Cathode current detecting method and detecting circuit capable of correctly detecting cathode current by clamping leak current at 0 V

摘要

A cathode current detecting method wherein both a highlight detection pulse used to detect a white component and a cutoff detection pulse used to detect a black component are input to a signal input unit, and a cathode current flowing through a cathode is detected which corresponds to one of the highlight detection pulse and the cutoff detection pulse, includes the steps of: outputting a leak current detection pulse having the same magnitude as that of the cutoff detection pulse at a preselected timing; prohibiting an electron beam emitted from the cathode from flowing through an anode at the preselected timing; and detecting the leak current flowing through the cathode in response to the leak current detection pulse at the preselected timing to clamp a voltage corresponding to the leak current to a predetermined reference potential. A cathode current detecting circuit is provided wherein both a highlight detection pulse used to detect a white component and a cutoff detection pulse used to detect a black component are inputted to a signal input unit, and a cathode current corresponding to an electron beam flowing from a cathode to an anode based upon one of the highlight detection pulse and the cutoff detection pulse, of: includes a signal output circuit for outputting a leak current detection pulse having the same magnitude pulse as that of the cutoff detection pulse at a preselected timing; A current for prohibiting the electron beam emitted from the cathode from flowing at the preselected timing; a prohibit signal circuit for outputting a signal used to cause the prohibiting circuit to perform a prohibit operation in response to the output from the signal output circuit at the preselected timing; and a clamping circuit for detecting a leak current flowing through the cathode in response to the leak current detection pulse at the preselected timing to clamp a voltage corresponding to the leak current to a predetermined reference potential.