What actually is a current source? Watch
In circuits we talk about voltage sources and current sources. Now, a voltage source is a battery, I know what a battery is and I can visualise it and understand how it works. But what actually IS a current source? Can somebody name me a physical object that is a current source or give me a picture of one or is it just an abstract idea of current just being 'added' to that point in a circuit by some device? Thanks.
From an engineering perspective, the definition of voltage and current sources are indeed rather abstract.
Voltage source: is envisioned as a two terminal black-box that maintains a fixed voltage drop across it's own terminals regardless of the load resistance placed across the terminals. i.e. the voltage source supplies whatever current is necessary to maintain the p.d. across the load.
In practical reality, this can only be achieved for a limited maximum load current. e.g. a battery approximates a voltage source over a limited range of currents. But because it has an internal resistance, as the current demanded by the load increases, voltage is lost and the output voltage across the terminals droops.
In practical circuits, feedback loops around operational amplifiers are used to maintain accurate reference voltage sources.
Current source: is envisioned as a two terminal black-box that maintains a constant current regardless of the load resistance. i.e. the current source develops any necessary p.d. across the load in order to maintain a constant current.
Again, in practice, the range of loads over which constant current can be maintained is limited by the physical implementation of the circuit.
Practical implementation is a semiconductor current mirror:
The BJT devices need to have closely matched characteristics and are therefore selected specifically to comply.
Rbias is fixed and sets up a constant reference current in the LH transistor which is mirrored through the RH load irrespective of the load resistance (within the circuits compliance limits).
Thank you for your detailed response. Could you please give me a name of a device that IS a current source? Like, a battery is a voltage source, what is a current source? I'm curious what it is in a real life situation, so say you were building a circuit and you wanted to add a current source, what physical object would you use for that purpose? Thanks.
Here are others:
Oh ok so you can't get an object which is a current source, but more it's a specific setup of multiple components that supplies extra current?
The tighter and wider the range over which you want to control the current source, then the more complex and difficult to implement the circuit becomes.