[SOLVED] transistor current I cbo

why there is Icbo current in transistor?


it is measured when emitter is open. but why it is necessary to measure?

Hi,

let´s say you have a high ohmic load. let´s say 10MOhms,

then every nanoampere of Icb0 causes a voltage (error) of 10mV. (100nA ---> 1V)

Klaus

thanks, klaus.
will u explain me in detail?
:razz:

It's a measure of the amount of Ic you would see if the transistor was entirely switched off (unbiased), in other words the leakage current caused by impurities and occasional electron mobility in the semiconductor materials. In critical applications, especially ones where the transistor may be running at very low collector current, the leakage may become signficant. It is also highly temperature dependant, Icbo increases with temperature.

In days of old, Icbo could be a serious problem, especially in transistors made from Germanium where it could be several mA and contribute to the bias current where it could cause temperature stability problems and even "thermal runaway" in extreme cases. Silicon transistors have much lower Icbo so it is less of a problem with modern devices.

Brian.

Hi,

what detail?

An example:
The value may be called "leakage" current. It´s like when you close the water faucet at your kitchen sink, but from time to time there comes a drop of water out of it.

Klaus