Dynamic focusing circuit for a monitor

Claim 1

A dynamic focusing circuit for a monitor having a microcomputer which generates a mode control signal by determining a mode when inputting horizontal and vertical synchronization signals, and for providing a dynamic focus voltage to a focus grid of a cathode ray tube through a flyback transformer according to the mode control signal, comprising: a synchronization process section for outputting horizontal and vertical synchronization signals of one polarity by inputting the horizontal and vertical synchronization signals; waveform control signal generation section for generating a waveform control signal synchronized with the horizontal and vertical synchronization signals of the synchronization process section; a focus signal generation section for generating horizontal and vertical focus signals according to the waveform control signal of the waveform control signal generation section; a buffer for generating a dynamic focus signal by summing the horizontal and vertical focus signals of the focus signal generation section; a parabolic waveform signal output section for amplifying the dynamic focus signal and applying the amplifying dynamic focus signal to the focus grid through the flyback transformer; a gain control section for controlling a voltage magnitude of the horizontal and vertical focus signals of the focus signal generation section according to the mode control signal; and a waveform adjustment section for adjusting a waveform of the horizontal and vertical focus signals of the focus signal generation section by inputting the mode control signal; wherein the waveform adjustment section includes a switching section for turning one and off according to the mode control signal, a first capacitor connected between an output terminal of the switching section and a terminal of the focus signal generation section, and a second capacitor connected between the terminal of the focus signal generation section and ground, the first and second capacitors are connected in parallel with respect to the terminal of the focus signal generation section; wherein the switching section includes a first transistor for turning on and off according to the mode control signal and a second transistor for turning on and off in reverse order corresponding to the turning on and off of the first transistor, the first capacitor being connected to the collector of the second transistor.