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| 型號(hào)： | AN5179K |
| 英文描述： | TV Sound and Video Receiver Circuit |
| 中文描述： | 電視聲音和視頻接收器電路 |
| 文件頁(yè)數(shù)： | 2/5頁(yè) |
| 文件大?。?/td> | 96K |
| 代理商： | AN5179K |
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www.dynexsemi.com
AN5177 Application Note
Fig. 2 Turn-on waveforms
Fig. 3 Simplified version of gdu turn-off section - in reality 10x 470
μ
F capacitors used
TURN-OFF BY GATE COMMUTATION
At turn-off, the voltage mis-sharing,
V, is very dependent on Itm,
Cs, and
t
gs
.
V = I
tm
.
t
gs
/Cs
I
TM
This is the current being turned-off. This current is relatively low
in a current source inverter. By contrast, currents can be very
high in a voltage source inverter and this leads to high values of
V. Consequently, Cs values must be high to compensate.
t
gs
This is the difference in storage time between the GTOs in
series. Traditionally, GTOs are turned off slowly, typically with
dIg/dt = -40A/
μ
s. With this condition,
t
values are fairly large.
The gate drive unit described achieves turn off current rates of
250A/
μ
s so that tgs and
t
gs
are much smaller.
Cs
Snubber capacitor values need to be high to reduce the effect of
high
t
gs
. It follows that if
t
gs
can be reduced so can Cs.
TURN-OFF BY CURRENT REVERSAL
This is the reverse recovery mode, as with a diode and
conventional thyristors and is only applicable to reverse blocking
GTOs. In this recovery mode the gate drive unit has no effect.
Sharing considerations are as for fast recovery diodes. Thus, to
minimise the value of the snubber capacitor the difference
between the reverse recovery charge values of the GTOs, (
Qs)
must be kept to a minimum.
SELECTING THE VALUE OF Cs
Cs must be sized for (a) minimising delay time variations at turn-
on, (b) conventional GTO gate commutated turn-off and (c) GTO
reverse recovery, if appropriate. The requirement for turn-off
usually dominates. Clearly, the aim must be to reduce the value
of Cs to as low a value as permitted by the application and the
GTO specification. Using a gate drive which delivers a higher
turn-off gate current rate can help to reduce the required value
of Cs.
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相關(guān)代理商/技術(shù)參數(shù) |
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