Abstract: A supply circuit is provided for operation of an electromagnetic load of a vehicle provided with generator (dynamo) and battery, and more particularly for operation of at least one solenoid valve of a fuel-injection system of an internal-combustion engine of the vehicle. A circuit arrangement is proposed which connects the load (6) for a buildup of its excitation to the generator (3) and then establishes a connection to the battery (13) for the maintenance of sufficient excitation and interrupts the connection to the generator (3).

Abstract: A circuit capable of driving inductive loads below a chip substrate voltage level while minimizing on-chip power dissipation and eliminating parasitic effects. Two negative voltage drive modes are included in the circuit design. The first drive circuit forces a low negative voltage referenced to the circuit output voltage across an inductive load referenced to ground to provide a slow recirculation of the current in the inductive load. The second drive circuit forces a large negative voltage referenced to the circuit output voltage across the inductive load to provide a fast collapse of the inductive load. The switching regulator switches off when the current to the inductive load reaches a first value and switches on when the recirculating current from back e.m.f. reaches a second value. The switching regulator initially provides a higher level of power when first tuned on.

Abstract: In a d.c. solenoid in which a thermistor having a positive temperature coefficient is connected in series with a main coil, a subcoil is connected in parallel with the series connection of the main coil and the thermistor, so that a large magnetic force can be produced at the solenoid energization starting time, and generation of heat from the thermistor can be suppressed to prevent burn-out of the main coil due to continuous current supply. Both the main coil and the subcoil, when energized alone, are capable of actuating the solenoid. The d.c. solenoid is applied to a valve in a vaporized fuel absorption system.

Abstract: A microprocessor controlled electrical contactor monitors the voltage and peak current produced by a first voltage pulse gated to the coil of the contactor electromagnet and adjusts the conduction angle of the second pulse to deliver a constant amount of electrical energy to the electromagnet coil despite variations in coil resistance and supply voltage so that the contactor contacts can be consistently closed with low impact velocity and minimum contact bounce. Normally, the third and subsequent pulses are gated to the coil at constant conduction angles selected so that the contacts consistently touch and seal on a preselected pulse with declining coil current. Under marginal conditions, determined by the peak current produced by the first pulse, the third and subsequent pulses are gated at substantially full conduction angles to assure contact closure. If the voltage or current produced by the first pulse is below a predetermined value, closure is aborted.

Abstract: In a printing device employing a solenoid for driving a printing hammer, provided are switching member for ON/OFF operating electric current flowing through the solenoid coil, voltage generating member for generating voltage in accordance with the electric current, converting member for converting the generated voltage to a digital value, chopping member for comparing the converted digital value with a predetermined comparison value, while for turning on the switching member when the converted value is smaller than the predetermined comparison value and turning off the switching member when the converted value is larger than the predetermined comparison value, detecting member for detecting voltage relating to a driving operation of said solenoid, and controlling member for controlling the predetermined comparison value so as to be varied in an amount based upon the detected voltage. Thus, the current flowed through the solenoid is controlled so as not to be largely varied.

Abstract: An electronic contactor controller circuit able to handle high currents and voltages includes an integrated circuit power circuit switch which provides a measuring output signal representative of the load current to an operational amplifier current to voltage convertor. The output voltage of the operational amplifier is provided to an input of a comparator, and at least one reference voltage, from reference voltage generating circuitry, is provided to the other input of the comparator. The comparator outputs a signal to control a timer circuit, which in turn controls the current switch.

Abstract: The solenloid coils 26, 27 of a hydraulic spool valve may be selectively connected in series or parallel by a switch unit 101. The series connection is used during normal control operations, but if the valve spool 4 becomes jammed the unit switches over to the parallel connection. This quadruples the coil current, and the attendantly increased magnetic drive force enables the spool to shear through the contaminant particles entrained in the hydraulic fluid that are causing the jamming.

Abstract: A non-volatile memory circuit for use with an E.sup.2 PROM includes redundant, parallel connected, floating node MOSFET memory cells for storing complementary information. The non-volatile memory cells are connected in parallel to a volatile memory circuit via a voltage level shifter circuit for writing operations, and via twin mixed PMOS and NMOS transistors for reading operations. With the combined complementary non-volatile memory cells and the twin mixed pairs of transistors, the stored information is retained in the event that one of the memory cells fails.

Abstract: A circuit arrangement for providing a store of energy for actuating an electrically operable device, incorporating a reservoir capacitor, comprising a transformer having low resistance windings, the primary winding of which is connectable to an alternating current high voltage supply in series with at least one resistance capacitor, and the secondary winding of which is connected to the reservoir capacitor through a rectifier, the capacitor being connectable to an electrically operable device, with the turns ratio of the transformer such as to produce a secondary current of sufficient magnitude to charge the reservoir capacitor in the time available for successive operations or successive operational sequences of the device.

Abstract: A solid-state flipper control circuit for controlling the operation of a pinball machine includes a flipper, a flipper switch, and a solenoid coil for controlling the movement of the flipper. The flipper switch is formed as a microswitch having a common terminal connected to a ground potential and normally-open contact terminal. A solid-state driver circuit is provided which is responsive to the activation of the microswitch for generating momentarily a first voltage on its output terminal so as to move the flipper to the actuated position. The solid-state driver circuit includes a timer for automatically disconnecting the first voltage after a predetermined time and for generating subsequently a second voltage so as to hold the flipper in the actuated position until the microswitch is deactivated.

Abstract: An apparatus for dampening current in a coil has a switchable member which controls the current level in the coil and a flyback circuit that allows current in the coil to slowly dissipate when the switchable member changes from an "ON" to an "OFF" state. The flyback circuit has a high resistance when the switchable member changes from the "ON" to the "OFF" state so that the coil current is dampened as quickly as possible without creating a destructive voltage and low resistance when the switchable member is in the "ON" state to conserve energy. A signaling device creates a voltage signal as a function of current passing through the flyback circuit and a receiving device varies the resistance of the flyback circuit in response to the voltage signal. The apparatus is particularly suited for use in a motor control circuit.

Abstract: A method and apparatus for electronically detecting when a solenoid has closed, or nearly closed, indirectly senses changes in the inductance of the solenoid's coil as the solenoid closes. When the inductance has changed by a selected amount, the solenoid is assumed to have closed, or nearly closed, and current through the coil is promptly reduced. Preferably, changes in the inductance of the coil are sensed by establishing a plurality of current peaks in the coil, and sensing the current's decay time between peaks. When the decay time of a measured current peak exceeds the decay time of a previously measured current peak by a selected amount, it is assumed that the solenoid has closed, or nearly closed.

Abstract: A control for an inductive load switches current on and off to regulate about a command value, a decaying recirculation current flowing through the load during the switch off periods. The current is sensed during the switch on periods and charges a capacitor to provide a simulation signal representing the motor current. The capacitor is allowed to discharge through a resistor during the switch off periods at the rate of the decaying recirculation current. The simulation signal is compared to the command value to control the switching. The simulation signal is sensed during a command value of zero current to determine offset errors for calibration purposes.

Abstract: A control circuit unit for controlling the energization of a solenoid of a solenoid-operated capacity control unit incorporated in a a variable capacity compressor, typically, a variable capacity wobble plate type refrigerant compressor for a car air-conditioner, having a switching unit for establishing an electric conduction of the energizing circuit of the solenoid when the solenoid-operated valve is actuated for changing the compressor capacity, and an electric energizing voltage control circuit used to apply a high electric starting voltage to the solenoid emergizing circuit at a predetermined initial starting time of the solenoid, and a low electric retaining voltage required for retention of the energization of the solenoid valve after the predetermined starting time has elapsed.

Abstract: An electromagnetic solenoid drive apparatus for use in a vehicle for turning on an electromagnetic solenoid from a battery every time when a command switch is turned on comprises first and second resistors connected in series to each other on an electric line for flowing an electric current through the electromagnetic solenoid; a first switching element turned on in a state in which an output voltage of the battery is lower than a predetermined threshold voltage and short-circuiting both ends of the first resistor; a timer circuit operated for only a constant time in association with the turning-on operation of the command switch; and a second switching element turned on during only the operating period of the timer circuit and short-circuiting both ends of the second resistor.

Abstract: A chopper circuit is provided for driving of electromagnets and/or step motor coils (8;26) in particular for a matrix printer, where the inductivity of the coil generates in connection with the applied voltage a maximum current, which current, however, is set lower by desired factor, whereby the current ripples (7a) are generated by chopping. These current ripples (7a) can be changed, that is, set to an optimum value depending on frequency inductivity and resistance of an electromagnetic coil (8) or, respectively, of a magnet coil winding (26).

Abstract: An electronic driver circuit for the open loop control of the energization of a solenoid coil, forming part of an electromagnetic solenoid actuator valve, in response to a control pulse produced by a control circuit and where the predetermined schedules are a function of the inductance and resistance of the coil, the desired peak output voltage from the coil and the desired average holding current through the coil.

Abstract: In a circuit for controlling a pulsating current through an inductor, particularly the coil of an electromagnetic valve, the inductor is connected in series with a semiconductor switch and in parallel with a free-running diode. Furthermore a desired-value voltage is fed to a controller the output of which is connected via a pulse-width modulator to a control input of the semiconductor switch. A current flows through the inductor and the semiconductor switch, during a state of conduction of the semiconductor switch, to be measured. The current measurement is gated, in response to pulse-width modulation at the controller, and is then integrated for improved measurement of the current.

Abstract: A method and apparatus for controlling the operation of an electromagnet by comparing the frequency of its holding current pulses against a reference frequency and by initiating another energization cycle if a difference exceeding a predetermined value is detected.

Abstract: In a current detector for use with a pulse-driven electromagnetic actuator drive circuit, a solenoid current detector is disclosed which operates by use of a solenoid current detection resistor to sample an instantaneous solenoid current value at intervals of a predetermined pulse voltage period, and calculates the average current value for the solenoid by calculation based on the sampled value.

Abstract: A method and apparatus for solenoid driver control of high speed solenoid actuators which includes supplying a high regulated level of acceleration current to operate the actuator, monitoring and controlling the current requirements of solenoid actuation, automatically reducing the solenoid current at a rapid rate to a lesser level of regulated solenoid hold current for the remaining duration of actuator operation, and rapidly reducing the solenoid current between acceleration and holding levels and for rapid solenoid release. Current is controlled at the different levels using switch mode power control techniques for power efficiency.

Abstract: A solenoid drive circuit, when providing a holding current to a solenoid by means of periodically turning a drive transistor on and off, by-passes a Zener diode until immediately before the end of a holding period as a result of an on state of a first switching transistor, and interrupts the by-pass of the Zener diode as a result of an off state of the first switching transistor during a time period immediately before the end of the holding period, as above-mentioned, until the lapse of a predetermined time after the end of the holding period. Thereby, current due to a counter-electromotive force is utilized in order to shorten the on time of the drive transistor to thereby save the supply of electric power. Moreover, by interrupting the by-pass of the Zener diode immediately before the end of the holding period, an off-responsibility of current flowing through the solenoid is not disturbed at the end of the holding period.

Abstract: The circuit according to the invention comprises a hysteresis comparator 9 connected to a transistor 2 controlling the current flowing in an inductive load 1. The voltage taken across the terminals of a measurement resistor 3 is compared with a reference voltage established by a source 6. According to the invention, a feedback loop 10 establishes a proportional action of the transistor 2 on the current in the load 1 when the voltage at S exceeds a predetermined threshold. In this way an oscillation is obtained between two values on either side of a nominal value, these two values being associated with the thresholds of the hysteresis comparator. Application to the production of an integrated circuit for the control of the ignition coil of an internal combustion engine.

Abstract: A current regulator for an inductive load especially for a coil of an electromagnetic solenoid valve. The current flow through the coil is regulated and compared by means of an operational amplifying nominal current value. The inductive load comparator is initially controlled by a first conductive diode. A second diode having a higher voltage rating than that of the first diode is rendered conductive whenever the nominal current value in an inductive coil decreases rapidly. The current regulator ensures that the magnetic energy in the inductive load remains unchanged when the nominal current value remains constant or changes in small amounts. When a rapid decrease of the coil current occurs, the second diode is rendered conductive.

Abstract: The invention provides a control circuit arrangement for solenoid valves, which has a timer adapted to supply the solenoid valve with a higher attraction current during an adjustable time starting with the beginning of a switching signal for the solenoid valve. After the time interval a low hold current flows until the end of the switching signal. For this purpose there is a semiconductor switch adapted to switch the flow of current through the solenoid valve. A logic gate arrangement is connected with an input of the switch and the gate arrangement is supplied with the output signal of the timer arranged to be triggered by the switching signal and the output signal of an oscillation generator. This circuit arrangement makes is possible to reduce a higher attraction current to a lower hold current in a simple and cheap manner, there only being a small overall size and as significant advantages it is possible for the arrangement to be converted for complementary logic.

Abstract: A solenoid control circuit provides energy to selected solenoids to control actuation of a control valve of a fuel injector and, hence, the timing and duration of fuel delivered to each cylinder of an internal combustion engine. The current provided to each solenoid is also controlled to provide a three tier current waveform having a pull-in current level, a hold-in current level, and an intermediate current level. Energizing the solenoid at the pull-in current level starts movement of the control valve. After the control valve starts to move, the current level is reduced to the intermediate level, which is less than the pull-in current level, but great enough to continue movement of the control valve. Further reduction of the current level to the hold-in level, which is less than either of the other current levels but sufficient to hold the control valve at the moved position. The solenoid is then de-energized and the control valve returned to its initial position to stop the flow of fuel to the engine.

Abstract: A comparator comprising two differential input stages (Q1 to Q4 and Q5 to Q8) which are connected in parallel and fed by a common constant circuit source (Q.sub.B) whose current is passed either to both or only to the one or only to the other differential input stage, depending on whether the common-mode input voltage of the comparator is within, above or below a voltage range that is between the voltage values of the two poles (VC, VE) of a supply voltage source (B) of the comparator, and comprising a common current mirror circuit (Q9, Q10) which is associated with the outputs of both differential input stages and from which the comparator output signal is derived. At least one (Q1 to Q4) of the two differential input stages operates in common-base connection, with this differential input stage (Q1 and Q4) receiving its supply current from the common-mode input voltage source.

Abstract: A PWM solenolid operated valve control arrangement which substantially eliminates supply voltage dependent variability of the valve without the expense or inefficiency of a conventional voltage regulator. The coil of the solenolid valve is pulse-width-modulated in relation to the commanded output result and the energization periods are submodulated in relation to the magnitude of the supply voltage. The effective voltage applied to the coil, and hence the operating characteristics of the solenoid valve, are thereby made substantially independent of supply voltage variations.

Abstract: Such electronic control systems contain safety circuits for device components endangered by excessive currents or excessive voltages, which are constructed only for a pulse operation and not for higher relative switch-on times.In order to shield the effectors (users) already in the pre-stage against undesirable high currents or, respectively, voltages, such that a punch through of these destroying voltages or, respectively, currents can be excluded for practical purposes, it is disclosed that an effector (1) is controllable in operating condition and simultaneously a reference voltage (R1/R2) can be switched on within the permissible tolerance region where, upon the exceeding of the tolerance region, the effector (1) can be switched off.

Abstract: A solenoid driver system drives a solenoid, such as a solenoid in a glue applicator or any like apparatus incorporating a solenoid, and which requires control of the solenoid in response to a signal voltage. The solenoid driver system generates a turn on signal that enables the solenoid, such as that of a glue gun applicator, to energize quickly because of a rapid rise solenoid signal. A solenoid driver stage of two switching transistors and two high voltage fast recovery diodes are connected to a control pulse through a high side optical isolator and a high side buffer, and a low side optical isolator and a low side buffer. The low side circuit includes a trigger circuit and a delay circuit connected to a gate along with a free-running oscillator for periodically energizing the low side drive of the circuit in a mode as long as the input signal is energized. This ensures that the amount of current dissipated in the solenoid coil is small.

Abstract: The invention relates to solid-state circuitry, including a freewheeling circuit, for controlling the operation of an electromagnetically actuated fuel intake or exhaust valve of an internal combustion engine by alternatingly energizing, by way of a current switching element, the coil of the electromagnet at a high level of current for attracting the armature of the electromagnet into engagement with the stator, thus driving the valve into its open or closed position, and maintaining, by way of a transistor, lower level current pulses in the coil sufficient to maintain the engagement.

Abstract: An actuator circuit for an inductive load includes a first low impedence source of direct current at a relatively high voltage, a second low impedance source at a lower voltage, a switching arrangement responsive to an input signal for connecting a load across the first source at the beginning of the signal and for a predetermined initiating interval thereafter, and at the end of the interval switching the load from the first to the second source, and a feedback control for limiting the current through the load to a first, constant value during the initiating interval and to second, lower constant value thereafter. The circuit cuts off the load when the input signal ceases or it removed.

Abstract: In an electromagnetic coil drive device an operation coil excites an electromagnet. A switching element is turned on and off by application of a pulse signal thereto and supplies the operation coil with a power supply voltage. A voltage detecting circuit detects the power supply voltage and a gain circuit delivers a closing level signal in accordance with the voltage detected by the voltage detecting circuit. The gain circuit also delivers a holding level signal based on the detected voltage after a predetermined period of time. The level of the holding level signal is higher than that of the closing level signal. A reference wave generating circuit generates a triangular wave. A comparing circuit compares the triangular wave with the closing level signal to thereby generate a closing pulse signal having a predetermined cycle.

Abstract: A safety control device for an actuator of a flap solenoid valve, such as for an automatic transmission. The device includes a current control device which is connected to a shunt resistor for measuring the current through the solenoid valve and the current control device. It also includes a control package which measures the time between the starting of the power to the solenoid valve and the moment when the current reaches a threshold intensity. The control package compares this time with a time range which indicates the proper operation of the solenoid valve so that if the time falls outside this time range, the control package instructs the current control device to cut power to the solenoid valve.

Abstract: An electromagnetic contactor or controller is taught in which the voltage which is impressed across the electromagnetic armature winding is controlled with an algorithm to enhance the closing operation. A microprocessor is utilized to implement the algorithm.

Abstract: A drive circuit for an inductive load includes a switching device connected in series with the load and controlled by a constant frequency oscillator. The mark/space ratio of the signal supplied to the switching device by the oscillator can be varied in accordance with the output of a comparator 18 which compares the measured instantaneous value of the current flowing in the load with a calculated value of the current.

Abstract: A defect detector circuit for an inductive load driving circuit which has a surge comparator circuit for comparing a surge generated from an inductive load when the current of the inductive load is interrupted with a reference value on the basis of an output from a surge absorber circuit for absorbing the surge, and a surge time deciding circuit for outputting a defect signal when a time that the surge amount exceeds the reference value does not fall within a set range on the basis of the output from the surge comparator circuit.

Abstract: A method for providing a power management for a DC solenoid actuator includes the steps of initially supplying a first number of DC current pulses to the actuator and after a first time interval reducing the number of pulses applied to the solenoid in direct proportion to an output voltage of a source of the DC power. The method further includes the step of changing the duration of the first time period in direct proportion to the output voltage of the source of the DC power.

Abstract: Commencing with the first print hammer(s) "out", or actuated, on each print line the hammer drive current is boosted 10% for a period, ranging from 25%=650 microseconds for single part forms to 50% for multi-part forms, of the total print hammer flight time. Earlier striking hammers on each print line strike harder, alleviating displaced first-printed characters on single part forms and light characters on multipart forms due to hammer energy loss in forms compression.

Abstract: A power supply for controlling a solenoid actuated lock includes high and low frequency pulse generators, the outputs of which control a switching transistor. The low frequency pulses seat the solenoid plunger, and the high frequency pulses maintain the plunger in the seated position.

Abstract: A magnetic flowmeter includes circuitry for applying a first relatively high voltage across the electromagnet coils of the meter for a controlled length of time to build the coil current to a desired level and circuitry for applying a second, relatively low voltage across the electromagnet coils after the application of the high voltage to maintain the coil current at the desired level. The coil current is sampled at predetermined times during the application of the relatively low voltage and the length of time the relatively high voltage is applied is varied to eliminate differences in consecutive coil current samples. The actual level of the coil current is controlled by a magnetic amplifier which includes a saturable reactor. The voltage waveform applied to the electromagnetic coil reverses in polarity each half cycle due to a bridge circuit which is connected to a power supply of a single polarity.

Abstract: In a method for controlling an injection valve for an internal combustion engine in which the magnet coil of the injection valve is connected to pulsate current by means of a semiconductor switch to an operating voltage in such a way that, during a first time interval, a current which is sufficient to open the injection valve flows and that, following same, there is possibly a second time interval which is dependent on the intended injection time and has a current sufficient for holding the valve open. The first time interval is terminated by disconnection when the current has reached a peak valve which is dependent in accordance with a predetermined function on the operating voltage.

Abstract: An improved dual limit solenoid driver control circuit is disclosed in which solenoid current is sensed and provided as an input to two separate comparators (24, 25). Each comparator receives, during a solenoid pull-in (initial) period (T.sub.1), fixed maximum and minimum reference threshold levels which determine the maximum and minimum current limits (I.sub.max, I.sub.min) for solenoid current during initial pull-in excitation. Subsequently during a hold period T.sub.2 following the pull-in period, each of the comparators receives different maximum and minimum thresholds so as to establish holding solenoid current limits (H.sub.max, H.sub.min). The outputs of the compartors are connected as inputs to a set/reset flip flop (32) whose output controls the operation of a solenoid driver circuit (15). A monostable multivibrator (33) reacts to an initial control pulse (41) to produce a predetermined pull-in time pulse (43) that results in the maximum and minimum pull-in solenoid current limits.

Abstract: A low voltage supply control system provides on command a voltage doubling of the supply voltage to the fuel injector coils of a fuel injection system. The command signal is responsive to the magnitude of the battery voltage falling below a predetermined level at any time during the operation of the fuel injection systems be it on cold starting or during a component failure in the power generating system of the vehicle during operation. The advantage of this system is that the impedance of the fuel injector coils is typically many times higher than that of coils used without the low voltage supply control system. Overall the cost advantages of the low voltage supply control system are very attractive.

Abstract: A load current control device operates so as to control the magnitude of a current delivered to a load by varying a duty factor. With this control device, a fundamental value is determined on the basis of an instruction of an input signal, and a reference duty factor and a reference current value are determined on the basis of the fundamental value. The control device further operates to correct the reference duty factor on the basis of a difference between the magnitude of a current actually flowing in the load and the reference current value to turn on and off a power supplied in accordance with the corrected duty factor, therby to control the magnitude of the load current. In addition, when the above-said difference is out of a predetermined range, this load current control device outputs a signal indicative of abnormal condition.

Abstract: A proportional solenoid valve control circuit uses a solenoid current driver, a feedback circuit for providing a feedback signal representative of an output current supplied by the drive means, input signal means for connection to a source of a control signal representative of a desired current to be supplied by the driver means, signal comparison means for comparing the feedback signal with the control signal to produce an error signal representing the difference therebetween, timer means connected to the comparison means for producing an output signal having a frequency dependent on the magnitude of the error signal and a circuit for applying the output signal to the current driver to produce the output current from the driver proportional to the output signal.

Abstract: A device is provided that begins an electrical starting mode in a parallel circuit configuration providing an improved speed of response and after an interval of time, current is switched to a series circuit configuration for operation during a run mode. The device is initially energized at several times the power normally required to activate a coil and switching means is thereafter utilized to reduce power to a normal requirement soon after the coil is energized. Specific hardware is provided in the form of schematic diagrams for defining the operation of the invention.

Abstract: An improved solenoid driver control circuit is disclosed in which solenoid current is sensed and provided as an input to a comparator means comprising two separate comparators (24, 25). The comparator means receives a solenoid current sense signal (45) and maximum and minimum reference threshold levels which determine maximum and minimum current limits (I.sub.max, I.sub.min ; H.sub.max, H.sub.min) for solenoid current during initial pull-in excitation and subsequent hold excitation. Pull-in time (T.sub.1) is defined by a monostable multivibrator (33) reacting to a control pulse (41) to produce a predetermined pull-in time pulse (43) such that the pull-in time is independent of sensed solenoid current. During pull-in time a boost driver switch (53) applies high boost voltage to a power source terminal (16) which supplies solenoid current, and in response to achieving the maximum pull-in current limit (I.sub.max) lower battery voltage is provided at the power source terminal.

Abstract: Disclosed is an arrangement for controlling the current in a solenoid. A microcomputer is used to control three states of a 3-state output device (high impedance, high and low) which are designed to correspond to three current modes of the solenoid: no current, full current and reduced current. The 3-state output device produces a signal which is used to control a solenoid drive circuit. The drive circuit includes first means for generating a first drive signal in response to the 3-state signal being in the high impedance state or the low state, and second means for generating a second drive signal in response to the 3-state signal being in the high impedance state or the high state. The circuit further includes third means for coupling the first and second drive signals to the solenoid such that the current in the solenoid is controlled according to the states of the 3-state signal.

Abstract: A control unit and method for operating a gap-type electromagnetic clutch or brake is provided which reduces audible chatter, screeching caused by belt slippage and related wear and tear on the driving and driven components. The operating winding of the clutch or brake is energized to cause the gap between an armature and rotor to close, energization of winding is then reduced to initially reduce the torque coupling between the armature and rotor and finally energization of the winding is gradually increased to full energization so as to provide a gradually increasing torque coupling between the armature and rotor.