What is a current mirror? скачать в хорошем качестве

What is a current mirror?

A high level walk through of the workings of a basic current mirror. NOTE: Here I have ignored the base emitter currents by assuming beta for both these transistors is infinite. Have also assumed the transistors are identical (same beta values etc). Also I have ignored the fact that temperature will effect this circuit. If building this in an IC there are other factors to also consider. But this is a very simplified example of the overall logic of how mirrors work. So please be aware: This is not a rigorous explanation. A lot of details have been left out to keep the essence of how this works easier to understand. Note for example: Very good comment from Bob Berg below. As he rightly points out that the resistor Rpg must always be greater than the load for the mirror to work properly. If we were to increase the load resistor so that it equals the value of Rpg then the current through Q2 will still be roughly the same. But it will become noticeably less than the current through Q1 if the load resistance is then increased to a higher value than the Rpg value.