Cascode HEMT Driving Through Asymmetrical CMOS for Fast Switch-Off
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Solution Overview
Problem
Existing cascoded configurations in switching mode power supply systems face inefficiencies during switch-OFF transitions due to diode drop losses and slow transition times, particularly in using rectifiers.
Innovation Solution
A cascode circuit method controlling High Electron Mobility Transistors (HEMTs) through state transitions, where a P-channel MOSFET source is connected to a capacitor and the HEMT drain, using a controller to manage switch states and charge balancing between capacitors for faster and lossless transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rectifier is used in the cascode circuit, then the circuit provides reliable switching mode operation, but diode drop losses occur reducing efficiency
Solution Approach 1:
The patent changes the operating parameters by replacing the rectifier diode with an active P-channel MOSFET switch. The MOSFET operates in its resistive region during the off-transition, dynamically adjusting its resistance to minimize voltage drop and energy loss while maintaining the necessary switching functionality. This parameter change from passive diode to active transistor enables lower conduction losses.
Solution Approach 2:
The patent substitutes the passive rectifier mechanism with an active electronic switching mechanism. Instead of relying on the inherent rectifying properties of a diode, the system uses controlled MOSFET switching with capacitive charge transfer to achieve the same voltage reversal and current blocking functions, but with significantly reduced power losses.
2Device complexity
If simple coupling of normally ON and normally OFF devices is used, then the circuit structure is simple, but the switch-OFF transition is slow
Solution Approach 1:
The patent applies preliminary action by pre-charging the capacitor connected to the P-channel MOSFET source before the switch-OFF transition. This stored charge is then rapidly transferred to the HEMT gate during the transition, actively pulling the gate voltage below the threshold to accelerate the turn-off process. The capacitor is recharged during the subsequent on-state, preparing for the next transition.
Solution Approach 2:
The patent introduces a capacitor as an intermediary energy storage element between the P-channel MOSFET and the HEMT gate. This capacitor acts as a charge pump, transferring charge rapidly during transitions to force the HEMT gate voltage below the threshold, thereby accelerating the switch-OFF transition without requiring complex active driver circuits.
3Stability of the object's composition
If the first switch is kept ON to maintain HEMT ON state, then the HEMT remains conductive, but the capacitor charge is discharged reducing efficiency
Solution Approach 1:
The patent implements self-service by using the HEMT's own drain current to recharge the capacitor during the on-state. The capacitor automatically recovers its charge from the power supply through the conducting HEMT, preparing for the next transition without external intervention. This self-recharging mechanism eliminates the need for separate charging circuits and minimizes energy losses.
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 avoids diode drop losses and accelerates switch-OFF transitions by stabilizing drain voltages and efficiently managing charge storage, enhancing the performance of switching mode power supply systems.
Implementation Method 1
a low voltage P-channel MOSFET whose source is connected to a capacitor
Implementation Method 2
charging a capacitance C through a channel with a resistive behavior
Implementation Method 3
the switch-OFF transition is forced to be faster by balancing a charge between the VCC capacitor and a cascoded driver switch output capacitance
Data Source
AI summary
Disclosed is a method of controlling a High Electron Mobility Transistor (HEMT) through a cascode circuit, the cascode circuit including first and second switches, a capacitor connected to a source of the first switch, a source of the HEMT being connected to the drain of the first switch, and a controller for controlling the first and second switches. The method is achieved by defining state A, where the first switch is controlled to be OFF resulting in the HEMT being OFF and the second switch is controlled to be ON allowing the capacitor to be charged and stabilizing the drain voltage of the HEMT at around the HEMT gate threshold voltage. The method further defines state B, where the first switch is controlled to be ON resulting in the HEMT being ON and the second switch is controlled to be OFF almost all the time, thereby preserving the charge stored in the capacitor. Moreover, the method provides transitioning from state A to state B to turn the HEMT ON; and transitioning from state B to state A to turn the HEMT OFF, wherein the first switch is switched-OFF and the second switch is switched-ON allowing for quicker charge of the output capacitance of the first switch from the capacitor to keep the HEMT OFF.