I want to build a 12v DC to 5v USB with 3 outputs ... Should the outputs be tied together or separate for each output ??? Also I am trying to keep it as pure signal as possible and does anyone have any build thread or design ??



Thanks
Jay Sr

 

I recently built a 12V to 5V USB adapter. I used a LM2576 switching buck regulator. The LM2576 is a pretty old "simple switcher". The schematic is right out of the app. notes. They are very forgiving. I'll post a schematic if you want but you can get the app note by googling lm2576.

If you want a really clean output just put a Pi filter on the output.

You could go linear depending on the current requirements. A linear regulator (LM7805) will dissipate 7 watts for every amp you draw, so it will get hot real quick. Normally not the way to go.

Yes, USB power connections will be in parallel.

Ebay sells a lot of inexpensive switching regulator boards.

Mark

 

The POWER outputs should be tied together. Depending on what you are charging, you may need to apply a voltage to the data pins to get the device to accept a charge from your charger. You can search around and find what an iPhone needs to see, for instance.

If the data pins are not needed, then leave them all disconnected and you're done.

There are very cheap, commercial adapters to do what you want. Why are you building one?

 

I recently built a 12V to 5V USB adapter. I used a LM2576 switching buck regulator. The LM2576 is a pretty old "simple switcher". The schematic is right out of the app. notes. They are very forgiving. I'll post a schematic if you want but you can get the app note by googling lm2576.

If you want a really clean output just put a Pi filter on the output.

You could go linear depending on the current requirements. A linear regulator (LM7805) will dissipate 7 watts for every amp you draw, so it will get hot real quick. Normally not the way to go.

Yes, USB power connections will be in parallel.

Ebay sells a lot of inexpensive switching regulator boards.

Mark

LOL I used to live in Tuscan AZ...

I have several of these cheap Chinese ones but I can't get the proper voltage.. I want a design that will output a super clean 5v with a couple amps so I can charge a couple cell phones with it and the voltage will not drop and very minimal voltage ripple ...

 

OK, linear is out, switching is in. Just charging cell phones does not require super clean. Adding a filter won't hurt.
Go to Ebay and search, "buck regulator" and I am sure you will what you are looking for.

Yea, I know the "Tuscan" thing. Right now it is so hot, most people drive with kitchen mitts on. I have a nice pair of racing welding gloves that I use.

Mark

 

Ebay has a ton of 1A and 2A converters already in a cigarette lighter package, direct with USB charging port, for a few bucks each;

http://www.ebay.com/itm/DC-12V-24V-...Power-Adapter-Cigarette-Lighter-/370794564084

 

Beware of that $22.99 shipping.

 

I want to build a 12v DC to 5v USB with 3 outputs ... Should the outputs be tied together or separate for each output ??? Also I am trying to keep it as pure signal as possible and does anyone have any build thread or design ??



Thanks
Jay Sr

Recently I bought a car cigar adaptor to USB 5V charger in Poundland, for £1. The instructions say it can run anywhere from 12V to 24V and supply 2A out.

The one I opened used a MC34063 chip, for a one off/easy availability, I'd consider this supply route as an alternative to making up the minimum order from Farnell.

Its all through hole PCB, so easy to trace out the circuit.

 

Beware of that $22.99 shipping.

Thanks for catching that!

They are available from other vendors with free shipping from overseas. Don't pay for shipping!

That was just the first one I grabbed from a google search.

 

Thanks for catching that!

They are available from other vendors with free shipping from overseas. Don't pay for shipping!

That was just the first one I grabbed from a google search.

In the UK we have organised crime in the shape of Royal Mail (not even sure they're allowed to keep the "Royal" now they're privatised) - they charge a racketeering 'handling charge' to collect any duty on things arriving in country by post.

A few years back I ordered a kit from Jaycar in Australia, the duty collected was £4 - that and the 'handling charge' came to over 50% of what I paid for the kit!

Its basically blackmail - cough up or your goods will be "disposed of".

 

Thanks for catching that!

That was just the first one I grabbed from a google search.

Unfortunately this is the result of another ebay effort to reduce the fall out of all the complaints of brokerage fees etc by buyers imported sales off ebay.
They came up with this idea of using Pitney-Bowes to handle the exportation and set an automatic fee schedule for shipments that covers shipping and Brokerage.
Unfortunately for those sellers that offer the automatic rate, it results in a exorbitant shipping rate, I for one do not buy anything from sellers using this method.
I either use the ones that specify USPS etc or contact them to see if they will co-operate and use USPS or even UPS, as I clear my own shipments.
Much of the changes in ebay policy is to reduce any potential aggravation and attempt to smooth the ripples.
Unfortunately, the ones that have always played by the rules are the ones to suffer.
Max .