AN871 APPLICATION NOTE

2/13

Figure 1. Triac triggering in the 4 quadrants

On - state

In conduction, the thyristor structure is auto saturated and the voltage drop is in the order of 1 to 2 volts

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)

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.

(+) A2

A1

QUADRANT 1

la

G

+lg

(-) A2

A1

QUADRANT 4

la

G

+lg

(+) A2

A1

QUADRANT 2

la

G

-lg

(-) A2

A1

QUADRANT 3

la

G

-lg

(A)

on-state current-voltage

characteristic of a thyristor

surge current versus duration

0

0,5

1

1,5

2

2,5

3

5

200

0,01

01

1

10

400

600

800

10

15

VF (V)

S = surface of the

sicon die

(B)

Duration (ms)

IF (A)

Peak Current (A)