AN871 Datasheet, PDF (2/13 Pages) STMicroelectronics – In power electronics the choice of the switch to be used is always very important

AN871 APPLICATION NOTE
Figure 1. Triac triggering in the 4 quadrants
(+) A2
(+) A2
la
G
A1
+lg
QUADRANT 1
la
G
A1
-lg
QUADRANT 2
(-) A2
la
G
A1
-lg
QUADRANT 3
(-) A2
la
G
A1
+lg
QUADRANT 4
On - state
In conduction, the thyristor structure is auto saturated and the voltage drop is in the order of 1 to 2 volts
for a current density in the range of 1 to 10 A/mm².
This switch can operate with average currents in the range of few amps in continuous mode and overall,
this on-state characteristic provides a very good behavior in high current pulse operation (see Figure 2).
Figure 2. Low voltage drop at high level of current (A) provides a high surge current capability (B)
IF (A)
15
10
5
S= 4 mm²
S= 1,5 mm²
Peak Current (A)
800
S = surface of the
sicon die
600
S= 4 mm²
400
S= 1,5 mm²
200
0
VF (V)
0,5 1 1,5 2 2,5 3
(A)
on-state current-voltage
characteristic of a thyristor
0,01
(B)
01
1
10
Duration (ms)
surge current versus duration
Switching - off
The thyristor turns off automatically when the load current decreases below the holding current level (IH)
which is generally in the range of few milliampere.
In car applications SCR and triacs are ideal for switching circuits associated with relays or any other circuit
which use a mechanical or semiconductor switch to interrupt current, and for capacity discharge circuits.
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