1N5819 PCB Design Guide: Footprint, Pinout, and Alternatives

The 1N5819 is a 1 A, 40 V Schottky barrier rectifier in a through-hole DO-41 package — the diode you reach for when a standard PN rectifier's forward drop would burn too much voltage or its slow recovery would kill efficiency in a switcher. As a Schottky, the metal-semiconductor junction delivers a forward voltage of 0.600 V max at 1 A, roughly half the 1.1 V a PN junction would drop at the same current, and it switches with essentially zero reverse recovery charge. Those two numbers — low VF and no trr — are why this part sits on the output of so many buck converters, across so many relay coils, and in series with so many DC barrel jacks.

The tradeoff is reverse leakage. A Schottky barrier leaks orders of magnitude more than a PN junction, and the leakage doubles roughly every 25 °C. Vishay guarantees 1.0 mA max reverse current at 25 °C and 10 mA at 100 °C, both at the full 40 V blocking voltage. In a battery-powered device or a precision analog front-end, 10 mA of leakage at operating temperature can drain more energy than the forward drop ever saved. The 40 V reverse rating is the highest in the 1N581x family, but it is still low by rectifier standards: a 12 V rail with an inductive transient can sail past 40 V, so a design that runs near the rating needs a TVS or snubber upstream — the guardring on the die is for transient overvoltage protection, not repetitive avalanche.

The mistakes that kill 1N5819s or the circuits around them are predictable: dropping one into a 1N4007 socket without checking the reverse voltage, treating the 0.600 V forward drop as a constant at all currents, ignoring the thermal resistance penalty of short leads on a tight board, and assuming reverse leakage at 25 °C is representative of what happens after the board warms up. Each is covered below.

What breaks boards

1. 01

   Reverse leakage is 1 mA at 25 °C — and 10 mA at 100 °C. Size your thermal budget for the hot number.

   A Schottky's reverse leakage is temperature-dependent in a way a PN junction's is not. Vishay's datasheet gives 1.0 mA max at 25 °C and 10 mA max at 100 °C at the full 40 V rated blocking voltage. In a reverse-polarity protection circuit on a 12 V rail, that is 120 mW of quiescent dissipation per diode at elevated temperature before the load even draws current. In a battery-powered design, 10 mA of leakage can dominate the sleep budget. If the diode runs near its 125 °C TJ max — for example, 1 A forward at 0.6 V in still air — the leakage contributes additional self-heating, and the positive feedback between temperature and leakage can push the junction past its limit. Check IR at the maximum expected ambient plus self-heating rise, not at room temperature.

2. 02

   40 V VRRM is the family's highest rating, but it is not generous. Do not treat it as a universal 1N4007 replacement.

   The 1N5819 is the top-voltage member of three (1N5817 = 20 V, 1N5818 = 30 V, 1N5819 = 40 V), and its non-repetitive peak (VRSM) is only 48 V. A standard 1N4007 is rated 1000 V. If a circuit was originally designed around a 1N4007, the designer likely never thought about the reverse voltage at all — and swapping in a 1N5819 without checking what the diode actually sees in reverse can put it one inductive spike away from failure. The 1N5819 belongs in low-voltage circuits where you need Schottky speed and low drop; if the rail is above 24 V nominal, or if there is any flyback energy, check the peak reverse voltage with margin. Use a 1N4007-class diode for high-voltage or mains-frequency rectification.

3. 03

   Forward voltage at your actual operating current is lower than 0.6 V — and that can mislead both thermal and dropout calculations.

   The datasheet guarantees VF ≤ 0.600 V at 1.0 A and VF ≤ 0.900 V at 3.1 A. But the forward characteristic curve (Figure 1) shows that at 100 mA the typical VF is approximately 0.3 V. If you calculate dissipation as 1 A × 0.6 V = 600 mW and you are only drawing 200 mA, the real dissipation is closer to 200 mA × 0.35 V = 70 mW — an order of magnitude less. This works for you when sizing heatsinking but can work against you in a low-dropout budget: if the circuit depends on the 0.6 V drop to limit inrush or set a bias point, the lower actual VF at lighter loads may not provide the expected headroom. Size for the VF at your specific operating current, not the headline 1 A number.

4. 04

   RθJA of 50 °C/W assumes 0.375-inch leads and 1.5-inch-square copper pads. Short leads on a tight board run hotter.

   The datasheet's typical junction-to-ambient thermal resistance of 50 °C/W is measured with the diode mounted on a PCB with 0.375-inch (9.5 mm) lead length and 1.5-inch × 1.5-inch (38 mm × 38 mm) copper pads on each lead. Bend the leads right at the body to fit a cramped footprint, and the copper area that carries heat away from the die shrinks — RθJA increases, and the junction temperature rises for the same forward current. At 1 A and 0.6 V forward drop, 50 °C/W gives a 30 °C rise above ambient, yielding TJ = 55 °C at 25 °C ambient — workable. But if the real mounting pushes RθJA to 80 °C/W, the same current produces a 48 °C rise and the junction hits 73 °C, where reverse leakage is already climbing. Leave generous lead length and copper area, or derate the forward current for cramped layouts.

5. 05

   The guardring protects against overvoltage transients, not sustained avalanche. Do not design to the VRSM limit.

   The datasheet lists 'Guardring for overvoltage protection' as a feature, and the maximum non-repetitive peak reverse voltage (VRSM) is 48 V for the 1N5819. Both refer to transient events — a brief spike, not a steady-state overvoltage or repetitive avalanche operation. There is no avalanche energy rating on this datasheet, and Schottky diodes are not designed for repetitive avalanche breakdown the way some avalanche-rated MOSFETs or TVS diodes are. If the circuit subjects the diode to recurring reverse voltage excursions above the 40 V VRRM, add external clamping; do not count on the guardring to absorb the energy cycle after cycle.

Key specifications

Verified against the manufacturer datasheet on 2026-07-10. Confirm the current revision before production use.

Alternatives

• SS14: SMD equivalent: 1 A, 40 V Schottky barrier rectifier in SMA (DO-214AC). Same electrical ratings in a surface-mount package for reflow assembly.
• 1N4007: 1 A, 1000 V standard PN rectifier in DO-41. Slower (no Schottky speed) but with far more reverse-voltage headroom. Use when the rail exceeds 24 V or when reverse leakage must stay in the nanoamp range.
• SB140: Another through-hole 1 A, 40 V Schottky from onsemi/Diodes Inc in DO-41. A multi-source alternative; check the specific manufacturer's datasheet for exact VF, IR, and thermal resistance values before substituting at the margins.

Common questions

1N5819 vs 1N4007: which one do I need?

They solve different problems. The 1N5819 is a Schottky: low forward drop (0.600 V max at 1 A), essentially zero reverse recovery, and suited to low-voltage switching supplies, freewheeling, and reverse-polarity protection on rails up to about 24 V. The 1N4007 is a standard PN rectifier rated 1000 V: slower and with a higher forward drop (about 1.1 V at 1 A), but its reverse leakage is nanoamps, not milliamps, and it handles the voltage. Use the 1N5819 when you need low drop and fast switching; use the 1N4007 when voltage headroom or low leakage matter more.

How hot does a 1N5819 get at 1 A?

At 1 A forward current and the worst-case VF of 0.600 V, dissipation is 600 mW. With the datasheet's typical RθJA of 50 °C/W (assuming 0.375-inch leads and generous copper pads), the junction rises 30 °C above ambient. At 25 °C ambient, TJ is 55 °C — well within the 125 °C maximum. But a cramped layout with short leads can raise RθJA to 80 °C/W or more, pushing TJ to 73 °C at the same current. Derate the forward current or provide adequate copper area if the board is tight.

Can I use a 1N5819 for reverse-polarity protection?

Yes, for low-voltage DC inputs. Place it in series with the positive rail (anode to input, cathode to load): the Schottky's low forward drop means less voltage lost to the protection diode than a standard rectifier. The tradeoff is reverse leakage: at elevated temperature, the diode's reverse current can draw milliamps from a connected but reversed supply, and in a battery application that leakage drains the cell even when polarity is correct if the diode is placed in shunt (crowbar) configuration. For series protection on a 5 V or 12 V rail at moderate current, the 1N5819 is a fine choice.

What is the SMD equivalent of the 1N5819?

The SS14 in SMA (DO-214AC) is the closest surface-mount equivalent: same 1 A average current and 40 V reverse voltage. The SS14 has its own datasheet; while the die is similar, the SMA package's smaller lead frame and reduced copper area mean thermal performance differs from the through-hole DO-41. Check the SS14's specific RθJA and derating curves rather than carrying over DO-41 numbers.