AC08FSM datasheet(181/223 Pages) TECCOR

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Application Notes

AN1008

AN1008 - 3

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Thyristor Product Catalog

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Figure AN1008.4

Relationship of Maximum Current Rating to Time

I2t Rating — SCR and Triac

The I2t rating gives an indication of the energy-absorbing capabil-

ity of the thyristor device during surge-overload conditions. The

rating is the product of the square of the RMS current (IRMS)2 that

flows through the device and the time during which the current is

present and is expressed in A2s. This rating is given for fuse

selection purposes. It is important that the I2t rating of the fuse is

less than that of the thyristor device. Without proper fuse or cur-

rent limit, overload or surge current will permanently damage the

device due to excessive junction heating.

PG: Gate Power Dissipation — SCR and Triac

Gate power dissipation ratings define both the peak power (PGM)

forward or reverse and the average power (PG(AV)) that may be

applied to the gate. Damage to the gate can occur if these ratings

are not observed. The width of the applied gate pulses must be

considered in calculating the voltage and current allowed since

the peak power allowed is a function of time. The peak power

that results from a given signal source relies on the gate charac-

teristics of the specific unit. The average power resulting from

high peak powers must not exceed the average-power rating.

TS, TJ: Temperature Range — SCR and Triac

The maximum storage temperature (TS) is greater than the maxi-

mum operating temperature (actually maximum junction temper-

ature). Maximum storage temperature is restricted by material

limits defined not so much by the silicon but by peripheral materi-

als such as solders used on the chip/die and lead attachments as

well as the encapsulating epoxy. The forward and off-state block-

ing capability of the device determines the maximum junction (TJ)

temperature. Maximum blocking voltage and leakage current rat-

ings are established at elevated temperatures near maximum

junction temperature; therefore, operation in excess of these lim-

its may result in unreliable operation of the thyristor.

Characteristics

VBO: Instantaneous Breakover Voltage — SCR and Triac

Breakover voltage is the voltage at which a device turns on

(switches to on state by voltage breakover). (Figure AN1008.1)

This value applies for open-gate or gate-resistance termination.

Positive gate bias lowers the breakover voltage. Breakover is

temperature sensitive and will occur at a higher voltage if the

junction temperature is kept below maximum TJ value. If SCRs

and triacs are turned on as a result of an excess of breakover

voltage, instantaneous power dissipations may be produced that

can damage the chip or die.

IDRM: Peak Repetitive Off-state (Blocking) Current

SCR

IDRM is the maximum leakage current permitted through the SCR

when the device is forward biased with rated positive voltage on

the anode (DC or instantaneous) at rated junction temperature

and with the gate open or gate resistance termination. A 1000

Ω

resistor connected between gate and cathode is required on all

sensitive SCRs. Leakage current decreases with decreasing

junction temperatures. Effects of the off-state leakage currents

on the load and other circuitry must be considered for each cir-

cuit application. Leakage currents can usually be ignored in

applications that control high power.

Triac

The description of peak off-state (blocking/leakage) current for

the triac is the same as for the SCR except that it applies with

either positive or negative bias on main terminal 2.

(Figure AN1008.2)

IRRM: Peak Repetitive Reverse Current — SCR

This characteristic is essentially the same as the peak forward

off-state (blocking/leakage) current except negative voltage

is applied to the anode (reverse biased).

VTM: Peak On-State Voltage — SCR and Triac

The instantaneous on-state voltage (forward drop) is the

principal voltage at a specified instantaneous current and

case temperature when the thyristor is in the conducting state.

To prevent heating of the junction, this characteristic is mea-

sured with a short current pulse. The current pulse should be

at least 100 µs duration to ensure the device is in full conduc-

tion. The forward-drop characteristic determines the on-state

dissipation. See Figure AN1008.5, and refer to “IT: Current

Rating” on page AN1008-2.

Figure AN1008.5

On-state Current versus On-state Voltage (Typical)

ITM

di/dt

Time

t = 8.3 ms for 60 Hz

10 ms for 50 Hz

(ITM)

15 and 25 A TO-220

TC = 25 ˚C

40 A TO-218

0.6

0.8

1.0

1.2

1.4

1.6

1.8

Positive or Negative

Instantaneous On-state Voltage (vT) – Volts

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