Now, when you connect the battery as per the circuit diagram, with correct polarity, it causes the transistor to turn ON and allows the current to flow through it. Working of Reverse Polarity Protection Circuit Using P-Channel MOSFET Components required for making the circuit hardware is mentioned below. Now, if the supply voltage is more than the Vgs then you have to drop the voltage between the gate terminal and source. You just have to connect the gate terminal of the MOSFET to the ground. If the supply voltage is less than the Gate-to-Source voltage (Vgs) of P-channel MOSFET then you only need the MOSFET without diode or resistor. The circuit consists of a P-Channel MOSFET, Zener diode and a pull-down resistor. Using a P-Channel MOSFET for Reverse Polarity Protection is more reliable than other methods, because of low voltage drop and high current capability. Reverse Polarity Protection using P-Channel MOSFET But bridge rectifier consists of four diodes, hence the amount of power waste will be twice of the power waste in the above circuit with single diode. You can even use a Full-bridge rectifier for reverse polarity protection, as it is regardless of polarity. Be aware while choosing a Schottky diode, because lots of Schottky diodes comes with high reverse current leakage so make sure that you will choose one with low reverse current (less than 100uA).Īt 4 Amps, power loss by a Schottky diode in the circuit will be:
But in case of low voltage operating system, even a small amount of voltage drop is unacceptable.Īs we know the voltage drop across a general purpose diode is 0.7V so we can limit this voltage drop by using Schottky diode because its voltage drop is around 0.3V to 0.4V and it can also withstand with high current loads. When the input supply voltage is high a small voltage drop may no matter, especially when the current is low. Using a Diode is the easiest and cheapest method for Reverse Polarity Protection but it has a problem of power leakage. There are some simple methods to protect the circuit from reverse polarity connection such as using a diode or Diode Bridge or by using P-Channel MOSFET as a switch on HIGH side. So, in this situation Reverse Polarity Protection Circuit would be a useful addition to the circuit. Generally all the devices come with Reverse Polarity Protection Circuit but if you have any battery operated device which don’t have reverse polarity protection then you always have to be careful while changing the battery otherwise it can blow up the device. There are many other ways, to power up electronic devices, like adapter, solar cell etc but the most common DC power supply is Battery. Batteries are most convenient power source to supply voltage to an electronic circuit.
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