---
title: "Diode circuit current, eta 1.74, 6 V"
subject: "Electronics Devices and Circuit"
chapter: 1
key: "semester_3/electronics_devices_and_circuit:diode-current-eta-1p74-6v"
source: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/diode-current-eta-1p74-6v
site: BCT Engineering
---

# Diode circuit current, eta 1.74, 6 V

Electronics Devices and Circuit · Chapter 1: Diodes

- Asked in: 2070 Ashad, 6 marks
- Video: [Diode Current Equation || Lecture 10 Electronic Devices & Circuit || Explained in Urdu / Hindi](https://www.youtube.com/watch?v=uwg1sZuMPYQ) — Tuition Point
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/diode-current-eta-1p74-6v
- Whole chapter: https://www.bctengineer.com/md/semester_3/electronics_devices_and_circuit/chapter-1

## Question

In the given circuit, the diode used has its η = 1.74 and it conducts 1mA at forward bias voltage of 0.7V. Find the current flow in the circuit.
[Figure: V = 6 V source in series with R = 660 Ω and a diode D, current I = ?]

## Short answer

Using iterative KVL and diode equation, the diode voltage converges to 0.79 V. The circuit current is I = (6 − 0.79) / 660 ≈ 7.9 mA.

## Answer

The circuit is a source in series with a resistor and a diode. Use the diode equation with KVL and iterate.

#### Given
V = 6 V, R = 660 Ω, η = 1.74, ID = 1 mA at 0.7 V, VT = 25 mV, so η VT = 43.5 mV.

#### Equations
```text
VD = 0.7 + η VT ln(I / 1 mA) = 0.7 + 0.0435 ln(I/1 mA)
I  = (6 - VD)/660
```

#### Iteration
| Step | VD guess (V) | I = (6 - VD)/660 (mA) | New VD (V) |
|---|---|---|---|
| 1 | 0.700 | 8.030 | 0.7907 |
| 2 | 0.7907 | 7.893 | 0.7899 |
| 3 | 0.7899 | 7.894 | 0.7899 |

Converged: VD = 0.790 V.

```text
I = (6 - 0.790)/660 = 7.89 mA
```

**Answer: I ≈ 7.9 mA** (VD ≈ 0.79 V).

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What is eta VT here?
   A. 43.5 mV
   B. 1.74 mV
   C. 25 mV
   D. 660 mV
   Answer: A. 1.74 x 25 mV = 43.5 mV. (Key point: Given)

2. Which equation links I and VD?
   A. I = VD/660
   B. I = (6 - VD)/660
   C. I = (6 + VD)/660
   D. I = 6/660
   Answer: B. VDD = I R + VD. (Key point: KVL)

3. With VD = 0.7 V, what is I?
   A. 9.09 mA
   B. 8.03 mA
   C. 4 mA
   D. 1 mA
   Answer: B. I = (6 - 0.7)/660 = 8.03 mA. (Key point: First iteration)

4. What is the final current?
   A. About 0.79 mA
   B. About 9 mA
   C. About 7.9 mA
   D. About 8.0 mA
   Answer: C. VD converges to 0.790 V, so I = 7.89 mA. (Key point: Result)

## Close variants set in other exams

- [Diode circuit current, eta 1.74, 10 V](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Adiode-current-eta-1p74-10v) — Electronics Devices and Circuit, chapter 1, asked 4×
- [Diode circuit current, eta 1.74](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Adiode-current-eta-1p74) — Electronics Devices and Circuit, chapter 1, asked 4×

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