AN871 Datasheet, PDF (7/13 Pages) STMicroelectronics – In power electronics the choice of the switch to be used is always very important

AN871 APPLICATION NOTE
Figure 7. Typical circuit using triac as a bidirectional switch to control each door separately
+Vbat.
RELAY
(LOCKING / UNLOCKING)
CONTROL
BUS
µCONT
G1
INTERFACE
G2
G3
T1
M1
G1
T2
M2
G2
T3
M3
G3
+Vbat.
Gate control circuit
In this circuit, the terminal A1 of the triac is sometimes connected to the ground or to the battery voltage.
Therefore, a small interface circuit is needed to drive the gate from a standard micro controller output.
This interface circuit can be done either with passive components (AC coupling with a capacitor) or with
transistor and diodes providing a direct coupling more interesting to use standard triac without particular
requirement concerning gate triggering current (see Figure 8).
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