Part 3 Diods OpAmps - Electronic & Computer...

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www.brunel.ac.uk/about/acad/sed Diodes (Basic Theory) N P P N R Vs Forward Bias R Vs Reversed Bias
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www.brunel.ac.uk/about/acad/sed Diode Curves ~0.7 for Si ~0.3 for Ge
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www.brunel.ac.uk/about/acad/sed Diode Characteristics • Knee voltage (Barrier potential) – The forward voltage when the current starts to increase rapidly – V = 0.7 (Si), V = 0.3 (Ge) • Bulk Resistance (R B ) – The resistance of the diode after the knee voltage – r B = r N + r P – Typical value = 1 ohm
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www.brunel.ac.uk/about/acad/sed Diode Characteristics • Current Limiting Resistor I = (V S – V D ) / R • Maximum Power Dissipation The maximum power that the diode can dissipate without degrading its performance or reducing its life P = V D * I R Vs V D
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www.brunel.ac.uk/about/acad/sed Diode Characteristics • Maximum Forward Current (I F ) The maximum current that the diode can safely handle without degrading its performance or reducing its life
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www.brunel.ac.uk/about/acad/sed Examples • A diode has r P = 0.13 ohm and r N = 0.1 ohm, what is its bulk resistance? Solution r B = r N + r P = 0.13 + 0.1 = 0.23 ohms
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www.brunel.ac.uk/about/acad/sed Example • Find the diode current, Vs = 10 V, R = 1000 ohm, (assume silicon diode) I = (Vs – Vd ) / R = (10 – 0.7) / 1000 = 9.3mA R Vs V D
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www.brunel.ac.uk/about/acad/sed Example • The voltage across 1N4001 is 0.93 V when the current is 1A, what is the power dissipated by the diode? • P = V D * I = 0.93 * 1 = 0.93 Watt
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www.brunel.ac.uk/about/acad/sed Diode Behaviour
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www.brunel.ac.uk/about/acad/sed One way model (Ideal) Use an ideal diode to calculate the load current, voltage, power, diode power, and total power • I L = 10/1K = 10mA • V L = 10 V • P L = 10 x 10m = 0.1 Watt • P D = 0 X 10m = 0 Watt • P T = 0 + 0.1 = 0.1 Watt 1K Vs 10V 1N4001
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www.brunel.ac.uk/about/acad/sed 2 nd approximation Model 0.7V I V P N 0.7V Forward bias 0.7V Reverse bias
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www.brunel.ac.uk/about/acad/sed Example Use the 2 nd approximation model to calculate the load current, voltage, power, diode power, and total power • I L = (10-0.7)/1K = 9.3mA • V L = 9.3mA 1K = 9.3 V • P L = 9.3 x 9.3m = 86.5 mW • P D = 0.7 X 9.3m = 6.51mW • P T = 6.51 + 86.5 = 93 mW 1K Vs 10V 1N4001
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Part 3 Diods OpAmps - Electronic & Computer...

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