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Improved Howland Current Pump Stability. Tim Green Senior Analog Applications Engineers Precision Analog Linear Applications July 19, 2013. Improved Howland Current Pump IL Accuracy Circuit. RT allows for trim to optimum Z OUT and improved DC Accuracy. Ideal Op Amp.

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Improved howland current pump stability
Improved Howland Current Pump Stability

Tim Green

Senior Analog Applications Engineers

Precision Analog Linear Applications

July 19, 2013


Improved howland current pump il accuracy circuit
Improved Howland Current PumpIL Accuracy Circuit

RT allows for trim to optimum ZOUT and improved DC Accuracy

Ideal Op Amp


Improved howland current pump v i dc accuracy calculations
Improved Howland Current PumpV-I DC Accuracy Calculations

1% Resistors (w/RT=0) could yield only 9% Accuracy at T=25°C

Still useful for V-I control in Motors/Valves  V-Torque Control

Outer position feedback adjusts V for final position


Improved howland current pump simplified equation
Improved Howland Current PumpSimplified Equation


Improved howland ac analysis
Improved Howland AC Analysis

RI

RF

Op Amp sees differential [(-IN) – (+IN)] feedback

b=b- -b+ (Must be positive number else oscillation!)



Improved howland 1 b plot full load
Improved Howland 1/b Plot - Full Load


Improved howland 1 b calculation no load full load
Improved Howland 1/b CalculationNo Load & Full Load

Change in RO from No Load to Full Load

has no significant impact on the 1/b Plot


Improved howland tina transient analysis circuit
Improved Howland Tina Transient Analysis Circuit

RI

RF


Improved howland tina transient analysis results
Improved Howland Tina Transient Analysis Results


Improved howland modified 1 b for stability
Improved HowlandModified 1/b for Stability


Improved howland ac analysis final design for stability
Improved Howland AC AnalysisFinal Design for Stability

RI

RF


Improved howland ac analysis 1 b final design for stability
Improved Howland AC Analysis1/b - Final Design for Stability

fcl


Improved howland ac analysis loop gain final design for stability
Improved Howland AC AnalysisLoop Gain - Final Design for Stability

fcl


Improved howland ac transfer analysis il vin final design for stability
Improved Howland AC Transfer AnalysisIL/VIN - Final Design for Stability

RI

RF


Improved howland ac transfer analysis il vin final design for stability1
Improved Howland AC Transfer AnalysisIL/VIN - Final Design for Stability


Improved howland transient analysis il vin final design for stability
Improved Howland Transient AnalysisIL/VIN - Final Design for Stability

RI

RF


Improved howland transient analysis il vin final design for stability1
Improved Howland Transient AnalysisIL/VIN - Final Design for Stability


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