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Document Number: 83690

196

Rev. 1.5, 07-May-08

BRT21/BRT22/BRT23

Vishay Semiconductors

Optocoupler, Phototriac Output,

Zero Crossing

Note

As per IEC 60747-5-2, § 7.4.3.8.1, this optocoupler is suitable for "safe electrical insulation" only within the safety ratings. Compliance with the

safety ratings shall be ensured by means of protective circuits.

POWER FACTOR CONSIDERATIONS

A snubber is not needed to eliminate false operation of the

TRIAC driver because of the high static and commutating

dV/dt with loads between 1.0 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

commutating 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 heldoff 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 1. 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

provides

a

larger

photocurrent

which

causes

the

phototransistor to turn-on before the commutating spike has

activated the zero cross network. Figure 2 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.

Fig. 1 - Shunt Capacitance vs. Load Current

SAFETY AND INSULATION RATINGS

PARAMETER

TEST CONDITION

SYMBOL

MIN.

TYP.

MAX.

UNIT

Climatic classification

(according to IEC 68 part 1)

40/100/21

Comparative tracking index

CTI

175

399

6000

V

630

V

200

mW

400

mA

175

°C

Creepage distance

standard DIP-6

7

mm

Clearance distance

standard DIP-6

7

mm

Creepage distance

400 mil DIP-6

8

mm

Clearance distance

400 mil DIP-6

8

mm

iil410_01

400

350

300

250

200

150

100

50

0

0.001

0.01

0.1

1

Ta = 25 °C, PF = 0.3

IF = 2.0 mA