Light emitting device drive circuit and vehicle lamp using the same

A vehicle lamp comprising:

• a light emitting device;
• and
• a light emitting device drive circuit for supplying a predetermined output current IL0 to a light emitting device to drive the light emitting device, the light emitting device drive circuit comprising:
• a power conversion unit for receiving an input electric power and performing an electric power conversion on the input electric power in accordance with a control signal so as to generate the predetermined output current;
• a current detection unit for detecting an output current IL of the power conversion unit;
• a temperature detection unit for detecting a case internal temperature TD, which is an interior temperature of a case for accommodating the light emitting device drive circuit;
• a regulation unit being operable to:
• a) detect whether a temperature TL of the light emitting device has reached a first predetermined temperature TLmax based on TD, IL, and a temperature rise coefficient α in connection with IL, the temperature rise coefficient α being set in advance so that TL satisfies a relationship of TL=TD+α·IL, and
• b) generate a regulation signal for reducing IL0 so that TL does not exceed TLmax in the event that a result of the detection indicates that TL has reached TLmax;
• and
• a control unit for controlling IL0 in accordance with the regulation signal from the regulation unit.

A vehicle lamp comprising:

• a light emitting device;
• and
• a light emitting device drive circuit for supplying a predetermined output current IL0 to a light emitting device to drive the light emitting device, the light emitting device drive circuit comprising:
• a power conversion unit for receiving an input electric power and performing an electric power conversion on the input electric power in accordance with a control signal so as to generate the predetermined output current;
• a current detection unit for detecting an output current IL of the power conversion unit;
• a temperature detection unit for detecting a case internal temperature TD, which is an interior temperature of a case for accommodating the light emitting device drive circuit;
• a regulation unit being operable to:
• a) detect whether a temperature TL of the light emitting device has reached a first predetermined temperature TLmax based on TD, IL and a temperature rise coefficient α in connection with IL, the temperature rise coefficient a being set in advance so that TL satisfies a relationship of TI=TD+α·IL, and
• b) generate a regulation signal for reducing IL0 so that TL does not exceed TLmax in the event that a result of the detection indicates that TL has reached TLmax;
• and
• a control unit for controlling IL0 in accordance with the regulation signal from the regulation unit,
• wherein the regulation unit includes a regulation signal generation unit,
• wherein the regulation signal generation unit detects whether TL has reached TLmax by detecting whether TD has reached a second predetermined temperature TDth which is set in advance so as to satisfy a relationship of TDth=TLmax−α·IL0, and generates the regulation signal so as to prevent TD from exceeding TDth in the event that a result of the detection indicates that TD has reached TDth,
• wherein the regulation unit further comprises a temperature decrease detection unit for detecting a decrease in temperature of the light emitting device based on IL and a in the event that IL0 has been decreased,
• wherein the regulation signal generation unit regulates the regulation signal so that TD does not exceed a third predetermined temperature TDmax by changing TDth in a range that TDth does not exceed TDmax in accordance with a variation of the decrease in temperature from the temperature decrease detection unit in the event that IL0 has been decreased,
• wherein the current detection unit generates a current detection signal in accordance with IL,
• wherein the temperature detection unit generates a temperature detection signal in accordance with TD,
• wherein the temperature decrease detection unit includes an amplifier circuit which utilizes the temperature rise coefficient α as an amplification factor and the temperature decrease detection unit generates a temperature decrease signal in which a value of the current detection signal is amplified in the event that the value of the current detection signal has decreased, and
• wherein the regulation signal generation unit comprises:
• a comparison signal generation circuit for generating a comparison signal in accordance with TDth and changing the comparison signal in accordance with a variation of the temperature decrease signal;
• and
• a regulation signal generation circuit for receiving the comparison signal and the temperature detection signal and generating the regulation signal in which the value of the current detection signal is regulated based on a difference in value between the comparison signal and the temperature detection signal.