Looking for BJT that has very low collector leakage current.

I am looking for small signal BJT that has very low leakage current when the base is biased at about 0.2V. I have issue of transistors drawing collector current when the base is at about 0.25V that is way less than the normal turn on of 0.6V to 0.7V. I am currently using BC546 or 556, and KSA992 or KSC1831 transistors, they leak too much. I need transistor with as low collect capacitance as possible ( low Ccb and Cce).

BTW, how do I look for this on the data sheet? Looking at leakage at Vceo?

Thanks

Would you mind to tell target leakage, capacitance and voltage numbers?

FvM said:

Would you mind to tell target leakage, capacitance and voltage numbers?

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Thanks for the reply, capacitance of 8pF or less, only about 5V. I really cannot say about the leakage. I am more interested in knowing how to read from the datasheet. Do I read the leakage at Vceo and Vcbo spec?

Hi,

Some things come into my mind:
You have to understand the "turn_off_voltage" of a bjt. It specifies the voltage at a dedicated collector current. It does not say, that at lower V_BE the collector current is zero.

And you have to understand the "leakage_current" of a bjt. It usually is specified at V_BE is zero.

And you have to understand that your requirement uses a V_BE somewhere inbetween those two specified transistor states, thus you can expect a collector current inbetween the two specified values.
This is a very unusual requirement, thus you rarely will find information about it in the datasheets.

This leads to my question:
Why do you want to use the bjt especially in this situation?
* Why don't you drive V_BE close to zero ... to avoid increased collector current?
* Or if impossible, why don't you use a collector connected circuit that is less sensible for the increased collector current?

If you post your circuit you could get more helpful answers.

Klaus

Added:

I really cannot say about the leakage.

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This makes no sense for me: Complaining about "too high current" but not having a clue what "too high" means.
In my eyes: A proper design starts with deciding the requirements. After that you start to design the schematic ... not the other way round.