A 7 V DC supply is applied across a silicon diode in series with a 1 kΩ resistor. What is the approximate current flowing through the diode?
Electronics and Communication Engineering
Electronic Devices and Circuits
Difficulty: Easy
Choose an option
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A7 mA
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B6.3 mA
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C0.7 mA
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D0
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E10 mA
Answer
Correct Answer: 6.3 mA
Explanation
Introduction / Context:Diode bias problems are common in introductory electronics. When a forward bias voltage is applied with a series resistor, the diode drop is approximately constant (≈0.7 V for silicon), and the remainder of the supply drops across the resistor. Current is then easily computed using Ohm’s law.
Given Data / Assumptions:
- Supply voltage Vs = 7 V.
- Series resistor R = 1 kΩ.
- Forward diode drop Vd ≈ 0.7 V for silicon at normal currents.
Concept / Approach:Current through the circuit is set by the voltage across the resistor: I = (Vs − Vd)/R. Diode drop is assumed constant for estimation.
Step-by-Step Solution:
Vs = 7 V, Vd = 0.7 V.Voltage across resistor = 7 − 0.7 = 6.3 V.I = 6.3 / 1000 = 0.0063 A = 6.3 mA.Verification / Alternative check:
Checking: If diode drop were taken as 0.65 V, current would be 6.35 mA, still ≈ 6.3 mA. The approximation is valid.Why Other Options Are Wrong:
7 mA: ignores diode drop.0.7 mA: divides incorrectly by 10.0: false, since diode is forward biased.10 mA: requires different values of resistor/supply.Common Pitfalls:
Forgetting to subtract diode drop; mixing forward drop of Si vs Ge diodes.Final Answer:
6.3 mA