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:
Dec. 11, 2007
Filed:
Mar. 18, 2005
Isao Yamamoto, Kyoto, JP;
Kyoichiro Araki, Kyoto, JP;
Noboru Kagemoto, Kanagawa, JP;
Rohm Co., Ltd., , JP;
Abstract
A charge pump circuit boosts a voltage of a battery so as to generate a drive voltage for an LED. A constant current circuit generates a constant current to feed through the LED. A monitoring circuit monitors a cathode potential of the LED, i.e., a voltage across the constant current circuit. A control circuit receives a result of monitoring from the monitoring circuitand increases a step-up ratio of the charge pump circuit when the voltage across the constant current circuit drops below a minimum voltage that guarantees a constant current. The control circuit sets an externally requested constant current value in the constant current circuit. When a change from a large current to a small current is requested, the control circuit returns the step-up ratio of the charge pump circuit to 1.0.