Electronics > Projects, Designs, and Technical Stuff
Power Supply Design : Questions about Dual Supply and Transformer
TimNJ:
--- Quote from: NiHaoMike on August 19, 2020, 12:49:55 am ---
--- Quote from: TimNJ on August 18, 2020, 10:31:39 pm ---And you will never beat the cost of commercial audio products. When I was about 16, I thought I could make a 3 x 50W amp that was cheaper and better than anything you could buy in a store.
--- End quote ---
Amplifier boards and surplus telecom PSUs are really cheap nowadays, definitely well under the cost of a preassembled amplifier of equal specs. I guess it depends on if you call the board a "commercial audio product".
--- End quote ---
Maybe? I don't know...in my experience, everything added up pretty quickly...that is, taking the "Hi-Fi" route, circa 2010. (Class A/B, big-ass toroid, big heatsinks, etc.) I too recall the eBay PCBs being quite inexpensive. But, after all the mounting hardware, connectors, enclosure, etc...it wasn't cheap anymore.
I also should note that I have *ahem* taste for expensive parts.
MosherIV:
Hi
Using a buck converter to reduce mains voltage is unusual to say the least and highly dangerous as others have pointed out.
Commercial SMPS rectify mains to high voltage DC, this stage is highly dangerous because
1. It is HV
2. It is DC
3. Mains means that there is a LOT of power
This HV DC is then pulsed at high freq (40KHz and higher) into a high freq transformer with a high power switching FET. Either the freq or the pulse width is varied. The output side of the transformer is smoothed with output cap and monitored for output voltage. The monitor is typically done with an opto isolator. The transformer and opto isolator provide the galvanic isolation.
The regulation and pulse control is done by dedicated controller chip.
The high freq makes the transformer physically smaller than mains freq transformer. The smaller transformer also makes them far cheaper than the mains freq equivilant. These high freq transformers are custom made for each power supply design.
This type of SMPS is most common for mains psu. They are tricky to design and get right, mainly due to the transformer. No you cannot get then off the shelf, they are designed and made to order.
What I am try to tell you is that these small high freq transformers are not available by looking at electronics suppliers. I got the feeling that you were looking at main freq transformers that step down.
An alternative to your approach is to use a lower output voltage transformer eg 12V and use a boost converter instead. However, to get 20A you will need 12V 80ish A transformer! Common voltage (12V is a good one) are more common than the 42V ones you are looking at
Another way to do it is to parallel up transformers, just make sure the transformers are wired in phase!
Eg you can use 2 45V 10A transformers. The disadvantage of using parallel transformer is that it is much heavier and a little less efficient.
Dulus:
--- Quote ---but you don't need to take the piss out of me, what was your first time working with AC like, I'm generally curious?
--- End quote ---
I'm from 220Vac land, so it was terrifying. And i got zapped a couple of times from the main filter cap that's charged to 300VDC and pulsing like a motherf***....
Dont make a big fuss about it, we should be able to tease people a little bit.
I really dont want to stretch the discussion, but other people may read these posts in the future and get carried on the way you are.
So i reiterate:
Mains AC is dangerous.
People can die. It may not be you.
You clearly dont know even the essentials about mains power electronics, yet you go the distance, even finishing the layout before clearing your schematic with experienced people.
Dont do it. You'll hurt someone.
You cant build a high power supply on the first run. Learning doesent begin this way.
No architects first project is a skyscraper.
Start small, start simple. As you can see, people are here to help. And have a bit of fun on the side :)
And again i'm saying it, if you are determined still, even after this many warnings....
Take pictures :-DD
Pawelr98:
--- Quote from: MosherIV on August 18, 2020, 07:30:59 am ---Most people, professional or hobbiest, do not make their own mains Switch Mode Power Pupply.
Part of the reason is that the high freq transformers are not available off the shelf, they are made to order due to the characteristics being very specific to each psu.
Most audio hobbiests either build simple unregulated linear psu or
Buy a SMPS rated for their project.
No you are not going to find a transfors in that power range cheap!
--- End quote ---
Making a switching power supply is fairly easy.
No off the shelf transformers ?
Winding a switching transformer is easy.
Just take a transformer from an ATX power supply and rewind it.
Primary on such transformer is usually 20T+20T or so.
Unwind the first part of the primary and then remove the windings you don't need.
Wind the new ones, put a good layer of isolation and wind the primary again.
Design problems ? Feedback-less IR2153 is not very safe (no overcurrent protection) but it's pretty much the simplest supply one can make.
IR2161 does have overcurrent protection, still no regulation.
Those chips however may run with a primitive feedback when in resonant mode.
If you want proper regulation then jump at 494 or any more recent IC.
Reusing an ATX power supply may be a better option, if you know how to modify it to output +-48V.
At such power level (500W) half-bridge is a reasonable topology.
Then I was also making Flyback supplies for low power levels using UC3845 just fine.
Off-the-shelf transformers but with secondary rewired in series instead of parallel for higher output voltages or symmetrical ones.
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