Electronics > Projects, Designs, and Technical Stuff

switching-PSUs: why can't you usually exceed the 50% of declared power?

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PKTKS:

--- Quote from: strawberry on May 24, 2020, 11:27:30 am ---What can be found in cheap psu: They use BJT even today. Input filter cap size less than ~1uF per watt. Poorly designed control loop (oscilation, voltage overshoot !) and controller. Stadard instead of low ESR. Poor quality enemaled copper wire. Heat and loss is not a thing (POWER). Rock and sand do not improve encapsolated psu heat disipation. Poor conductivity silicone rubber thermal pads.

500w psu have to disipate ~100w@80% of heat.

--- End quote ---

There is nothing wrong using BJTs in FULL BRIDGE and HALF BRIDGEs

MY BENCH  1200W (60V@20A) is a HALF BRIDGE uc38xx current mode
based one - and does the job just fine.

Under 600W ATX half bridges are cheaper
they also DON'T REQUIRE TRUE SINE WAVE INVERTERS
YOU CAN COMBINE 2 to have affordable high power in case
they cost less and do the job

drawback is that you have a lot of bad ones and you need
to choose very carefully you also need to balance the system

And cheap systems (like those used SOHO or POS) just
do not require a 600W PFC with true sine inverter to operate.

Below 350W real power a cheap ATX with much more cheap
non -sinus inverter will more than half the budget.

REASON to use them?  COST.

Paul

wraper:

--- Quote from: PKTKS on May 24, 2020, 11:35:38 am ---There is nothing wrong using BJTs in FULL BRIDGE and HALF BRIDGEs

MY BENCH  1200W (60V@20A) is a HALF BRIDGE uc38xx current mode
based one - and does the job just fine.

--- End quote ---
Again you promoting and defending trash PSUs. In bench PSU efficiency it is no so critical, we often use even linear PSUs. What's wrong with BJT is guaranteed subpar efficiency / high heat dissipation. And when talking about ATX PSUs in particular, that nowadays you will find them only in trash models.
EDIT: and when you find them in driving transformer in bench PSU, usually it's either because PSU is old or model is produced for a long time. Or simply because it's a cheap trash too.

PKTKS:

--- Quote from: wraper on May 24, 2020, 11:52:05 am ---Again you promoting and defending trash PSUs. In bench PSU efficiency is no so critical, we often use even linear PSUs. What's wrong with BJT is guaranteed subpar efficiency / high heat dissipation.

--- End quote ---

Yes, I have literally dozens of them without problems.
I use them literally for decades including several small
PSUs for bench work - all half-bridge design - all BJT based

I use HIGH COST PFC based ones in HIGH END PC GAMERs
where the cost literally explodes any budget.

A TRUE SINE WAVE INVERTER au pair with that ATX is also required
and considering benefits - IMHO  they do not worth the money.

For the record: I AM NOT "PROMOTING" garbage.
Stop saying such shit

I am putting simple facts. Where they are not needed
those expensive solutions are expensive crap

My bench uses 5 HALF BRIDGE BJT based PSUs for decades
daily based - nothing wrong with that.

SOHO and POS give a shit if 70% 80% or 90% ratings
they care about monthly TOC (ownership cost)

Me too.  I give a shit if 80% plus gold or shit.
I care about total monthly cost
Paul

wraper:

--- Quote from: PKTKS on May 24, 2020, 12:01:25 pm ---SOHO and POS give a shit if 70% 80% or 90% ratings
they care about monthly TOC (ownership cost)

--- End quote ---
Yeah, and garbage you advocate for has higher cost of ownership in any country where electricity price is not dirt cheap.

--- Quote ---For the record: I AM NOT "PROMOTING" garbage.
Stop saying such shit
--- End quote ---
Then why everyone laughed at you in the last thread where you praised PSU which internally is basically the same as trash discussed in this thread?

PKTKS:

--- Quote from: blueskull on May 24, 2020, 12:15:22 pm ---I have yet to see a BJT PSU anywhere other than in very old industrial framed SMPSs and those cheapest 5V 1A adapters.

Even the cheapest junk phone chargers now use MOSFET-based monolithic flyback ICs.

In China, you can get a 5V 2.4A primary chip for somewhere around $0.15, so why bother with BJTs?

--- End quote ---

My opinion about those small cheap patented supervisor
adapters is unprintable.

I have a box of failed ones - supervisors (OBxx and TOPxx) are mostly
RCC (very poor ratings) designs..

patented and almost dispensable garbage.

Last month I just ditch 7 failed IOT of those.

They just do not worth the hassle...
Paul

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