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Effect of overdrawing current?

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Gandledorf

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Lets say I have a power supply which provides me 12V @ 500mA. I wire an LED with a voltage drop of 3V, and a 10 ohms resistor. Assuming my LED can sustain a constant forward current in excess of 1A, what would happen? I'm attemting to draw 900mA from a 500mA source. Does it cap at 500mA? What is the behavior?

Under the same vein, say I have 12V @ 500mA supplied from a "power brick" connected to the mains. My project only requires 5V @ XmA. Is there a way to step down the voltage and step up the current?
 

stevez

Active Member
Without knowing a lot more about the supply it's hard to tell what would happen if you overloaded it. In general it's reasonable to expect that the voltage will drop off significantly. Depending on overcurrent protection and design it might fail completely or sit there and deliver some amount of current.
 

Gandledorf

New Member
Lets say in one example it is a standard "power brick" (schematics unknown), as I suggested, and in another example it is a switching regulator.
 

crust

Member
The swich mode converter will go into a discontinuous mode where the current through the inductor coasts to 0. So for some period of time no power will flow into the load.

I have no idea what a power brick is.
 

Gandledorf

New Member
crust said:
The swich mode converter will go into a discontinuous mode where the current through the inductor coasts to 0. So for some period of time no power will flow into the load.

I have no idea what a power brick is.
It's the generic power supply that comes with most laptops, cell phones, etc. You have a plug into the mains which hooks into a brick looking case (usually heavey), that provides a regulated XV at XmA out through a female power connector.
 

crust

Member
I would guess that if you draw more current than it is designed for, you might be able to do it for a short amount of time or for a slightly higher than rated current. I believe many of those are switch mode converters (as opposed to linear) so you will probably get into the discontinous conduction mode.
 
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