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參數(shù)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(shù)： | 20/21頁 |
| 文件大?。?/td> | 418K |
| 代理商： | AN-937 |
AN-937 (v.Int)
If the converter is loaded with a
constant and predictable load, a zener
can provide the necessary regulation.
Otherwise a three-terminal regulator
or a small zener-driven MOSFET may
be necessary.
The circuit in Figure 35a is similar to
the previous one, except that the
higher switching frequency is higher
(500 kHz) and the transformer is
smaller. The remaining three gates in
the package are connected in parallel
to drive the MOSFET and reduce the
switching losses. The switching
waveforms are shown in Figure 35b.
The output resistance (Rout) of this
circuit is higher than the circuit shown
in Figure 33a, mainly because the
stray inductance of the smaller transformer is higher and the effects of the stray inductance are higher. Figure 37a shows a push-
pull operated at 500 kHz. The single gate oscillator produces a 50% duty cycle output, while the remaining gates in the package
are used to drive the push-pull output stage. The primary of the transformer sees half the voltage compared to the previous
circuit, therefore the number of turns at the primary were reduced to half.
10. PHOTOVOLTAIC GENERATORS AS GATE DRIVERS
A photovoltaic generator is a solid state power supply powered by light, normally an LED. The combination of the LED and the
photovoltaic generator in one package is called a Photovoltaic Isolator or PVI and is available in a 8-pin DIP package. As a
voltage source, the PVI can function as a “dc transformer” by providing an isolated low current to a load. While an optoisolator
requires a bias supply to transmit a signal across a galvanic barrier, the PVI actually transmits the energy across the barrier.
More information on the PVI can be found in Application Note GBAN-PVI-1 which appears in the Microelectronic Relay
Designer’ s Manual. This data book also contains the data sheet for the photovoltaic isolator, the PVI1050. A circuit is also
provided in the AN to significantly speed up turn off of the switch. As a gate driver the PVI has significant limitations: its short
circuit current is in the order of 30 microA with a very high internal impedance. Its simplicity, however, makes it appealing in
solid-state relay replacements, where switching times are not important and switching transients are not present.
A typical application is the ac switch described below. The IGBT and the power MOSFET are not suited to switching AC
waveforms directly. The IGBT can only conduct current in one direction while the power MOSFET has an anti-parallel diode
that will conduct during every negative half-cycle. Bidirectional blocking capability can be achieved by connecting two power
MOSFETs source to source, or two IGBTs with anti-parallel diodes emitter to emitter, as shown in Figure 39.
+12V
Figure 35a.
500 kHz Forward converter
13
12
11
100
1
μ
F
IRFD110
1N4148
1K
6K
5
6
4
CD4093
220p
12V
RTN
1
μ
F
T1
4X
IN4148
V
0
R
L
f = 500kHz
T1: CORE: PHILIPS 266CT125-3E2A (od=0.375", Ae=0.072CM^2, AL=2135
PRIMARY: 4T, AWG 30, SECONDARY: 7T, AWG30
9
8
10
1
2
3
14
7
30
25
20
15
10
0
10
20
30
50
40
Load current (mA)
O
Figure 36.
Load current vs. output voltage,
Rout = 27.7 Ohms
Drain Voltage: 10V/div.
Gate voltage: 5V/div.
Horiz.: 250ns/div.
Figure 35b.
Waveforms associated with the
circuit in Figure 35a
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