GaN-MOSFET SMPS Switching Stage for Controlled Gate Charging
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Solution Overview
Problem
Conventional Switched Mode Power Supplies (SMPS) face issues with Electromagnetic Interference (EMI) and inefficiencies due to uncontrolled charging of gate-source capacitance and parasitic capacitance during switching, as well as the need for transformers and current-sensing resistors, which increase size, weight, and losses.
Innovation Solution
A switching stage in SMPS using a GaN transistor connected in series with a MOSFET, with a controller providing a low-ohmic path between the mid-node and the gate terminal, utilizing parasitic capacitance energy to charge the gate-source capacitance efficiently, and eliminating the need for transformers and current-sensing resistors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If conventional current-sensing resistors and transformers are used, then current measurement and power supply isolation are achieved, but circuit losses increase and device size increases
Solution Approach 1:
The patent extracts and eliminates the current-sensing resistor from the circuit by using the gate resistor serving dual purposes. The gate resistor previously only provided gate driving function, but now it also performs current sensing by measuring the voltage drop across it during MOSFET conduction, thereby removing the dedicated sensing resistor and reducing circuit losses and complexity
Solution Approach 2:
The gate resistor is given multiple functions: it provides gate driving capability and simultaneously serves as a current-sensing element. By making the gate resistor multi-functional, the patent reduces the total component count, eliminates the need for separate current-sensing resistors, and simplifies the overall circuit structure while maintaining both gate control and current measurement functions
2Object-affected harmful factors
If uncontrolled gate charging is used, then circuit simplicity is maintained, but EMI increases and switching efficiency decreases
Solution Approach 1:
The controller preliminarily charges the gate-source capacitance through a controlled path before the main switching action. By pre-charging the gate through the gate resistor in a controlled manner before the MOSFET turns on, the patent reduces sudden current spikes and dv/dt during switching transitions, thereby lowering EMI while maintaining circuit efficiency
Solution Approach 2:
The patent implements feedback control by using the voltage across the gate resistor to sense the switching state and adjust the charging/discharging control accordingly. The controller monitors the gate resistor voltage and uses this feedback information to regulate the gate charging process, ensuring controlled switching that minimizes EMI while maintaining efficient operation
3Loss of energy
If parasitic capacitance energy is dissipated, then circuit simplicity is maintained, but power efficiency decreases
Solution Approach 1:
Instead of dissipating the energy stored in parasitic capacitances during MOSFET turn-off, the patent recovers this energy and redirects it to charge the gate-source capacitance during the next turn-on cycle. The energy that would normally be lost as heat in the parasitic capacitance is now captured and reused to drive the gate, improving overall power efficiency while managing the energy flow through controlled switching paths
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 design reduces EMI, enhances power density and efficiency, and lowers hardware costs by optimizing energy usage and eliminating unnecessary components, while maintaining reliable and swift switching.
Implementation Method 1
charging a gate-source capacitance of the MOSFET from the mid-node
Implementation Method 2
a switching element comprising a GaN transistor connected in series with a Metal-Oxide-Semiconductor, MOS, Field Effect Transistor, FET
Data Source
AI summary
A switching stage of a Switched Mode Power Supply (SMPS), the switching stage including a switching element including a GaN transistor connected in series with a Metal-Oxide-Semiconductor (MOS) Field Effect Transistor (FET), thereby defining a mid-node in between the GaN transistor and the MOSFET, a controller arranged for driving a gate terminal of the MOSFET based on an Pulse Width Modulation (PWM) input signal, and the controller includes first switch circuitry arranged for providing a low ohmic path between the mid-node and the gate terminal of the MOSFET and control circuitry arranged for controlling the switch circuitry based on the PWM input signal.