Logic level and Snubberless TRIACs

AN439

12/16

2.3

Typical applications

2.3.1

Logic level TRIACs

These TRIACs can be directly controlled by logic circuits and microcontrollers like the ST6

or ST7 series. Outputs of ST6/ST7 can sink currents up to 20 mA per I/O line, and therefore

drive TW and SW.

These TRIACs are ideal interface for power components supplied by 110 V or 220 V, such

as valves, heating resistances, and small motors.

The specification of the critical (dI/dt)c on both resistive and inductive loads offers:

●

Knowledge of the security margin of the circuit in relation to the risk of the spurious

triggering

●

Optimization of the performance of the TRIAC used, which results in a cost reduction

Figure 11.

Light dimmer circuit with ST6/ST7 (SW TRIACs type is recommended)

2.3.2

Snubberless TRIACs

The commutation of Snubberless TRIACs is specified without a (dV/dt)c limitation. The

external snubber circuit can be suppressed for TRIAC turn-off and leads to a noticeable cost

reduction. Nevertheless, a snubber circuit is sometimes used to eliminate spurious

triggering due to fast line transients (see Figure 13).

critical (dI/dt)c value and also static dV/dt, Snubberless TRIACs are used in circuits which

need high safety margin, such as:

●

Static relays in which the load is not well defined. With standard TRIACs, it is difficult to

adapt the snubber to all possible cases. Snubberless TRIACs resolve this problem (see

Figure 12).

5.6V zener

diode

SW TRIACs

type

VDD

1

RESET

PB0

15

PB1

14

4

3

OSCIN

OSCOUT

PA0

PA1

PB2

PB3

PB4

PB5

19

18

11

10

13

12

ST6/ST7

NMI

TEST

VSS

5

6

20

3 x

4.7M

220k

100k

100k

220k

220k

22k

LINE

100

MODE

8MHz

10p

10p

TOUCH

SENSOR

7

0V

0V

0V

0V

0V

0V

0V

+5V

+5V

+5V

820

1/2W

220n

400V

1N4148

100u

6.3V

0V

+5V

820

1/2W

220n

400V

1N4148

100u

6.3V

0V

+5V

NEUTRAL

A1

A2

G

5.6V zener

diode

SW TRIACs

type

VDD

1

RESET

PB0

15

PB1

14

4

3

OSCIN

OSCOUT

PA0

PA1

PB2

PB3

PB4

PB5

19

18

11

10

13

12

ST6/ST7

NMI

TEST

VSS

5

6

20

3 x

4.7M

220k

100k

100k

220k

220k

22k

LINE

100

MODE

8MHz

10p

10p

TOUCH

SENSOR

7

0V

0V

0V

0V

0V

0V

0V

+5V

+5V

+5V

820

1/2W

220n

400V

1N4148

100u

6.3V

0V

+5V

820

1/2W

220n

400V

1N4148

100u

6.3V

0V

+5V

NEUTRAL

A1

A2

G