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. 17, 2001
Filed:
Dec. 23, 1999
Denso Corporation, Kariya, JP;
Abstract
A direct-current power supply circuit, incorporated in an IC card, includes a coil for receiving an amplitude-modulated signal from an external device through electromagnetic induction. A full-wave rectifying circuit rectifies the amplitude-modulated signal received by the coil. The rectified output signal is used to charge a smoothing capacitor. A clamp circuit controls the terminal voltage of the smoothing capacitor to a predetermined level so as to produce a power supply voltage. The clamp circuit controls an output transistor to stabilize the power supply voltage to a constant level. Furthermore, the direct-current power supply circuit includes a short-circuit preventing circuit to forcibly turn off the output transistor when the electric potential difference between both ends of the coil is smaller than a predetermined value, thereby preventing the power supply voltage from suddenly decreasing due to delay of operation of the circuit elements when the coil output becomes zero due to amplitude modulation.