to add up the 2 output voltages if you dismantle circuit board from casing and connect gnd1 to vout2,is that going to make a problem to current regulations or 'both' currents will keep setting to vout12/load
--- What's being discussed is voltage regulated power supplies connected in series, so "current regulation" is irrelevant.
Since they're supposed to be voltage sources and have, ideally, zero output impedance, they'll each regulate their output voltages to remain constant as long as they can each supply the current required by the load.
Here: (View in Courier) 17V / +-----------+ | | [PS2]5V | | | GND | | | +--12V [RL] | | [PS1]12V | | | GND | | | +-----------+
--- JF
Don't forget big diodes across each. Else, in case of a sudden short ...
*POOF*-- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
Good Idea but ... Make sure you evaluate it. I've had power supplies that got very "angry" when the output got pulled even a little bit below ground. Another concern is what happens when one of the supplies goes soft. What happens when your controller keeps brownout-resetting and banging the servo system against the stops? This kind of configuration creates additional failure modes that might not be part of a typical product failure analysis. You want to learn about it while on the bench, not when installed in the field powering that robotic arm.
-- Oops... That won't work; I missed the part about "current mode power supplies". Sorry 'bout that...
why not-do you think there is going to be some weird small signal transfer function
-- Sounds like you want to fight. OK, here's my mistake: Current mode voltage sources, when connected in series, will still yield devices with, ideally, zero output impedance. Your mistake: Assuming that voltage sources in series will regulate current.
The practical issue is behavior of the supplies when in series. This will depend largely on the supplies themselves and how they start up and limit.
At start up, you can't count on them all starting at the same time. At limit, you can't count on them limiting at the same current level, or in the same manner. The most tolerant limiting method would be constant current without a foldback or hiccoughing characteristic. This can be checked buy inspection. Sometimes it's mentioned in the spec.
For the sake of reducing damage during start-up or limiting, anti-parallel diodes rated for the individual supply current should be located across each output.
Some outputs have a terminal hardwired or resistively/capacitively coupled to the frame or to safety earth. Obviously such a connection will affect suitability.
With current-programmed units, the lowest current program will dominate until that output zeros or reverses, at which time the second highest program takes over.
RL
-- Why reiterate the obvious?
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