Switching Power Supply Considerations
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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 critical than ever. This is because power supplies with high switching frequencies are extremely sensitive to diode parameters such as current handling capability.
Schottky diodes are the most commonly used due to their low forward voltage drop, which decreases power loss of the power supply. However, as frequencies increase, the selection of a suitable Schottky diode becomes a challenging process. 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 important factor when choosing a Schottky diode for power supplies with high switching frequencies. اس اس آر is the time it takes for the minority carrier to recombine at the pn junction once the diode is turned off. A shorter reverse recovery time is better 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 low minority carrier lifetime and a suitable design that minimizes the amount of minority carrier storage at the pn junction.
Forward Voltage Drop (VF)
Forward voltage drop is the minimum voltage required for the diode to start conducting. 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 minimum VF of 0.3V for high-frequency applications.
Current Handling Capability
Current handling capability is the ability of the diode to resist high peak currents without failing. This parameter is crucial when selecting a Schottky diode for applications that require high-frequency switching as high peak currents are often encountered in some cases.
When choosing a Schottky diode, you should select ones that have a good current handling capability than the design current rating of your design.
On-Resistance (RDS(ON))
On-resistance is the resistance of the diode when it is switching. It directly affects the overall performance as higher RDS(ON) results in increased power loss.
You should look for Schottky diodes with a small on-resistance, which is unique to the industry. The on-resistance is temperature-dependent, so it is necessary to balance a balance 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 greater power loss of the diode.
When selecting a Schottky diode, you should choose ones that have a good heat dissipation which translates to a high thermal rating.
Slope Resistance (rs)
Slope resistance is the resistance of the diode when it is in operation and a bias is applied. It is critical in lowering power loss in the diode of a switching power supply.
When selecting a Schottky diode, you should look for ones with a low slope resistance of smaller than 0.5 ohms to reduce power losses.
Package Type and Design
The package type and formulation of the Schottky diode also play a crucial role in high-frequency switching applications. For example, a Schottky diode attached to a copper plate increases efficiency.
Select the right pair of package and design for your high-frequency application.
Schottky diodes are the most commonly used due to their low forward voltage drop, which decreases power loss of the power supply. However, as frequencies increase, the selection of a suitable Schottky diode becomes a challenging process. 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 important factor when choosing a Schottky diode for power supplies with high switching frequencies. اس اس آر is the time it takes for the minority carrier to recombine at the pn junction once the diode is turned off. A shorter reverse recovery time is better 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 low minority carrier lifetime and a suitable design that minimizes the amount of minority carrier storage at the pn junction.
Forward Voltage Drop (VF)
Forward voltage drop is the minimum voltage required for the diode to start conducting. 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 minimum VF of 0.3V for high-frequency applications.
Current Handling Capability
Current handling capability is the ability of the diode to resist high peak currents without failing. This parameter is crucial when selecting a Schottky diode for applications that require high-frequency switching as high peak currents are often encountered in some cases.
When choosing a Schottky diode, you should select ones that have a good current handling capability than the design current rating of your design.
On-Resistance (RDS(ON))
On-resistance is the resistance of the diode when it is switching. It directly affects the overall performance as higher RDS(ON) results in increased power loss.
You should look for Schottky diodes with a small on-resistance, which is unique to the industry. The on-resistance is temperature-dependent, so it is necessary to balance a balance 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 greater power loss of the diode.
When selecting a Schottky diode, you should choose ones that have a good heat dissipation which translates to a high thermal rating.
Slope Resistance (rs)
Slope resistance is the resistance of the diode when it is in operation and a bias is applied. It is critical in lowering power loss in the diode of a switching power supply.
When selecting a Schottky diode, you should look for ones with a low slope resistance of smaller than 0.5 ohms to reduce power losses.
Package Type and Design
The package type and formulation of the Schottky diode also play a crucial role in high-frequency switching applications. For example, a Schottky diode attached to a copper plate increases efficiency.
Select the right pair of package and design for your high-frequency application.
