# US 8,148,903 B2 · Light emitting diode driving circuit > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,148,903 B2 - Document ID: US8148903B2 - Status: Granted - Kind: B2 - Application number: 12/141,577 - Filed: 2008-06-18 - Published: 2008-12-25 - Granted: 2012-04-03 - Earliest claimed: 2007-06-21 - Assignees: Dongbu HiTek Co., Ltd. - Inventors: Sung-Man Pang - Web page: https://patentgrep.com/patent/US8148903B2 ## CPC - H05B 45/12: using optical feedback - H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL ## Abstract A LED driving circuit that may control current flow into an LED on a current path according to the amount of light sensed from the LED. An LED driving circuit for driving at least one LED may include at least one of: An optical sensor for receiving light emitted from the LED and generating a feedback signal having a level corresponding to an amount of the received light. A current regulator provided on a path through which current of the LED flows for regulating an amount of current flowing into the LED according to a comparison of the feedback signal with a first reference signal. ## Claims ### Claim 1 An apparatus comprising a light emitting diode (LED) driving circuit configured to drive at least one LED, wherein the circuit comprises: an optical sensor configured to receive light emitted from said at least one LED and generate a feedback signal corresponding to an amount of light received by the optical sensor; and a current regulator configured to regulate an amount of current flowing into said at least one LED according to a comparison of the feedback signal with a first reference signal, wherein the current regulator comprises: a first reference signal generator configured to generate the first reference signal, a comparator configured to compare a level of the feedback signal with a level of the first reference signal; a first transistor connected between a negative electrode of said at least one LED and a reference voltage source, where the first transistor is driven in response to the comparison of the feedback signal with the first reference signal; and a first load connected between the first transistor and the reference voltage source, wherein the first reference signal generator comprises: an operational amplifier comprising a positive input terminal configured to receive a second reference signal; a second load connected between a negative input terminal of the operational amplifier and the reference voltage source; a second transistor configured to supply a reference current to the second load in response to an output of the operational amplifier; a current mirror configured to generate a mirror current of the reference current; and a first resistor, wherein the mirror current flows into the first resistor and wherein the first reference signal corresponds to a voltage across both ends of the first resistor. ### Claim 2 (depends on 1) The apparatus of claim 1, wherein the reference voltage source is grounded. ### Claim 3 (depends on 1) The apparatus of claim 1, comprising a switch configured to selectively supply the feedback signal to the current regulator. ### Claim 4 (depends on 1) The apparatus of claim 1, wherein the current regulator is connected between a negative electrode of said at least one LED and the reference voltage source. ### Claim 5 (depends on 4) The apparatus of claim 4, wherein the reference voltage source is grounded. ### Claim 6 (depends on 1) The apparatus of claim 1, comprising: a voltage inspector configured to inspect a voltage of said at least one LED and generate a control signal; and a charge pump configured to supply a voltage to said at least one LED according to the control signal. ### Claim 7 (depends on 2) The apparatus of claim 2, wherein: the charge pump is configured to supply to said at least one LED the voltage corresponding to an operation mode; and the operation mode is determined according to the control signal designating one of a plurality of operation modes having different voltage gains. ### Claim 8 (depends on 2) The apparatus of claim 2, wherein the voltage of said at least one LED is a voltage supplied to said at least one LED. ### Claim 9 (depends on 6) The apparatus of claim 6, wherein the voltage of said at least one LED is a voltage across both electrodes of said at least one LED. ### Claim 10 (depends on 1) The apparatus of claim 1, wherein the optical sensor comprises: a light receiving diode configure to receive light emitted from said at least one LED; and a third load connected between the light receiving diode and the reference voltage source, wherein the feedback signal is derived from a voltage at a connection point of the light receiving diode and the third load. ### Claim 11 (depends on 10) The apparatus of claim 10, wherein the reference voltage source is grounded. ### Claim 12 (depends on 10) The apparatus of claim 10, wherein the light receiving diode comprises: a negative electrode connected to a charge pump; and a positive electrode connected to the third load. ### Claim 13 (depends on 10) The apparatus of claim 10, wherein the light receiving diode comprises: a negative electrode connected to a positive electrode of said at least one LED; and a positive electrode connected to the third load. ### Claim 14 (depends on 10) The apparatus of claim 10, wherein: the first load comprises a second resistor connected between a positive electrode of the light receiving diode and the reference voltage source; and the feedback signal is a voltage across both ends of the second resistor. ### Claim 15 An apparatus comprising light emitting diode (LED) driving circuit configured to drive at least one LED, wherein the circuit comprises: an optical sensor configured to receive light emitted from said at least one LED and generate a feedback signal corresponding to an amount of light received by the optical sensor; and a current regulator configured to regulate an amount of current flowing into said at least one LED according to a comparison of the feedback signal with a first reference signal, wherein the current regulator comprises: a comparator configured to compare the feedback signal with the first reference signal; a reference signal generator configured to generate a second reference signal in response to the comparison of the feedback signal with the first reference signal; an operational amplifier comprising a positive input terminal connected to the reference signal generator; a first transistor connected between a negative electrode of said at least one LED and a reference voltage source, wherein the first transistor is driven by an output of the operational amplifier; and a load connected between a negative input terminal of the operational amplifier and the reference voltage source, wherein reference signal generator comprises: a second transistor through which a reference current flows, wherein the second transistor is driven in response to the comparison of the feedback signal with the first reference signal; a first resistor connected between the second transistor and the reference voltage source; a current mirror configured to generate a mirror current of the reference current; and a second resistor, wherein the mirror current flows into the second transistor and wherein the second reference signal corresponds to a voltage across both ends of the second resistor. ### Claim 16 (depends on 15) The apparatus of claim 15, wherein the reference voltage source is grounded.