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Hello there,
We are using the OPA455 in an improved Howland current source topology. Our goal is to be able to deliver +/-2mA to a maximum compliance of +/-75V. I had a few questions:
1. The quiescent current of the OPA455 is rated at 3.2 - 3.7mA when Iout=0mA. We are using +/-75V at the rails, so a maximum VDD-VSS = 150V. We will supply a maximum of 2mA peak to peak at the output load. What is the right way to estimate the power consumption/efficiency of this chip with this information?
2. Do you have suggestions on any alternative options to have a lower quiescent current for the same application?
Thanks!
Ashwati
Hi Ashwati,
1Q: What is the right way to estimate the power consumption/efficiency of this chip with this information?
Assume the quiescent current is 3.7mA, OPA455's internal power loss will be approx. 37mA*150Vdc = 0.56W. Since your improved howland current source is only +/-2mA, the peak heat dissipation is not very high, see the AC power calculation slide below.
2Q. Do you have suggestions on any alternative options to have a lower quiescent current for the same application?
All HV power amplifiers will have comparable level of quiescent currents in the family. There are two additional V-I converter circuits that may meet your application requirement, which it does not require to use power amplifier, hence lower quiescent current.
https://www.ti.com/lit/ug/slau502/slau502.pdf?ts=1614815713241
The application notes can be readily scaled up for higher voltage application (only works as sourcing current).
If you need drive +/-2mA (source and sink in current), it is possible to use INA146/IN148/INA149, difference amplifiers to generate the current. Since I do not know your design requirements, I just post these threads and you can decide on your own.
If you need additional questions or assistant, please let us know.
Best,
Raymond
