Systems and methods for closed loop control to ensure a constant current output with a changing load resistance

• US 10,441,790 B2
• Filed: 11/17/2016
• Issued: 10/15/2019
• Est. Priority Date: 11/18/2015
• Status: Active Grant

• Current Assignee: Case Western Reserve University
• Original Assignee: Case Western Reserve University
• Inventors: Durand, Dominique M.
• Primary Examiner(s): Stice, Paula J
• Application Number:
  US15/353,923
• Publication Number:
  US 20170136242A1
• Time in Patent Office: 1,062 Days
• CPC Class Codes: A61N 1/0551 Spinal or peripheral nerve electrodes
• CPC Class Codes: A61N 1/36128 Control systems
• CPC Class Codes: A61N 1/36139 with automatic adjustment
• CPC Class Codes: A61N 1/3614 based on impedance measurement
• CPC Class Codes: A61N 1/3615 Intensity
• CPC Class Codes: A61N 2/006 for magnetic stimulation of nerve tissue
• CPC Class Codes: A61N 2/02 using magnetic fields produced by coils, including single turn loops or electromagnets A61N2/12 takes precedence
• CPC Class Codes: G05B 19/042 using digital processors G05B19/05 takes precedence
• CPC Class Codes: G05B 2219/45117 Medical, radio surgery manipulator
• CPC Class Codes: G16H 20/30 relating to physical therapies or activities, e.g. physiotherapy, acupressure or exercising
• CPC Class Codes: G16H 20/40 relating to mechanical, radiation or invasive therapies, e.g. surgery, laser therapy, dialysis or acupuncture

Abstract

A closed loop control system automatically ensures that an output of a device is constant. The system can receive an input to set a fixed value for a variable (e.g., a current, a heart rate, a tissue perfusion, an ion level, etc.), and this variable can be delivered to a feedback component. The system can also include the device to deliver the variable to a load. The feedback component can be coupled to the delivery device to sample the output of the delivery device at different times. Based on the sampling, the feedback component can vary a property of the delivery device related to the delivery of the variable to the load to ensure that the variable remains constant at the fixed value. In some instances, the system can be implemented as a stimulator that delivers the constant current of a current source and has a low output impedance of a voltage source.

Claims

1. A stimulator with a low output impedance, the stimulator comprising:

a voltage source configured to generate an input voltage waveform;

a variable gain voltage amplifier configured to receive the input voltage waveform from the voltage source and provide an output voltage to a load; and

a feedback component, coupled to a current return of the adjustable gain amplifier, comprising a set point voltage source configured to generate a set point voltage and an amplifier configured to compare an output of a current power detector circuit to the set point voltage,

wherein the feedback component is configured to determine the voltage delivered to the load by sampling current into the load over a time period, estimating a power based on the current into the load over the time period, and

wherein a gain of the adjustable gain amplifier is adjusted based on a difference between the output of the current power detector and the set point voltage so the current power output to the load remains constant.

2. The stimulator of claim 1, wherein the power is estimated by calculating a root mean square of the current into the load.

3. The stimulator of claim 1, wherein the current power detector comprises a resistor in series with the load to sample the current into the load and a differential amplifier with a constant gain to determine the output of the current power detector.

4. The stimulator of claim 1, wherein the circuit further comprises a second amplifier configured to receive the output and the set point voltage and provide the difference between the output of the current power detector and the set point voltage to adjust the gain of the adjustable gain amplifier.

5. The stimulator of claim 1, wherein the stimulator is configured to reduce charge accumulation at a tissue-electrode interface, wherein the load is tissue.