| What must be further understood is that | | | | relays, contactors and switches all will exhibit this |
| mechanical relays, contactors, and switches | | | | type of behavior. |
| operate in a random manner with respect to the | | | | Solid-state triac devices may be used to interrupt |
| electrical signal to be switched. Imagine a 60Hz | | | | the flow of electricity in a manner that is |
| AC power circuit. A mechanical relay, contactor | | | | synchronous with the AC current waveform. |
| or switch will interrupt this circuit in a random | | | | Triacs are three-terminal, solid-state |
| manner with respect to the AC power waveform | | | | semiconductor devices which permit the flow of |
| passing through it. If the circuit is interrupted at | | | | AC current through two terminals so long as the |
| a moment when the AC current flow is low, then | | | | third, the trigger, is energized. Triacs have the |
| little reverse voltage will result. If however, the | | | | additional, highly desirable property that electrical |
| circuit is interrupted at an instant when the AC | | | | current flow stops when current flowing through |
| current flow is high, then a corresponding high | | | | the device is zero. This may seem obvious, but |
| reverse voltage will result. | | | | imagine the following: AC Current is flowing |
| What meaning does this have for the electronic | | | | through your inductive circuit. You now wish to |
| product design engineer? Mechanical circuits are, | | | | turn that circuit off. You do so by removing the |
| in fact, circuits that interrupt the flow of electricity | | | | trigger signal from your solid state triac device. |
| in a ‘random’ manner - random, of | | | | The device continues to conduct electricity until |
| course, with respect to the AC current flowing | | | | the AC current waveform reaches zero, at which |
| through that circuit at any particular instant. In a | | | | time no further AC current flows until the device |
| circuit that exhibits high inductance, such as a | | | | is triggered again. The action of the solid state |
| motor circuit, a solenoid circuit, or an | | | | triac device ensures that the circuit is broken only |
| electromagnetic circuit; reverse voltage can get | | | | when zero current is actually flowing. |
| very high. High voltages can damage and pit | | | | Return to our inductive circuit. The solid state |
| mechanical contacts. High voltages can cause | | | | triac device ensures that the circuit’s energy |
| noise and disturbance to other nearby sensitive | | | | flow is interrupted only when the AC current |
| circuitry. | | | | waveform reaches its instantaneous zero. The |
| Energy is stored in the electro-magnetic field that | | | | stored energy in the circuit’s electro-magnetic |
| surrounds an inductive circuit. The stored energy | | | | field will be at or near zero when the current |
| is high when the corresponding current flow in | | | | flowing through that circuit is at or near zero. |
| that circuit is high. Upon circuit interruption, the | | | | With no field energy, there will be nothing to |
| flow of current through the circuit immediately | | | | cause the high voltages we previously observed in |
| stops. As current flow stops, the circuit’s | | | | mechanical switching systems. The solid state |
| electro-magnetic field collapses sending its unit of | | | | triac device guarantees that circuit interruption will |
| stored energy back into the wires from which it | | | | occur only at the zero-current instants thereby |
| came. If the current is high, and the field is large, | | | | eliminating the worry of high voltage switching |
| then a high voltage will be created. Mechanical | | | | transients. |