Switch-mode oximeter LED drive with a single inductor

• US 20050187447A1
• Filed: 02/25/2004
• Published: 08/25/2005
• Est. Priority Date: 02/25/2004
• Status: Active Grant

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Nellcor Puritan Bennett Incorporated (Medtronic Plc)
• Inventors: Petersen, Ethan, Chew, Bradford B., Shea, William
• Granted Patent: US 7,120,479 B2
• Time in Patent Office: Days
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

A light emitter drive circuit for an oximeter which utilizes a single inductor for driving multiple light emitters. The inductor is connected to a switching circuit to multiple energy storage circuits, such as capacitors. These are alternately charged up, using the same inductor. Subsequently, the capacitors are alternately discharged for their corresponding light emitters through the same inductor. Also, the magnetic susceptibility of the LED drive circuit is reduced by using magnetic flux canceling in the inductor. In one embodiment, a toroidal inductor is used with geometric symmetry and its magnetic flux. In another embodiment, a dual core closed bobbin shielded inductor is used.

Claims

1. A light emitter drive circuit for an oximeter comprising:

a voltage generating circuit;

an inductor coupled to said voltage generating circuit;

a first switching circuit coupled to a first node of said inductor;

first and second energy storage circuits connected to said first switching circuit, such that current from said inductor can be steered by said first switching circuit to one of said energy storage circuits;

a second switching circuit coupled to a second node of said inductor; and

first and second light emitter drive lines connected to said second switching circuit, such that energy from said first and second energy storage circuits can be alternately coupled to said first and second light emitter drive lines.

2. The circuit of claim 1 wherein said first and second energy storage circuits comprise first and second capacitors.

3. The circuit of claim 1 wherein said drive lines are configured to drive light emitters that are back-to-back.

4. The circuit of claim 3 wherein said second switching circuit is an H-bridge drive circuit including four transistors.

5. The circuit of claim 1 wherein said voltage generating circuit is a voltage regulator separate from a supply voltage for a remainder of said oximeter.

6. The circuit of claim 1 further comprising a resistor and a capacitor in parallel with said inductor.

7. The circuit of claim 1 wherein said inductor is a magnetic flux canceling inductor.

8. The circuit of claim 7 wherein said inductor is a toroidal inductor.

9. The circuit of claim 7 wherein said inductor is a dual core closed bobbin shielded inductor.

10. The circuit of claim 1 further comprising a sample and hold circuit connected to said second node of said inductor.

11. The circuit of claim 1 further comprising at least a third energy storage circuit.

12. An LED circuit for an oximeter comprising:

a voltage generating circuit;

an inductor coupled to said voltage generating circuit;

a first switching circuit coupled to a first node of said inductor;

first and second capacitors connected to said first switching circuit, such that current from said inductor can be steered by said first switching circuit to one of said capacitors;

an H-bridge drive switching circuit including four transistors coupled to a second node of said inductor; and

first and second light emitter drive lines, for LEDs in a back-to-back configuration, in the middle of said H-bridge, such that energy from said first and second capacitors can be alternately coupled to said first and second light emitter drive lines.

14. The circuit of claim 12 wherein said inductor is a toroidal inductor.

15. The circuit of claim 12 wherein said inductor is a dual core closed bobbin shielded inductor.

13. A light emitter drive circuit for an oximeter comprising:

a voltage generating circuit;

first and second energy storage circuits;

a magnetic flux canceling inductor coupled to said voltage generating circuit and at least one of said energy storage circuits; and

switching circuitry configured to first steer current into said energy storage circuits, and then provide energy from said first and second energy storage circuits to drive lines for light emitters.