The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jul. 04, 1995
Filed:
Feb. 09, 1994
Dean C Buck, Loveland, CO (US);
Hewlett-Packard Company, Palo Alto, CA (US);
Abstract
A power supply circuit limits the voltage on a filter capacitor driven by rectified half-cycles of an input AC waveform. A FET switch in series with the current charging the filter capacitor is opened as soon as the charge on the filter capacitor is adequate. A voltage triggered latch circuit is responsive to the rectified AC input applied through a decoupling diode to the filter capacitor, and supplies a control signal to the FET switch. A further sensing circuit can monitor the current charging the filter capacitor, and can trigger the latch to open the FET switch as needed to limit initial in-rush current during the initial application of AC power. The decoupling diode decouples the rectified peaks provided by the rectifiers from the voltage on the filter capacitor. This allows the filter capacitor to charge whenever the rectified input has an instantaneous voltage greater than the capacitor's (and the FET switch is closed), but also allows the output waveform from the rectifier to fall to zero during the zero crossings of the input waveform. That in turn resets the latch, and the process of gating the charge to be accepted by the filter capacitor is then repeated during the next half-cycle of the input AC waveform.