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Schottky diode

A diode with a low forward drop (0.3–0.5 V), used in power paths: reverse polarity protection, OR-ing two supplies, flyback across motors.

What it does#

A Schottky diode conducts with about 0.3–0.5 V drop instead of 0.7 V and switches very fast. That makes it the default for power: less voltage and less heat lost per ampere. The catalog has SS14 (40 V, 1 A, SMA) and B5819W (40 V, 1 A, SOD-123), both listed under the Diode generic.

Uses#

  • Reverse polarity protection: a diode in series with the input; a reversed plug just blocks. Costs ~0.4 V (see the P-MOSFET alternative that costs almost nothing).
  • OR-ing supplies: USB and a battery both feed one rail; whichever is higher supplies it, and neither back-feeds the other.
  • Flyback: across inductive loads switched by a MOSFET.
Example circuit: VBUS (5 V) through D1 and VBAT (3–4.2 V) through D2 both feed VSYS. With USB in, VSYS ≈ 4.6 V and the battery is idle.
VBUS (5 V) through D1 and VBAT (3–4.2 V) through D2 both feed VSYS. With USB in, VSYS ≈ 4.6 V and the battery is idle. Open the schottky_power_or example from this page in PCB Canvas: “Insert into my schematic”.

Pitfalls#

  • Leakage. Schottkys leak in reverse, more when hot: a few µA to mA. Fine for power, not for precision or very low-power standby.
  • Voltage drop at load. The datasheet’s 0.5 V is at 1 A; at 2 A it is more and the diode gets hot. Size it for the real current.
  • OR-ing a LiPo this way wastes 0.3–0.5 V of the battery. Better load sharing uses a P-MOSFET instead of D2, as the climate sensor example project does.

Footprint#

  • SS14 in SMA and B5819W in SOD-123: both easy to hand solder, both JLCPCB basic parts (SS14: C2480, B5819W: C8598), so neither adds an extended-part fee.