29. Reverse Polarity Protection Diode
1. Component Purpose
If someone accidentally connects the 12V power supply backwards, the reversed voltage can instantly destroy ICs and other sensitive components on the board.
A series Schottky diode on the input line blocks current when polarity is reversed (diode is reverse-biased), protecting the entire board. A Schottky type is chosen instead of a standard diode because it has a much lower forward voltage drop (≤0.5V vs ~0.7V for standard), meaning less wasted power during normal operation.
Required: Schottky · ≥1A · ≥30V · Vf ≤0.5V · SMA · SMD · −40°C to +125°C · RoHS
2. How to Find It on DigiKey
Go to DigiKey.com → Discrete Semiconductor Products → Diodes - Rectifiers - Single
Apply these filters:
- Diode Type (Technology) → Schottky
- Voltage - DC Reverse (Vr) → 30V or higher
- Current - Average Rectified (Io) → 1A or higher
- Voltage - Forward (Vf) → Check datasheet for ≤0.5V
- Supplier Device Package → SMA (DO-214AC)
- Part Status → Active
Tip: DigiKey lists Vf at a specific test current (usually the rated current). Make sure Vf ≤0.5V at the test current shown, not just at very low current.
3. Key Specifications & What They Mean
| Specification | Required | Why |
|---|---|---|
| Diode Type | Schottky | Low Vf; minimizes voltage loss in series path. |
| Avg Current (Io) | ≥1A | Board draws 500mA; 2× margin for safety. |
| Reverse Voltage (Vr) | ≥30V | Must block full 12V reverse with margin. |
| Forward Voltage (Vf) | ≤0.5V | Keeps power loss low during normal use. |
| Package | SMA | Standard SMD package for this current level. |
| Temp Range | −40°C to +125°C | Industrial operating conditions. |
| RoHS | Yes | Compliance required. |
4. Selecting a Safe, Production-Ready Part
The filtered list will show many matching parts. Before you pick one, check: Is it Active? Is stock available? Is the manufacturer reputable? Is a datasheet available?
Full checklist: How to Select a Safe, Production-Ready Component — EWskills Guide