1. Diode Theory
Chap - 3
Release 1-Sep-2010
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2. Chapter Objectives Define diodes
Explain the concept of a bias in a diode
Explain the types of diodes
Identify the use of diode in a rectifier (half wave, full wave and bridge rectifiers)
Identify the use of diodes and rectifiers in a computer
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3. Recall
Semiconductors have four electrons in their outer shell. Semiconductors do not give up or accept electrons
Germanium and silicon are most common examples of semiconductors
The process of doping increases the conductivity of semiconductors
When a pure semiconductor is doped with arsenic, an N-type material is created which contains large number of free electrons
When a pure semiconductor is doped with gallium, P-type material is created which contains large number of holes
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4. Diodes
Diode is an electronic device which allows current to flow only in one direction
Diodes are formed by joining the N-type and P-type semiconductors
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5. Barrier Voltage
Barrier voltage prevents the further combination of electrons and holes which limits the size of depletion region
Barrier Voltage is higher for a silicon PN junction diode as compared to germanium PN junction diode
Barrier Voltage cannot be measured because it exists inside the junction diode
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6. Home work
What is the barrier voltage value for silicon and germanium diode?
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7. Diode Biasing
The voltage applied to the semiconductor diode is referred to as bias voltage.
The type of bias voltages:
Forward Bias
Reverse Bias
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8. Forward Bias
A forward biased diode conducts current in the forward direction
A forward biased diode conducts current as long as a high external bias voltage with correct polarity is applied
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9. Reverse Bias
Extremely small current flows through the diode during reverse biasing. The minority carriers are forced towards the junction where they combine and support an extremely small current
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10. Types of Diode I
There are several diodes available in the market. Each
type of diode has its own characteristic, which make
them suitable for different electronic devices.
PN Junction Diode
These are standard types of diodes. They are formed by combining a P-type and an N-type semiconductor. These diodes are used in radio frequency applications.
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11. Types of Diode II Zener Diode
PN junction diode
Zener Diode
Zener diodes have a low pre-determined Reverse Breakdown Voltage called Zener Voltage (Vzk).
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12. Types of Diode III Light Emitting Diode
The LED diodes are used in television sets to indicate whether the television is on or is on a standby mode.
Photodiode
Photodiodes are used for detecting light in optical fibers and other light-sensitive applications.
Dfd
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13. Home work Show the sample components of LED and photo diode.
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14. Types of Diode IV Schottky Diodes
It is used in radio frequency applications.
PIN Diodes
Used in power rectifiers and RF protection circuits.
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15. Use of diode in a Rectifier - I
The description of the following types of rectifiers would explain the use of diodes in each of them:
Half wave Rectifier
Full wave Rectifier
Bridge Rectifier
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16. Use of diode in a Half wave Rectifier - I
A rectifier which converts an AC signal into DC by allowing either positive or negative cycle of an incoming AC signal is called a Half Wave rectifier. The output is a series of positive or negative pulses, depending on how diode is connected in the circuit.
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17. Use of diode in a Half wave Rectifier -II
A silicon diode is placed in series with the load so that current can flow in only one direction and not in the other.
During positive cycle diode is forward biased . So that the diode offers very low resistance and allow the current flow.
In the negative half cycle, the diode is reverse biased and hence it conducts no current.
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18. Hands on Perform the practical of Half-wave rectifier on Oscilloscope
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19. Use of diode in a Full wave Rectifier - I
A rectifier which converts an AC signal into DC by allowing both positive and negative cycles of an
incoming AC signal is called as a Full Wave rectifier.
In Full wave rectifier, circuit uses two diodes D1 and D2 with center tapped transformer.
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20. Use of diode in a Full wave Rectifier - II
During the positive half cycle of secondary, diode D1 becomes forward biased and D2 is reverse biased. Hence diode D1 conducts and D2 does not.
During negative half cycle, D2 becomes forward biased and D1 is reverse biased. Hence D2 conducts and D1 does not.
The output of a full wave rectifier is shown below.
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21. Use of diode in a Bridge Rectifier- I
Bridge rectifier contains four diodes D1, D2, D3 and D4.
During the positive half cycle of secondary voltage,
the end P becomes positive and Q negative. Thus diode D1 and D3 become forward biased and start
conducting. D2 and D4 are reverse biased.
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22. Use of diode in a Bridge Rectifier- II
During negative half cycle of secondary voltage, the end P becomes negative and end Q positive. Then diodes D2 and D4 are forward biased and D1 and D3 becomes reverse biased.
The output wave form is shown below.
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23. Use of diodes and rectifiers in a computer
Diodes are used to create power supplies and voltage doublers.
Rectifiers are specific assemblies of diodes , which act as a power regulator for your computer.
Rectifiers help in reducing power losses, and thus help in creating a cooler operating temperature.
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24. Summary - I
Diode is an electronic device which allows current to flow only in one direction
Barrier voltage prevents the further combination of electrons and holes which limits the size of depletion region
Bias voltage is the voltage applied across a semiconductor diode
A forward biased diode conducts current in the forward direction
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25. Summary - II
A reverse biased diode conducts current in the opposite direction
PN junction, Zener, Light Emitting Diode (LED), Photodiode and Schottky are the most widely used types of diodes
Rectifier is an electronic circuit used for converting an alternating current to direct current.
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26. Summary - III
A rectifier which converts an AC signal into DC by allowing either positive or negative cycle of an incoming AC signal is called a Half Wave rectifier.
A rectifier which converts an AC signal into DC by allowing both positive and negative cycles of an incoming AC signal is called as a Full Wave rectifier.
Release 1-Sep-2010
Jetking Infotrain Ltd.