Patent ID: 7505035
Filing Date: 2009-03-17
Classification: G09G

Abstract:
1. A power-down circuit for a display device having a main power line carrying a main power supply voltage, a ground power line carrying a ground voltage lower than the main power supply voltage, and a display voltage generator that boosts the main power supply voltage to generate a display voltage higher than the main power supply voltage and outputs the display voltage on a display power line, the power-down circuit comprising: a voltage detector connected to the main power line and generating a shutdown signal, the shutdown signal having a first state when the main power supply voltage is above a predetermined level and a second state when the main power supply voltage falls below the predetermined level; a switch having a control terminal, for connecting the display power line to the ground power line responsive to a voltage applied to the control terminal; and a control circuit for connecting the control terminal of the switch to the ground power line when the shutdown signal is in the first state, and connecting the control terminal of the switch to the display power line through a voltage dropping element when the shutdown signal is in the second state; wherein the control circuit comprises: a pulse generator generating a pulse when the shutdown signal changes from the first state to the second state; a first transistor having a control terminal receiving the pulse from the pulse generator, and having current terminals connected to the display power line and the control terminal of the switch; and a second transistor controlled by the shutdown signal, having current terminals connected to the ground power line and the control terminal of the switch.