basic electric circuit question regarding voltage & current.?

Question

I am studying circuits, and I've only been working with ideal voltage and current sources.

An ideal voltage source only supplies voltage. Say if i have a circuit with a 12V source in series with a resistor of 2 ohms. the current through this loop is 6 Amps.

An ideal current source (i know these don't exist in reality) supplies current only. So if i have a current source of 6 amps in series with a resistor of 2 ohms, my voltage across the resistor is 12 Volts.

Ok so in real life, a power supply supplies both voltage and current, hence the name,

say i have a power supply, or battery, that puts out 12 volts and supplies 4 amps of current.
I hook this power supply to a complicated circuit, but its equivalent just looks like a 2 ohm resistor in series. What is the current around this loop?

ohms law we have I = V/R

I = 12V / 2 ohms = 6 amps

How can there be 6 amps in the loop if the power supply only gives out 2 amps?

Will this power supply blow up?
Will it only supply 2 amps, and the voltage will drop to 4 volts?
what exactly will happen?
Is this circuit configuation impossible?

Can you give any examples of how exactly a power supply works?

Answer 1

Rather than saying "an ideal voltage source only supplies voltage"...say



"an ideal voltage source supplies an invariant value of voltage". These sources supply both voltage and current...but the voltage is a fixed value regardless of what is connected.

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Rather than saying "an ideal current source only supplies current"...say



"an ideal current source supplies an invariant value of current". These sources supply both voltage and current...but the current is a fixed value regardless of what is connected.



AND, these don't really exist, because if such a device were hooked up to nothing, it would create an infinite voltage across its terminals.



You can design a current source, but it will saturate at the voltage of the voltage sources used to power it.

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"Ok so in real life, a power supply supplies both voltage and current"



Well, all power supplies supply both voltage and current.



What makes a real voltage source different from an ideal voltage source, is the fact that a real voltage source contains an internal resistance, and always delivers a voltage slightly less than what it is designed to deliver.

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When a power supply is rated with both a value of voltage and current...



The value of voltage is what it supplies no matter what is connected

The value of current is an upper limit of the device, such that it safely operates. Less current can of course be drawn.

Answer 2

the power supply will only put out 4 amps, if you draw 6 amps, generally the fuses protecting the power supply will blow.



they usually have voltage regulators in them to keep the voltage a constant 12 volts or whatever at the rated amps.



you can find diagrams of them online but they use electronic parts, transistors, to keep the voltage constant at the rated load, maximum amps draw.

Answer 3

Ancient Greeks. Girolamo Cardano found out about electric earlier than William Gilbert about 50 years.