Coreless printed-circuit-board (PCB) transformers and operating techniques therefor
Optimal operating techniques are disclosed for using coreless printed-circuit-board (PCB) transformers under (1) minimum input power conditions and (2) maximum energy efficiency conditions. The coreless PCB transformers should be operated at or near the ‘maximum impedance frequency’ (MIF) in order to reduce input power requirement. For maximum energy efficiency, the transformers should be at or near the “maximum efficiency frequency” (MEF) which is below the MIF. The operating principle has been confirmed by measurement and simulation. The proposed operating techniques can be applied to coreless PCB transformers in many circuits that have to meet stringent height requirements, for example to isolate the gates of power MOSFET and IGBT devices from the input power supply.
1. A method of operating a coreless planar transformer, wherein said transformer is operated at an optimum frequency which is at or near the frequency at which the impedance of a transformer equivalent circuit is at its maximum and which is less than the resonant frequency of the transformer, and wherein the transformer is operated at a frequency of between 100 kHz and 20 Mhz;
wherein said transformer is operated by a high-frequency carrier signal modulated by a low frequency non-zero switching signal, said carrier signal being at said optimum frequency; and
wherein said switching signal is a frequency of less than 300 kHz.
2. A method of driving a gate of a power MOSFET or IGBT device comprising isolating said gate from a power supply by means of a coreless planar transformer and driving said gate at an optimum frequency which is at or near the frequency at which the impedance of a transformer equivalent circuit is at its maximum and which is less than the resonant frequency of the transformer;
wherein said gate is driven at a frequency in the range of from about 100 kHz to 20 Mhz;
wherein a low frequency non-zero switching signal is used to modulate a high-frequency carrier signal input to said transformer, and wherein said carrier signal is demodulated after said transformer to drive said gate at said low switching frequency, said carrier signal being at said optimum frequency; and
wherein said switching signal is a frequency of less than 300 kHz.