Diodes

A diode is a one-way valve for current. It conducts when the anode is more positive than the cathode by roughly its forward voltage vf, and blocks current the other way until the reverse voltage gets large enough to break it down. de:volt ships three: the rectifier diode, the Schottky diode, and the Zener diode. For the transient-clamping TVS diode see /parts/protection; for light-emitting diodes see /parts/leds.

How a diode conducts

Current flows anode → cathode (the direction the schematic triangle points). Once it conducts, the diode holds a roughly constant drop across itself equal to vf — about 0.7 V for a silicon rectifier — and the rest of the circuit sets the current. Reverse the voltage and the diode blocks, behaving like an open switch, until the reverse voltage exceeds the part’s rating.

On every diode here the cathode is the banded end — the stripe printed across one end of the body marks pin k (K). Get the band backwards and the diode blocks the current you wanted to pass.

Rectifier Diode

A general-purpose silicon rectifier, 1N4001-class. The default workhorse for steering DC and surviving high reverse voltages.

Pinout

Specs

vf is editable in the Inspector. Common uses:

• Reverse-polarity protection. In series with the supply, a rectifier passes current only when the battery is the right way round — at the cost of the 0.7 V drop.
• Freewheeling (flyback). Across an inductive load such as a relay or motor, reverse-biased in normal operation, the diode gives the inductor’s collapsing current somewhere to go when the drive switches off — clamping the spike that would otherwise punch through the driving transistor. See /parts/transistors.
• Rectifying AC into pulsing DC.

Schottky Diode

A Schottky trades reverse-voltage headroom for a much lower forward drop and faster switching. Where a silicon rectifier loses ~0.7 V, the Schottky loses only ~0.3 V.

Pinout

Specs

Reach for a Schottky on small-battery power rails, where every tenth of a volt of drop matters, and in fast-switching paths where the rectifier would be too slow. The trade-off is the modest 40 V reverse rating — don’t use it where the line can swing far negative.

Zener Diode

A Zener is built to be run backwards. In reverse it blocks normally until the voltage reaches its breakdown value vz, at which point it conducts hard and pins the voltage across itself at vz. That makes it a cheap voltage reference or clamp.

Pinout

Specs

To use it, reverse-bias it: cathode (K, banded) toward the positive node, anode toward GND, fed through a series resistor that sets the current. Above vz the diode holds the cathode at vz regardless of small supply changes. Keep at least the knee current (iz_knee, 5 mA) flowing for a clean clamp.

+V ── R_series ──┬── Vout (clamped at vz)
                 │
              [Zener]   (K up toward +V, A to GND)
                 │
                GND

vz sets the breakdown voltage and is shown in the Inspector. Simulator caveat: in v1, vz is not varied by the Monte Carlo analysis — every run uses the nominal breakdown, so a Monte Carlo sweep won’t show spread on a Zener reference even though a real part has a tolerance.