Testing of Power supply

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hi to all, I have designed a power supply of 3.5v,0.15A and ISO 5v,0.05A specification with input supply of 85-265 AC.During testing of output voltages and current it shows -->

1) output voltage @3.5v with load resistance of 22ohm,it gives Vo=3.4v and Io=140mA

2)Output voltage @5v with load resistance of 100ohm,it gives Vo=2.5v and Io=30mA where there is 'No any load connected @3.5v'

3)output voltage @5v with load  resistance of 100ohm,it gives Vo=5v and Io=50mA where there is 'load connected @3.5v'

My question is that how does load resistance affects (which connected to3.5v) to 5v supply during testing of supply? Please find the attachment of power supply design.

Attachment(s): 

Last Edited: Sun. Jan 14, 2018 - 07:30 AM
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What else would you expect? No power supply is perfect and the schematic you attached shows a power supply that is substantially less than perfect. Isolated, yes, but very likely  with mediocre regulation. I would expect the 3.5V output to be regulated a bit better than the 5.0V output (since the feedback is from the 3.5V output). 

 

I would consider the numbers you quote as "not that bad" for that circuit.

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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    You are testing it in an unfair way. This kind of power supply relies on the fact that there is always some load on the 3.5V output. Due to the high input voltage, when the main switch turns off, there is a spike on both secondary windings. Without load on them, a part of the output voltage seen is due to those spikes, so little energy is pumped on the transformer. A load on the 5V output first kills the spikes and the voltage drops so much. This is less seen on the 3.5V output. They appear because the leakage inductance on the transformer. Make sure the windings are well coupled.

    If there are times that the load on the 3.5 section disappears, than a "burning" resistor is needed. Since you power it with 3 phase AC, I suppose is not a problem wasting a bit of energy on a burning resistor. If this is burning resistor is not practical, then you need to add some turns on the isolated winding, increase the voltage and use an LDO to bring it back to 5V.

    That zener diode in series with the optocoupler is not going to give you a very good regulation. Think of using the famous TL431.

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Since there is no (or very low) load on the 3.5 output & it is held up with 1000uf, the regulator sees everything as being fine, even while barely driving it.  Meanwhile the 5V section with a load, quickly drains down.

 

At these very low power levels, why not  use 2 transformers & regulate them separately?  Or perhaps the outputs don't need isolation from each other....the  3.5V output can easily drive a boost circuit to give 5V, at 0.05A

 

You could possibly combine the outputs into one feedback, (see this app note https://pdfserv.maximintegrated.com/en/an/AN294.pdf) to drive your coupler led

 

Take a look at the following paper..it has A LOT OF INFO you will find useful for dual supply regulation:

https://www.onsemi.com/pub/Collateral/TND351-D.PDF        ....also see the magic cap on page 13

 

When in the dark remember-the future looks brighter than ever.

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3 phase input for a < 1W power supply ???

 

At these power levels from mains input efficiencyis probably not such a big deal.

Why not just make a single output 5V power supply and make the 3V5 with a linear regulator?

 

What is your experience level?

If "experienced" you would not have started this thread.

If "beginner" you should not be messing with mains level voltages (At least use an insulation transformer).

 

But small power supplies are such bog standard items. why bother at all ?

Is it really worth designing something yourself if you can buy the supply below for USD 2 ???

--------------------------

Some time ago I bought 10 power supplies from ali "HLK-PM01".

I have tried abusing them a bit. They deliver about 1A short circuited (and get a bit warm if short circuited for half an hour, but not exstremely hot)

https://www.aliexpress.com/whole...

 

To be sure I should open one and look what's inside.

Hmmm.

19:19 ...

20:07 ...

 

Spend some time opening one.

Module is fully potted with an elastic but somewhat brittle potting compound which is fairly easy to remove.

Main components:

Input:
MB6F    Bridge rectifier.
4.7uF 400V 105Celcius Elco.
AP8012    www.electrodragon.com/w/images/2...

Output:
7x    resistors 0604
3x    ceramic capacitors.
1x    SS26 diode
1x    transistor?
2x    470uF 105C Capacitor
1x    Inductor

Feedback:
1x    P185 Optocupler (4 legs, not 6 ???)
1x    102 KX250Vac X1Y1 capacitor.

 

I'm quite happy with what I see.

Insulationg gap etc also looks good.

A few remarks though:

I do not see any EMI filtering on the input. Just a bridge recifier and Elco.

I'm not sure if the High Voltage cap & opto coupler in the feedback are good enough for "European standards".

No (CE) mark on the housing which makes them probably a no-no for where I live.

 

(Open foto in new window or download for higher resolution).

Paul van der Hoeven.
Bunch of old projects with AVR's:
http://www.hoevendesign.com

Last Edited: Sun. Jan 14, 2018 - 07:21 PM
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WHY on earth would you be using 3 phase power?  That's great for 20Horsepower motors or 5000watts type of things.

You could get plenty of power from one of the phases.

At a minimum you need some fusing , TVS and other protections if you are connecting to any sort of line voltage, especially higher-power 3 phase.

A 3 phase short would immediately destroy your circuit board to smoldering bits.

 

 

 

 

When in the dark remember-the future looks brighter than ever.

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I'll bet that the three input phases are not actually connected the way they are shown in that diagram!

 

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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1N4007 diodes are the fairly high voltage type...caps rated >450V...sounds suspicious to me. 

 

The output power is rather low...maybe it's a 3-phase powered doorbell.

When in the dark remember-the future looks brighter than ever.

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I’d be checking the voltage rating on the resistors - 0805 is not a good choice. There’s other safety critical components that aren’t specified.

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I am "beginner" in design of power supply.

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I am "beginner" in design of power supply.

You should probably use something like a 12V wall-wart as your source to a supply circuit --build up your design to run from that & to learn & experiment.

A big safety mistake to start out by messing with 3 phase power, or even line voltage.  You could wind up with a blown scope, or worse.

When in the dark remember-the future looks brighter than ever.

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avrcandies wrote:
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Where did you get the magic circuit around Q1? I gather it is for low voltage lockout. Seems a bit suspect to me.
The 10R input resistors should be fusible so the whole doesn’t go up in flames if there is a fault. C4 is especially critical - must ge a Y class cap and if you’re feeding the circuit three phase, then it has to have an adequate voltage rating.

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Actually, I designed this power supply through online website as per my requirement and got such output while testing...  

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That tells us a lot then.........

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RCM wrote:

Actually, I designed this power supply through online website as per my requirement and got such output while testing...  

 

Was that using the tools on the Power Integration website?

'This forum helps those who help themselves.'

 

pragmatic  adjective dealing with things sensibly and realistically in a way that is based on practical rather than theoretical consideration.