I am trying to use the 11-pin OPA541AP transconductance amplifier (plastic pack) to drive a load (and that load is a current controlled device). The amplifier is properly heat sinked and I am using thicker leads to support the current.
The input signal is a voltage: Vdc+Vac sin(wt) from an Agilent 33250A function generator.
I am using a 1 ohm power resistor as the external current limiting resistor. According to the specs, that should support a current of about 750mA. I need about 1 amp, but this will do for my purpose.
The problem is that the voltage across a test 10 Ohm resistor is showing that my sine wave is getting current limited at both ends. I think the reason is that the minimum voltage I can output is about 1 mV (from the Agilent), and the gain on the OPA541AP is about 97 dB (about 70,000). That explains why the current would be cut off.
To do my work, I have two options:
1. Reduce the input voltage (that means I could use an inverting 741 amplifier to attenuate the 1 mV excitation by a certain factor). The problem with that is that S/N ratio worsens with such low amplitudes, and though I have not yet looked at the spec, this may be close to the input offset voltage of the OPA541AP.
2. Find some way to reduce the gain of OPA541AP so that I am outputting less current. The circuits shown in the datasheet produce voltage sources, not current sources.
Any ideas ? I noticed that pins 6 and 9 are NCs. Can these be used in some undocumented fashion to do this ?