Thomson Consumer Electronics S.a.

Wolfgang Heidebroek

Chun Hsing Wu

Zeith W Hsing

A television receiver has a switched mode power supply for regulating output voltages including the B+ output to a flyback transformer, by generation of output pulses to a power transformer. A controller for the power supply is coupled in two feedback loops, one responsive to a pulse width modulator coupled to the flyback transformer and the other comparing the output voltage with an internal reference for free running operation. The first feedback loop takes precedence and is active in the run mode of the television receiver. In the standby mode when horizontal rate pulses are absent, the second feedback loop takes over. The second feedback loop has a different reference level than the first, such that when switching from the run mode to the standby mode a transition interval occurs in which no pulses are output by the controller, thereby causing the B+ voltage to the flyback transformer to fall. During this transition interval, horizontal scanning signals continue at falling amplitude, and a signal is input to the kinescope drivers, thereby collapsing the picture and draining the ultor voltage on the screen anode. The reoccurrence of controller pulses when the output voltage of the power transformer has fallen to the new lower reference level is used to positively switch operation of the receiver at the conclusion of the transition interval.

Run/standby control with switched mode power supply

A television receiver includes a high voltage kinescope driver amplifier having an input for receiving a video signal and a further input for receiving a character input signal from a low voltage character amplifier. When switching from a 'run' mode to a 'stand-by' mode, a control circuit generates a turn-off command signal for disabling the kinescope high voltage supply and concurrently initiating turn-off of the receiver deflection circuit at a controlled rate during a transition interval between the 'run' and 'standby' operating modes. The turn-off command is further applied during the transition interval to an input of the character amplifier so as to over-ride any character signal which may be present to drive the output of the character amplifier to a maximum brightness level which, in turn, over-rides any video signal applied to the high voltage amplifier. Accordingly, the kinescope is driven to a maximum brightness level during the transition interval regardless of the values of either the video signal or the character signal thereby fully discharging the kinescope, avoiding potential spot burn and preventing after-glow.

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Singapore, Singapore

Wolfgang Heidebroek