Getting 5v from 110v on-board

[Oznog]

What's a simple, cost-effective way to get 5v power out of 110v, with on-board components? Preferably isolated.

Sure, there are those 110v-5v USB power, isolated transformer "mini-wall-warts"- only a couple of bucks. But that's not an on-board solution, I can't have a second power cord, and can't wire this wart up inside the case.

I didn't see any cheap, tiny transformers on Mouser. There were some 110v-to-5v modules but they were quite expensive- ~$6 IIRC- and weren't even isolated. Whatever components those 5v USB wall supplies use, I can't find them.

A FWB with large cap followed by a large resistor and 5v zener would do it, but the heat is substantial. If the circuit's drawing 50mA, that's 7.5W in the resistor at all times, even when it's "off" (the controller's asleep) and drawing no current. That resistor would be expensive and the plastic case wouldn't even be safe with that much heat sourcing inside it.

In theory you could rip apart the wart, pull the components, and reuse them on the board. But for production that's not desirable at all, it's a problem to source and extract the components and there's no guarantee the device will always contain the same components.

 

[tronitech]

PCB mounted transformer, FWB, a couple of caps and 7805 (with heatsink)?

You don't say what current you need?

If your after something cost effective why can't you use a wallwart? Just needs a little imagination in your printed circuit board design, the pins can often be soldered.

 

[ronsimpson]

In theory you could rip apart the wart, pull the components, and reuse them on the board. But for production that's not desirable at all, it's a problem to source and extract the components and there's no guarantee the device will always contain the same components.

I can find the components. Re-engineering (copying the design) is done every day. The transformer is the hard to find part. If this is what you want to do I can send you information.

What power level. 5V 1A?

 

[ronv]

They are easier to find in the catalog.

https://www.mouser.com/ProductDetail/Tamura/3FS-210/?qs=dKoSqUwwxaXLfi6Qio6HDw==

 

[Oznog]

Well I don't know the exact current. If it drives a relay, it might be like 60mA. If it's a thyristor control like I recommended, it could be more like 5mA, but that depends on being able to use the sleep functions properly, and I'm not the one writing the code.

ronv, yeah it's an option, but $3.68 for the xfmer alone is a significant parts cost. Much more power than needed, too.

ronsimpson, finding the parts like the tiny transformer in that supply would be the goal here. All I can say is Mouser doesn't seem to carry a cheap one like that. Unless I'm looking at it wrong- this is highly plausible, Mouser has a notoriously useless search engine and this is a particularly difficult case. This one is closer to the spec:
https://www.mouser.com/ProductDetail/Xicon/41PG120/?qs=s%252baPvRSmhksqop%252bspQPSElScBJrBgDRXr8GD%252bQ9dQAw%3d
But still a $3 component. Not a bad price I guess, but still hard to compete with the fact that there's USB power supplies out there for $1. I'm aware that complete Chinese products often sell for less than the cost of a single component purchased through a known supplier. Still, it seems like you'd be able to source a 5v transformer for $1-$2 after some looking.

 

[KMoffett]

Unless you are manufacturing on a fairly large scale, I doubt you are going to beat the $6 module by building your own. Most of the major IC companies have switch mode power supply circuit designs. But, you get into having custom wound, high frequency, isolation transformers. The SMPS wall warts are economy of scale because of production in the 10s to 100s of thousands. No free lunch.
Ken

 

[ronsimpson]

60mA or 5mA that 12:1. You need to pick a power level.
I assume the 110V you talk about is AC from the power line.

I included some reading!
This is how the low power wall worts are made.

 

[Oznog]

Unless you are manufacturing on a fairly large scale, I doubt you are going to beat the $6 module by building your own. Most of the major IC companies have switch mode power supply circuit designs. But, you get into having custom wound, high frequency, isolation transformers. The SMPS wall warts are economy of scale because of production in the 10s to 100s of thousands. No free lunch.
Ken

I'm not trying to build a module, just a minimal of components to get 5VDC power from 110VAC, on-board, with easily sourceable components.

 

[KMoffett]

I'm not trying to build a module, just a minimal of components to get 5VDC power from 110VAC, on-board, with easily sourceable components.

Call it a module, power supply section, or what ever, it's the same thing, with the same components mounted together in a different ways.
Old saying:"You can have a good, quick, and cheap...pick two!" Its all a trade off.
So what's the output current?
Can you tolerate much heat dissipation?
What is the maximum space allowed for the power supply section?
Can your circuit tolerate switching noise from a SMPS?
In what quantities do you want it come in under $6?

Ken

 

[Oznog]

I took another look inside a cheap USB wall mini-wart:
A transformer about 10mm on a side
3x TO-92 devices
1 opto
3 electrolytic caps
1 polyester film cap
4 diodes
9 resistors

No ASICs.

 

[ronv]

The guys are right. There is a lot of magic in the volume. Think about building 20 disk drives and selling them retail for $100.
Having said that if it's all inside one box with no 5 volts to the outside world you might be able to do it pretty cheap with a non-isolated capacitor supply.

 

[Oznog]

I'm just saying, a lot of these 5v USB supplies are made. They're common. The transformer that goes into them IS made in volume, and SHOULD be available on the parts market, like $1-$2. But I haven't found it. It's unusual that Mouser doesn't have something to reasonably fit this bill.

 

[KMoffett]

Oznog,

As I said before, these are all custom transformers. They're each designed to work efficiently with the particular designers' circuits. I've never seen the type of transformers used in those little wall warts available off-the-shelf through any of the major electronic component or or even surplus vendors. There are many companies that will custom wind them for your, but you have to supply all the spec's and buy in quantity. Some will do one-offs...but you don't even want To go there...$$$$.

Ken

 

[ronsimpson]

I'm just saying, a lot of these 5v USB supplies are made. They're common. The transformer that goes into them IS made in volume, and SHOULD be available on the parts market, like $1-$2. But I haven't found it. It's unusual that Mouser doesn't have something to reasonably fit this bill.

The really small transformers are harder to make and the price does not go down with size. As stated above they are custom made. Coilfraft.com does make them. The isolation (primary to secondary) is the same on all sizes of transformers. In a big transformer the isolation is a small percentage. In a 1cm transformer the isolation is a large percentage of the transformer.

The primary to secondary isolation must be tested on every unite. The government (UL, VDE, CSA, etc.) watches over isolation transformers.

I hear you saying "$1" but it could cost that just to get a VDE stamp on the part. It might cost $10,000 to get UL listing on the transformer and you only make 10,000 parts that $1/part. If you only make 10 parts that $1000/part.

 

[szhighstar]

yes, transformer are customized, when you supply input voltage and current/output voltage and current/ frequency/convert type, we can design and customize for you, it costs about USD5000 for UL approved, it costs about USD1500 for EN61558 approved, price depends on your requirement quantity and MOQ.

 

[KMoffett]

Oznog,

Are those $6 modules looking any better?

Ken