Patent ID: 8716954

Claim:
An LED drive circuit for driving an LED comprising: a reactor accumulating power energy to supply a current to the LED; a switch element configured to pass a current through the reactor as being ON and to supply energy accumulated in the reactor to the LED as being OFF; a current detector detecting a current passing through the switch element; a constant current circuit configured to generate a first control signal to control a current passing through the switch element to be constant based on a current value detected by the current detector; a disconnection detector configured to generate a second control signal to keep the switch element OFF if determined that a current equal to or over a predetermined value passes through the switch element when a predetermined time elapses after the timing at which the switch element changes its state from ON to OFF, according to a current detected by the current detector and the first control signal generated by the constant current circuit; and a driver of the switch element configured to drive the switch element according to the first control signal generated by the constant current circuit and keeps the switch element OFF in case of a disconnection according to the second control signal generated by the disconnection detector in priority to the first control signal, wherein the current detector is a resistor that is connected in series with the switch element and generates a voltage corresponding to a current passing through the switch element, wherein the disconnection detector includes: a delay circuit configured to provide the first control signal generated by the constant current circuit with a predetermined delay and outputs the delayed signal; a comparator comparing the voltage generated by the resistor with a predetermined reference voltage and outputs a comparison result; and a latch circuit configured to generate a latch signal if determining that a disconnection has occurred and outputs the latch signal as the second control signal, according to the output from the delay circuit and the output from the comparator.