What Is a Power Transformer?
A power transformer is a transformer designed to convert high-power AC voltage and isolate circuits. It's the first stage of power supplies.
What Does It Do?
It converts the mains, e.g. 230 V, into the lower (e.g. 12 V) or higher voltage the device needs, and at the same time galvanically separates the user from the mains (safety).
VA (Power) Rating
A power transformer's capacity is given in VA (volt-amperes). The power the load draws must be below this value; if exceeded, the core saturates, the windings heat up and efficiency drops.
| Parameter | Meaning |
|---|---|
| VA | The power it can carry |
| Primary/secondary V | Input/output voltage |
| Efficiency | Output power / input power |
Losses and Efficiency
There are two kinds of loss: copper loss (from winding resistance, rising with current) and iron loss (in the core, related to voltage). A good power transformer offers over 90% efficiency; the losses appear as heat.
Where Is It Used?
Linear power supplies, plug-type adapters, industrial equipment, audio amplifiers and mains distribution systems.
Common Mistakes
- Insufficient VA: if the load exceeds the power, the transformer heats up and the voltage drops.
- Skipping cooling: heat management is needed at high power.
- Wrong voltage: the primary voltage must be chosen to suit the mains (110/230 V).
Frequently Asked Questions
Is VA the same as watts?+
Is a switching power supply transformer different?+
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