Pulse oximeter having a low power led drive

• US 6,226,539 B1
• Filed: 05/26/1999
• Issued: 05/01/2001
• Est. Priority Date: 05/26/1999
• Status: Expired due to Term

• Current Assignee: Covidien LP (Medtronic Plc)
• Original Assignee: Mallinckrodt Incorporated (Mallinckrodt plc)
• Inventors: Potratz, R. Stephen
• Primary Examiner(s): Winakur, Eric F.
• Assistant Examiner(s): Szmal, Brian
• Application Number:
  US09/320,145
• Time in Patent Office: 706 Days
• Field of Search: 600/323, 600/322, 600/310, 600/326, 600/473, 600/476, 600/39, 600/41
• US Class Current: 600/323
• CPC Class Codes: A61B 2560/0209 adapted for power saving
• CPC Class Codes: A61B 5/14551 for measuring blood gases

Abstract

A photometer (10) includes a light source (12) operable to direct light toward a sample (14), a detection circuit (16) operable to detect the light after it has passed through the sample, and a drive circuit (18) for powering the light source. The drive circuit includes an input (20) for coupling with a source of power and energy storage circuitry (22) coupled with the input. The energy storage circuitry is operable to store energy from the source of power when switched to a charging state and to deliver current to the light source in a ramped manner when switched to a discharge state so that the current peaks at a selected time. The drive circuit delivers a controlled amount of current to the light source that peaks only after the detection circuit has settled so that power is not wasted at the startup of the oximeter.

Claims

1. A photometer comprising:

a light source operable to direct light toward a sample;

a detection circuit operable to detect the light after it has passed through the sample; and

a drive circuit for powering the light source, the drive circuit including

an input for coupling with a source of power, and

energy storage circuitry coupled with the input and operable to store energy from the source of power when switched to a charging state and to deliver current to the light source in a ramped manner so that the current peaks at a selected time when switched to a discharge state.

2. The photometer as set forth in claim 1, the drive circuit further including switching circuitry for selectively switching the energy storage circuitry between the charging state and discharge state.

3. The photometer as set forth in claim 1, the energy storage circuitry including:

a capacitor for storing a charge when the energy storage circuitry is switched to the charging state and for discharging the charge to the light source when the energy storage circuitry is switched to the discharge state; and

an inductor wired between the input and the capacitor for charging the capacitor when the energy storage circuitry is switched to the charging state and for delivering the charge from the capacitor to the light source when the energy storage circuitry is switched to the discharge state.

4. The photometer as set forth in claim 3, wherein the capacitor and the inductorform a tuned circuit operable to resonate such that a partial half wave of current is allowed to peak while the energy storage circuitry is in the discharge state.

5. The photometer as set forth in claim 2, the switching circuitry including a first transistor wired between the input and the energy storage circuitry for switching energy from the power source to the energy storage circuitry.

6. The photometer as set forth in claim 5, the switching circuitry further including a second transistor wired between the energy storage circuitry and the light source for switching current from the energy storage circuitry to the light source.

7. The photometer as set forth in claim 1, the light source comprising a light emitting diode.

8. A drive circuit for powering a light source in a photometer, the drive circuit comprising:

an input for coupling with a source of power; and

energy storage circuitry coupled with the input and operable to store energy from the source of power when switched to a charging state and to deliver current to the light source in a ramped manner so that the current peaks at a selected time when switched to a discharge state.

9. The drive circuit as set forth in claim 8, further including switching circuitry for selectively switching the energy storage circuitry between the charging state and discharge state.

10. The drive circuit as set forth in claim 8, the energy storage circuitry including:

a first capacitor for storing a charge when the energy storage circuitry is switched to the charging state and for discharging the charge to the light source when the energy storage circuitry is switched to the discharge state; and

an inductor wired between the input and the first capacitor for charging the first capacitor when the energy storage circuitry is switched to the charging state and for delivering the charge from the first capacitor to the light source when the energy storage circuitry is switched to the discharge state.

11. The photometer as set forth in claim 10, wherein the capacitor and the inductor form a tuned circuit operable to resonate such that a partial half wave of current is allowed to peak while the energy storage circuitry is in the discharge state.

12. The photometer as set forth in claim 9, the switching circuitry including a first transistor wired between the input and the energy storage circuitry for switching energy from the power source to the energy storage circuitry.

13. The photometer as set forth in claim 12, the switching circuitry further including a second transistor wired between the energy storage circuitry and the light source for switching current from the energy storage circuitry to the light source.

14. The photometer as set forth in claim 8, the light source comprising a light emitting diode.

15. The photometer as set forth in claim 10, further including a second capacitor coupled with the first capacitor for measuring the current delivered to the light source when the energy storage circuitry is switched to the discharge state.

16. A photometer comprising:

a light source operable to direct light toward a sample;

a detection circuit operable to detect the light after it has passed through the sample; and

a drive circuit for powering the light source, the drive circuit including

an input for coupling with a source of power,

switching circuitry for selectively switching the drive circuit between a charging state and a discharging state,

a capacitor for receiving and storing a charge when the drive circuit is in the charging state and for discharging the charge to the light source when the drive circuit is in the discharging state, and

an inductor for charging the capacitor when the drive circuit is in the charging state and for delivering the charge from the capacitor to the light source when the drive circuit is in the discharging state.

17. The photometer as set forth in claim 16, the inductor and capacitor operating together to restrict delivery of the charge until a predetermined time period has passed following switching of the drive circuit to a discharging state.

18. The photometer as set forth in claim 17, delivery of the charge being restricted to a ramp function peaking a predetermined time period after switching of the drive circuit to a discharging state.

19. A photometer comprising:

a light source operable to direct light toward a sample, the light source having a voltage drop value;

a detection circuit operable to detect the light after it has passed through the sample;

a drive circuit coupled with the light source and the microprocessor and operable to power the light source, the drive circuit including

an input for coupling with a source of power,

switching circuitry for selectively switching the drive circuit between a charging state and a discharging state, with the charging state being limited in duration to a charging time, and

a storage capacitor for storing a charge when the drive circuit is in the charging state and for discharging the charge to the light source when the photometer is in the discharging state; and

a compensation circuit coupled to the drive circuit and the light source and operable to determine the voltage drop value of the light source and to adjust the charging time of the charging state to compensate there for.

20. A method for delaying peak charge delivery to a light source element of a photometer, the light source element having a voltage drop value, the method comprising the steps of:

determining the length of a desired delay period;

selecting and configuring a capacitive energy storage element and an inductive control element based on the length of the desired delay period;

determining the voltage drop value of the light source element;

charging the capacitive energy storage element with a charging pulse, the charging pulse having a pulse width based on the determined voltage drop value of the light source element; and

discharging the capacitive storage element through the inductive control element to result in delaying the peak charge delivery to the light source by the length of the desired delay period.