Showing papers on "Buck converter published in 1994"

A low-voltage CMOS DC-DC converter for a portable battery-operated system

Abstract: Motivated by emerging battery-operated applications that demand compact, lightweight, and highly efficient DC-DC power converters, a buck circuit is presented in which all active devices are integrated on a single chip using a standard 1.2 /spl mu/ CMOS process. The circuit delivers 750 mW at 1.5 V from a 6 V battery. To effectively eliminate switching loss at high operating frequencies, the power transistors achieve nearly ideal zero-voltage switching (ZVS) through an adjustable dead-time control scheme. The silicon area and power consumption of the gate-drive buffers are reduced with a tapering factor that minimizes short-circuit current and dynamic dissipation for a given technology and application. Measured results on a prototype IC indicate that on-chip losses at full load can be kept below 8% at 1 MHz. >

Inductorless DC-to-DC converter with high power density

Abstract: A new type of switching-mode power supply containing no inductors or transformers is proposed. The controlled transfer of energy from a unregulated DC source to a regulated output voltage is realized through a switched-capacitor (SC) circuit. A duty-cycle control is used; the driving signals of the transistors in the SC circuit are determined by the feedback circuit. The absence of magnetic devices makes possible the realization of power converters of small size, low weight and high power density, able to be manufactured in IC technology. High efficiency, small output voltage ripple and good regulation for large changes in the input voltage and/or load values are other positive features of the new type of DC-to-DC power converter. The input-to-output voltage conversion ratio is flexible; the same converter structure can provide a large range of constant desired values of the output voltage for a given input voltage, by predetermining the steady-state conversion ratio. The frequency response shows good stability of the designed converter. The experimental results obtained by using a prototype of a step-down SC-based DC-to-DC converter confirmed the theoretical expectations and the computer simulation results. >

Reduction of voltage stress in integrated high-quality rectifier-regulators by variable-frequency control

Abstract: The Integrated High-Quality Rectifier-Regulators (IHQRRs) suffer from relatively high stress on the internal-energy storage capacitor and, consequently, on primary-side semiconductors. As a result, they are not practical in applications with the universal input-voltage range. In this paper, a variable-frequency control that reduces the voltage stress and makes the IHQRRs suitable for universal input-range applications is described. Evaluation results of a 90 W, experimental BIBRED power converter that uses the proposed variable-frequency control are presented. >

Analysis and design of LCL-type series resonant converter

Abstract: A series resonant converter modified by adding an inductor in parallel with the transformer primary (or secondary) is presented. This configuration is referred to as an "LCL-type series resonant converter". A simplified steady-state analysis using complex AC circuit analysis is presented. Based on the analysis, a simple design procedure is given. Detailed experimental results obtained from a MOSFET-based 640 W converter are presented to verify the analysis. A narrow variation in switching frequency is required to regulate the output voltage for a very wide change in load, and the converter has load short-circuit capability. It is shown that by placing the parallel inductor on the secondary side, the parasitics of the high-frequency transformer can be used profitably. >

Synchronously rectified buck-flyback DC to DC power converter

Abstract: A synchronously rectified buck-flyback converter is described which provides multiple synchronous regulated outputs. A synchronous buck converter provides the main output and a synchronous flyback converter, utilizing the primary inductor of the buck converter, provides the secondary output. The converter utilizes a split-feedback signal, whereby each of the regulated outputs provides a component of the signal and a switch controller synchronously activates and deactivates rectification switches based on the feedback signal, required output levels and load. The switches are synchronously controlled such that a power input switch is operated in anti-phase to a control switch for each regulated output.

A general unified large signal model for current programmed DC-to-DC converters

Abstract: A general and unified large signal averaged circuit model for current programmed DC-to-DC converters is proposed. In the averaged circuit model, the active switch is modeled by a current source, with its value equal to the averaged current flowing through it, and the diode is modeled hy the voltage source, with its value equal to the averaged voltage across it. The averaged circuit model has the same topology as the switching converter. The large signal averaged circuit model for current programmed buck, boost, buck-boost and Cuk converters are proposed, from which the large signal characteristics can be obtained. The steady-state and small signal transfer functions of the current programmed DC-to-DC converters can all be derived from their large signal averaged circuit models. The large signal characteristics of the current programmed buck converter are studied by both the phase plane trajectory and the time domain analysis. Experimental prototypes for a current programmed buck converter, with and without an input filter, are breadboarded to verify the analysis. >

Buck converter with operating mode automatically determined by the load level

Abstract: A DC-to-DC (buck) converter comprises a PWM regulation loop and a hysteretic control loop, which are alternatively enabled by a mode selection circuit of the converter in function of the load level. When the level of load drops below a preset limit related to a design load level, the converter passes from a PWM control mode to a hysteretic control mode, thus eliminating switching losses during periods of operation at relatively low load level.

Maximum-power-tracking using positive feedback

Abstract: Certain recent publications report the use of switching power converters, supplied by photovoltaic arrays and employing positive feedback, as maximum power trackers. This paper explains the principle applied, and compares it to other known approaches. A simplified mathematical model that can be used for evaluation of the performance, is derived. Possible improvements are suggested. >

Clamped continuous flyback power converter

Abstract: Size reduction in a clamped power converter can be achieved, and stability of the converter under no-load and transient loads can be substantially improved, by operating the converter in a continuous flyback mode.

Development of a DC distributed power system

Abstract: This paper presents design considerations for power converter modules used in a distributed power system, including front-end power converter modules and load power converter modules. The system is designed for a universal input voltage of 90-260 V AC, with a bus voltage of 48 V DC. Several versions of the 600 W power factor corrected front-end power converter modules have been evaluated. One configuration includes a zero-voltage-transition PWM boost PFC circuit followed by a zero-voltage-switched active-clamp forward power converter. The second configuration uses an interleaved active-clamp flyback power converter for both the power factor correction and bus voltage regulation. 150 W and 300 W load power converter modules with 5 V output have been developed using the active clamp forward power converter topology and low-profile magnetics. >

Bilateral power converter for a satellite power system

Abstract: A bilateral power converter (10) for a satellite power system comprises a battery (12), an inductor (14), a switching means (18, 20), and a controller (16). The battery (12) preferably has a first and second terminals. The inductor (14) is coupled to the first terminal of the battery (12) and the switching means (18, 20). The switching means (18, 20) selectively couples the second end of the inductor (14) to a bus (28) or to ground ill response to a control signal. The controller (16) monitors the bus (28) voltage, current flow to the battery (12) and the current flow through the switching means (18, 20). The controller (16) also receives control signals from the satellite's computer (13) and automatically regulates the voltage on the bus (28) by adjusting the duty cycle of the signal output by the controller (16) to the switching means (18, 20). Responsive to the duty cycle of the signal output by the controller (16), the bilateral converter (10) acts either as a buck converter or a boost converter to charge or discharge the battery according to the amount of power on the bus (28).

A new ZCS-ZVS-PWM boost converter with unity power factor operation

Abstract: This paper introduces the self-resonance concept as a new way to obtain power converters without switching losses. Using this new approach, a self-resonant ZCS-ZVS-PWM boost power converter is presented. It is suitable for high switching frequency, high power operation and wide range of power. The converter control is done by using PWM technique, with constant frequency operation. The complete theoretical analysis and simulation results for the self-resonant PWM boost power converter, operating without power factor correction, are presented. Moreover, experimental results for this new boost converter, operating with unity power factor, support the validity of this new approach. >

Efficient switched mode power converter circuit and method

Abstract: A method and apparatus are disclosed for sustaining efficiency of switched mode power converters over wide load ranges. The method and apparatus can be used with any switched mode power converter having at least one synchronous rectifier (Q2) capable of being enabled or disabled and coupled, either by direct connection or otherwise, to an inductor (L1) and a diode rectifier (D1), to provide a current path for the inductor current when the synchronous rectifier (Q2) is disabled. The power converter is initialized by enabling the synchronous rectifier (Q2). Occasionally, the synchronous rectifier (Q2) is disabled, and the energy stored in the inductor (L1) is detected by sensing a voltage representative of the energy stored in the inductor (L1). A power level signal is then generated indicating whether the power converter is operating above a selected threshold. The power converter is configured in response to the power level signal by enabling the synchronous rectifier (Q2) if the power level is above the threshold or by disabling the synchronous rectifier (Q2) otherwise. The steps of disabling, detecting, generating, and configuring are repeated.

Power supply unit for electric motor vehicle

Abstract: A main switch with a low withstand voltage usable to prevent a leak current from flowing from a floated running power supply by way of the main switch even when the insulation between the main switch and the body grounding is reduced. A running power supply for supplying power to a running motor, which includes a plurality of batteries connected in series to each other, is kept in the floating state with respect to the body grounding. Moreover, there is provided a step-down DC-DC converter of an input-output insulation type. A diode and a main switch are provided from a battery constituting part of the running power supply in this order to supply a starting power or starting signal to the DC-DC converter for starting the DC-DC converter. Thus, power is supplied to the input side of the DC-DC converter from the running power supply, to obtain a step-down accessary power supply VB.

A BIFRED converter with a wide load range

Abstract: In this paper, the boost integrated flyback rectifier energy DC-DC (BIFRED) power converter which incorporates power factor correction, output voltage hold-up and input-to-output isolation is examined The particular problem of high bulk capacitor voltage at light loads is addressed and it is shown how this may be resolved if the boost and flyback sections of the power converter are allowed to operate discontinuously The criteria for ensuring correct operation in the discontinuous mode are investigated It is shown that operating in this mode places no restrictions on the minimum load and simplifies the control loop design >

Negative impedance peak power tracker

Abstract: A peak power tracker apparatus is used for controlling the negative impedance of converter for transferring maximum power from a solar array source to a battery and load typically used in space vehicles, by capacitive differentiation sensing the solar array source voltage for sensing the peak power point at which the source voltage first begins to become unstable and collapses, and then providing a step down control signal which controls a current mode pulse width modulator to control the converter to vary the negative impedance into the solar array then reserving back to a stable point at which the tracker then provide a linear ramp signal to the modulator to control the converter to drive the source voltage again to the peak power point, so as to alternate the feedback loop and source voltage between a stable point and the peak power point so as to transfer maximum power while preventing the source voltage to pass through an unstable point for discontinuous but stable operation at peak power transfer which is independent of array performance and is adaptable to a wide range of power sources.

Highly efficient rectifying and converting circuit for computer power supplies

Abstract: A power supply for producing a regulated dc output from an ac primary input incorporates a convention rectifying and filtering circuitry feeding a switching circuit for providing a high frequency, substantially rectangular voltage waveform to a high frequency transformer. The output of the transformer is provided to a synchronous buck converter having a grounded line and an ungrounded line, with a first FET switch in the ungrounded line and a second FET switch connected from the output of the first FET switch to the grounded line. A controller in the synchronous buck converter switches the FETs according to the input voltage waveform to achieve rectification. In another aspect, two FETs are placed in opposite polarity in the ungrounded line and switched together, and the controller also alters the duty cycle of the switching in accordance with the magnitude of a regulated output produced from the output of the synchronous buck converter, to achieve precise regulation. Power supplies are provided with multiple outputs of different regulated voltage, which may be externally enabled and disabled.

A choppingless converter for switched reluctance motor with unity power factor and sinusoidal input current

Abstract: This paper describes a new converter topology for switched reluctance motor drives. The new topology consists of a pair of boost-buck power converters and a machine converter. The boost converter lets the system deliver sinusoidal input current and enhances the DC source voltage having the capability of fast current rise/decay of the stator windings. It also provides DC voltage regulation. The buck converter is used to regulate the DC source voltage responding to the motor speed variations. The wide pre-voltage regulation by the two power conversion stages eliminates the high voltage-choppings to control the stator winding currents. This enables the machine-drive converter to work in single pulse-current mode, hence, removing the switching losses. >

Method and apparatus for increasing switching regulator light load efficiency

Abstract: A method and apparatus for increasing the light load efficiency of a DC-DC converter by reducing the quiescent power of the control section. In accordance with the invention, the DC-DC conversion is first started using a first regulator circuit to power the converter controller. When the converter output reaches an adequate level, the converter controller power input is switched to the output of the converter. At the same time, the first regulator circuit is turned off, whereby the converter controller continues to operate from the converter output, which has a voltage substantially less than the power supply input voltage. Because controllers all draw about the same current, the lower input voltage to the controller lowers the power consumption thereof, improving the efficiency of the regulator, particularly when subjected to light loads. Various embodiments are disclosed.

Booster power converter having accelerated transient boost response

Abstract: A booster power converter particularly suited for an automobile and having a compensation network that responds to a sudden negative input voltage excursion. The booster power converter responds to the negative input excursion by preventing its boosted output from falling below a predetermined voltage level so that voltage regulators, normally connected to the output stage of the booster power converter, are not distrupted in performing their desired regulation. The compensation network, upon sensing a decrease of the booster voltage below a predetermined lower limit, generates a control signal which causes the booster power converter to seek and obtain a maximum duty cycle operation. Upon sensing an increase of the booster voltage above a predetermined upper limit, the compensation network removes the control signal causing the booster power converter to cease operation at its maximum duty cycle, and return to its normal duty cycle of operation.

Steady-state analysis including parasitic components and switching losses of buck and boost DC-DC PWM converters under any operating condition

Abstract: A detailed analysis of DC-DC buck and boost converters operated both in continuous and discontinuous current modes is reported. Expressions for the voltage transfer functions and efficiencies of these two basic topologies have been derived in a closed form. These equations describe the converter behaviour for both constant output voltage and constant input voltage operation. Voltage transfer functions are derived so that the load regulation characteristics of the converters are closely described, including those for continuous current mode operation. Because of this, they can be effectively used to design a converter circuit responding to any given design specification. Both the equations for the efficiencies and voltage transfer functions are general and the values of the parasitic parameters to be introduced can be found on the component data sheets or derived from simple measurements. Because of this, results of the analysis presented can be effectively used in the optimization of the converter circuit...

Control conditions to improve conducted EMI by switching frequency modulation of basic discontinuous PWM preregulators

Abstract: In this paper the authors analyze the operation conditions to control basic discontinuous AC-DC preregulators with variable switching frequency. The correct use of variable switching frequency control can lead to a reduction of conducted EMI generated. The basic PWM converters (buck, boost, buck-boost, sepic, Cuk and zeta) are studied. The authors achieve results which allow them to operate the converters under the condition proposed maintaining a very small low-order harmonic-current content. Some simulation examples using a buck-boost as DCM-PFP show the amplitude reduction of the high order harmonic content. Experimental results using a sepic converter show the feasibility of the approach. >

A power controlled current source, circuit and analysis

Abstract: A control method for a buck power converter configuration as a power controlled current source providing an ideal ballast curve for high intensity discharge (HID) lamps is developed. Corresponding large signal transient characterization and stability investigation of the circuit is also presented. >

Power factor corrected switching power supply

Abstract: In an AC to DC power converter (off line switcher) and a method of converting AC power to DC power in high voltage systems the flyback converter's low side semiconductor switch has a lower breakdown voltage than its high side semiconductor switch. The lower breakdown voltage is achievable by means of a shunt regulator that controls a clamp voltage across the low side switch. The efficiency of the converter's post regulator is improved by processing only a fraction of the system's total power output.

A family of single-switch ZVS-CV DC-to-DC converters

Abstract: A family of single-switch ZVS-CV (zero voltage switching and clamped voltage) DC/DC power converters, i.e., buck, boost, buck/boost, Cuk, Zeta, and Sepic, are presented. Each power converter is realized by employing a commutation inductor circuit which is connected in parallel with either a transistor or a freewheeling diode in a conventional PWM power converter. The steady-state characteristics of these converters are analyzed, including the voltage conversion ratio, the ZVS condition and the input and output current ripple characteristics. These analytical results are confirmed by experiments. The proposed technique is quite simple and output voltage control is easy. >

Analysis and implementation of a full-bridge constant-frequency LCC-type parallel resonant converter

Abstract: A comprehensive analysis of the full-bridge constant-frequency LCC-type parallel resonant converter (LCC-PRC) is presented. Owing to operation under constant frequency, the filter designs are simplified and utilisation of magnetic components are improved. The LCC-PRC takes on the desirable characteristics of the pure series and the pure parallel converter, thus removing the main disadvantages. A useful analytic technique, based on classical AC complex analysis, is introduced for designing the LCC-PRC. By using a proper transformation on the state variable, the converter is analysed by means of a two-dimensional state-plane diagram, which shows that the converter possesses three operation modes (I, II, III). It is shown that operating the converter in mode II provides the desirable higher efficiency for a wide load range. A CPU (8031) is used to control the phase-shift time. Its control characteristic is very accurate and the cost is low. Finally, a constant-frequency controlled full-bridge LCC-type parallel resonant converter (LCC-PRC) using the CPU (8031) control is implemented.

Flyback power converter with spike compensator circuit

Abstract: An improved electrical power converter is disclosed. The electrical power converter utilizes a pulse width modulator responsive to the voltage across a tertiary winding of the power transformer. The electrical power converter includes a feedback control circuit for providing a regulating voltage to the pulse width modulator that is substantially proportional to the voltage across the tertiary winding with the voltage spikes caused by any leakage inductance in said power transformer removed. The feedback control circuit includes a spike compensator circuit that utilizes leakage inductance produced voltage spikes to compensate for output voltage degradation due to heavy loads.

DC/DC converter for a variable voltage load

Abstract: The invention relates to a circuit for converting input source energy into output load energy, for example a flyback converter for charging a storage capacitor for defibrilation from a low-voltage battery in an implantable defibrilator. The invention allows the input current to pass through the flyback inductor for a fixed duration and it allows the output current to pass for a duration which is directly proportional to the average voltage of the battery and inversely proportional to the voltage of the capacitor which is charged. When the invention is used in proximity to an electromagnetic communications system, a control circuit, in order to avoid interference, enables and inhibits the converter with a maximum frequency which is substantially below the operating frequency of the system. Moreover, the control circuit drives the converter in such a way that the cycles of energy transfer from the source to the storage capacitor take place at a minimum fundamental frequency which is substantially above the frequency of the system.

Closed-loop characteristics of voltage-mode-controlled pwm boost dc-dc converter with an integral-lead controller

Abstract: A complete analysis of a voltage-mode-controlled pulse-width-modulated (PWM) boost DC-DC power converter is presented using a previously derived small-signal model for continuous conduction mode (CCM). All parasitic components such as the equivalent series resistance (ESR) of the filter capacitor, the ESR of the inductor, the transistor on-resistance, and the diode forward resistance and offset voltage are included in the model. A design procedure for an integral-lead controller including the loading effect of the voltage divider in the feedback loop is given. The Bode plots of the closed-loop control-to-output transfer function, input-to-output transfer function, input impedance, and output impedance are determined and illustrated for three values of the duty cycle. Step response plots of the PWM boost converter in the open-loop and closed-loop cases are shown for changes in line voltage and duty cycle.

A unity power factor resonant AC/DC converter for high frequency space power distribution system

Abstract: This paper presents analysis and design of a resonant AC/DC converter topology, suitable for use in an advanced single-phase, sine-wave voltage, high-frequency power distribution system, of the type that was proposed for a 20 kHz Space Station Primary Electrical Power Distribution System. The converter comprises a transformer, a double tuned resonant network comprising of series tuned and parallel tuned branches, a controlled rectifier and an output filter. A symmetrical phase control technique which generates fundamental AC current in phase with the input voltage is employed. Steady-state analysis of the converter in continuous current mode of operation is provided and the performance characteristics presented. The proposed converter has close-to-unity rated power factor (greater than 0.98), a wide range of output voltage control (0 to 100%), low total harmonic distortion in input current (less than 8%), and high conversion efficiency (greater than 92%). Finally, selected experimental results of a bread-board converter are presented. >