Experiment No.8

Summary

Vary the base resistor and measure changes in voltage and current for Vce, Vbe, Ic, and Ib. Then plot a load line.

Setup the following circuit on a bread board. Use a 470R for Rc and a BC547 NPN transitor.

Pick five resistors between 2K2 and 1M for Rb. You want a range of resistors that allow you to see Vce when the trnsistor is the saturated switch region and when it is in the active amplifier region. I used 47K, 220k, 330k and 1M, but this can vary depending on your transistor. Some may need to use 2k2. Put one resisitor in place, and measure and record voltage drop across Vce and Vbe. Also measure and record the current for Ic and Ib. Then change the Rb resistor and do all the measurements and record the new readings. Do this for each of the resistor values above.

Your voltage drop measurements across Vce should vary from below 0.3 v ( showing the transistor is in the saturated switch region) to above 2.0v (showing the transsistor is in the active amplifier region) If this is not the case, you may have to try a smaller or bigger resistor at Rb. Talk to your teacher to get a different size resistor, and redo your measurements.

Discuss what happened for Vce during this experiment. What change took place, and what caused the change?

During this experiment the Vce has more volatge gain when ever there is more resistance.

Discuss what happened for Vbe during this experiment. What change took place if any, and what caused the changed?

In this experiment the Vbe is at 0.7V because the transistor only passes the current when it exceeds 0.7V. When the transistor is fully saturated then the Vbe should above the 0.7V.

Discuss what happened for Ib during this experiment. What change took place, and what caused the change?

In this experiment the change is that the current is always very small when crossing the base. Therefore usually the micro amps and since the current is small it is not used for equation.

Discuss what happened for Ic during this experiment. What change took place, and what caused the change?

In this Experiment I have noticed that the bigger the resistor the less current is across the collector.

Plot the points for Ic and Vce on the graph below to create a load line. Plan the values for so you use up the graph space. Use Ic as your vertical value, and Vce as your horizontal value. Using Vbe on the Vce on the Vce scale, plot the values of Ib so the finished graph looks similar to fig 13.

Calculate the Beta (Hfe) of this transistor using the above graph.

At 2590mV B = 1.19/0.01

= 119

At 1420mV B = 3.43/0.01

= 343

At 1066mV B = 4.22/0.01

= 422

Explain what the load line graph is telling you. Discuss the region s of the graph where the transistor is saturated, Cut-off, or in the Active area.

According to the load line which I have constructed shows me that my transistor is in saturated, active and cut-off regions. My readings of Ic is 5.16mA, Vce is 0.609V and Ic is 4.96mA, Vce is 91.6mV these are both located at the suturated region, iilustrating me that these points Ic is very high whereas Vce is low therefore large amount of collector current can flow.