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:
Apr. 18, 1995
Filed:
Jan. 13, 1994
Hisaya Okumura, Kawasaki, JP;
Kabushiki Kaisha Toshiba, Kanagawa, JP;
Abstract
A photo-coupler apparatus has a light emitting diode, a photo-diode array, an output MOSFET which is driven by the photoelectromotive force generated by said photo-diode array, and a circuit for limiting the gate voltage of said output MOSFET below a certain value. Said limiting circuit includes a first resistor for detecting output currents, an NPN transistor, a second resistor, and a PNP transistor. In this structure, the voltages developed across the first and second resistors are used to drive the NPN and PNP transistors respectively. In addition, the NPN transistor is connected to the gate of said MOSFET through said second resistor. According to this structure, the gate voltage of the output MOSFET is kept below a certain value by being controlled with the PNP transistor which is driven by the NPN transistor. Thus, stable protection against excessive current is achieved. In addition, a resistor having a small value can be used as the first resistor so as to reduce the heat loss of this apparatus.