NCP1200
Improving the Output Drive Capability
The NCP1200 features an asymmetrical output stage used
to soften the EMI signature. Figure 25 depicts the way the
driver is internally made:
V
CC
Q
1
2
3
NCP1200
4
8
7
6
5
2N2907
Rd
To Gate
2N2222
2
40
7
1
12
5
Q\
3
Figure 26. Improving Both Turn−On and
Turn−Off Times
1
2
3
4
NCP1200
8
7
6
5
2N2907
1N4148
To Gate
Figure 25. The higher ON resistor slows down
the MOSFET while the lower OFF resistor
ensures fast turn−off.
In some cases, it is possible to expand the output drive
capability by adding either one or two bipolar transistors.
Figures 26, 27, and 28 give solutions whether you need to
improve the turn−on time only, the turn−off time or both. Rd
is there to damp any overshoot resulting from long copper
traces. It can be omitted with short connections. Results
showed a rise fall time improvement by 5X with standard
2N2222/2N2907:
Figure 27. Improving Turn−Off Time Only
1
2
3
4
NCP1200
8
7
6
5
1N4148
To Gate
2N2222
Figure 28. Improving Turn−On Time Only
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