N.K. Poon

A low cost DC-DC stepping inductance voltage regulator with fast transient loading response

A fast transient converter modified from a buck converter is proposed. It employs a stepping inductance method by which the output inductor of a buck converter is replaced by two inductors connecting in series. One has large inductance and the other has small inductance. An inductor with small inductance will take over the output inductor during transient load change and speed up dynamic response. In steady state, the large inductance takes over and keeps substantially small ripple current and minimizes RMS loss. An experiment of a 2 V DC-DC converter put under a 20 A transient load change demonstrates the merit of this approach. It is a low cost method applicable to converters with an output inductor.

Essential-coupling-path models for non-contact EMI in switching power converters using lumped circuit elements

This paper proposes a simple lumped circuit modeling approach for describing noncontact EMI coupling mechanisms in switching power converters. The resulting model assumes a minimum number of noise sources and contains essential coupling paths that allow easy physical interpretations. Essentially, all capacitive couplings are represented by an equivalent noise voltage source and six coupling impedances, whereas all inductive couplings are represented by an equivalent noise current source and three coupling impedances. The resulting coupled noise appears as currents flowing into the terminals of the line-impedance-stabilization-network (LISN). The equivalent voltage source can be conveniently approximated as the switching-node-to-zero voltage, which is typically a rectangular pulse of a few hundred volts. The equivalent current source can be modeled as the current flowing around a loop containing the equivalent voltage source and parasitics such as winding capacitance of the power transformer, the snubber capacitance and connection inductances. Also, the coupling impedances can be estimated by making simplifying assumptions about the geometry of the components and tracks, or by direct measurements. Simulations and experiments verify how inductive and capacitive couplings through each path may produce substantial EMI measured by the LISN. Being based on a lumped circuit approach, the proposed model is easy to apply in practice for understanding, diagnosing and approximating EMI behaviors.

A PFC voltage regulator with low input current distortion derived from a rectifierless topology

This paper presents an ac–dc converter topology for realization of power factor correction (PFC) voltage regulators for applications where the mains frequency is high and a low input current harmonic is required, e.g., in aircraft power systems. The proposed converter represents a minimal configuration consisting of two basic converters, which can be systematically derived from a previously proposed general synthesis procedure for rectifierless ac–dc converters. The proposed PFC converter has incorporated a control method which drastically reduces the circulating power and hence raises the efficiency to a level comparable to existing PFC converters. The proposed PFC converter can completely eliminate any crossover distortion, which can be significant for supply systems having a high mains frequency. In addition, the proposed converter allows bidirectional energy flow ensuring all inductors work in continuous conduction mode hence eliminating the distortion due to the abrupt change of dynamic response when the operating mode changes. Analysis and design of the power and control circuits will be given and discussed. An experimental system will be presented for verification purposes.

A constant-power battery charger with inherent soft switching and power factor correction

A battery charging circuit, which operates as a constant power source, is proposed in this paper. By maintaining a constant output power throughout the charging process, the circuit reduces the size of thermal installation which would normally be required in the cases of constant-voltage or constant-current charging. The proposed circuit takes the form of a half-bridge converter with an additional small inductor and two extra diodes connected in parallel to two dividing capacitors. Constant power delivery is achieved by the discontinuous-voltage-mode operation of the two dividing capacitors, each of which is connected in parallel with a diode. The circuit enjoys low voltage and current stresses, and achieves soft switching with no extra components. When used off-line, the converter maintains a high input power factor and a low level of input current harmonic distortion that meets international regulations. All the above characteristics are determined only by the values of the circuit parameters, the control mechanism being noncritical. A 12 V 65 W prototype was built to demonstrate the merits of this circuit.

Synthesis of input-rectifierless AC/DC converters

This paper discusses the basic construction procedure and topological possibilities of creating AC/DC converters out of simple DC/DC converters. It is shown that two separately controlled DC/DC converters are sufficient for producing a regulated DC output and shaping the input current, from an AC voltage source, without the need for input rectifiers. Some design constraints are discussed, emanating from the limitation of the conversion ratios that can be achieved by particular DC/DC converters. Selected topologies are verified experimentally. This kind of rectifierless converter find applications in airborne power supplies where zero-crossing distortions are significant because of the inevitable phase-lead effect of the input rectifier bridge.

Comparison of three topologies for VRM fast transient application

This paper compares three topologies for voltage regulator modules (VRMs) for fast transient applications. The topologies are the most popular multi-phase converter, a synchronous rectifier buck converter topology and a recently introduced new stepping inductor converter. Analysis and simulation show that the stepping inductor topology gives the fastest response with minimal amount of output filter capacitance.

Common-Mode Noise Cancellation in Switching-Mode Power Supplies Using an Equipotential Transformer Modeling Technique

Electromagnetic interference (EMI) is a significant challenge in the design of high-efficiency switching-mode power supplies due to the presence of common-mode (CM) noise. In many power-supply designs, a variety of noise suppression schemes must be implemented in order to meet EMI requirements. Most of these schemes create power loss that lead to efficiency and thermal issues. In this paper, a transformer construction technique is proposed that effectively reduces the CM noise current injecting across the isolated primary and secondary windings. This technique is based on the zero equipotential line theory. A transformer design with the proposed CM noise cancellation technique can achieve high conversion efficiency as well as substantial CM noise rejection.

A novel ZVS direct coupling converter (DCC)

A novel DC-DC power converter with a ZVS topology is introduced. An amplitude modulated squarewave train is generated and the output can be controlled by the amplitude of this squarewave train. As energy is directly transferred to the output, it is known as a direct coupling converter (DCC). This topology results in a simple configuration and inherent ZVS characteristics. This extends switching power supply modulation techniques to cover AM, FM and PWM. Theoretical analysis and results from an experimental prototype are presented in this paper.

A PFC topology with low input current distortion suitable for aircraft power supplies

This paper presents an AC-DC converter topology for realization of PFC converters for applications where the mains frequency is high and a low input current harmonics is required, e.g., in aircraft power systems. The proposed topology eliminates crossover distortion due to the presence of input rectifiers and the inevitable input current phase lead. The idea is to stack a DC voltage on top of the AC mains voltage to prevent voltage polarity reversal in the input, eliminating the input bridge rectifier. This eliminates the crossover distortion, which can be significant for supply systems having a high mains frequency. In addition, the proposed PFC converter allows bidirectional energy flow, ensuring all inductors work in continuous conduction mode and hence eliminating the distortion due to the abrupt change of dynamic response when the operating mode changes. Analysis and design of the power and control circuits will be given and discussed. An experimental system will be presented for verification purposes.

A low output ripple DC to DC converter topology using voltage overlapping technique

A new converter topology is proposed which uses voltage overlapping method with certain overlapping period that can theoretically provide smooth and regulated DC output voltage without the need of an output filter. An isolated DC/DC converter prototype with output voltage and current of 2.5 V and 15 A respectively was built to demonstrate its operation. Very low output ripple is observed.