I often hear people in the industry complain that every time the LED lamp is broken and the power supply is broken, the most unreliable LED lamp is the power supply. Maybe he is telling the truth. However, it is also necessary to analyze in depth the cause of the LED power supply damage.
Recently, the LED lamps in my home have also broken down. When I take it down, it turns out that the power supply is broken, but although this is the case, it should be carefully analyzed.
First look at its shape photo:
1. Using inexpensive low-quality components, we can see that its rectifier bridge (left side in the figure) is composed of four rectifier diodes instead of an integrated rectifier bridge. We know that the cost of four diodes is much lower than that of an integrated rectifier bridge, because there are many companies that can produce diodes, because the production of diodes can be done with some of the simplest semiconductor production equipment that has been eliminated in the past, and that can be produced. There are not many companies that integrate rectifier bridges, because they must have high-quality integrated circuit production equipment and raw materials, which can be produced by some large manufacturers, and the price is certainly much more expensive than the four diodes. In fact, high back pressure diodes are not easy to do, and general manufacturers do not necessarily produce highly reliable high-pressure diodes. Later, I measured it with a multimeter, and I found out that there is a rectifier diode that is broken, and the electrolytic capacitor is still good.
So is there no problem with the integrated rectifier bridge? This is not the case, and there are many times when electrolytic capacitors are broken down without protection. In addition, when selecting the voltage resistance and power consumption of components, please try to leave room for it, such as the withstand voltage of electrolytic capacitors. Although the rated voltage is only 220Vx1.4=308V at 220V, my piece The electrolytic capacitor withstand voltage on the power board is 400V, which should be enough, but we usually use 450V withstand voltage electrolytic capacitor, so the insurance factor can be larger.
2. No protective components are used . As can be seen from the photo, this power supply is not equipped with any protective device. However, as a power source connected to the mains, it is necessary to add protective components. That is because there are various surge voltages on the power grid. It may be a lightning strike at a long distance or a high-power device on the power grid. High voltage pulses caused by switching. If you do not protect this high voltage pulse, it is easy to break through the electrolytic capacitor.
LED luminaire power protection device LED power protection device has two main functions, one is to protect the power supply itself, to prevent damage from external influences. On the other hand, it protects the external circuit environment from external circuits due to the operation or damage of the LED luminaire.
The main protection devices are as follows:
1. Varistor The varistor is used to protect the LED lamp itself. It can be said that regardless of the power source, switching power supply, and linear power supply used in the LED lamp, this protection is required. It is used to protect the surge voltage that often occurs on the mains network. The so-called surge voltage is mainly caused by short-time high-voltage pulses caused by lightning strikes or high-power electrical equipment starting and stopping. Among them, lightning strikes are the main reason. Lightning strikes can be divided into direct lightning strikes and indirect lightning strikes. Direct lightning strikes refer to direct lightning strikes on the power supply network. This possibility is rare, and most large-scale power supply grid systems have lightning protection measures. Indirect lightning strikes refer to surges transmitted by lightning-induced electricity on the grid. This surge is highly probable because 1800 thunderstorms occur every moment in the world, with 600 lightning strikes per second. Each lightning strike induces a surge voltage on the nearby grid. The width of a surge pulse is usually only a few microseconds or less, and the amplitude of the pulse can be as high as several thousand volts. Mainly because of its high amplitude, it has the greatest impact on the damage of electronic equipment. If left unprotected, all kinds of electronic devices are easily damaged. Fortunately, the protection of the surge is very simple, just add a surge-proof varistor, usually it is connected in parallel before the rectifier.
The principle of such a varistor is such that there is a non-linear resistor whose resistance is close to an open circuit within a specified threshold range, and once the applied voltage exceeds the threshold, its resistance immediately approaches zero. This makes it easy to absorb this surge. Moreover, the varistor is a recoverable device that can be protected after the surge is absorbed.
Its main indicators are: 1) maximum continuous operating voltage (divided into AC and DC, such as DC 415V), 2) varistor voltage (threshold, such as 510V), refers to the starting voltage when the current is greater than 0.1mA. 3) The maximum limiting voltage is the maximum peak voltage Vp above the varistor capable of withstanding the peak current Ip (eg 200A), for example 845V; in fact, because the surge is usually only a small width (a few microseconds) The narrow pulse, its voltage and current relationship can not be described by a resistor, because it is actually a nonlinear device.
2. Negative temperature coefficient resistance NTC
Many LED power supplies are equipped with electrolytic capacitors behind the rectifier. The charging current of the electrolytic capacitors when they are just turned on is usually very large, often measured in several amperes. If there are many such power supplies in a room at the same time, then The added charging current will cause the grid of this room to generate a very large instantaneous current enough for the safety switch to jump off. Therefore, in order to avoid such a situation, in the LED power supply, a negative temperature coefficient resistor (NTC) needs to be installed in front of the electrolytic capacitor, which is characterized by a small resistance at ordinary times, and its resistance value when encountering an instantaneous large current. Because of the heat, it instantly becomes extremely large, which limits the large current at this moment. When the large current passes, it quickly returns to the usual small resistance, thus avoiding the external impact of the LED power supply.
3. The function of the fuse is similar to that of a normal fuse. When the LED load is short-circuited for various reasons, the fuse that it itself will immediately disconnect the short-circuited load, so as not to affect the tripping of the external circuit.
The positions of the above three protection devices in the circuit of the LED power supply are as follows:
Some so-called "no power supply" "AC LED" light engine products open the internal structure can clearly see that no protective components are added, only the high-end flicker-free electrolytic capacitor light engine adds all the protection circuits, such as Philae's light engine:
4. There are two kinds of lightning street lights for LED street lights, one is solar street light, and the other is AC circuit light. Because solar street lights do not need to be connected to the power grid, there is no surge problem, but because it is often set up in an open place, there is a high possibility of direct lightning strikes. Therefore, most solar street lights need to be equipped with lightning rods to directly introduce lightning strikes into the ground.
Electric network lights, in addition to sometimes need to install lightning rods, anti-surge is the most important problem, and because the power supply circuit may be long in the field, so the possibility of direct lightning strikes, the surge will become Widely damaging wide pulses require more effective surge protection.
In this case, a small varistor is not enough, but must be changed into a gas lightning protection tube. This is a gas discharge tube with a gas discharge gap formed by a metal electrode and a porcelain tube sealed, using a ceramic insulator and an electrode. The welded outer casing ensures the airtightness of the discharge gap.
Conclusion In summary, in fact, do a highly reliable LED drive power is not difficult, as long as the following points:
1. Use high quality components. In fact, some people with common sense know why some components are cheap and some are expensive. The difference lies in reliability, so don't sacrifice reliability in order to pursue cheapness, and finally ruin the reputation of your company.
2. There should be room for selecting the device parameters, such as withstand voltage. You can't assume that the mains voltage is 220V. Generally, we all need to consider at least the voltage may be as high as 265V or even higher. Therefore, there must be room for any engineering design.
3. The circuit design must use protection devices. The circuit without protection device is equal to the lock of your home door. Do you dare to live without a lock?
4. A good circuit board should also be coated with three anti-paint. The so-called three-proof paint is moisture-proof, salt-proof, anti-mildew, plus dustproof, leak-proof, and better waterproof (IP67). This allows the long life of the board to be more assured.
5. Some exported boards also require CE, UL certification, and some ROHS certification (ie, lead-free certification), so as to avoid lead poisoning when recycling these boards.
To achieve the above points, the life of the power supply can also be up to tens of thousands of hours. In the past, many home appliances, like TV sets, have not been used for more than ten years, which means that high reliability can be achieved.
Unfortunately, almost 80% of the LED power supplies on the market today are designed to reduce costs without any protection devices. This method of using people to harm others is really to be condemned by the public!
On the other hand, LED lamps that use such power cut-off power supplies are generally cheaper. We also want to advise consumers, the old saying of the Chinese: a price of goods, cheap and not good! If you want to buy long-life LED lamps, you should buy a little more expensive products.
Recently, the LED lamps in my home have also broken down. When I take it down, it turns out that the power supply is broken, but although this is the case, it should be carefully analyzed.
First look at its shape photo:
1. Using inexpensive low-quality components, we can see that its rectifier bridge (left side in the figure) is composed of four rectifier diodes instead of an integrated rectifier bridge. We know that the cost of four diodes is much lower than that of an integrated rectifier bridge, because there are many companies that can produce diodes, because the production of diodes can be done with some of the simplest semiconductor production equipment that has been eliminated in the past, and that can be produced. There are not many companies that integrate rectifier bridges, because they must have high-quality integrated circuit production equipment and raw materials, which can be produced by some large manufacturers, and the price is certainly much more expensive than the four diodes. In fact, high back pressure diodes are not easy to do, and general manufacturers do not necessarily produce highly reliable high-pressure diodes. Later, I measured it with a multimeter, and I found out that there is a rectifier diode that is broken, and the electrolytic capacitor is still good.
So is there no problem with the integrated rectifier bridge? This is not the case, and there are many times when electrolytic capacitors are broken down without protection. In addition, when selecting the voltage resistance and power consumption of components, please try to leave room for it, such as the withstand voltage of electrolytic capacitors. Although the rated voltage is only 220Vx1.4=308V at 220V, my piece The electrolytic capacitor withstand voltage on the power board is 400V, which should be enough, but we usually use 450V withstand voltage electrolytic capacitor, so the insurance factor can be larger.
2. No protective components are used . As can be seen from the photo, this power supply is not equipped with any protective device. However, as a power source connected to the mains, it is necessary to add protective components. That is because there are various surge voltages on the power grid. It may be a lightning strike at a long distance or a high-power device on the power grid. High voltage pulses caused by switching. If you do not protect this high voltage pulse, it is easy to break through the electrolytic capacitor.
LED luminaire power protection device LED power protection device has two main functions, one is to protect the power supply itself, to prevent damage from external influences. On the other hand, it protects the external circuit environment from external circuits due to the operation or damage of the LED luminaire.
The main protection devices are as follows:
1. Varistor The varistor is used to protect the LED lamp itself. It can be said that regardless of the power source, switching power supply, and linear power supply used in the LED lamp, this protection is required. It is used to protect the surge voltage that often occurs on the mains network. The so-called surge voltage is mainly caused by short-time high-voltage pulses caused by lightning strikes or high-power electrical equipment starting and stopping. Among them, lightning strikes are the main reason. Lightning strikes can be divided into direct lightning strikes and indirect lightning strikes. Direct lightning strikes refer to direct lightning strikes on the power supply network. This possibility is rare, and most large-scale power supply grid systems have lightning protection measures. Indirect lightning strikes refer to surges transmitted by lightning-induced electricity on the grid. This surge is highly probable because 1800 thunderstorms occur every moment in the world, with 600 lightning strikes per second. Each lightning strike induces a surge voltage on the nearby grid. The width of a surge pulse is usually only a few microseconds or less, and the amplitude of the pulse can be as high as several thousand volts. Mainly because of its high amplitude, it has the greatest impact on the damage of electronic equipment. If left unprotected, all kinds of electronic devices are easily damaged. Fortunately, the protection of the surge is very simple, just add a surge-proof varistor, usually it is connected in parallel before the rectifier.
The principle of such a varistor is such that there is a non-linear resistor whose resistance is close to an open circuit within a specified threshold range, and once the applied voltage exceeds the threshold, its resistance immediately approaches zero. This makes it easy to absorb this surge. Moreover, the varistor is a recoverable device that can be protected after the surge is absorbed.
Its main indicators are: 1) maximum continuous operating voltage (divided into AC and DC, such as DC 415V), 2) varistor voltage (threshold, such as 510V), refers to the starting voltage when the current is greater than 0.1mA. 3) The maximum limiting voltage is the maximum peak voltage Vp above the varistor capable of withstanding the peak current Ip (eg 200A), for example 845V; in fact, because the surge is usually only a small width (a few microseconds) The narrow pulse, its voltage and current relationship can not be described by a resistor, because it is actually a nonlinear device.
2. Negative temperature coefficient resistance NTC
Many LED power supplies are equipped with electrolytic capacitors behind the rectifier. The charging current of the electrolytic capacitors when they are just turned on is usually very large, often measured in several amperes. If there are many such power supplies in a room at the same time, then The added charging current will cause the grid of this room to generate a very large instantaneous current enough for the safety switch to jump off. Therefore, in order to avoid such a situation, in the LED power supply, a negative temperature coefficient resistor (NTC) needs to be installed in front of the electrolytic capacitor, which is characterized by a small resistance at ordinary times, and its resistance value when encountering an instantaneous large current. Because of the heat, it instantly becomes extremely large, which limits the large current at this moment. When the large current passes, it quickly returns to the usual small resistance, thus avoiding the external impact of the LED power supply.
3. The function of the fuse is similar to that of a normal fuse. When the LED load is short-circuited for various reasons, the fuse that it itself will immediately disconnect the short-circuited load, so as not to affect the tripping of the external circuit.
The positions of the above three protection devices in the circuit of the LED power supply are as follows:
Some so-called "no power supply" "AC LED" light engine products open the internal structure can clearly see that no protective components are added, only the high-end flicker-free electrolytic capacitor light engine adds all the protection circuits, such as Philae's light engine:
4. There are two kinds of lightning street lights for LED street lights, one is solar street light, and the other is AC circuit light. Because solar street lights do not need to be connected to the power grid, there is no surge problem, but because it is often set up in an open place, there is a high possibility of direct lightning strikes. Therefore, most solar street lights need to be equipped with lightning rods to directly introduce lightning strikes into the ground.
Electric network lights, in addition to sometimes need to install lightning rods, anti-surge is the most important problem, and because the power supply circuit may be long in the field, so the possibility of direct lightning strikes, the surge will become Widely damaging wide pulses require more effective surge protection.
In this case, a small varistor is not enough, but must be changed into a gas lightning protection tube. This is a gas discharge tube with a gas discharge gap formed by a metal electrode and a porcelain tube sealed, using a ceramic insulator and an electrode. The welded outer casing ensures the airtightness of the discharge gap.
Conclusion In summary, in fact, do a highly reliable LED drive power is not difficult, as long as the following points:
1. Use high quality components. In fact, some people with common sense know why some components are cheap and some are expensive. The difference lies in reliability, so don't sacrifice reliability in order to pursue cheapness, and finally ruin the reputation of your company.
2. There should be room for selecting the device parameters, such as withstand voltage. You can't assume that the mains voltage is 220V. Generally, we all need to consider at least the voltage may be as high as 265V or even higher. Therefore, there must be room for any engineering design.
3. The circuit design must use protection devices. The circuit without protection device is equal to the lock of your home door. Do you dare to live without a lock?
4. A good circuit board should also be coated with three anti-paint. The so-called three-proof paint is moisture-proof, salt-proof, anti-mildew, plus dustproof, leak-proof, and better waterproof (IP67). This allows the long life of the board to be more assured.
5. Some exported boards also require CE, UL certification, and some ROHS certification (ie, lead-free certification), so as to avoid lead poisoning when recycling these boards.
To achieve the above points, the life of the power supply can also be up to tens of thousands of hours. In the past, many home appliances, like TV sets, have not been used for more than ten years, which means that high reliability can be achieved.
Unfortunately, almost 80% of the LED power supplies on the market today are designed to reduce costs without any protection devices. This method of using people to harm others is really to be condemned by the public!
On the other hand, LED lamps that use such power cut-off power supplies are generally cheaper. We also want to advise consumers, the old saying of the Chinese: a price of goods, cheap and not good! If you want to buy long-life LED lamps, you should buy a little more expensive products.
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