Datasheet MOC3051M, MOC3052M, MOC3053M (ON Semiconductor) - 6

link to page 7 link to page 7 link to page 7 link to page 5 link to page 5 link to page 7
MOC3051M, MOC3052M, MOC3053M APPLICATIONS INFORMATION Basic Triac Driver Circuit LED Trigger Current vs. Pulse Width
The random phase triac drivers MOC3051M, Random phase triac drivers are designed to be phase MOC3052M and MOC3053M can allow snubberless controllable. They may be triggered at any phase angle operations in applications where load is resistive and the within the AC sine wave. Phase control may be external generated noise in the AC line is below its accomplished by an AC line zero cross detector and a guaranteed dv/dt withstand capability. For these variable pulse delay generator which is synchronized to the applications, a snubber circuit is not necessary when a noise zero cross detector. The same task can be accomplished by insensitive power triac is used. Figure 7 shows the circuit a microprocessor which is synchronized to the AC zero diagram. The triac driver is directly connected to the triac crossing. The phase controlled trigger current may be a very main terminal 2 and a series resistor R which limits the short pulse which saves energy delivered to the input LED. current to the triac driver. Current limiting resistor R must LED trigger pulse currents shorter than 100 ms must have have a minimum value which restricts the current into the increased amplitude as shown on Figure 4. This graph shows driver to maximum 1 A. the dependency of the trigger current IFT versus the pulse The power dissipation of this current limiting resistor and width. IFT in this graph is normalized in respect to the the triac driver is very small because the power triac carries minimum specified IFT for static condition, which is the load current as soon as the current through driver and specified in the device characteristic. The normalized IFT current limiting resistor reaches the trigger current of the has to be multiplied with the devices guaranteed static power triac. The switching transition times for the driver is trigger current. only one micro second and for power triacs typical four Example: micro seconds. IFT = 10 mA, Trigger PW = 4 ms IF (pulsed) = 10 mA × 3 = 30 mA
Triac Driver Circuit for Noisy Environments
When the transient rate of rise and amplitude are expected
Minimum LED Off Time in Phase Control Applications
to exceed the power triacs and triac drivers maximum In phase control applications, one intends to be able to ratings a snubber circuit as shown in Figure 8 is control each AC sine half wave from 0° to 180°. Turn on at recommended. Fast transients are slowed by the R−C 0° means full power and turn on at 180° means zero power. snubber and excessive amplitudes are clipped by the Metal This is not quite possible in reality because triac driver and Oxide Varistor MOV. triac have a fixed turn on time when activated at zero degrees. At a phase control angle close to 180° the driver’s
Triac Driver Circuit for Extremely Noisy Environments
turn on pulse at the trailing edge of the AC sine wave must As specified in the noise standards IEEE472 and be limited to end 200 ms before AC zero cross as shown in IEC255−4. Figure 10. This assures that the triac driver has time to switch Industrial control applications do specify a maximum off. Shorter times may cause loss of control at the following transient noise dv/dt and peak voltage which is half cycle. super−imposed onto the AC line voltage. In order to pass this environment noise test a modified snubber network as
Static dv/dt
shown in Figure 9 is recommended. Critical rate of rise of off−state voltage or static dv/dt is a triac characteristic that rates its ability to prevent false
LED Trigger Current versus Temperature
triggering in the event of fast rising line voltage transients Recommended operating LED control current IF lies when it is in the off−state. When driving a discrete power between the guaranteed IFT and absolute maximum IF. triac, the triac driver optocoupler switches back to off−state Figure 3 shows the increase of the trigger current when the once the power triac is triggered. However, during the device is expected to operate at an ambient temperature commutation of the power triac in application where the below 25°C. Multiply the datasheet guaranteed IFT with the load is inductive, both triacs are subjected to fast rising normalized IFT shown on this graph and an allowance for voltages. The static dv/dt rating of the triac driver LED degradation over time. optocoupler and the commutating dv/dt rating of the power Example: triac must be taken into consideration in snubber circuit IFT = 10 mA, LED degradation factor = 20% design to prevent false triggering and commutation failure. IF at −40°C = 10 mA × 1.25 × 120% = 15 mA
www.onsemi.com 6