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

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

3. 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

4. Improved Howland Current Pump Simplified Equation

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

6. Improved Howland AC Analysis- +

7. Improved Howland 1/b Plot - Full Load

8. Improved Howland 1/b Calculation No Load & Full LoadIL 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

9. Improved Howland Tina Transient Analysis CircuitRI RF

10. Improved Howland Tina Transient Analysis Results

11. Improved Howland Modified 1/b for Stability

12. Improved Howland AC Analysis Final Design for StabilityRI RF

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

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

15. Improved Howland AC Transfer Analysis IL/VIN - Final Design for StabilityRI RF

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

17. Improved Howland Transient Analysis IL/VIN - Final Design for StabilityRI RF

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