GaN Converter Driver Circuit With Isolated Current Sensing
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Solution Overview
Problem
In switch mode power converters using GaN power commutation switches, the influence of the current sensing resistor on the gate-source voltage can lead to oscillation, linear operation, or high drain-source on-resistance, due to the close turn on threshold voltage of GaN transistors to the typical gate drive voltage.
Innovation Solution
The driver circuit decouples the sensing path from the energy storage component during the switching on of the GaN switch, preventing the voltage drop across the sensing component from affecting the energy storage component, thereby ensuring a stable turn-on voltage for the GaN switch.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sensing resistor is connected in series with the GaN switch to provide current sensing feedback, then current sensing function is achieved, but voltage spikes on the sensing resistor reduce the gate-source drive voltage and cause oscillation or linear operation
Solution Approach 1:
The circuit is divided into two separate ground paths: one for the sensing function and one for the gate drive function. The sensing resistor RCS is connected between the source terminal and a first ground, while the energy storage component C4 is connected between the source terminal and a second ground. This segmentation isolates the voltage spikes on the sensing path from the gate drive path, allowing current sensing to function while preventing voltage reduction on the gate-source drive voltage.
Solution Approach 2:
A separate ground path acts as an intermediary between the sensing resistor and the energy storage component. By providing a dedicated ground reference for the gate drive circuit that is electrically isolated from the sensing path, the intermediary ground prevents the voltage spikes on the sensing resistor from affecting the gate-source drive voltage, thus maintaining both sensing accuracy and switch operation stability.
2Loss of energy
If the gate drive voltage is set close to the turn on threshold voltage to enable efficient operation, then power efficiency is improved, but the circuit becomes sensitive to voltage variations and may oscillate or operate in linear mode
Solution Approach 1:
The ground reference is segmented into two separate paths: one for sensing (first ground) and one for gate drive (second ground). This segmentation ensures that voltage variations on the sensing path do not affect the gate drive voltage, allowing the gate drive voltage to be set close to the turn-on threshold for efficient operation while maintaining operational stability through isolation from sensing path voltage spikes.
3Measurement precision
If the energy storage component is charged through the sensing resistor, then the sensing function is maintained, but the charging current influences the sensing voltage and affects the feedback control loop
Solution Approach 1:
The circuit uses separate ground paths to segment the charging current path from the sensing signal path. The energy storage component C4 is charged through a path that references the second ground, while the sensing resistor RCS references the first ground. This segmentation allows the charging current to flow without influencing the sensing voltage, maintaining both sensing accuracy and feedback signal integrity.
Solution Approach 2:
The separate ground path acts as an intermediary that isolates the charging current from the sensing circuit. By providing an independent reference for the energy storage component charging path, the intermediary ground prevents charging current-induced voltage drops on the sensing resistor from corrupting the feedback signal, thus preserving both sensing accuracy and feedback loop performance.
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 approach prevents voltage spikes on the sensing component from reducing the gate-source drive voltage of the GaN switch, ensuring stable turn-on and operation of the GaN switch without influencing the sensing function.
Implementation Method 1
An energy storage component provides a certain turn on voltage between a gate and a source of the GaN switch
Implementation Method 2
A sensing component is connected to the GaN switch for sensing a parameter, such as a peak current of the power commutation
Data Source
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AI summary
A driver circuit is for driving a GaN power commutation switch of a switch mode power converter. A sensing component is connected to the GaN switch for sensing a parameter such as a peak current of the power commutation. An energy storage component provides a certain turn on voltage between the gate and source of the GaN switch. The charging and discharging of the energy storage component is regulated, and the sensing is disabled with timing which is synchronized with the charging and discharging function of the energy storage component. It is prevented that a voltage across the sensing component reduces the generated gate-source drive voltage of the GaN switch.