Texas Instruments Evaluation Board for the LM5020 LM5020EVAL/NOPB LM5020EVAL/NOPB Scheda Tecnica
Codici prodotto
LM5020EVAL/NOPB
User's Guide
SNVA082B – March 2004 – Revised May 2013
AN-1314 LM5020 Evaluation Board
1
Introduction
The LM5020 evaluation board is designed to provide the design engineer with a fully functional non-
isolated flyback power converter to evaluate the LM5020 controller.
isolated flyback power converter to evaluate the LM5020 controller.
The performance of the evaluation board is as follows:
•
Input range: 30V to 75V (100V peak)
•
Output voltage: 3.3V
•
Output current: 0.2 to 4.5A
•
Measured efficiency: 85% at 1.5A, 83% at 4.5A
•
Board size: 1.25 × 2.5 × 0.5 inches
•
Load Regulation: 1.5%
•
Line Regulation: 0.1%
•
Line UVLO, Current Limit
The printed circuit board consists of 2 layers of 2 ounce copper on FR4 material with a total thickness of
0.050 inches. Soldermask has been omitted from some areas to facilitate cooling. The unit is designed for
continuous operation at rated load at < 40°C with normal convection cooling.
0.050 inches. Soldermask has been omitted from some areas to facilitate cooling. The unit is designed for
continuous operation at rated load at < 40°C with normal convection cooling.
2
Theory of Operation
The flyback converter is an inductive based converter in which inductive energy is stored by applying a
voltage across an inductor in a similar manner to that of a boost converter. Here the similarity ends. A
second coupled winding of the inductor transfers the energy to a secondary side rectifier after the voltage
has been removed from the first winding. This allows the converter input and output grounds to be
configured either isolated or non-isolated. There is also a voltage/current ratio change possible by altering
the winding ratio between the first winding and the second winding. A semi-regulated auxiliary winding can
also be provided.
voltage across an inductor in a similar manner to that of a boost converter. Here the similarity ends. A
second coupled winding of the inductor transfers the energy to a secondary side rectifier after the voltage
has been removed from the first winding. This allows the converter input and output grounds to be
configured either isolated or non-isolated. There is also a voltage/current ratio change possible by altering
the winding ratio between the first winding and the second winding. A semi-regulated auxiliary winding can
also be provided.
The flyback transformer is actually a coupled inductor with multiple windings wound on a single core. For
simplification, we will refer to the first, driven winding, as the primary and the main output winding as the
secondary winding of the flyback transformer.
simplification, we will refer to the first, driven winding, as the primary and the main output winding as the
secondary winding of the flyback transformer.
The transformer’s primary inductance is typically made as large as is practical. However, the airgap
necessary to store the cycle energy lowers the obtainable inductance. The higher the primary inductance,
the less input ripple current will be generated and the less input filtering will be required.
necessary to store the cycle energy lowers the obtainable inductance. The higher the primary inductance,
the less input ripple current will be generated and the less input filtering will be required.
As shown, the LM5020 directly drives a MOSFET switch to apply voltage across the primary. When the
switch turns off, the secondary applies a forward current to the output rectifier and charges the output
capacitor. In applications where the input voltage is considerably higher than the output voltage, the turns
ratio between primary and secondary will reflect the input/output voltage ratio and the duty cycle.
switch turns off, the secondary applies a forward current to the output rectifier and charges the output
capacitor. In applications where the input voltage is considerably higher than the output voltage, the turns
ratio between primary and secondary will reflect the input/output voltage ratio and the duty cycle.
The LM5020 is a full-featured controller providing an internal start-up regulator, soft start, over-current and
under-voltage lockout.
under-voltage lockout.
All trademarks are the property of their respective owners.
1
SNVA082B – March 2004 – Revised May 2013
AN-1314 LM5020 Evaluation Board
Copyright © 2004–2013, Texas Instruments Incorporated