Correct Answer

Concept & PrincipleElectricalElectronics

Option C

$\mu A$

Quick Summary: The reverse current, also known as reverse saturation current ($I_0$ or $I_S$), in a standard silicon PN junction diode is very small and typically ranges in the micro-ampere ($µA$) or nano-ampere ($nA$) range at room temperature. This current is primarily due to the flow of minority charge carriers across the junction under reverse bias conditions.

💡 Explanation

The reverse current, also known as reverse saturation current ( $I_0$ or $I_S$ ), in a standard silicon PN junction diode is very small and typically ranges in the micro-ampere ( $µA$ ) or nano-ampere ( $nA$ ) range at room temperature. This current is primarily due to the flow of minority charge carriers across the junction under reverse bias conditions.

🔢 Key Formulas

$I_D = I_S (e^{\frac{V_D}{n V_T}} - 1)$ — The Shockley diode equation, where $I_S$ is the reverse saturation current

$I_R \approx I_S$ — The approximation for reverse current under reverse bias ( $V_D < 0$ )

⚙️ Working Principle

When a diode is reverse-biased, the potential barrier at the junction increases, preventing majority carriers from crossing. However, thermal energy generates electron-hole pairs, allowing minority carriers to cross the junction. Since the number of thermally generated minority carriers is small, the resulting reverse saturation current remains extremely low and is essentially independent of the applied reverse voltage until the breakdown voltage is reached.

📌 Key Points

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Reverse current is primarily dependent on temperature rather than the applied reverse voltage.
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For silicon diodes, $I_S$ is generally smaller than in germanium diodes due to the larger energy band gap.
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Reverse saturation current approximately doubles for every $10°C$ rise in temperature.

✅ Advantages

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Minimizes power dissipation in the OFF state
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Allows for high-efficiency rectification

❌ Disadvantages / Limitations

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Temperature sensitivity can lead to thermal runaway
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Limits the high-temperature operating range of circuits

🛠️ Applications / Uses

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Signal detection and rectification
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Voltage clamping and clipping circuits

📄 Additional Information

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Germanium diodes typically have higher $I_S$ (in the range of $\mu A$ ) compared to silicon diodes ( $nA$ range).
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Option A (KA) represents massive current, Option B (mA) is typical for forward current, and Option D (A) is for high-power devices.

📊 Diagram / Illustration

✅

C is correct — The reverse current in a diode is typically of the order of $\mu A$ (micro-amperes) due to the low concentration of thermally generated minority charge carriers.

Core Concepts Used

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PN Junction Diode Reverse Bias Minority Charge Carriers Reverse Saturation Current

💡 EXAM TIP

Always remember that while forward current depends on the barrier potential and resistance, reverse current is a leakage phenomenon dominated by ambient temperature.

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