What Is a Transformer?
A transformer is a passive component that steps AC voltage up or down by coupling two coils through a common magnetic core, while also electrically separating the two circuits.
How Does It Work?
The alternating current through the primary winding creates an alternating magnetic field in the core. This field induces a voltage in the secondary winding. There's no direct electrical connection between them; energy is transferred only by the magnetic field.
Why Only AC?
Induction happens only if the magnetic field is changing. Since DC produces a steady field, a transformer can't transfer DC; so it works only with AC or pulsed signals.
Turns Ratio
The output voltage is set by the ratio of the turns: Vs/Vp = Ns/Np. If the secondary has more turns the voltage rises (step-up), if fewer it falls (step-down). As voltage rises, current falls; power (excluding losses) is conserved.
| Type | Turns | Effect |
|---|---|---|
| Step-up | Ns > Np | Voltage ↑, current ↓ |
| Step-down | Ns < Np | Voltage ↓, current ↑ |
| Isolation | Ns = Np | Separation only |
Where Is It Used?
Mains power distribution, adapters, audio circuits, current measurement and everywhere isolation is needed.
Special Transformer Types
There are special types by task: the isolation transformer for galvanic separation, the current transformer for safely measuring high current, and the pulse transformer for signal/switching circuits.
Common Mistakes
- Feeding with DC: a transformer doesn't transfer DC; the primary acts like a short and can burn.
- Power limit: if the rated power (VA) is exceeded, the core saturates and heats up.
- Frequency: a transformer designed for low frequency is inefficient at high frequency.
Frequently Asked Questions
Does a transformer increase power?+
What does galvanic isolation mean?+
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