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1. (WO1998052273) SWITCHED-MODE POWER SUPPLY, AN ELECTRIC SHAVER, AND A METHOD OF CONVERTING DIRECT VOLTAGES
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CLAIMS

1. A switched-mode power supply comprising a transformer (2) having a primary winding (4) connected to a first pair of direct voltage terminals (8, 10) in a primary circuit via a first controllable switching element (6) and having a secondary winding (22) included in a secondary circuit via a unidirectional element (26) and a load (24) to be powered, characterized in that the switched-mode power supply further comprises a second controllable switching element (34) which, in series with the secondary winding (22) and the load (24) to be powered, is connected to a second pair of direct voltage terminals (38, 40).

2. A switched-mode power supply as claimed in Claim 1, characterized in that the second pair of direct voltage terminals (38, 40) is connected to the first pair of direct voltage terminals (8, 10).
3. A switched-mode power supply as claimed in Claim 1 or 2, characterized in that the first pair of direct voltage terminals (8, 10) is connected to input voltage terminals (12, 14) via a rectifier bridge (16).
4. A switched-mode power supply as claimed in Claim 1, characterized in that at least one terminal of the second pair of direct voltage terminals (38, 40) is connected to one terminal of a pair of input voltage terminals (12, 14).
5. A switched-mode power supply as claimed in Claim 4, characterized in that the input voltage terminals (12, 14) are connected to the first pair of direct voltage terminals (8, 10) via a rectifier bridge (16).
6. A switched-mode power supply as claimed in Claim 1, 2, 3, 4 or 5, characterized in that one terminal (38) of the second pair of direct voltage terminals (38, 40) can be connected to a node between the secondary winding (22) and the unidirectional element (26) via a switch (42), and the second controllable switching element (34) is connected between the node and the other terminal (40) of the second pair of direct voltage terminals.
7. A switched-mode power supply comprising: a first series arrangement of an inductive element (22), a controllable switching element (34) and a load (24) to be powered, and a second series arrangement of the inductive element (22), the load (24) to be powered and a unidirectional element (26), characterized in that the inductive element (22) is a winding of a transformer (2) having another winding (4) arranged in series with a further controllable switching element (6) to receive a direct voltage.
8. An electric shaver comprising: a rechargeable battery (24), an electric motor (30), a switch (32) for connecting the motor (30) to the battery (24), and a switched-mode power supply as claimed in any one of the preceding Claims, for energizing at least the battery (24) and/or the motor (30).
9. A method of converting direct voltages, in which by means of a first switching element a periodically interrupted direct voltage is applied to a first winding of a transformer which, via a unidirectional element, has a second winding connected to a load to be powered, characterized in that the second winding is also used as a self-inductance which, in series with a second switching element and the load to be powered, is arranged to receive a further direct voltage, the unidirectional element acting as a freewheel diode.
10. A method of converting direct voltages by means of a first series arrangement of an inductive element, a controllable switching element and a load to be powered, and a second series arrangement of the inductive element, the load to be powered and a unidirectional element, characterized in that for the inductive element a winding of a transformer is used, which transformer has another winding arranged in series with a further controllable switching element to receive a direct voltage.