Showing papers on "LC circuit published in 1989"

Electronic blackboard and accessories such as writing tools

Abstract: A characteristic and the position of an implement with a tuned circuit having one of plural resonant frequencies are determined. AC energy at the plural different resonant frequencies is supplied to a two-coordinate direction coil arrangement of a position sensing tablet. The tuned circuit changes the current flowing in the coil arrangement at the implement resonant frequency. The current change is used to signal the implement position and characteristic. The implement may be an eraser for supplying a signal to an electronic display and for removing a mark from a surface of a visual display overlaying the tablet of the eraser. A housing includes a surface for erasing the marking and two tuned circuits each having a reactance positioned close to opposite edges of the erasing surface. Two switches, when activated, cause the tuned circuits to have different resonant frequencies. The switches are respectively activated when opposite eraser edges are being pushed against the display surface. The implement may also be one of a plurality of markers, each for a different color. Another display responds to the signals to display the position and colors of the markings and selectively remove markings from areas corresponding to the eraser position.

Design of a liquid crystal based tunable electrooptic filter.

Abstract: Procedures for designing a tunable liquid crystal (LC) electrooptic filter are illustrated. Selective filtering of one of the two mixed laser lines is used as an example for calculation. It is demonstrated that a LC filter can select a desired beam to pass while rejecting the other one, or vice versa, by switching the voltage biased on the LC cell. The switching times are determined by the liquid crystal properties, thickness, and biased voltage. A multilayered structure is proposed to improve the response times and power loading capability.

Surgery operating device

Abstract: PURPOSE: To effectively cut and machine a hard tissue by forming an ultrasonic vibrator to be a bolt fastening Langevine type vibrator and composing the feedback circuit of a vibration feedback type oscillator of a vibrating voltage detecting circuit, phase comparator, low-pass filter, error amplifier and voltage control oscillator. CONSTITUTION: A vibration feedback type oscillator 1 rectifies the current of an alternative current power supply by a rectifier circuit 2 and makes the direct current power source for driving circuit elements in the oscillator 1 and for driving the bolt fastening Langevine type vibrator of hand pieces 12 and 13. The current flows from the rectifier circuit 2 to an overload control circuit 3 and an amplitude adjusting circuit 4. By varying the output voltage of the amplitude adjusting circuit 4, the amplitude of ultrasonic vibration generated in the hand pieces 12 and 13 can be adjusted. For oscillation, a reference frequency, outputted from a feedback circuit 11 is inputted to an amplifier circuit 5, amplified, passe through a filter 6 and a transformer 7 and is inputted to an amplifier circuit 8. The signal current of a resonance frequency from the transformer 7 is amplified by the amplifier circuit 8, boosted in voltage by a transformer 9, passes through a matching circuit 10 and is inputted to the feedback circuit 11. COPYRIGHT: (C)1990,JPO&Japio

On-board tire pressure indicating system performing temperature-compensated pressure measurement, and pressure measurement circuitry thereof

Abstract: A reliable indication of temperature-compensated pressure is provided from each of the wheels of a vehicle to an operator within the vehicle. A piezoresistive transducer bridge is supplied by a constant current source in one embodiment, and by a voltage of constant amplitude in another embodiment. Voltage to the bridge is reversed on a periodic basis. The use of constant current enables compensation for temperature-induced drift in transducer bridge output. The use of constant voltage enables compensation for ambient temperature, and provides an absolute, rather than a relative indication of pressure or "flatness" within the tire. Voltage polarity reversal permits compensation of amplifier offset voltage. Energy is transmitted to an from the wheel by means of a tuned circuit which is excited by a primary coil when the vehicle's engine is running. The secondary coil mounted on the wheel may be either short-circuited or selectively opened and closed to alter the operation of the primary coil, thus providing an indication of tire pressure, that indication being detected and processed by suitable microcomputer circuitry which may exist on board the vehicle. Most of the active circuit elements of the invention may be implemented in a single monolithic integrated circuit, which can be attached to a tire valve.

Zero voltage switching half bridge resonant converter

Abstract: A DC to DC converter combines a half-bridge inverter with a resonant rectifier through a series LC circuit which conducts power at substantially a single frequency. Energy stored in the parasitic capacitors of the two power switches are transferred from one parasitic capacitor to the other in order to enhance efficiency of operation. The transfer is controlled by controlling the relative phase between the voltage and current in the inverter section.

Capacitive pressure sensor

Abstract: A pressure sensor (10) includes a pair of capacitors (C1, C2), at least one of which is variable responsive to an applied fluid pressure (DELTAP) to predictably change capacitance value. A tuned oscillator circuit (14) having an inductive impedance includes the variable capacitor and simulates a resonant inductive-capacitive circuit not including an inductor. The tuned circuit (14) oscillates to provide a signal with a period which is a function of the variable capacitance value, and of the applied fluid pressure. Additional elements are provided for precise measurement of the variable signal, correction for temperature effects, correction of measurement aberrations, and production of an output signal in a preferred format.

Feedback-coupled high-frequency power oscillator

Abstract: A high-frequency power oscillator is built around a power amplifier utilizing semiconductors in a complementary or quasi-complementary stage which operate in a switching mode of operation. The output of the amplifier supplies high-frequency oscillations to a load impedance through an output filter composed of a series-resonant circuit and a parallel-resonant circuit. A feedback driving voltage is obtained from the output filter in a manner providing a first portion of the driving voltage from a voltage present in the parallel-resonant circuit for voltage feedback and a second portion of the driving voltage obtained by current inverse feedback from the current in the series-resonant circuit. These two components of the driving voltage are combined in an addition circuit and supplied to an input of the power amplifier through a pulse modification stage. In the case of high load impedances the operating frequency is as close as possible to the resonant frequency of the parallel resonant circuit and the superimposed current inverse feedback prevents the provision of an operating frequency that would approach the resonant frequency of the series-resonant circuit even when the losses in the series-resonant circuit are small. The ability to use a low-loss series-resonant circuit makes possible increased operation reliability, safety and efficiency.

Adjustable output level signal transmitter

Abstract: An adjustable output level transmitter includes a direct current energy source, an L-C tank circuit and a switching means for sequentially coupling the capacitors of the tank circuit to the direct current energy source and ground. The output signal frequency is equal to the resonant frequency of the L-C tank circuit and the output signal level is a function of which capacitors of the L-C tank circuit are sequentially coupled to the energy source. The circuit functions in a Class D mode with the inherent advantages of minimal power loss and very high efficiency. Due to the manner of switching utilized, the output signal frequency is very stable and unaffected by the mode of capacitor switching.

Steady state analysis of the parallel resonant converter with LLCC-type commutation network

Abstract: A novel converter topology known as LLCC-type parallel resonant converter (PRC-LLCC), in which the tank circuit consists of two inductors and two capacitors, is introduced. Using the state-plane approach, the steady-state analysis of the PRC-LLCC operating in the continuous conduction model is carried out. It is shown that by using the state variable transformation technique the steady-state response of the converter can be represented by two state-plane diagrams. Using these diagrams and the circuit equations, a set of control characteristic curves which are useful for converter design is derived. Based on these curves, a design procedure along with a specific design example is given. The correctness of the analysis results is verified via computer simulations. >

Non-resonance AC power source apparatus

Abstract: An AC power source apparatus to be used in an AC corona generator necessary for a de-electrifica­tion/separation process, which is one of electrographic image forming processes, or in a case where a low fre­quency AC power source is required, has a construction such that a high-frequency pulse, whose time ratio is modulated trapezoidally with time, is applied to switching elements (2, 3) connected in inverse-series across a primary winding of a transformer (1), an inductance element (5) having a regenerative diode (6) and a reset winding is inserted between an intermediate tap of the primary winding of the transformer and a DC power supply input terminal (12), and an LC filter is formed by stray capacitance of a secondary winding of the transformer, whereby a desired output waveform can be produced with a simple circuit construction.

Resonant DC to DC converter switching at zero current

Abstract: A novel resonant DC-to-DC converter has a source of direct current which is switched through a primary inductor, or the primary winding of a transformer in a primary circuit, to provide energy to an LC tank circuit. The sinusoidal, AC tank voltage is impressed upon an output winding that feeds an output smoothing inductor through a full wave rectifier. The resultant direct current output is made availabe to a load. A unidirectional switch operates in response to a switch control to perform the switching in the primary circuit at near zero current conditions. The switch control opens the unidirectional switch to end the current pulse. The length of the current pulse is proportional to the magnitude of the load.

Optimal topologies of resonant DC/DC converters

Abstract: Generalized and optimal topologies of zero-voltage-switching and zero-current-switching resonant DC/DC power converters are presented. It is shown that many equivalent topologies of the converters can be derived from each of the generalized topologies. The generalized topologies of the converters show clearly which of the parasitic capacitances and inductances can be absorbed into the LC resonant circuit. Utilizing this fact, optimal topologies that are the most suitable for high-frequency operation are derived. In the optimal topologies, the greatest possible number of parasitic reactances is included harmlessly in the resonant circuit. Optimum layout and component selection guidelines for the converters are given. High-order resonant converters are also developed. >

Synchronization circuit for a resonant flyback high voltage supply

Abstract: A synchronization circuit for a resonant flyback high voltage supply for use in providing a high voltage output for a CRT. The circuit includes driving circuitry including an input power filter providing power to a coupled inductor which transmits power to a four stage multiplier circuit. Power is switched on and off by a power FET. The synchronization circuit reduces power loss in the FET by using variations in operational frequency to meet varying loads. By reducing the frequency as load increases, the flyback waveform is allowed to complete its resonant cycle before turning on the power FET. An anode resonant flyback regulator including a pulse width modulator controls the FET in response to signals provided by a negative slope detector circuit and feedback voltage. Over current shutdown capability is further provided by a current sensing latch.

Electrically-tunable bandpass filter

Abstract: A bandpass filter is disclosed which may be used in a superheterodyne receiver in front of the first mixer. The bandpass filter provides a narrow front end filter which is tuned automatically as the local oscillator frequency is changed. In the present exemplary embodiment, a series tuned reflective notch filter is coupled to a node of a balanced resistive bridge in such a manner that the tuned circuit presents a short circuit to the node at the filter's resonant frequency to thereby assure a maximum transfer of signal from the input to the output of the circuit at a desired frequency. At all other frequencies, the series tuned reflective notch filter will present essentially an open circuit across the node of the resistive bridge so that the node is balanced and no transmission occurs. The inclusion of the series reflective notch filter thereby produces a bandpass characteristic from the circuit input to output. By using back to back varactor diodes in the reflective notch filter, the center frequency of the passband can be changed by changing the tuning voltage applied to the varactors. In the configuration of the present invention, the varactor diodes are protected from high signal levels which are not within the narrow passband of the filter. For this reason, the filter is inherently less susceptible to the generation of intermod products than filters of a conventional design.

Nonlinear resonant switch and converter

Abstract: A nonlinear resonant switch (10) for power conversion devices and a converter using the switch are described. The switch optimizes converter efficiency by switching only when current is zero and by limiting the peak current to a value near that provided by conventional PWM converters. A nonlinear reactor (28-32) having a winding (28) in series with the switch and a tank circuit (26,36) is biased to saturation at low currents but is driven into an unsaturated condition by high currents so that a resultant high series inductance mitigates further current increase. Several converter topologies incorporating this improvement are shown.

High-frequency parallel resonant converter for X-ray generator utilizing parasitic circuit constants of high voltage-transformer and -cables

Abstract: The authors describe a resonant PWM (pulse-width-modulated) inverter-linked DC-DC converter which uses the high-voltage transformer parasitic LC circuit parameters as resonant components and the high-voltage cable input capacitance as smoothing filter. Theoretical results obtained by computer-aided simulation and experimental results obtained by a test circuit including prototype transformers are illustrated and discussed from a practical point of view. The phase-shift PWM control for adjusting the DC output voltage of the resonant converter is presented. One of the advantages of this converter is minimization of circuit components; this kind of circuit topology can minimize the size and weight of power supply systems and can be applied to the filament heating circuit connected to the cathode of the X-ray tube. >

Resonance damping apparatus for LC filter of power converter

Abstract: The present invention discloses an apparatus for damping resonance of an LC type low-pass filter provided on the DC input side of a power converter having a DC input terminal. The apparatus comprises an electric circuit connected in parallel to a reactor constituting the LC type low-pass filter. The electric circuit has an impedance which takes a substantially minimum value at a frequency equal to the resonance frequency of the LC type low-pass filter.

Self oscillating power stage for inverted rectifier power supply

Abstract: A self-oscillating inverted rectifier has a series-resonant circuit connected between a load and the selector terminal of an electronically controllable switch, the other terminals of which are connected respectively to d.c. sources of different potential. Phase detection and feedback circuits provide a rectangular control wave for connecting and disconnecting the resonant circuit to each d.c. source only at null transits of the current in the resonant circuit. The feedback circuit includes a control circuit supplied with a regulation voltage, which may be derived from the load, whereby the switch is intermittently prevented from connecting the resonant circuit to energizing d.c. for an integral number of half cycles of the resonant frequency. The load may be a high-frequency electrosurgical device or, more generally, a rectifier circuit providing accurately regulated d.c. power to a variable load.

The development of a thick-film non-contact shaft torque sensor for automotive applications

Abstract: The system described uses a novel thick-film capacitive torque sensor, which is applied to the rotating shaft. The capacitive sensor forms part of a rotating resonant circuit, which is excited across an air gap by means of inductive coupling. Variations in torque cause changes in the resonance frequency of the tuned circuit. The torque may be detected as a change in the resonance frequency, or as a change in referred impedance measured at the exciting coil. The prototype capacitive torque transducer was constructed from flexible printed circuit boards, which were bonded to the shaft. Subsequent sensors have been formed by printing thick-film conductor patterns. This novel approach provides a much simpler method of manufacturing the sensor. Two telemetry systems are discussed, one using a sweep frequency oscillator and one using a bridge circuit. It is shown that for most applications the bridge circuit is preferable.

Magnetic resonance apparatus with uncoupled RF coils

Abstract: In a magnetic resonance apparatus coils of an rf coil system are incorporated for detection of magnetic resonant signals at mutually different frequencies in resonant circuits having a zero impedance for the natural frequency and an infinite impedance for a given deviating frequency. In the switching circuits a coaxial cable is used having a length which has a reactance in parallel with a second reactance to form a tuned circuit adapted to the desired frequency.

Regulated switching power supply with complex output filter

Abstract: A power supply with a pulse width modulation switching mode voltage regulator having an output filter with an attenuation notch at the switching frequency of the pulse width modulator. The output filter comprises an input inductor and a series connected tank circuit with a shunt capacitor. The tank circuit is comprised of a shunt connected L-C circuit tuned to the switching frequency.

Ground-fault-protected series-resonant ballast

Abstract: A self-oscillating half-bridge inverter is powered from a power-line-operated DC voltage source and has a series-tuned high-Q LC circuit connected across its output. A pair of fluorescent lamps is series-connected across the tank capacitor of the LC circuit. An EMI filter is positioned between the inverter and the power line, thereby to minimize electro-magnetic interference. This same EMI filter also acts to produce a control signal in case a ground fault current were to occur; which control signal is used for preventing the magnitude of the ground-fault current from exceeding acceptable limits.

ac susceptibility apparatus for measuring the transition temperature of high‐Tc crystals, sintered samples, and films

Abstract: We describe a simple ac magnetic susceptibility system which can be used to observe the superconducting transition temperature in the range 4.2–300 K. The apparatus is extremely flexible and has been tested using high‐quality YBa2Cu3O7−x single crystals with volume as small as 2×10−5 cm3, much larger sintered polycrystalline samples of the same compound, and finally thin films deposited over a surface area of 1 cm2. The system measures resonant frequency variations of a parallel LC circuit with the superconductor close to the inductor. Typical frequencies and fields are in the ranges 0.2–10 MHz and 1–2 mG ac in the inductor.

Double tuned circuit for distrubuted lumped capacitance observe coils

Abstract: A double tuned circuit for NMR appartus normally has a single inductor common to the two resonant circuit portions. In the present case the inductor is split to form two generally semi-cylindrical members (40,42), each member being H-shaped, with the cross piece of the H acting as a generator of the cylinder and the tips of the upright portions of the H lying adjacent the corresponding tips of the other member, and connected by chip capacitors (44-47). Capacitors and inductors connect portions of the H to ground and to two sources of RF energy of different frequency (64, 66), and a bridge capacitor (69) is provided between the two input circuit portions from the sources.

Varactor tuned microstrip ring resonators

Abstract: Varactor tuned microstrip ring resonators have been developed with more than 30 percent tuning bandwidth using packaged hyperabrupt junction varactor diodes. The experimental tuning bandwidth was found to be in very close agreement with the predicted value obtained using analysis based on transmission line modelling. The attractiveness of the approach presented lies in its simplicity, the tuned resonator could find applications in microwave oscillator circuits and frequency agile communication systems.

Power-factor-controlled electronic ballast

Abstract: A self-oscillating half-bridge inverter is powered from a power-line-operated rectifier means providing a DC voltage with a relatively high ripple content. The inverter is loaded by way of a series-tuned high-Q LC cirucit connected across this DC voltage. A pair of fluorescenet lamps is series-connected across the tank-capacitor of the LC circuit. Also connected across the DC voltage is an arrangement of three energy-storing capacitors charged in series and discharged in parallel; which arrangement results in the current drawn from the power line being of relatively high power factor and low harmonic distortion. Charging current for the energy-storing capacitors is derived from the high frequency current flowing through the LC circuit; and charging occurs only during periods near the peak of the power line voltage. An effect of the charging function is that of improving the crest factor of the current flowing through the fluorescent lamps compared with what it otherwise would have been in view of the high ripple content of the DC voltage.

Dielectric constant of evaporated SiO at frequencies between 13 and 103 GHz

Abstract: An integrated Josephson tunnel junction and microstrip resonator have been used to determine the dielectric constant of evaporated SiO. The method is straightforward in that it uses conventional microwave techniques to calculate the impedances for different frequencies and parasitic effects are negligible. A frequency-independent value of 5.5+or-0.4 was calculated for the 13- to 103-GHz range. At each resonant frequency a step appeared at the corresponding voltage in the current-voltage curve. For each resonant frequency, a dielectric constant was calculated. The constant does not change appreciably from the average value of 5.5 throughout the whole frequency range, in agreement with previous measurements. >

Electromagnetic interference filter protection circuit

Abstract: A protection circuit for use with an electromagnetic interference filter used in conjunction with a three phase power circuit operating at a particular line frequency includes three capacitors which are coupled to the output terminals of the electromagnetic interference filter. The electromagnetic interference filter and the power circuit have a resonant frequency which is substantially equal to the line frequency. The capacitors of the protection circuit have values which are selected to change the resonant frequency of the electromagnetic interference filter and power circuit such that the resonant frequency is not substantially equal to the line frequency. A protection circuit assembly for use with an electromagnetic interference filter includes a base plate, three ceramic capacitors, three heat conducting substrates, and a protective cover which is mounted on the base plate. The capacitors are mounted on the heat conducting substrates, and the substrates are mounted on the base plate.

Narrowband planar microwave active filter

Abstract: A new circuit design for narrowband microwave active filters is presented in the letter. By increasing the tank circuit unloaded Q-value an ideal one-section bandpass filter is realised.

Controlled series-resonance-loaded ballast

Abstract: A self-oscillating half-bridge inverter is powered from a DC voltage source and has a series-turned high-Q LC circuit connected across its output. A pair of fluorescent lamps is normally series-connected across the tank capacitor of the LC circuit. Whenever the lamp load is not so connected, the magnitude of the high-frequency current flowing through the LC circuit would tend to increase to destructively high levels. To prevent this from taking place, a negative feedback control circuit manifestly limits the magnitude of the high frequency current by reducing the forward conduction duty-cycle of each of the two bridge transistors whenever the peak current magnitude exceeds a pre-determined level. In particular, during normally loaded operation, each of the inverter's two transistors operate with a nearly 50% forward conduction duty-cycle. However, whenever the magnitude of the high frequency current exceeds a pre-determined level, the control circuit acts to shorten the forward conduction duty-cycle. As a result, with an unloaded high-Q series-tuned LC circuit connected across the inverter's output, the current through the LC circuit builds up to a certain level and remains there, thereby to provide a substantially fixed-magnitude output voltage suitable for properly starting the fluorescent lamps when they are connected. As soon as the lamps ignite, the resulting loading reduces the output voltage, thereby effectively removing the control circuit from operational involvement.