Experiment No.8 - Transistor Voltage drop

In this experiment we where to create a circuit and vary the base resistor and measure changes in voltage and current for Vce, Vbe, Ic and Ib. Then plot a load line.

I used a 470R for Rc and a BC547 NPN transistor

these are the reading I found

Vce is the voltade between the collector and emitter, You can see in the table as the Rb increases the Vce also increases. This shows that wih a higher resistor and less voltage getting to the base there is going to be a greater voltage drop.

The vbe is the voltage between the base and the emitter, as shown in the table there is very little change between the vbe . This is becasue the transistor only requires 0.7v to operate.

the higher the Rb the lower the Lb is going to be,this is because there is such a large resistance there is going to be less current at the base.

The Ic was lower as the resistance increased. The greater the Ic the more the transistor is on which is increased current flow.

Here is the graph which i plotted the table onto.

Beta = Vce at 1.25v = 5.9mA and 70MA

B = 0.0059 / 0.000070 = 84.2

The load line on the graph is showing the relationship of Ic and Vce. This load line on this graph is showing the transistor is saturated at 8.27mA at .7 volts and cuts off at 113.9MA.

Experiment No.7 - Transistor as a switch

In this Experiment I had to make a circuit and use a transistor as a switch and run some tests on it using a multimeter.

Vbe = .74v

This shows that the transistor has a knee voltage of .74 volts

Vce = 0.05v

There is only a voltage drop of 0.05v, this shows that the current is flowing through the transistor freely.

In this graph, in region A the transistor is in the "fully on" position and in region B it is in the "fully closed" posistion.

Power dissapating at a Vce of 3v,

Vce = 3 Ic = 14

Ic * Vce = Pd

14 * 3 = 42mW

Beta at at Vce of 2,3 & 4 volts

Vce2 = 20 / 0.8 = 25mA

Vce3 = 14 / 0.5 = 28mA

Vce4 = 5 / 0.2 = 25mA

Experiment No. 6 - meter check of a transistor

In this experiment I had to identify the legs of my transistor with a multimeter, I was able to refer to the representations to identify and test the transistors.

The multimeter was used to measure voltage drop between the legs, I tested them in NPN and PNP.

Experiment No. 5 - Capacitors

In this experiment I had to caculate how long it would take to charge 4 different capacitors then observe them charging on a scope.

First there was a circuit I had to put together which would be used to observe the time taken to charge the capacitors.

These are the results I got by using a simple formula - R x C x 5 = T, this is the time it takes to charge up to the applied voltage.

These are the images taken from the graph on the scope using the different capacitors and resistors.

100uF , 1Kohm 100uF , 0.1Kohm

330uF , 1Kohm 100uF , 0.47Kohm


Changes in the resistor affect the charging time by the larger the resistor the lower the current flow is going to be as it is restriced and if it is a smaller resistor more current flow will be able to pass so it will take less time to charge.

Changes in the capacitor affect the charging time because the larger the capacitor the longer it will take to charge as it can hold more charge ans with a smaller capacitor it hold less charge so it will take less time to charge.

Experiment No.4 - voltage drop

In this exercise we where given 1 resistor, 1 5v1 400mw zener diode and one 1N4007 diode. With these I made a circuit and measured voltage drop at given points.

Vs = 10 & 15v
R = 1k ohms

10 Volts 15 Volts

Volt drop v1 5.04v 5.16v

Volt drop v2 .74v .76v

volt drop v3 5.78v 5.93v

Volt drop v4 4.19v 9.02v

Caculated current A 4.19mA 9.02mA

With the Zener diode in reverse polarity it drops it rated voltage which is why V1 is around 5v. Because the other diode is in foward polarity it only uses up its rated .7v.

Experiment No.3 - resistors and diodes

In this experiment we where given 2 resistors and a 5v1 400mW Zener diode and built a circuit.


R= 100 ohms
RL = 100 ohms
Vs = 12v , 10v , 15v

value of Vz = 4.94v
value of Vz = 4.69v
Value of Vz = 5.07v

As the supply voltage drops ans increases the zener diode should hold 5.1v but as it is a cheap zener diode this does not happen.

This type of circuit would be used for voltage regulation

Then I reversed the polarity of the zener diode,

Now the value of Vz is .84v, thsi is because this is the foward rated voltage drop of the zener diode.

Experiment No.2 - Diodes

In this experiment we where given two types of diodes, one a rectifer diode and the other a LED, we had to identify the anode and cathode of these two diodes using a multimeter.

The cathode end of the recifier diode is shown by a silver strip going around the end of it.

The cathode end of the LED is shown by the shorter leg which is the cathode or a flat spot on the LED next to the cathode end.

Next I had to caculate the value of current flowing through the diode in a circuit. I made this circuit using a 5v input, a 1kohm resistor and a 1N4007 diode on a breadboard.

Caculated current flow

5v - .7 = 4.3mA

I = 4.3/1 = 4.3mA

Measured

4.7mA

This reading is a little higher than i thought it would have been, but there is not much difference between the two.

The maximum value of the current that can flow through the diode is 1A.

For the 1kohm resistor the maximum value of V's so the diode operates in asafe region is 1000vs.

Next I replaced the diode with the LED and caculated the current.

Caculated current flow

5v - 1.94 = 3.06

I = 3.06/1 = 3.06ma

Measured

3mA

I observed that the LED uses more voltage (voltage drop) than the diode, this is because the LED needs voltage to light up.