Diode types: rectifier, Schottky, Zener, LED, TVS
They are all called diodes but are used for completely different things. When to use each of the five types you see on schematics.
| Type | Characteristics | Where used |
|---|---|---|
| General rectifier (1N4007) | Vf about 0.7 to 1 V, slow | AC rectification, reverse-polarity protection |
| Schottky (SS34) | Vf about 0.3 to 0.5 V, fast | Switching converters, low-loss reverse protection |
| Zener | Accurate reverse breakdown voltage | Simple voltage reference, input clamp |
| LED | Vf 1.8 to 3.3 V, emits light | Indicators |
| TVS | Absorbs momentary overvoltage quickly | ESD, surge protection |
How to choose
- Average current and maximum reverse voltage: use at half the rating or less.
- Reverse recovery time: in a switching circuit a slow diode conducts backwards briefly as it turns off, causing loss and noise. So converters use Schottky or fast-recovery diodes.
- Leakage current: a Schottky's reverse leakage grows with temperature. It affects the standby current of battery devices.
An LED is driven by current
Once past Vf, an LED's current rises steeply, so driving it directly with a voltage burns it out. Always set the current with a series resistor or a constant-current circuit.