Improved Howland Current Pump Stability Tim Green Senior

Improved Howland Current Pump Stability Tim Green Senior Analog Applications Engineers Precision Analog Linear Applications July 19, 2013 1

Improved Howland Current Pump IL Accuracy Circuit RT allows for trim to optimum ZOUT and improved DC Accuracy Ideal Op Amp 2

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 3

Improved Howland Current Pump Simplified Equation 4

Improved Howland AC Analysis RI RF Op Amp sees differential [(-IN) – (+IN)] feedback b = b- - b+ (Must be positive number else oscillation!) 5

Improved Howland AC Analysis - + 6

Improved Howland 1/b Plot - Full Load 7

Improved Howland 1/b Calculation No Load & Full Load IL No Load 0 A RO fz 6. 29 W 75. 8 Hz fp DC 1/b Hi-f 1/b 31. 83 k. Hz 17. 62 d. B 77. 17 d. B Full Load 1 A 0. 308 W 44. 08 Hz 31. 83 k. Hz 19. 45 d. B 77. 15 d. B Change in RO from No Load to Full Load has no significant impact on the 1/b Plot 8

Improved Howland Tina Transient Analysis Circuit RI RF 9

Improved Howland Tina Transient Analysis Results 10

Improved Howland Modified 1/b for Stability 11

Improved Howland AC Analysis Final Design for Stability RI RF 12

Improved Howland AC Analysis 1/b - Final Design for Stability fcl 13

Improved Howland AC Analysis Loop Gain - Final Design for Stability fcl 14

Improved Howland AC Transfer Analysis IL/VIN - Final Design for Stability RI RF 15

Improved Howland AC Transfer Analysis IL/VIN - Final Design for Stability 16

Improved Howland Transient Analysis IL/VIN - Final Design for Stability RI RF 17

Improved Howland Transient Analysis IL/VIN - Final Design for Stability 18