Principle of proposed gate circuit

AN440

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1

Principle of proposed gate circuit

To drive the TRIAC in the 2nd and 3rd quadrants, a discharge capacitor is used as shown in

Figure 2.

Figure 2.

Basic diagram of the triggering circuit

When the transistor Tr is switched off, capacitor C is charged through resistance R2 and

diode D. The diode is used to avoid a capacitor charging current through the TRIAC gate. A

Schottky diode could be used to keep the voltage drop level below the gate non trigger

through R1 and Tr and a negative current flows through the TRIAC gate.

We have to consider different parameters to define all the components:

●

●

The time duration of the gate current pulse.

●

+ Vcc

LINE

I/O

MCU

GND

LOAD

D

R1

C

R2

R3

TRIAC

Tr

+ Vcc

GND

+ Vcc

I/O

MCU

GND

LOAD

D

R1

C

R2

R3

TRIAC

Tr

+ Vcc

GND