US Patent No. 10,433,381


Patent No. 10,433,381
Issue Date October 01, 2019
Title Led Drive Circuit
Inventorship Keisuke Sakai, Yamanashi (JP)
Takashi Akiyama, Sayama (JP)
Assignee CITIZEN WATCH CO., LTD., Nishitokyo-Shi, Tokyo (JP) CITIZEN ELECTRONICS CO...

Claim of US Patent No. 10,433,381

1. An LED drive circuit comprising:a bridge rectifier circuit;
an LED string made up by a plurality of LEDs being connected in series and supplied with a current from the bridge rectifier circuit; and
a current limiting circuit that has a current input terminal and a current output terminal connected onto a path that starts from the bridge rectifier circuit, and returns to the bridge rectifier circuit via the LED string, and a switch element having one end as the current input terminal and another end as the current output terminal, and having a control terminal, which limits a current that flows through the LED string to an upper limit current value or smaller, and further, decreases the current that flows through the LED string in accordance with an amount of rise in the voltage when the voltage at the current input terminal viewed from the current output terminal rises, by controlling a voltage applied to the control terminal of the switch element, and the upper limit current value is a current value flowing through the LED string when a threshold voltage, at which all of the LEDs of the plurality of LEDs included in the LED string turn on, is applied to the LED string.