Showing papers on "Constant current published in 1996"

Fully complementary differential output driver for high speed digital communications

Abstract: A terminating element is connected between the terminating ends of a transmission line pair. A switching mechanism coupled to the originating ends of the transmission line pair steers a constant current through the transmission line pair. In response to input control signals, the switching mechanism steers the constant current in a complementary fashion into one of the lines of the transmission lines pair to creates a differential output voltage across the terminating element. Controlling the differential voltage by manipulating current flow allows for acurate control over VOH and VOL levels. Since the terminating element is connected between terminating ends of the transmission line pair, nearly all of the constant current flowing the driver contributes to the differential output voltage, thereby reducing power undesirable power dissipation. Further, the alternating current flow through the transmission line pair creates a virtual ground at the center of the terminating element and thereby allows drivers in accordance with the present invention to obtain twice the output voltage swing of conventional transmission line drivers without requiring additional current. In this manner, a further reduction in power consumption is achieved.

Overcurrent protection circuit

Abstract: An overcurrent protection system which will give a rapid response to relatively small overcurrents. In a first aspect, the system can be connected between an electrical power supply (12) and an electrical load (26) to form an operating circuit. When so connected, the system protects the circuit from overcurrents, has a normal operating condition and a fault condition, and comprises: a circuit interruption element (24) having a normal state which permits the flow of a normal current, INORMAL, when the system is in the normal operating condition, and a fault state which permits the flow of at most a reduced current, substantially less than INORMAL, when the system is in the fault condition; and a control element (18), connected in series with the circuit interruption element, the control element having a variable resistance which is low when the current in the system does not exceed the normal current, INORMAL, by a predetermined current amount, and increases by at least a predetermined resistance amount when the current in the system exceeds the normal current, INORMAL, by the predetermined current amount; the circuit interruption element changing from its normal state to its fault state, thereby causing the system to change from its normal operating condition to its fault condition, when the resistance of the control element has increased by the predetermined resistance amount.

Solid state AC switch with self-synchronizing means for stealing operating power

Abstract: A solid state power switching circuit for alternating current loads, in which operating power for the circuit is diverted from the switched current during power stealing intervals self-synchronized with the alternating current waveform. During periods in which current to the load is commanded, a load current switch is maintained in a low impedance state except for the duration of a short power stealing interval each half-cycle of the supplied alternating current. Self-synchronization is achieved with a current detector which senses whether or not the magnitude of the current diverted during each power stealing interval exceeds a current threshold, and pulse generator logic which shifts the power stealing intervals in time relative to the alternating current waveform in response to the previously sensed current magnitude.

System for detection of electrical bioimpedance signals

Abstract: A system and method for detection of electrical bioimpedance signals in a human or animal body segment. The system comprises a constant current generator (12) for generating a periodic high frequency current output across a body segment in response to a periodic control signal, a controller (18) for generating a periodic control signal to control operation of the current generator (12) and an electrical bioimpedance detector (22) for detecting a voltage generated across the body segment by the flow of current in the segment. The electrical bioimpedance detector generates an output signal indicative of bioimpedance in the body segment. The periodic generation of a current across a body segment alleviates the potentially detrimental effects of a continuous current on body segment tissue and reduces interference with the function of certain pacemakers.

Constant current source employing power conversion circuitry

Abstract: An energy source for supplying power to a rechargeable battery or the like provides a constant current input to the front end of a transformer. In order to compensate for varying inductances found in the primary winding of the transformer, a special resistor network is provided to precisely control the duty cycle of the current output.

Apparatus and method for electrical system measurements including battery condition, resistance of wires and connections, total electrical system quality and current flow

Abstract: An apparatus and method for measuring electrical characteristics of an energy delivery system utilizes a voltage sensitive circuit such as a voltmeter, a controllable current source or sink and a microcomputer. The microcomputer controls the current source or sink in order to source at least one predetermined current pattern or to sink at least one predetermined current pattern from a portion of an energy delivery system. The voltage sensitive circuit responds to a voltage developed in response to the current pattern and the microcomputer calculates at least one electrical characteristic of the energy system as a result of the response.

Method for charging a secondary battery and charger used therefor using constant current and constant voltage

Abstract: A secondary battery charging method and a charger used therefor, in which the method uses a constant current and a constant voltage such that the secondary battery is first charged with the constant current until the terminal voltage of the battery becomes a reference voltage higher than the full charging voltage for the battery and then further charged with the constant voltage which is equal to the full charging voltage. These two charging operations are switched by using various kinds of detection and control circuits, so that the secondary battery is properly charged in a short time. Further, the charger of the present invention is provided with a circuit for charging a plurality of battery cells simultaneously or separately.

Temperature dependent circuit, and current generating circuit, inverter and oscillation circuit using the same

Abstract: Constant current is generated by a constant current generating circuit. This constant current is divided by a current dividing circuit, and current having temperature dependency is generated by a temperature dependent circuit based on the constant current. This current and the divided current are added in an adding circuit, and driving current is supplied to a ring oscillator. In the ring oscillator, one gate input of each of the odd number of stages of inverters is connected to an output of an inverter in the previous stage, and the other gate input thereof is connected to an output of an inverter in the second previous stage.

Differential stage logic circuit

Abstract: An ECL stage has its current consumption adapted to its operation speed. For this purpose, the load resistor and the bias current source are adjustable so that the product of the current value of the source by the resistor value is substantially constant.

Start up circuit and current-foldback protection for voltage regulators

Abstract: A circuit providing start-up capability and foldback protection to a voltage regulator. A start-up circuit provides a start-up signal to initiate current flow to a load and also provides a foldback signal to set a current limit threshold under an over-load or short-circuit condition. A signal generator circuit operating on the regulated output voltage of the voltage regulator provides a current limit signal and a start-up control signal. The start-up circuit provides the start-up signal in response to the start-up control signal. The current limit signal sets the current limit threshold under normal operating conditions after start-up.

Primary side lamp current sensing for minature cold cathode fluorescent lamp system

Abstract: A circuit for sensing a current in a fluorescent lamp. A control system comprises a buck regulator circuit for supplying a buck current, an inverter circuit for receiving the buck current and for generating a lamp voltage, a circuit for sensing a current in a fluorescent lamp, and a controller for controlling the buck regulator and the inverter. The inverter comprises a Royer-type inverter, a resonant tank, and a transformer. A current flows through a primary winding of the transformer to generate a voltage in a secondary winding of the transformer. The fluorescent lamp is coupled to the secondary winding of the transformer so that the fluorescent lamp is isolated from the remainder of the control system by the transformer. The circuit for sensing the current in the lamp senses a current in the Royer-type inverter which is representative of the current in the lamp. The circuit for sensing the current in the lamp is coupled to the controller for controlling the buck regulator and the inverter.

Megahertz operation of voltage-fed inverter for HID lamps using distributed constant line

Abstract: A novel type of solid-state ballast, which operates in the megahertz-range frequency, is presented in this paper. A circuit composed of a voltage-fed half-bridge inverter, a distributed constant line, and a parallel LC resonant circuit has been developed for this purpose. The high-intensity discharge (HID) lamp is connected to the output terminal of the inverter through the distributed constant line. Here, since the length of the line is adjusted to 1/4 of the propagation wavelength /spl lambda/, the output voltage of the voltage-fed inverter can be converted to a current source on the load side. Based on the experiment results, the ballast appears to be able to supply not only high voltage, but also constant current for ignition of the HID lamp. The experimental results from a prototype system are used to verify the theoretical procedure.

Organic thin-film el display device and its driving method

Abstract: PROBLEM TO BE SOLVED: To provide an organic thin-film EL display device whose driving voltage can be suppressed low and which does not have luminance variance with positions of pixels and is capable of luminance gray scale control even when the display device has high resolution, and a driving method thereof SOLUTION: Disclosed is the driving method for driving the organic thin-film EL display device by a current source connected to a voltage source of a driving voltage VCC while data electrodes are arranged on low-resistance-side wires and scanning electrodes are arranged on high-resistance-side wires in consideration of resistance values of wire electrodes of an X-Y matrix type organic EL display device and currents flowing to the wire electrodes, the driving voltage VCC being a specified voltage meeting the condition that the current source is in constant current operation without fail in spite of variance in wiring resistance with positions of pixels COPYRIGHT: (C)2007,JPO&INPIT

Series-parallel load-resonant converter for controlled-current arc welding power supply

Abstract: A power supply incorporating a series-parallel load-resonant converter, capable of very efficient operation over a wide range of output power is presented. The series-parallel load-resonant converter is shown to have three pairs of resonant frequencies. Operation of the circuit at each of these resonant frequencies maintains zero current switching and high frequency operation. Design mathematics is developed which allow series-parallel load-resonant converters to be designed with specific resonant frequencies and circuit resistances. A new method of power control for series-parallel load-resonant converters is presented; the power delivered to the circuit and hence the load is shown to var substantially depending on which resonant frequency the circuit is excited at. Two series-parallel load-resonant converters are designed simulated, constructed and tested. There is good agreement between the simulation and experimental results. One of the circuits produces an output current of 200 A while the second demonstrates the new power control technique pulsing between 55 A and 145 A while running at frequencies of 63 kHz and 100 kHz. The new power supply is particularly suited to arc-welding. It contains an active rectifier and draws near unity power factor.

Power supply unit and power supply unit for electric vehicle

Abstract: PROBLEM TO BE SOLVED: To shorten reserve charging time for prompt power feed to load by forming a constant current circuit in parallel to a main relay for reserve charging in a capacitor. SOLUTION: A constant current circuit is formed out of a control transistor 16 for switching control, a choke coil 18, a flywheel diode 20, and a voltage/ current detecting part 19, and the choke coil 18 and the flywheel diode 20 smooth outputted current. A control circuit 7 switch-control the control transistor 16 so that the outputted current detected at the voltage/current detecting part 19 may be a prescribed value. If a key switch 9 is turned on, a discharge relay 3 turns off. The control transistor 16 is switching-controlled with a main relay 2 OFF, and a smoothing capacitor 11 is charged by constant current generated by it. As a result, reserve charging is always conducted by constant current, it is thus possible to shorten reserve charging time largely for prompt power feeding start to load.

Circuit for telephone set comprising a light-emitting diode power supply

Abstract: A circuit comprising a transistor (T1) is connected in series to a resistor (RM) for measuring the line current; the whole is connected to the terminals (1,2) of the line. According to the invention, a light-emitting diode (18) is connected in series to a variable current source (20), the whole being connected in parallel to the emitter/collector path of the transistor (T1), and the variable current source, which receives a monitoring signal that represents the line current, produces a current that varies between a zero current and a maximum current for an average line current that varies between a low threshold and a high threshold.

Secondary battery charging method and apparatus which controls protecting voltage level of battery protecting circuit

Abstract: A secondary battery is connected to a protecting circuit. The protecting circuit interrupts charging of the secondary battery when the battery voltage of the secondary battery reaches a first protecting voltage which is higher than a first voltage, the first voltage being the full charge voltage of the secondary battery. After constant current charging of the secondary battery, the secondary battery is charged until the battery voltage of the secondary battery becomes higher than the first protecting voltage for achieving rapid charging of the secondary battery. When the secondary battery is charged in this condition, the protecting voltage of the protecting circuit is changed over to a second protecting voltage which is higher than the first protecting voltage for this preventing the protecting circuit from operating.

Electrostatic capacitance type displacement meter

Abstract: PROBLEM TO BE SOLVED: To improve the measurement accuracy and measurement range of an electrostatic capacitance type displacement meter which measures the change in the spacing between counter electrodes by utilizing the electrostatic capacitance formed between these electrodes. SOLUTION: The sensor electrode 5 with a guard ring set to face a measuring object is connected to the inversion input of an operational amplifier 9 via the central conductor 7a of a shielded wire 7 and a reference capacitor is connected between the output of this operational amplifier 9 and this input. The external conductor 7b of the shielded wire is connected to the non-inversion input of the operational amplifier 9 and the operational amplifier 9 and the reference capacitor are connected to a shielding case 8 for shielding static electricity, by which a detecting circuit 100 is constituted. This detecting circuit 100 is made into a floating structure with respect to the circuit ground together with the shielding case 8. The detecting circuit 100 is driven together with the shielding case 8 by an AC signal and further the amplitude of the AC signal is so controlled that the specified output of the detecting circuit 100 is obtd., by which the measuring capacitor is subjected to constant current driving and, therefore, the detection sensitivity is high. Since the amplitude value of the AC signal and the measured displacement are in a proportional relation, the excellent linearity is obtd. and the accuracy and measurement range are improved. COPYRIGHT: (C)1997,JPO

Power saving PLL circuit

Abstract: A phase lock loop includes a voltage controlled oscillator (VCO), a phase comparator for comparing the phases of the output of the VCO and a reference signal, a charge pump circuit, including a plurality of current sources, for supplying a control voltage by charging or discharging a capacitor based on the outputs of the current sources, and a current source controller for controlling the current output of the current sources by a n-bit current control signal. Charge current and discharge current by the charge pump circuit are controlled in n bits so that a rapid synchronization during lock-in and a low jitter after lock-in can be obtained.

Low cost electronic ultracapacitor interface technique to provide load leveling of a battery for pulsed load or motor traction drive applications

Abstract: A battery load leveling arrangement for an electrically powered system in which battery loading is subject to intermittent high current loading utilizes a passive energy storage device and a diode connected in series with the storage device to conduct current from the storage device to the load when current demand forces a drop in battery voltage. A current limiting circuit is connected in parallel with the diode for recharging the passive energy storage device. The current limiting circuit functions to limit the average magnitude of recharge current supplied to the storage device. Various forms of current limiting circuits are disclosed, including a PTC resistor coupled in parallel with a fixed resistor. The current limit circuit may also include an SCR for switching regenerative braking current to the device when the system is connected to power an electric motor.

High-precision current source using low-loss, single-switch, three-phase AC/DC converter

Abstract: A three-phase AC/DC converter based on isolated Cuk topology feeding an inductive load is presented. The main goal is to get a compact, highly stable current source to feed an electromagnet. A high power factor is achieved, at constant duty-cycle and switching frequency, by discontinuous input current mode operation. The converter presents a linear relationship between the duty-cycle and the output current, making it easier to design the control system. Additionally the voltage stress on the power transistor is constant and does not depend on the duty-cycle. An auxiliary circuit allows zero voltage turn-off while limiting the over-voltage on the switch produced by the transformer leakage inductance. Pulse-width modulation (PWM) control is used to reduce sensitivity to line disturbances and to eliminate the 300-Hz ripple on the output current. Experimental measurements taken on a 400-W prototype confirm theoretical forecasts.

Temperature insensitive current source

Abstract: A circuit is presented which can produce a temperature insensitive, constant current value. The constant current source comprises transistor pairs which mirror a temperature dependent current into a node along with another temperature dependent current. The node thereby receives two temperature dependent currents, wherein one is inversely dependent to that of the other. More specifically, one current may increase as temperature increases, whereas the other current decreases as temperature increases. The two currents may thereby be construed to offset one another such that the output of a common node produces a current output which does not change with either an increase or decrease in temperature imputed upon the current source component.

Method and control circuit for a switching regulator

Abstract: A control circuit for a switching regulator having an inductor, comprising a first input for receiving a current measurement signal proportional to the magnitude and direction of current in the inductor, (or proportional to the difference in current in two inductors for an AC system having more than one phase); the current measurement signal being compared with a reference current representing the desired current in the inductor, the circuit having a processor to determine the timing of switching instances, and to control switching of said inductor between a positive voltage (charging configuration while the current is positive) and a negative voltage state (discharging configuration while the current is positive), where the processor determines the difference between said current measurement signal and said reference current signal to generate a current error signal representative of the difference or representative of the polarity of the difference, and the processor calculates timing of switching instances to achieve an average current error signal close to zero, based on timing of previous switching instances relative to zero crossing times of the current error signal during a previous excursion.

Battery charging method

Abstract: A voltage at the time of full charging of a battery being charged is set to be larger for a lithium ion battery than for a nickel cadmium battery. Charging of the battery is then carried out using a constant current circuit and a fixed voltage circuit. If the item being charged is a lithium ion battery, a current detection circuit detects when the charging current is less than a prescribed value, a control circuit switches off a switch and the charging is halted. If the item being charged is a nickel cadmium battery, a -ΔV detection circuit detects when the terminal voltage for the battery becomes low (-ΔV) and the charging is halted. Different types of batteries of the same shape can therefore be charged in the same charging equipment while damage to the batteries during the charging operation is prevented.

DC actuator control circuit with voltage compensation, current control and fast dropout period

Abstract: The DC actuator control circuit with voltage compensation, current control and fast dropout period employs an electronic chopper incorporating an oscillator having a variable duty cycle controlled by sensing of coil current. Coil current is sampled through a series resistor by a feedback amplifier which increases or decreases the period in which the switch for the coil circuit remains on to sustain average coil current at the desired MMF. A threshold detector provides an initial triggering signal to initiate operation of the actuator and the control circuit responsive to a predetermined source voltage and a gate signal generator responds to the triggering signal with a time constant sufficient to drive the coil through a pickup interval. Inrush current is limited by the oscillator through sensing of coil current. A dropout switch for opening the sustaining current return circuit which opens upon removal of source voltage provides a high impedance for rapid current drain from the coil thereby eliminating regeneration effects.

Auto ranging current monitor with common mode correction

Abstract: An improved current monitor for measuring current over a wide dynamic range. The current monitor includes a low current channel, a high current channel, and a switch for selecting the low current channel if the measured current is below a predetermined level and the high current channel if the current is above the predetermined level. The output of the high current channel is voltage encoded by adding a fixed offset. The current monitor determines that the measured current is from the low current channel if the reading is below the offset and from the high current channel if the reading is above the offset. A current level output device automatically outputs a decoded current reading based on this determination. The current monitor also incorporates a low current error compensation circuit to compensate for parasitic current when the current monitor is using the high current channel. The current monitor also incorporates a device for reducing the common mode error voltage to zero in the differential amplifiers used to convert current across shunt resistors in the low and high current channels to a voltage signal.

Series resonant converter, and method and apparatus for control thereof

Abstract: A welding power supply that includes a series resonant converter, including at least one switch and at least one capacitor is disclosed. The converter includes a switching circuit including an enable input. A voltage sensing circuit that determines the earliest safe switching time of the switch is provided. The safe switching time is the time that will prevent a peak voltage on the capacitor from exceeding a predetermined threshold for a next cycle of the converter. The voltage sensing circuit provides an enable signal to the enable input when the earliest switching time has passed, to enable the switching circuit. A pair of welding output terminals connected to the series resonant converter receives the output. A controller including a curve shaper, for providing a constant current output in the welding range is also disclosed. The controller also provides an adaptive hot start that provides varying amounts of energy in response to the welders skill.

DAC with feedback control for current source bias during non-display period

Abstract: A D/A converter of a current output type desirably compensates for changes in the switching characteristic that arise in each constant current circuit. The D/A converter generates an analog output current that is in response to the level of input digital data and outputs it from an output side by switching each of output currents of a plurality of constant current circuits either to the output side or to a non-output side, in response to the input digital data. The D/A converter performs feedback control, for values of the output currents for the constant current circuits, based on an analog output current at the non-output side during a period when the output currents of all of the constant current circuits are connected to the non-output sides.

Charge pump circuit with source-sink current steering

Abstract: A charge pump circuit includes a current mirror circuit of current-sourcing and current-sinking FETs and a current steering circuit of cross coupled differential pairs of FETs. Nominal current flowing in the current-sourcing and current-sinking FETs is set. The current is for charging and discharging a capacitor of an external filter. During charging of the capacitor, the current through the current-sourcing FET is directed to the capacitor and the current through the current-sinking FET is directed from a low impedance voltage source. During discharging of the filter capacitor, the current through the current-sourcing FET is directed to the low impedance voltage source and the current through the current-sinking FET is directed from the capacitor. The current flowing in the current-sourcing and current-sinking FETs is nominally constant, regardless of the tri-state condition, charging or discharging, with the result that power supply noise is reduced. Current change in the power supply rails is reduced when switching from current-sourcing to current-sinking or vice versa. By using cascode FETs in both of the current-sourcing and current-sinking FET circuits, power supply noise rejection is improved.

CMOS current source circuit

Abstract: An improved CMOS current source circuit capable of constantly generating a certain reference voltage irrespective of an analog supplying voltage, a substrate temperature, and a temperature variation, which includes a start unit for driving the CMOS current source circuit in accordance with a start signal; a bias current generating unit driven by the start unit for generating a bias current in accordance with an analog voltage, a substrate voltage, and a temperature variation; a current input unit for inputting a bias current; and a current compensation unit for receiving a bias current through the current input unit and for compensating the bias current in accordance with an analog voltage, a substrate voltage, and a temperature variation and for generating a reference current.