Abstract: This invention relates to a control circuit for a buck power factor correction (PFC) stage. Buck PFC stages are commonly used in low cost, high efficiency power converters. These buck PFC stages are typically controlled using a very slow control loop with a crossover frequency of the order of 10 to 20 Hz. However, such a slow response is unsuitable for applications requiring overvoltage protection. The present invention overcomes the problems with the known control circuits for buck PFC stages by implementing a two stage control circuit having a fast outer loop control circuit and a slow inner loop control circuit. The fast outer loop control circuit is in operation during low load conditions and the slow inner loop control circuit is only active under load.

Abstract: The present invention relates to a power converter (90) and a method of operating same. There are numerous advantages to operating power converters using a series resonant converter (1, 21). This approach is particularly suitable for minimizing switching losses in the power converter when it is operated at high frequency. However, there are problems with the known converters in that they are prone to generate noise in the acoustic spectrum due to the fact that the converter stages are often operating at different frequencies. The present invention relates to a power converter and a method of operating same that enables the operating frequency of the converter to be controlled by a control circuit over a predetermined range of the resonant frequency. This allows reduction in acoustic noise generation and facilitates frequency smearing that will in turn reduce spectral peaks. This is achieved while maintaining output ripple within acceptable ranges.

Abstract: A sensing arrangement and method a sense winding is used to provide a voltage which represents the voltage appearing across an in-circuit magnetic component. In a flyback phase, when the component is supplying the output, that voltage represents an output voltage and in a supply phase, the supply voltage. This arrangement provides a solution to the problem of the disparity in magnitude of sense winding output during the two phases by proving a pull-up resistor arranged to apply bias to the voltage measured, the pull-up being to a first level during the supply period and to a second value during the flyback period, the first and second levels being selected such that the voltage across the sense winding is scaled differently during the supply period and the flyback period. The invention is suitable for use in a transformer based flyback power converter in which the magnitude disparity problem may be exacerbated by a turns ratio.

Abstract: The present invention provides an isolated regulating power converter with opto-coupled feedback of output (Vo) with respect to a reference level (Vset) for regulation to a converter controller. The sense of the feedback signal is such that the opto-coupler LED is ON when Vo<Vset and OFF when Vo>Vset with the effect that the LED current and power loss is zero during the times when Vo>Vset, as is normal case for many controllers at low or no load. This saves power under such circumstances. Additionally, as the LED does not load the output during this time, the proportion of time for which Vo>Vset is increased, meaning that the timing at which the switch must again be on to meet demand is extended, producing a further power saving.

Abstract: This invention relates to a transformer (1) for multi-output power supplies such as those commonly found in electronic equipment. The transformer comprises a magnetic core (3) and a plurality of windings (5, 7, 9) at least some of which are fractional windings, arranged about the magnetic core. The transformer comprises a dual transformer structure with a pair of transformers, a main transformer (11) and an auxiliary transformer (13). In a preferred embodiment, the main transformer and the auxiliary transformer are connected together. In this way, readily available magnetic components may be used in the construction of the transformer and the simple construction allows for a large cross-sectional area of transformer to be deployed so that reduced turn counts of windings may be used.

Abstract: The present invention relates to a transformer assembly (1) and a process for manufacturing same. The transformer (1) comprises a primary winding (5) wound on a PCB (9) and a secondary winding (7) mounted adjacent to the primary winding. The primary winding comprises a spiral coil, for example of wire or insulated wire, wound on the PCB. Gate drive windings (31, 33) are incorporated in the PCB (9) and there is therefore very close coupling between the primary winding and the gate drive windings. Furthermore, the secondary winding (7) is a center-tapped secondary having two halves. A flux balance winding (13) is provided to connect the two halves of the center-tapped secondary winding (7) and minimize leakage inductance thereby reducing power loss and spiking effects and obviating the need for complex control arrangements.

Abstract: This invention relates to a power converter (1) comprising a converter input (3), a converter output, a power factor pre-regulation stage (5), an isolation stage (7) and a control unit (9). The power factor pre-regulation stage (5) further comprises a buck power factor correction (PFC) circuit (15) and a bulk capacitor (25) fed by the buck PFC circuit. The amount of line current provided to the bulk capacitor (25) by the buck PFC circuit (15) may be adjusted according to the converter requirements in order to keep the voltage across the bulk capacitor (25) sufficient to ensure uniform operation of the power converter. Monitoring of the voltage across the bulk capacitor (25) and monitoring of the isolation stage (7) output current is provided to determine when additional current is to be applied to the bulk capacitor (25) and to ensure the power converter (1) operates within pre-defined parameters.

Abstract: The present invention provides an isolated regulating power converter with opto-coupled feedback of output (Vo) with respect to a reference level (Vset) for regulation to a converter controller. The sense of the feedback signal is such that the opto-coupler LED is ON when Vo<Vset and OFF when Vo>Vset with the effect that the LED current and power loss is zero during the times when Vo>Vset, as is normal case for many controllers at low or no load. This saves power under such circumstances. Additionally, as the LED does not load the output during this time, the proportion of time for which Vo>Vset is increased, meaning that the timing at which the switch must again be on to meet demand is extended, producing a further power saving.

Abstract: A sensing arrangement and method a sense winding is used to provide a voltage which represents the voltage appearing across an in-circuit magnetic component. In a flyback phase, when the component is supplying the output, that voltage represents an output voltage and in a supply phase, the supply voltage. This arrangement provides a solution to the problem of the disparity in magnitude of sense winding output during the two phases by proving a pull-up resistor arranged to apply bias to the voltage measured, the pull-up being to a first level during the supply period and to a second value during the flyback period, the first and second levels being selected such that the voltage across the sense winding is scaled differently during the supply period and the flyback period. The invention is suitable for use in a transformer based flyback power converter in which the magnitude disparity problem may be exacerbated by a turns ratio.

Abstract: The present invention relates to an AC/DC converter (1) of the type having an AC/DC conversion stage (2) and a DC/DC conversion stage (3), the AC/DC conversion stage (2) comprising an input filter stage (4), an input rectifier stage (5) and a tracking boost converter stage. The boost converter stage in turn comprises an input choke (10), a boost diode (16) and a bulk capacitor (17). The bulk capacitor (17) is arranged to store a range of voltages substantially proportional to the input voltage of the converter. The DC/DC stage (3) is arranged to receive the range of voltages from the bulk capacitor (17) and is controllable to provide a desired DC output regardless of the voltage received from the bulk capacitor (17). This is achieved through careful combination of components and use of output feedback control to control the voltage applied to an isolated transformer (41) in the DC/DC stage.