Help required with transistor question

[chukabuka]

Hello all.

Ref the attatched cursit diagram, can anyone offer an answer as to why the transistor works?

 

[chukabuka]

re my previous post

sorry, forgot to include diagram, here it is:

 

[Jakes21]

There is a current (IB) flowing into the base of the transistor which switches the transistor on.now current can flow from the collector to the emitter

 

[UTMonkey]

It sort of depends on your definition of working.

The transistor in this configuration is being used as an amplifier (small signal in, big signal out).

Your example is known as an inverting amplifier, which means that at the positive peak of the input signal you "should" see a peak negative signal (measured below the 3K3 resistor).

To provide a decent amplification of an AC signal (which alternates around 0 volts) the circuit provides a bias via the 390k resistor to lift the entire signal above 0 volts probably to 2.5-3 volts (you need to do this or you will only see the positive peaks of the signal).

A useful feature of this circuit is that the placing of the 390k resistor provides negative feedback which attempts to stabilise any variations in supply (and in a small way gain) variations.

When I first stumbled on this circuit there was loads of great help on this site, and plenty of examples of "better" amplifiers - but this one provides a useful starting point.

Hope this helps

Regards

Mark

 

[chukabuka]

thanx for response, but the question was { why }, not { how }.
Anyone else got an idea?

cheeers

 

[Roff]

thanx for response, but the question was { why }, not { how }.
Anyone else got an idea?

cheeers

I don't understand what you mean. Are you implying that the circuit is a sentient being, and has free will? That it can choose to work, or not?

 

[crutschow]

The "why" is that it works because it obeys the laws of physics (In the case of the transistor that includes the laws of semiconductor quantum physics).

Any explanation beyond that goes to the metaphysical or philosophical.

 

[Willbe]

The "why" is that it works because it obeys the laws of physics (In the case of the transistor that includes the laws of semiconductor quantum physics).

Any explanation beyond that goes to the metaphysical or philosophical.

Why? It was "intelligently designed."

 

[silvarblade]

t { why }, not { how }.
Anyone else got an idea?

cheeers

This is new!Puting it in abc it works first of all because its designed like that and when you give a supply.