Power Converter Gate Drive Slew Modulation for EMI Reduction
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Solution Overview
Problem
Power converters experience increased electromagnetic interference (EMI) due to large di/dt and dv/dt, which are used to reduce switching losses and maintain efficiency at high frequencies, particularly in switching converters with larger area transistors.
Innovation Solution
The solution involves modulating the slew rate of drive signals for high-side and low-side drivers in power converters using slew control logic, which actively changes the slew rate of drive signals over multiple switching cycles, averaging out peaks and valleys in the frequency spectrum to reduce EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If large di/dt and dv/dt are used in drivers, then switching losses are reduced and efficiency is maintained at high switching frequencies, but electromagnetic interference (EMI) is increased
Solution Approach 1:
The patent applies dynamics by making the slew rate of drive signals variable rather than fixed. The driver circuit dynamically adjusts the slew rate based on operating conditions, allowing optimization of switching performance while controlling EMI. This is achieved through control circuitry that modifies the rate of change of drive signals in response to system state.
Solution Approach 2:
The patent changes the parameter of slew rate from a fixed value to a variable parameter that can be adjusted. By modifying the slew rate parameter dynamically, the system can reduce EMI during certain operating phases while maintaining efficient switching during others, thus resolving the contradiction between energy loss and electromagnetic interference.
2Speed
If larger area transistors are used in switching converters, then resistance is reduced and faster switching frequencies are enabled, but switching losses and EMI are increased
Solution Approach 1:
The patent makes the drive signal characteristics dynamic by implementing variable slew rate control. This allows the system to exploit the benefits of larger transistors for faster switching while dynamically managing the rate of change to control EMI, rather than having a fixed relationship between transistor size and signal edges.
Solution Approach 2:
The patent changes the slew rate parameter to optimize the trade-off between switching speed and EMI. By adjusting this parameter, the system can achieve high switching frequencies enabled by larger transistors while controlling the harmful electromagnetic effects that would otherwise increase with faster switching.
3Device complexity
If fixed rise and fall times are used in drive signals, then circuit design is simplified, but EMI cannot be effectively reduced across varying operating conditions
Solution Approach 1:
The patent introduces dynamic control of drive signal characteristics through variable slew rate adjustment. While this increases control complexity, it enables effective EMI reduction across varying operating conditions by adapting the drive signal properties to match system requirements, rather than using a one-size-fits-all fixed approach.
Solution Approach 2:
The patent employs parameter changes in the slew rate to optimize EMI performance. By making the rise and fall time parameters variable rather than fixed, the system can adapt to different operating conditions and effectively reduce EMI, accepting the trade-off of increased control complexity.
Data Source
AI summary
A circuit includes a high-side driver having a high-side slew control input, a high-side drive input and a high-side drive output. A low-side driver has a low-side slew control input, a low-side drive input and a low-side drive output. Drive control circuitry has a high-side drive control output, a low-side drive control output, and a slew control output. The high-side drive control output is coupled to the high-side drive input, the low-side drive control output is coupled to the low-side drive input. The slew control output is coupled to at least one of the high-side slew control input and the low-side slew control input, and the drive control circuitry is configured to provide a slew control signal at the slew control output. The high-side and/or low-side driver is configured to modulate a slew rate of a drive signal at a respective drive output thereof based on the slew control signal.