Document Number: 83628 For technical questions, contact: optocoupleranswers@vishay.com
www.vishay.com
Rev. 1.8, 20-Oct-10 5
IL4116, IL4117, IL4118
Optocoupler, Phototriac Output, Zero
Crossing, Very Low Input Current
Vishay Semiconductors
TRIGGER CURRENT VS. TEMPERATURE AND VOLTAGE
The trigger current of the IL4116, IL4117, IL4118 has a
positive temperature gradient and also is dependent on the
terminal voltage as shown as the fig. 7.
Fig. 7 - Trigger Current vs.
Temperature and Operating Voltage (50 Hz)
For the operating voltage 250 V
RMS
over the temperature
range - 40 °C to 85 °C, the I
F
should be at least 2.3 x of the
I
FT1
(1.3 mA, max.).
Considering - 30 % degradation over time, the trigger
current minimum is I
F
= 1.3 x 2.3 x 130 % = 4 mA
INDUCTIVE AND RESISTIVE LOADS
For inductive loads, there is phase shift between voltage and current, shown in the fig. 8.
Fig. 8 - Waveforms of Resistive and Inductive Loads
The voltage across the triac will rise rapidly at the time the
current through the power handling triac falls below the
holding current and the triac ceases to conduct. The rise
rate of voltage at the current commutation is called
commutating dV/dt. There would be two potential problems
for ZC phototriac control if the commutating dV/dt is too
high. One is lost control to turn off, another is failed to keep
the triac on.
Lost control to turn off
If the commutating dV/dt is too high, more than its critical
rate (dV/dt
crq
), the triac may resume conduction even if the
LED drive current I
F
is off and control is lost.
In order to achieve control with certain inductive loads of
power factors is less than 0.8, the rate of rise in voltage
(dV/dt) must be limited by a series RC network placed in
parallel with the power handling triac. The RC network is
called snubber circuit. Note that the value of the capacitor
increases as a function of the load current as shown in fig. 9.
Failed to keep on
As a zero-crossing phototriac, the commutating dV/dt
spikes can inhibit one half of the TRIAC from keeping on If
the spike potential exceeds the inhibit voltage of the zero
cross detection circuit, even if the LED drive current I
F
is on.
21611
V
RMS
(V)
I
FT
(mA)
0.0
0.5
1.0
1.5
2.0
2.5
0 50 100 150 200 250 300 350
100 °C
85 °C
50 °C
25 °C
21607
Resistive load
Commutating dV/dt
AC line
voltage
AC current
through
triac
Voltage
across triac
I
F(on)
I
F(off)
Inductive load
Commutating dV/dt
AC line
voltage
AC current
through
triac
Voltage
across triac
I
F(on)
I
F(off)
