On Monday, March 30, 2015 at 2:37:33 PM UTC-7, Gareth Magennis wrote:
Hmm, I keep hearing such things, but so far I haven't come across a SMPS
that will not sit there quite happily supplying voltage, without a dummy
load in sight.

The early SMPS units included frequency-modulating schemes (high output
current required higher oscillator frequency). Modern ones mainly use
pulse-width modulation (duty cycle modulation) at a fixed frequency.

An FM-SMPS power supply has greater ripple at low frequencies (unless one
overspecifies the filter capacitors), and is slow to correct output
deviations, so is likely to have unsuitable output
and/or to trigger fault detection circuitry and shut down.

PWM-SMPS circuits, on the other hand, have no particular difficulty
when the duty cycle gets very low, and the low-output-current load
that causes low duty cycle, keeps the output capacitor nearly ripple-free.