U.S. Philips Corporation

Lammert Ter Heide

Robert H Munnig Schmidt

A flyback converter for charging a battery (6) from different input voltages in which, during the forward interval, a linearly increasing current flows through a transformer primary winding (n.sub.1). The current is turned off by a first switch (S.sub.1) at a value dictated by switching means (3). During the flyback interval the energy stored in the transformer (T.sub.r) is supplied to the battery as a charging current via the secondary winding (n.sub.2) and a diode (D.sub.1). The voltage pulses appearing across the secondary winding during the forward intervals are applied to an integrator (11) via a third switch (S.sub.3). The integrator intergrates these voltage pulses. If the output voltage of the integrator (11) exceeds a first threshold value a threshold circuit (12) is activated and turns on a second switch (S.sub.2) to disable the flyback converter. If subsequently the output voltage of the integrator decreases below a second threshold value, the second switch is turned off again by the threshold circuit so that the flyback converter can be restarted. In this way the average value of the voltage across the secondary winding during the forward intervals is maintained substantially constant. Thus, the flyback converter constitutes a constant-power source, the power supplied to the battery (6) being constant and independent of the input voltage.

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Drachten, Netherlands

Lammert Ter Heide