Common-Mode Choke Level-Shifter for High-Side Switch Timing
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Solution Overview
Problem
Existing methods for controlling high-side power switches in totem-pole power circuits are limited by speed, require complex circuitry, and incur significant recovery time or high flyback voltages, especially when dealing with large high-side voltages and non-complementary switch polarities.
Innovation Solution
Applying switch drive pulses to a common-mode choke for level-shifting, which allows for efficient magnetic reset without a floating drive supply, using a single magnetic device to convey both ON and OFF pulses with excellent timing integrity and simplicity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a transformer is used to convey control signals to high-side switches, then good timing integrity can be obtained, but resetting magnetizing currents incurs significant recovery time or high flyback voltages
Solution Approach 1:
The patent changes the fundamental parameter of the magnetic device from a transformer with magnetizing current requirements to a common-mode choke that operates with differential signals. This parameter change eliminates the need for magnetizing current reset, thereby removing the recovery time penalty while maintaining good timing integrity through the choke's differential mode operation.
Solution Approach 2:
Instead of using a transformer that requires magnetizing current reset, the patent inverts the approach by using a common-mode choke where the differential signal inherently resets the magnetic field during normal operation. The choke's common-mode windings are configured such that differential signals produce opposing magnetic fields that cancel each other, eliminating the need for separate reset mechanisms.
2Measurement precision
If a transformer is used to convey control signals to high-side switches, then good timing integrity can be obtained, but handling high flyback voltages is required
Solution Approach 1:
The patent changes the operating mode from transformer differential mode (which generates flyback voltages) to common-mode choke differential mode. The common-mode choke's symmetric winding configuration causes differential signals to produce equal and opposite magnetic fields that cancel, eliminating flyback voltage generation while preserving timing integrity through the choke's common-mode rejection properties.
Solution Approach 2:
The patent converts the potential harmful effect of magnetic field buildup into a beneficial cancellation effect. By configuring the common-mode choke with symmetric windings, the differential signal's magnetic fields oppose each other and cancel, transforming what would be a harmful flyback voltage into a useful self-resetting mechanism that improves timing integrity without generating harmful voltages.
3Adaptability or versatility
If P-channel devices are used in totem-pole power circuits, then complementary switch polarities are achieved, but the switches are either less conductive or slower
Solution Approach 1:
The patent creates a universal common-mode choke driver that can drive both N-channel and P-channel high-side switches with the same circuit topology. The differential signal configuration and common-mode choke operation are polarity-agnostic, allowing the same circuit to efficiently drive either switch type without requiring complementary polarities, thereby enabling the use of faster N-channel devices in non-complementary totem-pole configurations.
Solution Approach 2:
The patent inverts the traditional approach of requiring complementary switch polarities by using a common-mode choke that naturally handles differential signals regardless of switch polarity. This inversion allows non-complementary totem-pole configurations using identical N-channel switches, eliminating the speed limitation imposed by P-channel devices while maintaining proper high-side switching operation.
4Measurement precision
If a common-mode choke is used for level-shifting, then excellent timing integrity is achieved, but the choke must be reset during pulses
Solution Approach 1:
The patent implements a self-resetting common-mode choke mechanism where the differential drive signal itself performs the reset function. During each pulse, the differential current through the choke's symmetric windings creates opposing magnetic fields that cancel and automatically reset the choke, eliminating the need for external reset circuitry while maintaining excellent timing integrity through the choke's common-mode operation.
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 provides excellent timing integrity and simplifies the circuitry by allowing small inductance for bistable switches and larger inductance for non-bistable switches, eliminating the need for a floating drive supply and reducing reset disturbances, while enabling efficient level-shifting for high-side switches.
Implementation Method 1
the common mode choke has plenty of time to be magnetically reset by convenient circuitry
Implementation Method 2
switch drive pulses, instead of being applied to one or more transformers, are applied to a common-mode choke. These pulses are thereby level-shifted to a high-side voltage to drive a high-side switch
Data Source
AI summary
In one embodiment, a level-shifter for driving a high-side power switch with sub-nanosecond timing integrity, without requiring a high-side gate-drive power supply, is provided. A drive source is connected to the gate of a power switch through a common-mode choke, and the latter level-shifts the common-mode voltage of the drive signal to the common-mode level of the power switch. The same level-shifter may also be used to drive a low-side power switch to avoid ground bounce.