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Voltage Doubler and Primary Rectifier

On power supplies without active PCF circuit you will find a voltage doubler. The voltage doubler uses two big electrolytic capacitors. So the bigger capacitors found on the power supply belongs to this stage. Like we mentioned before, the voltage doubler is only used if you are connecting your power supply to a 127 V power grid.

Voltage DoublerFigure 13: Electrolytic capacitors from the voltage doubler.

Electrolytic CapacitorsFigure 14: Electrolytic capacitors from the voltage doubler removed from the power supply.

Next to the two electrolytic capacitors you will find a rectifying bridge. This bridge can be made by four diodes or by a single component, see Figure 15. On high-performance power supplies this rectifying bridge is connected to a heatsink.

Rectifying BridgeFigure 15: Rectifying bridge.

On the primary you will also find a NTC thermistor, which is a resistor that changes its resistance according to the temperature. It is used to reconfigure the power supply after it is used for a while and it is hot. NTC stands for Negative Temperature Coefficient. This component resembles a ceramic disc capacitor and is usually olive green.

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Gabriel Torres is a Brazilian best-selling ICT expert, with 24 books published. He started his online career in 1996, when he launched Clube do Hardware, which is one of the oldest and largest websites about technology in Brazil. He created Hardware Secrets in 1999 to expand his knowledge outside his home country.