SiC and Si MOSFET Parallel Switching for Power Supply Loss Reduction
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Solution Overview
Problem
Conventional switching power supplies face significant switching losses and high power consumption in standby mode due to the characteristics of Si MOSFETs, particularly the output capacitance and gate charge, which are not effectively mitigated by existing frequency reduction and burst switching controls, especially when using high-power FETs.
Innovation Solution
The implementation of a switching power supply configuration that utilizes a high-power SiC MOSFET as the main switching device and a low-power Si MOSFET in parallel, with a control circuit that switches the SiC MOSFET only when the auxiliary voltage is above a threshold, and switches the Si MOSFET when it falls below this threshold, allowing for efficient operation and reduced switching losses across varying load conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a high-power Si MOSFET is used as the switching device to meet the rated power capacity, then the power capacity is satisfied, but switching loss increases significantly due to output capacitance and gate charge characteristics
Solution Approach 1:
The patent divides the switching function into two separate devices: a main switching device (high-power SiC MOSFET) for handling the rated power capacity and a secondary switching device (low-power Si MOSFET) for handling light-load and standby operations. This segmentation allows each device to be optimized for its specific operating range, with the secondary device having minimal output capacitance and gate charge to reduce switching loss during light-load conditions.
Solution Approach 2:
The patent changes the material parameter of the main switching device from Si to SiC, which fundamentally alters the device characteristics. SiC MOSFETs have lower on-resistance and faster switching speeds compared to Si MOSFETs, reducing conduction loss and switching loss while maintaining the required power capacity.
2Loss of energy
If frequency reduction control or burst switching control is applied to reduce switching loss, then power consumption in standby mode decreases, but the effectiveness is limited when using high-power FETs due to their inherent output capacitance and gate charge
Solution Approach 1:
The patent segments the operating modes by introducing a secondary switching device that is activated during light-load and standby conditions. This secondary device has minimal output capacitance and gate charge, making frequency reduction control and burst switching highly effective in these modes, thereby significantly reducing power consumption in standby mode while maintaining reliability.
3Loss of energy
If the switching frequency is reduced to decrease switching loss, then power consumption in standby mode is reduced, but the ability to maintain stable output voltage under varying load conditions is compromised
Solution Approach 1:
The patent implements dynamic switching between two operating modes: heavy-load mode using the main SiC MOSFET at higher switching frequencies to maintain stable output voltage, and light-load/standby mode using the secondary Si MOSFET at reduced switching frequencies to minimize power consumption. The control circuit dynamically adjusts the switching frequency and device selection based on load conditions, resolving the contradiction between switching loss reduction and output voltage stability.
4Loss of energy
If a high-power SiC MOSFET is used as the main switching device, then switching loss is reduced and power conversion efficiency is improved, but the device complexity increases due to the need for parallel secondary switching device and control circuit
Solution Approach 1:
The control circuit is designed with multi-functionality, handling both heavy-load mode control (activating main SiC MOSFET) and light-load/standby mode control (activating secondary Si MOSFET). The control circuit universally manages switching frequency adjustment, device selection, and output voltage regulation across all operating conditions, reducing the need for separate dedicated circuits and minimizing overall system complexity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration significantly reduces switching losses and power consumption in standby mode while maintaining high power conversion efficiency under heavy loads by leveraging the performance of SiC MOSFETs and optimizing the switching of Si MOSFETs based on auxiliary voltage levels.
Implementation Method 1
a transformer T in which one end of a primary coil Ta is connected to a positive output terminal of the diode bridge circuit DB. The other end of the primary coil Ta of the transformer T is connected to a switching device Q that switches current flowing through the primary coil Ta ON and OFF.
Implementation Method 2
a main switching device made of a SiC MOSFET, configured to be attached to a primary coil of a transformer so as to switch a current flowing in the primary coil ON and OFF
Implementation Method 3
a diode D that rectifies an AC voltage induced in a secondary coil Tb of the transformer T as the switching device Q is switched ON and OFF
Data Source
AI summary
A switching power supply includes a SiC MOSFET (a main switching device) that switches a main current flowing through a primary coil of a transformer ON and OFF as well as a Si MOSFET (a secondary switching device) that has a lower power capacity than the main switching device and is arranged in parallel therewith. A control circuit includes a driver circuit that respectively switches the main switching device and the secondary switching device ON and OFF on the basis of a control signal generated in accordance with an output voltage obtained from a secondary coil of the transformer. The control circuit further includes an enable control circuit that disables the ON/OFF switching of the main switching device when a voltage of an auxiliary voltage obtained from an auxiliary coil of the transformer is less than a prescribed threshold voltage.