Simple negative pole protection circuit without voltage drop

Traditional negative voltage protection methods use diodes to prevent circuit damage. Generally speaking, a series diode allows current to pass only when the correct polarity is used (as shown in Figure 1). The disadvantage of this method is that power consumption is wasted due to the voltage drop on the diode. If the input current is 1 ampere, the circuit of Figure 1 will consume 0.7 watts of power, while the circuit of Figure 2 will consume 1.4 watts of power. The design concept proposed here adopts a simple method to avoid the existence of voltage drop and save power.

Protection circuit ">

Choose a relay to work with negative voltage. For example, use a 12-volt relay in a 12-volt power system. When you provide the correct polarity bias to the circuit, diode D1 is reverse biased, keeping the switch relay S1 closed. Then, the input and output power lines will be collected to the correctly connected relay ports, allowing current to flow to the end of the circuit. Diode D1 blocks the current from flowing to the relay, and this protection circuit does not consume any power.

This simple negative protection circuit has no voltage drop. If the wrong polarity bias is provided to the circuit, diode D1 is forward biased, opening the relay. The open relay will cut off the supply voltage to the end of the circuit, causing light-emitting diode D3 to turn on, indicating reverse bias. This circuit only consumes power in the case of reverse polarity. Unlike field effect devices or semiconductor switches, the relay contact switch has a low open resistance, which means that there is no voltage drop between the input voltage and the protection circuit. Therefore, this design is very suitable for systems with only a limited voltage range.