To provide a protection circuit in which judgement precision of lighting status of a lamp is improved by leaps and bounds and a lamp driving device having the protection circuit.
The protection circuit has a first detection resistor R1 connected to an electrode on low voltage side of a first lamp 30a, a second detection resistor R2 which is connected to an electrode on low voltage side of a second lamp 30b and has a resistance value equal to or higher than that of the first detection resistor R1, and a second diode D2 which is connected between the electrode on low voltage side of the first lamp 30a and the electrode on low voltage side of the second lamp 30b and shuts off passage of electric current output from the second lamp 30b. A judgment circuit 402 compares a detection voltage obtained from the electric current flowing in a region connected to the electrode on the low voltage side of the first lamp 30a to which the second diode D2 is connected with a prescribed reference voltage, and based on the comparison result, judges lighting status of the first lamp 30a and the second lamp 30b.
Iwa Saki Kokuni
Masakazu Ito
Shunichi Takahashi
Toshio Takamatsu