Improved Linear Regulator Design Based on LM3445 Non-Isolated LED Application

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Overview:
This article is based on the LM3445 non-isolated LED application improved linear regulator solution, detailing its working principle. We will derive and analyze this linear regulation formula. The results of the calculations were verified by actual experimental results and proved to be very closely matched.
In order to evaluate the feasibility of mass production, we thoroughly studied and analyzed the output current tolerance. The results prove that it is difficult for conventional solutions to achieve full mass production current tolerance, especially in the current trend of higher output applications required by the market.
To solve this problem, we recommend using a simple linear regulator compensation circuit. We validated this proposed solution from both theoretical and experimental measurements. The final total current tolerance required for actual mass production is analyzed based on the derived output current and linear regulation rate formula. Based on the results obtained, we have found that great progress has been made in meeting this practical requirement. Finally, the test results and calculation results are compared based on the prototype; they are verified to match very well.

1. Introduction With the increasing indoor lighting of LEDs, non-isolated and isolated solutions are becoming more and more popular. In particular, high linearity regulated high PF and accurate constant current mode solutions have become the dominant solutions in the market. However, because the output voltage becomes higher and wider, the traditional L3445 non-isolated application cannot meet this margin requirement, further limiting the application of the LM3445.
In view of the above problems, the main goal of this paper is the high output applications required for precise linear regulation. In this article, the general working principle is explained by some formulas in Chapter 2. Using these formulas, we can solve the final output current. In order to evaluate the results, Chapter 3 introduces a unified formula through which the output current is simplified. In addition, Chapter 3 further details the current margin analysis. Chapter 4 gives some examples of prototype-based design. The calculation results and simulation results are given and compared with the experimental results. Their match proved to be very good. However, after in-depth research, we found that it is still difficult to meet the current tolerance requirements for mass production.
To solve this problem, we propose a proposed compensation circuit in Chapter 5. This compensation circuit was verified by calculation and simulation experiments. Finally, experiments have shown that the circuit significantly improves linear regulation and current margin performance. With this circuit, improved linear regulation will be more competitive in practical applications, especially in LED R30/PAR30/A19/E27 LED lighting applications.

2. Schematic of the traditional non-isolated LM3445 solution Figure 1 shows a traditional non-isolated solution for higher PF. In order to explain how it works, we define the parameters as follows:
Vout: LED output voltage
I: equivalent time value in a single time period
Kfeed: Input feed forward coefficient of AC voltage
Rs: current sense resistor
Rup:toff charging resistor
Cchar: toff charging capacitor
Vinmin: AC input voltage minimum
Vinmax: AC input voltage maximum
Vinac: AC input voltage
_noimp: no improved linear regulator circuit function
_imp: Improve linear regulator circuit function

Figure 1 Traditional non-isolated feedback loop diagram for high PF (please read the PDF for details)