US Patent No. 10,368,408

LIGHT EMITTING DEVICE AND LED LIGHT BULB


Patent No. 10,368,408
Issue Date July 30, 2019
Title Light Emitting Device And Led Light Bulb
Inventorship Hiroyasu Kondo, Yokohama (JP)
Masahiko Yamakawa, Yokohama (JP)
Yasuhiro Shirakawa, Yokohama (JP)
Ryoji Tsuda, Yokohama (JP)
Atsuji Nakagawa, Himeji (JP)
Toshitaka Fujii, Himeji (JP)
Tomohiko Inoue, Himeji (JP)
Assignee Toshiba Materials Co., Ltd., Yokohama-Shi (JP)

Claim of US Patent No. 10,368,408

1. A light emitting device comprising:a first white light source, including N pieces, with N being a natural number equal to or more than 2, of first white light emitting diodes electrically connected in series to one another in a forward direction, and emitting a first white light having a first color temperature;
a second white light source, including M pieces, with M being a natural number less than N, of second white light emitting diodes electrically connected in series to one another in a forward direction and a first resistance element electrically connected in series to the second white light emitting diodes and having a first resistance value, the second white light source being electrically connected in parallel to the first white light source, and emitting a second white light having a second color temperature lower than the first color temperature; and
a control circuit,
the device emitting a mixed white light of the first white light and the second white light,
wherein each of the first and second white light emitting diodes includes:
a light emitting diode element which emits light having an emission peak wavelength in a range of from 370 nm to 420 nm; and
a phosphor which emits white light by being excited by the light of the light emitting diode element, consisting of a blue phosphor, a green phosphor, and a red phosphor, each of the blue, green, and red phosphors containing at least one element selected from the group consisting of europium and cerium,
wherein a drive voltage of the first white light source is higher than a drive voltage of the second white light source, and
wherein the control circuit controls a current to be supplied to the first and second white light sources so that a color temperature of the mixed white light is higher as a total luminous flux of the mixed white light is higher.