Patent ID: 6483725
Filing Date: 2002-11-19
Classification: H02M

Abstract:
A DC/DC conversion circuit (1) comprising a transformer (2) with a primary winding (3), a secondary winding (4), and an auxiliary winding (5); a switching transistor (T) which forms a series circuit with the primary winding (3) between first and second DC voltage input connection terminals (6; 7); a start circuit (R1, C1) which is connected to a control electrode of the switching transistor (T) for switching on the latter when the DC voltage input connection terminals (6; 7) are powered; a control transistor (Q) connected to the control electrode of the switching transistor (T) for switching off the switching transistor (T) in dependence on a current flowing in said series circuit during operation; and a voltage control circuit (8) connected to the auxiliary winding (5) and the control transistor (Q) for controlling an output power supplied at the secondary winding (4) of the transformer (2) during operation through switching-on of the switching transistor (T) in a controlled manner in dependence on the value of a current flowing in the primary winding (3), characterized in that the conversion circuit (1) is designed such that during operation a voltage required for switching the switching transistor (T) on is built up on the control electrode thereof in a time period whose length is inversely proportional to the value of the output power supplied to the secondary winding.