Patent ID: 8314600

Claim:
A constant current driving system for stabilizing an output current, the constant current driving system comprising: a power switch, comprising: a first end, coupled to an input voltage source; a second end; and a control end, for receiving a switch control signal; wherein the input voltage source provides an input voltage; wherein when the switch control signal is asserted, the first end of the power switch is coupled to the second end of the power switch; an inductor, comprising: a first end; and a second end, for providing an output current and an output voltage; a first diode, comprising: a negative end, coupled to the first end of the inductor; and a positive end, coupled to a ground end; and a constant current driving circuit, comprising: a latch, comprising: an output end, for outputting the switch control signal; a set end, for receiving an ON signal; and a reset end, for receiving a OFF signal; wherein the latch outputs the switch control signal according to the ON signal and the OFF signal; an ON timer, for detecting whether the output current has reached a predetermined peak current value, and generating the OFF signal accordingly, the ON timer comprising: a peak current sensing resistor, comprising: a first end, coupled to the second end of the power switch, for generating a peak current sensing voltage; and a second end, coupled to the first end of the inductor, for generating a reference voltage source; and a first comparator, comprising: a first input end, for receiving the peak current sensing voltage; a second input end, for receiving a turn-on threshold voltage; and an output end, coupled to the reset end of the latch, for outputting the OFF signal; wherein a difference between the turn-on threshold voltage and a voltage generated by the reference voltage source is a constant; wherein when the peak current sensing voltage is higher than the turn-on threshold voltage, the first comparator outputs the OFF signal representing turn off; an OFF timer, for outputting the ON signal to control a time for which the switch control signal is unasserted according to the output voltage and the switch control signal; and a load, coupled between the second end of the inductor and the ground end of the constant current driving system.