107_16 - 1 Electrical Engineering Technology EET 107...

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Unformatted text preview: 1 Electrical Engineering Technology EET 107 Introduction to Circuit Analysis Lecture # 16 Professor Robert Herrick Purdue University © EET 107 - 16 Introduction to Circuit Analysis 2 Summary VDR – Voltage Divider Rule Real Voltage Supplies Purdue University © EET 107 - 16 Introduction to Circuit Analysis 3 VDR Voltage Divide Rule Purdue University © EET 107 - 16 Introduction to Circuit Analysis 4 VDR – Voltage Divider Rule SERIES CIRCUITS ONLY ! ! ! Same Purdue University © CURRENT ! ! ! EET 107 - 16 Introduction to Circuit Analysis 5 Establish References + VR1− + VR2− R1 R2 I E R3 RT Series Circuit: + VR3 − I = IR1 = IR2 = IR3 R T = R1 + R 2 + R 3 Purdue University © EET 107 - 16 Introduction to Circuit Analysis 6 VDR – Voltage Divider Rule + VR1− + VR2− R1 R2 I E RT Ohm’s Law R3 + VR3 − VR1 = R1 I VR2 = R2 I VR3 = R3 I Circuit I = E/RT Purdue University © EET 107 - 16 Introduction to Circuit Analysis 7 VDR – Voltage Divider Rule Ohm’s Law VR1 = R1 ( E/RT ) = ( R1 / RT ) E VR2 = R2 ( E/RT ) = ( R2 / RT ) E VR3 = R3 ( E/RT ) = ( R3 / RT ) E Purdue University © EET 107 - 16 Introduction to Circuit Analysis 8 VDR – Voltage Divider Rule SHORT CUT + VR1− R1 E RT R2 No current calculation R3 VR1 = ( R1 / RT ) E ( R1 / RT ) is the fraction of E dropped across R1. is fraction Purdue University © EET 107 - 16 Introduction to Circuit Analysis 9 VDR – Resistances in Series + R1 E − V R12 RT R2 R3 Combination of R1 and R2 in series. VR12 Purdue University © EET 107 - 16 R1 + R2 E = R T Introduction to Circuit Analysis 10 VDR – Voltage Divider Rule Current I must be the SAME SAME to apply VDR ! ! ! Purdue University © EET 107 - 16 Introduction to Circuit Analysis 11 Voltage Divider Rule Example 1 Purdue University © EET 107 - 16 Introduction to Circuit Analysis 12 Establish References + VR1− I E 12V + VR2− R1 1k R2 2k VDR R3 3k + VR3 − Magnitude Only CURRENT direction still establishes POLARITY ! POLARITY Purdue University © EET 107 - 16 Introduction to Circuit Analysis 13 VDR Example - RT + VR1− + VR2− R1 1k R2 2k I E 12V RT R3 3k + VR3 − RT = R1 + R2 + R3 RT = 1kΩ + 2kΩ + 3kΩ = 6kΩ Purdue University © EET 107 - 16 Introduction to Circuit Analysis 14 VDR – Find Resistor Voltage Drops + VR1− I E 12V R1 1k R2 2k VR1 = ( 1kΩ / 6kΩ ) 12V = 2V 2V + VR2− R3 3k + VR3 − VR2 = ( 2kΩ / 6kΩ ) 12V = 4V 4V VR3 = ( 3kΩ / 6kΩ ) 12V = 6V 6V Doubling R, doubles the voltage. Same results as using Ohm’s law without “I” calculation. Purdue University © EET 107 - 16 Introduction to Circuit Analysis 15 VDR – Current I Calculation Buried 2mA + VR1− I E 12V + VR2− R1 1k R2 2k R3 3k + VR3 − VR1 = ( 1kΩ / 6kΩ ) 12V Swap E and R1 VR1 = ( 12V / 6kΩ ) 1kΩ VR3 = ( 2mA ) 1kΩ = 2V Purdue University © EET 107 - 16 Introduction to Circuit Analysis 16 VDR – Resistances in Series + E 12V − VR12 R1 1k RT R2 2k VR12 R3 3k VR12 Purdue University © R1 + R2 E = R T 1 kΩ + 2 kΩ 12 V = 6 V = 6 kΩ EET 107 - 16 Introduction to Circuit Analysis 17 +6 V VDR – Bubble Notation a R1 1k + VR1 − E = ( 6V) – (−6V) = 12V 12V + VR2 − VR1 = ( 1kΩ / 6kΩ ) 12V = 2V 2V + VR3 − VR23 = Vbd = ( 5kΩ / 6kΩ ) 12V = 10V 10V b R2 2k c R3 3k d −6 V Purdue University © EET 107 - 16 Introduction to Circuit Analysis 18 BJT - Voltage Divider Bias Example 2 Purdue University © EET 107 - 16 Introduction to Circuit Analysis 19 BJT – Voltage Divider Bias +E supply R1 IR1 B relatively 0 mA IB b IR2 R2 Beta independent circuit Good beta β > 50 50 Q IR1 >> IB IR1 ≅ IR2 essentially series essentially series Purdue University © EET 107 - 16 Introduction to Circuit Analysis 20 BJT – Voltage Divider Bias +E supply +E supply R1 + VR1 − VB = VR2 b VB R2 Essentially Series + VR2 − Q R2 E supply VB = R +R 2 1 0V See Ch. 8 example. Purdue University © EET 107 - 16 Introduction to Circuit Analysis 21 MOSFET Example 3 Purdue University © EET 107 - 16 Introduction to Circuit Analysis 22 MOSFET – Voltage Divider Bias +Esupply R1 + VR1 − Essentially Series Ilamp IR1 ≅ IR2 Q R2 + VR2 − +V GS − IG=0A VGS = VR2 R2 VGS = R +R 1 2 E supply See Ch. 8 example design problem. Purdue University © EET 107 - 16 Introduction to Circuit Analysis 23 Real Voltage Supplies Purdue University © EET 107 - 16 Introduction to Circuit Analysis 24 IDEAL Voltage Supply – Fixed Output 0 mA E 12 V + open 12 V − (a) 1 mA R 12 k E 12 V (b) + 12 V − 1A E 12 V R 12 + 12 V − (c) E = 12 V with varying loads (a) I = 0A (b) I = 1mA (c) I = 1A Purdue University © EET 107 - 16 Introduction to Circuit Analysis 25 Never SHORT a Voltage Supply ∞A E 12 V Bad news ! ! I = 12V / 0Ω = ∞A Real power supplies are current limited. Purdue University © EET 107 - 16 Introduction to Circuit Analysis 26 UNLOADED Real Voltage Supplies Rsupply Esupply Rsupply External supply terminals Isupply Esupply + Vsupply − VNL - No Load Voltage VOC - Open Circuit Voltage Vsupply = VNL = VOC = Esupply Purdue University © EET 107 - 16 Introduction to Circuit Analysis 27 LOADED Real Voltage Supplies Rsupply + VRsupply − Esupply Isupply + Iload Vsupply Rload − + Vload − KVL walkabout and Ohm’s Law Loaded Vsupply = Esupply − Isupply Rsupply Purdue University © EET 107 - 16 Introduction to Circuit Analysis 28 VDR - LOADED Real Voltage Supplies Rsupply + VRsupply − Esupply Isupply + Vsupply Iload Rload − Vsupply = Vload Purdue University © + Vload − Rload E supply = Rload + Rsupply EET 107 - 16 Introduction to Circuit Analysis 29 IDEAL Supply Resistance Rsupply + VRsupply − Isupply Esupply + Vsupply − Ideal Supply Iload Rload + Vload − Rsupply = 0Ω SHORT Rload E supply = E supply Vsupply = Vload = R + 0Ω load Purdue University © EET 107 - 16 Introduction to Circuit Analysis 30 Power Supply Example No load voltage = 20 V Supply resistance = 1 Ω Load resistance = 100 Ω Find Iload, Vload, and VRsupply Purdue University © EET 107 - 16 Introduction to Circuit Analysis 31 IDEAL Supply Resistance 20V 1Ω Rsupply + VRsupply − Isupply Esupply + Vsupply − Iload Rload 100Ω + Vload − Series Circuit Isupply = Iload = 20V / 101Ω = 198mΑ Vsupply = Vload = 198mΑ × 100 Ω = 19.8V VRsupply = 20V – 19.8V = 0.2V Purdue University © EET 107 - 16 Introduction to Circuit Analysis 32 Maximum Load Current Power Supplies are Rated MAXIMUM Load Current at a specified voltage For example: 1 A at 20 V Purdue University © EET 107 - 16 Introduction to Circuit Analysis 33 Power Supply Example MAX rating of 1A at 20V under full load. Esupply Its N0 LOAD voltage is 20.2V Find its internal resistance. See Ch. 8 – more examples Purdue University © EET 107 - 16 Introduction to Circuit Analysis 34 IDEAL Supply Resistance 20.2V 1A Rsupply + VRsupply − Isupply Esupply + Vsupply − Iload Rload + Vload − 20V VRsupply = 20.2V – 20V = 0.2V Series Circuit Rsupply = 0.2V / 1A = 0.2Ω Purdue University © EET 107 - 16 Introduction to Circuit Analysis 35 Load Percent Voltage Regulation Quantify the Quality of a Real Power Supply VNL − VFL 100% %VR = V FL Ideally VNL = VFL So ideally %VR = 0% Purdue University © EET 107 - 16 Introduction to Circuit Analysis 36 Load Percent Voltage Regulation Our example: VNL=20.2V VFL = 20V VNL − VFL 100% %VR = V FL 20.2 V − 20 V 100% = 1% %VR = 20 V Purdue University © EET 107 - 16 Introduction to Circuit Analysis 37 Summary VDR – Voltage Divider Rule Real Voltage Supplies Purdue University © EET 107 - 16 Introduction to Circuit Analysis ...
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