Say goodbye to the era of profiteering: revealing the design of LED tube power supply
Two kinds of constant current control methods <br> The following is to say, two kinds of constant current control mode switching power supply, resulting in two practices. These two approaches, whether they are principles, device applications, or performance differences, are quite large.
First of all, the principle. The first one is represented by the current constant current LED dedicated IC, mainly like the 9910 series, AMC7150. All the brands that now use the LED constant current drive IC are basically this kind, and call him constant current IC type. But I think this kind of constant current IC is doing constant current, but the effect is not so good. The control principle is relatively simple. It is to set a current threshold in the primary circuit of the power supply. When the primary MOS is turned on, the current of the inductor rises linearly. When it rises to a certain value, When this threshold is reached, the current is turned off, and the next cycle is triggered by the trigger circuit. In fact, this constant current should be a current limit. We know that when the inductance is different, the shape of the primary current is different. Although there are the same peaks, the current average is different. Therefore, when such a power supply is generally mass-produced, the consistency of the constant current size is not well controlled. There is also a characteristic of such a power supply, generally an output. The current is trapezoidal, that is, the wave current, the output is generally not electrolytically smooth, which is also a problem, if the current peak is too large, it will affect the LED. If the output stage of the power supply does not have the power supply that is electrolyzed to smooth the current, it basically belongs to this type. That is to judge whether it is this control mode, it depends on whether the output is electrolytically filtered or not. It has always been called a pseudo constant current, because its essence is a current limiting, not a constant current value obtained by comparison with an op amp.
The second constant current mode should be called a switching power supply type. This control method is similar to the constant voltage control method of the switching power supply. Everyone knows to use TL431 for constant voltage because it has a 2.5 volt reference inside and then uses a resistor divider. When the output voltage is a little higher, or lower, a comparison voltage is generated, and the PWM signal is controlled by amplification. Therefore, this control method can control the voltage very accurately. This control method requires a reference. An op amp is needed. If the reference is accurate and the amplifier amplification is large enough, then it is very accurate. Similarly, to do constant current, you need a constant current reference, an op amp, and resistance overcurrent detection. Signal, and then use this signal to amplify, to control the PWM, but unfortunately it is not very good to find a very accurate reference signal, commonly used triode, this is the reference temperature drift, and can be used to take the diode about 1V conduction value Benchmark, this can also be, not high, the best is to use the operational amplifier plus TL431 as the benchmark, but the circuit is complicated. However, the constant current power supply with such constant current accuracy is still well controlled. The constant current of this mode control must be electrolytically filtered, so the output power is smooth DC, not pulsating. The method was sampled. So to determine which one is only to see if its output has electrolysis.
Two constant current control modes determine the use of two different types of devices, which determine the difference in the use of the two circuit devices, the difference in performance, and the cost.
The LED power supply made by the constant current type control IC represented by the 9910 series is actually current limiting, and the control is relatively simple. Strictly speaking, it is not the mainstream mode of switching power supply control. The mainstream mode of switching power supply control must be Benchmarks and op amps. But this IC can only be used for LEDs, it is difficult to use for other things, just because LEDs have very low ripple requirements. But because it is only used for LED, so the price is higher now. Basically, it is made by using 9910 plus MOS tube. The output is electroless. Generally, I see that many people use the word inductor to do the power conversion inductor. This kind of power supply, the chip of the general manufacturer. There are pictures on the data, basically all of them are buck. I don't say much, and there are more people who are better than me.
The second is based on me, that is, the constant current driver of the switching power supply control mode. This is the common switching power supply chip as the core conversion device, such a lot of chips, such as PI's TNY series, TOP series, ST's VIPER12, VIPER22, Fairchild's FSD200, etc., even using only triode or MOS tube RCC, etc. can be done. The benefits are low cost and good reliability. Because the ordinary switching power supply chip is not only good price, but also a classic product that has been used extensively. Such an IC is generally integrated with a MOS tube, which is more convenient than the 9910 plus MOS, but the control method is more complicated, and it is necessary to add a constant current control device, and a triode or an operational amplifier can be used. The magnetic component can be used with a word inductor or a gas. High frequency transformer with gap.
I love to use a transformer, because the cost of the inductor is very low, but I don't think it has the ability to load, and the adjustment is not flexible. Therefore, I think the better device choice is that the common integrated MOS switching power supply chip plus high-frequency transformer is the most ideal choice in terms of performance and cost. It does not need to use any constant current IC, that kind of thing, Not easy to use, expensive.
Finally, to say, the most important way to distinguish between these two power supplies is to see if their output has electrolytic capacitors for filtering.
Regarding the power supply problem <br> Whether it is the power supply of the current limiting constant current control or the constant current power supply controlled by the operational amplifier, the power supply problem must be solved. That is, the switching power supply chip needs a relatively stable DC voltage for its operation. Chip-powered, the chip's operating current varies from one MA to several MAs. There is a kind of FSD200, NCP1012, and HV9910. This kind of chip is high-voltage self-feeding. It is convenient to use, but high-voltage feeding causes the IC heat to rise because the IC has to withstand about 300V DC, as long as it has a little current. Even if it is an MA, it has zero damage of zero watts. Generally, the LED power supply is only about ten watts. If you lose a few watts, you can pull down the power efficiency by a few points. There is also a typical QX9910. Use the resistor to pull down the power, so the loss is on the resistor. Lose it a few watts. There is magnetic coupling, which is to use a transformer to add a winding to the main power coil, just like the auxiliary winding of the flyback power supply, so as to avoid losing the power of a few watts. This is why I don't isolate the power supply. One of the reasons for using a transformer is to avoid the loss of the power of a few watts, and to raise the efficiency a few points.
Introduction to non-isolated buck power supply design method <br> Non-isolated buck type is a commonly used power supply structure, which accounts for almost 90% of fluorescent lamp power supply. Many people think that the power supply is not isolated. One, when it comes to isolation, think of the buck type, it is thought that the lamp is not safe - after the power supply is damaged. In fact, the buck type is only one kind, there are two basic structures, namely, boost, and buck-boost , that is, BOOST AND BUCK-BOOST, the latter two power supplies even if damaged, will not affect the LED, there is such a benefit.
Now LED fluorescent lamp power supply, the manufacturer of the lamp is generally required to be placed in the lamp tube, such as the T8 lamp tube. A small part of the external. Do not know why this is the case. In fact, the built-in power supply is difficult to do, the performance is not good. But I don't know why there are so many people asking for it. It may be down with the wind. The external power supply should be said to be more scientific and more convenient. But I also have to follow the wind, what the customer wants, what do I do? However, it is quite difficult to do the built-in power supply. Because the external power supply has almost no shape, it doesn't matter how big it is to be done. The built-in power supply can only be made into two types, one of which is the most used, that is, placed under the light board and placed on the light board.
The following is the power supply, so the power supply is required to be very thin, otherwise it can not be installed. And this can only cause the components to fall down, and the line on the power supply is only lengthened. I don't think this is a good way. But everyone generally likes to do this. I will do it. There is less use, put the two ends, that is, placed on both ends of the lamp, so that it is better to do something, and the cost is lower. I also have I have done it, basically these two built-in shapes.
Problems with such power supply requirements and circuit structure
My opinion is that because the power supply is built into the lamp, and the heat is the biggest killer of LED light, the heat must be small, that is, the efficiency must be high. Of course, there must be a high-efficiency power supply. For the T8 one meter long lamp, it is best not to use a power supply, but to use two, one at each end to dissipate the heat so that the heat is not concentrated in one place. The efficiency of the power supply depends mainly on the structure of the circuit and the devices used. First, the circuit structure, some people say that to isolate the power supply, I think it is absolutely unnecessary, because this kind of thing is originally placed inside the lamp body, people basically touch No. There is no need to isolate, because the efficiency of the isolated power supply is lower than that of the non-isolation. The second is that it is better to output a high voltage and a small current. This kind of power supply can make the efficiency higher. Nowadays, the BUCK circuit is commonly used. , that is, the buck circuit. It is best to make the output voltage more than one hundred volts, the current is set at 100MA, such as driving one hundred and twenty, preferably three strings, each string of forty, the voltage is one One hundred and thirty volts, the current is 60MA. This kind of power supply is used a lot. I just think that it is a little bad. If the switch tube is out of control, the LED will be finished. Now the LED is so expensive. I am more optimistic about the boost circuit. The benefits of the circuit, I have said repeatedly, first, the efficiency is higher than the buck, and second, the power supply is broken, the LED light will not be bad. This will ensure that nothing is lost. If you burn a power supply, you only lose a few dollars. Burn an LED fluorescent lamp, just So I always push the booster power supply. Also, the boost circuit makes it easy to make the PF value high. The buck type is more troublesome. The advantage of my absolute boost circuit for LED fluorescent lamps is still Overwhelming is better than buck. It only has one year's shortcoming. In the case of 220V mains input, the load range is relatively narrow. Generally, it can only be applied to 100 to 140 strings or two strings of LEDs. The number, or the middle of the folder, is inconvenient to use. But now the LED fluorescent lamp, generally 60CM long is 100 to 140, one meter two, usually two hundred to two hundred Sixth, it is still possible to use. So now LED fluorescent lamps generally use non-isolated step-down circuits, and there is no isolation boost circuit. This kind of circuit is used for LED fluorescent lamps, which should be considered as my first.
Personally, there are many times when these practices are really ruined. Now let me ask about the advantages of LEDs compared to traditional lamps. First, energy saving, second longevity, then not afraid of switching, right. But the high PF method used now uses passive valley filling PF circuits. From the original driving method, that is, 48 ​​strings, 6 and 24, 12 strings and 12, in this case, in the case of 220V, the efficiency will drop by about 5 percentage points, so the LED fluorescent lamp power supply, the heat is higher, the lamp beads are also Will be affected a bit.
Another problem is that the 24-string 12-inch approach will make the wiring of the LED fluorescent lamp beads difficult to accept, and it is not easy to route. I think the best way is still 48 strings and a string of methods, mainly efficiency. High, low heat, and easy to route, not complicated.
What's more, there are still people who propose 24 and 12 strings. This method is only suitable for isolated power supply. It is not applicable at all. Some people who don't understand the common sense of power supply feel that they are not isolated power supply to achieve constant current 600MA output. In fact, he did not carefully try to put it in the lamp, as this is not hot. Therefore, what low-voltage and high-current current LED light power supply is really a practice.
The buck power supply also has its advantages. The first point is suitable for 220, but it is not suitable for 110. Because the voltage of 110V is low, the drop is lower, so the output current is large, the voltage is low, and the efficiency is not. Too high.
Step-down 220V AC, about 300V after rectification and filtering, after the step-down circuit, the voltage is generally reduced to about 150V DC, so that high-voltage and small-current output can be realized, and the efficiency can be high. Generally use MOS as the switch tube to do the power supply of this specification. My experience is that it can be as close as 90%, and it is difficult to go up. The reason is very simple. The chip generally has zero point and zero W. To a W, and the fluorescent tube power supply is only about ten W. So it is impossible to go up. Now the power efficiency is a very empty thing. Many people are blowing, but they can't actually reach it. Some people often say that 3W's power efficiency is 85 percent, and it is still isolated.
Tell everyone that even in the frequency hopping mode, the no-load power consumption is the smallest, it is 0.3W, and what is the output 3W low voltage, which can reach 85%, in fact, 70% is very good, anyway now Many people brag about not drafting drafts, can fool the layman, but now do not know much about LED power. I said that to be efficient, we must first do non-isolated, and then output specifications and high voltage and small current, which can save the conduction loss of power components, so the main loss of such LED power supply, one is the chip itself. Loss, this loss generally has a fraction of a few W to a W, and one is the switching loss. Using MOS as the switching transistor can significantly reduce this loss, and the loss of the triode is much larger. So try not to use triodes. There is also a small power supply, it is best not to save too much, do not use RCC, because the general manufacturers of RCC circuits simply do not do quality, in fact, the chips are also cheap, ordinary switching power supply chips, integrated MOS tubes At most, it costs only two yuan. It is not necessary to save a little bit. RCC only saves material costs. In fact, the cost of processing and repairing is higher, and it is not worth the loss.
The basic structure of the buck power supply is to string the inductor and load into the high voltage of 300V. When the switch is switched, the load is lower than 300V. There are many specific circuits and many online. I will not draw any more pictures. Now 9910, there are generally constant current ICs on the market that are basically implemented with this circuit. But this kind of circuit is when the switch tube breaks down, the whole LED light board is finished, which should be regarded as the worst place. Because when the switch tube breaks down, the entire 300V voltage is applied to the lamp board. The lamp board can only withstand more than one hundred volts, and now it is three hundred volts. This happens once. The LED must be burned. Drop it. Therefore, many people say that non-isolation is not safe. In fact, it means bucking, just because the vast majority of non-isolated is buck, so non-isolated damage must be considered bad. In fact, the other two basic non-isolated Structure, power supply damage, will not affect the LED.
The buck power supply should be designed as a high voltage and small current, and the efficiency can be high. In detail, why? Because of the high voltage and small current, the pulse width of the switch current can be made larger, so that the peak current is smaller, and that is, the inductor The loss is also smaller. It can be known through the circuit structure that the circuit is inconvenient to draw, and it is difficult to describe it any more. Just sum up, the advantage of the step-down power supply is that it is suitable for 220 high-voltage input, so that the voltage stress of the power device is small, suitable for high-current output, such as 100MA current, which is easier and more efficient than the latter two methods. To be high. The efficiency is relatively high, the loss on the inductor is small, but the loss on the switch is larger, because all the power through the load must be transmitted through the switch, but the output power is only partially passed through the inductor, such as 300V input. The 120-output step-down power supply has only 300-120, that is, the part of 180 has to pass through the inductor, and the part of 120 is directly turned into the load, so the inductance loss is relatively small, but the output power is all passed through the switch. Pipe conversion.
LED fluorescent lamps have bid farewell to the era of high prices <br> It is clear that LED has already bid farewell to the era of high profits. Many people who originally wanted to take profits in the LED fluorescent industry did not play. I can give you an account.
The main sign of the LED fluorescent lamp farewell to the high price era is the price reduction of the straw hat lamp. Now the brightness of the 120-degree straw hat lamp above 2000MCD (single luminous flux >6 lumens), 0.2 yuan has been sold, the original price At least 0.5 yuan. I will calculate a account, it will be calculated from the traditional PC tube plus straw lamp LED.
1.2 m LED fluorescent lamp, 264 LED lamp, 15W LED fluorescent lamp. PC tube, plus lamp board, plus ordinary LED fluorescent lamp constant current power supply, these three pieces add up, the cost can be fixed up to 30 yuan. The lamp bead is 0.2 yuan. Then, it is at most 60 yuan, adding up to a material cost of about 90 yuan, deducting other things, selling 150 yuan is reasonable. Therefore, LED fluorescent lamps are no longer high-priced era, and after another year, this price will break through. The 100 yuan mark, but the market promotion takes a while. People who do LED lighting must learn to adjust their mindset, and the era of profiteering is gone.
First of all, the principle. The first one is represented by the current constant current LED dedicated IC, mainly like the 9910 series, AMC7150. All the brands that now use the LED constant current drive IC are basically this kind, and call him constant current IC type. But I think this kind of constant current IC is doing constant current, but the effect is not so good. The control principle is relatively simple. It is to set a current threshold in the primary circuit of the power supply. When the primary MOS is turned on, the current of the inductor rises linearly. When it rises to a certain value, When this threshold is reached, the current is turned off, and the next cycle is triggered by the trigger circuit. In fact, this constant current should be a current limit. We know that when the inductance is different, the shape of the primary current is different. Although there are the same peaks, the current average is different. Therefore, when such a power supply is generally mass-produced, the consistency of the constant current size is not well controlled. There is also a characteristic of such a power supply, generally an output. The current is trapezoidal, that is, the wave current, the output is generally not electrolytically smooth, which is also a problem, if the current peak is too large, it will affect the LED. If the output stage of the power supply does not have the power supply that is electrolyzed to smooth the current, it basically belongs to this type. That is to judge whether it is this control mode, it depends on whether the output is electrolytically filtered or not. It has always been called a pseudo constant current, because its essence is a current limiting, not a constant current value obtained by comparison with an op amp.
The second constant current mode should be called a switching power supply type. This control method is similar to the constant voltage control method of the switching power supply. Everyone knows to use TL431 for constant voltage because it has a 2.5 volt reference inside and then uses a resistor divider. When the output voltage is a little higher, or lower, a comparison voltage is generated, and the PWM signal is controlled by amplification. Therefore, this control method can control the voltage very accurately. This control method requires a reference. An op amp is needed. If the reference is accurate and the amplifier amplification is large enough, then it is very accurate. Similarly, to do constant current, you need a constant current reference, an op amp, and resistance overcurrent detection. Signal, and then use this signal to amplify, to control the PWM, but unfortunately it is not very good to find a very accurate reference signal, commonly used triode, this is the reference temperature drift, and can be used to take the diode about 1V conduction value Benchmark, this can also be, not high, the best is to use the operational amplifier plus TL431 as the benchmark, but the circuit is complicated. However, the constant current power supply with such constant current accuracy is still well controlled. The constant current of this mode control must be electrolytically filtered, so the output power is smooth DC, not pulsating. The method was sampled. So to determine which one is only to see if its output has electrolysis.
Two constant current control modes determine the use of two different types of devices, which determine the difference in the use of the two circuit devices, the difference in performance, and the cost.
The LED power supply made by the constant current type control IC represented by the 9910 series is actually current limiting, and the control is relatively simple. Strictly speaking, it is not the mainstream mode of switching power supply control. The mainstream mode of switching power supply control must be Benchmarks and op amps. But this IC can only be used for LEDs, it is difficult to use for other things, just because LEDs have very low ripple requirements. But because it is only used for LED, so the price is higher now. Basically, it is made by using 9910 plus MOS tube. The output is electroless. Generally, I see that many people use the word inductor to do the power conversion inductor. This kind of power supply, the chip of the general manufacturer. There are pictures on the data, basically all of them are buck. I don't say much, and there are more people who are better than me.
The second is based on me, that is, the constant current driver of the switching power supply control mode. This is the common switching power supply chip as the core conversion device, such a lot of chips, such as PI's TNY series, TOP series, ST's VIPER12, VIPER22, Fairchild's FSD200, etc., even using only triode or MOS tube RCC, etc. can be done. The benefits are low cost and good reliability. Because the ordinary switching power supply chip is not only good price, but also a classic product that has been used extensively. Such an IC is generally integrated with a MOS tube, which is more convenient than the 9910 plus MOS, but the control method is more complicated, and it is necessary to add a constant current control device, and a triode or an operational amplifier can be used. The magnetic component can be used with a word inductor or a gas. High frequency transformer with gap.
I love to use a transformer, because the cost of the inductor is very low, but I don't think it has the ability to load, and the adjustment is not flexible. Therefore, I think the better device choice is that the common integrated MOS switching power supply chip plus high-frequency transformer is the most ideal choice in terms of performance and cost. It does not need to use any constant current IC, that kind of thing, Not easy to use, expensive.
Finally, to say, the most important way to distinguish between these two power supplies is to see if their output has electrolytic capacitors for filtering.
Regarding the power supply problem <br> Whether it is the power supply of the current limiting constant current control or the constant current power supply controlled by the operational amplifier, the power supply problem must be solved. That is, the switching power supply chip needs a relatively stable DC voltage for its operation. Chip-powered, the chip's operating current varies from one MA to several MAs. There is a kind of FSD200, NCP1012, and HV9910. This kind of chip is high-voltage self-feeding. It is convenient to use, but high-voltage feeding causes the IC heat to rise because the IC has to withstand about 300V DC, as long as it has a little current. Even if it is an MA, it has zero damage of zero watts. Generally, the LED power supply is only about ten watts. If you lose a few watts, you can pull down the power efficiency by a few points. There is also a typical QX9910. Use the resistor to pull down the power, so the loss is on the resistor. Lose it a few watts. There is magnetic coupling, which is to use a transformer to add a winding to the main power coil, just like the auxiliary winding of the flyback power supply, so as to avoid losing the power of a few watts. This is why I don't isolate the power supply. One of the reasons for using a transformer is to avoid the loss of the power of a few watts, and to raise the efficiency a few points.
Introduction to non-isolated buck power supply design method <br> Non-isolated buck type is a commonly used power supply structure, which accounts for almost 90% of fluorescent lamp power supply. Many people think that the power supply is not isolated. One, when it comes to isolation, think of the buck type, it is thought that the lamp is not safe - after the power supply is damaged. In fact, the buck type is only one kind, there are two basic structures, namely, boost, and buck-boost , that is, BOOST AND BUCK-BOOST, the latter two power supplies even if damaged, will not affect the LED, there is such a benefit.
Now LED fluorescent lamp power supply, the manufacturer of the lamp is generally required to be placed in the lamp tube, such as the T8 lamp tube. A small part of the external. Do not know why this is the case. In fact, the built-in power supply is difficult to do, the performance is not good. But I don't know why there are so many people asking for it. It may be down with the wind. The external power supply should be said to be more scientific and more convenient. But I also have to follow the wind, what the customer wants, what do I do? However, it is quite difficult to do the built-in power supply. Because the external power supply has almost no shape, it doesn't matter how big it is to be done. The built-in power supply can only be made into two types, one of which is the most used, that is, placed under the light board and placed on the light board.
The following is the power supply, so the power supply is required to be very thin, otherwise it can not be installed. And this can only cause the components to fall down, and the line on the power supply is only lengthened. I don't think this is a good way. But everyone generally likes to do this. I will do it. There is less use, put the two ends, that is, placed on both ends of the lamp, so that it is better to do something, and the cost is lower. I also have I have done it, basically these two built-in shapes.
Problems with such power supply requirements and circuit structure
My opinion is that because the power supply is built into the lamp, and the heat is the biggest killer of LED light, the heat must be small, that is, the efficiency must be high. Of course, there must be a high-efficiency power supply. For the T8 one meter long lamp, it is best not to use a power supply, but to use two, one at each end to dissipate the heat so that the heat is not concentrated in one place. The efficiency of the power supply depends mainly on the structure of the circuit and the devices used. First, the circuit structure, some people say that to isolate the power supply, I think it is absolutely unnecessary, because this kind of thing is originally placed inside the lamp body, people basically touch No. There is no need to isolate, because the efficiency of the isolated power supply is lower than that of the non-isolation. The second is that it is better to output a high voltage and a small current. This kind of power supply can make the efficiency higher. Nowadays, the BUCK circuit is commonly used. , that is, the buck circuit. It is best to make the output voltage more than one hundred volts, the current is set at 100MA, such as driving one hundred and twenty, preferably three strings, each string of forty, the voltage is one One hundred and thirty volts, the current is 60MA. This kind of power supply is used a lot. I just think that it is a little bad. If the switch tube is out of control, the LED will be finished. Now the LED is so expensive. I am more optimistic about the boost circuit. The benefits of the circuit, I have said repeatedly, first, the efficiency is higher than the buck, and second, the power supply is broken, the LED light will not be bad. This will ensure that nothing is lost. If you burn a power supply, you only lose a few dollars. Burn an LED fluorescent lamp, just So I always push the booster power supply. Also, the boost circuit makes it easy to make the PF value high. The buck type is more troublesome. The advantage of my absolute boost circuit for LED fluorescent lamps is still Overwhelming is better than buck. It only has one year's shortcoming. In the case of 220V mains input, the load range is relatively narrow. Generally, it can only be applied to 100 to 140 strings or two strings of LEDs. The number, or the middle of the folder, is inconvenient to use. But now the LED fluorescent lamp, generally 60CM long is 100 to 140, one meter two, usually two hundred to two hundred Sixth, it is still possible to use. So now LED fluorescent lamps generally use non-isolated step-down circuits, and there is no isolation boost circuit. This kind of circuit is used for LED fluorescent lamps, which should be considered as my first.
Personally, there are many times when these practices are really ruined. Now let me ask about the advantages of LEDs compared to traditional lamps. First, energy saving, second longevity, then not afraid of switching, right. But the high PF method used now uses passive valley filling PF circuits. From the original driving method, that is, 48 ​​strings, 6 and 24, 12 strings and 12, in this case, in the case of 220V, the efficiency will drop by about 5 percentage points, so the LED fluorescent lamp power supply, the heat is higher, the lamp beads are also Will be affected a bit.
Another problem is that the 24-string 12-inch approach will make the wiring of the LED fluorescent lamp beads difficult to accept, and it is not easy to route. I think the best way is still 48 strings and a string of methods, mainly efficiency. High, low heat, and easy to route, not complicated.
What's more, there are still people who propose 24 and 12 strings. This method is only suitable for isolated power supply. It is not applicable at all. Some people who don't understand the common sense of power supply feel that they are not isolated power supply to achieve constant current 600MA output. In fact, he did not carefully try to put it in the lamp, as this is not hot. Therefore, what low-voltage and high-current current LED light power supply is really a practice.
The buck power supply also has its advantages. The first point is suitable for 220, but it is not suitable for 110. Because the voltage of 110V is low, the drop is lower, so the output current is large, the voltage is low, and the efficiency is not. Too high.
Step-down 220V AC, about 300V after rectification and filtering, after the step-down circuit, the voltage is generally reduced to about 150V DC, so that high-voltage and small-current output can be realized, and the efficiency can be high. Generally use MOS as the switch tube to do the power supply of this specification. My experience is that it can be as close as 90%, and it is difficult to go up. The reason is very simple. The chip generally has zero point and zero W. To a W, and the fluorescent tube power supply is only about ten W. So it is impossible to go up. Now the power efficiency is a very empty thing. Many people are blowing, but they can't actually reach it. Some people often say that 3W's power efficiency is 85 percent, and it is still isolated.
Tell everyone that even in the frequency hopping mode, the no-load power consumption is the smallest, it is 0.3W, and what is the output 3W low voltage, which can reach 85%, in fact, 70% is very good, anyway now Many people brag about not drafting drafts, can fool the layman, but now do not know much about LED power. I said that to be efficient, we must first do non-isolated, and then output specifications and high voltage and small current, which can save the conduction loss of power components, so the main loss of such LED power supply, one is the chip itself. Loss, this loss generally has a fraction of a few W to a W, and one is the switching loss. Using MOS as the switching transistor can significantly reduce this loss, and the loss of the triode is much larger. So try not to use triodes. There is also a small power supply, it is best not to save too much, do not use RCC, because the general manufacturers of RCC circuits simply do not do quality, in fact, the chips are also cheap, ordinary switching power supply chips, integrated MOS tubes At most, it costs only two yuan. It is not necessary to save a little bit. RCC only saves material costs. In fact, the cost of processing and repairing is higher, and it is not worth the loss.
The basic structure of the buck power supply is to string the inductor and load into the high voltage of 300V. When the switch is switched, the load is lower than 300V. There are many specific circuits and many online. I will not draw any more pictures. Now 9910, there are generally constant current ICs on the market that are basically implemented with this circuit. But this kind of circuit is when the switch tube breaks down, the whole LED light board is finished, which should be regarded as the worst place. Because when the switch tube breaks down, the entire 300V voltage is applied to the lamp board. The lamp board can only withstand more than one hundred volts, and now it is three hundred volts. This happens once. The LED must be burned. Drop it. Therefore, many people say that non-isolation is not safe. In fact, it means bucking, just because the vast majority of non-isolated is buck, so non-isolated damage must be considered bad. In fact, the other two basic non-isolated Structure, power supply damage, will not affect the LED.
The buck power supply should be designed as a high voltage and small current, and the efficiency can be high. In detail, why? Because of the high voltage and small current, the pulse width of the switch current can be made larger, so that the peak current is smaller, and that is, the inductor The loss is also smaller. It can be known through the circuit structure that the circuit is inconvenient to draw, and it is difficult to describe it any more. Just sum up, the advantage of the step-down power supply is that it is suitable for 220 high-voltage input, so that the voltage stress of the power device is small, suitable for high-current output, such as 100MA current, which is easier and more efficient than the latter two methods. To be high. The efficiency is relatively high, the loss on the inductor is small, but the loss on the switch is larger, because all the power through the load must be transmitted through the switch, but the output power is only partially passed through the inductor, such as 300V input. The 120-output step-down power supply has only 300-120, that is, the part of 180 has to pass through the inductor, and the part of 120 is directly turned into the load, so the inductance loss is relatively small, but the output power is all passed through the switch. Pipe conversion.
LED fluorescent lamps have bid farewell to the era of high prices <br> It is clear that LED has already bid farewell to the era of high profits. Many people who originally wanted to take profits in the LED fluorescent industry did not play. I can give you an account.
The main sign of the LED fluorescent lamp farewell to the high price era is the price reduction of the straw hat lamp. Now the brightness of the 120-degree straw hat lamp above 2000MCD (single luminous flux >6 lumens), 0.2 yuan has been sold, the original price At least 0.5 yuan. I will calculate a account, it will be calculated from the traditional PC tube plus straw lamp LED.
1.2 m LED fluorescent lamp, 264 LED lamp, 15W LED fluorescent lamp. PC tube, plus lamp board, plus ordinary LED fluorescent lamp constant current power supply, these three pieces add up, the cost can be fixed up to 30 yuan. The lamp bead is 0.2 yuan. Then, it is at most 60 yuan, adding up to a material cost of about 90 yuan, deducting other things, selling 150 yuan is reasonable. Therefore, LED fluorescent lamps are no longer high-priced era, and after another year, this price will break through. The 100 yuan mark, but the market promotion takes a while. People who do LED lighting must learn to adjust their mindset, and the era of profiteering is gone.
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