Showing papers on "Forward converter published in 1992"

Small-signal analysis of the phase-shifted PWM converter

Abstract: The specific circuit effects in the phase-shifted PWM (PS-PWM) converter and their impact on the converter dynamics are analyzed. The small-signal model is derived incorporating the effects of phase-shift control and the utilization of transformer leakage inductance and power FET junction capacitances to achieve zero-voltage resonant switching. The differences in the dynamic characteristics of the PS-PWM converter and its PWM counterpart are explained. Model predictions are confirmed by experimental measurements. >

Pulse width modulated DC/DC converter with reduced ripple current coponent stress and zero voltage switching capability

Abstract: An improved DC to DC converter is provided in particular for converters with high power density requirements. The converter comprises an input voltage source and a capacitor connected in series to the voltage source. A switching transistor configuration connects the voltage source and the capacitor alternatively to the primary windings of a transformer. The secondary windings of the transformer are connected to a full-wave rectifier and a filter. The output voltage provided at the output of the filter is modulated by a controlling means.

Soft-switching full-bridge dc/dc converting

Abstract: The addition of an external commutating inductor and two clamp diodes to the phase-shifted PWM full-bridge dc/dc converter substantially reduces the switching losses of the transistors and the rectifier diodes, under all loading conditions. We give analyses, practical design considerations, and experimental results for a 1.5-kW converter with 60-V, 25-A output, operating at 100-kHz clock frequency and 95% efficiency.

Power system for parallel operation of AC/DC converters

Abstract: A plurality of AC/DC converters (11) connected in parallel, are provided in which any one of the power converters can fail with-out affecting the operation of the machine which the plurality of converters are providing power. The failed AC/DC converter can be removed and replaced by another converter without shutting down the system. The output voltage of each converter is sensed on the power supply side of a decoupling diode (17, 19, 21). This allows each one of the converters to operate with its own sense loop (25, 27, 31, 33, 35, 41, 43) and, therefore, the feedback loop does not open when a converter is removed and another used in its place. Via power limit circuit (45) each of the parallel connected AC/DC converters (11) is designed to provide a preset maximum power which is independent of AC line voltage variation. To limit the power, the control voltage is made inversely proportional to the average input AC line voltage. The output voltage of the AC/DC converter is made to vary as a function of the load. This allows all the converters in parallel to provide power to the load all the time.

Steady-state performance of DC motors supplied from photovoltaic generators with step-up converter

Abstract: A simple step-up converter circuit consisting of a single power transistor and an inductor is used as an interface between a PV (photovoltaic) generator and a shunt DC motor driving a centrifugal water pump. The step-up converter allows maximum power output from the PV generator to the motor at all insolation levels. Steady-state performance of the motor is vastly improved as its input voltage and current are stabilized by the regenerative action of the converter. The PV generator operates at maximum power regardless of insolation variations. The converter duty ratio can be set at a fixed optimal value which is valid for all insolation levels. This remarkable property makes this device economically attractive since it is easy to build and does not require any insolation-dependent control as compared to other peak-power tracking devices. >

Polyphase AC/DC converter

Abstract: A power converter for converting input AC power comprising N phase-to-phase input AC waveforms at a first frequency into overall output DC power, where N is an integer greater than two, includes N phase-to-phase AC/DC converters each receiving a phase-to-phase waveform and having outputs connected in series whereby the converter outputs are combined to develop the overall output DC power. The AC/DC converters are operated such that a parameter of the input AC power and a parameter of the overall output DC power are controlled.

High power factor AC/DC converter

Abstract: A high power factor AC/DC converter is disclosed. In the AC/DC converter in which a rectifying circuit RC1 rectifies a commercially available AC power supply Ei, a switching device turns on and off so that the rectified voltage is applied across the primary winding n1 of the transformer Tr1 to provide a high frequency voltage across the secondary winding n2, and the high frequency voltage is rectified by means of a rectifying circuit connected across the secondary winding so as to generate a predetermined DC output, a choke coil (L1) and a diode (D1) are interposed between the rectifying circuit (RC1) and a smoothing capacitor (C1) and a capacitor (C3) is interposed between a first junction and a second junction. The first junction connects the choke coil (L1) to the diode (D1) and the second junction connected the switching device (Q1) to the primary winding (n1) of the transformer (Tr1).

Analog-to-digital converter and method of fabrication

Abstract: A two-step analog-to-digital converter (300) and BiCMOS fabrication method to make the converter. The fabrication method provides pseudosubstrate isolation of digital CMOS devices from analog devices. The converter uses NPN current switching in a flash analog-to-digital converter (306) and in a digital-to-analog converter (310) for low noise operation. CMOS digital error correction (318) and BiCMOS output drivers (320) provide high packing density plus large output load handling. Timing control (330) aggregates switching events and puts them into intervals when noise sensitive operations are inactive. The fabrication method uses a thin epitaxial layer with limited thermal processing to provide NPN and PNP devices with large breakdown and Early voltages. Laser trimmed resistors provide small-long term drift due to dopant stabilization in underlying BPSG and low hydrogen nitride passivation.

DC-DC power converter including sensing means for providing an output when the reserve power of the converter falls below a predetermined amount for a given input voltage

Abstract: A DC to DC power converter in the form of a pulse-width modulator is shown which can sense via an indication of duty cycle how much reserve power is available for loads using the present input voltage. The device is for use at the end of a telephone line where the input voltage power supply impedance can be appreciable. When the reserve power, as detected in the power converter, reaches a minimum critical level, a signal is sent out requesting the voltage supply to increase the available voltage to the power converter.

Development of power electronics converters based on switched-capacitor circuits

Abstract: A new DC-to-DC converter is proposed that uses only switched capacitors. The energy conversion is based on controlled cyclical switching between two phases. The DC gain can be fixed by choosing an appropriate steady-state value of the duty ratio. The output voltage can be kept constant over a large range of loads. The output voltage ripple was less than 5% for most of the load range interval. By avoiding the use of magnetic elements, a small-size and lightweight converter can be built. The circuit is analyzed by using the state-space averaging method. The theoretical results have been confirmed by experimental data. >

2 MHz power converter with piezoelectric ceramic transformer

Abstract: A power converter with a new piezoelectric transformer is presented. The piezoelectric transformer, made of lead titanate solid solution ceramic, is operated with a thickness extensional vibration mode. This transformer can operate at high frequency, over several megahertz, with about 90% efficiency. The resonant frequency for the transformer is 2 MHz. The power converter with the transformer applies the theory for a class-E switching converter using an electromagnetic transformer. Maximum output power is obtained when the switching frequency is slightly higher than the resonant frequency. A 4.4 W output power is successfully obtained with 52% efficiency at 2.1 MHz switching frequency. >

A unity power factor forward converter

Abstract: A novel means of obtaining sinusoidal, unity power factor input currents in switched mode power supplies using minimum additional components is presented. The converter is topologically equivalent to a boost converter cascaded by a forward power converter, but is realized using only a single power stage. A detailed analysis of the operation is presented. A constant frequency current mode control provides excellent transient performance at the output and sinusoidal input currents at the input. Various tradeoffs involved in the design of the converter elements and control parameters are discussed in depth. All the results are backed up by experimental waveforms from a laboratory converter. >

PWM control and input characteristics of three-phase multi-level AC/DC converter

Abstract: The authors discuss the current control and pulse width modulation (PWM) pattern generation of a multilevel power converter which is capable of producing three levels of phase voltage. In the proposed current control, fast response is realized by introducing a converter model in the control algorithm and the effect of parameter difference between the model and an actual system is compensated for through proportional-plus-integral control of current difference. In PWM pattern generation, the balance of two capacitor voltages is taken into account. For the same sampling period, the current distortion factor of the proposed system can be approximately reduced to 60% of that of a conventional two-level power converter. The prototype was made using a digital signal processor, and simulation and experimental results were compared. >

Circuit models of PWM DC-DC converters

Abstract: A systematic method is presented for including parasitic resistances and offset voltage sources of power switches into averaged dynamic large-signal, DC, and small-signal circuit models of PWM converters operating in continuous conduction mode. This method is based on the principle of energy conservation. It is shown that the equivalent circuits can be manipulated, using the reflection rule, to simplify the models. A procedure of modeling the buck converter is detailed. Models of all buck-derived converters have the same structure as that for the buck converter, but expressions for averaged components are different. These expressions are given. A design equation for selecting the value of the filter capacitance is derived, and it is shown that the ripple voltage can be made dependent only on the equivalent series resistance of the filter capacitor. >

Fixed frequency DC to DC converter with a variable inductance controller

Abstract: A DC to DC converter (50, 60, 70) that includes a switching circuit (10) responsive to a DC input, a magnetic amplifier controller (20) responsive to the switching circuit for providing an AC output, and an AC current to DC voltage rectifying circuit (30) responsive to the output of the magnetic amplifier controller for providing a DC output voltage. The magnetic amplifier controller includes a variable inductance (L1) that cooperates with the switching circuit to form a resonant DC to AC inverter (110) that provides to the magnetic amplifier controller a current whose amplitude is controlled by the variable inductance. The magnetic amplifier controller provides an approximately sinusoidal output current which is a function of the current input thereto, and the DC voltage output of the AC current to DC voltage rectifier is a proportional to the input current provided by the magnetic amplifier controller. Thus, the DC voltage output of the DC to DC converter is controlled by the control current to the magnetic amplifier controller.

Power converter with plural regulated outputs

Abstract: A power converter comprises a power stage including a transformer, a pulse width modulator (PWM) for controlling the power stage, multiple output circuits providing individually regulated voltages, including switches for coupling the output circuits sequentially and cyclically to the power stage, and feedback circuitry for supplying respective feedback signals, each for a respective output circuit, as a control signal to the PWM synchronously with the coupling of the output circuits to the power stage, so that a single PWM and power stage serve for multiple output circuits. The converter can be a dc to dc converter or a four-quadrant switching amplifier. The PWM operates in current mode in conjunction with a current sensing resistor or transformer.

Voltage-resonant DC-DC converter

Abstract: A voltage-resonant DC-DC forward converter is provided with a snubber circuit in its secondary circuit. The snubber circuit comprises a series connection of a first capacitor and a first diode connected to both ends of the secondary winding of the main transformer to make up a loop of a secondary resonance circuit which allows a secondary resonance current to flow in the forward direction of the first diode, the forward direction being so directed that the first diode blocks the secondary resonance current from flowing at least while the second winding supplies a current to the smoothing circuit through a second diode for rectifying the secondary current. The converter is further provided with a regulation circuit for regulating the output voltage of the converter. The circuit has a transistor for controlling switching of the output current which varies linearly with time. The transistor is controlled by the sum of the voltage signal indicative of the output current and of the deviation signal indicative of the deviation of the output voltage from a prescribed value. When the sum exceeds the base-emitter threshold voltage, the transistor is turned on to switch off the output current.

Pipelined A/D converter

Abstract: There is disclosed a pipelined A/D converter including a plurality of A/D-D/A sub-blocks and one A/D sub-block successively connected in cascade form to determine a conversion output by several partial bits beginning from the most significant bit. Each of A/D-D/A sub-blocks includes a sample-and-hold circuit for successively sampling and holding an input analog signal fed to the sub-block, a partial A/D converter for performing A/D conversion on a hold output of this sample-and-hold circuit, a latch circuit for latching outputs of the partial A/D converter, a D/A converter for inversely converting outputs of the latch circuit to an analog signal, and a chopper amplifier for sampling the hold output of the sample-and-hold circuit with a delay of half a period, amplifying a difference between the sampled value and the inverse conversion output of the D/A converter during a succeeding interval of amplify mode, and outputting the amplified difference to a sub-block of a succeeding stage as a conversion residue.

Combination static/dynamic inverter

Abstract: A power converter provides an AC output selectively using power from either a battery source or an alternator. The power converter includes a static converter (100) that is connected to receive DC from a battery (30), converting the DC to a relatively high frequency AC using a pulse width modulator (200). The high frequency AC is transformed to a higher voltage AC that is rectified and is used to charge a capacitor bank (104). The DC on the capacitor bank is converted to 120 (or 240) volts AC at 50/60 Hz by an inverter comprising an inverter (106) to provide power for an AC load. As the requirement for power by the AC load increases above a predefined level, a dynamic converter (24a) is energized to supply power to charge the capacitor bank in place of the static converter. The dynamic converter draws its power from a three-phase alternator (12) that includes three-phase AC output terminals connected to three-phase primary windings (140) of a transformer having a plurality of secondary windings. Secondary windings (168) produce a substantially higher voltage than the voltage from the alternator, and their output signal is rectified to charge the capacitor bank. The battery is charged with current supplied (after rectification) by secondary windings (148). Rectified DC supplied from the output of secondary windings (146) is supplied to the field winding of the alternator and controlled in response to the voltage developed across the battery terminals by rectified signal output from secondary windings (148). As the AC load draws power from the capacitor bank (through the H-bridge), the voltage of the battery charging current supplied by secondary windings (148) drops, causing a voltage regulator circuit (34) to increase the field winding current, and thereby increasing the power supplied by the alternator to compensate the greater load.

DC to DC/DC to AC power conversion system

Abstract: A pulse width modulation DC to DC converter operates in an open loop mode to convert the DC output of the AC to DC converter (36) to a desired, predetermined DC level (221) using pulse width modulation techniques and a switching configuration (32) substantially similar to that of the AC to DC converter (36).

High power factor power supply

Abstract: An off-line switching power supply includes an ac rectifier and a dual-output switching converter having one output coupled between the ac rectifier and the input to the dual-output converter in order to provide a high power factor, the other output of the dual-output switching converter providing a dc voltage as the power supply output. The outputs of the dual-output converter are fully decoupled so as to allow independent control of the ac input current and the power supply output voltage. In a preferred embodiment, a full-wave ac rectifier bridge is coupled in series with the second output of the power converter via an input resonant boosting converter. A full-bridge dc-to-ac converter is coupled between the dc link and ground for providing an ac signal to excite the boosting converter and for providing another ac voltage through a transformer to an output rectifier to generate a regulated dc output voltage. The amplitude of the regulated output voltage is controlled by pulse width modulation, while active frequency control of the boosting converter is provided to control the amplitude of the ac input current. Alternatively, frequency control of the boosting converter is passive, i.e., depends on the gain characteristics of the boosting converter resonant circuit. As a result of the complete decoupling of the input boosting converter and the power supply output voltage, the off-line switching power supply is capable of drawing high quality current waveforms from the ac source while producing a regulated dc output voltage with fast transient response.

A high power, high frequency, DC to DC converter for space applications

Abstract: The authors describe a regulated, nonisolated Weinberg boost converter with the following advantages: breadboard efficiency from 95 to 97% at 500 W to 1 kW output power; continuous output current with small current ripple; a boost regulator without right-half plane zero effect giving a high bandwidth response; low switching losses (typically 1% at a switching frequency of 350 kHz); conductance control producing typical first order response: and a wide bandwidth voltage regulation loop (10 kHz, with 80 degrees phase margin), giving superior transient response and reduced output filtering. >

Noise Analysis of DC-to-DC Converter with Random-Switching Control

Abstract: The effectiveness of random-switching control, by which the switching-noise spectrum is spread and its level is reduced, is briefly described through experimental results. The noise spectrum by random switching is analyzed in a general approach including a noise-generation model and a switching function with a random process. Taking the normal distribution as an instance, the amount of random perturbation is quantitatively analyzed. The validity of the analysis was confirmed experimentally by a series of pulses serving as an ideal switching-noise. >

Analysis and design of a fixed frequency LCL-type series resonant converter

Abstract: A fixed-frequency LCL-type series resonant power converter which uses an inductive output filter is proposed. Steady-state analysis of the converter is presented using complex AC circuit analysis. Based on the analysis, a simple design procedure is given. Detailed experimental results obtained from a MOSFET-based 500 W converter are presented to verify the analysis. The proposed converter requires a narrow variation in pulse-width while maintaining a lagging power factor mode of operation for very wide variation in the load. >

A new high frequency, zero-voltage switched, PWM converter

Abstract: A high-efficiency, high-power-density converter operating at constant frequency and switching at zero voltage is presented. Zero voltage switching (ZVS) conditions are achieved over a broad input voltage and output current range. Continuous power transfer from the input to the output minimizes the output filter requirements, and, by using the integrated magnetics technique, high power density can be achieved. By employing the same configuration as classical pulse width modulation (PWM) topologies, a new family of ZVS-PWM converters can be derived. An experimental 5 V, 100 A converter was designed and built. The converter operates from an input voltage of 200 to 430 VDC, at a 400 kHz switching frequency. >

Master-slave half-bridge dc-to-ac switchmode power converter

Abstract: The invention pertains to a switchmode DC to AC converter, and particularly to a master-slave half-bridge converter. The slave half-bridge power converter (C1, C2, T51, T61) is controlled by a lower power self-oscillating half-bridge master converter (C1, C2, T11, T21). More particularly, the invention pertains to a high frequency ballast for gas discharge devices (H), especially, for high pressure sodium lamps (H), completed by a high voltage ignition apparatus (N32, R71, D71, C71, S71, N72, N71).

Single-switch three-phase AC/DC converter with high power factor and wide regulation capability

Abstract: A single-ended pulse width modulated (PWM) three-phase rectifier is presented. It is capable of high power factor and wide output voltage regulation while using high-frequency transformer insulation. The circuit behavior is investigated with the assumption of discontinuous input current operation. Design criteria are derived. The actual converter performances are verified on a 1.5 kW prototype, fed by a 380 V AC supply, in which insulation and voltage adaptation are realized by a 50 Hz transformer. Resulting AC current distortion is below 7%, efficiency is better than 90%, and power density is in the range of 0.4 kW/1. >

Step-up voltage converter with overcurrent protection

Abstract: A step-up converter is utilized to convert a first lower input voltage to a second higher output voltage. The circuit includes a soft start capability such that ringing due to excessive voltage and current is substantially eliminated. In addition, this converter includes an overcurrent protection mechanism if a load failure or other overcurrent condition occurs.

Universal power adapter for converting AC/DC voltage to DC voltage

Abstract: A universal power adapter comprised of a standard IEC three-wire socket, an AC/DC power supply detector circuit, an AC/DC power supply selector circuit, an AC/DC power supply pre-treating circuit, a DC power supply transformer circuit, a feedback and regulating circuit, and a DC output circuit, wherein said standard IEC three-wire socket connects an AC or DC input voltage to said AC/DC power supply selector circuit and said AC/DC power supply pre-treating circuit for converting into a DC voltage via said AC/DC power supply detector circuit, said DC voltage being treated through said DC power supply transformer circuit and said feed back and regulating circuit to provide a DC working voltage for output through an output device.

Zero voltage switching power converter with secondary side regulation

Abstract: A circuit for utilizing the magnetizing current in the transformer of a converter to reset the transformer's core and to provide a zero-voltage-switching condition on the converter's primary switch and to regulate the output voltage is disclosed. The power converter includes a transformer having a primary winding and a secondary winding, the secondary winding being coupled to an output load and a primary switch connected in series between the primary winding and a voltage source. The closing of the primary switch causes energy to be stored in the transformer and the opening of the primary switch causes the energy to be released from the transformer. The utilization circuit includes a series combination of a storage capacitor and a first switch coupled in parallel with one of the transformer's windings to capture the energy released from the transformer. The captured energy is used to reset the transformer's core and to create a zero voltage switching condition across the primary switch. A second switch means is connected in series with the secondary winding of the transformer and is operated to prevent the loading effects of the secondary from interrupting the creation of the zero-voltage switching condition. A secondary side regulation circuit is included to both regulate the output voltage and to prevent the loading effects of the secondary circuit from interfering with zero-voltage switching in the primary circuit.