Coreless Power Transformer Technology in Isolated Gate Driver Circuits

Key Takeaways

• The prime objective of isolated gate drivers is to provide electrical isolation between driver circuits and power converters.

• Coreless power transformers consist of metal spirals separated from each other over silicon oxide insulation.

• The lack of magnetic core in coreless power transformers prevents problems like magnetic core saturation, frequency limitations, and core losses.

Coreless power transformers are processed using semiconductor manufacturing technology

In electric transportation, aerospace applications, and industrial power systems, wide bandgap devices (especially silicon carbide) are trending. Silicon carbide (SiC) based power electronics used for power management and energy conversion in automotive and industrial systems are integrated into human-machine interfaces (HMIs). These HMIs are connected to controllers and communication peripherals, which support power electronic circuit operations.

The gate driver circuits of power converters are one such control circuit used for turning on and off power semiconductor switches to satisfy load requirements. According to VDE-0884-10 and UL 1577 standards, galvanic isolation between the control circuit and the high power circuit is required.

Coreless power transformers are a modern solution available to provide reinforced galvanic isolation between the control and power circuits. In this article, we will discuss the importance of galvanic isolation and coreless power transformer isolation in gate drivers. 

The Importance of Galvanic Isolation in Gate Driver Circuits 

The prime objective of isolated gate drivers is to provide electrical isolation between driver circuits and power converters for the sake of protection. Device failures, damages, and in the worst cases, human casualties, can be eliminated to a great extent from the control side by incorporating galvanically isolated gate drivers. 

The power levels in control circuits are low compared to the high voltages and high current ratings of power electronic converters. In the absence of isolation, the leakage current path loops across the gate driver circuit and power converter. The unwanted leakage currents are detrimental to human interactions on the control side and also lead to power electronic device failures.

Galvanic isolation in gate drivers:

• Isolates the high voltage side of the power converter from low voltage control circuits.

• Prevents high voltage spikes from damaging the control system.

• Protects personnel working on the control side.

• Increases noise immunity; blocks common-mode noises.

• Prevents disruptive ground loop formation in systems with large ground potential differences.

Coreless Power Transformer Technology

Pulse transformers, optoisolators, and isolated gate driver ICs are some of the traditional methods employed for providing gate driver isolation. However, these conventional techniques fail to address issues in automotive and industrial power systems. The need for excellent integration,  high efficiency, and safety in electric vehicles—and industrial power electronics—resulted in the development of new coreless power transformer technology for gate driver isolation.

Coreless power transformer technology provides total isolation between the high side and low side of electric drives and power management systems. Coreless power transformers are processed using semiconductor manufacturing technology. These transformers consist of metal spirals separated from each other over silicon oxide insulation. Each transformer has two chips: a transmitter and a receiver chip. The coreless power transformer is placed on either of the chips and the upper winding of the transformer is connected to the other chip using bond wires.   

The Advantages of Coreless Power Transformers

The advantages of coreless power transformers are:

1. High reliability due to electric shock resistance.
2. No aging.
3. High insulation properties.
4. Low production costs, as no manual winding process is required.
5. The ability to transmit pulses at MHz rates.
6. Applicability in high switching frequency circuits and high DC link voltage systems.
7. The lack of magnetic core prevents magnetic core saturation, frequency limitations, and core losses.
8. Supports active shutdown when the power supply is not connected to gate drivers.
9. UnderVoltage LockOut (UVLO) feature enables IGBT and MOSFET gate drivers.
10. Eliminates excessive power dissipation, breakdowns, and the malfunctioning of gate driver ICs, which are common in traditional level-shift technology-based transformers.

Coreless power transformer technology-based gate drivers are a significant element in the latest electric vehicles, spacecraft, and industrial power conversion systems. Cadence software offers tools to simulate coreless power transformer parameters such as winding inductance, leakage inductance, coupling coefficient, and the quality factor.

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