High-Side Gate Driver for Linear MOSFET Voltage Ramping
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Solution Overview
Problem
Switching circuits with MOS transistors experience non-linear voltage transitions due to variable depletion capacitance, leading to prolonged turn-on times and increased power dissipation, while attempting to speed up transitions can induce undesirable electromagnetic interference (EMI).
Innovation Solution
A high side gate driver circuit biases the gate of the high side transistor with a current proportional to the inverse of the square root of the drain-gate voltage, maintaining a constant ratio of current to capacitance, enabling linear output voltage transitions, reducing EMI, and minimizing power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a MOS transistor is used for switching, then the switching circuit can control power supply to motors and lights, but the variable depletion capacitance causes non-linear voltage transitions and prolonged turn-on times
Solution Approach 1:
The patent changes the gate current parameter from constant to variable, specifically proportional to the inverse of the square root of the drain-gate voltage. This parameter transformation compensates for the variable depletion capacitance effect, maintaining a more linear voltage transition and reducing turn-on time without causing excessive EMI.
Solution Approach 2:
The patent implements feedback by monitoring the drain-gate voltage and adjusting the gate current accordingly. The gate current is made proportional to 1/√(Vdg), creating a feedback mechanism that compensates for the non-linear capacitance behavior and achieves faster, more controlled switching transitions.
2Loss of time
If a higher gate current is applied to increase the ramp up rate and shorten turn-on time, then the transition speed improves, but electromagnetic interference (EMI) increases
Solution Approach 1:
Instead of applying a uniformly high gate current, the patent transforms the current parameter to be proportional to 1/√(Vdg). This creates a dynamically adjusted current profile that provides sufficient drive strength to shorten turn-on time while avoiding the excessive current levels that generate harmful EMI.
Solution Approach 2:
The patent makes the gate current dynamic rather than static, adjusting it in real-time based on the drain-gate voltage. This dynamic adjustment allows the system to optimize switching speed at each moment of the transition while maintaining EMI within acceptable limits throughout the switching cycle.
3Reliability
If the output voltage ramps up in a non-linear manner due to variable depletion capacitance, then the transistor transitions from off to on, but the transition period becomes relatively long and power dissipation increases
Solution Approach 1:
The patent changes the gate current parameter from constant to variable (proportional to 1/√(Vdg)), which transforms the non-linear voltage ramp into a more linear transition. This parameter transformation reduces the overall transition period and minimizes the energy dissipated during switching, improving both reliability and energy efficiency.
Data Source
AI summary
A switching circuit includes a first transistor and a driver circuit. The first transistor has a first current electrode coupled to a first power supply voltage terminal to receive a first power supply voltage, a control electrode, and a second current electrode coupled to an output terminal. The driver circuit has an output coupled to the control electrode of the first transistor, the driver circuit for providing a bias current to the control electrode of the first transistor that is proportional to an inverse of a square root of a voltage between the first current electrode and the control electrode of the first transistor. A voltage at the output terminal increases linearly during a turn-on period of the first transistor.