Current source with indirect load current signal extraction

• US 7,642,762 B2
• Filed: 01/29/2007
• Issued: 01/05/2010
• Est. Priority Date: 01/29/2007
• Status: Active Grant

• Current Assignee: Analog Devices International Unlimited Company (Analog Devices, Inc.)
• Original Assignee: Linear Technology Corporation (Analog Devices, Inc.)
• Inventors: Zhang, Jindong, Xie, Manjing
• Primary Examiner(s): Laxton; Gary L
• Application Number:
  US11/698,874
• Publication Number:
  US 20080180075A1
• Time in Patent Office: 1,072 Days
• Field of Search: 323/282, 323/284, 323/285, 323/351, 315/209.R, 315/224, 315/225, 315/291
• US Class Current: 323/282
• CPC Class Codes: H02M 3/156 with automatic control of output voltage or current, e.g. switching regulators
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/375 using buck topology
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A switching circuit for supplying current to a load has a switching element, an inductive element coupled to the switching element, and a load current extraction circuit responsive to current in the inductive element for producing a load current signal as a simulated current approximating current in the load.

Claims

1. A switching circuit for supplying an output current to a load, comprising:

a switching element,

an inductive element coupled to the switching element to deliver current to the load,

a capacitive element between the inductive element and the load, current in the load being different from current in the inductive element due to a current component flowing through the capacitive element, and

a load current extraction circuit responsive to current in the inductive element for producing a load current signal representing the current in the load, the load current signal being produced as a simulated current approximating the current in the load so as to take into account influence of the capacitive element on the current in the load.

2. The circuit of claim 1, wherein the load current extraction circuit is configured to have a characteristic similar to a respective characteristic of output circuitry of the switching circuit.

3. The circuit of claim 2, wherein the load current extraction circuit is configured to a have a dynamic response similar to a dynamic response of the output circuitry when the output current supplied to the load is controlled.

4. The circuit of claim 1, further including an output capacitor coupled to the inductive element.

5. The circuit of claim 4, wherein the load includes a light-emitting diode (LED).

6. The circuit of claim 5, wherein the load current extraction circuit is configured to have a transfer function that matches a transfer function of a low-pass filter formed by the output capacitor and the LED.

7. The circuit of claim 6, wherein the load current extraction circuit includes a differential amplifier.

8. The circuit of claim 1, wherein the switching element and the inductive element are connected in a step-down switching regulator configuration.

9. The circuit of claim 1, wherein the current in the inductive element is sensed using a sense resistor coupled in series with the inductive element.

10. The circuit of claim 1, wherein the current in the inductive element is sensed using DC resistance of the inductive element.

11. A switching circuit for supplying an output current to a load, comprising:

a switching element,

an inductive element coupled to the switching element

an output capacitor coupled to the inductive element, and

a load current extraction circuit responsive to current in the inductive element for producing a load current signal as a simulated current approximating current in the load,

wherein the load includes a light-emitting diode (LED),

the load current extraction circuit is configured to have a transfer function that matches a transfer function of a low-pass filter formed by the output capacitor and the LED, and to have a frequency response determined by capacitance of the output capacitor and dynamic resistance of the LED.

12. A switching circuit for supplying an output current to a load, comprising:

a switching element,

an inductive element coupled to the switching element

an output capacitor coupled to the inductive element, and

a load current extraction circuit responsive to current in the inductive element for producing a load current signal as a simulated current approximating current in the load,

wherein the load includes a light-emitting diode (LED),

the load current extraction circuit is configured to have a transfer function that matches a transfer function of a low-pass filter formed by the output capacitor and the LED, and

the load current extraction circuit includes a differential amplifier, a first RC circuit coupled between an inverting input and an output of the differential amplifier, and a second RC circuit coupled between a non-inverting input of the differential amplifier and a power supply terminal.

13. The circuit of claim 12, wherein each of the first and second RC circuits includes a resistive element and a capacitive element connected in parallel.

14. A system for driving a LED, comprising:

a switching regulator for producing an output current supplied to the LED, the switching regulator including an inductive element and an output capacitor, current in the LED being different from current in the inductor due to a current component flowing through the output capacitor, and

a current sensing circuit responsive to current in the inductive element to produce a load current signal for controlling the output current, the current sensing circuit is configured to process the current in the inductive element so as to produce the load current signal as a simulated current approximating the current in the LED so as to take into account influence of the output capacitor on the current in the LED.

15. The system of claim 14, wherein the current sensing circuit is configured to have a transfer function that matches a transfer function of a low-pass filter provided by the output capacitor and the LED.

16. A system for driving a LED, comprising:

a switching regulator for producing an output current supplied to the LED, the switching regulator including an inductive element and an output capacitor, and

a current sensing circuit responsive to current in the inductive element to produce a load current signal for controlling the output current, the current sensing circuit is configured to process the current in the inductive element so as to produce the load current signal as a simulated current approximating current in the LED,

wherein the current sensing circuit is configured to have a frequency response determined by capacitance of the output capacitor and dynamic resistance of the LED.

17. A method of controlling a switching circuit having an inductive element, a load, and a capacitive element between the inductive element and the load, the method comprising the steps of:

sensing current in the inductive element, current in the load being different from current in the inductor due to a current component flowing through the capacitive element, and

processing the sensed current so as to produce a load current signal as a simulated current approximating the current in the load so as to take into account influence of the capacitive element on the current in the load.

18. The method of claim 17, wherein the load current signal is produced to control an output current of the switching circuit.

19. The method of claim 18, wherein the load current signal is produced by simulating a dynamic response of output circuitry of the switching circuit when the output current is supplied to the load.

20. A method of controlling a switching circuit having an inductive element, the method comprising the steps of:

sensing current in the inductive element, and

processing the sensed current so as to produce a load current signal as a simulated current approximating current in a load of the switching circuit,

wherein the load current signal is produced to control an output current of the switching circuit, by simulating a dynamic response of output circuitry of the switching circuit when the output current is supplied to the load, based on a mathematical model of a low-pass filter provided by the load and a capacitor in the output circuitry.