Transistors｜Evaluation
Importance of MOSFET Recovery Characteristics for Off-Resonance of LLC Converters
2024.05.08
Points of this article
・In an LLC converter, when there is deviation from the anticipated resonance condition, a shoot-through current occurs due to the recovery current in the MOSFET body diode, thus increasing switching losses and, in the worst case, culminating in MOSFET destruction.
・In order to reduce the risk of such destruction, a MOSFET having a body diode with excellent recovery characteristics should be selected, to reduce the shoot-through current value.
This fourth article explains what is the most important takeaway of this section: the importance of the MOSFET recovery characteristics for off-resonance of LLC converters.
- ■ Basic Configuration of an LLC Converter
- ■ Features of LLC Converter Operation
- ■ Basic Operation of LLC Converters
- ■ Importance of MOSFET Recovery Characteristics for Off-Resonance of LLC Converters
Importance of MOSFET Recovery Characteristics for Off-Resonance of LLC Converters
When we examine the waveforms and current paths in an LLC converter in region (2), explained in the previous article, we find an interval in which current flows in the body diode. However, in steady-state operation, the body diode is never turned off during this interval, and so in general a recovery current does not occur.
Next, as an example of LLC converter operation in region (3), Fig. 5 shows the operation waveforms of an LLC converter in an overloaded state. Upon examining the Q1 and Q2 drain current waveforms in Fig. 5, we see that ZCS operation rather than ZVS operation is occurring. Hence a shoot-through current is occurring due to a recovery current in the body diodes, MOSFET switching losses are increased, and in the worst case, MOSFET destruction may occur.
Fig. 5. LLC converter operation waveforms for overloaded conditions
Thus in region (3), a shoot-through current occurs as a result of deviation from the anticipated resonance condition. Fig. 5 shows waveforms in an overloaded state, but off-resonance may also occur to cause a shoot-through current in other situations, such as when the input voltage is low, there are sudden fluctuations in the load conditions, or upon power supply turn-on. Hence in order to prevent MOSFET destruction due to off-resonance, MOSFETs with excellent body diode recovery characteristics should be selected to reduce shoot-through current values.
The R60xxVNx series of MOSFETs aptly meet these requirements. The R60xxVNx series models are the latest generation of PrestoMOS™ MOSFETs, which are super-junction MOSFETs featuring fast recovery characteristics. Fast recovery performance means that losses due to shoot-through currents can be reduced, making such devices an excellent choice as primary-side MOSFETs in LLC converters. For more information on the R60xxVNx series and on PrestoMOS™, please visit the following page:
Transistors
Basic
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Basics of Transistors
- Transistor Fundamentals: Structure, Types, and Operating Principles
- Bipolar Junction Transistor (BJT) Basics: Operation and Applications (NPN & PNP)
- NPN Transistor: Low-Side Switch Fundamentals
- PNP Transistor: High-Side Switch Fundamentals
- What is a Digital Transistor?
- Digital Transistor Selection
- ON Resistance
- Total Gate Charge
- How to select＜Selecting Transistors to Ensure Safe Operation＞
- Junction Temperature ＜Calculating Transistor Chip Temperature＞
- What is a Load Switch?
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Basics of MOSFETs
- What are MOSFETs? – MOSFET Parasitic Capacitance and Its Temperature Characteristic
- What are MOSFETs? – MOSFET Switching Characteristics and Temperature Characteristics
- What are MOSFETs? – MOSFET Threshold Values, ID-VGS Characteristics, and Temperature Characteristics
- What are MOSFETs? – Super-junction MOSFET
- What are MOSFETs? – Types and Features of High Voltage Super-Junction MOSFET
- What are MOSFETs? – Fast trr SJ-MOSFET：PrestoMOS™
- MOSFET Thermal Resistance and Power Dissipation: Packages Capable of Back-Surface Heat Dissipation
- Introduction
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Confirming the Suitability of a Transistor in Actual Operation – Introduction
- Confirmation of the Chip Temperature
- Confirmation of Suitability in Actual Operation and Preparations
- Confirmation that Absolute Maximum Ratings are Satisfied
- Confirmation that Operation is within the SOA (Safe Operating Area)
- Confirmation that Operation is within the SOA Derated at the Actual Operating Temperature
- Confirmation that Average Power Consumption is within the Rated Power
- Summary
- Summary
Evaluation
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The Importance of the Recovery Characteristics of Primary-side Switching Elements in LLC Converters －Introduction－
- Basic Configuration of an LLC Converter
- Features of LLC Converter Operation
- Basic Operation of LLC Converters
- Importance of MOSFET Recovery Characteristics for Off-Resonance of LLC Converters
- The Importance of the Recovery Characteristics of Primary-side Switching Elements in LLC Converters ーSummaryー
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The Importance of the Reverse Recovery Characteristics of Switching Elements in Inverter Circuits －Introduction－
- Types of Inverter Circuits and Energization Methods
- Basic Operation of 3-Phase Modulation Inverter Circuits
- Comparison of Losses in a PrestoMOS™ MOSFET and a Standard SJ MOSFET Using Double-Pulse Tests (Actual Measurement Results)
- Comparison of Efficiency of a PrestoMOS™ MOSFET and a Standard SJ MOSFET in a 3-Phase Modulation Inverter Circuit (Simulations)
- The Importance of the Reverse Recovery Characteristics of Switching Elements in Inverter Circuits －Summary－
- Mechanisms of MOSFET Destruction
- About Double-Pulse Tests
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Improving the Power Conversion Efficiency of Phase Shift Full Bridge Circuits – Introduction
- Basic Configuration of a PSFB Circuit
- Basic Operation of PSFB Circuits
- Guidelines Relating to Operation of Switching Elements Under Light Loading
- Guidelines Relating to Operation of Switching Elements Under Heavy Loading
- Evaluation of Efficiency
- Improving the Power Conversion Efficiency of Phase Shift Full Bridge Circuit – Summary –