Have you noticed that the LED lights for home use are becoming less and less durable now, and they are generally claimed to be guaranteed for one year. After one year, the luminous intensity drops sharply, which is also called light decay. Even if we want to continue to use it reluctantly, the light decay will be more serious later, and it will definitely be broken and not bright within 2 years.
Normally, the lifespan of an LED is 100,000 hours. The quality of the lamp beads in our home is definitely not that good. I will calculate it based on the lifespan of 20,000 hours. Even if the light is turned on for 12 hours a day, it will have a lifespan of 4.5 years. The time is not that long, and it should be able to last longer, so why does our lamp fail after one year?
Today we will disassemble a finished lamp to see what it is.
Dismantling pictures
Circuit Analysis – Capacitance
Inside the red circle is a capacitor for power filtering, which is an electrolytic capacitor. This kind of capacitor has a relatively long life, generally 7 or 8 years is no problem. High quality ones can be used for more than 10 years. But this kind of capacitor is particularly afraid of one thing, high temperature. At high temperature, the electrolyte inside it will volatilize quickly, resulting in a decrease in capacitance and an increase in the ripple of the power supply. After reaching a certain level, the components on the circuit will not work.
Circuit Analysis – Resistors
Look at the red arrow pointing, it is a power resistor, 22 ohms. The position of this resistor in the circuit is as shown in the figure below:
the figure below does not represent the real circuit, it is just an example
The red arrow points here. If it is normal, a fuse will be placed, and its resistance value is very small, close to 0, so as not to consume power in vain. But the manufacturer put a resistor here.
We know that the resistance will hinder the flow of current in the circuit, and at the same time, it will also generate heat. For this 24W lamp, the current on the resistance is about 0.11A, and the power consumed by the resistance is 0.26W.
Causes of damage to LED lamps
If we look back at the previous disassembly diagram, we will find that the resistors and capacitors are very close together, and they are close together on purpose, which is obviously done on purpose. This causes heat from the resistor to directly heat up the capacitor. And a plastic case is added outside this group of components, which will cause the heat to be unable to dissipate, resulting in a greater temperature rise and aggravating the aging of the capacitor. This is also the direct reason why the lamps will be broken after one or two years.
Causes of serious LED light decay
As mentioned earlier, the life of LED can be used for many years. There is a premise here that the LED lamp works in a normal state. When the working current of the LED exceeds the rated current, the luminescence will become stronger, but the lifespan will be greatly shortened. This is just in line with the needs of some unscrupulous factories. Use cheap low-brightness lamp beads to pretend to be high-brightness lamps by increasing the current. Lamp beads not only save costs, but also cause rapid aging of lamp beads, allowing consumers to buy again in a short period of time.
our countermeasures
After understanding the previous reasons, our countermeasures are very clear:
1. We only need to short-circuit the power resistor to greatly extend the life of the circuit.
2. The 7th pin of the chip in the picture is connected to a current sampling resistor. The resistance value is generally a few tenths to several ohms. The larger the resistance, the smaller the actual brightness. In the disassembled lamp, 3.3 ohms and 2 ohms are used in parallel, and the equivalent resistance is 1.25 ohms. I directly soldered off the 3.3 ohm, so that the sampling resistor becomes 2 ohm. But the price is that the brightness of the lamp is lower, so for friends who want to do this, you need to buy a more powerful lamp. Such as 36W or 50W. Although it will be more expensive, the life of the lamp can be extended several times, which is still very cost-effective.
Precautions
Modifying the circuit by yourself requires a certain amount of hands-on ability, and there is also a certain degree of danger. At the same time, the warranty will be lost. Please operate with caution.