Light-Emission Drive Circuit Pull-Up PMOS Latch-Up Prevention

The patent changes the electrical parameters of the pull-up device by using a PMOS transistor instead of a simple resistor, and introduces a switching section that dynamically adjusts the pull-up resistance based on the voltage level at the strobe terminal. This parameter change allows the device to maintain high pull-up resistance when voltage is low (preventing latch-up) while providing adequate pull-up function when voltage is high (preventing LED always-on condition).

The patent makes the pull-up resistance dynamic by introducing a switching section controlled by the voltage at the strobe terminal. When the voltage is low, the switching section turns on the PMOS transistor to provide strong pull-up; when the voltage is high, the switching section turns off the PMOS transistor to prevent reverse current. This dynamic behavior resolves the contradiction between preventing LED always-on and preventing latch-up breakage.

The patent merges the pull-up function and the latch-up prevention function into a single integrated circuit within the driver IC. The PMOS transistor and switching section are combined to form a unified pull-up device that simultaneously provides pull-up capability and prevents reverse current flow. This integration eliminates the need for separate buffer devices, thereby improving reliability while avoiding increased manufacturing costs.

The patent makes the pull-up device multi-functional by designing it to perform both the traditional pull-up function (preventing LED always-on) and the additional function of preventing latch-up breakage. The PMOS transistor with switching section serves dual purposes: providing pull-up current when needed and blocking reverse current when voltage levels conflict. This universality eliminates the need for additional buffer devices.