Estimating Output Current Tolerance Of A Primary–Side-Regulated Constant-Current Flyback Converter (Part 1): The Analytical Model

by Stéphanie Cannenterre, ON Semiconductor, Toulouse, France, How2Power Today, Jan 15 2018

Focus:
The primary-side-regulated (PSR) flyback converter is widely used in the LED drive market and in the portable electronic market for travel adapters. In such converters, the output current can be estimated by sensing the current in the primary-side MOSFET. LED driver manufacturers are usually targeting ±5% accuracy on current regulation at a given input voltage. Using worst- case circuit analysis techniques, this article will detail how to estimate the accuracy of the flyback output current and compare the obtained results against the ±5% target. The first part of this article derives an analytical model of the primary-side constant-current flyback control scheme. After reviewing the differences between primary-side-regulated and secondary- side-regulated flybacks, it then derives the analytical model of the PSR flyback, then verifies the model experimentally using a 10-W LED driver based on the NCL30082 controller IC.

What you’ll learn:

• How to model the output current and predict the output current tolerance of a primary-side regulated flyback converter

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