Showing papers on "Pulse-frequency modulation published in 2018"

Integrated Half-Bridge CLLC Bidirectional Converter for Energy Storage Systems

Abstract: This paper proposes an integrated half-bridge CLLC (IHBCLLC) resonant bidirectional dc–dc converter suitable as an interface between two dc voltage buses in various applications including energy storage systems. This converter is an integration of a half-bridge CLLC resonant circuit and a buck/boost circuit. Compared with the traditional pulse frequency modulation and phase-shift controlled CLLC resonant converter, for the proposed convertor, the high voltage gain can be obtained from pulse width modulation. Synchronous pulse width modulation is adopted for the converter, and the switching frequency is equal to the resonant frequency. The CLLC resonant circuit can help MOSFETs to achieve soft switching and high voltage gain. The simulation analysis of the modulation schedule and operating principle of the proposed converter prove that the converter is able to achieve zero-voltage switching or zero-current switching. Experimental results obtained from a 1-kW converter prototype confirm the theoretical analysis and the simulation results.

A 10-MHz 2–800-mA 0.5–1.5-V 90% Peak Efficiency Time-Based Buck Converter With Seamless Transition Between PWM/PFM Modes

Abstract: Time-based controllers are well suited for implementing both single- and multi-phase wide bandwidth high switching frequency pulsewidth modulation (PWM)-based dc–dc converters. They also consume very little quiescent current but their light load efficiency is severely degraded by switching losses. We explore pulse frequency modulation (PFM) that is commonly used to improve light load efficiency in voltage-mode controllers and extend its operation to time-based controllers. To maintain high efficiency even in the presence of dynamic load variations, we present techniques to perform automatic and seamless switching between PWM/PFM modes. Fabricated in a 65-nm CMOS, the prototype buck converter using the time-based PWM/PFM control achieves 90% peak efficiency and >80% efficiency over a load current range of 2–800 mA. Output voltage changes by less than 40 mV during PWM to PFM transitions.

A Pulse Frequency Modulation Interpretation of VCOs Enabling VCO-ADC Architectures With Extended Noise Shaping

Abstract: In this paper, we propose to study voltage controlled oscillators (VCOs) based on the equivalence with pulse frequency modulators (PFMs). This approach is applied to the analysis of VCO-based analog-to-digital converters (VCO-ADCs) and deviates significantly from the conventional interpretation, where VCO-ADCs have been described as the first-order $\Delta \Sigma $ modulators. A first advantage of our approach is that it unveils systematic error components not described by the equivalence with a conventional $\Delta \Sigma $ modulator. A second advantage is that, by a proper selection of the pulses generated by the PFM, we can theoretically construct an open loop VCO-ADC with an arbitrary noise shaping order. Unfortunately, with the exception of the first-order noise shaping case, the required pulse waveforms cannot easily be implemented on the circuit level. However, we describe circuit techniques to achieve a good approximation of the required pulse waveforms, which can easily be implemented by practical circuits. Finally, our approach enables a straightforward description of multistage $\Delta \Sigma $ modulator architectures, which is an alternative and practically feasible way to realize a VCO-ADC with extended noise shaping.

A Single-Stage Integrated Boost-LLC AC–DC Converter With Quasi-Constant Bus Voltage for Multichannel LED Street-Lighting Applications

Abstract: Single-stage boost-LLC ac–dc converters are popularly utilized as the front-end stage of multichannel LED street-lighting drivers. Pulse frequency modulation (PFM) strategy with a duty cycle of 0.5 is commonly utilized in these ac–dc converters. However, PFM has the following drawbacks: 1) high bus voltage limits the ac input voltage range, which makes it only suitable for the input voltage range of 85~135 V and 2) the maximum bus voltage can reach up to three times of the minimum bus voltage, which increases the difficulty of the LLC design. This paper proposed a hybrid modulation strategy, which consists of a bus voltage control loop using asymmetric pulsewidth modulation and an output voltage control loop using PFM. The stable output voltage and the quasi-constant bus voltage can be simultaneously achieved. Furthermore, by increasing bus voltage ripple and employing the twin-bus configuration, the short-lifetime electrolytic capacitors are eliminated, and the efficiency of the total LED driver can be greatly improved. Therefore, universal-input operation, high efficiency, low cost, and long lifetime are the key innovations of the proposed solution. A universal-input 100-W prototype is built to demonstrate the feature of the proposed solution. The experimental results show that the converter achieves a peak efficiency of 92.5% at the input voltage of 130 V and a high power factor value of above 0.95 over the whole input voltage range. With the proposed modulation strategy, the maximum bus voltage is just 500 V under universal input voltage condition, which is greatly lower than that of the traditional PFM controlled boost-LLC converters.

Partially Isolated Single-Magnetic Multiport Converter Based on Integration of Series-Resonant Converter and Bidirectional PWM Converter

Abstract: Recent power systems, such as renewable energy systems consisting of solar panels and rechargeable batteries, contain multiple power sources and need multiple converters in proportion to the number of power sources, resulting in increased system complexity and cost. This paper proposes a multiport converter (MPC) integrating a bidirectional PWM converter and series-resonant converter. Not only is the switch count halved with the proposed MPC, but also magnetic components can be integrated, reducing the circuit complexity and volume. A 150-W prototype of the proposed MPC was built for the experimental verification. The measured voltage conversion characteristics and transient responses demonstrated that the proposed MPC could control load and battery voltages independently by pulse width modulation and pulse frequency modulation controls, respectively.

Spread Spectrum Technique to Reduce EMI Emission for an LLC Resonant Converter Using a Hybrid Modulation Method

Abstract: A spread spectrum technique has been introduced to mitigate electromagnetic interference (EMI) in power converters. However, this technique is difficult to apply to resonant converters that use a pulse frequency modulation (PFM), because the spread spectrum can induce large output voltage fluctuations by PFM's switching frequency variations. In this letter, a hybrid control method using the PFM and phase shift modulation is proposed to obtain tight output voltage regulation under the spread spectrum operation of an LLC resonant converter. The performance of the proposed hybrid control method is experimentally verified using a 500 W prototype LLC resonant converter.

A Low-Cost Constant Current Control Method for DCM and CCM in Digitally Controlled Primary-Side Regulation Flyback Converter

Abstract: Primary-side regulation (PSR) flyback converter with a discontinuous conduction modulation (DCM) mode is widely used in small-power applications. To introduce higher output power, a continuous conduction modulation (CCM) mode is used in which an analog to digital converter of high cost is always required. In this paper, to reduce the cost, a novel digital peak current control method is proposed to realize constant output current control in both DCM mode and CCM mode. However, there exists a time length calculation error that cannot be avoided in the critical condition between DCM mode and CCM mode. The output current will be lower than the nominal output current. Thus, a hysteretic multimode control method with two pulse width modulation modes and two pulse frequency modulation modes is utilized to eliminate the time length calculation error. In the proposed control, only a low-speed digital to analog converter and three comparators are used, which greatly reduced the cost, and high accuracy of output current can be obtained. The proposed control scheme was then verified through a field-programmable gate array (FPGA)-controlled 3.76–15 V/3.76 A PSR flyback converter. In the prototype, the accuracy of the output current is within ±1.5% for the universal load range.

Variable Time Step Control for Six-Step Operation in Surface-Mounted Permanent Magnet Machine Drives

Abstract: The six-step operation of surface-mounted permanent magnet machine drives in a flux weakening region has many advantages compared to the pulse width modulation mode, such as the reduced switching loss and fully utilized inverter output voltage. However, if the ratio of the sampling frequency to the fundamental frequency is low in fixed sampling system, the low-frequency oscillation in the current can be incurred in the six-step operation. The low-frequency current causes a system stability problem and reduces system efficiency due to an excessive heat and high power loss. Therefore, this paper proposes the variable time step controller for six-step operation. By updating an output voltage, sampling phase currents, and executing the digital controller synchronized with the variable sampling time, the turn on and off switch signals for six-step operation can be generated at the exact moment. As a result, the low-frequency oscillation in the phase current can be eliminated. In addition, the system transfer function of the proposed control method is discussed for the system stability and system dynamic analysis. The effectiveness of the proposed method is verified by the comparative simulation and experimental results.

A Digitally Controlled Fully Integrated Voltage Regulator With 3-D-TSV-Based On-Die Solenoid Inductor With a Planar Magnetic Core for 3-D-Stacked Die Applications in 14-nm Tri-Gate CMOS

Abstract: A fully integrated digitally controlled buck voltage regulator, featuring hysteretic and pulse frequency modulation control for maximum light load efficiency, with 3-D through-silicon-via-based on-die solenoid inductor with a planar magnetic core in 14-nm tri-gate CMOS, demonstrates 111 nH/mm2 inductance density and 80% conversion efficiency. The inductance density demonstrated is 20 $\times $ higher than comparable on-die lateral- or spiral-based inductor densities leading to higher light load efficiency.

A 6.6kW SiC bidirectional on-board charger

Abstract: This paper proposes a bidirectional architecture to implement an on-board charger (OBC) including an interleaved totem bridgeless PFC and Mode-Switched (MS) DC-DC converter. In the charging mode with the relay on, the MS DC-DC converter behave as a high efficiency Pulse Frequency Modulation (PFM) LLC converter since the charging mode is the most majority application scenario for the OBC. The PFC output voltage is regulated between 360 V to 400 V feeding into the DC-DC converter, so that 900 V SiC MOSFETs can be used both in the AC-DC and DC-DC stage to realize high frequency and high efficiency owing to the fast switching speed and high voltage rating with low on-resistance. The synchronous rectification (SR) is applied on the secondary side MOSFETs of the LLC converter to further improve the efficiency taking advantage of the bidirectional full-bridge topology. In the discharging mode with the relay off, the MS DC-DC stage is a two-stage converter. The reverse operation of the LLC converter operates as a DC-DC transformer (DCX) at the resonant point, and its output voltage is regulated to the bus voltage by a boost converter because the reverse gain of the LLC converter is lower than 1. A 6.6 kW SiC MS bidirectional OBC of DC-DC stage is built. In the charging mode, the peak efficiency is 96.37% at 6.6 kW with 380 V input voltage and 336 V output voltage. In the discharging mode, the peak efficiency is 96.87% at 3.3 kW with 346 V input voltage and 380 V output voltage.

Evaluation of Carrier-Based Modulation Techniques With Common-Mode Voltage Reduction for Neutral Point Clamped Converter

Abstract: Common-mode voltage output is closely associated with switching states in three-phase three-wire neutral point clamped converter. Detailed analysis shows avoiding redundant states can effectively improve the common-mode voltage, so this paper proposes a pulse width modulation (PWM) technique with zero redundant state to reduce the common-mode voltage output, and evaluates their performance with the conventional PWM schemes. This paper also takes the compensation of neutral point potential deviation into consideration. Laboratory test results are presented to verify the effectiveness of the proposed scheme.

A Low-EMI, High-Reliability PWM-Based Dual-Phase LED Driver for Automotive Lighting

Abstract: Light-emitting diode (LED) drivers for automotive lighting applications adopt pulsewidth modulation (PWM) vis-a-vis pulse frequency modulation because its ensuing electromagnetic interference (EMI) spectrum is predictable and easily mitigated. Nevertheless, present-day PWM control schemes adopted in LED drivers suffer from imprecise output current and subharmonic oscillation, which compromises reliability. In this paper, we present a PWM-based LED driver that features low EMI and high reliability. These attributes are achieved by our proposed average current control (ACC), proposed accuracy-enhanced on-chip current sensors, and our adoption of a dual-phase power stage. The ACC eliminates subharmonic oscillation by means of considering the complete inductor current profile vis-a-vis peak current adopted elsewhere. Also by means of the dual-phase power stage, good current balance and small current ripple are obtained. Collectively, the aforesaid substantially improves the reliability. To improve electromagnetic compatibility (EMC), the proposed accuracy-enhanced on-chip current sensors are monolithically realized with the ACC and power transistors—to the best of our knowledge, the first for a PWM-based dual-phase LED driver. The prototype LED driver, realized in a 130-nm BCDLite process, has an input voltage range of 5–16 V, output to drive 1–3 series-connected LEDs, provides a current regulation accuracy of at least 96.2%, dimming frequency up to 20 kHz, features a peak power efficiency of 94.7%, settling time of $5~\mu \text{s}$ , LED current range of 0.4–2.4 A, and current ripple factor of 8%. When benchmarked against the state-of-the-art LED drivers, our design features the highest peak power efficiency, the shortest settling time, highest current driving capability, and the lowest current ripple factor.

A Dual-Output Switched Capacitor DC–DC Buck Converter Using Adaptive Time Multiplexing Technique in 65-nm CMOS

Abstract: This paper presents an area- and power-efficient dual-output switched capacitor (DOSC) dc–dc buck converter for wearable biomedical devices. The DOSC converter has an input voltage range between 1.05 and 1.4 V and generates two simultaneous regulated output voltages of 1 and 0.55 V. The DOSC consists of two main blocks: a switched capacitor regulator and an adaptive time multiplexing (ATM) controller. The switched capacitor regulator generates a single regulated voltage using pulse frequency modulation based on a predetermined reference voltage. In addition, the ATM controller generates two simultaneous output voltages and eliminates the reverse current using pulse width modulation during the switching between the output voltages. Addressing the reverse current problem is important to reduce the output voltage droop and improve the performance. The proposed converter supports load currents of 10– $350~\mu \text{A}$ and 1– $10~\mu \text{A}$ at load voltages of 1 and 0.55 V, respectively. The DOSC circuit is fabricated in 65-nm CMOS, and it occupies an active area of 0.27 mm2. Measured results show that a peak efficiency of 78% is achieved at a load power of $300~\mu \text{W}$ .

Time-Division Multiplexing Control of Multi-Input Converters for Low-Power Solar Energy Harvesters

Abstract: Many autonomous sensor nodes use small photovoltaic (PV) panels oriented toward the direction that provides the highest energy yield in the worst case scenario. Since all those panels operate at similar irradiance and temperature conditions, they can be properly biased at the same bias point by using a single maximum power point tracker (MPPT). But in applications that involve several PV panels with dissimilar orientations, using an MPPT tailored to each panel would increase system cost. A better design option is to implement the MPPT with a single multiple-input converter shared through time-division multiplexing (TDM) control. However, existing TDM controls are usually based on pulsewidth modulation converters wherein the high switching frequency of transistors results in excessive power losses for low-power systems. Consequently, low-power MPPTs are instead usually based on pulse frequency modulation (PFM) converters. This paper proposes a novel TDM control method for MPPTs based on PFM converters.

High-linear digital hydraulic valve control by an equal coded valve system and novel switching schemes:

Abstract: This study proposes a novel digital hydraulic valve system using multiple equal size on/off valves and a circulating switching control, with an aim to increase the resolution and the linearity of t...

A Low-Power Forward and Reverse Body Bias Generator in CMOS 40 nm

Abstract: This brief presents a low-power forward and reverse body bias (FRBB) generator with body bias (BB) switches to dynamically set BB voltage. The reverse BB (RBB) P-well generator uses pulse frequency modulation (PFM)-based switching capacitor power converter to achieve low power consumption in a wide load current range of 1–30 $\mu ~\text{A}$ . The FBB adopts class-AB output stage and an over-current indicator to detect large body diode forward conduction leakage current. BB switch is introduced to dynamically configure the FRBB generated voltage. The proposed FRBB with BB switch is fabricated in a CMOS 40-nm triple well process, occupying an area of around 0.1 mm2. The 300k digital gates are used as the load for test. The measured active current for FBB and RBB are 13 and $5~\mu \text{A}$ , respectively.

Buck-Boost Buck CCM-DCM Converter for PV Based DC Standalone System

Abstract: A Buck-boost Buck CCM-DCM Converter (BBCDC) suitable for Solar Photo-voltaic(PV) based DC standalone system is proposed in this paper. The PV panel and battery storage system is integrated through a bi-directional buck-boost converter operating in CCM mode. The load is integrated to PV and battery through a buck converter operating in DCM mode. These two converters share two switches leading to reduction in switch count and increase in overall efficiency of the system. Maximum Power Point Tracking (MPPT) is done through Pulse Width Modulation (PWM) and the load voltage control is achieved by Pulse Frequency Modulation (PFM). The proposed converter and a control strategy devised for it is validated through detailed simulation studies.

Dual-phase DC–DC buck converter with light-load performance enhancement for portable applications

Abstract: In modern portable devices, except during short periods of busy time, application processors work at low-power state most of the time to prolong battery life. Thus, high efficiency and low consumption are essential for their power management under light-load conditions. This study presents a dual-phase DC-DC buck converter with light-load performance enhancement for power supply. As load decreases, the converter could transfer the adaptive-on-time-based control strategy from pulse-width modulation to pulse-frequency modulation to enhance efficiency. An extra power-save mode is introduced into design to minimise the power consumption at extremely light load. Besides, a novel current-balance circuit with additional offset elimination block is implemented, which results in equal distribution of load current between phases over wide load range. Moreover, instead of a conventional high precision and fast response comparator, a simple comparator with self-calibration is used in zero-current switching circuit to reduce design complexity, as well as to improve light-load efficiency. The converter is fabricated in 0.18-μm Globalfoundry CMOS process. Experimental results show that 91% peak efficiency and 6 μA standby quiescent current is achieved. With the aid of mode switching, current-balance and zero-current switching, the light-load performance enhancement is verified by measurements.

A Single-Stage Direct-Conversion AC–DC Converter for Inductively Powered Application

Abstract: An innovative single-stage ac–dc converter for low power, low frequency skin depth wireless power transfer is presented. The power conversion efficiency (PCE) of a wireless power receiver is limited by the cascaded two-stage design, which constitutes a rectifier and a voltage regulator. Owing to the proposed ON-/OFF-mode regulating rectifier, the voltage rectification and regulation are achieved simultaneously in one stage, thereby improving the PCE substantially. The output voltage regulation is accomplished by incorporating the pulse skipping modulation and the pulse frequency modulation control into the structure. In addition, there is no bulky inductor utilized in the proposed one-stage design. Therefore, the footprint and cost of the receiver can be minimized effectively. The proposed design has been fabricated in 0.18- $\mu \text{m}$ standard CMOS process. Measurement results show that a peak power transfer efficiency of 93.48% is achieved at a regulated output voltage of 2 V in an output power range of 2–80 mW.

Modulation Classification Using Received Signal's Amplitude Distribution for Coherent Receivers

Abstract: In this letter, we propose a modulation classification algorithm which is based on the received signal's amplitude for coherent optical receivers. The proposed algorithm classifies the modulation format from several possible candidates by differentiating the cumulative distribution function (CDF) curves of their normalized amplitudes. The candidate with the most similar CDF to the received signal is selected. The measure of similarity is the minimum average distance between these CDFs. Five commonly used quadrature amplitude modulation formats in digital coherent optical systems are employed. Optical back-to-back experiments and extended simulations are carried out to investigate the performance of the proposed algorithm. Results show that the proposed algorithm achieves accurate classification at optical signal-to-noise ratios of interest. Furthermore, it does not require carrier recovery.

Self-adaptation load change control strategy for three-phase staggered parallel LLC resonant converter

Abstract: The resonant frequency of LLC resonant converter has a wide range of switching frequency due to load changes and it easily enters high frequency band during light load and no-load conditions. Therefore, this study proposes a self-adaptation load change control strategy. According to different load conditions, the converter automatically selects the best control mode among three control methods, which are pulse-frequency modulation, symmetrical pulse-width modulation and burst. By fully utilising the characteristics of the load-independent point in the gain curve and the relationship between the resonant current and the load, the switching conditions between the control strategies are further designed and optimised. In addition, based on the adaptive load change control strategy, the design value of k (the ratio of the excitation inductor to the resonant inductance of the transformer) is increased, which solved the disadvantage of large change of the switch range. And the converter can not only effectively control the output voltage during light load, but also works in the soft-switching state, which can improve the working efficiency of the converter to above 91%. Finally, taking a three-phase staggered parallel LLC resonant converter as the research object, an experimental prototype was developed based on SiC devices to verify the correctness and rationality of the proposed control strategy.

A Power Factor Corrected Electric Vehicle Battery Charger Using Boost Converter

Abstract: This paper presents a power factor corrected (PFC) boost converter based half bridge LLC resonant converter (LLC) for electric vehicle battery charging application. The proposed converter utilizes a boost converter as a front end converter operating in continuous inductor conduction mode (CICM) to achieve unity power factor at AC mains, and LLC to facilitate the EV battery charging. The boost converter is operated in pulse width modulation (PWM) at fixed frequency, whereas LLC converter uses pulse frequency modulation (PFM) technique to maintain power delivered to the battery. A 2kW rating prototype of the proposed converter is designed and implemented using TMS320F28035 microcontroller. The performance of proposed converter is presented under various load and line conditions

Performance Comparison of Primary Side PFM and Secondary Side PWM for SS Wireless Power Transfer CC/CV Control Strategy

Abstract: Wireless Power Transfer (WPT) system for Electric Vehicle (EV) battery charging application popularity is increasing due to the safety, convenience, and eco-friendly issue. Nowadays, Lithium-Ion battery is well known as one of the potential options for EV. However, Constant Current/Constant Voltage (CC/CV) control strategy needs to be adopted for achieving high efficiency charging and maintaining battery lifetime. By analyzing the gain curve, Pulse Frequency Modulation (PFM) can be used to perform CC/CV charging due to the load variation. The operating switching frequency needs to be considered and limited to prevent instability of the system. A typical drawback in the PFM control is the use of serial communication module for feedback data transmission from the secondary to the primary side. Therefore, the rectifier side controlled WPT can be a solution to remove the feedback communication part. In this paper, Pulse Width Modulation (PWM) applied in the secondary side (rectifier) for achieving CC/CV charging is investigated and compared with the traditional PFM control. The comparison study is verified by implementing a 3kW Series-Series (SS) WPT topology in the Power Simulation (PSIM) software. It shows that the secondary side PWM control strategy can achieve 94% efficiency during the $35 \Omega $ load in CC mode, while the primary side PFM control only can achieve 88% efficiency.

A Partially Pixel-Parallel DROIC for MWIR Imagers With Columnwise Residue Quantization

Abstract: This paper presents a partially pixel-parallel digital readout integrated circuit that overcomes the limitation of achievable digital resolution seen in megapixel-format infrared digital focal plane arrays (IR-DFPAs). It incorporates 5-bit in-pixel pulse frequency modulation (PFM)-based charge-to-digital converters and 10-bit successive approximation register (SAR) column analog-to-digital converters (ADCs). To increase the readout resolution, the residue charge at the end of the integration phase is fine converted to a 10-bit digital word and combined with the in-pixel data. This method is a compromise between fully pixel-parallel and fully column-parallel conversion approaches and favors the ever-growing trend toward small pitch FPAs by allowing a compact pixel size. A prototype consisting of a $32\times32$ array of pixels, 32 column SAR ADCs, and a timing controller block is designed and fabricated in a 90-nm bulk CMOS process. A modified version of the conventional PFM-based pixel is designed to help hold the residue charge. The design is targeted at medium-wave IR-DFPAs with frame rates up to 400 Hz. A signal-to-noise ratio of 79 dB is achieved with a full-well capacity of 2.4 Me-.

A study on the characteristics of mobile X-ray device using supercapacitor as internal power.

Abstract: Mobile X-ray device is widely employed because it is useful for diagnosis in patients having mobility difficulties and in medical emergencies. As various devices for X-ray generation have continued to be developed, X-ray devices can now be used more safely and effectively. However, mobile X-ray devices generate relatively low X-ray doses due to the limitation of the power input. Therefore, the use of mobile X-ray devices is limited to thin parts of body. In this study, a new device was designed in order to increase the usefulness of mobile X-ray devices by offsetting the weaknesses of the existing mobile X-ray devices, rendering them useable independently. A supercapacitor and battery were used as the internal power source for the X-ray generation in the manufactured device. The pulse width modulation (PWM) method is applied to control the tube voltage and current required for generating the X-ray, and the pulse frequency modulation (PFM) method is applied to the control to generate the high voltage in order to enhance the precision and efficiency. The manufactured X-ray device was used to evaluate the control signal, frequency, and output characteristics according to changes in tube voltage and current. Based on the results of X-ray generation, it is confirmed that precise control was achieved by X-ray generation increases linearly with increasing tube voltage and tube current. This means that precise control of the manufactured mobile X-ray device is passible. In addition, the study confirmed that stable output was achieved by checking the tube voltage, tube current and exposure rate during the exposure times by high power condition.

An Efficient and Small Area Multioutput Switched Capacitor Buck Converter for IoTs

Abstract: This paper presents an area and power efficient multioutput switched capacitor (MOSC) DC-DC buck converter targeting ultra-low power and IoT devices. The MOSC converter has a variable input voltage range between 1.05V to 1.4V and generates regulated simultaneous multiple output voltage levels of 1V and 0.55V. Adaptive digital time multiplexing controller is employed to enable multiple power domains. In addition, a pulse frequency modulation is utilized to regulate the output voltages over a wide range of load current. The proposed converter supports a load current of 10μA to 350μA and to 10μA at a load voltage of 1V and 0.55V, respectively. Adaptive time multiplexing and pulse width modulation are implemented through a finite state machine to eliminate the reverse current issue. This problem arises during the switching from a low load voltage of 0.55V to a high load voltage of 1V. The MOSC circuit is fabricated in 65nm CMOS technology and it occupies an active area of 0.27mm2. Moreover, both MIM and MOS capacitors are utilized to further reduce the area of MOSC converter. Measured results shows that the peak efficiency of 78% is achieved at a load power of 300μW.

A new control method for series resonant inverter with inherently phase-locked coil current with induction cookware applications

Abstract: In this paper, a new control method for induction cookware applications with series resonant inverter has been proposed. Generally, the output power of series resonant inverter is controlled by pulse frequency modulation (PFM). However, PFM has a large turn off current and a high switching frequency as the output power decreases, resulting in a large switching turn off loss and poor efficiency. To beat these limitations, pulse width modulation (PWM), PWM-PFM mixed control, and pulse density modulation (PDM) methods have been investigated. However, they have still limitations such as control complexity or loosing zero voltage switching (ZVS) characteristics. The most powerful advantage of the proposed method is the simplicity, since the only on-time is used as the control variable. Also, it has inherent soft switching characteristics with ZVS turn-on and zero current switching (ZCS) turnoff of low side switches and zero voltage and ZVZCS turn-on of two high side switches. The effectiveness of the proposed method has been verified by 200V input voltage and 2.8kW output prototype.

Low-ripple PFM Buck Converter Employing Background Calibration

Abstract: This paper presents a background calibration technique to adapt the inductor peak current of Pulse Frequency Modulation (PFM) buck converters across different load, supply and external components values. The design minimizes the idle-state time and achieves high power efficiency results while sustaining Discontinuous Conduction Mode (DCM) operation. The proposed feedback circuit compares the idle-state time to a reference idle time and updates inductor peak current value in the next switching cycle using simple logic. A replica circuit matched to the PMOS switch is introduced to generate a constant inductor peak current regardless inductance, input and output voltage values. The design is implemented in UMC130nm technology from a 1.4V to 3.6V input supply. This regulator handles a wider inductor values from 1μH to 4.7μH while ensuring efficiency above 88%. The voltage ripple magnitude is minimized across all the load range from 5mA to 100mA while its variations are 70% lower than the other conventional techniques.