Transistor Switching, Minimum current for base?

Thread Starter

Ishiyuu

Joined May 25, 2016
3
Hello all,

I have a very general question that seems to not yet have been answered. In a circuit I am designing, What I want is a 2n2222 transistor to only fire above a certain current. In a simulator, I am applying a 361.1uA current to the base, and am getting a 36.1 mA current. In reality, is it possible to completely limit the emitter current to 0 without the base being 0?
 

dl324

Joined Mar 30, 2015
11,516
Welcome to AAC!

How close to 0 do you require? Even with a large base resistor, there will be some leakage current.

For anyone to be able to comment on the circuit you're simulating, you need to post a schematic.
 

Thread Starter

Ishiyuu

Joined May 25, 2016
3
Welcome to AAC!

How close to 0 do you require? Even with a large base resistor, there will be some leakage current.

For anyone to be able to comment on the circuit you're simulating, you need to post a schematic.
Welcome to AAC!

How close to 0 do you require? Even with a large base resistor, there will be some leakage current.

For anyone to be able to comment on the circuit you're simulating, you need to post a schematic.
Welcome to AAC!

How close to 0 do you require? Even with a large base resistor, there will be some leakage current.

For anyone to be able to comment on the circuit you're simulating, you need to post a schematic.
My apologies. My primary objective is to create a circuit whereby after 1 second of conducting, the circuit becomes "opened" for a period of time, where the base and collector connected cannot conduct current. I want to create this circuit in the most simple way as possible, without the use of gates or IC's.
 

dl324

Joined Mar 30, 2015
11,516
If you want the transistor to be saturated for a certain period after being triggered, you can make a discrete one shot to drive the switch. That will take 3 transistors, a capacitor, and some resistors.

From wikipedia: https://en.wikipedia.org/wiki/Multivibrator
upload_2016-5-25_7-54-31.png

You could try using an RC network on the base of a transistor, but you won't get a sharp on-off transition.
 

AnalogKid

Joined Aug 1, 2013
8,590
What I want is a 2n2222 transistor to only fire above a certain current. In a simulator, I am applying a 361.1uA current to the base, and am getting a 36.1 mA current. In reality, is it possible to completely limit the emitter current to 0 without the base being 0?
Yes. First, there is a minimum base-emitter voltage below which no base current flows. Once Vbe is large enough and base current does start to flow, there is a minimum current necessary to start collector-emitter conduction. These values are on the datasheet.

ak
 

wayneh

Joined Sep 9, 2010
16,399
In reality, is it possible to completely limit the emitter current to 0 without the base being 0?
No. If there is any base current whatsoever, it appears at the emitter. It cannot accumulate in the transistor!

Now, you could have a base-collector current if the collector voltage falls below the base voltage. But I don't think that's what you are asking.
 
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