# Difference between revisions of "Lab 13 RS"

DC Bipolar Transistor Curves

Data sheet for transistors.

Using 2N3904 is more srtaight forward in this lab.

# Transistor circuit

1.) Identify the type (n-p-n or p-n-p) of transistor you are using and fill in the following specifications.

I am going to use n-p-n transistor 2N3904. Below are some specifications from data shits for this type of transistor:

Value Description
Collector-Base breakdown voltage
Emitter-Base Breakdown Voltage
Maximum Collector-Emitter Voltage
Maximum Collector-Emitter Voltage
Maximum Collector Current - Continuous
Transistor Power rating()
,
40 300 ,
70 300 ,
100 300 ,
60 300 ,
30 300 ,

2.) Construct the circuit below according to the type of transistor you have.

Let .

variable power supply

.

Find the resistors you need to have

, , and

By measurements I was able to find that . So I am going to use this value. Also let picks up . So my current .

Now to get  I need to use
To get  I need to use
To get  I need to use


3.) Measure the emitter current for several values of by changing such that the base current A is constant.

I used:





and




Below is the table with my measurements:

And below is my currents and power calculation:

Here:





and I have used approximation

4a.) Repeat the previous measurements for . Remember to keep so the transistor doesn't burn out

I used:




and




Below is the table with my measurements:

And below is my currents and power calculation:

Here:





and I have used approximation

4a.) Repeat the previous measurements for . Remember to keep so the transistor doesn't burn out

I used:




and




Below is the table with my measurements:

And below is my currents and power calculation:

Here:





and I have used approximation

5.) Graph -vs- for each value of and above. (40 pnts)

Bellow is my plot for the case of

Bellow is my plot for the case of

Bellow is my plot for the case of

6.) Overlay points from the transistor's data sheet on the graph in part 5.).(10 pnts)

I can not really do it because there are not good points to compare from data sheet. I can take for example this data from data sheet:

And from the table above I can only extract the range of like

1)

2)


And my measurements looks like:

1)

2)

3)


First point to note that from my measurements and from data sheet are different so I can not really overlay them and compare. Second, I have specific values of , otherwise from data sheet I have the range of . And third, I can't really plot this range of from data sheet on my plots just because my plot doesn't have the axis.

All I can do here is to say that my measured are inside the range of data sheet .

# Questions

1) Compare your measured value of or for the transistor to the spec sheet? (10 pnts)

I will calculate my from my measurements above in active region like:

1):

2):

3):


And above values of are in agreement with range of from the spec sheet which is from 30 to 300. But I can not say nothing more because 1) my current doesn't correspond to published in data sheet. 2) My calculation is for specific value of current. But in the data sheet the range of is reported for specific values of and .

2) What is for the transistor? (10 pnts)

3) The base must always be more positive (negative) than the emitter for a npn (pnp) transistor to conduct I_C.(10 pnts)

4) For a transistor to conduct the base-emitter junction must be forward biased.(10 pnts)

5) For a transistor to conduct the collector-base junction must be reversed biased.(10 pnts)

# Extra credit

Measure the Base-Emitter breakdown voltage. (10 pnts)

I expect to see a graph and a linear fit which is similar to the forward biased diode curves. Compare your result to what is reported in the data sheet.

I used:





Below is the table with my measurements and current calculations:

Here I have used exact formula to calculate :




And bellow is my plot for the Base-Emitter breakdown voltage

The fitting line is . The intersection this line with x-axis gives the forward turn on voltage:




Actually what we are measuring here is better to call the forward turn on voltage for base-emitter junction (Base-Emitter breakdown voltage is for reverse current measurement). From the data sheet this point (called the base-emitter saturation voltage) is 0.65 V and this point is inside my predicted values