Contents
What is current source practically?
A practical current source is a two terminal device having some resistance connected across its terminals. Unlike ideal current source, the output current of practical source depends on the voltage of the source. The more this voltage, the lesser will be the current.
How are current sources made?
A current source can be made with a current mirror, where two BJT transistors are biased with the same base-emitter voltage to give the same (well, almost, the difference is two base currents) collector current.
How is a practical current source different from an ideal current source?
A practical current source is a two terminal device having some resistance connected across its terminals. Unlike ideal current source, the output current of practical source depends on the voltage of the source. The more this voltage, the lesser will be the current.
Is the output current independent of the source?
An ideal current source has infinite parallel resistance connected to it. Therefore, the output current is independent of voltage of the source terminals. No such current source exists in the world, this is just a concept. However, every current source is designed to approach closer to the ideal one. It is represented by the symbol as shown below.
Can a battery be an exact current source?
Much like voltage sources, current sources are only a theoretical construct. A battery can be a resonably close approximation to a voltage source, but it is not exact. Howeer unlike voltage sources, which are approximated by batteries, there is no simple component that approximates a general current source particulkarly well.
Are there any real sources of infinite current?
In the same way, real voltage sources cannot deliver infinite current, real resistors have some residual series inductance, and the only use for a light inextensible string is for tethering a spherical cow. Of course they exist. There are many cases, where current sources are applicable: