AN1009
Application Notes
Primary Purpose — Decrease threshold
Examples of Gate Terminations
sensitivity
Primary Purpose
(1) Increase dv/dt capability
(2) Keep gate clamped to ensure VDRM
capability
Related Effects
(1) Affects gate signal rise time and di/dt
Zener
optional
rating
(2) Isolates the gate
(3) Lower tq time
Related Effect — Raises the device latching
Primary Purpose — Isolate gate circuit DC
and holding current
component
Related Effects — In narrow gate pulses
and low impedance sources, Igt followed by
reverse gate signals which may inhibit con-
duction
Primary Purpose
(1) Increase dv/dt capability
(2) Remove high frequency noise
Related Effects
(1) Increases delay time
(2) Increases turn-on interval
(3) Lowers gate signal rise time
(4) Lowers di/dt capability
(5) Increases tq time
Curves for Average Current at Various
Conduction Angles
SCR maximum average current curves for various conduction
angles can be established using the factors for maximum aver-
age current at conduction angle of:
30° = 0.40 x Avg 180°
60° = 0.56 x Avg 180°
90° = 0.70 x Avg 180°
120° = 0.84 x Avg 180°
Primary Purpose
(1) Decrease DC gate sensitivity
(2) Decrease tq time
The reason for different ratings is that the average current for
conduction angles less than 180° is derated because of the
higher RMS current connected with high peak currents.
Note that maximum allowable case temperature (TC) remains the
same for each conduction angle curve but is established from
average current rating at 180° conduction as given in the data
sheet for any particular device type. The maximum TC curve is
then derated down to the maximum junction (TJ). The curves
illustrated in Figure AN1009.4 are derated to 125 °C since the
maximum TJ for the non-sensitive SCR series is 125 °C.
Related Effects
(1) Negative gate current increases holding
current and causes gate area to drop out of
conduction
(2) In pulse gating gate signal tail may
cause device to drop out of conduction
Primary Purpose — Select frequency
Related Effects — Unless circuit is
“damped,” positive and negative gate current
may inhibit conduction or bring about spo-
radic anode current
125
Current: Halfwave Sinusoidal
Load: Resistive or Inductive
Conduction Angle: As Given Below
Case Temperature: Measured as
Shown on Dimensional Drawings
120
115
110
105
Primary Purpose
Conduction Angle
(1) Supply reverse bias in off period
100
(2) Protect gate and gate supply for reverse
95
90
85
80
transients
(3) Lower tq time
Related Effects — Isolates the gate if high
impedance signal source is used without
sustained diode current in the negative cycle
5.1
7.2
10.8 12.8
10 12
0
2
4
6
8
14
16
Average On-state Current [IT(AV)] – Amps
Figure AN1009.4
Typical Curves for Average On-state Current at
Various Conduction Angles versus TC for a
SXX20L SCR
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AN1009 - 2
©2002 Teccor Electronics
Thyristor Product Catalog
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