| 摘要 |
A hybrid or combination solid state/electromechanical relay circuit combines the advantageous features of solid state and electromechanical relays but avoids their disadvantageous features. An electromechanical relay includes a coil and a pair of contacts which close in response to energization of the relay coil; this pair of contacts being coupled between the load and the ac source. The relay coil is coupled through a switch to a source of dc coil voltage and is also connected to ground. A triac has its first and second main electrodes coupled in parallel to the pair of contacts of the electromechanical relay between the ac source and the load. A capacitor has one lead connected to the first lead of the relay coil and a second lead connected to the gate of the triac. On application of power to the coil, the capacitor charges through the triac, mining it on prior to the coil voltage of the relay reaching its design pick-up voltage. Then during switch dormancy, the coil-energized relay contacts carry the load. Likewise, upon opening of the switch, the capacitor supplies gating current to the gate of the triac device prior to opening of the relay contacts. The make or break current is carried by the triac, but the steady state current is carried by the relay contacts. The capacitor can be optically coupled to and electrically isolated from the triac device, through a bi-directional LED arrangement, and either a phototransistor pilot stage or a phototriac.
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