Low Ic and Ib in a BC847C NPN BJT...is it OK?

Supposing i am switching a BC847C BJT ON with just 100uA of base current.

Suppose also that i have a large value collector resistor such that the collector current is also only 100uA when the BC847C is saturated.

.....is this an OK scenario?, or do BJTs have minimum currents (Ic & Ib) below which they do not work properly?

BC847C datasheet
https://www.rectron.com/data_sheets/BC847C.pdf

Supposing i am switching a BC847C BJT ON with just 100uA of base current.

Suppose also that i have a large value collector resistor such that the collector current is also only 100uA when the BC847C is saturated.

.....is this an OK scenario?, or do BJTs have minimum currents (Ic & Ib) below which they do not work properly?

Click to expand...

Hi Treez
It depends on what you mean by ok scenario ! why do you need to do it with IC= 100uA ?
I've a good suggestion . try to take a look into the out put curve of that transistor and then see the quiescent point that you are looking for and then see VCE in such a quiescent point . then you'll find your answer as well .
Best Wishes
Goldsmith

i need to do it with as low as 100uA of current because there is many BJTs, and the overall power consumption must be very low, so i have to reduce the collector and base currents


Also, i looked at the graphs of VBE vs Ic (in the below datasheet) and it appears to suggest that theres no problem with these low currents?....would you agree?......

BC847C datasheet
**broken link removed**


...it seems amazing to me that a device can be operating as normal with 100uA of current flowing....its tiny current

100 µA isn't a particularly low collector current, BC847 current gain is almost constant down to Ic of 10 µA (and even below, but without a manufacturer specification).

Increasing cutoff current at high temperatures and transit frequency drop will however enforce a minimal operation current, depending on the application.

...it seems amazing to me that a device can be operating as normal with 100uA of current flowing....its tiny current

Click to expand...

They designed this transistor for you !! ha ha !

Also, i looked at the graphs of VBE vs Ic (in the below datasheet) and it appears to suggest that theres no problem with these low currents?....would you agree?.....

Click to expand...

Of course there is no problem ! it is why i told you try to look into the curves from the datasheet because you can easily find what you need !

Good Luck
Goldsmith

treez said:

Supposing i am switching a BC847C BJT ON with just 100uA of base current.

Suppose also that i have a large value collector resistor such that the collector current is also only 100uA when the BC847C is saturated.

.....is this an OK scenario?, or do BJTs have minimum currents (Ic & Ib) below which they do not work properly?

BC847C datasheet
https://www.rectron.com/data_sheets/BC847C.pdf

Click to expand...

datasheet shows a dc gain of typical ~580. (geometric mean of Min & Max gain)

If you drive the base through a 47k resistor using a 5v source, and use a 47K resistor in collector load with a 5v supply, then you should get your required results.
Check it out !!


cheers !