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參數(shù)資料
| 型號(hào)： | AN4840 |
| 英文描述： | Gate triggering and the use of gate characteristics |
| 中文描述： | 門(mén)觸發(fā)和特點(diǎn)的門(mén)使用 |
| 文件頁(yè)數(shù)： | 4/5頁(yè) |
| 文件大?。?/td> | 77K |
| 代理商： | AN4840 |
TGD-1X
4/5
www.dynexsemi.com
of the gate drive. Gate drive output is often defined in terms of
its open circuit voltage and internal source resistance.
To select the correct gate drive load line it is useful to draw
several possibilities onto the characteristic curve (fig 1). Compare
the 20V, 10
line drawn onto the logarithmic and linear axis
versions. Clearly, the linear version is much easier to work with.
The first requirement for the load line is that it must pass through
the
‘
preferred gate drive area
’
to the right of the appropriate I
,
V
limit point. For operation down to -40
C, this is point B. For
+25
C minimum operation temperature, point A applies. Load
line 10V, 14.3
is adequate for 25
C operation but load line 10V,
16.6
is not since it crosses the 25
C
‘
zone of uncertain
triggering
’
.
Unfortunately, most applications demand gate drive levels well
above the minimum, with good di/dt performance being the most
demanding. For DCR1596 a 20V, 10
load line is preferred.
This load line lies well to the right of Point B. Note also that 10
watts peak power is not exceeded.
MORE ON I
, V
, GATE PULSE WIDTHS AND
RECOMMENDED GATE DRIVE
Two basic circuit connections should be considered.
1)
Using single thyristor elements.
2)
Using series and parallel combinations.
First consider single thyristor elements.
Low values of triggering I
and V
are satisfactory for simple
resistive loads with minimal overload currents and low di/dt. In
this near-ideal situation a simple pulse of 10
μ
S or less would
suffice, with Ig only slightly more than I
GT
.
In practice, this situation is unrealistic and an appropriate gate
pulse shape must be chosen to match the application. Fig. 3
shows the general shape for a single gate pulse. It consists of
an initial short, fast rising high amplitude section followed by a
longer, low amplitude
“
back-porch
”
section.
The back-porch section has to be long enough to allow an
inductive load anode current to rise to the device latching current.
In most applications a CR snubber network is connected across
the thyristor. Because of the high di/dt of the snubber discharge
current on thyristor triggering the initial gate pulse should be of
high amplitude and rate of rise. Where the load itself is capacitive,
or very low inductance, circuit di/dt levels are even higher and
hard gate drives are needed. For example, the gate drive
recommendation for DCR1596 to achieve its di/dt ratings of
300A/
μ
s is 20 volt, 10 ohms, with current rise time less than
0.5
μ
s. High gate drive is only necessary for the duration of the
turn-on period - a few microseconds. After that the gate
amplitude may be allowed to fall to a low maintaining value, i.e.
the back-porch current.
The function of the back-porch current is to allow the thyristor to
be retriggered if the anode current transiently dips below the
holding current value. However, it is quite common for the gate
signal to be needed for several milliseconds after initial triggering.
This is done by providing a train of pulses for the duration of the
triggering period since a single long pulse would require too
much power from the gate drive.
SERIES AND PARALLEL COMBINATIONS
All the above remarks relating to triggering of single thyristors
apply equally to series and parallel combinations. An additional
requirement is to ensure that all thyristors in the combination turn
on as nearly together as is possible. This is done by reducing the
D t
value, i.e. the difference between individual device delay
times. For this, a hard gate drive is also required.
GATE DRIVE RECOMMENDATIONS
From the above it is clear that a hard gate drive (high current, high
voltage, fast rise time) is needed for the majority of applications.
A low power gate drive is likely to cause triggering problems. The
basic pulse should have a high current front end and low current
back-porch. In some situations a train of these pulses may be
needed.
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PDF描述 |
|---|---|
| AN4853 | Thyristor and diode measurement with a multi-meter |
| AN4870 | The effect of temperature on thyristor performance |
| AN4999 | Turn-on of thyristors in parallel |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| AN4853 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:Thyristor and diode measurement with a multi-meter |
| AN486-2 | 制造商:NEW SURPLUS HARDWARE 功能描述: |
| AN4869 | 制造商:DYNEX 制造商全稱:Dynex Semiconductor 功能描述:Power Assemblies |
| AN4870 | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:The effect of temperature on thyristor performance |
| AN48800A | 制造商:PANASONIC 制造商全稱:Panasonic Semiconductor 功能描述:Low current consumption, high sensitivity CMOS Hall IC One-way magnetic field operation |
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