Siew-Chong Tan

A new visit to an old problem in switched-capacitor converters

The energy-efficiency issue of the switched-capacitor converters is still a highly controversial topic that requires a more in-depth exploration. This paper will address the issue by dissecting the analysis of the entire efficiency problem into two parts. In the first part, the efficiency analysis of charging the capacitor of an RC circuit under different aspects (partial charging, full charging, at zero capacitor voltage, at non-zero capacitor voltage, etc.) will be conducted. In the second part, the efficiency analysis of discharging the capacitor of an RC circuit with resistive and capacitive loads will be covered. A complete evaluation of the overall efficiency is then performed in terms of both the charging and discharging efficiencies of the capacitor. Additionally, it is shown in this paper that the claim that quasi-switched-capacitor converters are more lossy than switched-capacitor converters is a common misconception.

Switched-capacitor converter configuration with low EMI emission obtained by interleaving and its large-signal modeling

The switched-capacitor converters are ideal switching-mode power supplies for portable electronic consumers due to their light weight, small size, and high power density. However, they suffer from a discontinuous input current waveform with large di/dt, what leads to significant electromagnetic interference (EMI) emission. This paper proposes a configuration of switched-capacitor converters connected in parallel with their inputs and outputs interleaved. The interleaving times are calculated by taking into account the fast capacitor-charging characteristic, and the need to have the nominal operating point on its linear part for increasing the regulation range at changes in the input voltage and load. To improve control performance and avoid the use of small-signal linearization in the control design, a large-signal approach is adopted for modeling the converter, allowing for a design of a sliding mode control.

Interleaved switched-capacitor converters with adaptive control

The switched-capacitor converters are ideal switching-mode power supplies for consumers portable electronic devices due to their light weight, small size, and high power density. However, they suffer from a discontinuous input current waveform with large di/dt, which leads to significant electromagnetic interference (EMI) emission. This paper proposes a configuration of switched-capacitor converters connected in parallel, with their inputs and outputs interleaved and adaptively controlled. The interleaving operation is performed by using an original type of control in which both the capacitors charging time Ton and switching frequency are adjusted to get the line and load regulation. It is shown that, for a given range of variation of the supply voltage and load, there always exists a solution [Ton, TS] assuring both output voltage regulation and a perfect interleaving. Experimental results are provided to validate the feasibility of the proposed scheme. Precise interleaving and good line and load regulation are maintained for all the designated range, including the transient times.

Robust current control for boost PFC converters from a sliding mode viewpoint

In this paper, we propose a methodology to derive a pulse-width modulation (PWM) control for the inner current loop of the boost power factor correction (PFC) converter. The methodology is based on the general sliding mode control theory. It leads to a robust current control that achieves accurate input current tracking under all practical conditions. The design of the control parameters is also presented, which is based on the existence condition and the frequency response analysis. The derived control can be implemented in analog circuitries as an application-specific controller or as an add-on feedforward control embedded in standard PFC controller circuits. Copyright

On the driving techniques for high-brightness LEDs

High-brightness light-emitting diodes (HBLEDs) are conventionally driven in the amplitude mode (AM) or pulse-width-modulation (PWM) mode. High luminous efficacy is obtained with AM, but precise dimming is difficult to achieve and such AM-driven LEDs suffer from significant color variations. PWM offers excellent dimming capability and color stability but the LEDs acquire lower luminous efficacies compared to AM. The advantageous features of both conventional methods can be united in a single generalized methodology as proposed in this paper. It utilizes pulsating current while enables simultaneous adjustments of the current levels and duty cycle for achieving a predetermined luminous efficacy and dimming range of interest to the users. The dimming dynamics using the proposed method is investigated through a detailed parametric study by experiments and numerical calculations.

Switched-capacitor converters with multiphase interleaving control

This paper proposes a configuration of switched-capacitor converters with multiphase interleaving control that can perform conventional switched-capacitor voltage conversions with little electromagnetic interference over a wide range of operating condition. This is achieved by having multiple units of switched-capacitor converter connected in parallel and a unit selection control scheme which works along the interleaving control to vary the number of converters in operation. By having the capacitors of inactive units connected to the output and the converters operating with output interleaving operation, the output capacitor that is typically required in switched-capacitor converters for maintaining a small voltage ripple is made redundant in this configuration.

Transient mitigation of DC-DC converters using an auxiliary switching circuit

This paper presents a method of mitigating the transient overshoots of DC-DC converters operating with large load disturbances. The method involves a small auxiliary power circuit with a complementary control scheme that provides a smooth absorption and release of excess energy from and to the main DC-DC converter in the events of large load changes. This control mechanism interactively mitigates the large transient overshoots which would otherwise appear at the converter output. Since the control scheme involves an adjustable-energy-storage feature, the proposed solution is effective for any level of step-load change within a pre-specified range.

Analysis of a high-voltage-gain hybrid switched-capacitor buck converter

This paper presents an analysis on the effect of having different number of capacitors n in the first-stage switched-capacitor circuit of an improved hybrid switched-capacitor buck converter for high-voltage-gain conversion. Various aspects of the topology, operation, and efficiency are investigated. It is shown that a higher n in the step-down capacitor stage does not necessarily lead to an overall improved power efficiency.

Implementation of bi-level current driving technique for improved efficacy of high-power LEDs

Presently, amplitude mode (DC mode) and pulsewidth modulation (PWM) represent the two main driving techniques used in LED drivers. The dimming function with PWM driving technique is attractive although lower luminous efficacy and stresses on the LEDs due to pulsating power are the disadvantages in comparison to amplitude mode. This paper introduces a current driving technique to improve the luminous efficacy over the conventional PWM technique while maintaining the dimming capability. This is achieved by introducing a DC-offset into the conventional PWM current waveform. It is found that the luminous efficacy increases with increasing DC-offset while the stresses due to pulsating power are reduced. Implementation and verification of the proposed driving technique using a prototype driver are presented.

Design of Pulsewidth-Modulation Based Sliding Mode Controllers for Power Converters in Discontinuous Conduction Mode

This paper presents an approach of designing fixed-frequency pulsewidth-modulation based sliding mode controllers for power converters operating in the discontinuous conduction mode. The basic concept and design issues are discussed. Preliminary verification and evaluation of the derived controllers are performed through computer simulations using precise models of the systems