Known AC/DC power converters have utilized transformer-rectifier units (TRU's) comprising a transformer having a primary winding which receives input AC power and one or more secondary windings which are coupled to one or more rectifier circuits. The rectified transformer output is thereafter filtered to produce DC output power.
Typically, some sort of regulation scheme is utilized to maintain the DC output voltage within prescribed levels. One type of regulated AC/DC power converter is disclosed in Terry et al U.S. Pat. No. 2,642,558. This power converter includes a transformer having a primary winding coupled to an AC source and multiple secondary windings, one of which is coupled to a rectifier bridge for providing approximately half the desired output voltage at full load. A pair of additional secondary windings are coupled to the anodes of a pair of gas discharge tubes, the cathodes of which are coupled together to an output filter of the device. The gas discharge tubes are fired at a variable point in each half cycle of the AC waveform to in turn supply the proper additive voltage to the output of the full wave bridge so that the output voltage is maintained at a regulated value.
The AC/DC converter disclosed in Terry et al is rather comples in that it uses gas discharge tubes which are unreliable, large, have limited bandwidth and which must be commutated in order to turn off. The latter two factors in turn limit the maximum switching frequency and thereby prevent reduction of the output filter size. The Terry et al converter also requires the use of an auto-transformer separate and apart from the aforementioned transformer, and hence the size and weight of the overall converter are greater than would otherwise be the case if the auto-transformer were not needed. Further, the regulation scheme employed by Terry et al is unidirectional in nature, i.e. regulating voltage is always supplied in additive fashion to the output of the rectifier bridge. This means that the converter must be capable of supplying regulating voltage at a magnitude equal to the largest deviation of the desired output voltage from the voltage developed by the rectifier bridge.
Yenisey U.S. Pat. No. 3,270,270 disclosed a regulated power supply wherein an input AC power source is coupled to a first transformer primary winding. The AC power source is further coupled through a controlled switch to a second primary winding of the transformer. A pair of secondary windings of the transformer are coupled through rectifiers to output terminals of the device. A main portion of the output power is provided through the first primary winding while intermittent or variable power modulated by the controllable power switch is provided through the second primary winding and combined with the main output power to regulate same. In a further embodiment of the power supply, intermittent power is provided through each of a pair of primary windings, one of which adds intermittent power to the unregulated power and the second of which substracts intermittent power from the unregulated power.
The Yenisey device appears to disclose a bidirectional type of converter control; however, this regulation is accomplished on the primary side of the transformer. Inasmuch as the output voltage of the transformer is typically lower than the voltage on the primary side of the transformer, the Yenisey device must utilize power switches having high voltage capability. This requirement may be undesirable in certain circumstances since high-frequency switching devices which would permit a reduction in output filter size typically do not have high voltage capability together with the required current-handling capability. Furthermore, the Yenisey converter requires separate circuits for developing additive power and subtractive power. This unduly duplicates circuitry and increases the cost, size and weight of the converter.