
AN1009
Application Notes
http://www.teccor.com
+1 972-580-7777 
AN1009 - 2
2002 Teccor Electronics
Thyristor Product Catalog
Examples of Gate Terminations
Primary Purpose
(1) Increase dv/dt capability
(2) Keep gate clamped to ensure V
DRM
capability
(3) Lower t
q
 time
Related Effect
 — Raises the device latching 
and holding current
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 t
q
 time
Primary Purpose
(1) Decrease DC gate sensitivity
(2) Decrease t
q
 time
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
Primary Purpose
(1) Supply reverse bias in off period
(2) Protect gate and gate supply for reverse 
transients
(3) Lower t
q
 time
Related Effects
 — Isolates the gate if high 
impedance signal source is used without 
sustained diode current in the negative cycle
Primary Purpose
 — Decrease threshold 
sensitivity
Related Effects
(1) Affects gate signal rise time and di/dt 
rating
(2) Isolates the gate
Primary Purpose
 — Isolate gate circuit DC 
component
Related Effects
 — In narrow gate pulses 
and low impedance sources, I
 followed by 
reverse gate signals which may inhibit con-
duction
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°
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 (T
) 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 T
 curve is 
then derated down to the maximum junction (T
J
). The curves 
illustrated in Figure AN1009.4 are derated to 125 °C since the 
maximum T
J
 for the non-sensitive SCR series is 125 °C.
Figure AN1009.4
Typical Curves for Average On-state Current at 
Various Conduction Angles versus T
C
 for a
SXX20L SCR
Zener
optional
80
85
90
95
100
105
110
115
120
125
0
2
4
6
8
10
12
14
16
Average On-state Current [I
T
(AV)] – Amps
M
C
)
C
10
9
3
6
10
Current: Halfwave Sinusoidal
Load: Resistive or Inductive
Conduction Angle: As Given Below
Case Temperature: Measured as 
      Shown on Dimensional Drawings
Conduction Angle
7.2
10.8
12.8
5.1