Planar Transformer Gate Drive Without Low-Frequency Limits
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Solution Overview
Problem
Existing power switching circuits using planar transformers face challenges such as high costs, design complexity, low frequency limits, and limited coupling coefficients, which restrict their application in modern power electronics, particularly in high-isolation and high-frequency switching topologies.
Innovation Solution
A power switching circuit utilizing a planar transformer operated in flyback-mode, which reduces the need for auxiliary components, allows operation from existing DC supplies, and achieves higher output voltages without voltage boost circuitry, enabling efficient switching of power semiconductors from DC to several MHz frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional gate drive transformers are used, then electrical isolation is provided, but the low frequency limit prevents use in modern switching topologies operating at 50/60 Hz mains frequency
Solution Approach 1:
The patent replaces conventional magnetic core transformers with a planar PCB transformer implementation. This substitution enables the gate drive circuit to operate at mains frequency (50/60 Hz) and higher frequencies by using printed circuit board traces as windings, eliminating the frequency limitations of traditional transformer designs while maintaining electrical isolation.
Solution Approach 2:
The patent transitions from three-dimensional wound transformers to two-dimensional planar PCB structures. By laying out the primary and secondary windings as traces on PCB layers, the design achieves high isolation and wide frequency response in a planar format that can be integrated into modern switching topologies including NPC topology operating at mains frequency.
2Ease of manufacture
If planar transformers with direct gate drive are used, then cost is reduced and isolation is improved, but the low inductance creates a low frequency limit of 100-1000 kHz
Solution Approach 1:
The patent employs a resonant gate drive circuit that dynamically adjusts the operating frequency to match the resonant frequency of the planar transformer and gate capacitance. This dynamic operation enables the circuit to achieve full gate charge at frequencies below the traditional 100-1000 kHz limit, allowing operation at mains frequency and extending the usable frequency range of planar transformers.
Solution Approach 2:
The patent uses periodic resonant oscillations to charge the power switch gate. By operating at the resonant frequency of the LC circuit formed by the planar transformer inductance and gate capacitance, the circuit accumulates energy over multiple cycles to achieve sufficient gate charge, enabling low-frequency operation despite the low inductance of planar transformers.
3Speed
If modulated gate drive with planar transformers is used, then the low frequency limit is solved, but expensive and complex auxiliary components for driving and demodulating are required
Solution Approach 1:
The patent extracts and eliminates the modulation and demodulation stages from the gate drive circuit. By using direct resonant drive, the design achieves wide frequency response without requiring the expensive auxiliary components (modulators, demodulators, additional transformers) that characterize modulated gate drive approaches, thereby simplifying the overall circuit while maintaining frequency flexibility.
4Reliability
If planar transformers are used, then high isolation is achieved, but the limited coupling coefficient results in output voltage of only 40-60% of primary voltage
Solution Approach 1:
The patent uses resonant operation to dynamically build up voltage across the gate capacitance. The resonant LC circuit allows energy to oscillate and accumulate over multiple cycles, enabling the output voltage to exceed the input voltage despite the limited coupling coefficient of the planar transformer. This dynamic voltage buildup overcomes the static voltage ratio limitation.
Solution Approach 2:
The patent changes the operating parameters by operating at resonant frequency rather than DC or low frequency. This parameter change enables the planar transformer to achieve effective voltage transformation ratio greater than 1:1 by utilizing the resonant amplification effect, thereby overcoming the limited coupling coefficient and achieving full gate drive voltage from standard logic levels.
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 solution significantly reduces costs and complexity, enhances output voltage efficiency, and eliminates the low frequency limit, enabling high-isolation and high-frequency switching with reduced power requirements and increased efficiency in power electronics.
Implementation Method 1
A planar transformer in a flyback configuration is used to turn on a power switch or power semiconductor
Implementation Method 2
A primary current is then switched off and the stored energy in the transformer is dumped in the secondary side inducing an electrical pulse
Data Source
Figure 1~3
Figure 4~6
Figure 7a~7b
AI summary
The invention concerns a power switching circuit (1) comprising - a planar transformer (2) having a primary winding (2a) and a secondary winding (2b), - a power switch (3) having a control gate (4) in electrical connection with the secondary winding (2b), - a switching element (5) configured to provide switching on and off of an electrical current in the primary winding (2a) of the transformer (2), - flyback switching circuitry (6) configured to, in response to a control signal (17), send a turn-on electrical pulse by: - controlling the switching element (5) to switch on, to build up a current in the primary winding (2a), and - controlling the switching element (5) to switch off, to dump the energy stored in the transformer (2) in the secondary winding (2b) inducing the turn-on electrical pulse in the control gate (4) turning the power switch (3) on. The invention also concerns a machine or device incorporating a power switching circuit and a method for driving a control gate of a power switch.