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One can purchase $0.15 TI parts have <0.4mA quiescent current and output 3A. These things draw so little under no/low load circumstances that my cheaper 4-digit readout benchtop supplies cannot detect any draw.

https://www.ti.com/lit/ds/symlink/tps563201.pdf

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0.4 mA quiescent current is huge for very low-power designs though. If your system must spend the majority of its time consuming very little power, that level of constant current draw is a non-starter.

Well, typical $0.15 linear regulators will have similar or higher quiescent current

TPS7A20 is 6.5uA, $0.10/ku. TPS7A05 is 1uA, $0.19/ku. It's not that hard to do better than 400uA!

And if you don't mind coughing up when it counts... TPS7A02 is 25nA, $0.45/ku. Triple the price, but more than four orders of magnitude better leakage.

If money is no object, there are some interesting chips out there. The LTC3335 chip[0] is a buck-boost that claims to have a 680nA Iq. Not as low as the TPS7A02, but it looks like it could make up for that in efficiency if your design does anything other than sleep.

[0]: https://www.analog.com/media/en/technical-documentation/data...

I was looking for one for one of my project but this is above "I could have just 10 years worth of batteries instead of that" level of pricing

Do very low-power designs also involve "awake" current of 3A?) Asking unironically.)

Maybe 300mA order of magnitude is more common than 3A, but it's not inconceivable. Lots of designs wake up, burst some RF data at a few hundred mA transceiver load for a few tens of microseconds, then go back to sleep for another few seconds. There are some long-interval scientific instruments that need high-speed ADCs or DACs on battery power in remote locations, which might get into higher current than a few hundred mA. Some deep space crafts can sleep at very low power and run their transmitters at comparable currents. It's very situational.

Older cell phone standards used to burst to about 2.3A upon initial connection to a tower before the tower told the handset to dial it back. I don't know about modern cell phone standards.

400uA isn't "low"--that's roughly speaking a fully-awake MCU running at 10MHz.

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