Electronic principles - Chapter 3

Tham khảo tài liệu electronic principles - chapter 3, kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả
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Electronic principles - Chapter 3 Chương 3Lý thuyết diode Từ Vựng (1)• anode• bulk resistance = điện trở khối• cathode• diode• ideal diode = diode lý tưởng• knee voltage = điện áp gối• linear device = dụng cụ tuyến tính• load line = đường tải Từ Vựng (2)• maximum forward current = dòng thuận cực đại• nonlinear device = dụng cụ phi tuyến• Ohmic resistance = điện trở Ohm• power rating = định mức công suất• up-down analysis = phân tích tăng-giảm Nội dung chương 33-1 Các ý tưởng cơ bản3-2 Diode lý tưởng3-3 Xấp xỉ bậc 23-4 Xấp xỉ bậc 33-5 Trounleshooting3-6 Phân tích mạch tăng-giảm3-7 Đọc bảng dữ liệu3-8 Cách tính điện trở khối3-9 Điện trở DC của diode3-10 Đường tải3-11 Diode dán bề mặt Properties of Diodes Properties Figure 1.10 – The Diode Transconductance Curve2 ID (mA) • VD = Bias Voltage • ID = Current through Diode. ID is Negative Diode. for Reverse Bias and Positive for Forward IS Bias BiasVBR • IS = Saturation Current Current VD ~Vφ • VBR = Breakdown Voltage Voltage • Vφ = Barrier Potential Voltage Voltage (nA) Kristin Ackerson, Virginia Tech EE Spring 2002 Properties of Diodes Properties The Shockley Equation• The transconductance curve on the previous slide is characterized by The the following equation: the ID = IS(eVD/η VT – 1)• As described in the last slide, ID is the current through the diode, IS is the saturation current and VD is the applied biasing voltage. the• VT is the thermal equivalent voltage and is approximately 26 mV at room temperature. The equation to find VT at various temperatures is: temperature. VT = kT kT q k = 1.38 x 10-23 J/K T = temperature in Kelvin q = 1.6 x 10-19 C 1.38∀ η is the emission coefficient for the diode. It is determined by the way the diode is constructed. It somewhat varies with diode current. For a silicon diode η is around 2 for low currents and goes down to about 1 at higher currents at Kristin Ackerson, Virginia Tech EE Spring 2002 Diode Circuit Models DiodeThe Ideal DiodeThe The diode is designed to allow current to flow in The Model only one direction. The perfect diode would be a Model perfect conductor in one direction (forward bias) and a perfect insulator in the other direction (reverse bias). In many situations, using the ideal diode approximation is acceptable. diodeExample: Assume the diode in the circuit below is ideal. Determine theExample:value of ID if a) VA = 5 volts (forward bias) and b) VA = -5 volts (reversevaluebias)bias) a) With VA > 0 the diode is in forward bias RS = 50 Ω and is acting like a perfect conductor so: and ID = VA/RS = 5 V / 50 Ω = 100 mA ID + b) With VA < 0 the diode is in reverse biasVA _ and is acting like a perfect insulator, therefore no current can flow and ID = 0. therefore Kristin Ackerson, Virginia Tech EE Spring 2002 Diode Circuit Models DiodeThe Ideal Diode withThe This model is more accurate than the simple This Barrier Potential ideal diode model because it includes the Barrier approximate barrier potential voltage. Remember the barrier potential voltage is the + Vφ voltage at which appreciable current starts to flow. flow.Example: To be more accurate than just using the ideal diode modelExample:include the barrier potential. Assume Vφ = 0.3 volts (typical for aincludegermanium diode) Determine the value of ID if VA = 5 volts (forward bias).germanium RS = 50 Ω With VA > 0 the diode is in forward bias and is acting like a perfect conductor ID so write a KVL equation to find ID: so ...