Other diodes: Diode types
Schottky diode find many uses where a power rectifier is needed.
The Schottky diode rectifier has a number of very useful advantages over other types of diode and as a such can be utilised to advantage.
The Schottky diode has been used as a rectifier for many years in the power supply industry where its use is essential to many designs.
However it is still necessary to take account of the drawbacks of the Schottky diode power rectifier solution. This means that it is not suitable in every instance.
Advantages of using a Schottky diode rectifier
The Schottky diode power rectifier has a number of attributes that make the technology a good option in many instances:
- Low forward voltage drop: The low forward voltage drop offered by Scottky diode power rectifiers is a significant advantage in many applications. It reduces the power losses normally incurred in the rectifier and other diodes used within the power supply. With standard silicon diodes offering the main alternative, their turn on voltage is around 0.6 to 0.7 volts. With Schottky diode rectifiers having a turn on voltage of around 0.2 to 0.3 volts, there is a significant power saving to be gained. However it is necessary to remember that there will also be losses introduced by the resistance of the material, and the voltage drop across the diode will increase with current. The losses of the Schottky diode rectifier will be much less than that of the equivalent silicon rectifier in many applications.
- Fast switching speeds: The very fast switch speeds of the Schottky diode rectifier mean that this diode lends itself to use in switching regulator circuits, enabling higher efficiency levels to be achieved than if other types of power rectifier diode had been used.
Schottky diode rectifier design considerations
Schottky diode rectifiers offer many advantages, but when they are used, there are a number of design considerations to account for. These should be acknowledged in the circuit design being undertaken.
Some of the points to be taken into account include the following:
- Limited reverse voltage: As a result of its structure, Schottky diode rectifiers have a limited reverse voltage capability. The maximum figures are normally around 100 volts. If devices were manufactured with figures above this, it would be found that the forward voltages would rise and be equal to or greater than their equivalent silicon diodes for reasonable levels of current.
- High reverse leakage current: Schottky diode rectifiers have a much higher reverse leakage current than standard PN junction silicon diodes. Although this may not be a problem in some designs it may have an impact on others.
- Limited junction temperature: The maximum junction temperature of a Schottky diode rectifier is normally limited to the range 125°C to 175°C but check the manufacturers ratings for the given component. This compares to temperatures of around 200°C for silicon diode rectifiers.
- Adequate heatsink: Even though the Schottky diode offers a much lower forward voltage drop, in some power applications, significant levels of power can be dissipated. It is necessary to remember this and not assume that as the voltage drop is lower, that heatsinks will not be required. The maximum junction temperatures admissible are lower than for equivalent silicon diodes.
Schottky diodes are a very useful option to have when requiring a power rectifier. However they do have performance limitations and these must be taken into consideration when selecting the required technology for any power rectification application.
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