Semiconductors-transistors operation(2)

Quick Math
3 x 2.7 = 8.1 drop
11.6 - 8.1 = 3.5

With 0.7v on the base the transistor will be just active so it is a current amplifier with the current through the collector and emitter being about 100 times the current into the base. If you crank the base voltage a bit higher it will become saturated and you will get about 0.1 - 0.2 V drop across collector/emitter rather than the 3.4V that you currently have. (pun intended :)

sorry VBE voltage is 0.7V

VC = 11.6 - 5.4 V

VE  = 2.7V

VC and VE are voltage drops

You need to learn how to share circuit drawings if you want to ask effective questions here.  Maybe you could take a picture with your phone?

You can also describe, share, and simulate your circuit with LTI Spice.  It is free, and very useful.

There are at least 12 ways to connect two 1k resistors, a transistor, and an LED in series, and at least two of them make interesting (and different) circuits.

As far as what you are missing here:  The answer is base current.

You should always have a current limiting resistor between the base of the transistor and input voltage, typically 10x the output load.  10k would be a good value in this case. This allows you to measure the voltage drop across the base resistor and calculate the exact base current.

yes sorry i forgot i had a resistor to reduce base current too. This resistor is about 100 ohms

ok i will make a drawing for you

but i said where the voltage drops

So measure the voltage across the 100 ohm resistor to tell the base current, multiply that by the gain of the transistor from the manufacturer's data sheet to make a guesstimate of the collector current to calculate what the voltage drop across the resistors should be. What's left over should be your 3.4V.

All this voltage stuff is pretty irrelevant since transistors are current amplifiers, not voltage anythings.

"The voltage drop in the light emmiting diode is 2.7 volts"
If it is just an LED (no resistor) and it is on (forward biased), it is highly unlikely that the voltage is that high.  It acts like a diode and should have a voltage drop of about 0.7V when on.

Andyalder makes an excellent comment about transistors (or diodes, for that matter) that current is generally what you want to know about, not voltage.

>>  It acts like a diode and should have a voltage drop of about 0.7V when on.

That is not true.  There are all kinds of diodes.  The data sheet for the most generic diode at DigiKey is attached: It is a red LED from Cree, 300K  units in stock, and 15 cents each.

It has a forward voltage of 2.1V at 20mA.  If you look at the Digikey website, you will fine forward voltages between 2.1 and 3.4 volts.  None are as low as 0.7V.
Cree-LED-from-DigiKey.pdf

yes so if im right when you apply positive voltage(0.7 V) to the base many electrons get kinetic energy and move across the emmiter-base junction

very few of them recombine with holes and become base current and the rest because they already have kinetic energy move across the base-collector junction and become collector current

You really should think about current, not voltage.
If you apply a voltage to the base (I'm assuming an NPN transistor here) through a resistor, once the voltage gets above about 0.7V, current will flow to the emitter.  That current will pull Beta (a characteristic of the transistor, typically 500-1000 but could be much different) times that current through the collector to the emitter.

For example, imagine that you apply 1V above ground to a 100 ohm resistor to the base.  About 0.7V will drop over the base-emitter junction, leaving about 0.3V over the 100 ohm resistor.  That says there is about 3mA of current through the resistor, all of which goes through the base to the emitter.  That will pull much more (Beta x 3mA) current through the collector to the emitter.

Now, all of this is also very dependent on the rest of the circuit.  Learn about the three basic circuits: common base, common collector, and common emitter.  While the basic function of the transistor is the same, the end result is very different based on the topology and surrounding parts (resistors in the simplest cases).

The things to know about those three circuits are: current gain, voltage gain, voltage polarity (is the output voltage the same polarity as input or is it inverted?), input impedance, and output impedance.  That will get you most of the way through understanding basic transistor circuits.

Not an expert on LEDs but as far as I know they don't act as diodes when measuring voltage across them and current through them, more like a diode with a very efficient light bulb in series. About 2.7V lights some white ones but others need more or less to make light come out of them. The main reason they call them diodes is just because they blow up if you connect them the wrong way around :(

Off to watch bigclive blowing up a few more LED panels on youtube :)

you can alsodraw a picture in Word, or any sketch program