2.Switching Characteristics of Diode AMIT SIR lecture 1_repaired.pdf
- 1. Department of Electrical and Electronic Engineering Khulna University of Engineering & Technology Khulna-9203 Course code : EE 2113 Digital Electronics Presented By Amit Kumer Podder Assistant Professor Switching Characteristics of Diode And Transistor 1
- 2. Switching Circuit 10/5/2020 Amit Kumer Podder 2 A circuit which can turn ON or OFF current in an electrical circuit is known as a switching circuit. A switching circuit essentially consists of two parts viz. (i)a switch and (ii)associated circuitry. What is Switching Circuit? A switch is a device that can turn ON or OFF current in an electrical circuit. It is the most important part of a switching circuit. What is Switch? The switches can be broadly classified into the following three types (i) Mechanical switch (ii) Electro-mechanical switch or Relay (iii) Electronic switch
- 3. Switch 10/5/2020 Amit Kumer Podder 3 Mechanical Switch Limitation A switch which is operated mechanically to turn ON or OFF current in an electrical circuit is known as a mechanical switch. The familiar example of a mechanical switch is the tumbler switch used in homes to turn ON or OFF power supply to various appliances such as fans, heaters, bulbs etc. i. In the closed position, the switch carries the whole of the load current. For a large load current, the switch contacts have to be made heavy to enable them to carry the necessary current without overheating. This increases the size of the switch. ii. If the load current carried by the circuit is large, there will be sparking at the contacts of the switch during breaking operation. This results in the wear and tear of the contacts. iii. Due to high inertia of a mechanical switch, the speed of operation is very small
- 4. Switch 10/5/2020 Amit Kumer Podder 4 Electro-mechanical Switch or Relay It is a mechanical switch which is operated electrically to turn ON or OFF current in an electrical circuit. When the switch S is closed, the lever is pulled downward and the armature A closes the relay contacts 1 and 2. This turns ON current in the circuit. When switch S is opened, the solenoid is de-energised and the spring pulls the lever and hence the armature A upwards. Consequently, the relay contacts 1 and 2 are opened and current flow in the circuit is interrupted.
- 5. 10/5/2020 Amit Kumer Podder 5 Electro-mechanical Switch or Relay (i) The relay or electro-mechanical switch requires a small power for its operation. (ii) The switch in the relay coil carries a small current as compared to the load current. This permits the use of a smaller switch in the relay coil circuit. (iii)The operator can turn ON or OFF power to a load even from a distance. This is a very important advantage when high voltages are to be handled. (iv) There is no danger of sparking as the turning ON or OFF is carried by the relay coil switch which carries a small current. Advantages Limitations The speed of operation is very small; less than 5 operations per second. A relay has moving parts and hence there is considerable wear and tear.
- 6. 10/5/2020 Amit Kumer Podder 6 Electronic Switch It is a device which can turn ON or OFF current in an electrical circuit with the help of electronic devices e.g., transistors or tubes. Electronic switches have become very popular because of their high speed of operation and absence of sparking.
- 7. 10/5/2020 Amit Kumer Podder 7 Electronic Switch (i) It has no moving parts and hence there is little wear and tear. Therefore, it gives noiseless operation. (ii) It has smaller size and weight. (iii)It gives trouble free service because of solid state. (iv) It is cheaper than other switches and requires little maintenance. (v) It has a very fast speed of operation say up to 𝟏𝟎𝟗operations per second. On the other hand, the mechanical switches have a small speed of operation e. g. less than 5 operations in a second. Advantages
- 8. 10/5/2020 Amit Kumer Podder 8 Study Area We will learn mainly how Diode and Transistor acts as an switch
- 9. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 9 Whenever a specified voltage is exceeded, the diode resistance gets increased, making the diode reverse biased and it acts as an open switch. Whenever the voltage applied is below the reference voltage, the diode resistance gets decreased, making the diode forward biased, and it acts as a closed switch. The following circuit explains the diode acting as a switch.
- 10. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 10 P-type Material N-type Material Anode cathode 𝑝𝑝𝑜 𝑛𝑝𝑜 𝑝𝑛𝑜 𝑛𝑛𝑜 P-type N-type 𝑥 = 0 The majority carriers in P-type (holes) = The majority carriers in N-type (electrons) = The minority carriers in P-type (electrons) = 𝑛𝑝𝑜 The minority carriers in N-type (holes) = 𝑝𝑛𝑜 𝑝𝑝𝑜 𝑛𝑛𝑜
- 11. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 11 𝑝𝑝𝑜 𝑛𝑝𝑜 𝑝𝑛𝑜 𝑛𝑛𝑜 P-type N-type 𝑥 = 0 P-type Material N-type Material During Forward biased Condition − The minority carriers are more near junction and less far away from the junction.
- 12. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 12 𝑝𝑝𝑜 𝑛𝑝𝑜 𝑝𝑛𝑜 𝑛𝑛𝑜 P-type N-type 𝑥 = 0 P-type Material N-type Material During reverse bias condition − Majority carriers doesn’t conduct the current through the junction and hence don’t participate in current condition. The minority carriers will cross the junction and conduct the current, which is called as Reverse Saturation Current.
- 13. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 13
- 14. Diode as a Switching Device 10/5/2020 Amit Kumer Podder 14 Storage time − The time period for which the diode remains in the conduction state even in the reverse biased state, is called as Storage time. Transition time − The time elapsed in returning back to the state of non-conduction, i.e. steady state reverse bias, is called Transition time. Reverse recovery time − The time required for the diode to change from forward bias to reverse bias is called as Reverse recovery time. Forward recovery time − The time required for the diode to change from reverse bias to forward bias is called as Forward recovery time.
- 15. Transistor as a Switching Device OFF Condition When the base input voltage is enough negative, the transistor is cut off and no current flows in collector load. As a result, there is no voltage drop across RC and the output voltage is *ideally. i.e., 𝐼𝑐= 0 and 𝑉𝑐𝐸 = 𝑉 𝑐𝑐 10/5/2020 Amit Kumer Podder 15
- 16. Transistor as a Switching Device ON Condition When the input base voltage is positive enough that transistor saturates, then 𝐼𝑐(𝑠𝑎𝑡) will flow through 𝑅𝑐 . Under such conditions, the entire 𝑉 𝑐𝑐 will drop across collector load 𝑅𝑐 and output voltage is ideally zero i.e., 𝐼𝑐 = 𝐼𝑐(𝑠𝑎𝑡) = 𝑉𝑐𝑐 𝑅𝑐 𝑉𝐶𝐸 = 0 10/5/2020 Amit Kumer Podder 16
- 17. Thank You 10/5/2020 Amit Kumer Podder 17