Help me to design a Power Supply

[Nikhil_Med]

Hello,

We are designing a product which has a feature of charging 2 mobile phones at a time.

For this I need to design a circuit which has two USB outputs which give out 5V 1A on each pin.

The input to this circuit will be a 230V domestic power supply.

Please help me with the circuit which will do this for me. Also I want to do this preferably without using a transformer as it is adding up a lot to the cost. I want to keep the cost as low as possible using a RC type of circuit.

Regards,
Nikhil

 

[Les Jones]

Using a capacitor is not suitable for this application. There will be no isolation so it will be dangerous. The output will be at mains potential. Also the size of capacitor required will be too large. A transformer is required for isolation weather it operates at mains frequency (50 or 60 HZ) or at high frequency (tens or hundreds of KHZ) in a switch mode supply. I suggest just buying a ready made USB supply rated at 2 amps or greater and making an adapter with 2 USB sockets. If you live in the UK B&M stores have a 4 output USB supply rated at 500 mA per port for about £5.00 I think 500 mA would be enough to charge a phone.

 

[alec_t]

It will be cheaper, and a lot SAFER, to buy a ready-made supply than to build one. You MUST have mains isolation. Surely your life is worth more than the price of a safe supply?

 

[Nikhil_Med]

Firstly, Thank you Les and Alec. I live in India. Well we cannot use a bought out power supply as the monthly requirement we are forecasting is 1000 units. I tried opening a faulty Apple iPhone charger and found that it does not use a transformer. It is so light in weight too. I need to build one myself to make it most cost effective.

 

[alec_t]

I tried opening a faulty Apple iPhone charger and found that it does not use a transformer.

I bet it does. There'll be a lttle sugar-cube sized high frequency transformer in there somewhere .

 

[Les Jones]

There will be a transformer in the apple charger but it will be very small as it will be working with a high frequency. It will probably be about a 15mm cube.
This picture shows the transformer in the unit that gives 4 x 5 volts at 500mA The connectors on the left are the USB sockets.

 

[dr pepper]

Nice little supply, they're getting smaller, you can get 10w supplies smaller than a domestic plug top.

Consumer products more and more use smps's as a seperate pcb, from a reputable smps designer, as it removes a lot of the problems with design and certification, unless its a high volume mass produced piece of kit where they can afford to develop their own smps.

Mr Med if your producing a lot of these then I'd suggest you get professinal assistance, or use a well tried and tested circuit, or you might end up with lots of returns, or worse an incident.

Checkout my location Mr Jones, you cant be that far from me.

 

[MikeMl]

Here is what they think of power safety and codes in India:

 

[Les Jones]

Hi dr pepper,
My location is Ormskirk.
Regards
Les.

 

[dr pepper]

I'm just outside Preston, Ok of I shout you might not hear, but I'm close compared to others on this forum.
Theres a coupel of guys from Rochdale knocking about here too.

 

[Les Jones]

It's nice to have a rough idea where people are located. One of my pet hates on the model engineers forum (https://www.model-engineer.co.uk/) is people asking for help and not giving any idea of location. It is often difficult to try to talk someone through diagnosing an electrical problem when you do not have any idea of their level of knowledge. It is so much easier when you can actually work on the problem.

Les.

 

[JimB]

Driving the thread even further off topic:

the model engineers forum https://www.model-engineer.co.uk/

I often visit that site for a good read, but I am not registered there.

JimB
(Myford ML7 and Denford NovaMill)

 

[KeepItSimpleStupid]

5V 1A won't get you anywhere without the enumeration IC.

 

[dr pepper]

I have a model engineer mate, and funny enough got to know him through a US forum, he's half a mile away.

Jim, I have a myford speed 10 and a trident horiz mill with a vertical attachment, also theres a nodding donkey but some of the important bits are missing so i cant use it, I hope to com accross them one day.