115A_1_EE115A_W10-Chap3

115A_1_EE115A_W10-Chap3 - Chapter 3 Diode Circuits h 3.1...

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Unformatted text preview: Chapter 3 Diode Circuits h 3.1 Ideal Diode 52 h 3.2 PN Junction as a Diode h 3.3 Applications of Diodes Diode Circuits CH3 Diode Circuits 53 h After we have studied in detail the physics of a diode, it is time to study its behavior as a circuit element and its many applications. Diode’s Application: Cell Phone Charger CH3 Diode Circuits 54 h An important application of diode is chargers. h Diode acts as the black box (after transformer) that passes only the positive half of the stepped-down sinusoid. Diode’s Action in The Black Box (Ideal Diode) CH3 Diode Circuits 55 h The diode behaves as a short circuit during the positive half cycle (voltage across it tends to exceed zero), and an open circuit during the negative half cycle (voltage across it is less than zero). Ideal Diode CH3 Diode Circuits 56 h In an ideal diode, if the voltage across it tends to exceed zero, current flows. h It is analogous to a water pipe that allows water to flow in only one direction. Diodes in Series CH3 Diode Circuits 57 h Diodes cannot be connected in series randomly. For the circuits above, only a) can conduct current from A to C. IV Characteristics of an Ideal Diode ∞ = = ⇒ = R V I R = = ⇒ ∞ = R V I R CH3 Diode Circuits 58 h If the voltage across anode and cathode is greater than zero, the resistance of an ideal diode is zero and current becomes infinite. However, if the voltage is less than zero, the resistance becomes infinite and current is zero. Anti-Parallel Ideal Diodes CH3 Diode Circuits 59 h If two diodes are connected in anti-parallel, it acts as a short for all voltages. Diode-Resistor Combination CH3 Diode Circuits 60 h The IV characteristic of this diode-resistor combination is zero for negative voltages and Ohm’s law for positive voltages. Diode Implementation of OR Gate CH3 Diode Circuits 61 h The circuit above shows an example of diode-implemented OR gate. Input/Output Characteristics CH3 Diode Circuits 62 h When V in is less than zero, the diode opens, so V out = V in . h When V in is greater than zero, the diode shorts, so V out = 0. Diode’s Application: Rectifier CH3 Diode Circuits 63 h A rectifier is a device that passes positive-half cycle of a sinusoid and blocks the negative half-cycle or vice versa. h When V in is greater than 0, diode shorts, so V out = V in ; however, when V in is less than 0, diode opens, no current flows thru R 1 , Vout = I R1 R 1 = 0. Signal Strength Indicator ω s 1 sin 1 ) ( 1 2 / 2 / , p T p T p T out avg out V V tdt V T dt t V T V = = ∫ ∫ 2 T t ≤ ≤ for t p V out V ω sin = CH3 Diode Circuits 64 h The averaged value of a rectifier output can be used as a signal strength indicator for the input, since V out,avg is proportional to V p , the input signal’s amplitude....
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115A_1_EE115A_W10-Chap3 - Chapter 3 Diode Circuits h 3.1...

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