U.S. Philips Corporation

Patrick E Smeets

Antonius A Marinus

Guy L De Bondt

The power supply apparatus serves to convert an electric direct voltage, acting as an input voltage, into an output voltage and comprises positive and negative input terminals (1, 3) which are arranged to receive the input voltage. The power supply apparatus also comprises a first series connection (7) of, at least a first coil (9) and a controllable switching element (11), which series connection interconnects the input terminals (1, 3), and a limiter circuit (29) which comprises a first capacitor (31) and a second series connection (33) of at least a second coil (35), a first rectifier element (37) and a second rectifier element (39), said second series connection being connected parallel to the first series connection in such a manner that the cathodes of the first and second rectifier elements are oriented towards the positive input terminal (1), one electrode of the first capacitor being connected to the anode of the second rectifier element and its other electrode to the junction (43) of the first coil and the switching element. The second series connection (33) also comprises an auxiliary voltage source (55) which is arranged to supply a direct voltage amounting to approximately half the input voltage and whose positive pole is oriented towards the positive input terminal (1). The presence of the auxiliary voltage source (55) prevents that upon switching off of the switching element (11) a voltage jump occurs across the switching element, which jump could cause an undesirably high energy dissipation in the switching element and also a disturbance (EMI).

Power supply apparatus comprising an improved limiter circuit

A power supply apparatus including at least one coil and a controllable switching element and a peak-limiting circuit for limiting the maximum voltage across the switching element. The peak-limiting circuit includes a capacitor and a series connection of a first rectifier element and a resistor, as well as a second rectifier element which connects one end of the series connection to the positive input terminal of the apparatus. The energy dissipation in the resistor is dependent on the duty cycle of the switching element. The duty cycle in turn is dependent on the load of the power supply apparatus. Consequently, when the load of the power supply apparatus is small, the dissipation of the apparatus will be substantially lower.

Power supply apparatus with improved efficiency

In a standby mode, a switched-mode power supply circuit may be operated in a burst mode with reduced secondary voltages (Vo1, Vo2) for supplying a standby voltage (Vo1) at a very high efficiency. In a normal operating mode of the power supply, a control circuit (1) is maintained in its on-state by a power supply voltage (Vcc) generated by the power supply. The control circuit (1) supplies control pulses (Vd) for switching the power supply. The burst mode is obtained by decreasing the power supply voltage (Vcc) generated for the control circuit (1) to such an extent that, without any further provisions, the control circuit (1) reaches an off-state in which no control pulses (Vd) are generated. In the standby mode, the control circuit (1) is supplied with current by a power supply circuit (4). In the off-state, the control circuit (1) takes up a smaller power supply current (Icc) from the power supply circuit (4) than it is supplying and the power supply voltage (Vcc) increases until the control circuit (1) reaches the on-state and starts generating the control pulses (Vd). In the on-state, the control circuit (1) takes up a larger current from the power supply circuit (4) than it is supplying and the power supply voltage (Vcc) decreases until the control circuit (1) reaches the off-state again. In this way, the power supply, in the standby mode is each time active during first periods and inactive during second periods. To bring the power supply voltage to the standby mode, the power supply voltage (Vcc) generated for the control circuit (1) is decreased in such a way that also the secondary voltage (Vs1, Vs2) are decreased.

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Eindhoven, Netherlands

Patrick E Smeets