Constant Off-time Research Articles

A Novel Full-Bridge Boost LCL-Type DC/DC Converter with a Constant Off-Time: Analysis Design, and Experimental Results

A Novel Full-Bridge Boost LCL-Type DC/DC Converter with a Constant Off-Time: Analysis Design, and Experimental Results

Retracted: Improved Quadratic Boost High-Gain DC-DC Converter Based on Constant Off-Time Control Mode

Retracted: Improved Quadratic Boost High-Gain DC-DC Converter Based on Constant Off-Time Control Mode

Fast-Response Variable Frequency DC–DC Converters Using Switching Cycle Event-Driven Digital Control

This paper investigates a new method to model and control variable-frequency power converters in a switching-synchronized sampled-state space for cycle-by-cycle digital control. There are a number of significant benefits in comparison to other methods including fast dynamic performance together with ease of design and implementation. Theoretical results are presented and verified through hardware and simulations of a current-mode buck converter with constant on-time and a current-mode boost converter with constant off-time. Dynamic voltage scaling for microprocessors and LiDAR are among the applications that can benefit.

Improved Quadratic Boost High-Gain DC-DC Converter Based on Constant Off-Time Control Mode

A non-isolated modified quadratic boost high-gain DC-DC converter is proposed to overcome the problems of limited boost capability and high switching stress in quadratic boost converters. The proposed converter has two topologies. The operating principles of the two topologies are analyzed, and the voltage gain and switching stress of the circuit topologies are theoretically derived and compared with existing converters. The proposed converter increases the output gain while reducing switching stress and improving conversion efficiency. A simulation model is built in MATLAB/Simulink, and the simulation results verify the correctness of the theoretical calculations. A prototype was built, and the feasibility of the converter design was verified by comparing the theoretical derivation and the prototype test results.

Resonant Asymmetrical Half-Bridge Flyback Converter

The active clamp flyback (ACF) converter is gradually becoming popular in the application field of low or medium output power range due to its advantage of soft switching and high conversion efficiency. An asymmetric half-bridge (AHB) flyback converter has been proposed in previous studies. The main advantages of the AHB flyback are the same number of components as the ACF converter and the soft switching technique. In this paper, an AHB flyback converter with constant off-time (COT) plus pulse frequency modulation (PFM) is proposed, so that the resonant time is not affected by the input voltage and load, and can achieve a wide range of zero voltage switching (ZVS) operating range. Compared to pulse width modulation (PWM), the PFM control with COT can make the system more stable. Finally, a prototype circuit with a specification input of 48 V to an output of 2.5 V/8 A is made for verification.

A General Approach to Sampled-Data Modeling for Ripple-Based Control—Part II: Constant ON-Time and Constant OFF-Time Control

This part is the second part of this article and mainly presents the sampled-data modeling method for the dc–dc converters with the constant <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> -time (COT) and constant <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -time (COFT) controls. Compared with the constant frequency control in the first part, the duty cycle perturbation signal in the COT/COFT control is found to have two sets of narrow pulse signals in each switching period. Then, by establishing the relationship between the two sets of signals and using Shannon's sampling theorem, the transfer functions of the modulator and the loop gain are derived. Based on the theoretical results, the phenomenon that a current-mode constant <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> / <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> time controlled buck converter is stable at any duty cycle, and the instability of a voltage-mode constant <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">on</small> / <sc xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">off</small> -time controlled buck converter with the smaller time constant of the output capacitor could be predicted. Moreover, the sampled-data modeling method is further extended to the digital control by taking a digitally current-mode controlled buck converter as an example. Simulation results are provided to confirm the validity of the proposed modeling method.

A Fast Switching Current Controlled DC/DC Converter for Automotive Applications

Automotive industry requires integrated circuits with both low cost, to maintain product competitiveness, and high efficiency, moving towards solutions as green as possible. Each electronic device within the car needs for a regulator to provide a steady supply to ensure correct and safe operation. Among all regulator, DC/DC Converters are the most valid solution to achieve a high efficiency-price ratio. The DC/DC Converter needs for a control loop to monitor the load operation. The basic control loop topologies are well known in the state-of-the-art. The paper presents a DC/DC Buck Converter for automotive applications designed in low cost technology with an upgraded version of the Peak Current Mode Control which uses a constant off-time. For chip area reduction, an n-channel power-DMOS is chosen as power transistor. The design of each block composing the circuit is presented. To guarantee DC-DC Buck converters high-efficiency and low cost (in terms of external components) increasing switching frequency is mandatory. A  1.5 MHz switching frequency has been chosen to reduce external components size. The device is optimized by design to be able to achieve 94.4% efficiency using a 3V  3A load. The post-layout simulations of the system are shown, confirming the expected circuit behavior also including the presence of wiring parasites. A PCB is also designed to test the packaged die to ultimately demonstrate the chip’s robustness and suitability in a real automotive application.

Quasi‐constant‐frequency variable off‐time control technique for buck‐type DC–DC converter

There are two weaknesses in conventional constant off-time controlled buck-type DC–DC converters: which are varied switching frequency and poor output-regulation accuracy. To make the switching frequency immune to the variation of the input voltage and the reference voltage and provide both high output-regulation accuracy and a fast transient response for buck-type DC–DC converters, a new control method, called the quasi-constant-frequency variable off-time control technique, is proposed. Circuit simulation results validate the correctness of the theoretical analysis.

Improved transient response of controllers by synchronizing the modulator with the load step: application to v2ic

V 2 I c is a ripple-based control with an excellent performance for load transients and reference voltage tracking because it exhibits a feedforward of the load current and the error of the output voltage. However, if V 2 I c is modulated with constant frequency, constant on-time or constant off-time, its dynamic response is hindered by delays in the response. This paper proposes a technique that synchronizes the clock of the converter to initialize the duty cycle when a worst-case load transient occurs using the current through the output capacitor to detect load transients. It is exemplified on a V 2 I c control but it is applicable to most of controllers as it only acts on the modulator.

Structural and textural study of electrodeposited zinc from alkaline non-cyanide electrolyte

Pulse electrodeposition was used to produce zinc deposits from an alkaline non-cyanide electrolyte with additives. The influence of additives’ concentration and pulse parameters, such as ON-time, OFF-time, and pulse peak current density on the grain size, surface morphology, and crystal orientation were investigated. In an additive-free electrolyte, increase in OFF-time at constant ON-time and peak current density decreases the grain size while the latter increases with increasing ON-time at constant OFF-time and peak current density. A progressive decrease of grain size was observed with increasing peak current density up to 5 Adm−2 at constant ON-time and OFF-time in both additive-free electrolyte and bath containing additives. Zinc with an average crystallite size of 34 nm was obtained at 5 Adm−2 from electrolyte containing additives. The preferred orientation of the zinc deposits obtained at 6 ms (ON-time), 51.5 ms (OFF-time) and 5 Adm−2 (peak current density) with electrolyte containing additives was prismatic [10.0] plane.

Influence of pulse parameters on the microstructure and microhardness of nickel electrodeposits

Square-wave cathodic current modulation was used to electrodeposit fine-grained nickel from an additive-free and saccharin-containing Watts bath. The influence of pulse on-time, off-time, peak current density and saccharin on the grain size, surface morphology, crystal orientation, and microhardness was determined. The study showed that at constant off-time and peak current density, the crystal size of the deposits was found initially to decrease with pulse on-time before it started to increase with further increase in on-time. The crystal orientation progressively changed from a (111) texture at the on-time of 0.1 ms to a strong (200) texture at an on-time of 8 ms. An increase in the pulse off-time at constant on-time and peak current density resulted in a progressive increase in crystal size. However, the crystal orientation remained unaffected with increasing off-time. An increase in peak current density resulted in considerable refinement in crystal size of the deposits. The crystal orientation progressively changed from an almost random distribution at the lowest peak current density of 0.2 A/m 2 to a strong (200) texture at a peak current density of 2.0 A/m 2. The nanocrystalline nickel with grain size in the order of 30 nm can be produced from saccharin-containing Watts' baths. In contrast, when using an organic-free Watts' bath and similar pulse-plating conditions, the grain size can only be refined down to about 80–100 nm. The microhardness of deposits is related with grain size: when the grain size is large, the microhardness is consistent with Hall–Petch law (HPL); when the grain size is ultrafine, “nano-effect” would be generated, the microhardness is against HPL.

Quantitative texture analysis in pulse reverse current electroforming of nickel

The crystallographic texture of nickel deposits is known to be related to its magnetic and mechanical properties. However, up to now, most of the texture analyses of electrodeposited nickels have been semi-quantitative and still use a nickel sulphate bath, which is mainly for decorative industrial applications. In this paper, a quantitative texture analysis using ODF (orientation distribution function) has been carried out to study the effect of a pulse reverse current on the crystallographic texture of electroformed nickels, with the use of a nickel sulphamate bath, which is now commonly used for functional industrial applications and micro- or precise components. It was found that the [100] fibre texture with different orientation densities was formed at different on-times and off-times. With a constant off-time of 0.5 ms, an increase in on-time led to a gradual decrease in the orientation density of the [100] texture, whereas with a constant on-time of 5 ms, an increase in off-time has affected the change of the orientation density of the [100] texture in a more complicated manner. All of these phenomena are considered to be related to the change of the amount of inhibiting chemical species such as nickel hydroxide adsorbed on the cathode surface and the nickel deposition rate.

自励昇圧型発振回路を用いた蛍光ランプ用点灯回路の検討

The operating characteristics of the self-excited step-up type inverter for a fluorescent lamp is investigated by simulation using input voltage of rectified 50Hz AC. The envelope curves of voltage and current waveforms of high-frequency oscillation with discharge load are calculated and compared with the measured curves. The obtained results are as follows.(1) Output voltages and currents of the inverter are a function of OFF-time of the switch in the circuit.(2) envelope curves of output voltage and current are proportionally modulated by the input voltage in the case of small input inductance and constant OFF-time.(3) Output envelope curves can be flattened by controlling the OFF-time via the input voltage.

比例弁による油圧シリンダの力制御に関する研究 学習制御とオフ時間一定ＰＷＭ制御を組合せた場合

In this study, the force control of hydraulic cylinders was carried out using a system consisting of a single proportional-type valve with a built-in overlap-type 4-way valve, two pressure sensors and personal computer. For the force control by using On/Off operation to the valve, we adopted a learning control and a PWM (Pulse Width Modulation) control with a constant off-time which is relatively short.For the purpose of obtaining a high response, the PWM control with a constant off-time which is modified a general PWM control by an off-time being constant was introduced to the force control. The system was good in response with a stable off-time of 2ms. In this case, the time lag from the electric current off to the valve closure was about 1ms. In the first place, the on-time table of the PWM has been prepared for the desired force and the error in the learning control. Also, the on-time table is corrected by the control which is in progress; therefore, this control response becomes higher than the case before learning. The thrust fluctuation of the hydraulic cylinder was able to be made smaller by controlling the spool position in the off-time of the valve.

Design of single-winding energy-storage reactor for DC-to-DC converters using air-gapped magnetic-core structues

A procedure is presented for designing air-gapped energy-storage reactors for nine different dc-to-dc converters resulting from combinations of three single-winding power stages for voltage stepup, current step-up and voltage stepup/current stepup and three controllers with control laws that impose constant-frequency, constant transistor on-time and constant transistor off-time operation. The analysis, based on the energy-transfer requirement of the reactor, leads to a simple relationship for the required minimum volume of the air gap. Determination of this minimum air gap volume then permits the selection of either an air gap or a cross-sectional core area. Having picked one parameter, the minimum value of the other immediately leads to selection of the physical magnetic structure. Other analytically derived equations are used to obtain values for the required turns, the inductance, and the maximum rms winding current. The design procedure is applicable to a wide range of magnetic material characteristics and physical configurations for the air-gapped magnetic structure.

Table-Aided Design of the Energy-Storage Reactor in DC-to-DC Converters

A new procedure for the selection of magnetic cores for use in energy-storage dc-to-dc power converters that eliminates the need for an automated computer search algorithm and stored data file is presented. The converter configurations included in the procedure are the three commonly encountered single-winding converters for voltage stepup, for current stepup and voltage stepup/current stepup, and for the two-winding converter for voltage stepup/current stepup. For each converter configuration, three types of controllers are considered: constant-frequency, constant on-time, and constant off-time. Using concepts developed from analyses of these converters by considering the transfer of energy by means of an energystorage inductor or transformer, a special table of parameters calculated from magnetic core data is constructed, which leads to a considerably simplified design procedure.