1. Lecture 1 diode and applications_Updated 2.pdf
- 1. Lecture #1: Diodes & applications VNU-University of Engineering and Technology Faculty of Electronics and Telecommunications 1 2/9/2023
- 2. Outline 1. Introduction 2. The ideal diode 3. The real diode 4. Applications 5. Other diode 2 2/9/2023 Textbook: Adel. S. Sedra, Kenneth C. Smith. Microelectronic Circuits. Oxford University Press. 2011/2014 (Chapter 4). References: Thomas L. Floyd, Electronic devices, 9th edition, Prentice Hall (Section 2).
- 3. 1. Introduction • Diode is a semiconductor device which conduct the current in one directly only. The name diode comes from dielectrodes, that is, 2 electrodes. • Two terminals: Anode (A+) and Cathode (K-). • When the positive polarity is at the anode, the diode is forward biased and is conducting. • When the positive polarity is at the cathode, the diode is reversed biased and is not conducting. • If the reverse-biasing voltage is sufficiently large, the diode is in reverse-breakdown region and large current flows though it. 3 2/9/2023
- 4. (d) Equivalent circuit in the forward direction (a) Diode circuit symbol 2. The Ideal Diode 2.1 Current-Voltage characteristic • The ideal diode may be considered the most fundamental nonlinear circuit element (b) i-v characteristic (c) Equivalent circuit in the reserve direction 4 2/9/2023
- 5. 2. The Ideal Diode 2.2 Some applications – The rectifier (2) Rectifier circuit (1) Input waveform (3) Output waveform 5 2/9/2023 Another example is in our cars: the alternator charges the battery when the engine is running, but when the engine stops, a diode prevents the battery from discharging through the alternator.
- 6. Exercise 1 2/9/2023 6 For the circuit as shown:
- 8. 2. The Ideal Diode 2.2 Some applications – Diode Logic Gates 8 2/9/2023
- 9. • Assuming the diodes to be ideal, find the values of I and V. Exercise 2 9 2/9/2023
- 10. Exercise 3 Find the values of I and V in the circuits shown in below Fig. 1.4 10 2/9/2023 Fig. 1.4
- 12. 3. The Real Diode 3.1 The I-V characteristic • Knee voltage 12 2/9/2023
- 13. 3. The Real Diode 3.1 The I-V characteristic or 13 2/9/2023
- 15. Exercise 6: Find the change in diode voltage if the current changes from 0.1 mA to 10 mA. 15 2/9/2023 • Solution: we have V2 - V1 = 2.3 × VT × log(I2/I1) = 60 × log (10/0.1) = 120 (mV) Exercise 7: A silicon junction diode has v = 0.7 V at i = 1 mA. Find the voltage drop at i = 0.1 mA and i = 10 mA. Solution: we have V2 - V1 = 2.3 × VT × log(I2/I1) o i = 0.1 mA: V2 – 700 = 60 × log(0.1/1) => V2 - 700= -60 =>V2 = 640 mV = 0.64 V. o i = 10 mA: V2 – 700 = 60 × log(10/1) => V2 = 700 + 60 = 760 (mV) = 0.76 V.
- 16. 3. The Real Diode 3.1 The I-V characteristic 16 2/9/2023 Knee voltage •
- 17. 3. The Real Diode 3.2 Modeling the Diode Forward Characteristics • The exponential model: The most accurate description of the diode operation in the forward region is provided by the exponential model. Two ways for obtaining the solution of the 2 above equations: ✔ Graphical Analysis using the exponential model ✔ Iterative analysis using the exponential model 17 2/9/2023 (Kirchhoff loop)
- 18. • Graphical analysis using the exponential model 3. The Real Diode 3.2 Modeling the Diode Forward Characteristics 18 2/9/2023
- 19. • Iterative analysis using the exponential model 3. The Real Diode 3.2 Modeling the Diode Forward Characteristics 19 2/9/2023 Two equations can be solved using a simple iterative procedure, as illustrated in the following exercise.
- 21. 3. The Real Diode 3.2 Modeling the Diode Forward Characteristics • 21 2/9/2023 To speed up the analysis process, we must find a simpler model for the diode forward characteristic.
- 23. 3. The Real Diode 3.2 Modeling the Diode Forward Characteristics The small signal model: vD(t) = VD + vd(t) 23 → This is the small signal model of the diode, which applies for signal that has amplitude smaller than 5mV or iD = ID + id with The dynamic resistance:
- 25. Consider the circuit shown in the below figure for the case in which R = 10k. The power supply V+ has a DC value of 10 V on which is superimposed a 60Hz sinusoid of 1V peak amplitude. (This “signal” component of the power-supply voltage is an imperfection in the power-supply design. It is known as the power-supply ripple. More on this later.) Calculate both the dc voltage of the diode and the amplitude of the sine-wave signal appearing across it. Assume the diode to have a 0.7-V drop at 1-mA current. Exercise 11 a) Circuit for the Example b) Circuit for calculating the dc operating point c) Small signal equivalent circuit 25 2/9/2023
- 27. 3. The Real Diode 3.3 Zener diode Operation in the Reverse Region 27 2/9/2023 (knee current) (maximum current)
- 28. Exercise 12 28 Figure 4.19. (a) Circuit for example; (b) The circuit with the Zener diode replaced with its equivalent circuit model.
- 31. 4. Some application circuits using diodes 4.1 Rectifier circuits • Half-Wave Rectifier • Full-Wave Rectifier • Bridge Rectifier 31 2/9/2023 Fig.: Block diagram of a DC power supply Ripple Still contains a time-dependent
- 32. 4. Some application circuits using diodes 4.1 Rectifier circuits • Half-Wave Rectifier 32 2/9/2023
- 34. 4. Some application circuits using diodes 4.1 Rectifier circuits • Half-Wave Rectifier Real Diode? 34 Fig.: A simple circuit used to illustrate the effect of a filter capacitor. Fig.: Input & output waveforms assuming an ideal diode. Let the input vI be a sinusoid with a peak value Vp, and assume the diode to be ideal. The circuit provides a dc voltage output equal to the peak of the input sine wave. There is no way for the capacitor to discharge.
- 35. 4. Some application circuits using diodes 4.1 Rectifier circuits • Half-Wave Rectifier 35 2/9/2023 Ideal diode is peak-to-peak ripple voltage
- 36. 4. Some application circuits using diodes 4.1 Rectifier circuits • Full-wave Rectifier 36 2/9/2023
- 39. 4. Some application circuits using diodes 4.1 Rectifier circuits • The Bridge Rectifier 39 2/9/2023 Noted: the PIV is about half the value for the full-wave rectifier with a center-tapped transformer. This is another advantage of the bridge rectifier.
- 42. 4. Some application circuits using diodes 4.2 Limiting Circuits • Limiter/clipper circuits Transfer characteristic for a double limiter circuit 42 2/9/2023
- 43. 4. Some application circuits using diodes 4.2 Limiting Circuits • Limiter/clipper circuits 43 2/9/2023 double-anode zener
- 44. Exercise 16 Assuming the diodes to be ideal, describe the transfer characteristic of the circuit shown in the beside figure. 2/9/2023 44 • Solution: 2 diodes are cut-OFF for -5 ≤ vI ≤ +5 & vo = vI For vI ≥ -5 V: D2 is ON, D1 is OFF For vI ≤ -5 V: D1 is ON, D2 is OFF
- 45. 4. Some application circuits using diodes 4.3 Clamping Circuits • The Clamped Capacitor or DC Restorer 45 2/9/2023 A Clamper Circuit is a circuit that adds a DC level to an AC signal. As the DC level gets shifted, a clamper circuit is called as a Level Shifter. It shifts the waveform to a desired DC level without changing the shape of the applied signal (but only shifts the amplitude of the signal). Types of Clampers: Clamp circuits are categorised by their operation: negative or positive, and biased or unbiased. • Positive Clamper ✔Positive clamper with positive Vb ✔Positive clamper with negative Vb • Negative Clamper ✔Negative clamper with positive Vb ✔Negative clamper with negative Vb
- 46. 2/9/2023 Lecture # 1 - Diodes 46 4. Some application circuits using diodes 4.3 Clamping Circuits Positive Clamper Initially when the input is given, the capacitor is not yet charged and the diode is reverse biased. @ t0 the -25 V input signal appears across R1 & D1 (the C is a short at the first instant). The initial voltage across R1 & D1 causes a voltage spike in the output. The charge time of C1 through D1 is almost instantaneous, the duration of the pulse is so short → it has a negligible effect on the output. @ t1 the D1 is off (as open circuit) → KVL: VO = Vi + VC1 = 50 V. From t1 to t2, C1 has small discharge thru R1 so it has the voltage VC1 about +23 V and the VO drops from +50 V to +48 V. @ t2 the Vi changes from +25 V to -25 V. The input is now series opposing with the +23 V across C1. This leaves VO = -25 + 23 = -2 V. D1 is on. From t2 to t3, C1 charges from +23 V to +25 V; VO reaches to 0 volts. @ t3 the Vi and VC1 (voltage of C1) are again series adding. → VO is again +50 V. During t3 and t4, C1 discharges 2 V through R1. Then circuit operation from t3 to t4 is the same as it was from t1 to t2. D1 R1 C1 Vi VO
- 47. 2/9/2023 Lecture # 1 - Diodes 47 4. Some application circuits using diodes 4.3 Clamping Circuits Negative Clamper Initially when the input is given, the capacitor is not yet charged and the diode is reverse biased. In this case, you must explain how does the circuit works by yourself at home.
- 48. 2/9/2023 Lecture # 1 - Diodes 48 4. Some application circuits using diodes 4.3 Clamping Circuits ❑ Positive Clamper For the input signal is AC sin-wave, you must explain how does the circuit works by yourself at home. ❑ Negative Clamper
- 49. 2/9/2023 Lecture # 1 - Diodes 49 4. Some application circuits using diodes 4.3 Clamping Circuits ❑ Positive Clamper with negative biasing Vb ❑ Positive Clamper with positive biasing Vb The positive clamper can be biased with another voltage source to further shift the input signal waveform. The positive biasing further shifts up the waveform by the amount of the biasing voltage. The negative biasing lower down the waveform by the amount of the biasing voltage.
- 50. 4. Some application circuits using diodes 4.3 Clamping Circuits 50 2/9/2023 ❑ Negative Clamper with negative biasing Vb ❑ Negative Clamper with positive biasing Vb Positive Biasing The positive biasing of the negative clamper adds a positive or upward shift by the amount of biasing voltage to the negative clamped waveform. It shifts the waveform up to the positive level due to positive basing. The negative biasing of the negative clamper further shifts downward the input signal waveform.
- 51. 5. Some other types of diodes 5.1 Photo diode Photo Diode 51 2/9/2023
- 52. 5. Some other types of diodes 5.2 Light-emitting Diode (LED) 52 2/9/2023
- 53. HW #1: Select 10 HWs in the text-book from the list • Section 4.1: The ideal diode, from exe. 4.1 to exe. 4.16. • Section 4.2: The terminal characteristics of junction diodes, from exe. 4.17 to 4.31. • Section 4.3: Modeling the diode forward characteristic, from exe. 4.32 to 4.56. • Section 4.4: Operation in the Reverse breakdown region – Zener diodes, from exe. 4.57 to exe. 4.64. • Section: rectifier circuits, from exe 4.65 to exe. 4.84. • Section 4.6: limiting and clamping circuits, from exe. 4.85 to exe. 4.95. 2/9/2023 53