An Isolated Power Factor Corrected Power Supply Utilizing the Transformer Leakage Inductance

Abstract

The widespread use of electronic devices increases the need for compact power factor corrected power supplies. This paper describes an isolated power factor corrected power supply that utilizes the leakage inductance of the isolation transformer to provide boost inductor functionality. The bulk capacitor is in the isolated part of the power supply allowing for controlled startup without dedicated surge limiting components. A control method based on switch timing and input/output voltage measurements is developed to jointly achieve voltage regulation and input power factor control. A prototype design is implemented with detailed measurements and waveforms shown to confirm the desired functionality.

An Improved Single-Stage PFC AC–DC Power Supply

“…This is a factor of 1.6 higher than the case in [4] with no ZCS in the active rectifier with the same leakage inductance and switching frequency. This increase is due to two factors:…”

“…A prototype power supply using the improved ZCS control has been designed targeting a power level of 1.25kW to illustrate the zero current switching as well as operation at a higher power level than the 300W in [4]. An nominal output voltage level of 125V at 10A is chosen with the source being from the 230V ±10% AC grid.…”

“…For many applications such as electric vehicle chargers, portable inverter welders and plasma cutters, light weight is an important consideration. The single stage architecture in [4] is based on using a single magnetic core for a transformer whose leakage inductance is used in a step up (boost) configuration.…”

“…However, the design in [4] requires hard switching of the switches in the secondary side active rectifier.…”

“…A discontinuous conduction mode (DCM) and continuous conduction mode (CCM) can be identified dependent on whether the inductor current I L returns to zero in each half period T /2 as detailed in [4]. The discontinuous conduction mode inherently provides for zero current switch on of the shorting switches M3 and M4 and no recovery losses in the diodes D1 and D2, but the continuous conduction mode requires switch on with non zero current values and hard turn off of the diodes with the associated recovery loss.…”