US 7,679,353 B2 · Constant-current circuit and light-emitting diode drive device therewith

Abstract

A constant-current circuit includes a first transistor for supplying a current based on a control signal input to a gate of the first transistor so as to serve as a current source, a second transistor for supplying a current to a load based on the control signal input to a gate of the second transistor, a voltage regulation unit for controlling a drain voltage of the first transistor according to a drain voltage of the second transistor, a current detector for detecting a value of a current flowing through the first transistor and output a current according to the detected value, and a controller for controlling each gate voltage of the first and second transistors according to the value detected by the current detector so that the current flowing through the first transistor becomes a predetermined value. The first and second transistors are MOS transistors having the same conductivity.

Drawings

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Drawings

Claims20

Dependent claims

A constant-current circuit, comprising:

a first transistor formed of a MOS transistor and configured to supply a current based on a control signal input to a gate of the first transistor to serve as a current source;
a second transistor formed of a MOS transistor having the same conductivity as the first transistor and configured to supply a current to a load based on the control signal input to a gate of the second transistor that includes a source connected to ground, the gate connected to the gate of the first transistor, and a drain connected to the load;
a voltage regulation unit configured to control a drain voltage of the first transistor according to a drain voltage of the second transistor;
a current detector configured to detect a value of a current flowing through the first transistor and output a current according to a detected value;
a controller configured to control a gate voltage of the first transistor and a gate voltage of the second transistor according to the value detected by the current detector so that the current flowing through the first transistor becomes a predetermined value, wherein the controller comprises an error amplifier;
and
a delay circuit configured to delay a voltage output from the controller for a predetermined time and output a delayed voltage to the gates of the first and second transistors.

4 more elements

A light-emitting diode drive circuit comprising a constant-current circuit configured to generate a predetermined constant current and supply the constant current to a light-emitting diode, wherein the constant-current circuit includes:

a first transistor formed of a MOS transistor and configured to supply a current based on a control signal input to a gate of the first transistor to serve as a current source;
a second transistor formed of a MOS transistor having the same conductivity as the first transistor and configured to supply a current to a load based on the control signal input to a gate of the second transistor that includes a source connected to ground, the gate connected to the gate of the first transistor, and a drain connected to the load;
a voltage regulation unit configured to control a drain voltage of the first transistor according to a drain voltage of the second transistor;
a current detector configured to detect a value of a current flowing through the first transistor and output a current according to a detected value;
a controller configured to control a gate voltage of the first transistor and a gate voltage of the second transistor according to the value detected by the current detector so that the current flowing through the first transistor becomes a predetermined value, wherein the controller comprises an error amplifier;
and
a delay circuit configured to delay a voltage output from the controller for a predetermined time and output a delayed voltage to the gates of the first and second transistors.

4 more elements

An external load drive circuit comprising a constant-current circuit configured to generate a predetermined constant current and supply the constant current to a light-emitting diode, wherein the constant-current circuit includes:

a first transistor formed of a MOS transistor and configured to supply a current based on a control signal input to a gate of the first transistor to serve as a current source;
a second transistor formed of a MOS transistor having the same conductivity as the first transistor and configured to supply a current to a load based on the control signal input to a gate of the second transistor that includes a source connected to ground, the gate connected to the gate of the first transistor, and a drain connected to the load;
a voltage regulation unit configured to control a drain voltage of the first transistor according to a drain voltage of the second transistor;
a current detector configured to detect a value of a current flowing through the first transistor and output a current according to a detected value;
a controller configured to control a gate voltage of the first transistor and a gate voltage of the second transistor according to the value detected by the current detector so that the current flowing through the first transistor becomes a predetermined value, wherein the controller comprises an error amplifier;
and
a delay circuit configured to delay a voltage output from the controller for a predetermined time and output a delayed voltage to the gates of the first and second transistors.

4 more elements

Dependencies are inferred from the claim text.

Description4,045 words

Summary1,303 words

#The present patent application claims priority under 35 U.S.C. §119 from Japanese Patent Application No. 2007-008929, filed on Jan. 18, 2007 in the Japan Patent Office, the entire contents and disclosure of which are hereby incorporated by reference herein.

#1. Field of the Invention

#Preferred embodiments of the present invention generally relate to a constant-current circuit, and more particularly, to a light-emitting diode drive device using a constant-current circuit for outputting a constant current with high precision and reducing power consumption of the constant-current circuit by lowering an output voltage while maintaining the high precision in outputting the constant current.

Brief description of the drawings8 figures

#A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

#FIG. 1 is a block diagram showing a configuration example of a constant-current circuit of a preferred embodiment according to the present invention;

#FIG. 2 is a diagram showing example circuitry of the constant-current circuit shown in FIG. 1;

Detailed description2,562 words

#In describing preferred embodiments illustrated in the drawings, specific terminology is employed solely for the sake of clarity. It should be noted that the present invention is not limited to any preferred embodiment described in the drawings, and the disclosure of this patent specification is not intended to be limited to the specific terminology so selected. It is to be understood that each specific element includes all technical equivalents that operate in a similar manner and achieve a similar result.

#Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, preferred embodiments of the present invention are described.

#Referring to FIG. 1, a description is given of a constant-current circuit according to a preferred embodiment of the present invention.

Facts

Application

12/007,955Filed 17 Jan 2008

Priority

JP 2007-00892918 Jan 2007

Published

US 2008/0174253 A124 Jul 2008

Granted

16 Mar 2010

Term ends

17 Jan 2028

Estimated · how

20 years from earliest known nonprovisional domestic filing plus recorded patent term adjustment. Maintenance-fee lapses, terminal disclaimers and statutory extensions have not been checked. The continuity chain may be incomplete; this is not an enforceability determination.

Classification4 codes

H05B 45/397
Linear regulators: current mirror circuits
Y02B 20/30
Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps: semiconductor lamps, e.g. solid state lamps [SSL] light…
H05B
Electric heating
Y02B
Energy-efficient buildings

Timeline

18 Jan 2007Priority claimedJP 2007-008929
17 Jan 2008Application filedUS 12/007,955
17 Jan 2008Assigned to Ricoh Company, Ltd.assignment of assignor's interest
24 Jul 2008PublishedUS 2008/0174253 A1
16 Mar 2010GrantedUS 7,679,353 B2
12 Oct 2026TodayWithin its term
17 Jan 2028Term endsEstimated

Constant-current circuit and light-emitting diode drive device therewith

Life of this patent

Constant-current circuit and light-emitting diode drive device therewith

Life of this patent

Life of this patent

Abstract

Drawings

Drawings

Claims20

Description4,045 words

Drawings

Description4,045 words

Classification4 codes

Life of this patent