AN439

Logic level and Snubberless TRIACs

13/16

Figure 12.

Solid state relay diagram, using Zero Voltage Switching with opto-TRIAC

●

Motor drive circuits. The circuit Figure 12 shows an asynchronous motor controlled in

both direction by turning on each TRIAC alternately.

Figure 13.

Motor control circuit using Snubberless TRIACs (Ls + r = network for

series protection)

Note:

Series impedance (r + L) is needed to protect the blocked TRIAC in case of unwanted

overvoltage protection for both TRIACs (IEC 61000-4-5). Snubber networks (R1C1 and

R2C2) eliminate spurious triggering due to fast line transients (IEC 61000-4-4).

The specified (dI/dt)c for a Snubberless TRIAC is higher than the decreasing slope of its

including:

●

times higher (see Figure 14). Table 3 illustrates the component choice optimization by

using Snubberless TRIACs. For example, a 8 A Snubberless TRIAC is sufficient to

control a 110 V / 600 W motor instead of a 16 A standard TRIAC.

LOAD

R1

R2

C1

T

SSR

LOAD

R1

R2

C1

V

Mains

T

Solid State Relay

INPUT

LOAD

R1

R2

C1

T

SSR

LOAD

R1

R2

C1

V

Mains

T

Solid State Relay

INPUT

V

Mains

M

C

Start

Run

X2

r

L

R1

Gate

drive

circuit

C1

VDR

R2

C2

V

Mains

M

C

Start

Run

X2

r

L

R1

Gate

drive

circuit

C1

VDR

VDR

R2

C2