(14)
R
Bias
R
Osc
4(7)
V
GS
Waveforms
+
0
−
6(10)
S
Q
R
5(8)
50% DC
V(Pin1)
*
1.4
3 RS
+
0
−
25% DC
NS
Np
MCR
101
2N
3905
2N
3903
2(3)
EA
R
+
1.0 mA
2R
1(1)
5(9)
Ipk
+
R
C
R
S
N
S
Comp/Latch
3(5)
N
P
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 30. Isolated MOSFET Drive
Figure 31. Latched Shutdown
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