I've designed a constant current source based upon the LT8645S. See attached. It works well when the load is around 1-2Ω. But when I increase the load to 3-4 ohms, the current drops significantly.
The input voltage is 42V, but the output voltage is only reaching 18-24V, thus the current fall off.
The output of the AD8030 feedback opamp looks to be trying to regulate Vref, but I just don't see what the issue is.
Any help would be greatly appreciated.
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Thanks Fil. I ended up resolving this with feedback from stack exchange.
Turns out that the common mode input voltage was going higher than the supply voltage (4.5Amps * 4Ohm = 18V) of the opamp. I solved it by selecting a high voltage op-amp, which also happened to be an over-the-top amplifier. LT6015. And then powering the opamp from the same input supply as the current source.