LIGHT EMITTING APPARATUS

• US 20080203946A1
• Filed: 02/15/2008
• Published: 08/28/2008
• Est. Priority Date: 02/22/2007
• Status: Active Grant

• Current Assignee: Koito Manufacturing Company Limited
• Original Assignee: Koito Manufacturing Company Limited
• Inventors: Kitagawa, Takayoshi, Ito, Masayasu, Murakami, Kentarou
• Granted Patent: US 7,741,788 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H05B 45/382 with galvanic isolation between input and output
• CPC Class Codes: H05B 45/48 having LEDs organised in strings and incorporating parallel shunting devices

Abstract

In conduction of light emitting diodes LEDs 1 to 4, a switching signal 101 is converted into a voltage V2 or 0V through a signal converter 26 in accordance with a logic level thereof The voltage obtained by the conversion is compared with a voltage V1 on both ends of a resistor R1 through an operational amplifier 20 to open/close an output loop by an NMOS transistor 22, a current If of the light emitting diodes LEDs 1 to 4 is limited to a current If1 so as not to exceed a maximum current, and a current defined with an ON duty of the switching signal 101 is caused to flow as a mean current to the light emitting diodes LEDs 1 to 4 to inhibit an overshoot current from flowing to the light emitting diodes LEDs 1 to 4 while the output loop is closed.

Claims

1. Alight emitting apparatus comprising:

a DC/DC converter to chop and transform an output of a DC power supply, to convert a voltage obtained by the transformation into a DC power and to supply the DC power to a load,

at least one semiconductor light source as the load of the DC/DC converter in an output loop of the DC/DC converter, and

a current limiting circuit to compare a signal corresponding to a first input switching signal with a signal corresponding to a current flowing to the at least one semiconductor light source, to open/close the output loop in accordance with a result of the comparison, and to cause a current to flow to the at least one semiconductor light source so as not to exceed a maximum current while the output loop is closed,

wherein the apparatus is arranged so that a current defined with an ON duty of the first switching signal is caused to flow as a mean current to the semiconductor light source.

4. The light emitting apparatus according to claim 1, wherein the current limiting circuit includes:

a tripolar semiconductor device in the output loop of the DC/DC converter,

a resistor to detect a current of the semiconductor light source,

a signal converter to convert the first switching signal into a signal having a different level in accordance with a logic level thereof, and

an operational amplifier to compare a signal obtained by the current detected through the resistor with a signal obtained by the conversion of the signal converter,

wherein the current limiting circuit is arranged to perform ON/OFF driving of the tripolar semiconductor device in accordance with a result of the comparison and to control an extent of an ON state of the tripolar semiconductor device which is ON.

2. A light emitting apparatus comprising:

a DC/DC converter to chop and transform an output of a DC power supply, convert a voltage obtained by the transformation into a DC power and supply the DC power to a load,

a plurality of semiconductor light sources as the load of the DC/DC converter in an output loop of the DC/DC converter,

a current limiting circuit to limit a current of the semiconductor light source, and

a switching device group to short-circuit or open both ends of at least one of the semiconductor light sources in response to an input switching signal, wherein the amount of light of the semiconductor light source is defined with an OFF duty of the switching signal.

3. A light emitting apparatus comprising:

a DC/DC converter to chop and transform an output of a DC power supply, convert a voltage obtained by the transformation into a DC power and supply the DC power to a load,

a plurality of semiconductor light sources as the load of the DC/DC converter in an output loop of the DC/DC converter,

a current limiting circuit to compare a signal corresponding to a first input switching signal with a signal corresponding to a current flowing to the semiconductor light source, to open/close the output loop in accordance with a result of the comparison, and to cause a current to flow to the semiconductor light source so as not to exceed a maximum current while the output loop is closed, and

a switching device group to short-circuit or open both ends of at least one of the semiconductor light sources in response to a second input switching signal,

wherein the amount of light of the semiconductor light source is defined with an ON duty of the first switching signal and an OFF duty of the second switching signal.

5. The light emitting apparatus according to claim 3, wherein the current limiting circuit includes:

a tripolar semiconductor device in the output loop of the DC/DC converter,

a resistor to detect a current of the semiconductor light source,

a signal converter to convert the first switching signal into a signal having a different level in accordance with a logic level thereof, and

an operational amplifier to compare a signal obtained by the current detected through the resistor with a signal obtained by the conversion of the signal converter,

wherein the current limiting circuit is arranged to perform ON/OFF driving of the tripolar semiconductor device in accordance with a result of the comparison and to control an extent of an ON state of the tripolar semiconductor device which is ON.