
Application Notes
AN1008
2002 Teccor Electronics
Thyristor Product Catalog
AN1008 - 3
http://www.teccor.com
+1 972-580-7777
Figure AN1008.4
Relationship of Maximum Current Rating to Time
I
2
t Rating — SCR and Triac
The I
2
t rating gives an indication of the energy-absorbing capabil-
ity of the thyristor device during surge-overload conditions. The 
rating is the product of the square of the RMS current (I
RMS
)
2
 that 
flows through the device and the time during which the current is 
present and is expressed in A
2
s. This rating is given for fuse 
selection purposes. It is important that the I
2
t rating of the fuse is 
less than that of the thyristor device. Without proper fuse or cur-
rent limit, overload or surge current will permanently damage the 
device due to excessive junction heating.
P
G
: Gate Power Dissipation — SCR and Triac
Gate power dissipation ratings define both the peak power (P
GM
) 
forward or reverse and the average power (P
G(AV)
) that may be 
applied to the gate. Damage to the gate can occur if these ratings 
are not observed. The width of the applied gate pulses must be 
considered in calculating the voltage and current allowed since 
the peak power allowed is a function of time. The peak power 
that results from a given signal source relies on the gate charac-
teristics of the specific unit. The average power resulting from 
high peak powers must not exceed the average-power rating.
T
S
, T
J
: Temperature Range — SCR and Triac
The maximum storage temperature (T
S
) is greater than the maxi-
mum operating temperature (actually maximum junction temper-
ature). Maximum storage temperature is restricted by material 
limits defined not so much by the silicon but by peripheral materi-
als such as solders used on the chip/die and lead attachments as 
well as the encapsulating epoxy. The forward and off-state block-
ing capability of the device determines the maximum junction (T
J
) 
temperature. Maximum blocking voltage and leakage current rat-
ings are established at elevated temperatures near maximum 
junction temperature; therefore, operation in excess of these lim-
its may result in unreliable operation of the thyristor. 
Characteristics
V
BO
: Instantaneous Breakover Voltage — SCR and Triac
Breakover voltage is the voltage at which a device turns on 
(switches to on state by voltage breakover). (Figure AN1008.1) 
This value applies for open-gate or gate-resistance termination. 
Positive gate bias lowers the breakover voltage. Breakover is 
temperature sensitive and will occur at a higher voltage if the 
junction temperature is kept below maximum T
J
 value. If SCRs 
and triacs are turned on as a result of an excess of breakover 
voltage, instantaneous power dissipations may be produced that 
can damage the chip or die.
I
DRM
: Peak Repetitive Off-state (Blocking) Current
SCR
I
DRM
 is the maximum leakage current permitted through the SCR 
when the device is forward biased with rated positive voltage on 
the anode (DC or instantaneous) at rated junction temperature 
and with the gate open or gate resistance termination. A 1000
 
resistor connected between gate and cathode is required on all 
sensitive SCRs. Leakage current decreases with decreasing 
junction temperatures. Effects of the off-state leakage currents 
on the load and other circuitry must be considered for each cir-
cuit application. Leakage currents can usually be ignored in 
applications that control high power.
Triac
The description of peak off-state (blocking/leakage) current for 
the triac is the same as for the SCR except that it applies with 
either positive or negative bias on main terminal 2.
(Figure AN1008.2)
I
RRM
: Peak Repetitive Reverse Current — SCR
This characteristic is essentially the same as the peak forward
off-state (blocking/leakage) current except negative voltage
is applied to the anode (reverse biased).
V
TM
: Peak On-State Voltage — SCR and Triac
The instantaneous on-state voltage (forward drop) is the
principal voltage at a specified instantaneous current and
case temperature when the thyristor is in the conducting state.
To prevent heating of the junction, this characteristic is mea-
sured with a short current pulse. The current pulse should be
at least 100 μs duration to ensure the device is in full conduc-
tion. The forward-drop characteristic determines the on-state
dissipation. See Figure AN1008.5, and refer to “IT: Current
Rating” on page AN1008-2.
Figure AN1008.5
On-state Current versus On-state Voltage (Typical)
I
I
TM
di/dt
Time
0
t
t =  8.3 ms for 60 Hz
       10 ms for 50 Hz
di
dt
(I
TM
)
t
=
15 and 25 A TO-220
TC = 25 C
40 A TO-218
0
0.6
0.8
Positive or Negative
1.0
1.2
1.4
1.6
1.8
Instantaneous On-state Voltage (v
T
) – Volts
0
10
20
30
40
50
60
70
80
90
P
I
T
)