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Applications of zero voltage crossing optically isolated triac drivers

Posted: 18 Jun 2009 ?? ?Print Version ?Bookmark and Share

Keywords:triac drivers? zero voltage crossing? circuit driving?

The zero-cross family of optically isolated triac drivers is an inexpensive, simple and effective solution for interface applications between low current DC control circuits such as logic gates and microprocessors and AC power loads (120-, 240- or 380V, single or 3-phase).

These devices provide sufficient gate trigger current for high current, high voltage thyristors, while providing a guaranteed 7.5kV dielectric withstand voltage between the line and the control circuitry. An integrated, zero-crossing switch on the detector chip eliminates current surges and the resulting EMI and reliability problems for many applications. The high transient immunity of 5,000V/?s, combined with the features of low coupling capacitance, high isolation resitance and up to 800V specified VDRM ratings qualify this triac driver family as the ideal link between sensitive control circuitry and the AC power system environment.

Optically isolated triac drivers are not intended for standalone service. They will, however, replace costly and space-demanding discrete drive circuitry having high component count consisting of standard transistor optoisolators, support components (including a full wave rectifier bridge, discrete transistor, trigger SCRs and various resistor and capacitor combinations).

This application note describes the operation of a basic driving circuit and the determination of circuit values needed for proper implementation of the triac driver. Inductive loads are discussed along with the special networks required to use triacs in their presence. Brief examples of typical applications are presented.

View the PDF document for more information.

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