OP177
Production
The OP177 features one of the highest precision performance of
any operational amplifier currently available. Offset voltage of the
OP177 is only 25 Î...
Datasheet
OP177 on Analog.com
LTspice
Production
LTspice® is a powerful, fast, and free SPICE simulator software, schematic capture and waveform viewer with enhancements and models for improving the simulation...
LTspice on Analog.com
Hi forum. First of all, thank you for your global active support.
I really need your help.
In the attempt to design a very accurate, high current source/sink for an automatic test system, I came across the application notes of the AD’s OP177 op-amp discussing an Howland Current Pump (HCP) with very high current output feature up to 100mA (figure 30 of page 10 of the OP177 | Data Sheet - Rev.H). Following the indication of the note describing a “Bilateral Current Source” basically a Howland Current Pump and adding 2 power transistor, with a load resistor of about 100 ohms you actually can get a current of -100mA / +100mA. (Source/Sink).
But as the Load Impedance increases to 200mA it drops to 60mA and so on.
I attach the LTSpice Simulation 4555.Figure 30. Bilateral Current Source - 100mA CURRENT SOURCE.asc
Now I need a stable current source/sink with very large load impedance interval (from 200 to 1.2k).
That’s why I have chosen the Howland Current Pump topology since one of its feature is to provide the same current with load change.
How is it possible to increase the current without driving the OpAmp into saturation?
Best regards and thanks.
Houseman
