LED lighting drive problem solving ideas

Cost, efficiency, flicker, and reliability are all issues that LED lighting developers need to consider. In this paper, MPS experts discuss the solutions of the above factors, such as solving the problem of LED flashing, dimming and poor startup in the camera, achieving high efficiency through soft switching control, eliminating gold lines and reducing The idea of ​​packaging to reduce costs.

Digital circuits and power devices have their own processes that make all DC-DC drivers available on a single wafer. What is wrong with this? There must be a lead wire in the middle of the connection between the two things. The trend of electrical energy is high frequency and large current, which requires very small parasitic parameters. If there is a lead wire, if the frequency is high, the parasitic current will increase, and voltage oscillation will occur. If you go to a high current, the impedance will be higher and the overall loss will increase. The MPSBCDFast process can support high frequency and current, and MPS products can be made much smaller than competitors. The first generation of MPS products has been smaller than the competition, only a quarter of the competitors, so the cost can be lower.

Eliminate gold wires, reduce packaging and reduce costs

Most of the ICs are connected by gold wires, and there are copper wires in China. The trend of high frequency and high current will bring about an increase in the cost of gold wire. With a larger current flow, the IC needs a thicker gold wire, which is bound to bring about an increase in cost. The package of MPS is connected with the soldering foot underneath by copper casting. The whole impedance of copper casting is much smaller than that of gold wire. In terms of heat dissipation, the IC connected to gold wire needs to add a lot of heat sink, but this package is every Each pin can be used as a heat sink. Simply speaking, it can dissipate heat through the area of ​​the PCB . In this way, the IC thermal resistance will be relatively small, and the same package can be made small. The smaller the package, the cheaper it is, and the cost can be reduced.

There are two types of LED lighting: one is DC input and the other is AC input. Let me first talk about the DC-DC aspect. Some PAR lamps now use pure DC instead of electronic transformers. Assume that the electronic transformer is a high frequency AC12V, even some high power lamps, such as 30W, 40W. What is the problem after switching to LED? After its load becomes much lighter, it will stop vibrating for a while. If you use a step-down IC, assume that 3 lights are placed at 10V. If you use buck to do it, you need to add a large amount to stabilize the voltage, such as 12V. If the voltage drops to 9V, it may not work. What if there is a large current? The electronic transformers are all kinds of when starting, but there are many without current limiting protection. If the current is large, the electronic transformer will be burned off when it is started. So when you step down, it's not very useful on MRS16. What kind of solutions can MPS do? The first is the MP2481, which is for 350 mAh, 1W, with 3 or 4 lamps in series. This is a 1.4M high frequency IC. The higher the frequency, the smaller the inductor current can be. This can be done in three ways: boosting, step-down, and step-down. Just talked about the electronic transformer, 12V, but the township town has a large range, the lowest voltage can be about 4.5V, compared to the current can be treated with relatively small. The entire peripheral components are very simple, no diodes, all protections are open, short-circuited. This is one of the few ICs in the industry that can provide buck-boost.

The lead-acid battery used in the car headlights is 12V. However, when the car is equipped with ignition, the voltage jump is very powerful. Sometimes it will jump to 20 volts or even 30 volts. This requires a high voltage IC to do it, and it can be as low as 9V or 8V. If a customer wants to do car lights, etc., the MP2483 is an option, and can also provide in-vehicle certification. Because of high-voltage technology, DC high voltage, the standard process can achieve about 30V. But going to high pressure, there is no such possibility.

How to solve the LED flashing inside the camera

Nowadays, there are many three-level schemes for general streetlights. The first one is PFC, which outputs DC voltage, and then there are many different power requirements, each of which requires a constant current. In this case, 500 mA, 350 mA can achieve 97%, close to 98% efficiency, very high, which is difficult to achieve in the industry. Therefore, MP4688 is suitable for street lights of 700 mAh and 350 mAh. In addition, some customers, for example, T8 lamps, need PFC, need to be isolated. Because of the input ripple made with a single-stage PFC, if you take a 122HZ HD camera to shoot, the light on the screen will flash. This kind of flicker is not very good if it appears on the film scene. What to do at this time? The front stage is also a PFC with a high voltage DC-DC. This DC-DC frequency is very high, it is easy to filter out the frequency of 100HZ, so there is no fixed ripple at the LED lamp end.

Flexible PCB , it's the PCB that very thin and could bent very easily. The board material could be PI ( Polyimide) and also could be FR4 and other materials. Normally, the flex PCB thickness is 0.05mm-0.4mm.

PCB = printed circuit board and PCBA = printed circuit board assembly. For PCB, it means the copper circuits be printed on a board, and so the main composition of PCB are copper and board.

The copper is the circuits material and the circuits designed by the PCB designers. Depends on the current in the circuits, the PCB copper thickness could be done with 0.5oz-10oz. But the PCB designers need be noted that the copper track width/space need be enlarged with the thickness. For example, the minimum copper track width/space could be 3mil/3mil with 0.5oz, but would be 4mil/4mil with 1oz.

The PCB board could be rigid PCB, could be flex PCB and also could be Flex-Rigid PCB. And the materials could be FR4, PI, Aluminum, Copper-based, Rogers, Teflon, etc. They have different applications. For example, FR4 PCB is the most commonly used for rigid PCB and almost good for all electronics products; PI is the most commonly used for flex PCB; Aluminum and copper-based have good thermal diffusivity and always used for LED PCB ; Rogers PCB and Teflon PCB are always used for High Frequency PCB, etc.

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