Negative-Feedback High-Efficiency AC Voltage Regulator

An ac voltage regulator capable of operating from the mains with excellent regulation and considerable power-handling capacity is achieved by means of a negative-feedback configuration that aims at high efficiency. Practical efficiencies as high as 95 percent and regulation as low as 0.02 percent are easily achieved with a little extra circuitry. To illustrate the scheme, a model ac regulator was built to deliver 90-W output power in a 137-Ω resistive load at V
o
= 111 V rms at 50 Hz from an input source fluctuating between V
in
= 115 to 140 V rms. The overall efficiency when the input is at the lower limit is 96.5 percent and the efficiency drops to 79.3 percent when the input is on the higher limit giving an average efficiency of 88 percent. The output voltage varies only by 0.1 V rms for a 25-V input fluctuation thus giving a regulation of 0.4 percent. In addition to the many applications as voltage stabilizers in television sets, refrigerators, and small motors, etc., this scheme is most suited as a general control element in many systems as temperature controller and speed controller, etc.