AC08FSM datasheet(129/223 Pages) TECCOR

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Application Notes

AN1002

AN1002 - 3

http://www.teccor.com

Thyristor Product Catalog

+1 972-580-7777

Figure AN1002.6

Latching and Holding Characteristics of Thyristor

Similar to gating, latching current requirements for triacs are dif-

ferent for each operating mode (quadrant). Definitions of latching

modes (quadrants) are the same as gating modes. Therefore,

definitions shown in Figure AN1002.2 and Figure AN1002.3 can

be used to describe latching modes (quadrants) as well. The fol-

lowing table shows how different latching modes (quadrants)

relate to each other. As previously stated, Quadrant II has the

lowest latching current sensitivity of all four operating quadrants.

Example of a 4 Amp Triac:

If IL(I) = 10 mA, then

IL(II) = 40 mA

IL(III) = 12 mA

IL(IV) = 11 mA

Latching current has even somewhat greater temperature depen-

dence compared to the DC gate trigger current. Applications with

low temperature requirements should have sufficient principal

current (anode current) available to ensure thyristor latch-on.

Two key test conditions on latching current specifications are

gate drive and available principal (anode) current durations.

Shortening the gate drive duration can result in higher latching

current values.

Holding Current of SCRs and Triacs

Holding current (IH) is the minimum principal current required to

maintain the thyristor in the on state. Holding current can best be

understood by relating it to the “drop-out” or “must release” level

of a mechanical relay. Figure AN1002.6 shows the sequences of

gate, latching, and holding currents. Holding current will always

be less than latching. However, the more sensitive the device,

the closer the holding current value approaches its latching cur-

rent value.

Holding current is independent of gating and latching, but the

device must be fully latched on before a holding current limit can

be determined.

Holding current modes of the thyristor are strictly related to the

voltage polarity across the main terminals. The following table

illustrates how the positive and negative holding current modes

of triacs relate to each other.

Example of a 10 A triac:

If IH(+) = 10 mA, then

IH(-) = 13 mA

Holding current is also temperature-dependent like gating and

latching shown in Figure AN1002.7. The initial on-state current is

200 mA to ensure that the thyristor is fully latched on prior to

holding current measurement. Again, applications with low tem-

perature requirements should have sufficient principal (anode)

current available to maintain the thyristor in the on-state condi-

tion.

Both minimum and maximum holding current specifications may

be important, depending on application. Maximum holding cur-

rent must be considered if the thyristor is to stay in conduction at

low principal (anode) current; the minimum holding current must

be considered if the device is expected to turn off at a low princi-

pal (anode) current.

Figure AN1002.7

Typical DC Holding Current vs Case Temperatures

Example of a 10 A triac:

If IH(+) = 10 mA at 25 °C, then

IH(+)

≈ 7.5 mA at 65 °C

Relationship of Gating, Latching, and

Holding Currents

Although gating, latching, and holding currents are independent

of each other in some ways, the parameter values are related. If

gating is very sensitive, latching and holding will also be very

sensitive and vice versa. One way to obtain a sensitive gate and

not-so-sensitive latching-holding characteristic is to have an

“amplified gate” as shown in Figure AN1002.8.

Typical Ratio of

at 25 °C

Type

Operating Mode

Quadrant I

Quadrant II

Quadrant III Quadrant IV

4A Triac

1.2

1.1

10 A Triac

1.1

Time

Holding Current Point

Zero Crossing Point

Principal

Current

Through

Thyristor

Gate Pulse

Gate

Drive

to Thyristor

Latching

Current

Point

IL In given Quadrant

()

IL Quadrant 1

()

------------------------------------------------------------------------

Typical Triac Holding Current Ratio

Type

Operating Mode

IH(+)

IH(-)

4 A Triac

1.1

10 A Triac

11.3

2.0

1.5

1.0

-40

-15

+25

+65

+100

Case Temperature (T

C) – ˚C

INITIAL ON-STATE CURRENT = 200 mA dc

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