The present invention relates to power converters, and more particularly to providing a power factor correction circuit that eliminates an inrush current limit circuit for a power converter.
An important consideration in the design of power converters is that a power converter provide a high power factor. Power factor correction (PFC) circuits are commonly used in desktop computers where a high power factor is required. The power factor of power converters generally refers to the ratio of the true power to the product of the voltage and current in the circuit. A high power factor is one which approximates or exceeds 0.9, with the maximum power factor being 1.0.
One type of power converter, a boost-type power converter, is a well-known and practical choice for a high power-factor converter used in motor drive and power supply applications. While this converter circuit realizes the line current waveform needed to comply with line harmonic standards, both present and anticipated, and can provide a nearly full conduction angle, a boost converter requires the output voltage to always be higher than the peak input voltage. If a lower voltage is needed as, for example, in motor drives operating at lower speeds, then, the voltage reduction function must be performed separately. This adds to the converter cost and complexity. Boost-type converters must also have power on input current surge limiting circuits, and output short-circuit current limiting circuits.
Buck-type power converters are also generally well-known in the art, and are frequently used in DC to DC converters. They can also used as AC to DC power converters. A major limitation of buck-type converters is that the duration for which power can be extracted from a single-phase line supply (input conduction angle) decreases when the converter output voltage increases. A consequence of this limitation is the cost of the power converter increases while the benefits derived from using it decrease, especially when a wide range of output voltages (motor speeds) is required.
A need exists for a power factor correction circuit that avoids limitations of prior art circuits. In particular, a need exists for a power factor correction circuit that eliminates an inrush current limit circuit and that allows the DC voltage to be lower than the peak of AC line voltage. The present invention addresses such a need.
The present invention provides aspects for a power converter with power factor correction circuit. The aspects include a buck/boost circuit for achieving a DC voltage from an AC input voltage signal line without developing an inrush current from the AC input voltage and a DC/DC converter circuit coupled to the buck/boost circuit for converting the DC voltage to a desired voltage level. The PFC circuit in accordance with the present invention is straightforward, cost effective and capable of being easily adapted to current technology.