Need help to understand transistors...

[tussi]

Hi. Can anyone explain to me how to use a npn/pnp transistor(or where I can find some info), and what to look for in the datasheet?? I am a bit confused..

 

[Optikon]

Hi. Can anyone explain to me how to use a npn/pnp transistor(or where I can find some info), and what to look for in the datasheet?? I am a bit confused..

Mainly used in two modes.. as a small signal ampifier or as a switch.
What to look for in the datasheet will depend on what you are using it for as some applications require certain parameters and other do not.

take a couple chapters of this and call us in the morning.

 

[electronist]

the switch mode of transister is easy to grasp but in case of amplifier ckts you will require to have a good knowledge of transistors and semiconductor physics. & that will take time. Every book based on basic electronics will naturally cover the topic of transisters.,

 

[tussi]

Thanks for replying to my question. I have read the document, but I cant figure out the base voltage and current min/max for the active area and where the transistor is saturated. I have a datasheet from a 2n2222, can anyone help me locate this in the datsheet??

 

[Optikon]

Thanks for replying to my question. I have read the document, but I cant figure out the base voltage and current min/max for the active area and where the transistor is saturated. I have a datasheet from a 2n2222, can anyone help me locate this in the datsheet??

Look at Figure 4 in your datasheet. See the flatter part of the curve? (more horizontal) that is the saturation region. It can happen when your base current tries to generate a collector current that the collector circuit cannot support.

You cannot figure the base voltage for what? There really is no current min (limited probably by noise floor) but the maximum for this part in this package is 600mA. I'm confused about what you want to know about the base voltage??? Base voltage when it is saturated? That will depend on the circuit you are using it in.. Saturation can fully be described by Ib, Ic and Vce. no need for Vb..

 

[tussi]

Hi. Thanks for all help so far.. But I still don't understand this...

Can I put any cind of voltage levels into to the base, and just controll it with the current?? I am a bit confused... There shuld be 0,7 v over base --> emitter...??? Do I need a voltage over 0.7v to "start" the transistor????? This was not easy..

In the datasheet i found:
V(BR) EBO Emittter-base Breakdown
Voltage (IC = 0) IE = 10 mA 5V

VBE (s at )* Base-emitter Saturation
Voltage
IC = 150 mA IB = 15 mA 1.3V
IC = 500 mA IB = 50 mA 2.6V
Are this the maximum voltage input?

I have never worked with npn/pnp just fet's and there i must have a specific voltage level into the gate.

I want to learn how to amplify ac signals and dc levels. I use a fet as switch so it's the active area i am interresting in.

 

[Optikon]

Hi. Thanks for all help so far.. But I still don't understand this...

Can I put any cind of voltage levels into to the base, and just controll it with the current?? I am a bit confused... There shuld be 0,7 v over base --> emitter...??? Do I need a voltage over 0.7v to "start" the transistor????? This was not easy..

In the datasheet i found:
V(BR) EBO Emittter-base Breakdown
Voltage (IC = 0) IE = 10 mA 5V

VBE (s at )* Base-emitter Saturation
Voltage
IC = 150 mA IB = 15 mA 1.3V
IC = 500 mA IB = 50 mA 2.6V
Are this the maximum voltage input?

I have never worked with npn/pnp just fet's and there i must have a specific voltage level into the gate.

I want to learn how to amplify ac signals and dc levels. I use a fet as switch so it's the active area i am interresting in.

I would not say these voltages are the maximum you can input. Rather, you must know that these voltages put it in saturation mode (part of I-V curves) maximums are stated elsewhere like Vcbo etc...

When you worked with fets, you operated them in the "triode" region where they act like switches. Bipolars can be in a similar mode called saturation. But if used as an amplifier, they are NOT saturated but rather sit somewhere on the Vbe--Ic curve and can amplify input signal. You must "bias" the transistor to sit somewhere on this curve. Then your _small_ signal input can move it up and down this curve and the output will be an amplified version of this. All of this usually takes place with Vbe not changing by much. For amplifiers, you should not think about anything that you thought about with your fets as switches.


Bipolar transistors usually just come out of cutoff mode at around Vbe = 0.63V and at about Vbe=0.7V they are saturated.

My advice would be to keep reading intoductory transistor material until you feel comfortable with how they work as basic amplifying devices. Only then, crack open a datasheet. Looking at them now if you don't understand what they do, is a waste of your time. Try grasping the operation first!