A review of the state of the art in RPWM (random pulse width modulation) theory and practice is presented. Topics covered include principles of RPWM, means of randomization, a review of the existing RPWM techniques, power spectra, implementation issues, and documented effects of RPWM on electric drive systems. A number of RWPM strategies have been reported, and a beneficial impact on acoustic noise and vibration has been unamiously agreed upon. Published studies have proven that significant improvement of the acoustic noise characteristics of the motors can be achieved at practically no extra expense in comparison with the systems with traditional, deterministic PWM strategies. >

Random pulse width modulation techniques for converter fed drive systems-a review

Novel designs for printed circuit board transformers, and in particular for coreless printed circuit board transformers designed for operation in power transfer applications, are disclosed in which shielding is provided by a combination of ferrite plates and thin copper sheets.

Planar printed-circuit-board transformers with effective electromagnetic interference (emi) shielding

A logic signal isolator comprising a transformer having a primary winding and a secondary winding; a transmitter circuit which drives said primary winding in response to a received logic signal, such that in response to a first type of edge in the logic signal, a signal of a first predetermined type is supplied to the primary winding and in response to a second type of edge in the logic signal, a signal of a second predetermined type is supplied to said primary winding, the primary winding and the transmitter being referenced to a first ground; and the secondary winding being referenced to a second ground which is galvanically isolated from the first ground and said secondary winding supplying to a receiver circuit signals received in correspondence to the signals provided to the primary winding, the receiver reconstructing the received logic signal from the received signals.

Signal isolators using micro-transformers

Gate drive circuits for modern power electronic switches, such as MOSFET and insulated gate bipolar transistor (IGBT), often require electrical isolation. This paper describes the modeling and experimental results of some coreless printed circuit board (PCB)-based transformers that can be used for MOSFET and IGBT devices at high-frequency (500 kHz to 2 MHz) operation. PCB-based transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits. With no core loss, coreless transformers are found to have favorable characteristics at high-frequency operations. This project demonstrates an important point that the size of the magnetic core can approach zero and become zero when the frequency is sufficiently high.

Coreless printed circuit board (PCB) transformers for power MOSFET/IGBT gate drive circuits

Gate drive circuits for power MOSFETs and insulated gate bipolar transistors (IGBTs) often require electrical isolation. Coreless printed circuit board (PCB) transformers have been shown to have desirable characteristics from a few hundreds of hertz to a few megahertz and can be used for both power and signal transfer at low-power level. At low operating frequency, the magnetizing inductance has such low impedance that the driving power requirement could become excessive. This paper describes the use of a coreless PCB transformer for isolated gate drive circuits over a wide-frequency range. Based on a resonance concept, the optimal operating condition that minimizes the power consumption of the gate drive circuits is developed and verified with experiments. The coreless PCB transformer demonstrated here confirms a fundamental concept that the size and volume of a magnetic core could approach zero and become zero if the operating frequency is sufficiently high. Coreless PCB transformers do not require the manual winding procedure and thus simplify the manufacturing process of transformer-isolated gate drive circuits and low-power converters. Their sizes can be much smaller than those of typical core-based pulse transformers. The electrical isolation of a PCB is much higher than that of an optocoupler.

Optimal operation of coreless PCB transformer-isolated gate drive circuits with wide switching frequency range

Power MOSFET and IGBT gate drives often face isolation and high voltage constraints. The gate drive described uses a printed circuit board based transformer combined with the memory effect of the power MOSFET input capacitance. This transformer is a bidirectional link between the ground referred control IC and the floating gate drive. It transfers energy and signal to the gate drive, provides full duty cycle range, perfect dV/dt immunity and virtually no voltage constraint. No floating auxiliary is required for the secondary circuit. If the short circuit protection is operated, an alarm signal is transmitted back to the primary through the same transformer. This circuit is perfectly suited to drive floating and/or isolated switches in motor drives, uninterruptible power supplies and AC switches. Due to the printed winding approach, cost reduction can be expected in the transformer manufacture automation. >

PCB based transformer for power MOSFET drive

As a consequence of PWM techniques, high frequency current ripple appears in power actuators generating acoustic noise at the corresponding frequency (switching noise). A PWM technique is presented for shaping the switching noise spectrum in such a way it can merge with the natural system noise. It consists of avoiding a discrete switching frequency spectrum by means of a pseudo-random PWM generator. Hence, the switching frequency is continuously and randomly variable over a given range. The switching noise is quasi-white in this range, and much less disturbing. Practical solution and results are presented for a motor drive application. >

J.M. Bourgeois

Papers

PCB based transformer for power MOSFET drive

PWM technique for acoustic noise reduction in power applications