Schottky diode

The Schottky diode or Schottky barrier diode, named after the German physicist Walter H. Schottky, is a semiconductor device that provides very fast switching between states forward and reverse conduction (less than 1ns in small 5mm diameter devices) and very low threshold voltages (also known as elbow voltages, although in English they refer to it as "knee", that is, knee).

Operation

At low frequencies a normal diode can easily switch when the bias changes from forward to reverse, but as the frequency increases the switching time can become very long, endangering the device.

The Schottky diode is made up of a metal-semiconductor junction (Schottky barrier), instead of the conventional P-semiconductor - N-semiconductor junction used by normal diodes.

Thus, the Schottky diode is said to be a "majority carrier" semiconductor device. This means that, if the semiconductor body is doped with N-type impurities, only the N-type carriers (mobile electrons) will play a significant role in the operation of the diode and the slow random recombination of N- and P-type carriers that has place in normal rectifier diodes, thus the operation of the device will be much faster.

Features

Diodo Schottky 1N5822 with a cut in its encapsulate. The semiconductor in the center forms a barrier of Schottky between a metal electrode (realizing a rectifying action) and a ohmic contact with the other electrode.

Diodo Schotky HP 5082-2800

The high switching speed allows rectifying very high frequency signals and eliminating excess current in high intensity circuits.

Unlike conventional silicon diodes, which have a threshold voltage —the forward voltage value above which the diode conducts— of 0.7 V, Schottky diodes have a threshold voltage of approximately 0. 2 V to 0.4 V being used, for example, as discharge protection for solar cells with lead-acid batteries.

The most obvious limitation of the Schottky diode is the difficulty of achieving relatively high reverse resistances when working with high reverse voltages. The Schottky diode finds a wide variety of applications in high-speed circuits for computers where high switching speeds are needed and, due to its low forward voltage drop, allows its operation with reduced energy expenditure. Another application of the Schottky diode is in variable frequency drives (inverters) and stepper motor driver circuits, when the driver circuit disconnects the motor windings, these diodes are responsible for draining the inductive current peaks that return from the windings. of a motor and return them to the DC bus so that they do not burn the IGBT transistors of the chopper, destroying the device. When the motor behaves as a generator, the current flows to the DC bus through the diodes and is not absorbed by the IGBTs.

The Schottky diode is used in various TTL logic ICs. For example, the circuits of the 74S, LS, ALS and AS series (Schottky, Low Power Schottky, Advanced Low Power Schottky, etc.) allow the switching times between the transistors to be much shorter since they are more superficial and smaller. so there is an improvement in the speed/power ratio. The ALS type allows more power and less speed than the LS, while the AL has twice the speed of the Schottky TTL with the same power.