Pulse Oximeter LED Circuit Using Capacitor Pulses for Low-Current Power
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current pulse oximeter designs require high power sources to continuously operate LEDs, making them unsuitable for integration into small, unobtrusive body-worn patches powered by low-current sources like coin cell batteries.
Innovation Solution
A pulse oximeter design that uses a capacitor to intermittently power LEDs, synchronized with a photodetector to minimize current draw, and synchronizes measurements with the patient's pulse cycle to reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a pulse oximeter uses continuous LED operation to ensure accurate blood oxygen measurements, then measurement precision is improved, but power consumption increases making it unsuitable for low-current battery sources
Solution Approach 1:
The patent implements periodic LED operation where the LED is driven in pulsed intervals rather than continuously. A capacitor charges during off-periods and discharges to drive the LED during measurement windows, creating a periodic action pattern that reduces average power consumption while maintaining measurement capability.
Solution Approach 2:
The capacitor is charged in advance during periods when the LED is not needed, storing energy beforehand. This preliminary charging action allows the LED to be driven at high current for brief measurement intervals without requiring the battery to continuously supply high current, thus reducing overall power consumption.
2Illumination intensity
If a pulse oximeter uses high current to drive LEDs for sufficient light output, then illumination intensity is improved, but the device cannot be powered by low-current coin cell batteries
Solution Approach 1:
The system uses periodic LED driving with the capacitor supplying current during active illumination periods. The LED receives high current pulses only when needed for measurement, while the capacitor recharges during off-periods, enabling high illumination intensity without continuous high current draw from the battery.
Solution Approach 2:
The capacitor acts as an intermediary energy storage device between the low-current battery and the high-current LED. It buffers the current mismatch by accumulating charge at low rates from the battery and releasing it at high rates to the LED, enabling the LED to operate at required current levels without requiring the battery to directly supply that current.
3Measurement precision
If a pulse oximeter continuously monitors blood oxygen levels, then measurement precision is improved, but battery life decreases
Solution Approach 1:
The system performs measurements in periodic intervals rather than truly continuously. The capacitor charges and discharges in cycles, enabling the LED to be driven only during measurement windows. This periodic operation maintains the ability to monitor blood oxygen levels over extended periods while significantly extending battery life compared to continuous operation.
Solution Approach 2:
While not truly continuous, the system maintains continuous monitoring capability through rapid periodic sampling. The capacitor ensures that measurement actions continue without interruption in the sense that the system is always ready to measure, with the capacitor pre-charged and the circuit always configured for measurement, even if the actual LED activation is intermittent.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate blood oxygen and heart rate monitoring using low-current power sources, extending the device's battery life and allowing integration into small, unobtrusive patches.
Implementation Method 1
a capacitor coupled to the low voltage power source and configured to provide charge to the LED
Implementation Method 2
An output of a photodetector may be connected to an integrating capacitor. When the LED is switched on, a portion of the photons emitted by the LED may be detected by the photodetector, which may convert these detected photons to a current
Implementation Method 3
electricity may be allowed to flow from the capacitor to a light-emitting diode (LED)
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Systems, methods, and devices of the various embodiments provide a device capable of determining a blood property based at least in part on the measurement of the amount of light received by a receiver circuit with a limited current capacity by charging a capacitor with a low voltage power supply and intermittently discharging the capacitor through a light emitting diode. In some embodiments the device may be a pulse oximeter capable of taking blood oxygen readings. In some embodiments the device may be a heart rate monitor to determine a heart rate based on an amount of light passed through tissue. The various embodiments may enable pulse oximeters and/or heart rate monitors to be incorporated into small unobtrusive body patches, while enabling the pulse oximeters to operate from a power output equivalent to that of a small coin cell battery or printed cell battery.