AN302 datasheet(5/10 Pages) STMICROELECTRONICS

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AN302

Holding current - the details

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Holding current - the details

The three examples in the previous chapter illustrate the importance of the holding current

parameter and the different problems it can cause if it is not taken into account at an early

stage in the design cycle.

If the device is to remain in the conducting state, it is imperative that the circuit in which it is

used ensures an operating current sufficiently high.

In our data sheets, for all types of TRIACs, the holding current, IH, is specified as a

maximum value. Then, corrections must be made to compensate for temperature variations.

2.1

Measuring the holding current

In Figure 6 push button R is used to fire the TRIAC. The value of the conducting current IT is

set to be much higher than the latching current IL. Increasing the resistance R causes the

current IT to decrease. The value of the holding current IH is the value of IT just before the

TRIAC is blocked.

The holding current is always measured with the gate unconnected, that is disconnected

from the trigger circuit and without bias. However, sensitive SCRs, that is, those with a gate

trigger current IGT of 200 µA or less, are measured with a 1 kΩ resistor connected between

gate and cathode.

For repeatable results, the TRIAC should be suitably turned on. The following guidelines

must be applied.

●

The initial value of current IT must be more than five times the latching current IL before

the test can begin.

●

If the holding current is measured by pulses (by an automatic tester, for example), the

TRIAC should be conducting for at least 500 µs before starting the test.

Figure 6.

Circuit for measurement of the holding current IH

Example:

BTA/BTB12-600C: IL (QI - QIII and QIV) = 40 mA,

so choose IT = 500 mA, IH maximum = 25 mA

For a TRIAC, IH has two values; IH+, when electrode A2 is positive with respect to electrode

A1, and IH-, when electrode A2 is negative with respect to electrode A1. In the

documentation only one maximum value is given for both quadrants. This value is always

the higher value.

±IT

≥ 33 ohms

V = ± 12V

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