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Best, most efficient way to get 5WDC from 120VAC 60Hz

nathanjseeley

First off, Not sure if this is the right place to be posting this, but I need help.

 

So I am working on making some phone chargers (my friend is knitting the "enclosures" for them, they are really cute) I am looking for the best way to take Standard US Household voltage and drop it to +5VDC.

 

I have two thoughts and am wondering which would be the best.

 

1. Use a chain of voltage regulators and a rectifying bridge to drop the voltage (more heat, possibly less weight)

 

2. Use a transformer to drop it from 120VAC to 12VAC then put it through the bridge and a 5V regulator (less heat, possibly heavier)

 

Which of these methods would you guys suggest, also is there going to be more to the circuit than just the Transformers, regulators and their associated hardware?

  • 0

    Use one of those "cute" 120VAC to USB power supplies cubes, like those provided for an iPad mini. All USB ports have a +5 volt power capability. I saw them at the Walgreens checkout for cheap. Plug your phone into a USB port on a computer and you can borrow the +5 volts from it as well.

     

    The simplest way to convert 120 VAC to +5 volts is a capacitor. Use it to drop the voltage to a zener regulator. You didn't say how much current. This technique is for low current, non-line isolated applications. Nobody is to come in contact with either lead of this supply for safety reasons.

  • 0

    I'ld use a transformer to change it to 5 volts, and then use a rectifier to change it to DC, and a capacitor to smooth out the voltage

     

    Edit: make sure you have proper cooling, because I dont want to be responsible for any injury or damage to property

  • 0

    Best, most efficient way would be to build a switch mode power supply by rectifying your ac directly to +/- 170 volts dc, then using a control unit turn it back to Ac at about 100 KHz or higher. This would enable you to use it on alot smaller transformer that in part gives you a greater efficiency, about 98%. So after you have 170 volt at 100 KHz you can with the help of your transformer turn into the required voltage. After that just recitify it again and you will have your Dc.

     

    The switch mode power supply can be build alot smaller and cheaper because of the transformer being use at higher frequency is ALOT smaller and cheaper than these needed for the standerd 60 Hz.

    You could always put a regulator on the output just to be sure but that limit the amount of current that can be use before the regulator over-heats.

     

    These switch modes are mostly use for high current and smaller sizes, like the chagers you get with most devices are all switch modes.

    The control unit I was talking about is usually a "PWM" pulse width modulation unit that turn the dc into a square wave for the transformar to be able to induce magnetic currents.

    Hope this helps.image

  • 0

    You need to define "best". If you want it small and cheap then rectifying the AC to a capacitor/inductor and using a FET to switch the volts on and off to the capacitor. Since you're only at 5V you can get away with halfwave rectifying the AC if you're going to draw < 5W.  You can almost get this 'off the shelf' with a Maxim chip. This is the 'cheap USB recharger' that sells for about $1.50 each on places like Alibaba. But if 'best' includes (won't start a fire when the transistor fails) you might want to stay away from those.