| 摘要 |
PURPOSE:To enable to attain measurement of transiently thermal resistance of a light emitting diode with high sensitivity without accompanying deterioration of the characteristic by a method wherein a driving current value is changed in a square wave type to drive the light emitting diode, and voltage changes generated at the leading and trailing edges of the square wave shape of the output voltage thereof are measure. CONSTITUTION:A DC voltage VB1 fed from a variable DC voltage source VS1 is applied to a switch SW to perform opening and closing at the prescribed time duration to form square wave pulses. The square wave pulses thereof are applied to a light emitting diode driving circuit DR. Radiation emitted from a light emitting diode LED is received by a phototransistor PHT applied with a DC voltage VB3 fed from a constant DC voltage source VS3 through a resistor R3, and the detected output voltage VIv thereof is led out. When a forward directional DC current IF1 is small sufficiently as shown in the figure, by measuring voltage changes DELTAVIv at the leading and trailing edges of the square wave shape of the detected output voltage VIv, the change DELTATj of a junction temperature and transiently thermal resistance Rth can be obtained from the correction value C0 of the ratio between the voltage change and the temperature change, and electric power loss DELTAPC basing on the expression (1), (2). |
