A voltage regulator in a television apparatus.

摘要

An input signal (from 100) at a horizontal frequency is coupled to a deflection circuit (99) through an isolation transformer (T3) during a power-on operation but not during a power-off operation. A voltage (VLIN) at a horizontal deflection frequency is developed in a linearity inductor (LLIN) of the deflection circuit. The voltage in the linearity inductor is rectified to produce a rectified signal (V121) that is coupled to an input terminal (110a) of a regulator oscillator (110) of a power supply. The rectified signal (V121) is coupled to the regulator oscillator (110) in an electrically nonisolated manner with respect to electrical shock hazard isolation, and is electrically isolated by the transformer (T3) from the input signal (from 100). The regulator oscillator (110) generates trigger pulses (Sc) for controlling the switching operation of an SCR switch (200) of the power supply to produce an output supply voltage (B+) that energizes the deflection circuit (99). The regulator oscillator (110) is energized during both power-up and power-off operation and is responsive to the rectified signal (V121) to cause the frequency of the trigger pulses (Sc) of the oscillator (110) to increase during power-off operation. The increased frequency causes the anode-to-cathode voltage of the SCR switch (200) to be small enough to prevent latching of the SCR switch during the power-off operation. By preventing SCR switch latching, audible parasitic vibrations in the power supply are avoided.