Transitors output polarity or phase

[walters]

Why does a Transitor which the polarity or phase of the input signal ?

I don't get how it does this? When you put a signal in at the base of the
transitor it flips the polarity or phase on the collector how does it
do this and why?

Something to do with the voltage drop?

 

[D.J.]

Hi Walters,

"When you put a signal in at the base of the
transitor it flips the polarity or phase on the collector how does it
do this and why? "

If I understand the question, your asking why, when you saay , hook the base up to positive the collector has a negative.

It's becuase your emitter is hooked up to negative. When you apply a positive to the base it switches inside the transitor, allowing negative to flow from the emitter to the collector.

If you need a more, in depth, explination, read this article:
http://www.amasci.com/amateur/transis.html
It is a very simple explination to how transitors work.

Hopefully I answered your question!

D.J.

 

[walters]

Thanks for the reply back

hook the base up to positive the collector has a negative.

Yes isn't that weird how does it do that?

It's becuase your emitter is hooked up to negative. When you apply a positive to the base it switches inside the transitor, allowing negative to flow from the emitter to the collector

It switches inside the transitor how does it do this inside i don't get it ?
this seem really weird for me and i can't picture this happening

 

[D.J.]

Hi Walter,

Read that link I posted on the message. It has a very easy way to understand what exactly goes on inside the transitor.

If I remember correctly their are two dielectrics inside the transitor. One for the emitter and the other for the collector. The dielectrics are silicone.

So when you apply positive on the base it reduces the silicone on the emitter allowing negative to the collector. When their is no voltage on the base the silicone dielectric is too big for the electrons to move past. When you apply to much voltage to the base, the silcone reduces so much that it stays that way, the transitor is now broke.

Don't quote me on any of this!

But if you want a better explanation, that also contains illistrations, go to the link I posted. Bill Beaty's explination is very helpful!

Regards

D.J.

 

[2ny]

When you put a signal in at the base of the
transitor it flips the polarity or phase on the collector how does it
do this and why? "

when inputting current into the base of the transistor, the collector current increases due to the beta, (current gain charateristics) of the transistor!
now the resistor in seris with the collector drops voltage comensurate to the input current.

phase in this case is brought about by increasing current(voltage)input causes a decreasing voltage at the collector terminal!

 

[walters]

phase in this case is brought about by increasing current(voltage)input causes a decreasing voltage at the collector terminal

That seems really hard to picture

 

[free1]

phase in this case is brought about by increasing current(voltage)input causes a decreasing voltage at the collector terminal

That seems really hard to picture

hi there,

may be u can find some info abouy transistor at hte website below,

http://www.geocities.com/bagtool/transistor.html

free.

 

[walters]

I have a problem of understanding how the transitor can flip or invert
the phase from the base to the collectors output

I just don't understand how the transitor can invert the phase
how does the transitor do this?

 

[samcheetah]

D.J. has given you the greatest link i ever found on the internet about transistors. i would suggest that you read it carefully.

let me explain this to you with some mathematics. the collector to emitter voltage is given by

Vce = Vcc - Ic*Rc

where Vcc is the supply voltage, Ic is the collector current and Rc is the collector resistor. now Ic depends on the base-emitter voltage (if the emitter is at ground, we can simply call it the base voltage). now look at the equation, if Vce is the difference of two things i.e. Vcc and Ic*Rc. now as the base voltage increases, the collector current increases (normal transistor action) and hence the factor Ic*Rc increases. and as Vcc is constant, Vce decreases. so when the base voltage increases, it increases the collector current thereby increasing the drop on the collector resistor. therfore the collector voltage decreases. this is how the phase is inverted.

consider that the signal at the base is a continuous analog signal. when signal is increasing the collector voltage is decreasing and vice versa.

let me explain this to u in another way. lets say we have the equation

A = 5 - X

where X is a variable. when X is 1, A is 4. and when X is 4, A is 1. therefore as X increases A decreases. now that X is dependent on the base voltage and the A is the collector voltage.

i hope you get the picture!

 

[Nigel Goodwin]

I have a problem of understanding how the transitor can flip or invert
the phase from the base to the collectors output

I just don't understand how the transitor can invert the phase
how does the transitor do this?

It's already been explained!.

It DOESN'T really invert it!.

A transistor is current driven, the base current is amplified by the current gain of the device and flows as collector current. Emitter current is the sum of the two. So an increase in base current provides an increase in collector current - NO inversion.

Where the inversion comes from is if you look at voltages instead of current!. The collector of a transistor is normally connected to it's supply via a load resistor - as the collector current increases the voltage drop across it increases. If you measure from the 0V rail, this gives an inverted voltage signal to that input to the base.

Incidently, a valve/tube gives the same effect (although they are voltage driven, and not current driven) - but anode current is directly proportional to grid voltage - so with the usual load resistor it effectively inverts.

 

[walters]

Thanks alot for you helping me out

so when the base voltage increases, it increases the collector current thereby increasing the drop on the collector resistor. therfore the collector voltage decreases. this is how the phase is inverted.

This sums it up in a nutshell

Is this based by a voltage drop to get the phase inverted?

I never seen a voltage drop inverted the phase like how this
collector resistor does i don't understand sorry?

 

[D.J.]

Hi Walter,

Their is no phase change going on. The transistor is a switch.

The negative is already their at the emitter, and by applying positive to the base, the negative is allowed to flow from the emitter to the collector.

The positive from the base is NOT being changed into negative.

The emitter, collector region is like a diode once you apply a signal to the base.

I have been refering to " place a positive to the base " only becuase I am used to using an NPN.

If you read the article I posted, you will see that all the base signal does, is reduce the insulating silicon to allow ngative to flow from emitter to the collector.

THE POLARITY IS NOT CHANGED. THE SIGNAL, IS JUST THAT, A SIGNAL TO ALLOW CURRENT TO FLOW FROM THE EMITTER OUT THE COLLECTOR.

Read this article:
http://www.amasci.com/amateur/transis.html
After reading this article if you have any troubles, write back.
I suggest you read this article it shows you what goes on inside the transistor, and therefore will help you understand how it works.

Hope this helps!

Regards

D.J.