I have a DC- adapter which gives me the output of 12V and 3.3A, I want to connect it to a device which requires 12V and a few hundred milli amps, would this damage the device? or any device would automatically draw the current it needs and not anymore ?
If it matters the device is a display driver. Datasheet.
Please, Help me understand the basics of current draw.
Rating on the adapter indicates that its output voltage is 12v and it can supply a maximum of 3.3A. when adapter is connected to a load, voltage will remain same. but output current depends on the load resistance.
In your case this adapter won't damage your display driver. instead it draws only required current from the adapter output.
The concept is just basics of ohm's law. imagine that you connect a 12 ohm resistor at the output of your adapter. according to ohm's law 12/12 = 1A. that means only 1A current flows through the resistor. Same here also. Current through the device depend on the voltage across the device and internal resistance of the device.
Yes, What tollinjose said.
Also, to add, the adapter's current rating cannot be BELOW the display driver's rated draw. It should be the same or more - your display driver will draw what it needs and no more. Voltage should be the same.
Similar with batteries, voltage should be the same, but capacity of replacement battery can be more, less, or same as original, affecting run time.
