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Lesson: Chapter 11 — Electronics

Smoothing and polarity protection 2 of 2

Protecting against reversed connections

Connecting a DC electronic device with + and − swapped can damage it. A diode in the supply lead prevents that.

Figure to be added

Figure 11.17 — (a) battery connected correctly through the protecting diode D, current flows; (b) battery reversed, the diode blocks the current.

Battery the right way round

The diode is forward biased and the device works.

Battery reversed

The diode is reverse biased, so no current reaches the device and it is not damaged.

Either way round

Design a circuit, using a bridge rectifier, that supplies an electronic device correctly whichever way the battery is connected.

Put the bridge between the battery and the device: its output is always the same way round, just as the LED in figure 11.12 lit for both battery connections.