Abstract: The invention relates to a dynamic focusing circuit with an output (1) for supplying a dynamic focusing voltage (Vf) to a focus electrode of a cathode ray tube (CRT). The dynamic focusing voltage (Vf) has, in succession, a falling edge, an almost flat part and a rising edge. A first transistor (T1) has a main current path (c1, e1) coupled between a supply voltage (V+) and the output (1). An arrangement of a secondary winding (Ls) of a transformer (T) and a current determining circuit (12) is coupled between the control input (b1) of the first transistor (T1) and the output (1). The current determining circuit (12) supplies a bias current (Ib). A second transistor (T2) has a control electrode (b2) for receiving an input voltage (Vi) related to a parabolically shaped input waveform (Vin), and a main terminal (c2) coupled to the control input (b1) of the first transistor to withdraw current (Id) from the control input (b1).

Abstract: A focusing waveform (Vf) is obtained by first generating (2) two intersecting triangular waveforms of opposite phase and half the deflection frequency. Subsequently, the difference between these two triangular waveforms is multiplied by itself for generating a second-order parabolic waveform at the deflection frequency, at which the parabolic waveform has a lower side which is located at zero and is not disturbed by DC offsets. In an advantageous embodiment of the invention, which is eminently suitable for multimedia applications, the focusing waveform has the correct form and amplitude, independent of the deflection frequency.