---
title: "Zener input range, 220 Ω, 20 V, 60 mA"
subject: "Electronics Devices and Circuit"
chapter: 6
key: "semester_3/electronics_devices_and_circuit:zener-range-vi-220ohm-20v"
source: https://www.bctengineer.com/q/semester_3/electronics_devices_and_circuit/zener-range-vi-220ohm-20v
site: BCT Engineering
---

# Zener input range, 220 Ω, 20 V, 60 mA

Electronics Devices and Circuit · Chapter 6: Power Supplies, Breakdown Diodes, and Voltage Regulators

- Asked in: 2081 Baisakh, 6 marks; 2074 Ashwin, 5 marks (asked 2 times)
- Video: [Zener Diode Regulation - Varying load resistance, Varying input voltage and Varying input resistance](https://www.youtube.com/watch?v=CO18uJ_LxE8) — Electric Circuits
- 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/zener-range-vi-220ohm-20v
- Whole chapter: https://www.bctengineer.com/md/semester_3/electronics_devices_and_circuit/chapter-6

## Question

Determine the range of values of Vi that will maintain the Zener diode of the figure below in ON state.
[Figure: source Vi, series resistor R = 220 Ω, Zener diode Vz = 20 V with izmax = 60 mA in parallel with load RL = 1.2 kΩ]

## Short answer

Load current IL = 20 V / 1.2 kΩ = 16.67 mA. For Zener ON, Vi(min) = 20 + 16.67mA × 220 = 23.67 V (Iz = 0). Vi(max) = 20 + (16.67+60)mA × 220 = 36.87 V (Izmax = 60 mA). Vi range: 23.67 V to 36.87 V.

## Answer

**Given:** R = 220 Ω, Vz = 20 V, IZmax = 60 mA, RL = 1.2 kΩ. The Zener is ON (in breakdown) when Iz is between 0 and IZmax, and Vo = Vz = 20 V.

#### Load current
IL = Vz/RL = 20 V / 1.2 kΩ = **16.67 mA** (constant, since Vz is fixed)

#### Minimum Vi
Zener just turns ON: Iz ≈ 0, so the series current IR = IL.

Vi(min) = Vz + IR R = 20 + (16.67 mA)(220 Ω) = 20 + 3.67 = **23.67 V**

#### Maximum Vi
The Zener current is at its maximum, Iz = 60 mA, so

IR(max) = IZmax + IL = 60 + 16.67 = 76.67 mA

Vi(max) = Vz + IR(max) R = 20 + (76.67 mA)(220 Ω) = 20 + 16.87 = **36.87 V**

#### Check
At Vi = 23.67 V: IR = 3.67/220 = 16.67 mA = IL, so Iz = 0 ✓. At Vi = 36.87 V: IR = 16.87/220 = 76.7 mA, Iz = 76.7 − 16.7 = 60 mA ✓.

**Answer: 23.67 V ≤ Vi ≤ 36.87 V keeps the Zener in the ON state.**

## Check yourself

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

1. While the Zener is ON, what is the load current and why is it constant?
   A. IL = Vi/RL, it changes with Vi
   B. IL = Vz/RL = 16.67 mA, because the load voltage is fixed at Vz
   C. IL = IZmax - Iz = 43.3 mA
   D. IL = Vz/R = 90.9 mA
   Answer: B. The load is across the Zener, so its voltage is 20 V regardless of Vi, giving 20/1200 = 16.67 mA. (Key point: Load current)

2. What condition defines the minimum Vi that keeps the Zener ON?
   A. Zener current is about zero, so the whole series current equals IL
   B. Zener current equals IZmax
   C. Load current is zero
   D. Series resistor current is zero
   Answer: A. At the threshold of turning ON, Iz ≈ 0 and IR = IL, so Vi(min) = 20 + 16.67 mA x 220 = 23.67 V. (Key point: Minimum Vi condition)

3. What is Vi(max)?
   A. 23.67 V
   B. 33.2 V, using IR = 60 mA only
   C. 56.4 V, using Vi = IR x R
   D. 36.87 V, since IR = 60 + 16.67 = 76.67 mA and Vi = 20 + 76.67 mA x 220
   Answer: D. At maximum Iz = 60 mA the series current also carries the load current, so IR = 76.67 mA and the drop in R is 16.87 V. (Key point: Maximum Vi)

4. What happens if Vi falls below 23.67 V?
   A. The Zener current exceeds 60 mA
   B. The load current becomes zero
   C. The Zener leaves breakdown (OFF) and the output is no longer held at 20 V
   D. The output rises above 20 V
   Answer: C. Below this Vi there is not enough current for both the load and Zener, so Iz would be zero and regulation is lost. (Key point: Result)

## Related in Electronics Devices and Circuit

- [Zener input range, 91 Ω, 8 V, 400 mW](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-range-vi-91ohm) — Electronics Devices and Circuit, chapter 6
- [Zener: range of load for VL = 5 V](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-load-range-5v) — Electronics Devices and Circuit, chapter 6
- [Zener regulator Vo, load effect, minimum RL](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-regulator-6v8-line-load) — Electronics Devices and Circuit, chapter 6, asked 2×
- [Zener current for two load values](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-current-rl-numeric) — Electronics Devices and Circuit, chapter 6
- [Zener with pass transistor: Vo and Iz](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-series-pass-numeric) — Electronics Devices and Circuit, chapter 6
- [Zener regulator output voltage and minimum RL](https://www.bctengineer.com/question.md?key=semester_3%2Felectronics_devices_and_circuit%3Azener-load-regulator-rz-6v8) — Electronics Devices and Circuit, chapter 6

## Related in other subjects

- [Zener network with two load values](https://www.bctengineer.com/question.md?key=semester_1%2Fbasic_electrical_and_electronics_engineering%3Azener-regulator-numerical-rl) — Basic Electrical and Electronics Engineering, chapter 3
- [Zener current: 18 V, 100 Ω, RL 1.2 kΩ](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Azener-current-18v-100) — Basic Electronics Engineering, chapter 2, asked 4×
- [Zener current: 16 V, 1 kΩ, RL 3 kΩ](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Azener-current-16v-1k) — Basic Electronics Engineering, chapter 2, asked 4×
- [Zener network: VL, IL, Iz, IR](https://www.bctengineer.com/question.md?key=semester_2%2Fbasic_electronics_engineering%3Azener-regulator-220-ohm) — Basic Electronics Engineering, chapter 2