Reverse Polarity Protection with Diodes
Reverse polarity protection is designed to protect a polarity-dependent circuit from damage in the case of incorrect polarity. In general, circuits that are operated with DC voltage are polarity-dependent. In addition to mechanical reverse polarity protection, there is also the option of electrical or electronic reverse polarity protection, which we will discuss in more detail here. It should be noted that mechanical reverse polarity protection is not possible if, for example, cables are connected directly.
Electronic reverse polarity protection can be implemented with the following circuit variants:
Diode in series to the power supply
The simplest electronic reverse polarity protection is a rectifier diode in the supply line to the electronic circuit. Here the current can only flow in the forward direction of the diode.
Note the forward voltage of the diode (silicon diode approx. 0.6 V and germanium diode approx. 0.3 V). This reduces the operating voltage for the subsequent circuit.
Diode in parallel with the power supply
Here, the diode is connected in parallel with the circuit in the reverse direction. In case of reverse polarity this diode becomes conductive and limits the voltage for the subsequent circuit to the value of the forward voltage (Ge 0.3 V or Si 0.7 V).
Advantage here: The circuit is directly connected to voltage, that means you no voltage drop caused by the diode has to be considered here. Disadvantage: In case of reverse polarity the fuse blows.
Bridge rectifier as reverse polarity protection
A foolproof variant of reverse polarity protection, because the correct polarity is always present in the subsequent circuit due to the rectification. However, it must be noted here that the voltage drops of two diodes must always be taken into account.