---
title: "Types of controlled sources"
subject: "Basic Electronics Engineering"
chapter: 1
key: "semester_2/basic_electronics_engineering:controlled-sources"
source: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/controlled-sources
site: BCT Engineering
---

# Types of controlled sources

Basic Electronics Engineering · Chapter 1: Basic Circuits Concepts

- Asked in: 2073 Bhadra, 4 marks
- Video: [Independent and Dependent (Controlled) Sources](https://www.youtube.com/watch?v=SfKw8bHk7-o) — ALL ABOUT ELECTRONICS
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/basic_electronics_engineering/controlled-sources
- Whole chapter: https://www.bctengineer.com/md/semester_2/basic_electronics_engineering/chapter-1

## Question

Describe different types of controlled source with figures.

## Short answer

Dependent sources have outputs controlled by a circuit voltage or current. The four types: voltage-controlled voltage source (VCVS, gain μ), current-controlled voltage source (CCVS, gain r in Ω), voltage-controlled current source (VCCS, gain g in S), and current-controlled current source (CCCS, gain β).

## Answer

A **controlled (dependent) source** is a source whose voltage or current is not fixed but depends on a voltage or current elsewhere in the circuit. It is drawn as a diamond. Transistors and op-amps are modelled with such sources. There are four types:

#### 1. Voltage controlled voltage source (VCVS)
Output voltage = μ × control voltage: Vo = μ Vx (μ is a dimensionless gain). Model of an op-amp or voltage amplifier.

#### 2. Current controlled voltage source (CCVS)
Output voltage = r × control current: Vo = r Ix (r in ohms, transresistance).

#### 3. Voltage controlled current source (VCCS)
Output current = g × control voltage: Io = g Vx (g in siemens, transconductance). Model of a FET or BJT (gm vbe).

#### 4. Current controlled current source (CCCS)
Output current = β × control current: Io = β Ix (β dimensionless). Model of a BJT: Ic = β Ib.

```text
    VCVS            CCVS            VCCS            CCCS
     /\              /\              /\              /\
    /+ \            /+ \            / ^\            / ^\
   < mu Vx>        < r Ix >        < g Vx>         < b Ix>
    \- /            \- /            \ |/            \ |/
     \/              \/              \/              \/
 voltage out     voltage out     current out     current out
 (+/- marks)     (+/- marks)     (arrow)         (arrow)
```

| Type | Controlling | Output | Gain |
|---|---|---|---|
| VCVS | voltage | voltage | μ |
| CCVS | current | voltage | r (Ω) |
| VCCS | voltage | current | g (S) |
| CCCS | current | current | β |

A dependent source is drawn with a diamond symbol, while an independent source uses a circle. The polarity (+/−) or arrow shows the reference direction of the output.

## Check yourself

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

1. What makes a controlled source different from an independent source?
   A. Its value depends on a voltage or current elsewhere in the circuit
   B. It has a fixed value
   C. It is drawn as a circle
   D. It has no output
   Answer: A. A controlled source's value depends on another voltage or current in the circuit; it is drawn as a diamond. (Key point: Dependent source definition)

2. Which controlled source is the model of a FET or BJT with Io = g Vx?
   A. VCVS
   B. CCVS
   C. VCCS
   D. CCCS
   Answer: C. A voltage controlled current source with transconductance g (siemens) models a FET or BJT (gm vbe). (Key point: VCCS)

3. Which source models a BJT as Ic = β Ib?
   A. CCCS
   B. VCVS
   C. CCVS
   D. VCCS
   Answer: A. The current controlled current source Io = β Ix models Ic = β Ib. (Key point: CCCS)

4. Which gain is in ohms (transresistance)?
   A. VCVS gain μ
   B. CCVS gain r
   C. VCCS gain g
   D. CCCS gain β
   Answer: B. CCVS gives Vo = r Ix, with r in ohms; μ and β are dimensionless and g is in siemens. (Key point: Gain units)

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