The classic improved Howland is used for bidirectional current output into grounded loads. This circuit requires strict component value selection and matching to achieve high accuracy and performance

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• Article «Simple, precise, bi-directional current source»
• Figure 1. The classic improved Howland is used for bidirectional current output into grounded loads. This circuit requires strict component value selection and matching to achieve high accuracy and performance
• Figure 2. This simple current source (Simple Source) circuit provides accuracy with a single resistor by floating the power supplies of the output stage. Isolated dual output DC to DC converters are readily available at many power levels as a check of your favorite
• Figure 3. Actual circuit used for testing of the grounded load current source. This circuit included the V_GS multiplier Q3 to provide the class A/B bias necessary for high frequency transient response testing. The 50 Ω source resistors on Q1 and Q2 elimi
• Figure 4. Output error of the circuit in Figure 3 plotted over a range of ±10 mA
• Figure 5. Test circuits to compare dynamic response of Simple Source (top) vs. Howland (bottom). Output signal is observed across R_TEST
• Figure 8. This is the simplest possible realization of this current output circuit although it trades off for lower output impedance and restricted output compliance range. Furthermore, it will have to be verified with the op amp of your choice as some op amps may