How can we protect circuit from reverse voltage polarity?

How can we protect circuit from reverse voltage polarity?
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We can protect circuit from reverse voltage by connecting diode in series but connecting diode in series is less efficient. So we can also protect circuit from reverse voltages by connecting p channel MOSFET. Connecting p channel MOSFET is more efficient as compared to diode. The load is applied between gate and source of mosfet and input voltage is applied between drain and Gate of mosfet.
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