Patent ID: 7425799

Claim:
A current detecting circuit of a half-bridge type HID lighting circuit comprising: a main circuit including: a first DC power supply; a series circuit of a pair of main switching devices, the series circuit of the pair of main switching devices being connected between output-terminals of the first DC power supply; a series circuit of a pair of first capacitors, the series circuit of the pair of first capacitors being connected between the output-terminals of the first DC power supply; a choke coil; a secondary coil connected to diodes; and a HID lamp, wherein the choke coil and the HID lamp are connected between a midpoint of the pair of main switching devices and a midpoint of the pair of first capacitors, so that the HID lamp is lit up by making the pair of main switching devices perform on-off operations in an alternating sequence, a charge circuit charging a second capacitor through a current which is proportioned to a voltage developed in the choke coil, the charge circuit including: a second DC power supply; a resistor, the resistor being connected to the both ends of the secondary coil through the diodes, respectively; a first pair of switching devices constituting a first Miller circuit, the first pair of switching devices being connected to the resistor and the second DC power supply; and a second pair of switching devices constituting a second Miller circuit, the second pair of switching devices being connected to the first pair of switching devices and the second DC power supply; and a discharge circuit setting a voltage of the second capacitor to OV when both of the pair of main switching devices are turned off, wherein the charge circuit detects the voltage of the second capacitor as a value which is proportioned to the current flowing to the main switching devices.