Richard Redl

• PhD
• Consultant at Redl Consulting

Hysteretic control provides unique advantages in DC-DC converter applications but it is less popular than other types of control because the switching frequency depends on the operating point, the feedback ripple and the component parasitics. Furthermore, it is difficult to predict the frequency due to the complex interaction of those factors. This...

Closed-form subharmonic oscillation conditions are derived and experimentally verified for the current-controlled boost converter in continuous conduction mode with closed voltage feedback loop. Typical voltage-loop phase-lag and type-II compensators are analyzed. The well-known open-voltage-loop instability condition becomes a special case. It is...

This paper presents the derivation and experimental verification of the closed-form subharmonic instability condition of the constant-frequency peak-current-controlled buck converter with closed voltage feedback loop. The well-known open-voltage-loop instability condition becomes a special case. The instability limits in the converter parameter spa...

A general closed-form subharmonic stability condition is derived for the buck converter with ripple-based constant on-time control and a feedback filter. The turn-on delay is included in the analysis. Three types of filters are considered: low-pass filter (LPF), phase-boost filter (PBF), and inductor current feedback (ICF) which changes the feedbac...

Feedforward control is a conceptually simple, highly effective and extremely robust, but not very well known or appreciated, technique for improving the dynamic regulation of switching regulators. Feedforward control is also used for stabilizing the switching frequency or the loop gain of free-running converters. The paper presents an overview of f...

Switching regulators with ripple-based control (i.e., ??ripple regulators??) are conceptually simple, have fast transient responses to both line and load perturbations, and some versions operate with a switching frequency that is proportional to the load current under the discontinuous conduction mode. These characteristics make the ripple regulato...

The various ripple regulator types have simple control structure, fast transient response, and (in some versions) a switching frequency that is proportional to the load current in discontinuous conduction mode. Those characteristics make the ripple regulators especially well-suited for power-management applications in computers and portable electro...

The various ripple regulator types have simple control structure, fast transient response, and (in some versions) a switching frequency that is proportional to the load current in discontinuous conduction mode. Those characteristics make the ripple regulators especially well-suited for power-management applications in computers and portable electro...

Buck converters using the output ripple as the PWM ramp have low circuit complexity and fast transient response but are sensitive to external noise due to the small ripple amplitude. This paper proposes the switched noise filter to reduce the noise sensitivity

A new four-switch full-bridge dc-dc converter topology is especially well-suited for power converters operating from high input voltage: it imposes only half of the input voltage across each of the four switches. The two legs of a full-bridge converter are connected in series with each other, across the dc input source, instead of the usual topolog...

This paper focuses on the power management solutions for desktop and mobile CPUs, with special emphasis on the control aspects and the related control IC requirements and architectures for VRM applications. The paper discusses the following topics: power converter topologies, load transient response, the ADOPTTM voltage positioning technology, main...

A dramatic increase in the number of line-powered electronic equipment (computers and other office equipment, electronic ballasts, variable-speed drives, and consumer electronics, e.g., color televisions) has taken place. These items of equipment draw distorted, and often fluctuating, line current; they also generate high-frequency conducted and ra...

A new high-frequency and high-efficiency electronic ballast for high-intensity discharge (HID) lamps is presented. The ballast features an integral resonant ignitor, high efficiency, power regulation, and optional hot strike and fast warm-up capabilities. The ballast can operate virtually any lamp without acoustic arc resonance. The paper presents...

A new four-switch full-bridge DC/DC converter topology is especially well-suited for power converters operating from high input voltage: it imposes only half of the input voltage across each of the four switches. The two legs of a full-bridge converter are connected in series with each other, across the DC input source, instead of the usual topolog...

This paper describes a novel passive power-factor correction circuit that ensures the compliance of the capacitively filtered single-phase rectifier with the EN61000-3-2 norm at a cost much lower than the known solutions. The circuit can be used to about 300 W. The additional components are a small inductor, a small capacitor and a diode

The optimized gain of the voltage-error amplifier and current-mode control provide instantaneous transient response and small DC shift of the output voltage for step changes in the load current. This paper analyzes the system, determines the best compensation, provides design guidelines for buck converters powering Pentium(R) II processors and pres...

High-frequency converters powered from high source voltage show significant improvements when operated with soft switching: reduced switching losses, which allow high switching frequency and size reduction of reactive components; reduced EMI/RFI noise; no need for complex and expensive snubbers; and exploitation of the parasitic circuit elements to...

A flyback-type of a transformer-coupled DC/DC power converter supplies a train of current pulses to charge an energy-storage capacitor to a desired high voltage, converting input DC power obtained from a lower voltage DC source. The energy-storage capacitor is charged to a specified voltage within a specified time with minimum peak and RMS currents...

In use far and wide for improved delivery and control of the electricity supply, power electronics systems are both the cause and remedy of the power system harmonic pollution problem. Here, the authors describe how an insidious side-effect of any solution involving power electronics converters is their generation of high-frequency pollution-namely...

The paper reviews the various inverter topologies for cold-cathode fluorescent lamps, discusses the analysis and control of the class E inverter, and introduces a new control IC developed for such inverters and also for ZVS DC/DC power converters. The IC features a zero-voltage detector, switch overdissipation protection, soft start, pulse-by-pulse...

The increasing number of line-powered electronic equipment causes severe pollution in the power distribution system mainly by producing distorted line currents and voltage. In this paper we review the various aspects of power-line pollution, and provide a general overview of how to combat the distortion caused by rectifier loads. We also consider t...

Due to its simplicity, the boost rectifier with automatic control is potentially the least expensive active line-harmonics reducing circuit. The filtered line current, however, shows considerable distortion when the peak input voltage is close to the output voltage. This paper presents an analysis of the circuit, discusses the compliance with EN610...

Very fast shutdown capability of a smart driver IC provides effective protection for an average-sized MOSFETs or IGBTs against the most frequently occurring short circuits. The operation of gate drive IC is described by looking at the effects of short circuits associated with the power semiconductor.

Recently, power electronics has become the dominant factor in the deterioration of the electromagnetic environment, causing declining quality of line power and increasing level of conducted EMI. This paper reviews the fundamentals of EMC in power electronics, including the terminology and categories of EMC, the propagation and generation of low-fre...

A new DC/DC power converter featuring zero voltage switching under all loading conditions is described. Control of the power converter is achieved with constant-frequency complementary pulse-width modulation of the two switches. In offline power supply applications, the power converter is able to provide automatic line-current shaping while retaini...

This paper introduces a new simplified control technique for high-quality rectifiers. The technique, called “input-current-clamping”, requires only a low-cost controller, while it ensures compliance with existing harmonic regulations. The authors present the regulations, the idealized waveforms obtainable with the proposed technique, the spectra of...

To improve the power factor and to comply with line-harmonics regulations, a power-factor-correction/line-harmonics-reduction circuit must be added to the capacitively filtered bridge or voltage-doubler rectifier. Passive solutions (i.e. circuits using only inductors and capacitors) are simple, reliable, and generate no EMI. In this paper we discus...

The paper introduces a new family of single-stage isolated power-factor-corrected power supplies with fast regulation of the output voltage, and discusses the most-important design issues, including all of the following: storage-capacitor voltage, dual-range and wide-range operation, device RMS currents, and line harmonic currents. In addition to t...

In this paper we address the issue of power quality in relation to the telecommunication power supply. After a general discussion of power quality and related global trends, we present a comprehensive list of line disturbances and investigate the effect of rectifier loads. Nonlinear loads, including rectifiers used in telecommunication power suppli...

The importance of power-factor correction and the related line-harmonics reduction is increasing as the amount of line-fed electronic equipment grows and the requirements of regulatory agencies tighten. This paper presents a comprehensive overview of power-factor correction in single-phase off-line switching-mode power supplies, including the defin...

At light load and/or high line, the peak-current-controlled boost power-factor corrector has considerable distortion. In this paper, the authors determine the line-current waveform and the distortion of the corrector, the shape of the ideal reference signal, and discuss and analyze three distortion-reducing methods. The distortion-reducing methods...

A primary-side controller (PSC) using current mode PWM and an error signal isolator (ESI) using PAM have been developed by TOKO, Inc. With overcurrent protection and slope compensation built in, the PSC boasts more features than its 8-pin rival, a 3842. The ESI, used with a bead-sized pulse transformer, replaces a TL431/optocoupler combination

A smart insulated gate transistor (IGT) driver IC featuring thermal protection, current limiting, and first-pulse wake-up has been developed by TOKO, Inc. The driver IC is available in a SOT89-5, a five-pin surface-mounted package capable of up to one watt of power dissipation. In a proprietary circuit configuration offered freely to the user of th...

The computer program DYANA calculates all important frequency-domain transfer functions and impedances, and time-domain step and impulse responses, for any switching regulator. The analysis includes the switching cell with its duty-ratio/frequency modulator, an error amplifier, an output post-filter, and an input filter. Both open-loop and closed-l...

A new family of single stage isolated power-factor correctors features fast regulation of the output voltage, one or two power switches operated in unison, a single control loop, and automatic shaping of the line current. We give topologies, steady-state analysis, design considerations, and experimental results

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. Po...

A new family of ICs for driving insulated-gate transistors is introduced. Three members of the family are designed for soft-switching converters and converters with synchronous rectifiers; two members are designed for converters with zero-voltage-switching or zero-current switching active snubbers. Due to their low stand-by current and a unique fir...

By adding a simple external commutating aid circuit to the full-bridge DC/DC converter with phase-shift control and by reducing the magnetizing inductance, optimum performance (i.e. ZVS operation and high conversion efficiency) can be achieved from full load down to almost zero load. An analysis is presented to determine the required and available...

At light load and/or high line, the peak-current-controlled boost power-factor corrector has considerable distortion. In this paper the authors determine the line-current waveform and the distortion of the corrector, the shape of the ideal reference signal, and discuss and analyze three distortion-reducing methods. The distortion-reducing methods a...

An analysis is presented for determining the commutating energy available for the clocked or passive-to-active leg of a full-bridge soft-switching power converter with an external commutating aid, as a function of the load current. It is shown that by properly choosing the values of the circuit inductances, soft switching can be achieved over a wid...

A primary-side controller (PSC) using current mode PWM and an error signal isolator (ESI) using pulse amplitude modulation (PAM) have been developed. With overcurrent protection and slope compensation built in, the PSC has more features than its 8-pin rival, a 3842. The ESI, used with a bead-sized pulse transformer, replaces a TL431/optocoupler com...

The operation and design trade-offs of the interleaved boost converter in continuous inductor-current mode in a high-power-factor preregulator circuit are investigated. By using interleaved converters, an overall reduction of boost inductor and electromagnetic interference (EMI) filter volume can be achieved, together with reduced switching losses....

An analysis and experimental verification for a Class E full-wave current-driven low dv / dt rectifier are given. Basic parameters of the circuit are derived using the time-domain analysis and Fourier series techniques. The rectifier diodes turn on and off at low dv / dt , yielding low switching noise and low switching losses. Diode parasitic capac...

The authors introduce a model for the input port of the high-frequency power-factor corrector and determine the gain of the current control loop. Both the model and the expression for the loop gain are entirely general and can be used for analyzing the source impedance and current control loop interaction of virtually any corrector with any current...

The authors show that a conceptually simple, general, and systematic analysis approach can be used to obtain a low-frequency model for any switching cell. The injected-absorbed-current dynamic analysis approach can be used with topologies with any number of state variables. General expressions for all six characteristic coefficients, defining the l...

The RMS, DC, and peak currents for five important power factor correctors with capacitive energy storage are presented. The correctors are a boost power converter with average current control and hysteretic control, a buck-boost power converter with automatic control, and a buck power converter with pulse width modulation (PWM) sinewave line curren...

The small-signal high-frequency model of the free-running current-mode-controlled converter is determined using the analysis method of injected-absorbed currents and introducing high-frequency correction terms. The model is valid up to one-half of the switching frequency. The model parameters (the characteristic coefficients of the switching cell)...

By introducing a simple high-frequency extension function (HFEF), it is possible to significantly improve the accuracy of the averaged small-signal dynamical model of the current-mode-controlled converter. The high-frequency extension function is an approximate description of the actual processes in the converter, and is therefore physically well-f...

In this chapter we shall analyze four power cells that use duty-ratio control at variable frequency. The first is the so-called Porter cell, a member of the current-fed converter family. (Practical current-fed converters have an inductor in series with the supply voltage. At the switching frequency the inductor has a high impedance that turns the s...

Second-order free-running hysteretic regulators (Fig. 9-1) have been around for a long time [1] but their analysis still intrigues the designer [2]. They represent the simplest possible type of switching regulators. The intrinsic advantage of hysteretic regulators is the small number of parts, resulting in high reliability and low cost. In spite of...

The basic building blocks of switching regulators are the dc/dc converters. Strictly speaking, they are dc-voltage-to-dc-voltage converters: a dc voltage at the converter input is transformed into a dc voltage at the converter output. The situation is fundamentally different in the case of the input and output currents. The waveform of those curren...

This chapter reviews several published papers concerned with problems that cannot be dealt with by application of the small-signal, low-frequency methods. In the chapter, we also point out other analytic approaches, without misleading or confusing the reader with imprecise or overly optimistic titles.

This chapter presents and analyzes the multiple-loop configuration that uses the integral of the inductor voltage as a second state variable, as applied to the elementary buck, buck-boost, and boost converters. The technique was developed by TRW in a NASA-sponsored research and development project at the beginning of the 1970s.

The switching regulators are complex structures with many parts and, consequently, relatively low intrinsic reliability. In critical applications redundancy is employed to improve the reliability. Two main methods can be distinguished. The first is based on the redundancy of different components in a single supply [1], and the second makes use of a...

The switching cell is one of the functional blocks in the closed-loop regulator structure. With the regulating loop closed, the controlled quantity of the switching cell is no longer an independent variable; it is determined by other functional blocks in the closed-loop system. The system shown in Figure 3–1 operates as follows. The input to an err...

The linear analysis methods [1] through [5] have contributed greatly to the understanding of the phenomena associated with the dynamic behavior of switching structures in open-loop or feedback configurations. The obtained mathematical expressions permit physical insight into the regulator operation. At the same time, they are applicable as quantita...

The elementary converters are the buck, boost, and buck-boost converters. They belong to the oldest and best-known family of switching converters, the single-switch minimum-topology circuits. The steady-state analysis of the elementary converters is quite easy.

According to the classification of analysis methods shown in Figure P1-1, the injected-absorbed-current method belongs to the class of the simplest linear methods whose validity is limited to low-frequency, small-signal phenomena. As will be explained in Chapter 14, the low-frequency limitation can be made less stringent by including the discrete (...

The most important control methods are those that control the inductor current. In this chapter we shall discuss in detail how the choice of the inductor current as the controlled quantity provides considerable improvement in the dynamic properties of the elementary power cells and in the ease of stabilizing the feedback loop that controls the outp...

The state-variables-averaging method [1], [2] was the first approach to result in a complete linear model of a switching power cell. It was a major contribution to the dynamic analysis of switching structures and has been adopted by other investigators (e.g., [3], [4]). Because of this, and in spite of some unfavorable opinions [5], this method was...

Probably the first electrotechnical application of the concept now known as feedforward was to improve the output characteristic of dc generators that had a separate field winding. As the output current increases, it creates a field component that counteracts the original field. Combined with increased internal resistive voltage drops, this results...

Shortly after the first publication [1] of the discovery referred to as the Ćuk converter or optimum topology converter, a controversy took place as to whether the configuration was really a new circuit or invention and even whether it was new at all [2], [3]. At any rate, the properties of this configuration, its extensions [4], the unexpected res...

The authors present an improved soft-switching full-bridge converter which is especially suitable for high-power application (e.g. more than 1 kW output) because of its inherently high efficiency. The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM (pulse width modulation) full-bridge DC-DC converter subst...

Optimum flyback-charging of an energy-storage capacitor is discussed. It charges the capacitor to a specified voltage within a specified time, with minimum peak current in the transistor and a transformer. Recommended methods are hysteretic current-mode control with current sensing in both transformer windings, peak-current-commanding current-mode...

An application-specific program, RESOCAD (RESonant converter CAD), is described that computes more than 250 times as fast as do general-purpose simulation programs, for single-ended, inductor-fed, zero-voltage-switching, series-resonant DC/DC converters and DC/AC inverters and for resonant rectifiers. The program computes steady-state periodic wave...

In capacitively coupled bridge converters, duty-ratio unbalanced can cause transformer saturation and resulting transistor destruction. Independently, modulation of the transistor storage time by variations of collector current can cause low-frequency system oscillation which leads also to transformer saturation, and additionally causes low-frequen...

Switching-mode dc/dc converters must be protected against overload, to prevent failure of the converter or the external current-carrying hardware. The authors collect, classify, analyze, and evaluate existing protection methods and describe a new negative-feedback frequency modulator which prevents short-circuit-current runaway. Test data prove the...

Switch-peak-current commanding current-mode control produces asymmetrical operation when used in capacitively coupled symmetrical dc/dc converters. This paper discusses the causes and effects of asymmetry, gives an analytical model, and proposes a negative-feedback corrector to eliminate the asymmetry. Test results on a 150-W off-line halfbridge co...

Near-optimum dynamic regulation of a dc-dc converter is obtained by adding feed-forward of output current and input voltage to a current-mode controller. The results are a) near zero output impedance and audio susceptibility, from dc to nearly the switching frequency, b) much reduced magnitude, duration, and energy content of the output-voltage tra...

The TÜNDE-M energetic particle instrument aboard the Vega 1 spacecraft detected intense fluxes of energetic (≥40 keV) ions in the vicinity of comet Halley, starting at a distance of 107 km from closest approach. Three regions of differing ion characteristics have been identified. An outer region, several million kilometers in extent, contains pick-...

Analytical results, design considerations, and experimental results at 1.5 MHz are presented, for a novel resonant high-frequency dc/dc converter. The circuit works virtually without dynamic losses at several-MHz switching frequency. The analysis gives the permissible area of the equivalent load impedance for lossless operation, presents a model fo...

Class E dc/dc converters can operate at high switching frequencies with very low switching power losses. Using commercially available power transistors and diodes, Class E converters can operate at switching frequencies in the low-MHz range, with efficiencies of about 85 percent. Previous papers dealt with the circuit parameter values needed to obt...

The article is about the scientific task of the charged particle analyzer PLAZMAG flying on the VEGA, space probe and about the physical background of the measurements. The sensors of the device face the Sun and the comet and measure the energy and mass spectrum of ion and electron components of lower energy than 25 keV. The authors present details...

The VEGA experiment is a two spacecraft mission planned for the observation of the planet Venus and Halley's comet and is the result of an international cooperation. The television system has the following tasks: to recognize and track the comet by controlling an electro-mechanical platform; to take pictures and send them to the Earth. The function...

TUNDE-M is one of the measuring devices of the spaceprobe sent out to the exploration of Halley's comet within the framework of the VEGA programme. The device - containing two telescopes built with two semiconductor detectors and one scintillation detector each - has the task to detect the ions from the comet, to determine their energy distribution...

Analytical results, design considerations and experimental results at 1.5 MHz are presented for a novel resonant high-frequency dc/dc converter. The circuit works virtually without dynamic losses at several-MHz switching frequency. The analysis gives the permissible area of the equivalent load impedance for lossless operation, presents a model for...

Instabilities of switching voltage regulators with different power circuit and controller combinations are presented, and analytical methods and expressions for the determination of the maximum usable gain are introduced. The effect of the amplified and fed-back output ripple voltage on the operation of the current comparator is used for analysis....

A survey of current sensing and overload protection methods for the three basic switching-mode voltage regulator types (buck, boost and buck-boost) is given. Expressions of the output characteristics and their limits of validity are presented for the two-threshold (hysteretic) and one-threshold (peak-sensing) protections. The effects of duty-cycle...

In class-D operation, the amplifier is made alternately conducting and nonconducting by means of a given switching frequency. The information to be amplified varies the width of the switching pulse. The utilization of a class-D amplifier as the modulator for an anode-modulated am transmitter appears to be advantageous from the viewpoint of efficien...