Here say is both constant current control mode switching power supply, resulting in the two approaches. These two approaches, either principle or device applications, or the performance differences are quite large.
First, that works. The first kind of constant current LED dedicated IC now represented mainly as 9910 series, AMC7150, who is now playing constant current led street light with solar panel brand basically this, and told him to constant IC type of bar but I believe that this so-called constant-current constant current IC to do, the effect is not how good. The control principle is relatively simple, that is, the primary side of the power supply circuit, a current threshold is set, when the primary MOS conduction, when the inductor current is a linear rise, when up to a certain value, reach this threshold, then shutdown current, and then the next cycle is triggered by the trigger circuit is turned on. in fact, this should be a constant current limiting, we know that when the inductance of a different time, the shape of the primary current is different , although there are the same peak, but the current average value is different. Therefore, as this is when the power supply is generally batch consistency constant size is not very good control. there is a feature of this power, the general output current is trapezoidal, namely a fluctuating current, the output is not normally smooth electrolysis, which is a problem if the peak current is too large, LED will have an impact. If the power output stage and did the kind of smooth current electrolysis power, basically fall into this category. That is to determine whether this type of control, to see its output there, and on the electrolytic filter. I had this constant it has been called false constant, because by its very nature is a kind of limiting, not after the op amp compares current value is obtained.
The second constant current mode, it should be called a switching power supply type. This is similar to the control mode and switching power supply constant voltage control mode. We all know that to do with TL431 constant, because it has an internal 2.5 V reference, and then use a resistor divider way. When the output voltage is a little high, or low point of time, it generates a comparison voltage, after amplification, to control the PWM signal, so this control voltage can be very precise control. This control method requires a reference, further need a op amp, if the reference quasi enough magnification op amp is large enough, then given very accurate. Also, do constant is the need for a constant current reference, an operational amplifier, resistor overcurrent detection, as signal, and then use this signal amplification, to control PWM, unfortunately now is not good to find very accurate reference signal, commonly used transistor, this big do baseline drift, there is that you can get the diode conduction value of about 1V to do benchmarks, this can be not high, the best is when the reference TL431 op amp plus, but the circuit complexity. But doing so constant current power supply, a constant current or a good control accuracy more. And this constant current mode control, the output must have to add electrolytic filter, so smoothing DC output power is not pulsating, then no pulsation method of sampling. So to determine what kind of long to see whether there is an electrolytic output on the line.
Two current control mode determines the use of two different types of devices, thus determining the difference between the two circuit devices using different performance, cost is also different.
In 9910 the series as the representative of constant current LED power supply control IC to do, is actually limiting, control is relatively simple, strictly speaking, it does not belong to the mainstream mode switching power supply control, switching power supply control of the mainstream model is a must benchmarks and the op amp, but it can only be used for this IC LED, it is difficult for the other stuff, just because LED requires very low ripple. But because it is only used for LED, so now the price is higher. The basic is to use the 9910 Canadian MOS pipe production, the output of non-electrolytic, in general I see a lot of people just do labor word inductance inductance of power conversion. This power, general manufacturers of chips information out there on the map, basically buck. I do not say, good at this man more than I do.
Second, I represented, that is, the constant current driver switching power supply control mode. This is an ordinary chip as the core switching power conversion devices, a lot of this chip, such as the PI's TNY series, TOP series, ST's VIPER12, VIPER22, Fairchild's FSD200, and even with only MOS transistors or tubes RCC, etc., can do. advantage is low cost, reliability is good. Because the average price of switching power supply chip is not only good, but all through the extensive use of classic products. In fact, as of this IC integrates general MOS, plus convenient than 9910 MOS, but the complexity of some of the control, the need for additional constant current control devices, you can use the transistor or operational amplifier. The magnetic elements can be labor word inductance, can also be used with gas gap of high-frequency transformer.
I love to use a transformer, while the cost is low because the inductor, but I think it does not work with a load capacity, furthermore adjust the amount is not flexible sense. So I think a better device selection, the ordinary MOS integrated chip plus a high-frequency switching power supply transformer, from the performance, cost, are the best choice, do not need to go with what constant current IC, that kind of stuff, and difficult to use, and expensive.
Whether doing constant current limiting control of the power amplifier control or constant current power supply problems to be solved. That is, when the switching power supply chip work is to require a relatively stable DC voltage supply for the chip, the chip working current ranging from one to several MA MA. One elephant FSD200, NCP1012, and HV9910, this chip is a high self-fed, it is easy to use, but the high pressure feed, resulting in increased caloric IC because IC to bear about 300V DC, just a little bit Current even if an MA, but also consumption of 0.3 watts of damage. General led street lighting Manufacturer but ten watts, about the loss of a few tenths of watts of power efficiency can be pulled down a few points. There is a typical elephant QX9910., With a pull-down resistor to take power, so that the loss in the resistance, some also have it lost a few tenths of watts it. There is a magnetic coupling, is to use a transformer on the main power coil plus a winding, as an auxiliary winding flyback power as to avoid loss of a few tenths off this watts of power. This is why I do not have to isolate the power supply one reason to use a transformer, is to avoid the loss of a few tenths of watts of power that will be efficient to mention a few points.
Non-isolated step-down power structure is now widely used, which accounted for almost ninety percent or more fluorescent power. Many people think that not only buck an isolated power supply, a say isolation, they think the buck to think of the lamp safe to say - in fact refers to the power supply damage after just a buck, there are two basic structure, that boost, and buck that bOOST AND BUCK-BOOST, even after the two power damage. not affect the LED, there is such a benefit.
Now LED power, lamp manufacturers generally do require placed inside the tube, such as T8 tubes put in. Few external part. I do not know why this should be. In fact, the built-in power supply also difficult, the performance is not good. But I do not know why there are so many people so request. Suifeng Dao may have been right. External power supply should be said that more scientific and more convenient to my son. But I also have to Suifeng Dao, what customers want, I'll do anything but do built-in power supply, there is considerable difficulty Oh, because an external power supply, the basic shape is not required, how much do want to do much, it does not matter what shape would like to make. Built-in power supply, can only make two, one is the most used, that is placed under the light board, put the lights on top of the plate.
Here is the power, the power to do so would require a very thin, or does not fit. And this can only be the element fallen power line on only lengthened. I think this is not a good idea. But we generally like to do so. I do. There is less used, put both ends of the tube that is placed in two, so well done, the cost is lower. I have done, is the basic shape of the two built-in.
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