Patent ID: 7250810

Claim:
A multi-mode charge pump drive circuit for driving a light emitting diode, comprising: a multi-mode charge pump for converting an input voltage source into a drive voltage to be supplied to the light emitting diode, wherein the multi-mode charge pump is operated with a plurality of modes, each of which provides a different multiplicative ratio for converting the input voltage source into the drive voltage; a switch control circuit for applying a switch control signal to the multi-mode charge pump so as to operate the multi-mode charge pump alternately between a charging phase and a discharging phase, wherein the switch control signal has a slew rate for determining a rate of transferring between the charging phase and the discharging phase; a current regulation circuit having a current setting unit and a current regulating unit, the current setting unit being used for determining a reference current, the current regulating unit having a current regulating terminal and a feedback detecting terminal, the current regulating unit being coupled to the light emitting diode so as to control a current flowing through the light emitting diode to become proportional to the reference current, the feedback detecting terminal being used for providing a feedback signal representative of a current regulation characteristic voltage; an error amplifier for generating an error signal based on a difference between the feedback signal and a reference voltage source; a variable resistance unit coupled between the input voltage source and the multi-mode charge pump for adjusting a variable resistance in response to the error signal; and a mode selection circuit for controlling the multi-mode charge pump to selectively operate at one of the plurality of modes, wherein at a moment when the mode selection circuit changes the mode of the multi-mode charge pump, the mode selection circuit applies a mode change signal to the switch control circuit so as to reduce the slew rate of the switch control signal.