Tap Switch Regulators

Tap switch regulators use a principle called turns ratio to regulate voltage. Turns ratio states that if the number of windings on the primary side of a transformer equals the number of windings on the secondary side, then the output current will equal the input current. By varying the number of windings on the primary, you can vary the output voltage. In tap switch regulators this is accomplished with a sensor and a set of silicon-controlled rectifiers (SCRs). The sensors detect changes in the voltage and send a message to the SCRs, which open or close to change the turns ratio and therefore the transformer output. The range of regulation depends on the use of the regulator. Tap switches for the personal computer market generally range from +10 percent to -15 percent. On a 120 volt circuit that would be from 102 volts to 132 volts. Regulators for other types of products may range from +15 percent to -27 percent.

An important consideration in deciding to purchase a tap switch regulator is the reliability of SCRs. SCR initial failure rates are very high. Some studies indicate that it may be as high as 14 percent. This means that proper burn-in is extremely important, so that bad SCRs can be identified and replaced.

In selecting tap switch regulators, it is important to select a good product from a quality manufacturer. It should also have the proper current-handling perimeters for the job it is doing. Given this, tap switch regulators can be very reliable.