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**Improved Howland Current Pump Stability**

Tim Green Senior Analog Applications Engineers Precision Analog Linear Applications July 19, 2013

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**Improved Howland Current Pump IL Accuracy Circuit**

RT allows for trim to optimum ZOUT and improved DC Accuracy Ideal Op Amp

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**Improved Howland Current Pump V-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

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**Improved Howland Current Pump Simplified Equation**

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**Improved Howland AC Analysis**

RI RF Op Amp sees differential [(-IN) – (+IN)] feedback b = b- - b+ (Must be positive number else oscillation!)

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**Improved Howland AC Analysis**

- +

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**Improved Howland 1/b Plot - Full Load**

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**Improved Howland 1/b Calculation No Load & Full Load**

IL RO fz fp DC 1/b Hi-f 1/b No Load 0A 6.29W 75.8Hz 31.83kHz 17.62dB 77.17dB Full Load 1A 0.308W 44.08Hz 19.45dB 77.15dB Change in RO from No Load to Full Load has no significant impact on the 1/b Plot

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**Improved Howland Tina Transient Analysis Circuit**

RI RF

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**Improved Howland Tina Transient Analysis Results**

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**Improved Howland Modified 1/b for Stability**

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**Improved Howland AC Analysis Final Design for Stability**

RI RF

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**Improved Howland AC Analysis 1/b - Final Design for Stability**

fcl

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**Improved Howland AC Analysis Loop Gain - Final Design for Stability**

fcl

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**Improved Howland AC Transfer Analysis IL/VIN - Final Design for Stability**

RI RF

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**Improved Howland AC Transfer Analysis IL/VIN - Final Design for Stability**

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**Improved Howland Transient Analysis IL/VIN - Final Design for Stability**

RI RF

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**Improved Howland Transient Analysis IL/VIN - Final Design for Stability**

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