I figure if I can boost the current output to 100 mA with less than a 3 mV voltage drop from the AD584 output, I can safely put the 7.5 V through the resistor and get a precise enough 75 mA current output for calibrating the DMMs. And if I can boost the output to something like 2-3 A then I can replace any batteries I need.

The AD584 datasheet has a schematic for boosting the power output, but it uses a Darlington pair that is obsolete, and even if it were available, would dissipate 18 watts (converting 15 V to 6 V at 2 A) which is way more heat than I want to deal with.

I'm thinking there should be a way to do something like the Darlington power amplifier, where the reference voltage regulates the output voltage, including filtering audio-frequency noise, but maybe using dual power supplies so the amplifier does not have to get so hot. Maybe I can power the AD584 with a battery and use the switching power supply, dialed to an appropriate level, to provide the necessary current.

For (1) I figure if I can boost the current output to 100 mA with less than a 3 mV voltage drop from the AD584 output, I can safely put the 7.5 V through the resistor and get a precise enough 75 mA current output for calibrating the DMMs, although I would really like 500 mA to get closer to full range (600 mA) without pushing the fuse limit. And for (2) if I can boost the output to something like 2-3 A then I can replace any batteries I need.

UPDATE #1 on (1):

Thanks to Tim Williams, I'm thinking the following will suffice for calibrating my ammeter. The AD584LH also supplies a precision 5.0 V reference. I have a bunch of NiMH AA batteries to use as V1_batt and a 10 Ω trim pot to use as R1_trim. I also have a second DMM which, while not great, should be good enough to use as AM_null, and which I think is more sensitive and accurate in trying to measure zero current than trying to measure zero voltage. I can buy a precision 10 Ω 4 W resistor. Then I adjust the trim pot until AM_null reads zero, and I have a 500 mA reference current. The result should be accurate to within the tolerances of the voltage reference, resistor references, and ammeter sensitivity, all of which should be good enough for my purposes of calibrating a 3 1/2 digit DMM. The fact that it requires manual, rather than automatic, trim, and is not directly traceable to NIST standards, is in keeping with my initial statement that I'm building a home breadboard device, not a commercial lab standard.

^{simulate this circuit – Schematic created using CircuitLab}

UPDATE #1 on (2)

I expected (based on an application note in the AD584 datasheet) that the solution to problem (1) would be some sort of linear amplifier. As it turns out, the solution to (1) in update #1 above does not amplify the output of the voltage reference and does require a low noise power supply, so it is not a basis for a solution to (2): a high power, low noise power supply to replace batteries.

However, imagine if someone did present a power amplification solution to problem (1). Apparently, people with pre-conceived notions of how to build a power supply could not fathom my idea, which to me remains pretty straightforward in theory, whether or not practical: If there were a linear amplifier design that boosted the current output of the voltage reference while maintaining the voltage via some form of feedback, then as long as the responsiveness of the feedback loop was fast and accurate enough, it would be sufficient to filter out audio frequency (i.e. < 20 kHz) noise from a noisy power source like an SMPS, and allow me to use it to replace batteries in battery-powered audio devices, which, because they expect clean power from batteries, lack any such input voltage filtering. Expecting responsiveness in the 100 kHz range did not and still does not seem unreasonable to me.

Maybe such a setup would not be ideal for mass production, but since I would have already had all or almost all of the components, it might make sense for me to use it rather than build something entirely different to achieve the same ends. I thought people here might be interested in thinking creatively about how to build an unconventional circuit, or educate me on why such a circuit would be impractical if not impossible.

END OF UPDATE #1

The AD584 datasheet has a schematic for boosting the power output of the voltage reference, but it uses a Darlington pair that is obsolete, and even if it were available, would dissipate 18 watts (converting 15 V to 6 V at 2 A) which is way more heat than I want to deal with.

I'm thinking there should be a way to do something like the Darlington power amplifier, where the reference voltage regulates the output voltage, including filtering audio-frequency noise, but maybe using dual power supplies so the amplifier does not have to get so hot. Maybe I can power the AD584 with a battery and use the switching power supply, dialed to an appropriate level, to provide the necessary current.