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參數資料
| 型號： | AN-937 |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Gate Drive Characteristics and Requirements for HEXFET |
| 中文描述： | 門驅動器的特點及要求的HEXFET |
| 文件頁數： | 6/21頁 |
| 文件大小： | 418K |
| 代理商： | AN-937 |
AN-937 (v.Int)
2. C-MOS can operate from higher supply voltages than 5V so that HEXFET
saturation can be guaranteed.
3. Switching times are longer than those for TTL (Table 2).
When C-MOS outputs are directly coupled to the gate of
a HEXFET
, the dominant limitation to performance is
not the switching time, but the internal impedance
(assuming that C-MOS are operated from a 10V or
higher voltage supply). It will certainly not be able to
turn OFF the HEXFET
as fast as the TTL, while the
turn-ON waveform will be slightly better than what can
be achieved with a 7407 with a 680 ohm pull-up
resistor. Of course, gates can be paralleled in any
number to lower the impedance and this makes C-MOS
a very simple and convenient means of driving
HEXFET
s. Drivers can also be used, like the 4049 and
4050 which have a much higher current sinking
capability (Table 2), but they do not yield any significant
improvement in current sourcing.
For better switching speeds, buffer circuits, like the one
shown in Figure 9, should be considered, not only to
provide better current sourcing and sinking capability,
but also to improve over the switching times of the C-
MOS output itself and the dv/dt noise immunity.
6. DRIVING HEXFET
S FROM LINEAR CIRCUITS
The complementary source follower configuration of Figure 9 can also be used in linear applications to improve drive capability
from an opamp or other analog source.
Most operational amplifiers have a very limited slew rate, in the order of few V/microsec. This would limit the bandwidth to less
than 25kHz. A larger bandwidth can be obtained with better operational amplifiers followed by a current booster, like the ones
shown in Figures 10 or 11. For a system bandwidth of 1MHz, the opamp bandwidth must be significantly higher than 1MHz and
its slew rate at least 30V/
μ
s.
V
H
680
IRF320
7407
680
12V
Figure 8.
High Voltage TTL driver and its waveforms
Figure 9.
Simple Interface to Drive HEXFETs from TTL
7407
1
K
V
H
LOAD
+12V
INPUT
8
7
2
4
5
6
1
3
IRF7307 OR IRF7507
To Order
Index
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