Option 1: How can AC electricity charge a DC device?

This option investigates the processes involved in transforming the alternating current delivered by the electrical supplier into low voltage direct current for use with small current electrical devices. Students investigate a variety of circuits to explore processes including transformation, rectification, smoothing and regulation. They use a variety of instruments to observe the effects of electricity.

On completion of this unit the student should be able to construct, test and analyse circuits that change AC voltage to a regulated DC power supply, and explain the use of transducers to transfer energy.

Key knowledge

240 V AC to 6 V DC

  • analyse the role of the transformer in the power supply system including the analysis of voltage ratio: \frac{N_1}{N_2}=\frac{V_1}{V_2 }
    (not including induction or its internal workings)
  • explain the use of diodes in half-wave and full-wave bridge rectification
  • explain the effect of capacitors with reference to voltage drop and current change when charging and discharging (time constant for charging and discharging, τ = RC ) leading to smoothing for DC power supplies
  • describe the use of voltage regulators including Zener diodes and integrated circuits
  • analyse systems, including fault diagnosis, following selection and use of appropriate test equipment
  • interpret a display on an oscilloscope with reference to voltage as a function of time.

Data transfer

  • apply the use of heat and light sensors such as thermistors and light-dependent resistors (LDRs) to trigger an output device such as lighting or a motor
  • evaluate the use of circuits for particular purposes using technical specifications related to potential difference (voltage drop), current, resistance, power, temperature and illumination
  • compare different light sources (bulbs, LEDs, lasers) for their suitability for data transfer
  • explain the use of optical fibres for short and long distance telecommunications.

(Source: vcaa.vic.edu.au)

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