Thyristor Semiconductor Products Page 20 Thyristor

2014 Littelfuse, Inc. Specifications are subject to change without notice. Revised: 12/14/14 Teccor brand Thyristors AN1001 P 3 P1 N 2 N 4 P5 MT1 MT2 SIDAC P N P N P N P 2 3 4 5 2 3 4 1 Equivalent Diode Relationship Schematic Symbol MT2 MT1 MT2 N N P MT1 MT2 Block Construction Schematic Symbol DIAC Load N P MT1 MT2 Cross-section of Chip Equivalent Diode Relationship MT1 MT2 Basic Operation The SIDAC is a multi-layer silicon semiconductor switch. using two Shockley diodes connected inverse parallel. Figure AN1001.7 also shows the schematic symbol for the SIDAC. Figure AN1001.7 SIDAC Block Construction The SIDAC operates as a bidirectional switch activated by voltage. In the off state, the SIDAC exhibits leakage currents (I DRM ) less than 5 A. As applied voltage exceeds the SIDAC V BO , the device begins to enter a negative resistance switching mode with characteristics similar to an avalanche diode. When supplied with enough current (I S ), the SIDAC switches to an on state, allowing high current to flow. When it switches to on state, the voltage across the device drops to less than 5 V, depending on magnitude of the current flow. When the SIDAC switches on and drops into regeneration, it remains on as long as holding current is less than maximum value (150 mA, typical value of 30 mA to 65 mA). The switching current (I S ) is very near the holding current (I H ) value. When the SIDAC switches, currents of 10 A to 100 A are easily developed by discharging small capacitor into primary or small, very high- voltage transformers for 10 s to 20 s. The main application for SIDACs is ignition circuits or inexpensive high voltage power supplies. Geometric Construction Figure AN1001.8 Cross-sectional View of a Bidirectional SIDAC Chip with Multi-layer Construction Basic Operation The construction of a DIAC is similar to an open base NPN transistor. Figure AN1001.9 shows a simple block construction of a DIAC and its schematic symbol. Figure AN1001.9 DIAC Block Construction The bidirectional transistor-like structure exhibits a high- impedance blocking state up to a voltage breakover point (V BO ) above which the device enters a negative-resistance region. These basic DIAC characteristics produce a bidirectional pulsing oscillator in a resistor-capacitor AC circuit. Since the DIAC is a bidirectional device, it makes a good economical trigger for firing Triacs in phase control circuits such as light dimmers and motor speed controls. Figure AN1001.10 shows a simplified AC circuit using a DIAC and a Triac in a phase control application. Figure AN1001.10 AC Phase Control Circuit Geometric Construction Figure AN1001.11 Cross-sectional View of DIAC Chip Fundamental Characteristics of Thyristors (continued)

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