Master the Basics: Protect Against Reverse Current

One of the easiest ways to accidentally damage an electronic device is by connecting power in the wrong direction. Whether it’s inserting batteries backward or mixing up red and black wires, reverse polarity mistakes happen—and they can be costly.

Why Reverse Current Protection Matters

Many electronic components are not tolerant of reverse voltages. Applying power backward can cause permanent damage. That’s why it’s a smart idea to include reverse current protection in your circuit designs.

The Simple Solution: A Diode in Series

To protect against reverse polarity, insert a diode in series with the positive voltage line of your DC power source:

• If power is connected correctly, the diode is forward biased and allows current to flow.
• If power is connected backward, the diode becomes reverse biased and acts like an open circuit, blocking the current and protecting your components.

The Voltage Drop Trade-Off

One downside of using a diode for protection is the forward voltage drop:

• A standard silicon diode drops about 0.6V.
• So, a 5V supply would only deliver about 4.4V to your circuit.

To reduce this voltage loss, use a Schottky diode:

• Forward voltage drop is much lower: typically 0.15V to 0.45V.
• Schottky diodes still offer sufficient reverse protection.

Schottky diodes have a special schematic symbol (a regular diode with extra bends at the cathode) and are slightly more expensive. While the cost difference is minor for hobby projects, it can add up in mass production.

Selecting the Right Diode

When choosing a diode for reverse current protection, consider:

• Forward current rating: The diode must handle the maximum current your circuit will draw.
• Safety margin: If a fault causes your circuit to draw too much current, the diode could overheat and fail.

To provide extra protection, use a fuse in series with the diode:

• The fuse acts like a wire under normal conditions.
• If current exceeds the fuse’s rating, the wire melts, breaking the circuit.
• This protects your components from high current faults.

How to Identify a Schottky Diode

Can’t read the tiny print on the diode? Use a digital multimeter (DMM):

• Set it to diode mode.
• A standard diode will show about 0.6V forward voltage.
• A Schottky diode will show something much lower.

Key Takeways

Protecting your circuits from reverse current is essential—and easy. A series diode provides simple, effective protection, especially when paired with a fuse. For minimal voltage drop, consider Schottky diodes—just be mindful of cost and current limits. With these precautions, you can safeguard your devices from common wiring mistakes and unexpected faults.