Transformer Current Ratio
The current ratio in a transformer shows how current changes between the primary and secondary windings. Unlike voltage, current varies inversely with the turns ratio.
Current Ratio Formula
In an ideal transformer, current is inversely proportional to the turns ratio:
::contentReference[oaicite:0]{index=0}Equivalent form:
Ip / Is = Ns / Np
- Ip = Primary Current
- Is = Secondary Current
- Np = Primary Turns
- Ns = Secondary Turns
Understanding the Relationship
- If voltage increases → current decreases
- If voltage decreases → current increases
- Current always moves opposite to voltage
This happens because power remains approximately constant:
Vp × Ip ≈ Vs × Is
Step-Up vs Step-Down
| Type | Voltage | Current |
|---|---|---|
| Step-Up | Increases | Decreases |
| Step-Down | Decreases | Increases |
Example Calculation
Given:
- Primary Current = 2A
- Primary Turns = 100
- Secondary Turns = 50
Find Secondary Current:
Is = (Np / Ns) × Ip Is = (100 / 50) × 2 Is = 2 × 2 = 4A
Important Notes
- Current ratio is inverse of voltage ratio
- Higher voltage → lower current
- Lower voltage → higher current
- Wire thickness determines current capacity
Quick Memory Trick
- More turns → More voltage → Less current
- Less turns → Less voltage → More current
- Voltage ↑ = Current ↓
Applications
- Power supplies
- Amplifiers
- Battery chargers
- Electrical distribution