LED characteristic analysis

1. The meaning of limit parameters

(1) Allowable power consumption Pm: The maximum value of the product of the forward DC voltage applied to the two ends of the LED and the current flowing through it. If this value is exceeded, the LED will heat up and be damaged.

(2) Maximum forward DC current IFm: The maximum forward DC current allowed to be applied. If this value is exceeded

, the diode may be damaged. (3) Maximum reverse voltage VRm: The maximum reverse voltage allowed to be applied. If this value is exceeded, the light-emitting diode may be broken down and damaged. (4) Working environment topm: The ambient temperature range in which the light-emitting diode can work normally. Below or above this temperature range, the light-emitting diode will not work normally and the efficiency will be greatly reduced.

2. The meaning of electrical parameters

(1) Spectral distribution and peak wavelength: The light emitted by a certain light-emitting diode is not a single wavelength

(2) Luminous intensity IV: The luminous intensity of a light-emitting diode usually refers to the luminous intensity in the normal direction (for cylindrical light-emitting tubes, it refers to its axis). If the radiation intensity in this direction is (1/683) W/sr, the light is 1 candela (symbol: cd). Since the luminous intensity of general LEDs is small, the luminous intensity is often measured in candela (mcd).

(3) Spectral half width Δλ: It indicates the spectral purity of the light-emitting tube. It refers to the interval between the two wavelengths corresponding to the 1/2 peak light intensity in Figure 3.

(4) Half-value angle θ1/2 and viewing angle: θ1/2 refers to the angle between the direction where the luminous intensity value is half of the axial intensity value and the luminous axis (normal direction).

Twice the half-value angle is the viewing angle (or half-power angle).

The coordinate of the perpendicular bisector (normal line) AO is the relative luminous intensity (i.e. the ratio of the luminous intensity to the maximum luminous intensity). Obviously, in the normal direction, the greater the angle away from the normal direction, the smaller the relative luminous intensity.

(5) Forward operating current If: It refers to the forward current value when the light-emitting diode emits light normally. In actual use, IF should be selected to be less than 0.6·IFm according to needs.

(6) Forward operating voltage VF: The operating voltage given in the parameter table is obtained under a given forward current. It is generally measured when IF=20mA. The forward working voltage VF of the light-emitting diode is between 1.4 and 3V. When the external temperature rises, VF will decrease.

(7) VI characteristics: The relationship between the voltage and current of the light-emitting diode.

When the forward voltage is less than a certain value (called the threshold), the current is extremely small and no light is emitted. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and light is emitted. The forward voltage, reverse current and reverse voltage of the light-emitting tube can be obtained from the VI curve. The forward reverse leakage current IR of the light-emitting tube is less than 10μA.