Transformer Turns Ratio
The turns ratio is one of the most important concepts in transformers. It determines how voltage and current are transformed between the primary and secondary windings.
What Is Turns Ratio?
The turns ratio is the ratio between the number of turns in the secondary winding and the number of turns in the primary winding.
- Np = Number of turns in primary
- Ns = Number of turns in secondary
Voltage Relationship
The voltage ratio depends directly on the turns ratio:
This means:
- If Ns > Np → voltage increases (step-up)
- If Ns < Np → voltage decreases (step-down)
Current Relationship
Current behaves opposite to voltage:
- Voltage increases → Current decreases
- Voltage decreases → Current increases
This is because power remains approximately constant:
Vp × Ip ≈ Vs × Is
Types Based on Turns Ratio
| Type | Condition | Effect |
|---|---|---|
| Step-Up | Ns > Np | Voltage increases |
| Step-Down | Ns < Np | Voltage decreases |
| Isolation | Ns = Np | Voltage unchanged |
Example Calculation
Given:
- Np = 100 turns
- Ns = 500 turns
- Vp = 12V
Calculate secondary voltage:
Vs = (Ns / Np) × Vp Vs = (500 / 100) × 12 = 60V
Practical Notes
- More turns → higher voltage
- Wire thickness affects current capacity
- Core material affects efficiency
Applications
- Power supplies
- Amplifiers
- SMPS circuits
- Audio transformers
Key Points
- Turns ratio controls voltage transformation.
- Voltage ratio equals turns ratio.
- Current changes inversely.
- Power remains approximately constant.
- Fundamental concept in all transformers.