High-Frequency Switching Requirements
When it comes to high-frequency switching applications, the quality of the the chosen secondary side diode used as the secondary side rectifier is more important than ever. This is because power supplies that switch at high frequencies are extremely sensitive to diode parameters such as forward voltage drop.
Schottky diodes are the preferred choice due to their good current handling capability, which increases efficiency of the power supply. However, as the frequency gets higher, the selection of a suitable Schottky diode becomes a daunting task. Let's break down the crucial factors and parameters to keep in mind when selecting a Schottky diode for high-frequency switching applications.
Reverse Recovery Time (TRR)
Reverse recovery time is the most significant parameter when choosing a Schottky diode for power supplies with high switching frequencies. It is the time it takes for the minority carrier to hide at the pn junction once the diode is turned off. A shorter reverse recovery time is preferable as it allows the diode to bounce back before the next switching cycle, reducing switching losses.
To minimize TRR, you should look for Schottky diodes with a small minority carrier lifetime and a suitable design that reduces minority carrier storage at the pn junction.
Forward Voltage Drop (VF)
Forward voltage drop is the minimum voltage required for the diode to conduct electricity. A lower VF is better as it decreases the power loss of the power supply.
When selecting a Schottky diode, you should look for ones with a low forward voltage drop of 0.3V for high-frequency applications.
Current Handling Capability
Current handling capability is the ability of the diode to withstand high peak currents without failing. This parameter is important when selecting a Schottky diode for high-frequency switching applications as peak currents can reach high levels in some cases.
When choosing a Schottky diode, you should select ones that have a better current handling capability than the design current rating of your design.
On-Resistance (RDS(ON))
On-resistance is the resistance between the anode and cathode when it is switching. It alters the efficiency of the power supply as higher RDS(ON) results in greater power loss.
You should look for Schottky diodes with a miniature on-resistance, which is unique to the industry. The on-resistance is dependent on temperature, so it is important to determine a compromise between RDS(ON) and junction to lead inductance.
Junction Temperature (TJ)
Junction temperature is the temperature inside the diode where it is switching. High junction temperature can lead to increased MTBF of the diode.
When selecting a Schottky diode, you should choose ones that have a good heat dissipation which translates to a upper limit temperature rating.
Slope Resistance (rs)
Slope resistance is the resistance between the anode and cathode when it is switching and a voltage is applied. It has a profound impact in minimizing power loss in the diode of a power supply with high-frequency switching.
When selecting a Schottky diode, you should look for ones with a low slope resistance of less than 0.5 ohms to reduce power losses.
رله ssr and Design
The package type and design of the Schottky diode also play a crucial role in applications that require high-frequency switching. For example, a Schottky diode sits on a copper plate increases efficiency.
Select the right pair of package and design for your application that requires high-frequency switching.