Capacitors charge differently based on the source used. When charged from a constant voltage source, capacitors exhibit exponential charging behavior. Conversely, when charged from a constant current source, the charging is linear, as demonstrated by the relationship Q = C × V. The discussion also highlights that the presence of components like transistors and zener diodes can influence the charging characteristics, with transistors potentially acting as constant current sources under specific conditions. Understanding these principles is essential for accurate circuit analysis and design.
PREREQUISITESElectronics students, circuit designers, and engineers looking to deepen their understanding of capacitor behavior in various charging scenarios.
It depends on how the capacitor is charged.
If the capacitor is charged from a constant voltage source, it will be charged exponentially as you say.
If the capacitor is charged from a constant current source, it will be charged linearly (as in your recent thread).
The current source will have to work harder and harder to keep its current constant though. ;)
If the capacitor is charged in another way, it will yet be different.
If you have a symbol in your circuit with the text "current source" next to it, it is also a current source. ;)
Note that your mediating transistor also needs constant voltage between the base and the emitter, before it will behave like a current source.
In your previous threads you have seen a couple of examples of that (for instance a zener diode).
What you need is that the current is the same whether the capacitor is full or empty.
If you can calculate the current in both those cases and it is the same, you have a current source.