Protection in electronic circuits is crusial factor. especially polarity reverse protection. Can you imagine what happen if our circuit not pretected to reverse polarity supply. All digital IC will be damage, and also electrolit capacitor will blow up. There two simple way to protect the circuit from reverse polarity
1. Using diode
Connect your positif terminal in circuit to cathode and positif terminal from your power supply to anode of diode. See the picture.
The andvantage using diode protection is low in cost and simple to configurate it
The disadvantage from this configuration are the supply to circuit will decrease about V junction of diode (0,7v for silicon diode and 0,3 for germanium diode) and diode cannot handle supply with higher current.
2. Using Mosfet
Connect the drain to positif terminal of power supply, the gate to ground and source to postif terminal of circuit. See below picture
The advantage using this configuration is can handle power supply with higher current.
The disadvantage is not low cost and need heatsink (for higher current)