CA1173503A - Direct current control in inductive loads - Google Patents
Direct current control in inductive loadsInfo
- Publication number
- CA1173503A CA1173503A CA000381170A CA381170A CA1173503A CA 1173503 A CA1173503 A CA 1173503A CA 000381170 A CA000381170 A CA 000381170A CA 381170 A CA381170 A CA 381170A CA 1173503 A CA1173503 A CA 1173503A
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- CA
- Canada
- Prior art keywords
- current
- cycles
- inductive
- source
- inductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P7/00—Arrangements for regulating or controlling the speed or torque of electric DC motors
- H02P7/06—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current
- H02P7/18—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power
- H02P7/24—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices
- H02P7/28—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices
- H02P7/285—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only
- H02P7/29—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only using pulse modulation
- H02P7/2913—Arrangements for regulating or controlling the speed or torque of electric DC motors for regulating or controlling an individual dc dynamo-electric motor by varying field or armature current by master control with auxiliary power using discharge tubes or semiconductor devices using semiconductor devices controlling armature supply only using pulse modulation whereby the speed is regulated by measuring the motor speed and comparing it with a given physical value
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
- H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
- H01H47/22—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current for supplying energising current for relay coil
- H01H47/32—Energising current supplied by semiconductor device
- H01H47/325—Energising current supplied by semiconductor device by switching regulator
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/156—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of output voltage or current, e.g. switching regulators
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M3/00—Conversion of dc power input into dc power output
- H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
- H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
- H02M3/10—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M3/145—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M3/155—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
- H02M3/1555—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only for the generation of a regulated current to a load whose impedance is substantially inductive
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Dc-Dc Converters (AREA)
Abstract
13130:CRH
DIRECT CURRENT CONTROL IN
INDUCTIVE LOADS
Abstract of the Disclosure A DC current control is provided for inductive loads which achieves high energy efficiency even though the supply voltage may be subject to considerable variations.
The inductive load may be a DC motor, a solenoid, or similar device. The electric power is applied directly to the inductive load through a switching means which closes the circuit to apply a charging current to the inductive load for fixed on periods of time.
A discharge path is provided for the inductive load when the switching means opens the charging circuit.
The discharge current is monitored, and when it decays to a selected value, the switching means is again closed for the fixed on charge time.
DIRECT CURRENT CONTROL IN
INDUCTIVE LOADS
Abstract of the Disclosure A DC current control is provided for inductive loads which achieves high energy efficiency even though the supply voltage may be subject to considerable variations.
The inductive load may be a DC motor, a solenoid, or similar device. The electric power is applied directly to the inductive load through a switching means which closes the circuit to apply a charging current to the inductive load for fixed on periods of time.
A discharge path is provided for the inductive load when the switching means opens the charging circuit.
The discharge current is monitored, and when it decays to a selected value, the switching means is again closed for the fixed on charge time.
Description
~7;~5~3 13130:CRH
DIRECT CURRENT CONTROL IN
INDUCTIVE LOADS
Background of the Invention 1. Field of the Invention This invention relates to methods and apparatus for controlling the current in ,an inductive device from a source of direct current electric power with high energy efficiency, even though the supply voltage from the source may be subject to conæiderable variations.
DIRECT CURRENT CONTROL IN
INDUCTIVE LOADS
Background of the Invention 1. Field of the Invention This invention relates to methods and apparatus for controlling the current in ,an inductive device from a source of direct current electric power with high energy efficiency, even though the supply voltage from the source may be subject to conæiderable variations.
2.~ The Prior Art The presently existing techniques for controlling the DC current in an inductive device may be placed in three major classes as follows:
a) Varying the Effective ~oltage at the Load This technique makes use of the relation-ship that the current, through a fixed resistance, is directly proportional to the voltage applied. The voltage applied to the load is monitored and the power source is directly or indirectly adjusted to maintain the required voltage. ~irect control of the power source (e.g. adjust-ing the current in the field winding of a generator) is most often impractical or impossible. Indirect control is accomplished by placing some form of electronic voltage 1~ 735(~3 13130:CRII -2-1 regulator between the power source and the load. A series type regulator allows for rapid and precise control of the applied voltage but often dissipates 60~ - 90~ of the supplied power. A switching type regulator normally dis-sipates less than 20% of the supplied power but suffersfrom slow response to step changes in output voltage re-quirements. The power inductors and the filter capacitors are often exotic and bulky for high current applications, although this is offset by the reduced needs of heat sinks.
A limitation of using voltage control to set the current in the load is if the load resistance changes (within one unit or from unit to unit), the current will chanc,~e in inverse proportion since the feedback circuits that are usually employed have no means of detecting this change of resistance.
b) Passively Limiting the Current Through the Load This technique makes use of the relationship that current is inversely proportional to rosistance with a constant applied voltage. Although the least energy efficient of the three techniques, this approach is most commonly used due to its simplicity. A resistor is in-stalled between the load and the power source. The value of the resistor is chosen such that the combined series resistance of the control resistor and the load limit the current to the desired value. If different values of currents are needed in one application, different resistor values are installed in the circuit via mechanical or electronic switches. This approach suffers several serious setbacks. Load resistance changes will change the load current, although not to the same extent as with voltage control. The resistor will dissipate as much or more power than a series regulator does (it is in fact a very simple series regulator). The most important limitation occurs when the supply voltage varies~
3S~g3 13L30:CRI-1 -3-1 Since the resistance value of the load and control resistor combination remains constant, the supplied load current will vary proportionally with the supply voltage. This lack of regulation can be intolerable in most situations. This approach is also lacking in energy and volume efficiencies. The resistor value is designed to produce the desired current at the minimum supplied voltage. As the voltage increases, the supplied current increases proportionately. The power dissipation, however, increases according to the square of the current change (e.g., a doubling of the input voltage doubles the current, but the power dissipation increase by four times). The resistor, then must be of a power rating to withstand the stresses at the maximum voltage.
c) Active~ Limiting the Current Through the Load In this technique" an active device (e.g., a transistor) is used to limit the current ~upplied to the load. A current sensing element (e.g., a resistor) is placed in series with the load and the voltage across this element is monitored. The control device is then set via electrondcs to adjust its effective resistance to limit the current to the desired amount. This system has merits in that the supplied current remains constant whether the load resistance changes or the input voltage varies. The power dissipation is similar to that of a series pass regulator. If the current range required is large, the sensing element may present a problem. A value that develops sufficient feedback voltage at low currents may be too large to allow the high end of the current range to be used at minimum supply voltage (too much resistance in the line).
~'7;~ `3 Summary of the Invention In accordance with the present invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a.) an inductor for supplying elecromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor, (c) means for actuating said switching means to apply electric current from the source to the inductor for predetermined fixed periods of time during all charging cycles, so that the charging cycles are of fixed time duration irrespective of changes in the load or of changes in the voltage of the source of direct current power, (d) means for discharging electric current from the inductor during periods of time constituting discharging cycles intermediate the charging cycles, and (e) sensing means responsive to the electric current which is discharged from the inductor during each discharging cycle for actuating said switching means to apply electric current from the source to the inductor to initiate a charge cycle and to terminate each discharge cycle when the electric current which is discharged from the inductor during discharge cycles decays to a predetermined value.
Also in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
- 4a 5~3 (a) an inductive device for supplying electromagnetic energy to a mechanical device, (b) means for applying electric current from the source to the inductive device periodically for fixed period of time during all charging cycles irrespect ve of changes in the electric power consumed by the inductive device or of changes in the voltage of the source of direct current power, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means including a freewheeling diode for discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and (d) control means responsive to the electric current which is discharged from the inductive device during each discharge cycle, for initiating charging cycles and discharging cycles alternately, with each charging cycle being initiated when the current which is discharged from the inductive device decays to a value that is substantially equal to the initial value of the electric current at the beginning of a charge cycle.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load in which the electric power is to be dissipated by transfer of the electromagnetic energy in the load to a mechanical device, - 4b 3S~3 (b) switching means for applying electric current from the source to the inductive load periodically for predetermined fixed periods of time during all charging cycles regardless of the duty cycle caused by changes in the operating conditions, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means for discharging electric current from the inductive load through a sensing resistor.
(d) means responsive to the current that is discharged from the inductive load through the sensing resistor for actuating said switching means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharing cycle when the electric current which is discharged from the inductive load decays to a value that is substantially equal to said initial value of the electric current at the beginning of a charge cycle.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load (b) control means for applying electric current from the source to the inductive load, (c) said control means providing uniform charging cycles of fixed periods of time for all operating conditions for applying energy to the inductive load and discharging cycles during which electric current is discharged from the inductive ~[} , - 4c - 1~'73~3 load and no energy is provided to the inductive load from sources other than the discharge current, with the charging cycles being of less time duration than the duration of the discharging cycles, and (d) sensing means responsive to said discharge current for actuating said control means to apply electric current rrom the source to the inductive load to initiate a charging cycle and terminate a discharging cycle when the electric current which is discharged from the inductive load decays to a predetermined value.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power to an inductor comprising:
(a) an inductor for supplying electromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor during charging cycles, ~ c) means for discharging electric current from the inductor during discharging cycles when power is not supplied through the switching means to the inductor, (d) means for providing a reference signal representative of the desired amount of current to be applied to the inductor, (e) means for providing a control signal that varies in accordance with the decay of the current which is discharged from the inductor during discharge cycles, and (f) control means responsive to said reference and r - 4d - .
S~I! 3 control signals for actuating the switching means for fixed period of time under all operating conditions to initiate charging cycles when said control signal decays to a predetermined value with respect to the reference signal.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power to an electric motor having inductive windings for receiving direct current power comprising:
(a) switching means for supplying power from the source of direct current power to the inductive windings of the electric motor, (b) means for actuating said switching means to apply electric current from the source to said inductive windings for predetermined fixed period of time during charging cycles, under all operating conditions, (c) means for discharging electric current from said inductive windings during period of time constituting discharging cycles intermediate the charging cycles, (d) means for sensing the decay of the electric current from said inductive windings during discharging cycles to provide a first control signal, (e) means for sensing the speed of rotation of the electric motor to provide a second control signal, and (f) control means responsive to said first and second control signals for initiating charge cycles and terminating discharge cycles when said control signals have a predetermined relationship.
- . . . .
- 4e ~7~3S~3 Further in accordance with the invention there is provided a method of controlling the flow of current from a source of direct current electric power to an inductive device for supplying electromagentic energy to a mechanical device compr:ising applying electric current from the source to the inductive device periodically for fixed periods of time for all operating conditions during charging cycles in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and terminating each discharge cycle and decays during the discharge cycle to a predetermined value.
Further in accordance with the invention there is provided a method of supplying energy from an inductive device to a mechanical device comprising causing the inductive device to apply electromagnetic energy to the mechanical device during charging cycles when the inductive device is energised from a source of direct current power, causing the inductive device to apply electromagnetic energy to the mechanical device during discharge cycles when the inductive device is discharged by applying current through a discharge path, and initiating charging cycles and discharging cycles alternately, with each charging cycle having a fixed period of time for all operating conditions which is intitated when the current which is discharged from the inductive device decays to a predetermined value.
- 4f ~.7~S~?3 Efficient direct current control in an inductive load is achieved in the present invention by applying the electric power directly to the inductive load element through a switching means which closes the circuit to apply a charging current to the inductive load for fixed on periods of time. A discharge path is provided for the inductive load when the switching means opens the charging circuit. In the preferred embodiment the discharge path comprises a freewheel diode and a resistor connected across the inductive load. The current in the discharge path is monitored, and when the ~73S~P3 - 4g clischarge current has decayed to a selected value, the switching means is again closed for the fixed on charge time.
Since the electric power is applied directly to the load element with very little loss in the control circuitry, substantially all of the electric power is dissipated in the inductive load itself. The electromagnetic energy which is stored in the inductive load may be employed to actuate a mechanical device, such as a solenoid or motor.
1~ 73SC~3 13130:CR~ 5-1 _ ief Descri~tion of the Drawings FIG. 1 illustrates the principles upon which the present invention are based, FIG. 2 is a diagram which illustrates the broad concept of the invention, FIG. 3 shows the idealized waveforms for the apparatus of Fig. 2, FIG. 4 shows the circuit of a type ~airchild 78S40 integrated circuit, FIG. 5 shows how the circuit of Fig. 4 may be em-ployed to provide the switching action, FIG. 6 shows how the circuit of Fig. 4 may be em-ployed to provide the switching action for applying higher power to an inductive load, FIG. 7 shows how the circuit of Fig. 6 may be em-ployed to provide the switching action for a solenoid, and FIG. 8 illustrates how the invention may be employed to control a DC motor.
:1~'73S~)3 13130:CRI~ -6-1 _escription of the Preferred Embodiments Eig. l(A) shows an inductor L placed in a series circuit with a swi~ch SWl and power source VIN. The free-wheel diode Dl or other unidirectional conductor for electric current is used to provide an alternate current path for the inductor when SWl is opened. Assuming no initial currents, the following holds true when SWl is closed:
VL L di (1) rt iL = L ~ VL dt (2) Due to the series circuit, when SWl is closed VL = VIN and is constant. Therefore, Equation (2) becomes:
. .
iL = LL t (3) Complications set in when one realizes that real-life inducto~s exhibit a finite resistance RL as illustrated in Fig. l(B). As current starts to flow, this resistance drops part of the voltage VRL, leaving a lower value for the inductance. Eventually VRL will equal VIN and the current will remain at a constant value. Solving equation (2) for this condition yields the standard charge curve:
iL = V~L~ (1 - e L ) (4) If the time period that iL is examined is short in relation to the time constant L/RL equation (4) can be approximated:
iL = Io + VIN Io RL t t2 ~ tl 1~73S~3 13130:CRII -7-1 where Io~ is the current at the start of the period t2 - t and t is a relative time from tl to t2. The current now appears to be a series of linear ramps with slopes dependent upon the current present in the inductor.
When SWl is opened, the inductance opposes any change in current and will develop a sourcing potential (back EMF
or inductive kick) to maintain the current. Since the coil voltage changes polarity, Dl conducts. Assuming a perfect diode, the inductor voltage and current become:
RL
VL = Io RL e L t ~6) RL
iL = I e L (7) where Io is the current through the inductor at the time the switch is opened.
As~with the charging current, if the change in dis-charge current examined is small in relation to the current value, the discharge current curve portion can be approxi-mated:
iL = Il - L t ¦ 2 tl (8) where Il is the current at the start of the period t2 - tl.
1~L7~5~3 13130:CRH -8-1 Fig. l(C) shows how the invention can be practiced using a switch SW2 in the place of the diode Dl. When SWl is closed to provide the charging current SW2 is open, and when SWl is open SW2 is closed to provide the discharge path.
The charging cycles to to tl will be of less duration than the discharge cycles tl to t2. In order to obtain more constant regulation, the charging cycle should be very short, e.g., 200 microseconds.
The present invention operates on the above-outlined principles as illustrated in broad concept in Figs. 2 and 3.
The switch SWl is turned on and off by a switch control circuit 20. A resistor Rs is employed in the dis-charge current leg to provide a control voltage Vs to the control circuit which compares Vs to a preset reference voltage VR and actuates SWl when Vs is equal to VR
The switch SWl is turned on for fixed periods of time to to tl. It is turned off for variable periods of time tl to t2 which are determined by the time required for the IR drops across Rs to equal VR.
In operation, a known current Io is established and flows i4 the inductor L when SWl is closed at time tO. The switch is opened after a brief fixed time tl. At this time the inductor current has reached a value Il. The current in the inductor-diode loop is monitored, and when the current has decayed bacX to the value of Io at time t2, the switch is closed again for the fixed charge time. This cycle is then repeated.
In order to avoid unwanted resistance during the charge time, decay current sensing is done in the diode leg of the circuit. If the time period tl - to is kept short, the effective current in the inductor is Io~
Fig. 3 shows idealized current waveforms for the inductor and the switch of Fig. 2. If the charge time tl - to is short enough to keep the current change Il - Io 1~l73S~)3 13130:CR~ -9-1 srnall compared to Io~ the inductor current is essentially a fixed DC value. The average supply current effectively becomes:
IIN Io tl - to o or the inductor current times the duty cycle (ratio of on time to cycle time). The duty cycle can be approximated (ignoring sense resistor loss):
tl - to Io~ (10) t2 _ to VIN
The system in Fig. 2 achieves the desired results in control~ing DC currents in inductive loads. The current in the coil is maintained by means of charge and discharge cycles, the circuit losses are minimized because the control element operates in a switching mode, and current sensing does not interfere with the main current source path. The current from the source VIN is applied directly to the load inductor L during the charge cycle to provide power efficiently, and the current produced by the inductor during the discharge cycle is also emloyed for efficiency.
The energy that is stored in the inductance provides an efficiency that is not produced by the prior art devices.
RS has small resistance so that little power is lost in developing Vs. No capacitive element is used in developing VS because immediate response is needed, and all of the 1~'73S(~3 13130:CR~T -10-1 stored engergy should be in the inductance.
The switch control circuit 20 may be a standard commercially available integrated circuit for switch regu-lation, such as the Fairchild 78S40, the Texas Instruments TI 497, or the 1524 or 3524 that are available from multiple sources. Such circuits may be connected to drive a transistor switch, sense the voltage drop across the current sense resistor RS and control the off time until the preset reference level VR is reached.
Fig. 4 shows the circuit of the Fairchild 78S40.
It comprises a fixed on period switching regulator, a voltage reference source, and an uncommitted operational amplifier. The on time is controlled by the capacitance Ct .
Fig. 5 shows the regulator of Fig. 4 in a circuit for controlling the current in an inductive load. This circuit can be used only if the input voltage and load currents are within the operational limits of the regulator. In Fig. 5 the operational amplifier is used to correct the polarity of the current sense signal (from negative-going to positive-going) and adjust the effective value prèsented to the ~egulator comparator (at the setpoint current the voltage output of the amplifier will equal VR). Ct is chosen to give an on-time consistent with the load time constant (L/R) and the response times of the switch, amplifier, and comparator. For a varied current output, VR would be varied.
Fig. 6 shows a similar current regulator for use with higher voltage and load current requirements. A
separate switch circuit (Ql~ Q2, Q3) was used because the input voltage and load currents of this system exceeded the operational limits of the 7~3S40. Rx was added to allow for electronic system turn-off. When the ON/OFF line is open, +V forces the output of the sense amplifier Al to always exceed VR, thus keeping the regulator from turning 1~735~3 13130:C~II -11-1 on. When the ON/OFF line is shorted to ground, the circuit operates in the normal mode. Ct was chosen at .01 ~ f to allow a 200 ~sec on time, which i5 considerably smaller than the typical time constant of the chosen load (100 msec min.) but still slow enough to allow adequate operation of Al and the switch system.
Several DC solenoids were used as loads. The circuit controlled the currents at the desired value regardless of the type of solenoid used or the nominal voltage rating of the solenoid used. Ct was varied in order to determine the change of efficiency resulting. Better circuit effi-ciency was noticed as the on time was decreased until the operational speeds of the amplifier and switch were reached.
The principle requirements of a solenoid driver are lS a high-current drive to move the plunger and, once the plunger has completed its travel, reduce the current to a much lower value that is suffi~ient to hold the plunger in place. Current practice is to apply the entire source supply across the solenoid for the time needed to move the solenoid. ~7hen this time is passed (either a fixed time period or plunger motion sensed by some device), à load reducti~n device (typically a resistor) is switched into the circuit (e.g., Patent No. 3,766,432).
Fig. 7 shows a solenoid driver using the current driver of Figure 6. When the "OPEN" signal is applied to Q4, Q6 is turned on (allowing the regulator to operate).
Also the one-shot multivibrator OSl is fired for a fixed period of time turning Q5 off during this time period.
This applies the entire +V to VR of the regulator (via RA) and the RF/ RI feedback ratio in the driver sets the value of the high pull-in current. The one-shot multi-vibrator is reset by an external plunger motion sensing system 30 having a switch which is closed when the solenoid is energized and moves its armature 31 upwardly. When the one-shot time is reset Q5 turns on.~ This action reduces 1~'735~3 13130:CR~l -12-1 VR by the resistance ratio of RB/(RA + RB). ~7ith a lower reference voltage to meet, the regulator reduces the output current by the same ratio so that Vs is substantially equal to VR, thus deriving the required holding current.
~hen the "OPEN" signal is removed, Q6 is turned off preventing the regulator from supplying any current to the solenoid.
The circuit of Fig. 7 is particularly suitable for use in well logging during the drilling operation for the well, where the power for operating the solenoid is obtained from a turbine generator that is actuated by the flow of mud used in the drilling operation. In such applications the voltage VIN may vary from 48 to 96 volts so that good regulation is essential in order to obtain substantially constant current for actuating the solenoid. It is essential that overheating caused by the electric circuitry be avoided, and the efficiency ,of the apparatus of this invention satisfies that requirement.
Fig. 8 illustrates the application of the current controller to operate a DC motor.
A RPM sensor 40 provides a voltage that is propor-tional t~ the speed of rotation of the DC motor 42. The sensor 40 may be a tachometer or an encoding disk. A
RPM set 44 serves to provide a voltage representative of the desired speed of rotation, and that may be adjustable if desired.
The outputs of RP~ sensor 40 and RPM set 44 are applied to a comparing amplifier 46 and the resultant control signal VR is applied to constant current driver of the general type discussed above with reference to Figs. 6 or 7 which supplies a regulated current to the motor 42.
In this circuit, not only are the efficiencies of the current regulator attained, but only the power needed to maintain the requested speed is applied to the motor, there-1~'7;~S~3 13130:CRH -13-1 by providing a very efficient means of controlling a DC
motor that is not achieved by the prior art.
The DC motor control arrangement is especially suitable for use in electric vehicles that are battery powered because the efficiency of the circuit serves to conserve the power of the batteries. With such an arrangement, the vehicle can travel farther between charges than vehicles using other existing circuit arrangements.
The preferred embodiments employ a freewheeling diode or other unidirectional conductor means to pro-vide the discharge path for the inductive load. However,a switching means electronically controlled by the control circuits may be employed to provide the discharge path, as illustrated in Fig. l(C).
a) Varying the Effective ~oltage at the Load This technique makes use of the relation-ship that the current, through a fixed resistance, is directly proportional to the voltage applied. The voltage applied to the load is monitored and the power source is directly or indirectly adjusted to maintain the required voltage. ~irect control of the power source (e.g. adjust-ing the current in the field winding of a generator) is most often impractical or impossible. Indirect control is accomplished by placing some form of electronic voltage 1~ 735(~3 13130:CRII -2-1 regulator between the power source and the load. A series type regulator allows for rapid and precise control of the applied voltage but often dissipates 60~ - 90~ of the supplied power. A switching type regulator normally dis-sipates less than 20% of the supplied power but suffersfrom slow response to step changes in output voltage re-quirements. The power inductors and the filter capacitors are often exotic and bulky for high current applications, although this is offset by the reduced needs of heat sinks.
A limitation of using voltage control to set the current in the load is if the load resistance changes (within one unit or from unit to unit), the current will chanc,~e in inverse proportion since the feedback circuits that are usually employed have no means of detecting this change of resistance.
b) Passively Limiting the Current Through the Load This technique makes use of the relationship that current is inversely proportional to rosistance with a constant applied voltage. Although the least energy efficient of the three techniques, this approach is most commonly used due to its simplicity. A resistor is in-stalled between the load and the power source. The value of the resistor is chosen such that the combined series resistance of the control resistor and the load limit the current to the desired value. If different values of currents are needed in one application, different resistor values are installed in the circuit via mechanical or electronic switches. This approach suffers several serious setbacks. Load resistance changes will change the load current, although not to the same extent as with voltage control. The resistor will dissipate as much or more power than a series regulator does (it is in fact a very simple series regulator). The most important limitation occurs when the supply voltage varies~
3S~g3 13L30:CRI-1 -3-1 Since the resistance value of the load and control resistor combination remains constant, the supplied load current will vary proportionally with the supply voltage. This lack of regulation can be intolerable in most situations. This approach is also lacking in energy and volume efficiencies. The resistor value is designed to produce the desired current at the minimum supplied voltage. As the voltage increases, the supplied current increases proportionately. The power dissipation, however, increases according to the square of the current change (e.g., a doubling of the input voltage doubles the current, but the power dissipation increase by four times). The resistor, then must be of a power rating to withstand the stresses at the maximum voltage.
c) Active~ Limiting the Current Through the Load In this technique" an active device (e.g., a transistor) is used to limit the current ~upplied to the load. A current sensing element (e.g., a resistor) is placed in series with the load and the voltage across this element is monitored. The control device is then set via electrondcs to adjust its effective resistance to limit the current to the desired amount. This system has merits in that the supplied current remains constant whether the load resistance changes or the input voltage varies. The power dissipation is similar to that of a series pass regulator. If the current range required is large, the sensing element may present a problem. A value that develops sufficient feedback voltage at low currents may be too large to allow the high end of the current range to be used at minimum supply voltage (too much resistance in the line).
~'7;~ `3 Summary of the Invention In accordance with the present invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a.) an inductor for supplying elecromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor, (c) means for actuating said switching means to apply electric current from the source to the inductor for predetermined fixed periods of time during all charging cycles, so that the charging cycles are of fixed time duration irrespective of changes in the load or of changes in the voltage of the source of direct current power, (d) means for discharging electric current from the inductor during periods of time constituting discharging cycles intermediate the charging cycles, and (e) sensing means responsive to the electric current which is discharged from the inductor during each discharging cycle for actuating said switching means to apply electric current from the source to the inductor to initiate a charge cycle and to terminate each discharge cycle when the electric current which is discharged from the inductor during discharge cycles decays to a predetermined value.
Also in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
- 4a 5~3 (a) an inductive device for supplying electromagnetic energy to a mechanical device, (b) means for applying electric current from the source to the inductive device periodically for fixed period of time during all charging cycles irrespect ve of changes in the electric power consumed by the inductive device or of changes in the voltage of the source of direct current power, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means including a freewheeling diode for discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and (d) control means responsive to the electric current which is discharged from the inductive device during each discharge cycle, for initiating charging cycles and discharging cycles alternately, with each charging cycle being initiated when the current which is discharged from the inductive device decays to a value that is substantially equal to the initial value of the electric current at the beginning of a charge cycle.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load in which the electric power is to be dissipated by transfer of the electromagnetic energy in the load to a mechanical device, - 4b 3S~3 (b) switching means for applying electric current from the source to the inductive load periodically for predetermined fixed periods of time during all charging cycles regardless of the duty cycle caused by changes in the operating conditions, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means for discharging electric current from the inductive load through a sensing resistor.
(d) means responsive to the current that is discharged from the inductive load through the sensing resistor for actuating said switching means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharing cycle when the electric current which is discharged from the inductive load decays to a value that is substantially equal to said initial value of the electric current at the beginning of a charge cycle.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load (b) control means for applying electric current from the source to the inductive load, (c) said control means providing uniform charging cycles of fixed periods of time for all operating conditions for applying energy to the inductive load and discharging cycles during which electric current is discharged from the inductive ~[} , - 4c - 1~'73~3 load and no energy is provided to the inductive load from sources other than the discharge current, with the charging cycles being of less time duration than the duration of the discharging cycles, and (d) sensing means responsive to said discharge current for actuating said control means to apply electric current rrom the source to the inductive load to initiate a charging cycle and terminate a discharging cycle when the electric current which is discharged from the inductive load decays to a predetermined value.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power to an inductor comprising:
(a) an inductor for supplying electromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor during charging cycles, ~ c) means for discharging electric current from the inductor during discharging cycles when power is not supplied through the switching means to the inductor, (d) means for providing a reference signal representative of the desired amount of current to be applied to the inductor, (e) means for providing a control signal that varies in accordance with the decay of the current which is discharged from the inductor during discharge cycles, and (f) control means responsive to said reference and r - 4d - .
S~I! 3 control signals for actuating the switching means for fixed period of time under all operating conditions to initiate charging cycles when said control signal decays to a predetermined value with respect to the reference signal.
Further in accordance with the invention there is provided a current regulator for controlling the flow of current from a source of direct current power to an electric motor having inductive windings for receiving direct current power comprising:
(a) switching means for supplying power from the source of direct current power to the inductive windings of the electric motor, (b) means for actuating said switching means to apply electric current from the source to said inductive windings for predetermined fixed period of time during charging cycles, under all operating conditions, (c) means for discharging electric current from said inductive windings during period of time constituting discharging cycles intermediate the charging cycles, (d) means for sensing the decay of the electric current from said inductive windings during discharging cycles to provide a first control signal, (e) means for sensing the speed of rotation of the electric motor to provide a second control signal, and (f) control means responsive to said first and second control signals for initiating charge cycles and terminating discharge cycles when said control signals have a predetermined relationship.
- . . . .
- 4e ~7~3S~3 Further in accordance with the invention there is provided a method of controlling the flow of current from a source of direct current electric power to an inductive device for supplying electromagentic energy to a mechanical device compr:ising applying electric current from the source to the inductive device periodically for fixed periods of time for all operating conditions during charging cycles in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and terminating each discharge cycle and decays during the discharge cycle to a predetermined value.
Further in accordance with the invention there is provided a method of supplying energy from an inductive device to a mechanical device comprising causing the inductive device to apply electromagnetic energy to the mechanical device during charging cycles when the inductive device is energised from a source of direct current power, causing the inductive device to apply electromagnetic energy to the mechanical device during discharge cycles when the inductive device is discharged by applying current through a discharge path, and initiating charging cycles and discharging cycles alternately, with each charging cycle having a fixed period of time for all operating conditions which is intitated when the current which is discharged from the inductive device decays to a predetermined value.
- 4f ~.7~S~?3 Efficient direct current control in an inductive load is achieved in the present invention by applying the electric power directly to the inductive load element through a switching means which closes the circuit to apply a charging current to the inductive load for fixed on periods of time. A discharge path is provided for the inductive load when the switching means opens the charging circuit. In the preferred embodiment the discharge path comprises a freewheel diode and a resistor connected across the inductive load. The current in the discharge path is monitored, and when the ~73S~P3 - 4g clischarge current has decayed to a selected value, the switching means is again closed for the fixed on charge time.
Since the electric power is applied directly to the load element with very little loss in the control circuitry, substantially all of the electric power is dissipated in the inductive load itself. The electromagnetic energy which is stored in the inductive load may be employed to actuate a mechanical device, such as a solenoid or motor.
1~ 73SC~3 13130:CR~ 5-1 _ ief Descri~tion of the Drawings FIG. 1 illustrates the principles upon which the present invention are based, FIG. 2 is a diagram which illustrates the broad concept of the invention, FIG. 3 shows the idealized waveforms for the apparatus of Fig. 2, FIG. 4 shows the circuit of a type ~airchild 78S40 integrated circuit, FIG. 5 shows how the circuit of Fig. 4 may be em-ployed to provide the switching action, FIG. 6 shows how the circuit of Fig. 4 may be em-ployed to provide the switching action for applying higher power to an inductive load, FIG. 7 shows how the circuit of Fig. 6 may be em-ployed to provide the switching action for a solenoid, and FIG. 8 illustrates how the invention may be employed to control a DC motor.
:1~'73S~)3 13130:CRI~ -6-1 _escription of the Preferred Embodiments Eig. l(A) shows an inductor L placed in a series circuit with a swi~ch SWl and power source VIN. The free-wheel diode Dl or other unidirectional conductor for electric current is used to provide an alternate current path for the inductor when SWl is opened. Assuming no initial currents, the following holds true when SWl is closed:
VL L di (1) rt iL = L ~ VL dt (2) Due to the series circuit, when SWl is closed VL = VIN and is constant. Therefore, Equation (2) becomes:
. .
iL = LL t (3) Complications set in when one realizes that real-life inducto~s exhibit a finite resistance RL as illustrated in Fig. l(B). As current starts to flow, this resistance drops part of the voltage VRL, leaving a lower value for the inductance. Eventually VRL will equal VIN and the current will remain at a constant value. Solving equation (2) for this condition yields the standard charge curve:
iL = V~L~ (1 - e L ) (4) If the time period that iL is examined is short in relation to the time constant L/RL equation (4) can be approximated:
iL = Io + VIN Io RL t t2 ~ tl 1~73S~3 13130:CRII -7-1 where Io~ is the current at the start of the period t2 - t and t is a relative time from tl to t2. The current now appears to be a series of linear ramps with slopes dependent upon the current present in the inductor.
When SWl is opened, the inductance opposes any change in current and will develop a sourcing potential (back EMF
or inductive kick) to maintain the current. Since the coil voltage changes polarity, Dl conducts. Assuming a perfect diode, the inductor voltage and current become:
RL
VL = Io RL e L t ~6) RL
iL = I e L (7) where Io is the current through the inductor at the time the switch is opened.
As~with the charging current, if the change in dis-charge current examined is small in relation to the current value, the discharge current curve portion can be approxi-mated:
iL = Il - L t ¦ 2 tl (8) where Il is the current at the start of the period t2 - tl.
1~L7~5~3 13130:CRH -8-1 Fig. l(C) shows how the invention can be practiced using a switch SW2 in the place of the diode Dl. When SWl is closed to provide the charging current SW2 is open, and when SWl is open SW2 is closed to provide the discharge path.
The charging cycles to to tl will be of less duration than the discharge cycles tl to t2. In order to obtain more constant regulation, the charging cycle should be very short, e.g., 200 microseconds.
The present invention operates on the above-outlined principles as illustrated in broad concept in Figs. 2 and 3.
The switch SWl is turned on and off by a switch control circuit 20. A resistor Rs is employed in the dis-charge current leg to provide a control voltage Vs to the control circuit which compares Vs to a preset reference voltage VR and actuates SWl when Vs is equal to VR
The switch SWl is turned on for fixed periods of time to to tl. It is turned off for variable periods of time tl to t2 which are determined by the time required for the IR drops across Rs to equal VR.
In operation, a known current Io is established and flows i4 the inductor L when SWl is closed at time tO. The switch is opened after a brief fixed time tl. At this time the inductor current has reached a value Il. The current in the inductor-diode loop is monitored, and when the current has decayed bacX to the value of Io at time t2, the switch is closed again for the fixed charge time. This cycle is then repeated.
In order to avoid unwanted resistance during the charge time, decay current sensing is done in the diode leg of the circuit. If the time period tl - to is kept short, the effective current in the inductor is Io~
Fig. 3 shows idealized current waveforms for the inductor and the switch of Fig. 2. If the charge time tl - to is short enough to keep the current change Il - Io 1~l73S~)3 13130:CR~ -9-1 srnall compared to Io~ the inductor current is essentially a fixed DC value. The average supply current effectively becomes:
IIN Io tl - to o or the inductor current times the duty cycle (ratio of on time to cycle time). The duty cycle can be approximated (ignoring sense resistor loss):
tl - to Io~ (10) t2 _ to VIN
The system in Fig. 2 achieves the desired results in control~ing DC currents in inductive loads. The current in the coil is maintained by means of charge and discharge cycles, the circuit losses are minimized because the control element operates in a switching mode, and current sensing does not interfere with the main current source path. The current from the source VIN is applied directly to the load inductor L during the charge cycle to provide power efficiently, and the current produced by the inductor during the discharge cycle is also emloyed for efficiency.
The energy that is stored in the inductance provides an efficiency that is not produced by the prior art devices.
RS has small resistance so that little power is lost in developing Vs. No capacitive element is used in developing VS because immediate response is needed, and all of the 1~'73S(~3 13130:CR~T -10-1 stored engergy should be in the inductance.
The switch control circuit 20 may be a standard commercially available integrated circuit for switch regu-lation, such as the Fairchild 78S40, the Texas Instruments TI 497, or the 1524 or 3524 that are available from multiple sources. Such circuits may be connected to drive a transistor switch, sense the voltage drop across the current sense resistor RS and control the off time until the preset reference level VR is reached.
Fig. 4 shows the circuit of the Fairchild 78S40.
It comprises a fixed on period switching regulator, a voltage reference source, and an uncommitted operational amplifier. The on time is controlled by the capacitance Ct .
Fig. 5 shows the regulator of Fig. 4 in a circuit for controlling the current in an inductive load. This circuit can be used only if the input voltage and load currents are within the operational limits of the regulator. In Fig. 5 the operational amplifier is used to correct the polarity of the current sense signal (from negative-going to positive-going) and adjust the effective value prèsented to the ~egulator comparator (at the setpoint current the voltage output of the amplifier will equal VR). Ct is chosen to give an on-time consistent with the load time constant (L/R) and the response times of the switch, amplifier, and comparator. For a varied current output, VR would be varied.
Fig. 6 shows a similar current regulator for use with higher voltage and load current requirements. A
separate switch circuit (Ql~ Q2, Q3) was used because the input voltage and load currents of this system exceeded the operational limits of the 7~3S40. Rx was added to allow for electronic system turn-off. When the ON/OFF line is open, +V forces the output of the sense amplifier Al to always exceed VR, thus keeping the regulator from turning 1~735~3 13130:C~II -11-1 on. When the ON/OFF line is shorted to ground, the circuit operates in the normal mode. Ct was chosen at .01 ~ f to allow a 200 ~sec on time, which i5 considerably smaller than the typical time constant of the chosen load (100 msec min.) but still slow enough to allow adequate operation of Al and the switch system.
Several DC solenoids were used as loads. The circuit controlled the currents at the desired value regardless of the type of solenoid used or the nominal voltage rating of the solenoid used. Ct was varied in order to determine the change of efficiency resulting. Better circuit effi-ciency was noticed as the on time was decreased until the operational speeds of the amplifier and switch were reached.
The principle requirements of a solenoid driver are lS a high-current drive to move the plunger and, once the plunger has completed its travel, reduce the current to a much lower value that is suffi~ient to hold the plunger in place. Current practice is to apply the entire source supply across the solenoid for the time needed to move the solenoid. ~7hen this time is passed (either a fixed time period or plunger motion sensed by some device), à load reducti~n device (typically a resistor) is switched into the circuit (e.g., Patent No. 3,766,432).
Fig. 7 shows a solenoid driver using the current driver of Figure 6. When the "OPEN" signal is applied to Q4, Q6 is turned on (allowing the regulator to operate).
Also the one-shot multivibrator OSl is fired for a fixed period of time turning Q5 off during this time period.
This applies the entire +V to VR of the regulator (via RA) and the RF/ RI feedback ratio in the driver sets the value of the high pull-in current. The one-shot multi-vibrator is reset by an external plunger motion sensing system 30 having a switch which is closed when the solenoid is energized and moves its armature 31 upwardly. When the one-shot time is reset Q5 turns on.~ This action reduces 1~'735~3 13130:CR~l -12-1 VR by the resistance ratio of RB/(RA + RB). ~7ith a lower reference voltage to meet, the regulator reduces the output current by the same ratio so that Vs is substantially equal to VR, thus deriving the required holding current.
~hen the "OPEN" signal is removed, Q6 is turned off preventing the regulator from supplying any current to the solenoid.
The circuit of Fig. 7 is particularly suitable for use in well logging during the drilling operation for the well, where the power for operating the solenoid is obtained from a turbine generator that is actuated by the flow of mud used in the drilling operation. In such applications the voltage VIN may vary from 48 to 96 volts so that good regulation is essential in order to obtain substantially constant current for actuating the solenoid. It is essential that overheating caused by the electric circuitry be avoided, and the efficiency ,of the apparatus of this invention satisfies that requirement.
Fig. 8 illustrates the application of the current controller to operate a DC motor.
A RPM sensor 40 provides a voltage that is propor-tional t~ the speed of rotation of the DC motor 42. The sensor 40 may be a tachometer or an encoding disk. A
RPM set 44 serves to provide a voltage representative of the desired speed of rotation, and that may be adjustable if desired.
The outputs of RP~ sensor 40 and RPM set 44 are applied to a comparing amplifier 46 and the resultant control signal VR is applied to constant current driver of the general type discussed above with reference to Figs. 6 or 7 which supplies a regulated current to the motor 42.
In this circuit, not only are the efficiencies of the current regulator attained, but only the power needed to maintain the requested speed is applied to the motor, there-1~'7;~S~3 13130:CRH -13-1 by providing a very efficient means of controlling a DC
motor that is not achieved by the prior art.
The DC motor control arrangement is especially suitable for use in electric vehicles that are battery powered because the efficiency of the circuit serves to conserve the power of the batteries. With such an arrangement, the vehicle can travel farther between charges than vehicles using other existing circuit arrangements.
The preferred embodiments employ a freewheeling diode or other unidirectional conductor means to pro-vide the discharge path for the inductive load. However,a switching means electronically controlled by the control circuits may be employed to provide the discharge path, as illustrated in Fig. l(C).
Claims (13)
1. A current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductor for supplying elecromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor, (c) means for actuating said switching means to apply electric current from the source to the inductor for predetermined fixed periods of time during all charging cycles, so that the charging cycles are of fixed time duration irrespective of changes in the load or of changes in the voltage of the source of direct current power, (d) means for discharging electric current from the inductor during periods of time constituting discharging cycles intermediate the charging cycles, and (e) sensing means responsive to the electric current which is discharged from the inductor during each discharging cycle for actuating said switching means to apply electric current from the source to the inductor to initiate a charge cycle and to terminate each discharge cycle when the electric current which is discharged from the inductor during discharge cycles decays to a predetermined value.
(a) an inductor for supplying elecromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor, (c) means for actuating said switching means to apply electric current from the source to the inductor for predetermined fixed periods of time during all charging cycles, so that the charging cycles are of fixed time duration irrespective of changes in the load or of changes in the voltage of the source of direct current power, (d) means for discharging electric current from the inductor during periods of time constituting discharging cycles intermediate the charging cycles, and (e) sensing means responsive to the electric current which is discharged from the inductor during each discharging cycle for actuating said switching means to apply electric current from the source to the inductor to initiate a charge cycle and to terminate each discharge cycle when the electric current which is discharged from the inductor during discharge cycles decays to a predetermined value.
2. A current regulator as claimed in claim 1, wherein the means for discharging electric current from the inductor is a unidirectional conductive device.
3. A current regulator as claimed in claim 1, wherein the means for discharging electric current from the inductor is a freewheeling diode.
4. A current regulator as claimed in claim 1, wherein the charging cycle time is short enough to keep the current change during each charging cycle small compared to the initial value of the charging current, thereby causing the inductor current to be substantially a fixed direct current value.
5. A current regulator as claimed in claim 1, wherein the inductor is the winding of a solenoid.
6. A current regulator as claimed in claim 1, wherein the inductor constitutes the windings of a direct current electric motor.
7. A current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive device for supplying electromagnetic energy to a mechanical device, (b) means for applying electric current from the source to the inductive device periodically for fixed period of time during all charging cycles irrespective of changes in the electric power consumed by the inductive device or of changes in the voltage of the source of direct current power, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means including a freewheeling diode for discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and (d) control means responsive to the electric current which is discharged from the inductive device during each discharge cycle, for initiating charging cycles and discharging cycles alternately, with each charging cycle being initiated when the current which is discharged from the inductive device decays to a value that is substantially equal to the initial value of the electric current at the beginning of a charge cycle.
(a) an inductive device for supplying electromagnetic energy to a mechanical device, (b) means for applying electric current from the source to the inductive device periodically for fixed period of time during all charging cycles irrespective of changes in the electric power consumed by the inductive device or of changes in the voltage of the source of direct current power, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means including a freewheeling diode for discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and (d) control means responsive to the electric current which is discharged from the inductive device during each discharge cycle, for initiating charging cycles and discharging cycles alternately, with each charging cycle being initiated when the current which is discharged from the inductive device decays to a value that is substantially equal to the initial value of the electric current at the beginning of a charge cycle.
8. A current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load in which the electric power is to be dissipated by transfer of the electromagnetic energy in the load to a mechanical device, (b) switching means for applying electric current from the source to the inductive load periodically for predetermined fixed periods of time during all charging cycles regardless of the duty cycle caused by changes in the operating conditions, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means for discharging electric current from the inductive load through a sensing resistor.
(d) means responsive to the current that is discharged from the inductive load through the sensing resistor for actuating said switching means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharing cycle when the electric current which is discharged from the inductive load decays to a value that is substantially equal to said initial value of the electric current at the beginning of a charge cycle.
(a) an inductive load in which the electric power is to be dissipated by transfer of the electromagnetic energy in the load to a mechanical device, (b) switching means for applying electric current from the source to the inductive load periodically for predetermined fixed periods of time during all charging cycles regardless of the duty cycle caused by changes in the operating conditions, in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, (c) means for discharging electric current from the inductive load through a sensing resistor.
(d) means responsive to the current that is discharged from the inductive load through the sensing resistor for actuating said switching means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharing cycle when the electric current which is discharged from the inductive load decays to a value that is substantially equal to said initial value of the electric current at the beginning of a charge cycle.
9. A current regulator for controlling the flow of current from a source of direct current power comprising:
(a) an inductive load (b) control means for applying electric current from the source to the inductive load, (c) said control means providing uniform charging cycles of fixed periods of time for all operating conditions for applying energy to the inductive load and discharging cycles during which electric current is discharged from the inductive load and no energy is provided to the inductive load from sources other than the discharge current, with the charging cycles being of less time duration than the duration of the discharging cycles, and (d) sensing means responsive to said discharge current for actuating said control means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharging cycle when the electric current which is discharged from the inductive load decays to a predetermined value.
(a) an inductive load (b) control means for applying electric current from the source to the inductive load, (c) said control means providing uniform charging cycles of fixed periods of time for all operating conditions for applying energy to the inductive load and discharging cycles during which electric current is discharged from the inductive load and no energy is provided to the inductive load from sources other than the discharge current, with the charging cycles being of less time duration than the duration of the discharging cycles, and (d) sensing means responsive to said discharge current for actuating said control means to apply electric current from the source to the inductive load to initiate a charging cycle and terminate a discharging cycle when the electric current which is discharged from the inductive load decays to a predetermined value.
10. A current regulator for controlling the flow of current from a source of direct current power to an inductor comprising:
(a) an inductor for supplying electromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor during charging cycles, (c) means for discharging electric current from the inductor during discharging cycles when power is not supplied through the switching means to the inductor, (d) means for providing a reference signal representative of the desired amount of current to be applied to the inductor, (e) means for providing a control signal that varies in accordance with the decay of the current which is discharged from the inductor during discharge cycles, and (f) control means responsive to said reference and control signals for actuating the switching means for fixed period of time under all operating conditions to initiate charging cycles when said control signal decays to a predetermined value with respect to the reference signal.
(a) an inductor for supplying electromagnetic energy to a mechanical load, (b) switching means for supplying power from the source of direct current power to the inductor during charging cycles, (c) means for discharging electric current from the inductor during discharging cycles when power is not supplied through the switching means to the inductor, (d) means for providing a reference signal representative of the desired amount of current to be applied to the inductor, (e) means for providing a control signal that varies in accordance with the decay of the current which is discharged from the inductor during discharge cycles, and (f) control means responsive to said reference and control signals for actuating the switching means for fixed period of time under all operating conditions to initiate charging cycles when said control signal decays to a predetermined value with respect to the reference signal.
11. A current regulator for controlling the flow of current from a source of direct current power to an electric motor having inductive windings for receiving direct current power comprising:
(a) switching means for supplying power from the source of direct current power to the inductive windings of the electric motor, (b) means for actuating said switching means to apply electric current from the source to said inductive windings for predetermined fixed period of time during charging cycles, under all operating conditions, (c) means for discharging electric current from said inductive windings during period of time constituting discharging cycles intermediate the charging cycles, (d) means for sensing the decay of the electric current from said inductive windings during discharging cycles to provide a first control signal, (e) means for sensing the speed of rotation of the electric motor to provide a second control signal, and (f) control means responsive to said first and second control signals for initiating charge cycles and terminating discharge cycles when said control signals have a predetermined relationship.
(a) switching means for supplying power from the source of direct current power to the inductive windings of the electric motor, (b) means for actuating said switching means to apply electric current from the source to said inductive windings for predetermined fixed period of time during charging cycles, under all operating conditions, (c) means for discharging electric current from said inductive windings during period of time constituting discharging cycles intermediate the charging cycles, (d) means for sensing the decay of the electric current from said inductive windings during discharging cycles to provide a first control signal, (e) means for sensing the speed of rotation of the electric motor to provide a second control signal, and (f) control means responsive to said first and second control signals for initiating charge cycles and terminating discharge cycles when said control signals have a predetermined relationship.
12. A method of controlling the flow of current from a source of direct current electric power to an inductive device for supplying electromagentic energy to a mechanical device comprising applying electric current from the source to the inductive device periodically for fixed periods of time for all operating conditions during charging cycles in which the current changes from an initial value to a larger value determined by the period of time during which the charging cycle takes place, discharging electric current from the inductive device in discharge cycles during periods of time intermediate the charging cycles, and terminating each discharge cycle and decays during the discharge cycle to a predetermined value.
13. A method of supplying energy from an inductive device to a mechanical device comprising causing the inductive device to apply electromagnetic energy to the mechanical device during charging cycles when the inductive device is energised from a source of direct current power, causing the inductive device to apply electromagnetic energy to the mechanical device during discharge cycles when the inductive device is discharged by applying current through a discharge path, and initiating charging cycles and discharging cycles alternately, with each charging cycle having a fixed period of time for all operating conditions which is intitated when the current which is discharged from the inductive device decays to a predetermined value.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US16976480A | 1980-07-17 | 1980-07-17 | |
| US169,764 | 1980-07-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1173503A true CA1173503A (en) | 1984-08-28 |
Family
ID=22617082
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000381170A Expired CA1173503A (en) | 1980-07-17 | 1981-07-06 | Direct current control in inductive loads |
Country Status (3)
| Country | Link |
|---|---|
| AU (1) | AU526883B2 (en) |
| CA (1) | CA1173503A (en) |
| GB (1) | GB2081942B (en) |
Families Citing this family (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3727283A1 (en) * | 1987-08-12 | 1989-02-23 | Mannesmann Ag | CHOPPER CIRCUIT FOR CONTROLLING ELECTROMAGNETIC AND / OR STEPPING MOTOR COILS, ESPECIALLY FOR A MATRIX PRINTER |
| DE19920306B4 (en) * | 1999-05-03 | 2008-02-28 | Stmicroelectronics Gmbh | Circuit device for controlling the current through an inductive load |
| DE19920307A1 (en) * | 1999-05-03 | 2000-11-16 | St Microelectronics Gmbh | Electrical circuit for controlling a load |
| US9112443B2 (en) * | 2012-08-30 | 2015-08-18 | Nxp B.V. | Current controlled actuator driver with improved accuracy at low current |
-
1981
- 1981-05-06 AU AU70193/81A patent/AU526883B2/en not_active Ceased
- 1981-05-07 GB GB8113925A patent/GB2081942B/en not_active Expired
- 1981-07-06 CA CA000381170A patent/CA1173503A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| AU7019381A (en) | 1982-04-08 |
| GB2081942B (en) | 1984-04-18 |
| AU526883B2 (en) | 1983-02-03 |
| GB2081942A (en) | 1982-02-24 |
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| MKEX | Expiry |