Transformerless power supply

[runman_up]

Does anyone know of a transformerless and CHEAP power supply that would supply 5V DC to at least 500mA suitable for a pic microchip + extra relays. Cheap components please that is why I am doing it transformerless- thanks

 

[runman_up]

120VAC 60hz

It does need to be hooked to standard US mains

 

[BobW]

The simplest way I can think of is to buy a cheap 5 volt transformerless wall wart, disassemble it and copy the circuit.

 

[bountyhunter]

Transformerless off AC main is too dangerous to even think about.

 

[Diver300]

For 500 mA you will spend less money by buying a cellphone charger and just using it as your power supply.

To get 500 mA without a transformer you would need a very large capacitor that would cost more, as well as being more dangerous.

 

[KMoffett]

The simplest way I can think of is to buy a cheap 5 volt transformerless wall wart, disassemble it and copy the circuit.

Why copy it? What the OP needs would be the little PCB that was just removed from the charger.
I use them all the time. $0.39-$0.99 for thrift stores...or free from friends. Be very careful cutting open the case. Only problem is figuring out a good (safe) way to mount them.

Oh, and they are not "transformerless". They're "switch mode power supplies". They have small, high-frequency switching transformers that isolate the output from the mains.

Ken

 

[Joe G]

old computer powersupply, cost is free

 

[runman_up]

Missing the point a touch

I can afford a transformer and I have made a normal power supply with a low cost transformer - the cost per unit is high compared with a transformerless power supply

Microchip offers aguide AN954 on these type of power supplies but they are for small current. I have seen them out there on commercially available products - anyone know how to do it?

 

[ericgibbs]

I can afford a transformer and I have made a normal power supply with a low cost transformer - the cost per unit is high compared with a transformerless power supply

Microchip offers aguide AN954 on these type of power supplies but they are for small current. I have seen them out there on commercially available products - anyone know how to do it?

hi,
If you can get a 10uF mains rated Capacitor [motor start type] that will give about 400mA at 110Vac 60Hz.

Also a 5V 5Watt Zener diode, it would be possible.

 

[alec_t]

.....possible, but NOT SAFE!

 

[ericgibbs]

.....possible, but NOT SAFE!

alec,
I fail to see any purpose in your post.? NOT SAFE in which way.????

The OP as already been told many times that a mains transformerless power supply is POTENTIALLY hazardous.

This type of supply is in common domestic use.

 

[Reloadron]

To my way of thinking while building a transformer-less AC mains power supply is not that difficult personally I wouldn't bother. Attached are a few images of what I use as a quickie for when the uC bug bites. The wall wart is a Tandy 120 VAC 12 VDC 1 amp that I haven't a clue where it came from. Nice feature is most wall warts have the plug included. The second image is just a LM7805 with a few capacitors mounted on a cheap Radio Shack piece of board. Literally maybe $7 in parts?

While the 7805 has never even gotten warm for my apps, if it does I'll just shove a little slip on heat sink on it. The thing works fine overall. Also, as mentioned wall warts in a variety of sizes and shapes as well as types can be had for next to nothing. While maybe a 9 volt wall wart would have been a better choice I happen to grab a 12 volt flavor.

I used battery snaps so a variety of my little uC proto boards can easily be connected to it. It doesn't get any simpler or cheaper.

Just My Take
Ron

 

[ericgibbs]

hi Ron
I would agree, for the peace of mind I would use a Wart.

I have lot of old mobile chargers, its a pity the guy is in the States, I would post him a couple.

E

 

[alec_t]

@Eric
Ok then, for NOT SAFE read POTENTIALLY HAZARDOUS . If OPs aren't aware of the hazard then they may not understand, or may disregard, an explanation as to why something is not safe. It doesn't hurt to repeat the safety/hazard warning.

 

[runman_up]

Thanks Wales - the issue is that they are on the market for wall mount apps in US- They do exist - I guess no one knows how - I will investigate by other means

 

[runman_up]

I have made a transformer power supply already supplying 600ma for $2.50 already - so $7 is not of any use

 

[KMoffett]

I can afford a transformer and I have made a normal power supply with a low cost transformer - the cost per unit is high compared with a transformerless power supply

Microchip offers aguide AN954 on these type of power supplies but they are for small current. I have seen them out there on commercially available products - anyone know how to do it?

"cost per unit"? Sounds like you are thinking of selling something.
Warning at the bottom of page 1: https://ww1.microchip.com/downloads/en/appnotes/00954A.pdf
You haven't explained the purpose of the overall circuit. With this type of power supply there can be "no" direct connection to external controls, devices or systems. A small, switch-mode power supply will be much, much smaller than the components you will need for the Microchip circuit with your current and regulation requirements. The 10uF capacitor eric mentioned will likely be over $10.

We'd rather help you solve your problem than help solve you solution.

Ken

 

[mvs sarma]

power supply can be definitely mad and i have few schematics that are designed good and reputed firms.
as a designer, O P might know it is non-isolated and he can be careful also.
even he can caution other friends for whom he makes to be careful.
but how about children and uninformed about the perils of shock that might bring life risk.
Life in general is NOT CHEAP?
i join the other members, surely advocating against non-isolated PSUs.
there are many, cell chargers with 50/60Hz transformer-less, but following that DC, it is converted to isolated DC by a ferrite transformer of cute size, thus it gains the reduction of mains transformer, at the same time giving isolation by SMPS mode miniature transformer.
finally such design can deliver around 500mA at 5V

the overall weight would be less. it would not be too costly if made in bulk.

 

[colin55]

You can get a box of 50 for free at any mobile phone shop.
I have 50.

I wouldn't touch a transformerless design for $1,000,000.

 

[ronsimpson]

I guess no one knows how - I will investigate by other means

Many of us have made them. I have even got one through UL, VDE and CSA and into production. To make a product to be sold in stores it must be "blessed" by the government. They do not like a transformer-less power supply! They will try very hard to keep you from passing the tests.

If you only want 10mA then this would be better. 500mA is hard.