What is the 1N5817 Schottky Diode?
The 1N5817 is a fast, low forward voltage drop Schottky diode rated at 1 A and 20 V. It's used for reverse polarity protection, power rectification, and freewheeling in low-voltage circuits.
1N5817 Key Features
Type: Schottky barrier diode
Forward Voltage Drop: 0.2V–0.45V
Max Reverse Voltage: 20V
Max Forward Current: 1A
Peak Surge Current: 25A (8.3ms half-sine)
Switching Speed: Fast
Power Loss: Low
Applications: Power supplies, reverse polarity protection, freewheeling diode
1N5817 Diode Pinout
1N5817 Pin Configuration
| Pin Number | Name | Description |
|---|---|---|
| 1 | Cathode | Negative terminal |
| 2 | Anode | Positive terminal |
Notes：
Be careful not to reverse the polarity, as incorrect connection may prevent current flow or damage components depending on the circuit design.
Typical Reverse Polarity Protection Circuit Using the 1N5817 Schottky Diode
When the input polarity is correct, current flows through D1 to power the load. If the input polarity is reversed, D1 conducts to ground, protecting downstream components.
Forward-biased (normal operation):
The 1N5817 has a forward voltage drop of approximately 0.2–0.4 V, allowing nearly the full supply voltage to reach the circuit.
Reverse-biased (fault condition):
The diode shorts the reverse voltage to ground, preventing damage to other components.
Key considerations:
- Ensure D1 can handle the system current (up to 1 A) and peak surge current (25 A).
- Account for power dissipation: at 1 A, a ~0.3 V drop results in ~0.3 W of heat—use adequate PCB copper or a heatsink if necessary.
- Ensure the reverse voltage does not exceed the VRRM (20 V) rating.
1N5817 Equivalent
| Model | VRRM (V) | VF@1A (V) | IR@25°C (mA) | IF(AV) (A) | IFSM (A) | Package |
|---|---|---|---|---|---|---|
| 1N5817 | 20 | 0.45 | 1.0 | 1 | 25 | DO-41 |
| 1N5818 | 30 | 0.55 | 1.0 | 1 | 25 | DO-41 |
| 1N5819 | 40 | 0.60 | 1.0 | 1 | 25 | DO-41 |
| SS12 (SMD) | 20 | ~0.45 | ~1.0 (≈1 mA) | 1 | 25 | SMA |
| SS14 (SMD) | 40 | ~0.60 | ~1.0 (≈1 mA) | 1 | 25 | SMA |
Selection Tips
- Voltage rating: Use a diode with the same or higher VRRM than your circuit's max reverse voltage.
- Forward drop: Higher VRRM (like 1N5819) means slightly higher VF—more voltage loss and heat.
- Package: Use SS12/SS14 if you need SMD and your board supports it; otherwise stick to DO‑41.
- Leakage and heat: All listed diodes have similar reverse leakage (~1 mA) and surge handling—no major difference here.
If your circuit runs below 20 V, 1N5817 is ideal. For higher voltage, use 1N5818 (30 V) or 1N5819 (40 V), but expect a slightly higher forward voltage. For SMD designs, use SS12 (20 V) or SS14 (40 V), and make sure the layout and cooling are suitable.
Conclusion
Choosing the right diode goes beyond just specs—it’s about matching the needs of your design. The 1N5817 and its equivalents offer flexible options for both through-hole and surface-mount builds. Whether you're optimizing for space, efficiency, or voltage margin, understanding these trade-offs helps ensure reliable circuit performance.
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