SNVAA87 august   2023 LMR38020

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
    1. 1.1 Micro Inverter System
    2. 1.2 Typical Power Tree and Design Requirements
  5. 2Conventional Flyback Design Challenges
    1. 2.1 SSR Design Challenges
    2. 2.2 PSR Design Challenges
  6. 3New Fly-Buck Design
    1. 3.1 LMR38020 Overview
    2. 3.2 Comparison with Conventional Flyback
    3. 3.3 Design Considerations
    4. 3.4 LMR38020 Fly-Buck Design Example
  7. 4Bench Test and Result
    1. 4.1 Start Up
    2. 4.2 Typical Switching Waveforms Under Steady State
    3. 4.3 Efficiency
    4. 4.4 Load Regulation
    5. 4.5 Short Circuit
    6. 4.6 Thermal Performance
  8. 5Summary
  9. 6References

Abstract

Solar Micro Inverter is able to help the solar photovoltaic PV system to achieve per-panel level Maximum Power Point Tracking (MPPT) to improve power yield performance even in unideal conditions such as cloud or tree shades or bird drops and dust on the PV panels. Micro Inverter are once costly specialty products, but they are becoming more and more affordable thanks to technology advancement in recent years, and they are one of the fastest growing market segments in the solar industry. Usually installed under the PV panel, micro inverter is required to have high power conversion efficiency, good thermal performance, small size and long lifetime.

The conventional auxiliary power supply is usually a Flyback, either secondary side regulated (SSR) or primary side regulated (PSR). SSR design needs extra TL431+optocoupler that means extra costs. The optocoupler also introduces some reliability issue due to light attenuation when aging. The PSR design circuit is simpler and cost less but the conventional PSR flyback's output performance is relatively poorer. In addition, conventional PSR Flyback also requires an extra auxiliary winding which usually increases the transformer size and can be another issue for micro inverter application requiring small size.

This article presents a new auxiliary power supply design for micro inverter based on LMR38020 Fly-Buck™, with advantages of ease of design, low counts of components in BOM, low cost, small transformer size and well performance on efficiency, thermal and regulation.