Triac is a power semiconductor devices, also known Triac, MCU control system, can be used as a power-driven device, reverse voltage problems triac control circuit is simple and therefore particularly suitable for exchange no contact switch is used. The triac are generally turned on some power larger appliances, and connected to the strong electric network, the trigger circuit interference problem is very important, usually through the optocoupler microcontroller control system trigger The signal is loaded into the SCR control electrode. In order to reduce the drive power and SCR trigger interference, AC circuit triac trigger often zero trigger circuit. Zero trigger in the voltage is zero or near zero instantly turned on. Since the zero crossing trigger, so the above-described circuit also need sinusoidal alternating zero crossing detection circuit.
A zero-crossing detection circuit
In order to improve efficiency, so that the trigger pulse and the AC voltage requirement for synchronization of every half cycle of the AC output to a trigger pulse and the trigger pulse voltage should be greater than 4V, the pulse width should be greater than 20us. FIG BT for the transformer, TPL521 – 2 optocoupler act as isolators. When the deadline sinusoidal AC voltage is near zero, optocouplers two light-emitting diodes, transistor T1 base bias resistor potentiometer, conduction, negative pulse signal output T1 end to microcontroller 80C51 external interrupts 0 input pin to cause an interrupt. Used in the interrupt service routine the timer accumulated phase shift, and then issued a synchronized triac trigger signal. The zero cross detection circuit A, B two voltage output waveform.
2 zero trigger circuit
MOC3061 optocoupler triac drive, also belong to an optocoupler, used to drive the triac BCR and play the role of isolation, R6 trigger current limiting resistor, R7 BCR gate resistor to prevent accidental trigger, improve the anti-jamming capability. When the microcontroller 80C51 of P1 0 pin output negative pulse signal T2 turns MOC3061 conduction, trigger BCR conduction is plugged into an AC load. Further, if the triac then inductive AC load, because ahead of the load current of the power supply voltage to a phase angle, therefore, when the load current is zero, the supply voltage is a reverse voltage, plus the self-inductance of the inductive load electromotive el, making triac withstand voltage value far exceeds the supply voltage. Although triac the reverse conducting, but easy to breakdown, so must the triac can withstand reverse voltages. Generally between the poles of an RC RC snubber circuit triac overvoltage protection, C2 in Figure 3, R8 RC RC snubber circuit in parallel triac.
Triac zero trigger circuit is mainly used in the control system are AC load control circuit, electric furnace, high-power AC motor can be controlled exchange equipment, work safety proven and reliable. This article focuses on the zero-crossing detection and trigger circuit. As for the software design is relatively simple, when the zero-crossing detection circuit zero crossing detection to generate an interrupt request, the interrupt service routine by the microcontroller 80C51 P1. Pins a trigger pulse to trigger triac conduction, space is limited , will not repeat them here.
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