Experiment No. 2

Diodes

Exercise : Using a multimeter , identify the anode and cathode of the diode and the LED.

Explain how you could identify the cathode without a multimeter.

On the diode there is a silver mark painted on one end which indicates the cathode side of the diode.

Table 1 : Data sheet of 1N4OO7 is as follows

Exercise : For Vs = 5V, R= 1k ohms, D= 1N4007 build the following circuit on a bradboard.

Calculate first the value of the current flowing through the diode, now measure and check your answer?

Calculated Value

I = V/R

5/1000 = 0.005A therefore the answer is 5mA

Measured Value

The measured value of the diode is 4.9mA

Is the reading as you expected; explain why or why not?

According to the Ohms Law A = V/R the answer I calculated and measured with the Ohmmeter is almost equal to each other i.e 5mA and 4.9mA.

Calculate the voltage drop across the diode, now measure and check your answer?

Calculated Value

0.576V

Measured Value

0.688V

Using the data sheet given in Table 1 above,

What is the maximum vaulue of the current that can flow through the given diode?

Maximum value of current is 1.0Amps at 75'c.

For R= 1K ohms. What is the maximum value of Vs so that the diode operates in a safe region?

The maximum value of Vs at which the diode will be in safe region is 1000Volts.

Replace the diode by an LED & calculate the current, then measure and check your answer?

Calculated Value

I = V/R

5/1000 = 0.005A therefore the answer is 5mA

Measured Value

The measured value of the LED is 2.19mA

What do you observe ? Explain briefly.

After carrying out the experiment I found out that the LED and the diode they both use slightly differrent amount of amps through the circuit even when you replace them with each other.

Experiment No.1

Here I have to obtain 6 resistors of different colours and calculate and measure the values using colour coding and Ohmmeter.

Now I have to choose two individual resistors and record there ohm resistance value measured by the ohmmeter.

Resistor 1 = 0.22M Ohms

Resistor 2 = 0.33K Ohms

Now I have to calculate and measure both the resistors in series.

Calculated Value 1 and 2 in series

0.22M ohms + 0.33K ohms = 0.55M ohms

Measured Value 1 and 2 in series

0.55M ohms

Now I have to calculate and measure both the resistors in parrallel.

Calculated value 1 and 2 in parallel

Rt = R1 X R2/R1 + R2 = 0.45 X 0.13/0.45 + 0.13 = 0.0585/0.58 = 0.10K ohms

Measured Value 1 and 2 in parallel

0.13K ohms

What principles of electricity have you demonstrated with this? Explain:

After carrying out the calculations i get to know that the resistance are to be added togerther in the series whereas in parallel the resistance is low than the individual resistance.

Diodes Information

Diodes
Diodes are semiconductor devices which might be described as passing current in one direction only. When the diode is connected in the forward bias arrangement the charge from source repels holes and electrons towards the junction if the voltages exceeds 0.6 - 0.7 volts then electrons crosses junction and joins with hole and current flows whereas in the reverse bias arrangement the from source attracts holes away from the junction.

Diodes can also be used as the voltage regulators, switching applications as current guides which also covers tuning devices, frequency multiplying devices and mixing devices which can be used to make logic decisions in digital circuits.

Zeners

• A zener diode is a special silicon diode
• When forward biased acts the same as an ordinary diode
• When reversed biased will conduct when the reverse voltage reaches a particular value
• The voltage drop is substantially constant as the current varies
• The voltage at which reverse conduction takes place is called the Zener voltage (VZ)
• Reverse voltage of zener diode makes it a valuable component for the regulation of the output voltage against both variation in the input voltage from an unregualated power supply or variation in the load resistance.
• The current through the zener will change to keep the voltage at within the limits of the threshold of zener action and the maximum power it can dissipate.

NOTE : The limits which are necessary for operation are that Vs > Vz, and that 1z >1zmin and less than 1zmax.

LED

As with the diode the LED must be connected in the forwad bias arrangement, this ensures the holes and electrons which cross the junction change energy levels and convert current directly into light.

Advantages of LED

• Emit light in proportion to the forward current through the diode
• Are low voltage devices that have a longer life than incandescent lamps
• physically small
• Respond quickly to changes in current (10 MHz) e.g Hi-stop light
• Shock and vibration resistant
• Low wattage
• Almost no heat generation
• LEDs have application in optical-fiber communication and diode lasers
  

Types of diode

The first diode is a semiconductor diode which could be a small signal diode of the 1N914 type commonly used in switching applications, a rectifying diode of the 1N4004 (400V 1A) type or even one of the high power, high current stud mounting types.

• Power Diodes (rectifier diodes)
  
• for higher power ratings the metal stud mount is more common

Resistors Colour Coding

The Resistors Colour Code

Number Colour

0 Black

1 Brown

2 Red

3 Orange

4 Yellow

5 Green

6 Blue

7 Voilet

8 Grey

9 White

• First two or three bands may be the numbers to write down


• Next band is the multiplier (how many zeros to add to the number )


• Gold multiplier makes one decimal place smaller, Silver makes two decimal places smaller


• Last band to right may be tolerance values


• Notice the examples on the right