Copyright 2001, Regents of University of CaliforniaEECS 42 Intro. electronics for CS Fall 2001 Lecture 5: 9/12/01 A.R. NeureutherVersion Date 9/10/01Lecture 5: September 12th, 2001Graphical Solutions and PowerA) Load line methodB) PowerC) Nonlinear elementsReading: Schwarz and Oldham 3.2-3.3Copyright 2001, Regents of University of CaliforniaEECS 42 Intro. electronics for CS Fall 2001 Lecture 5: 9/12/01 A.R. NeureutherVersion Date 9/10/01Summary• Load line method uses I vs. V for the element and finds the curve of I vs. V that satisfies the element.• The circuit in which the element is to function is then characterized by a plot of ILOADvs. VLOAD on the same axes by looking back into the circuit from the element and representing it as a Thevenin or Norton equivalent circuit.• The intersection of these two curves gives a point or points that simultaneously meet the constraints of the element and the constraints of the circuit.• Example: see 3.1 in text pp. 89 for an element; circuit is ideal voltage source and series resistor– Case 1: 3V source and 100 ohms series resistor => 2.5V and 5 mA– Case2: 1V source and 100 ohms series resistor => 1.5V and –5 mACopyright 2001, Regents of University of CaliforniaEECS 42 Intro. electronics for CS Fall 2001 Lecture 5: 9/12/01 A.R. NeureutherVersion Date 9/10/01• Power into the element is IEVEand is given by the rectangular area between the intersection point and the horizontal and vertical axes. – Case 1: (5 MA)(2.5V) = 12.5 mW– Case 2: (-5mA)(1.5V) = -7.5 mW• Power from the source is ISVS= IEVS– Case 1: (5 MA)(3V) = 15 mW (rest is into resistor)– Case 2: (-5mA)(1V) = -5 mW (rest is into resistor)• Nonlinear elements have I vs. V curves that are not straight butthe procedure is the same• Example: Light Emitting Diode – design a bias to produce 20 mA at 4 V– Three 1.5V batteries plus total of 25 ohms resistance– 9V battery plus 250 ohms of resistance– The former has better battery power to light efficiency but the latter is better in case high temperatures occur as the current versus voltage tends to double for every 5 degrees C.
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