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Power supplies: theory, diagnostics and fixing.

Summary

Many pieces of electronic equipment include a power supply (PSU or Power Supply Unit) to convert the incoming power to the form needed. This can generate heat which can lead to failures.

Why is a power supply needed?

A power supply performs some or all of the following purposes:

• Voltage conversion: The mains electricity supply is 240v, which is much too high for most electronic gadgets, and is dangerous if exposed so a reduction is required. In a few cases (e.g. a microwave oven), conversion to a higher voltage is required.
• Isolation: Even if the voltage is reduced, if there is still a direct electrical path to the mains it may still be dangerous. Professional power tools, especially if used outdoors, are often used with an isolation transformer simply to break that path.
• Rectification: The mains supply is AC, which means it reverses direction 100 times per second. Whilst this is fine for heating, some forms of lighting and most electric motors, electronics normally require DC, always going in the same direction. Rectification is the technical term for AC to DC conversion.
• Smoothing: AC momentarily drops to zero as it reverses direction, and if you simply rectify it, it will still be dropping to zero 100 times per second. Electronic equipment generally can't cope with this. Smoothing stores electrical energy to fill in the gaps.
• Regulation: Rectified and smoothed AC will generally still contain "ripple" as smoothing is imperfect, and te voltage will still vary if the mains supply varies. Electronic equipment often needs a supply which is not only very smooth but a precice voltage. Regulation provides this.

Safety

Consider whether your page should include a specific section on safety, if for example it deals with mains-powered equipment or high voltages, or if special care is required in handling hot or sharp tools, or hazardous substances.

External links

• External links as bullet points