If electronics has been your hobbly or profession for many years, I'm sure you've connected two identical linear regulators. An example would be connecting two 5 amp LM338 regulators to produce a 10 amp supply.
I've never done this with identical switchmode regulators, and I'm wondering if it's practical or even possible?
I've got two 20 volt - 3 amp brick style (also called table-top) switching power supplies. I'd like to combine the ouputs. In effect, you would end up with an 20 volt - 6 amp supply.
They are manufactured by Pihong. Model No. PSA60W-200.
Hell no! The two regulators will 'fight' over the exact output voltage.
It's dangerous & it won't work.
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W "Some people are alive only because it is illegal to kill them."
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All of which involve additional circuitry for load balancing that reduces regulation quality.
--
W "Some people are alive only because it is illegal to kill them."
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\\|/ \\|/ Perna condita delenda est
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I wouldn't do that. Amongst lots of other pathologies that can happen, just imagine if one comes up a few millisecond later than the other and feeds it from the back? KABLOUIE...
Subject: "Parallel Connecting Two Identical Switching PSUs" - which can't be done without a strong risk of letting out the magic smoke.
No problem, I'm keen to learn. So, how do you do it without additional components, & without reducing regulation quality?
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W "Some people are alive only because it is illegal to kill them."
. | ,. w ,
\|/ \|/ Perna condita delenda est
---^----^---------------------------------------------------------------
place a low drop out diode on the output of each supply so they dont fight with each other... the supply with the slighty higher voltage (and there will be one slightly higher even if its only by milivolts) will supply all the current until the load draws enough current to pull the voltage down slightly... at which point the other supply will begin to supply some of the current.
if the supplies have output voltage adjustment, you can attempt to get them balanced as closely as possible with a volt meter, but you would probably have more luck getting a current meter on the output of each supply (between the supply and the diode mentioned above), then adjust the output voltage under load until both supplies are providing current...
You will probably want to get stand alone panel meters for that -- they can be had on ebay cheap enough, and other sources (see the 4 digit panel meters thread started on 3/26 in this group) and leave them permanently attached since the settings will likely drift over time and will need to be tweaked now and again.
simpler by far to buy a higher current power supply !!
Reason that parallel power does not work for power supplies: foldback current limiting. Once one supply hits a limit (takes up too much load because its voltage was so slightly higher), then foldback current limiting kicks in. Only solution is a complete power down. But by that time, the other supply has also entered foldback current limiting.
Others have explained how to do parallel power supplies complete with constant tweaking. Of course, that can only work if both supplies are never outputting anywhere near to 100% load. Again, due to foldback current limiting.
depends on if the PSU cuts off at the current limit or folds back the voltage when going over-current -- I dont know about those particular supplies so its a toss up -- but cheap enough to try :)
Intel spec demands that ATX power supplies do what computer power supplies did even 30 years ago. That spec demands a computer power supply perform foldback current limiting - and even puts a number (I have forgotten it) to that current.
Foldback current limiting is why an overloaded power supply (with a slightly higher voltage) cuts out - leaving the other supply to provide all power and then also enter current limiting.
The use of bricks in parallel and series is a standard technique to produce redundancy and longer MTBF. It does require consideration for the topology used and the fault-isolation required.
Units with active output rectification must be orring diode isolated in the parallel case, as must be individual crowbar networks and regulation networks.
Techniques slope regulation can allow effective sharing without actual p-string sensing circuitry. Active orring diodes can also be configured with fixed forward voltage drops, easing centering adjustment requirements.
Best way to start is to look over the MFR app notes. If they do not supply typical applicatuion data, move on to another mfr.
1) It is required quite obviously by specs. 2) It is necessary for safety. 3) It is how computer supplies have been built before there was an IBM PC.
When can power supplies be used in parallel (ie for redundancy and longer MTBF)? When each power supply can provide 100% of the load by itself. That obviously is not the OPs question or intent.
Power supplies designed for parallel (because the load is too large for one supply) also include a communication circuit between those supplies - because those unique supplies are specially designed for parallel applications.
If it is so written. There are often good reasons not to include this in an application specification.
This need not be the case. Hardware designed to operate safetly off high current rails is better designed with source capacity in mind and suitable protection of reduced trace widths, as appropriate. This allows for increased redundancy, increased repairability and shorter down time.
Foldback limiting was initially required solely to reduce possible damage to linear regulator elements due to overstess under shorted load conditions. Switchers need not be thermally or electrically stressed by a continuous load short - though some lower-power topologies may be difficult to cheaply configure with constant current limiting characteristics.
No, it was not obviously the OP's intent to introduce redundancy, however the techniques used to do so are applicable in simple parallel connections, without redundancy. Few respondents seemed to understand this at the time.
It would be easier for the OP to parallel switchers that have certain characteristics, like constant current limiting, adjustable output voltage and a well defined regulation.
A number of techniques require differing types signal interconnection. A number of other techniques don't require this interconnection. The OP may best research this with his specific model of converter in mind.
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