AN303 datasheet(2/13 Pages) STMICROELECTRONICS

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Application examples

AN303

2/13

Doc ID 3654 Rev 3

Application examples

The importance of the latching current is highlighted by the following application examples.

1.1

Example 1: low power lamp control

In the application circuit shown in Figure 2 a TRIAC is used to control a 10 W signaling light.

For the European mains (Vrms = 230 V), the peak load current is about 61 mA. A Z01 device

could be used to control this load current, but the maximum latching current is specified as

50 mA if a Z0110 device is used in quadrant II. The peak load current is then very close to

the maximum latching current given in the datasheet. The device will turn off if the gate

current pulse is too short.

Figure 2.

Control of a low-power lamp

Thus, a TRIAC could not remain on if its latching current is higher than the load current at

the moment the gate current is removed (refer to Figure 2). For correct operation, a

continuous gate current should be applied or a longer gate current pulse should be applied.

For example, for a sinusoidal load current (I(t) = Ipeak x sin(ωt)), the pulse width is given by

the following equation (refer to AN302 for a complete definition of IH

(a)):

To reduce the pulse width duration, a more sensitive TRIAC could be used (for example, for

the Z0103 IL max is 15 mA in QII).

The minimum current that keeps a TRIAC conducting is called the hypostatic or holding current IH.

230 V

Lamp (10 W)

Main

current

Gate

current

tp >

· arcsin

HMAX

peak )

(

LMAX

peak )

(

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