Using USB or wall charger/transformer to power breadboard

Thread Starter

lefam

Joined Nov 30, 2010
33
Hi guys!

Is there any problem to use USB power directly from a PC (like a laptop) to power a breadboard?

What about wall chargers/transformers? Can I use them to power breadboards?

Thanks in advance!
 

thatoneguy

Joined Feb 19, 2009
6,359
I use an old phone charger to power some projects. You want to make sure the output is regulated at 5V, most are, but some aren't. Test this by putting 10 Ohm/5W resistor across the output temporarily to see if the voltage is still 5V, and that it returns to 5V once the load is removed.

Even if power is regulated, I suggest inserting a medium sized electrolytic (~100uF) and a 0.1uF cap across the power supply where it connects to the board, in addition to decoupling caps near all ICs.

I wouldn't recommend using a USB port from a functioning computer for a breadboard power supply, as small problems could destroy the USB controller. Most have short circuit prevention and current limiting, but some of the cheaper USB add in cards do not, as well as a few powered hubs, if a short occurs, the hub/card will be destroyed. Once a design is finalized and it is decided to take less than 100mA, USB power is usually OK.
 

Wendy

Joined Mar 24, 2008
22,138
Sure, you can use them as a source of power. I would not use power directly from a computer though, what happens if you do something that tries to blow out the port? There are a lot of ways for it to happen, it is not worth a computer. A wall wart is usually disposable comparatively speaking though.

Basic Bench Top Power Supplies
 
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Thread Starter

lefam

Joined Nov 30, 2010
33
Thanks for your answers.

So, in a USB, a short circuit happens when I directly touch the +5V and GND endpoints (pins)?
In a wall wart a short happens touching directly the (-) e (+) endpoints?

Are these the unique ways of generating a short?

How do I know if a wall wart is regulated?
 

Wendy

Joined Mar 24, 2008
22,138
Most times specs are written on the wall wart, including whether they are regulated or not. If it isn't recorded, just measure the voltage, if it is way above the voltage written on the wall wart it is not regulated.

Shorts are not the only bad things that can happen to a power supply. That can be planned for. It is possible to generate high voltage and feed it back into the power supply. Very bad things happen if it is a computer.
 

Thread Starter

lefam

Joined Nov 30, 2010
33
I am considering powering my breadboard with a wall wart.

Is it safe to just strip the wall wart connecting wires and connect to the breadboard? Is this the correct procedure.

Thanks for all your replies. I learned a lot!
 

thatoneguy

Joined Feb 19, 2009
6,359
Is it safe to just strip the wall wart connecting wires and connect to the breadboard? Is this the correct procedure.
If you measure it as correct voltage and a regulated supply, then yes. Most of the very small and lightweight wall warts that put out over 500mA are switching supplies, and fairly well regulated.
 

tyblu

Joined Nov 29, 2010
199
You'll want to connect (solder, wirewrap, etc.) the stripped, stranded wires to a solid core wire or a paper clip to make it easier to connect. The strands bend and flake off easily when plugging/unplugging from the breadboard, fall into the holes and short out adjacent nodes. If a paper clip, make sure you're not using more than ~30V, as it starts to tingle around that level ;)
 
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