MOC3051 Datasheet, PDF (6/8 Pages) Motorola, Inc – 6-Pin DIP Random-Phase Optoisolators Triac Drivers

MOC3051 MOC3052
APPLICATIONS GUIDE
Basic Triac Driver Circuit
The new random phase triac driver family MOC3052 and
MOC3051 are very immune to static dv/dt which allows
snubberless operations in all applications where external
generated noise in the AC line is below its guaranteed dv/dt
withstand capability. For these applications a snubber circuit
is not necessary when a noise insensitive power triac is
used. Figure 11 shows the circuit diagram. The triac driver is
directly connected to the triac main terminal 2 and a series
Resistor R which limits the current to the triac driver. Current
limiting resistor R must have a minimum value which restricts
the current into the driver to maximum 1A.
R = Vp AC/ITM max rep. = Vp AC/1A
The power dissipation of this current limiting resistor and
the triac driver is very small because the power triac carries
the load current as soon as the current through driver and
current limiting resistor reaches the trigger current of the
power triac. The switching transition times for the driver is
only one micro second and for power triacs typical four micro
seconds.
VCC RLED ^{TRIAC DRIVER}
POWER TRIAC
CONTROL
Q
AC LINE
R
LOAD
RET.
RLED = (VCC – VF LED – Vsat Q)/IFT
R = Vp AC line/ITSM
Figure 11. Basic Driver Circuit
Triac Driver Circuit for Noisy Environments
When the transient rate of rise and amplitude are expected
to exceed the power triacs and triac drivers maximum ratings
a snubber circuit as shown in Figure 12 is recommended.
Fast transients are slowed by the R–C snubber and exces-
sive amplitudes are clipped by the Metal Oxide Varistor MOV.
VCC RLED ^{TRIAC DRIVER}
POWER TRIAC
CONTROL
RET.
RS
R
MOV ^{AC LINE}
CS
LOAD
Typical Snubber values RS = 33 Ω, CS = 0.01 µF
MOV (Metal Oxide Varistor) protects triac and
driver from transient overvoltages >VDRM max.
Figure 12. Triac Driver Circuit for Noisy Environments
Triac Driver Circuit for Extremely Noisy Environments,
as specified in the noise standards IEEE472 and IEC255–4.
Industrial control applications do specify a maximum tran-
sient noise dv/dt and peak voltage which is superimposed
onto the AC line voltage. In order to pass this environment
noise test a modified snubber network as shown in Figure 13
is recommended.
POWER TRIAC
VCC RLED ^{TRIAC DRIVER}
R
CONTROL
RET.
RS
MOV ^{AC LINE}
CS
LOAD
Recommended snubber to pass IEEE472 and IEC255–4 noise tests
RS = 47 W, CS = 0.01 mF
Figure 13. Triac Driver Circuit for Extremely Noisy
Environments
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Motorola Optoelectronics Device Data