Systems and methods for closed loop control to ensure a constant current output with a changing load resistance
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.
1. A method comprising:
generating a set point voltage;
determining a voltage delivered to a load by sampling a current into the load at different times over a time period; and
estimating a power based on the current into the load over the time period;
comparing the voltage delivered to the load to the set point voltage; and
adjusting a gain of an adjustable gain amplifier based on a difference between the voltage delivered to the load and the set point voltage so that a current power output to the load remains constant.
2. The method of claim 1 , wherein the current into the load is an analog current.
3. The method of claim 1 , wherein the current into the load is a digital current.
4. The method of claim 1 , wherein the load provides a sampled variable comprising at least one of heart rate, tissue perfusion, and ion level.
5. The method of claim 4 , wherein the current power output comprises a current for neural stimulation.
6. The method of claim 1 , wherein the load provides a sampled variable comprising a detected magnetic field.
7. The method of claim 1 , wherein the estimating comprises calculating a root mean square of the current into the load.
8. The method of claim 1 , further comprising reducing charge accumulation at a tissue-electrode interface, wherein the load is tissue.
9. The method of claim 1 , wherein the current power is independent of an impedance of the load when the impedance of the load changes more slowly than a rate at which the gain of the adjustable gain amplifier is adjusted.