- Asked 4/28
- 2080 Baisakh · 5 marks
- 2072 Kartik · 6 marks
Diode circuit current, eta 1.74
Short answer
Iterate ID = (5–VD)/500 and VD = 0.7 + 0.0435 ln(ID/1mA). The solution converges to VD ≈ 0.793 V and ID ≈ 8.41 mA.
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: VDD = 5 V in series with a 500 Ω resistor and the diode]
Use the diode equation to relate current and voltage, then solve the circuit by iteration, starting from the 0.7 V point.
Given
VDD = 5 V, R = 500 Ω, η = 1.74, ID = 1 mA at VD = 0.7 V, VT = 25 mV (so η VT = 43.5 mV).
Diode equation (two points)
Since I2/I1 = exp[(V2 - V1)/(η VT)]:
VD = 0.7 + η VT ln(ID / 1 mA) = 0.7 + 0.0435 ln(ID/1 mA)
Circuit (KVL): ID = (5 - VD)/500.
Iteration
| Step | VD guess (V) | ID = (5 - VD)/500 (mA) | New VD = 0.7 + 0.0435 ln(ID) |
|---|---|---|---|
| 1 | 0.700 | 8.600 | 0.7937 |
| 2 | 0.7937 | 8.413 | 0.7926 |
| 3 | 0.7926 | 8.415 | 0.7927 |
The values have converged: VD ≈ 0.793 V.
ID = (5 - 0.793)/500 = 8.41 mA
Answer: ID ≈ 8.4 mA (VD ≈ 0.79 V).
A quick check with the constant-drop model (0.7 V) gives 8.6 mA, within 2.5 %, so the exponential effect is small.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- Diode circuit current, eta 1.74, 10 V · Electronics Devices and Circuit, chapter 1 · asked 4×
- Diode circuit current, eta 1.74, 6 V · Electronics Devices and Circuit, chapter 1 · asked 4×
- Diode current and voltage, VDD 5 V, R 1 kΩ · Electronics Devices and Circuit, chapter 1
- Diode current at 100°C (eta 1.8) · Electronics Devices and Circuit, chapter 1 · asked 4×
- Diode current and voltage, 0.1 V per decade · Electronics Devices and Circuit, chapter 1
- Unknown resistor from voltage across 500Ω · Basic Electrical Engineering, chapter 1 · asked 2×