Abstract: A low cost, high frequency, solid-state dimmable fluorescent ballast is disclosed which utilizes a resonant bridge inverter to provide high frequency sinusoidal power to the lamps. One embodiment of the invention includes auxiliary windings connected to the filaments of the lamps to be powered which utilize the inductance of the resonant bridge inductor coil to maintain the voltage across the filaments during dimming. A clamping circuit or auxiliary tuned circuit may be provided to prevent damage due to an over-voltage and over-current condition upon removal of a lamp during operation of the system. In an alternative embodiment, the auxiliary windings, are replaced by capacitors across each of the lamps to be powered. This also eliminates the need for the clamping circuit. If desired, a current splitting capacitance system may be used. Pulse width modulation of the inverter drive or variable AC or DC power supply input may be used to accomplish dimming.

Abstract: Programmed-waveform pulsewidth modulated (PWM) waveforms, applicable to ac-dc/dc-ac converters, are synthesized and analyzed in terms of several structural parameters. By invoking sensitivity studies and heuristics, optimal PWM structures are identified and contrasted. The results show total harmonic performance as a function of switching levels, waveform types, commutations per cycle, and filter bandpass.

Abstract: An electronic thermal printer has a thermal printhead to which is applied a train of pulses which is pulse width modulated. A power switch connects and disconnects the printhead from a DC power source. The pulse train is integrated, scaled and applied as an input to a comparator circuit. The thermal printhead has a temperature sensing diode whose output is applied, as a reference voltage, to the other input of the comparator. During a print cycle, the output of the temperature sensing diode is cut off and the reference voltage is capacitively stored and held as the reference voltage. The output of the comparator circuit clears a latch circuit whose input is provided by a system clock and whose output is connected to control the power switch. The comparator provides an output when the integrated voltage reaches the reference voltage, clearing the latch. Since the latch is supplied with signals from the system clock, a constant frequency is maintained. However, the varying output from the comparator clearing the latch provides varying pulse widths. In this manner, pulse width modulation of the voltage input pulses to the thermal printhead is achieved.

Abstract: Power delivered to the welding arc from a constant current rapid response power supply is controllable to maximize arc stability particularly in out-of-position welding operations. A first control modulates the output current from the power supply between a high value close to the maximum output value and a minimum value just sufficient to maintain the welding arc. The modulation is effected at a given frequency appropriately adjusted in accordance with the electrode material and diameter to maintain optimum spray metal transfer in the welding arc. A further control is effected by pulse width modulating the output from the power supply in accord with a set-in current programmed signal which is compared with a current feedback signal or, alternatively, a set in voltage programmed signal which is compared with a voltage feedback signal. This latter control provides for operation of the power supply in a constant current control mode or alternatively, a constant voltage control mode. Still further control of the power in the welding arc is effected by pulsing the current between base and peak levels at a relatively low frequency which enables control of the weld puddle in out-of-weld positions.

Abstract: A photovoltaic power supply and battery charging system comprises a photovoltaic solar energy power supply panel connected through a blocking diode to a secondary storage battery which, in turn, is connected to a suitable load. A temperature sensitive reference voltage is supplied to one input of a voltage comparator, the other input to which is connected to the battery and thereby varies in accordance with the variations of charge on the battery. A short circuit shunt switch is connected directly across the photovoltaic panel; and this shunt switch is opened for varying periods of time by the output of a variable pulse width generator. The pulse width generator, in turn, is connected to and is controlled by the output of the voltage comparator to produce pulses of different widths. The charging current supplied to the battery then occurs in the form of high current pulses of varying widths depending upon the charge state of the battery.

Abstract: Laser diodes modelocked to date are gain modulated in an external resonator. The reflection from the diode face internal to the resonator causes a dependence of gain upon frequency that cannot be described by a simple bell‐shaped function. Previous analyses treating modelocking by modulation of loss are generalized to treat modulation of gain with a general frequency dependence. We arrive at a limit on pulse width achievable with gain modulation of a laser diode in an external resonator and evaluate the limit for typical parameters.

Abstract: A stepper motor for use in peripheral devices such as electronic printing terminals has its coils selected for activation by selection circuitry, with its power provided by a switch mode current regulator. The switch mode regulator utilizes the selected motor winding as the storage element of the regulator and the voltage ramp derived from the current flow through the motor coil itself for comparison with a reference voltage. The output of the comparator circuit controls the state of a latch which has a fixed frequency clock input. The frequency of the latch output is fixed, but the on time and off time of the latch varies in accordance with the output of the comparator. A comparator and latch circuit therefore form a pulse width modulator which then regulates the on and off time of the switching regulator power transistor.

Abstract: Pulsewidth modulation (PWM) is frequently employed with static ac power supplies to control the amplitude and harmonic content of load voltage However, published work on the subject of PWM techniques has mainly dealt with variable-speed ac drive applications Consequently, PWM techniques compatible with constant frequency and constant (load) voltage applications, such as uninterruptible power supply (UPS) systems, have been largely ignored Several known and novel PWM techniques suitable for three-phase static UPS systems are analyzed, and attempts are made to evaluate them Optimum techniques are subsequently selected on the basis of the low-order harmonic attenuation obtained with each technique and the number of thyristor commutations (per cycle) required to implement each technique

Abstract: A novel feedback circuit for use in a DC-to-DC converter accurately adjusts the pulse width of the control pulses to a pair of switching transistors to minimize current imbalance. The switching transistors generate current pulses in the primary windings of a center tapped transformer. The feedback path senses the current pulses in the primary circuit of the transformer. A filter in the feedback path has a bandwidth centered at about the frequency of any current imbalance. The high gain, closed loop feedback path changes the slope of alternate linear ramp voltage pulses, and hence varies the pulse width of the pulses presented to the control terminals of the switching transistors.

Abstract: A modulator circuit for a matrix display device, the modulator circuit having pulse width and pulse amplitude control. The current amplitude for a selected picture element (row address-column address) varies during the pulse width of an excitation pulse in correspondence with the number of counting positions of a counting circuit used for determining the pulse width. A column conductor has an associated column excitation circuit in which a counting circuit for determining the excitation pulse width controls excitation switches which pass selectively currents from current source I A . . . 64I A of a current source circuit to the column conductor. The initial setting of the counting circuit determines the excitation pulse width, and the count positions of the counting circuit select the currents to be passed to the column conductor as the counting circuit is stepped by clock pulses to measure the duration of the excitation pulse.

Abstract: A production variable-frequency drive is described which uses an induction motor and a controlled-current inverter. The control loops of the drive have been arranged so that the performance of the drive is extended to zero speed and to the theoretical upper limit speed. Operating modes include torque smoothing by programmed dc link current, pulsewidth modulated (PWM) current shaping, and flux-controlled constant horsepower operation.

Abstract: This paper presents a new technique for harmonic reduction in inverters using sinusoidal pulsewidth modulation. In this inverter, the output wave with sinusoidal pulsewidth distribution can be kept in maximum degree of symmetry, and so it offers excellent harmonic control in comparison with any other modulation technique. Detailed analysis shows that the harmonics lower than the ninth (or the thirteenth) are all less than one percent of the fundamental component when the number of pulses per half cycle is over seven (or nine). These results are confirmed by the theoretical data obtained from the natural sampling, and the experimental observations for single-phase full-bridge sinusoidal pulsewidth modulated (SPWM) inverters. It is concluded that by the use of this new technique it is quite easy to design an inverter with a distortion-free sinusoidal output.

Abstract: Phase shift for the ramp-comparator pulsewidth modulator (PWM) between a continuous input control signal and the signal frequency component of the output is analyzed. It is shown that transport lag is not implicit to these PWM systems in general but rather depends upon the existence of explicit delays between the time at which a switching decision is made and the time at which that decision is executed.

Abstract: A low cost switching mode power supply particularly adapted for use in an electric vehicle is characterized by an extreme input voltage range, immunity to high input voltage transients, and stable operation. A negative voltage feedback arrangement applied to a controllable voltage clamp serves to continuously vary oscillation pulse width and frequency. The power supply includes an output filter capacitor, and, to compensate for phase lag introduced by the output filter capacitor, the negative feedback arrangement includes elements for introducing phase lead compensation. Preferably, the oscillation period is less than the duration of expected input voltage transients, and the power supply regulates right through such transients.

Abstract: Narrow pulses below 100 ps (f.w.h.m.) have been generated by applying 100 or 300 ps current pulses to a wide-stripe double heterostructure laser. The modulation current was increased to minimise the pulse width.

Abstract: The wide spread use of pulse width modulators in power supplies has created a need for computer models of the switching and control elements. This paper shows how to model switching regulators using the SPICE2 computer aided circuit analysis package for small signal ac, dc, and large signal transient simulations, both open and closed loop. With these models, a switching regulator design can be quickly and accurately evaluated at low cost.

Abstract: A theoretical treatment of the photoacoustic effect for a liquid enclosed in a cylindrical cell is given. Simple analytical expressions for the photoacoustic signal are derived for cw and pulse modulation schemes. Modulation frequency or pulse width dependence of the photoacoustic signal is discussed. For the cw modulation scheme it is found that more photoacoustic power is generated in a resonant cell than a nonresonant cell at the expense of bandwidth reduction. Conditions leading to 1/f dependence of the signal on modulation frequency are given. Experimental results are presented that support the simplified treatments. Eventual sensitivities of various excitation schemes under optimum conditions are calculated.

Abstract: Improved operation of a pulse width modulated inverter machine drive system is obtained by a control apparatus which regulates inverter switching device conduction by modifying switching signal waveforms transmitted to the inverter to eliminate switching pulses narrower than the minimum inverter switching device pulse width. By dropping the narrow inverter switching pulses in sequence during the exact interval which the pulses would otherwise occur and boosting the amplitude of remaining pulses, the control apparatus permits the inverter to smoothly transition from pulse width modulation operation to square wave operation without objectionable jumps in inverter output voltage.

Abstract: A controller system using high frequency switching by providing a bilateral switch gated on and off at a frequency about ten times the source frequency and the duty cycle determined by pulse width modulation of the high frequency waveform in accordance with window heater temperature

Abstract: A pulse signal generator produces a first pulse signal having a pulse width substantially equal to twice the travel time required for light to travel a braking distance. A light transmitter radiates a light beam signal representing the first pulse signal so as to cover a detection area in which the braking distance is contained. A photoreceptor receives the light signal reflected by an obstacle present in the detection area and converts the received light beam signal to a second corresponding electric pulse signal. A determination device determines whether the time width of a pulse of the first signal is larger than the time interval taken from the time when the corresponding pulse of the light signal is transmitted to the time when the pulse of the light signal is received by the receptor after reflection by the obstacle.

Abstract: An AC to DC power supply having a multi-channel, flyback inverter output section regulated via a fixed frequency, pulse width modulation controller. The controller indirectly regulates each channel by regulating an auxiliary channel, whereby the duty cycle of a switching transistor in the flyback inverter section is varied to maintain a constant DC voltage on the auxiliary channel and correspondingly on each output channel.

Abstract: A pulse width modulation (PWM) speed control for a DC electric motor includes an encoder for providing encoder pulses in reponse to incremental rotation of a shaft driven by the motor. A timer senses a time period between encoder pulses. After three consecutive sensed time periods, a microcomputer compares the sensed time periods with a desired time period corresponding to a desired motor speed, and provides a digital value which is a function of the comparison of the sensed and desired time periods. The ditigal value is supplied to a timer, which applies an energizing pulse to the DC motor for an interval which is a function of the digital value.

Abstract: A device for automatically controlling the intensity of light impinging on the face plate of a television camera (11) includes a shutter (17) which is operated through a pulse width modulator (23) so as to be opened for a length of time which varies inversely with the intensity of light entering the imaging light path be-tween the scene and the camera (11).

Abstract: A self-controlled polyphase synchronous motor drive system having means for producing rotor digital timing signals representative of the position of the rotor relative to the stator, means for producing pulse width modulation control signals wherein the pulse width thereof is responsive to a motor power factor command signal, a plurality of phase control means equal in number to the number of phases of the polyphase stator and responsive to the variable pulse width modulation control signals and including means for producing a modulated analog reference signal from one of two selected stator voltages and means for summing the amplitude modulated analog reference signal with an unmodulated analog reference signal produced from the other of the two selected stator voltages and for comparing the sum thereof with a threshold voltage signal to produce as an output therefrom two motor voltage derived digital timing signals for each phase of the polyphase stator in response to the speed of the motor such that an absence of voltage digital timing signals occurs at zero motor speed and voltage digital timing signals having distortion is produced at low motor speeds and digital gating command signal generating means responsive to the voltage digital timing signals from each of the phase control means and to the rotor digital timing signals for producing digital gating command signals having a leading edge determined by one of the voltage digital timing signals or that of a selected one of the rotor digital timing signals and the width of which is equal to 360 degrees divided by the number of phases of the polyphase stator is shown. A commutation margin detecting circuit and rotor position sensing circuit are also shown.

Abstract: An improvement in a communication system is disclosed having a transmitter which transmits a pulse width modulated control signal having a synchronizing pulse, a reference pulse, and at least one control function pulse encoded therein. At least one receiver receives the transmitted control signal and detects the pulses encoded therein. In response to each detected pulse, a timing circuit in each receiver provides a timing pulse having a width related to a reference signal. A reference controller compares the width of the detected reference pulse to the width of the timing pulse and provides a reference calibration signal at a level automatically selected to reduce the compared pulse width difference. A function controller may be provided to compare the width of the detected control function pulse to the width of the timing pulse, and to perform a control function in response to a predetermined compared width difference therebetween.

Abstract: A circuit arrangement for comparing a clock pulse train against a standard pulse train. The circuit includes an exclusive OR gate to which are inputted the pulse train to be tested, and a latch at the output of the gate, operated only upon a mismatch of the two pulse trains. Provision is also made to prevent operation of the latch within certain adjustable tolerance parameters as to pulse width and position of the pulse train.

Abstract: A motor servo circuit is disclosed. The motor in the motor servo circuit is driven by an output which is obtained by logically adding output pulses of a pulse stretcher circuit which stretches a pulse width of error pulses generated from an OR circuit when pulses inputted to the motor servo circuit and pulses outputted from a pulse generator in response to the input pulses are different in the pulse width to pulses having a predetermined pulse width which are generated at intervals of a predetermined member of the error pulses synchronizing therewith.