SCHOTTKY DIODES

Schottky Diodes

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1. Overview

Schottky diodes (a.k.a. Schottky barrier diode or hot-carrier diode) are diodes formed from a semiconductor-metal junction, rather than a semiconductor-semiconductor junction of a traditional diode. This creates a lower forward voltage drop than standard diodes (typically 0.3V instead of 0.7V), and consequentially also faster switching speeds. They are used in applications where:

  • The input voltage is small.

  • In high power applications in where the power consumption of the diode needs to be kept to a minimum (e.g. in a SMPS).

  • High switching speed applications.

2. How They Are Made

Unlike general purpose diodes which are formed from the junction of N-doped and P-doped semiconductors, Schottky diodes are formed from the junction of a semiconductor with a metal[1]. This semiconductor-metal junction is called a Schottky barrier, named after German physicist Walter H. Schottky.

3. Schematic Symbol And Designator

schottky diode schematic symbol
Figure 1. The schematic symbol and designator for the Schottky diode. Note the curls on the bar, which differs from the general-purpose diode symbol. The anode is the left pin and the cathode is the right pin.

4.1. BAT42/BAT43

The BAT42 and BAT43 are popular Schottky diodes, traditionally provided in the axial DO-35 package. Manufactured by Vishay and STMicroelectronics (among others). The main (and potentially only?) difference between the BAT42 and BAT43 seems to be that the forward voltage for the BAT42 is measured at 10 and 50mA, whilst for the BAT43 it is measured at 2 and 15mA.

4.2. 1N58xx Family

The 1N58xx family of Schottky diodes are typically provided in the DO-41 package. Part numbers increment from 1N5817 (20V, 1A) through to 1N5825 (40V, 5A).

1N58xx Schottky diode part number breakdown.
  1N58    17
  |       |
Family    |
          |
Voltage/Current Rating
17-19=1A,20-22=3A,23-25=5A

5. Guard Rings

Guard rings can be designed onto the silicon that makes up a Schottky diode to improve it’s robustness to over-voltage, by causing the diode to be driven into avalanche breakdown before the Schottky is damaged by excessive current[2].

One example of a Schottky diode with a guard ring is the Nexperia PMEG2020AEA 20V, 2A Schottky diode in a SOD-323 package:

Planar Maximum Efficiency General Application (MEGA) Schottky barrier rectifier with an integrated guard ring for stress protection, encapsulated in a SOD323 (SC-76) very small SMD plastic package[3].

— Nexperia PMEG2020AEA Datasheet

References


Authors

Geoffrey Hunter

Dude making stuff.

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This work is licensed under a Creative Commons Attribution 4.0 International License .

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