LED driver circuit

An LED driver circuit that controls driving of an LED lamp in response to an on/off state of a mechanical switch device, comprising:

• a first terminal to which a current path of the switch device is connected at one end thereof;
• a second terminal to which the current path of the switch device is connected at another end thereof, the switch device and a battery being connected in series between the first terminal and the second terminal;
• a detection circuit that periodically detects a current flowing to the first terminal and outputs a detection signal responsive to a result of the detection at a first node;
• a comparison circuit that compares a detection voltage responsive to the detection signal with a threshold voltage and outputs a comparison result signal responsive to a result of the comparison;
• and
• a control circuit that controls a current detection operation of the detection circuit and controls driving of the LED lamp based on the comparison result signal,
• wherein the control circuit determines that the switch device is in an on state and the current path is conductive between the one end and the another end if the comparison result signal indicates that the detection voltage is equal to or higher than the threshold voltage, and
• determines that the switch device is in an off state and the current path is interrupted between the one end and the another end if the comparison result signal indicates that the detection voltage is lower than the threshold voltage,
• wherein the detection circuit comprises:
• a first switch element that is connected to the first terminal at one end thereof and is turned on and off under the control of the control circuit;
• a detection capacitor that is connected to another end of the first switch element at one end thereof and to the first node at another end thereof;
• a detection resistor that is connected to the first node at one end thereof and to the second terminal at another end thereof;
• and
• a discharge resistor that is connected in parallel with the detection resistor and the detection capacitor between another end of the first switch element and the second terminal, the discharge resistor being connected to the another end of the first switch element at one end thereof and to the second terminal at another end thereof,
• the control circuit
• controls the first switch element to periodically switch on and off, and
• the detection circuit
• outputs the detection signal at the first node.