IL4217(2000) Просмотр технического описания (PDF) - Infineon Technologies

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IL4217
(Rev.:2000)

Triac Driver Optocoupler

Infineon Technologies 

Power Factor Considerations

A snubber isn’t needed to eliminate false operation of the

TRIAC driver because of the IL411’s high static and commutat-

ing dv/dt with loads between 1 and 0.8 power factors. When

inductive loads with power factors less than 0.8 are being

driven, include a RC snubber or a single capacitor directly

across the device to damp the peak commutating dv/dt spike.

Normally a commutating dv/dt causes a turning-off device to

stay on due to the stored energy remaining in the turning-off

device.

But in the case of a zero voltage crossing optotriac, the com-

mutating dv/dt spikes can inhibit one half of the TRIAC from

turning on. If the spike potential exceeds the inhibit voltage of

the zero cross detection circuit, half of the TRIAC will be held-

off and not turn-on. This hold-off condition can be eliminated

by using a snubber or capacitor placed directly across the

optotriac as shown in Figure 7. Note that the value of the

capacitor increases as a function of the load current.

The hold-off condition also can be eliminated by providing a

higher level of LED drive current. The higher LED drive pro-

vides a larger photocurrent which causer. the phototransistor

to turn-on before the commutating spike has activated the zero

cross network. Figure 8 shows the relationship of the LED drive

for power factors of less than 1.0. The curve shows that if a

device requires 1.5 mA for a resistive load, then 1.8 times (2.7

mA) that amount would be required to control an inductive

load whose power factor is less than 0.3.

Figure 7. Shunt capacitance versus load current

versus power factor

Figure 8. Normalized LED trigger current versus

power factor

Infineon Technologies, Corp. • Optoelectronics Division • Cupertino, CA (formerly Siemens Microelectronics, Inc.)

www.infineon.com/opto • 1-888-Infineon (1-888-463-4636)

4

IL4216/4217/4218

January 19, 2000-13

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