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6.2.4Chemical Reactions

Switch Mode Transformers — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 4 parts Lesson 11 of 21 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Section 1 of 4How It Works

6.2.4 Switch Mode Transformers
1
Mains electricity is first converted into direct current, and then electronic circuits switch it on and off very rapidly.
2
The rapid switching produces a changing magnetic field in the core at a high frequency, typically tens of kilohertz.
3
The high-frequency field induces a potential difference in a small secondary coil, which is then converted back to direct current.
4
Because the core only needs to carry the field at high frequency, it can be much smaller and lighter than a 50 Hz transformer core.

Section 2 of 4Advantages and Drawbacks

Size
  • A switch mode transformer has a small core, so the whole device can be made much lighter and more portable.
Efficiency
  • Good efficiency is achieved because less energy is lost as heat in a small, well-designed core.
Cost
  • Electronic switching components add cost and complexity compared with a simple laminated transformer.
Interference
  • Rapid switching can create electrical noise, so switch mode supplies need filtering components.

Section 3 of 4Everyday Uses

Everyday Uses
Laptop charger
  • The light, compact design is convenient for carrying with a portable computer.
Phone charger
  • The small size allows the transformer to fit inside the plug or charging block.
Television power supply
  • An efficient, lightweight internal supply converts mains electricity to the low voltages needed by the electronics.
Desktop computer power supply
  • Efficient conversion from mains electricity to low-voltage direct current keeps the internal components cool.

Section 4 of 4Exam Checklist & Tips

6.2.4 – Key Points for the Exam

  • Switch mode transformer A transformer that works at high frequency by switching a direct current on and off.
  • High frequency A rapid rate of change of current, typically tens of kilohertz in switch mode supplies.
  • Rectification The conversion of alternating current into direct current.
  • Efficiency The proportion of input energy that is transferred to useful output energy.
  • Mains supply The domestic alternating current supply, at 230 V and 50 Hz in the UK.

Common Mistakes

  • Saying a switch mode transformer works directly from a steady direct current in the mains;
    • the mains is alternating.
  • Thinking the transformer is smaller because of a different turns ratio;
    • it is smaller because of high-frequency operation.
  • Claiming switch mode transformers have no energy loss at all.
  • Confusing a switch mode transformer with a conventional 50 Hz transformer, which has a much larger core.

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Transformer Golden Equations Physics Standard

Transformer Turns Ratio & Efficiency

Ratio: Vp / Vs = Np / Ns = Is / Ip

  • Step-up reduces grid thermal loss (P = I2R).
  • Laminated core prevents eddy currents.