If the diode dropped ~0.7V, the voltage would be acceptable, but that diode would need to dissipate over 4 Watts (although I don't intend to push this PSU too close to its 6A limit). It would need a heatsink. I would prefer not to have to go that way.
The first 2 PSU I sent back and got refunded. But now a 3rd PSU has the same behaviour. Feels like "Groundhog Day"
+/-10 tolerance is very good for that type of supply. So it could be between 4.5V to 5.5V
How accurate is your voltmeter?
If it's +/-1% full-scale, that would be +/- 0.2V on the 20V scale.
So if your meter is reading 5.5V it could actually be anything between 5.3V and 5.7V
I realised there was a small but important inaccuracy in my first post. I am using a ws2812b strip, not a ws2812 strip. (There would be no problem if I was using a ws2812 strip, they are rated up to 7V.)
If the Vdd limit is 5.3V, then why are the electrical characteristics specified at 4.5-5.5V
Electrical Characteristics（TA=-20～+70℃，VDD=4.5～5.5V,VSS=0V,unless otherwise specified）
Good suggestion, I might email them, although I suspect the PSU range I have is discontinued.
Similar PSU in their current range have line regulation and load regulation figures much better than 10%, but the exact model equivalent to the one I have is not shown in the data sheet (in fact there's a blank line where it might have once been):
Those are switching power supplies. Switchers require a minimum load to maintain regulation, typically ~10%. You size the PS to 125% of the expected load. The block shown is a 5V/6A unit. 10% of 6A is 600mA minimum load! So yeah, 150mA is only ~2.5% of peak load, and that is under the ~600mA needed to maintain regulation.
I like to keep the PS within +-5% (.25V for a 5V supply). Ill bet if you put a 1A load on it, the voltage will solidify at 5V.
The reason the lightly loaded (higher voltage) PS doesn’t burn out your equipment, is that, as the current rises to "fry" something, the voltage drops into regulation, and everything stabilizes at the voltage source setpoint.
Notice the input voltage rating is 5V +- .5V or 10%. So a 5% power supply is 2× tighter tolerance than the board requires, and everything should be golden.
I expect the higher voltage is due to no load on the power supply. Also consider the wire size and what the drop will be when it is loaded. Test them again at about 80% of max load and see what you get.
I expect that manufactureres design their supply with a slightly higher voltage, to counteract wire losses when the supply is under load. Needed, because I definately wouldn't have used that wire gauge for 6Amp.
A Schottky diode should drop 0.2 to 0.4volt.
Open-frame supplies have a trimpot.
Leo..
Thanks everyone for your suggestions and reassurance, both on this topic and via PM. I'll continue to use this PSU and monitor it's performance in use, with larger loads, and update this topic.
So it looks to me that it has been designed to maintain 5V, or close to it, at the maximum current, at the expense of higher voltage at lower currents.
