Analysis of the current voltage curve of the hotte

2022-08-02
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Analysis of current and voltage curves of light-emitting diodes discussion on the significance of light-emitting diode parameters

this paper mainly introduces light-emitting, and focuses on the voltage and current curves and parameters of light-emitting diodes

analysis of current voltage curve of LED

draw volt ampere characteristic curves of red, green and blue LED in the same coordinate system

compare the volt ampere characteristic curves of red, green and blue light-emitting diodes to qualitatively judge the on voltage

it can be seen from the figure that the on voltage of red LED is the smallest, about 2.00v; Blue takes the second place, about 3.12v; The green LED

has a maximum on voltage of about 3.21v

it is easy to know from the volt ampere characteristic curve of LED. When the diode is turned on in the positive direction, the change of LED current with voltage at the beginning is almost invisible, and the LED does not emit light. However, when the voltage is greater than a certain value (after the starting voltage), the change rate of current with voltage increases linearly, and the red diode increases the fastest

analysis of working current of LED

design principle of LED circuit:

the reverse breakdown voltage of LED is about 5V. Its forward volt ampere characteristic curve is very steep. When it is used, the current limiting resistor must be connected in series to control the current through the tube. The current limiting resistance R can be calculated by the following formula: r = (e-uf)/if

where e is the power supply voltage, UF is the forward voltage drop of LED, and if is the general working current of LED

note: in the actual design, the current limiting resistance is often increased to reduce the working current and prolong the service life. The empirical value is ma

2. Characteristic analysis:

(1) there is no linear relationship between brightness and current. When the current reaches a certain value, the brightness changes little. As long as the current exceeds the maximum forward current, it will burn. The special main information is that the general current is selected at Ma

(2) light emitting diodes are current type devices. Generally, 10 Ma of static display has enough brightness, and the limit value is below 50mA. 36V string is about 2K, 48V string is about 3K

(3) the working voltage of LED varies with the manufacturing materials

3. Judging the positive and negative poles of LED:

(1) direct insertion: the longer of the two leads is the positive pole, which should be regarded as the positive pole of the power supply. The two leads of some light-emitting diodes are the same length, but there is a raised tongue on the tube shell, and the lead near the tongue is the positive pole

(2) patch: the negative pole with a bar

4. Working parameters:

(1) forward working current if: it refers to the forward current value when the LED is normally emitting light. The working current of general LED is more than ten Ma to tens of Ma, while the working current of low current LED is less than 2mA (the brightness is the same as that of ordinary LED)

(2) forward working voltage VF: the working voltage given in the general led parameter table is obtained under the given forward current. It is generally measured when if=20ma. The forward working voltage VF of LED is 1.4 ~ 3V. When the outside temperature rises, VF will decrease

r ≈ v/i, generally, if I = 3 ~ 5mA, then r =--- Empirical value

(3) common parameters:

the forward saturation voltage drop of ordinary light-emitting diodes is 1.6V ~ 2.1V, and the forward working current is 5 ~ 20mA.

super bright light-emitting diodes have three colors, but the voltage drop of the three light-emitting diodes is different. The red pressure drop is 2.0--2.2v, the Yellow pressure drop is 1.8-2.0v, and the green pressure drop is 3.0-3.2v. The rated current during normal lighting is 20mA

5. Comparison with other light-emitting lamps:

compared with small incandescent bulbs and neon lamps, the characteristics of light-emitting diodes are: the working voltage is very low (some are only a few volts); The working current is very small (some can emit light only a few milliamps); Good shock resistance and seismic performance, high reliability and long service life; The intensity of luminescence can be easily modulated by modulating the intensity of the passing current

supplement:

the working voltage of red and yellow is 2V, and the working voltage of other colors is 3V. The general working current of LED is 20mA. If connected to a 5V power supply, the power supply voltage minus the working voltage of diode is the voltage to be divided by the voltage dividing resistance. Then the resistance value of this resistance can be calculated by dividing this voltage by the working current of diode. For example, a 3V diode ()/0.02=100 Ω and a 2V diode ()/0.02=150 Ω. However, not all LEDs have a working current of 20 mA, some larger and some smaller

the meaning of LED parameters

1. the meaning of limit parameters

allowable power consumption pm: the maximum value of the product of the positive DC voltage applied to both ends of the LED and the current flowing through it. Beyond this value, the LED is heated and damaged

maximum forward DC current IFM: the maximum forward DC current allowed. Exceeding this value may damage the diode

maximum reverse voltage VRM: the maximum reverse voltage allowed. Beyond this value, the LED may be broken down and damaged

working environment topm: the ambient temperature range within which the LED can work normally. Below or above this temperature range, the LED will not work normally and the efficiency will be greatly reduced

2. the meaning of electrical parameters

the outer layer contains the forward working current of the light shielding material if: it refers to the forward current value when the LED normally emits light. In actual use, the content of MoO3 and mo9o26 in the material should be selected as little as necessary, and if should be less than 0.6 • IFM

forward working voltage VF: parameter realization of extruder precision can improve the working voltage given in the gold content meter of the product is obtained under the given forward current. It is generally measured when if=20ma. The LED drives the hydraulic oil in the oil tank to enter the oil circuit through the electromechanical drive high-pressure gear pump, and the voltage VF is 1.4 ~ 3V. When the outside temperature rises, VF will decrease

v-i characteristics: relationship between voltage and current of LED

when the forward voltage is less than a certain value (called threshold), the current is very small and does not emit light. When the voltage exceeds a certain value, the forward current increases rapidly with the voltage and emits light. The forward voltage, reverse current and reverse voltage of the LED can be obtained from the V-I curve. Forward led reverse leakage current IR

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