Pulse oximeter having a low power led drive

Details Pulse oximeter having a low power led drive Pulse oximeter having a low power led drive

1999-05-26

2001-05-01

Winakur, Eric F. (Department: 3736)

Surgery

Diagnostic testing

Measuring or detecting nonradioactive constituent of body...

C356S041000

Reexamination Certificate

active

06226539

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to photometers such as pulse oximeters. More particularly, the invention relates to a pulse oximeter having a low power drive for efficiently powering the light source of the oximeter.
2. Description of the Prior Art
Oximeters are used to measure the oxygenated fraction of hemoglobin in blood by analyzing the absorption of light transmitted through or reflected from the blood. A typical oximeter includes a light source such as a light emitting diode (LED) that generates and directs light toward a sample, a drive circuit for powering the LED, and a detection circuit that detects and analyzes the light from the LED after it has passed through the sample. After the LED is turned on, the detection circuit must “settle” before an accurate reading can be made. This results in inefficient power usage in existing oximeters because power delivered to the LED is wasted while the detection circuit is settling and because much of the current generated by the LED drive circuitry dissipates in resistive components of the circuitry.
OBJECTS AND SUMMARY OF THE INVENTION
The present invention solves the above-described problems and provides a distinct advance in the art of oximeters and other photometers. More particularly, the present invention provides a pulse oximeter having a low power LED drive that uses power more efficiently, especially during the settling time of the oximeter.
The oximeter of the present invention broadly includes 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 is configured to deliver a controlled amount of current to the LED that peaks only after the detection circuit has settled so that power is not wasted at the startup of the oximeter. The drive circuit is also configured to temporarily store and then deliver all of the energy from a source of power to the LED without dissipating much of the energy in resistive components.
The drive circuit includes an input for coupling with a source of power and energy storage circuitry 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.


REFERENCES:
patent: 5590652 (1997-01-01), Inai
patent: 5795292 (1998-08-01), Lewis et al.
patent: 5820550 (1998-10-01), Polson et al.
patent: 5974338 (1999-10-01), Asano et al.
patent: 5983122 (1999-11-01), Jarman et al.
patent: 5995855 (1999-11-01), Kiani et al.

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