BeginnerTopic 33 of 106Electrical Engineering
Dependent sources
Sources controlled by another voltage or current; used to model transistors and amplifiers.
In depth
Dependent sources produce voltage or current controlled by another voltage or current: VCVS, VCCS, CCVS, CCCS. They model transistors and amplifiers. Treat them as active sources in KCL/KVL but never turn them off in superposition.
Key points
- Gain parameters
- Op-amp model
- Thevenin with dependent sources needs a test source
ExampleA BJT is modelled as a current source of value β·i_b.
What is Dependent sources?
Sources controlled by another voltage or current; used to model transistors and amplifiers.
Why is it important to understand dependent sources?
Dependent sources model transistors and amplifiers, so you need them to analyse nearly any active circuit.
What is a dependent source?
A source whose value depends on another voltage or current in the circuit, such as a current source controlled by a base current.
How do I treat a dependent source in analysis?
Write its equation as a constraint in terms of the controlling variable, then solve it together with the rest of the circuit.
How is Dependent sources used in practice?
Typical applications include modelling a transistor as a current source controlled by base current, analysing an op-amp with an internal dependent voltage source and representing a gain stage in a small-signal equivalent circuit.
What should I learn before Dependent sources?
Study "Star-delta transformation" first (topic 32 of 106 in Electrical Engineering). It covers the groundwork this topic builds on.
What are the key points of Dependent sources?
Gain parameters. Op-amp model. Thevenin with dependent sources needs a test source.
Can you give an example of Dependent sources?
A BJT is modelled as a current source of value β·i_b.
What comes after Dependent sources?
The next topic is "RC circuit transient", which builds directly on this one.
How difficult is Dependent sources?
It is classed as Beginner in Electrical Engineering (topic 33 of 106). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.