Reverse polarity protection

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A reverse polarity protection prevents the DC power supply (swapping of negative and positive poles) or AC power supply (permutation of phase and neutral conductors) of a device, the wrong polarity ( reverse polarity ) and can thereby minimize damage.

Mechanical reverse polarity protection

Mechanical devices ensure that electrical connections cannot be made with incorrect polarity (exchange of plus and minus in DC applications ). This is achieved using plugs that can only be inserted in one position to the socket and thus prevent the connections from being reversed. Examples are coaxial plugs of plug-in power supplies or plug-in connectors in which lugs or the arrangement of the plug pins only allow one plug-in variant, such as the French plug type E or three-pin plugs from the Swiss SEV 1011 system .

Mechanical polarity reversal protection is also used in AC voltage applications when the assignment of the current paths is important (e.g. microphones, three-phase motors) or for electrical equipment with a connector system such as connector type E ; this is about protection against interchanging neutral and external conductors .

Electrical reverse polarity protection

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In the case of electrical reverse polarity protection with direct voltage, suitable circuits and components (e.g. reverse polarity protection diodes ) ensure that no damage is caused to the connected device when the electrical voltage is applied in the wrong polarity (e.g. if mechanical reverse polarity protection does not exist or fails) arises.

Circuit variants

  1. Diode in series with the supply voltage. If the polarity is reversed, the device receives no power
    Advantage: inexpensive, no current flows if the polarity is reversed
    Disadvantage: power loss and voltage drop across the diode
  2. Diode anti-parallel to the supply voltage; If the polarity is reversed, the voltage source is short-circuited via the diode, so a fuse (usually "flying" in the positive lead) is required for protection
    Advantage: with correct polarity no influence
    Disadvantage: short-term short circuit of the voltage source, fuse change after reverse polarity
  3. upstream bridge rectifier
    Advantage: always correct polarity
    Disadvantage: voltage drop and power loss
  4. A relay switches the supply voltage to the consumer with the help of a diode
    Advantage: hardly any voltage drop at the contacts
    Disadvantages: expensive, additional power loss in the relay coil
  5. A P-channel MOSFET allows current to flow via drain to source like a diode. The gate voltage is set via the Zener diode and resistor. A relatively high resistance reduces losses.
    Advantage: no current flows if the polarity is reversed
    Disadvantage: higher number of components