What is the lowest cost method for implementing a phase dimmable low ripple LED driver? Not a switching regulator, but a linear regulator that supports dynamic loads. Here are some of the most common issues related to using linear offline LED driver solutions.
TPS92411 functional block diagram
1. Why do lighting designers use electrolytic capacitors? No such component provides the corresponding bulk storage at the price of the electrolytic capacitor. They can be very reliable if carefully selected, procured, and processed during manufacturing and assembly. In fact, the notion that electrolytic capacitors are the least reliable component of an LED driver system is wrong because four to six other components are more susceptible to stability problems than electrolytic capacitors. The end of life of an electrolytic capacitor is usually defined as a 50% reduction in capacitance or a doubling of the equivalent series resistance (ESR). (The doubling of ESR has little effect here, but the life of the capacitor is close to the end time, so It may not increase by a factor of 1). Most of the problems with electrolyte products are that low-cost flyback power supplies (such as low-cost PC power supplies) can deliver extremely high ripple into short-lived devices, sometimes up to 85°C. The actual average service life of electrolyte products can be obtained through extensive research and calculations. It is not difficult to design a lamp circuit that meets the 50KHrs application requirements at operating temperatures below 85°C. Please note that providing three capacitors does not shorten the service life by 1/3. This is a loss mechanism, so the service life does not shorten. It should also be noted that the weaker electrolytic capacitors in flyback/boost bulb power supplies are typically biased. Small diameter electrolyte products have a shorter service life. The crux of the matter is that the electrolyte capacitor will not explode at the end of its useful life. If your circuit is designed to withstand capacitance reduction and resistance rise, then there may be no problem.
All single-stage power factor corrected LED power supply designs will require electrolytic capacitors to reduce ripple. It is not important that the power supply is switched mode, but the line frequency ripple must be reduced by a factor of two. Of course, different topologies provide better ripple performance, but the reality is that the market needs a very low-cost power solution to replace the lights. Therefore, I am here to ask a question of a negative attitude: tell us a low-ripple single-stage power factor-corrected LED driver that does not use electrolytic capacitors but has a total bill of materials cost of less than $1.50, as this is needed by the market. .
For the energy storage requirements of a single-stage power factor correction design, Texas Instruments (TI) has adopted the floating switch architecture of the TPS92411 to have the same storage requirements as other single-stage designs.
2. What is the significance of eliminating magnetic component capacitors and filter capacitors? There are many advantages to doing this. The first is cost. Silicon, plastic and copper are cheaper than most materials, especially ferromagnetic materials. Therefore, you can safely say that when everything is determined, the more silicon material the solution contains, the less the other "things", the cheaper it is. Furthermore, in terms of dimming performance, one of the main problems with phase dimming is the resonance between the filter circuit in the dimmer and the input filter of the switching regulator. Even low-EMI boost regulators require an EMI filter with at least two poles. Minimizing the reactive components in advance can significantly improve dimming performance and reduce the chance of scintillation in most cases. Therefore, the removal of the switching regulator and its associated magnetic components has great advantages (and is easy to design, easy to pass and easy to pass EMI certification).
3. Can I achieve 5-100% dimming with the TPS92411 using a low cost TRIAC dimmer? There is absolutely no problem, the actual effect is very good, better than most switch solutions.
4. Does the TPS92411 help achieve the same UL certification/LED safety isolation standards as transformer isolating switch mode drivers? We (industry) initially adopted a completely isolated solution because we did not have the materials needed to implement non-isolated technology, and that era has passed. In North America, few people are still using isolated drives because non-isolated drives can improve overall system cost and overall efficiency. Please pay attention to the internationalized 230V solution to upgrade this technology as soon as possible.
5. Can the TPS92411 be suitable for various voltage/current combinations like a normal constant current driver? Can I provide the same flexibility to choose any series/parallel string voltage under the same conditions? In the final analysis, it is still a cost issue. When considering dimming and efficiency and cost optimization, no single-stage, low-cost drive can drive a variety of loads without adjustment. It's important to note that we don't say that linear solutions (such as TPS92411-based solutions) are stronger than all switch-mode solutions in all respects, and that's not our goal. Our efforts are to provide the market with a variety of solutions for weighing performance, cost and complexity, and we believe these linear solutions will play a key role in low-cost solutions with the right performance.
6. Can I make a design and then adjust its final power level with a simple current sense resistor like a switch to ensure that the power stage is optimized for my cooling system? Yes, of course.
7. Can the TPS92411 operate efficiently with 90 to 130V AC? Yes, 85% efficiency can be achieved, and the line voltage will decrease after the increase, but the drop will not be too large. Under this wide voltage, there should be a 3% drop (adding a power stage can increase efficiency to over 88%, but this requires consideration of price/performance issues).
8. I heard that this topology is not suitable for the 0-10V DMX or DALI dimming solution currently required for commercial lighting. Is it true? No single-stage power factor correction LED driver can pulse-width modulate at higher frequencies without costly, otherwise ripple and other stroboscopic problems can occur. But they can be used for analog dimming, and the topology is fine. Most communication lines must be isolated from input and output currents, and the architecture does not hinder proper implementation.
For more details on TI's floating switch architecture and TPS92411, please click here. Click here to watch the video to see how the TPS92411 simplifies LED luminaire design by eliminating the need for inductors or transformers.
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