Do you know the common problems with light-emitting diodes?

The so-called light-emitting diode is actually the most common type of LED. There are two common types of electronic components: SMD light-emitting diodes and directly inserted light-emitting diodes. Plastic LED is a common light-emitting diode, LED metal shell, LED Nixie tube, etc. General LED is suitable for circuit signs, ultra high brightness LED lighting, outdoor LED displays, traffic indicator lights, car brake lights, etc. Do you know some common problems with light-emitting diodes? This article collects and organizes some issues related to light-emitting diodes, hoping to have great reference value for readers.

Why cannot white LED be used for overvoltage or overcurrent?

The most commonly used 5mm white LED has a normal working voltage range of 3.0-3.5V and a normal working current of 20ma. But many people mistakenly believe that the application of overvoltage or overcurrent to white LED will be brighter. The actual detection result is that the light flux increases significantly after 15 ma, but does not gradually increase to 30 ma after 20 ma, only 5% more than 20 ma. However, the LED is noticeably hot. There is also a lifespan experiment: working at 20ma for one month, the attenuation is only 5%, and the current luminous flux is still 95%. Working from 30 ma to 19 days, the luminous flux is only 50%. It can be considered that white LED can operate for 100000 hours under conventional standards and only have a lifespan of 600 hours when used under current conditions! Generally speaking, LEDs can be used for over 50000 hours, and some manufacturers claim that LEDs can run for about 10000 hours, but this does not guarantee that LED products can also use such time. Incorrect operations and processes can easily "destroy" LEDs, and over time, LEDs will gradually decrease. It is predicted that high-quality LED can still maintain over 60% of the original lighting brightness after 50000 hours. In order to increase the lifespan of LEDs, it is necessary to reduce or completely dissipate the thermal energy generated by LED chips. Thermal energy is an important reason for the termination of LED operation.

Why is the color of the light emitted by white LED always blue or dark?

This is because white LED itself covers the conversion material noctilucent powder on the 1ngan raw material that sends blue light, which will emit yellow light under the encouragement of blue light. Therefore, the mixture of blue and yellow light is considered white light in the eyes of people. From the emission spectrum of the white LED, it can be seen that it has two peaks, so there is no LED that truly sends white light. This kind of equipment is difficult to manufacture, because LED is characterized by sending only one wavelength of Monochromatic radiation, while real white light should produce a multi-color spectrum. Due to process relevance, including imported LEDs priced at over 10 yuan, there is also a situation where there is color difference at the edge of the light spot, which is only a small amount.

The white light-emitting diode has a white light ranging from slightly yellow to slightly purple. The common color temperature of white light emitting diodes is generally between 6500k and 8000k.

Which method is better for LED connection or series connection?

According to the power supply method and requirements of the power box, the key to selecting or connecting LEDs in series is to determine. Both parallel and series methods have their advantages and disadvantages. And the connection method only requires applying a lower voltage on both sides of each LED, but requires the use of a ballast resistor or current source to ensure that the brightness of each LED is consistent. If the bias current of each LED is different, its brightness will also be different, resulting in uneven brightness of the entire light source. However, using a ballast resistor or current source to ensure consistent LED brightness can shorten the battery's lifespan. The selection of series connection method can essentially ensure the consistency of each LED current, but requires a higher power supply current. When selecting and connecting LEDs, as the total current of the power supply is the sum of the currents of each LED, it is necessary to provide sufficient current.

In addition, when one of the LEDs is short circuited, the entire LED does not light up, but when one of the LEDs is short circuited, the other LEDs can still light up. When one of the LEDs is short circuited, the other LEDs will still light up; But when one of the LEDs is short circuited, the entire power supply will be short circuited, not only will the other LEDs not function properly, but it may also damage the power supply. Therefore, compared to the series connection method, the circuit has more advantages.

In specific applications, the LED array formed by series and parallel connection is usually chosen to overcome or reduce the aforementioned individual LED short circuits or short circuits, which may cause the entire LED to not light up or affect the entire circuit and power supply. The so-called series parallel connection refers to first using a small number of LEDs in series, then connecting the ballast resistor in series to form a loop, and then connecting several loops in parallel to form a "loop group". In addition, the series connection method can also be chosen, which is to connect multiple "loop groups" in series to form the entire lamp circuit based on the formed "loop group". This connection method not only reduces the impact of LED faults, but also reduces the ballast resistance to zero, converts several high-power resistors into dozens of low-power resistors, and changes from centralized installation to decentralized installation. This not only benefits resistance heat removal, but also makes the lamp design more compact.

What is the difference between spotlight LED and astigmatic LED? How to use it?

The luminous intensity value of a spotlight LED is high because its light source is self aggregated, and its luminous angle is generally small, resulting in a smaller range of illumination for the light source. Its light is like the beam of light emitted by a flashlight. The brightness of the light spot is very high, but the periphery of the light spot is not too high. Astigmatic LED has a low luminous intensity value, a large luminous angle, and can reach around 120 degrees. It has a wide range of light, symmetrical light, and is similar to a general lighting lamp. Although the brightness value of astigmatic LED is generally low, the total luminous flux (overall light source) is generally higher than that of spotlight LED.

Spotlight LED is most suitable for designated places with high brightness but small direct range, such as spotlights, down lights, flashlights, etc. Astigmatic LED is more suitable for general room lighting and places with gentle and uniform light sources. Therefore, the selection should be based on the actual situation to achieve the best lighting effect.

Can we choose other colors of LED light emitting diodes to replace white LED light emitting diodes?

Sure. However, it should be noted that the normal working voltage of various colors of LEDs varies greatly. For example, the normal working voltage of red and yellow LEDs is only around 2V, while the normal working voltage of blue and green LEDs is close to that of white LEDs, both of which are around 3V. Therefore, according to the working voltage of various pipelines, it is necessary to change the number of series or parallel pipelines, or change the resistance value of series current limiting resistors accordingly. Otherwise, the LED may exceed the normal working current, reduce its service life, and even burn out the LED. When using red or yellow LEDs, the number of series LEDs should be increased, or the current limiting resistor in series should be increased; When using blue or green LEDs, usually only the resistance value of the current limiting resistor is adjusted.

What is the reason why the light does not light up when the circuit is installed and powered on? How should I check?

Conduct specific analysis based on the actual circuit. However, most of the reasons are that the LED was not inspected before installation, or the positive and negative sides of the LED were carefully and incorrectly connected during installation and welding, or there was no soldering (the surface of the soldering was not firmly welded). Empty welding is the most important cause of faults, especially for those who lack welding experience. Secondly, excessive power or welding time of electric chromium iron can cause pipeline burns, and it is also possible that electric chromium iron may be electrified and cause LED penetration short circuit. In addition, some parts of the driving circuit are connected incorrectly or not soldered, and some circuits may also have adjusted component values that have not been adjusted.

Before installing and powering on the circuit, it should be carefully checked and checked for correctness before powering on. If the light does not turn on when powered on, the power should be immediately cut off and then checked. If power cannot be applied, the circuit board should be tapped to try to search for faults, especially when selecting a 220V power circuit.

If it is a circuit connected to a filter capacitor, a screwdriver or wire should also be used to check the short circuit of the filter capacitor before checking. This step is very important! Due to the residual high voltage on the filter capacitor exceeding 1.4 times the power supply current (such as a 220V power supply reaching 310V), to prevent the residual high voltage on the capacitor from damaging the body or destroying the LED during circuit connection!

Check the LED installed on the circuit board, first identify the negative sign of the LED tube vacancy, check if the LED polarity is staggered, and then touch the LED pin in series with two batteries. Pay attention to the consistency between the battery power polarity and the LED polarity, and check if the LED is on.

For the inspection of the driving circuit, it is necessary to carefully check whether the circuit is connected incorrectly according to the circuit diagram. Special attention should be paid to checking whether the polarity of the rectifier bridge (long pin is positive output, diagonal pin is negative output, and the other two pins are AC input) or the rectifier diode and its voltage regulator diode is correct (one end of the black or white line is negative), and whether the three levels of the crystal transistor or voltage regulator integrated circuit are incorrect.

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