Brett A. Miwa

High efficiency power factor correction using interleaving techniques

A highly efficient 1.5 kW power factor correction converter for computer applications is presented. Eight boost-topology switching cells are interleaved to meet stringent EMI input ripple specifications while operating at a very low switching frequency (25 kHz per cell) to minimize switching losses. The result is a system with very high conversion efficiency (94%-97%, including input bridge, bias supply, and EMI filter losses) over the 93-264 VAC input range. Key implementation details, including discontinuous inductor current operation, a combination of linear and bang-bang control algorithms for fast dynamic load response, and extended (100 ms) power outage ride-through capability, are described.<<ETX>>

Active Power Factor Correction for Switching Power Supplies

The harmonic-free utility/dc interface provides to the computer industry a means to extract more power from the wall outlet than the normal rectifier, with its heavily distorted input current, will allow. Due in part to the very high switch stresses in this interface, however, the cost appears to be too high to justify its use at this time. An alternate approach is proposed that focuses on power factor correction rather than harmonic reduction. Compared to the harmonic-free interface, the switch stress of this new approach is approximately a factor of two smaller.

Copper-based hybrid fabrication of a 50 W, 5 MHz 40 V-5 V DC/DC converter

A prototype 50 W, 40 V to 5 V DC/DC converter operating at 5 MHz and constructed with chip and wire hybrid techniques on a ceramic substrate with copper thick-film conductors is presented. A brief discussion of the thick-film process is given to point out the special issues concerning copper-based conductor systems. Some of the specific trade-offs that arise with regard to the construction of a power circuit with hybrid techniques are discussed. A method by which transformers may be fabricated to have very little leakage inductance, both internally and in their connection to rectifiers, is then described. The performance of a power circuit, the dual resonant forward converter is presented. >

Skip-duty control method for minimizing switching stress in low-power multi-level Dc-Dc converters

This paper addresses the problem of large sporadic transient voltages across the switches of low-power multi-level dc-dc converters and introduces a digital control-based method for their elimination. The physical origin of the large voltage transient spikes occurring at certain operating points, corresponding to zero current ripple operation, is explained. A control-based solution for the problem, based on the avoidance of the critical operating points, i.e. on skipping of critical duty ratio values, while maintaining tight voltage regulation and symmetric inductor current waveforms, is introduced. The effectiveness of the control method is demonstrated with a wide-input 10 V/ 3 A output, 1 MHz, three-level buck dc-dc experimental prototype, where it is shown that the skip-duty control completely eliminates the sporadic spikes.

Extended wide-load range model for multi-level Dc-Dc converters and a practical dual-mode digital controller

This paper addresses limitations of previous models of multi-level flying capacitor (ML-FC) dc-dc converters, in terms of not being able to predict instability in the regulation of the flying capacitor voltage under non-negligible inductor current ripple conditions, usually existing under light to medium load operating conditions. Assuming small-ripple approximation, linear ac equivalent circuit is derived for a general N-level FC dc-dc buck converter and, through a geometrical analysis, limitations of that model are explained. Also, related stability problems are addressed. Then, an extended mathematical model that takes into account the ripple component of the inductor current is derived and used in the design of a practical dual-mode digital controller, which for non-negligible ripple operating conditions changes its mode of operation. Validity of the model and the functionality of the introduced controller are verified both through simulations and experimental verifications. Performance of this controller is tested with a wide input 15 V/3 A, 250 kHz, 45 W, three-level experimental prototype.

Discontinuous conduction mode of multi-level flying capacitor DC-DC converters and light-load digital controller

A comprehensive analysis of step-down multi-level flying capacitor converters in discontinuous conduction mode of operation is presented, with the main goal of improving light-load power processing efficiency. In addition to that, a novel controller architecture is introduced for the operation of the converter under light-load conditions. In particular, controller artificially creates inductor current ripple around zero-current ripple operating regions enabling discontinuous conduction mode over full range of the conversion ratios. Experimental results obtained with wide input 6–12 V, wide output voltage 1 V–5.5 V, 10 mA < IOUT < 3 A, 20 KHz < fs < 500 KHz discrete prototype are presented, showing up to a 50% improvement of efficiency under light-load of operation.

Ripple minimizing digital controller for flying capacitor dc-dc converters based on dynamic mode levels switching

This paper introduces a new control method for dc-dc flying capacitor multi-level converters. Depending on the operating conditions, introduced controller dynamically changes the number of operating converters levels to minimize the output inductor current ripple improving power processing efficiency. For the converters with a narrow conversion range this controller also allows for a significant reduction of the inductor. The effectiveness of this control method is demonstrated on a 5-level dc-dc converter example, which number of levels is dynamically varied between 5 and 4 depending on the required conversion ratio. Experimental results obtained with wide input 12 V–36 V, wide output voltage 1 V–12 V/5 A, 2.5 MHz experimental prototype are showing up to a 25% lower losses compared to the 5-level converter operating in the conventional mode.

Second order sliding mode controlled point of load power supply

This paper describes the implementation of a second order sliding mode (SOSM) controller for a practical point-of-load (POL) power supply with realistic values of output capacitor equivalent series resistance (ESR) and equivalent series inductance (ESL). The SOSM control presented in this paper results in fast transient responses, has a current limiting feature, supports light load operation, and achieves constant frequency steady state operation. Experimental results are given for a 2.5 V - 5.5 V input, 0.6 V - 1.5 V output, 3 A prototype.