Marian K. Kazimierczuk

Electronic ballast for fluorescent lamps

A frequency-domain analysis is given for a Class D voltage-switching power inverter with a load resistance connected in parallel with a resonant capacitor. Using the fundamental component approximation, design equations are derived to provide easy-to-use design tools. The inverter is inherently short-circuit-proof, but cannot operate safely with an open circuit at the resonant frequency. Safe operation with an open circuit can be achieved if the operating frequency is sufficiently lower or higher than the resonant frequency. Experimental results are given for two F40 fluorescent lamps connected in series, using MTP5N40 MOSFETs. The operating frequency was 50 kHz at full power and 70 kHz at 20% of full power. At full power, the efficiency of the Class D inverter was 95.6% and the efficiency of the power factor corrector was 93%. The overall efficiency of the ballast was 89.4% at full power. >

Self-capacitance of inductors

A new method for predicting the stray capacitance of inductors is presented. The method is based on an analytical approach and the physical structure of inductors. The inductor winding is partitioned into basic cells-many of which are identical. An expression for the equivalent capacitance of the basic cell is derived. Using this expression, the stray capacitance is found for both single- and multiple-layer coils, including the presence of the core. The method was tested with experimental measurements. The accuracy of the results is good. The derived expressions are useful for designing inductors and can be used for simulation purposes.

Energy-conservation approach to modeling PWM DC-DC converters

A systematic method is presented for including parasitic resistances and offset voltage sources of power switches in averaged dynamic large-signal, DC, and small-signal circuit models of pulse-width modulated (PWM) converters operating in continuous conduction mode (CCM). This method is based on the principle of energy conservation. The approach takes into account the inductor current ripple. For zero-ripple current, the method gives the same results as the state-space averaging method. Reflection rules are introduced and used to simplify the models. As an example, a modeling procedure for the PWM buck converter is detailed. >

Stray capacitances of single-layer solenoid air-core inductors

This paper presents a method for predicting parasitic capacitances of solenoid HF inductors made of one layer of turns with circular cross sections, uniformly wound around a cylindrical nonconductive core. The method is based on an analytical approach to obtain the turn-to-turn and turn-to-shield capacitances of coils. The influence of the wire insulation is taken into account. An equivalent lumped parallel capacitance is derived. The method was tested by experimental measurements. The calculated and measured values were in good agreement in the considered cases. The derived expressions are useful for designing HF inductors and can also be adopted for modeling and simulation purposes.

Resonant DC/DC converter with class-E inverter and class-E rectifier

A new type of high-frequency high-efficiency resonant DC/DC converter is proposed, analyzed, and verified experimentally. It is called a class-E converter because it consists of a class-E inverter and a class-E rectifier. The class-E rectifier acts as an impedance inverter and is compatible with the class-E inverter. Consequently, the converter can operate with load resistances from a full load to infinity while maintaining zero-voltage switching of the transistor in the inverter and the diode in the rectifier. It operates safely with a short circuit at the output. Because of a high value of the load quality factor Q/sub 1/, a narrow frequency range suffices to regulate the DC output voltage over the whole load range. The measured relative bandwidth was delta f/f/sub min/=42.2% as the load resistance was varied from 70 Omega to open circuit. The measured efficiency at the full load was 89% with a 9 W output power at 1 MHz. A family of class-E/sup 2/ resonant DC/DC power converters is given. The possibility of reduction of class-E/sup 2/ converters to lower-order resonant and pulse-width-modulation converters is shown. >

Modeling the closed-current loop of PWM boost DC-DC converters operating in CCM with peak current-mode control

This paper derives the transfer function from error voltage to duty cycle, which captures the quasi-digital behavior of the closed-current loop for pulsewidth modulated (PWM) dc-dc converters operating in continuous-conduction mode (CCM) using peak current-mode (PCM) control, the current-loop gain, the transfer function from control voltage to duty cycle (closed-current loop transfer function), and presents experimental verification. The sample-and-hold effect, or quasi-digital (discrete) behavior in the current loop with constant-frequency PCM in PWM dc-dc converters is described in a manner consistent with the physical behavior of the circuit. Using control theory, a transfer function from the error voltage to the duty cycle that captures the quasi-digital behavior is derived. This transfer function has a pole that can be in either the left-half plane or right-half plane, and captures the sample-and-hold effect accurately, enabling the characterization of the current-loop gain and closed-current loop for PWM dc-dc converters with PCM. The theoretical and experimental response results were in excellent agreement, confirming the validity of the transfer functions derived. The closed-current loop characterization can be used for the design of a controller for the outer voltage loop.

Class E high-efficiency tuned power oscillator

The class E high-efficiency transistor tuned power oscillator, based on the class E power amplifier, is presented. Theoretical conditions for optimum operation of the oscillator are formulated. A new feedback-loop circuit is proposed and a corresponding oscillator design procedure is given. Experimental results show that the collector-voltage and collector-current waveforms and the collector efficiency of the oscillator are the same as in the class E amplifier with the same transistor and operating at the same frequency. The measured collector efficiency was over 95 percent with 3 W output at 2 MHz. The proposed oscillator is especially applicable at high frequencies because it minimizes the power dissipated during the transistor off-to-on transition, even if the switching time is an appreciable fraction of the signal period.

Power losses and efficiency of class-E power amplifier at any duty ratio

This paper presents an analysis of the effect of duty ratio on power loss and efficiency of the Class-E amplifier. Conduction loss for each Class-E circuit component is derived and total amplifier losses and efficiency are expressed as functions of duty ratio. Two identical 300-W Class-E amplifiers operating at 7.29 MHz are designed, constructed, and tested in the laboratory. Dependence of total efficiency upon duty ratio when using real components is derived and verified experimentally. Derived loss and efficiency equations demonstrate rapid drop in efficiency for low duty ratio (below approximately 30%). Experimental results very closely matched calculated power loss and efficiency.

Voltage loop of boost PWM DC-DC converters with peak current-mode control

A new transfer function from control voltage to duty cycle, the closed-current loop, which captures the natural sampling effect is used to design a controller for the voltage-loop of a pulsewidth modulated (PWM) dc-dc converter operating in continuous-conduction mode (CCM) with peak current-mode control (PCM). This paper derives the voltage loop gain and the closed-loop transfer function from reference voltage to output voltage. The closed-loop transfer function from the input voltage to the output voltage, or the closed-loop audio-susceptibility is derived. The closed-loop transfer function from output current to output voltage, or the closed loop output impedance is also derived. The derivation is performed using an averaged small-signal model of the example boost converter for CCM. Experimental verification is presented. The theoretical and experimental results were in good agreement, confirming the validity of the transfer functions derived.

Comparison of various methods for calculating the AC resistance of inductors

The paper reviews several expressions for high-frequency winding resistance of inductors proposed by several authors and compares the theoretical predictions calculated from these expressions with experimental results. It identifies the expressions that yield the most accurate prediction of the winding high-frequency resistance. The comparison shows that the method proposed by Dowell (1966) accurately predicts the AC resistance if the winding contains less than three layers. The methods proposed by several other authors accurately predict the high-frequency resistance only in certain frequency ranges. In addition, these expressions yield inaccurate results for the inductor quality factor. One expression, however, accurately predicts both the high-frequency winding resistance and the quality factor of inductors over a wide frequency range from the DC to the first resonant frequency. The paper concludes with a simple and accurate circuit model describing the frequency behavior of inductors.