Switch Mode Power Supplies


In this video i explain 2 basic types of power supply, there's the standard transformer-rectifier-smoothing style, and there's the Switch-Mode type.

For the same size of enclosure, the switch mode will be lighter, but can often supply more current, and the output ripple is greatly reduced.
This is important for sensitive equipment.



This diagram is associated with the video


It was intended to add some scope traces to the diagram, but this proved a bit difficult, so here's an explanation of what is going on.

1. This is the normal sinusoidal wave at 50 or 60 Hz
2. After passing through a bridge rectifier, the negative waves are inverted
3. the capacitor stores the voltage briefly, and the rising waves keep this charged, but there's a ripple, even so, it is a DC voltage.
4. This DC voltage is chopped using an inverter at between 50 kHz and 1 MHz, this output is AC at high frequency.
5. Again the AC is rectified
6. and finally smoothed with a capacitor.
7. due to the high frequency AC, and the short time the capacitor needed to store the voltage, the ripple is greatly reduced to almost nothing.

The sample and control regulate the voltage at the output to ensure the output doesn't overvolt when no load is connected.







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