System and method for controlling a current limit with primary side sensing using a hybrid PWM and PFM control
US7974107B2 · kind B2 · utility
Assignee
Inventors
Key dates
| Filing date | Aug 27, 2008 |
| Grant date | Jul 5, 2011 |
| Priority date | — |
| Expiry date | Feb 19, 2030 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH02M3/33523
- WIPO fieldElectrical machinery, apparatus, energy
- WIPO sectorElectrical engineering
Abstract
A hybrid constant current control system that uses both pulse width modulation (PWM) and pulse frequency modulation (PFM) control. When transitioning from constant voltage mode to constant current mode the present invention can continue to control using PWM. Thereafter, when the voltage has dropped, the present invention smoothly transitions to PFM mode. The point of transition is based upon the switching frequency and the lowest rated voltage of operation. The system and method avoids very short (narrow) Ton times which ensures accurate constant current (CC) control with bipolar junction transistor (BJT) devices. The present invention also avoids acoustic noise because the switching frequency is maintained at a high enough level to avoid such acoustic noise even when the energy transferred through the transformer is still substantial and the output voltage is not too low. In addition the output current limit is insensitive to variation in the inductance-input voltage ratio, and is minimized against leakage inductance.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.