Low voltage direct control universal pulse width modulation module

Information

  • Patent Grant
  • 6256185
  • Patent Number
    6,256,185
  • Date Filed
    Friday, July 30, 1999
    25 years ago
  • Date Issued
    Tuesday, July 3, 2001
    23 years ago
Abstract
An electrical control module and circuit for controlling a solenoid. The control circuit provides a constant voltage to a solenoid for a predetermined time period after which a pulse width modulated voltage is supplied. The circuit further includes components for reverse polarity protection, transient voltage protection, low gate drive voltage protection, reduced heat dissipation and improved magnetic drive under low input voltage conditions during application of the pulse width modulated voltage. The module may be used in conjunction with a single coil or a dual coil solenoid. The circuit may be utilized on a 12 volt or a 24 volt electrical system without adjustment.
Description




FIELD OF THE INVENTION




The present invention relates to electrical control modules and specifically to electrical control circuits for use with solenoids.




BACKGROUND OF THE INVENTION




A solenoid is a common electrical device used to convert electrical energy into mechanical energy. Solenoids are well known in the art and are often utilized as a means of moving a component a predetermined distance at a predetermined time. In its most basic form, a solenoid is an electromechanical device that converts electrical energy into linear or rotary motion. Electrical voltage passes through a coil of insulated copper wire producing a magnetic field, which moves a ferromagnetic plunger located within the core of the coil. Steel parts surround the coil to contain the flux path for maximum pull, push or rotational force. A solenoid can be used to open a valve, activate a switch, apply a brake or a number of other activities where mechanical movement is required and only an electrical energy source is available or practical.




A typical solenoid comprises a steel frame or shell that surrounds the coil of wire and directs the flux path. The coil assembly, when energized with an electrical voltage, creates the magnetic lines of force. A plunger, located within the coil assembly, reacts to the magnetic pull and moves to the center of the coil against a stop or pole piece. The pole piece provides a stop for plunger movement. However, it is often required in a solenoid application that the plunger be retained or held against the pole piece. In order to retain the plunger against the pole piece, a sufficient amount of electrical voltage must be continuously applied to the coil assembly.




To accomplish the plunger hold function, prior art solenoids have included two (2) coil assemblies. A first voltage is applied to the first coil assembly thereby causing the solenoid to perform its work, i.e. the movement of the plunger from its initial position to the pole piece. A second voltage is then applied to the second coil to retain the plunger in its position against the pole piece. The first coil is typically comprised of a heavier gage wire to provide greater ampere turns whereas the second coil is comprised of a lighter gage wire with fewer ampere turns. The first voltage is typically a relatively high voltage and the second voltage is a lower voltage. Solenoids having two coil assemblies have drawbacks including increased expense, increased size, increased weight, and the necessity for entire replacement when one coil burns out (even though the other coil is intact).




Other prior art devices utilize a single coil assembly solenoid, but also provide a control module that applies a high voltage to the coil assembly to perform the work and a lower voltage to the solenoid to perform the hold function. Typically, these dedicated controllers are neither robust nor equipped with versatile connection means to allow use with a broad range of solenoid coils. These prior art devices all exhibit various limitations that the present invention overcomes including a narrow operation voltage range and susceptibility to damage if connected to the power source with improper polarity.




The present invention provides further enhancements in that it allows for direct and continuous connection of the primary power source to the module's power input terminal and also for fixed and continuous connection of the solenoid coil(s) to the module. Control of the application of electrical energy to the solenoid coil(s) can be accomplished by applying a +8 volt to +30 volt (ground reference) low current (less than 10 milliamps) signal to the auxiliary input terminal of the module. This feature allows solenoid systems to be wired without the need for high current switches or relays to control the primary current to the solenoid which in many cases on engine applications exceeds 50 amps.




Other prior art devices utilize an electronic control module that provides a timed application of high energy to the heavier gage winding of a dual winding or dual coil solenoid; however the heavier winding coil becomes inactive after the initial “pull-in” period. Thereafter, the solenoid operates using only the lighter gage coil resulting in low efficiency. In such a system incorrect connections of the control module to the solenoid coils may result in damage to the solenoid and or the control module.




While pulse width modulation has been utilized in the past to control the movement of a solenoid, a pulse width modulation circuit having the structure and benefits, as set forth below, is believed to be novel. The inventor is not aware of any prior art that teaches the unique combination of components and resulting benefits.




SUMMARY OF THE INVENTION




It is an object of the present invention to provide a solenoid control module that can supply a solenoid with a first voltage to perform mechanical work and a second voltage to perform a mechanical hold function without prematurely burning out the solenoid coil assembly. It is a further object to provide a control module that can be used with both single and double coil assembly solenoids. It is a further object to provide a control module that will not damage or destroy the solenoid if the solenoid is improperly connected to the control module output. It is a further object to provide a control module that will not be damaged or destroyed if connected to the power source with improper polarity. It is a yet further object to provide a solenoid module that is well suited for applications in the internal combustion engine industry. For example, diesel engines often require solenoid to operate fuel on/off levers. Many engine applications require remote or automatic operation of throttle levers. These solenoids must be able to perform a specified amount of work during the retraction or extension of the solenoid plunger and then hold the plunger in a predetermined position for an extended period of time.




These and other objects are achieved by the present invention wherein an electrical control module supplies two different voltages to a single coil or double coil solenoid.




In one embodiment, the invention may be described as an electric circuit for controlling a solenoid including a first voltage control means for providing a first electrical voltage to the solenoid for a predetermined time period; the first voltage control means being connected to the solenoid; a second voltage control means for providing a second electrical voltage to the solenoid; the second voltage control means also being connected to the solenoid; and the second voltage being a pulse width modulated voltage. The second means may include a free wheeling diode for maintaining a continuous current through the solenoid during pulse width modulation with reduced power dissipation and improved magnetic drive to the solenoid. In a preferred embodiment, the free wheeling diode is a Schottky diode. A transient voltage suppressing means may be provided for protecting the circuit from an over voltage condition. In another preferred embodiment, the transient voltage suppressing means is a transient absorption zener diode.




The circuit includes a first, a second and a third output connections, said first and second output connections being adaptable for connection to a single coil solenoid and said first, second and third connections being adaptable for connection to a double coil solenoid. Resistor means and capacitor means are provided to determine the predetermined time period of the first voltage control means.




The circuit preferably includes reverse polarity protection means associated with said first and second voltage control means for opening said circuit in the event that the polarity of said circuit is reversed. A fuse may also be provided, the fuse being sized to open when a reverse polarity condition is detected. In addition, low voltage protection means may be provided for disabling the first and second voltage control means when an inadequate input voltage is supplied to said circuit. The input voltage is preferably in the range of 8 volts to 30 volts.




In another embodiment, the solenoid control circuit comprises two switching means; a semi-conductor means for providing a mono-stable and an a-stable signal to said switching means; a voltage supply source being switchably connected to said solenoid; said semi-conductor means being connected to said switching means; said switching means being connected to said solenoid; said mono-stable signal supplying a constant voltage to said solenoid for a predetermined time period; and said a-stable signal providing a pulse width modulated voltage to said solenoid at the expiration of the predetermined time period.




In a third embodiment, a system for controlling the voltage applied to a solenoid includes a voltage supply source; a voltage control means, said voltage control means being connected to said voltage supply source; and first and second switching means, said first and second switching means being connected to said voltage control means and to said solenoid. The voltage control means is capable of supplying a predetermined mono-stable signal to said first and second switching means and an a-stable signal to said first and second switching means for producing a constant voltage output and a pulse width modulated voltage output respectively. The system may include a free wheeling diode, the free wheeling diode being connected to said first and second switching means. In a preferred embodiment, the free wheeling diode is a Schottky diode.











DESCRIPTION OF THE DRAWINGS





FIG. 1

is a diagrammatic view of a single coil solenoid, the control module and a power supply showing the solenoid plunger fully extended.





FIG. 1



a


is a diagrammatic view of a double coil solenoid, the control module and a power supply showing the solenoid plunger fully extended.





FIG. 2

is a diagrammatic view of a single coil solenoid, the control module and a power supply showing the solenoid plunger being retracted.





FIG. 2



a


is a diagrammatic view of a double coil solenoid, the control module and a power supply showing the solenoid plunger being retracted.





FIG. 3

is a diagrammatic view of a single coil solenoid, the control module and a power supply showing the solenoid plunger in the “hold” position.





FIG. 3



a


is a diagrammatic view of a double coil solenoid, the control module and a power supply showing the solenoid plunger in the “hold” position.





FIG. 4

is a detailed schematic circuit diagram of the control module of the present invention connected to a single coil solenoid.





FIG. 5

is a detailed schematic circuit diagram of the control module of the present invention connected to a dual coil solenoid.











DETAILED DESCRIPTION




Although the disclosure hereof is detailed and exact to enable those skilled in the art to practice the invention, the embodiments herein disclosed merely exemplify the invention that may be embodied in other specific structure and/or methodologies. While the preferred embodiment has been described, the details may be changed without departing from the invention, which is defined by the claims.




The present invention, referred to at reference numeral


10


in the figures, is a solenoid control module. The module


10


operates at relatively low direct current voltages (i.e. 8 to 30 volts direct current). The solenoid module


10


supplies and controls the voltage applied to a coil or coils of a solenoid assembly. The module provides a continuous voltage to a solenoid for purposes of performing work and then provides a pulse width modulated voltage to maintain the solenoid in a hold position.




As shown in

FIGS. 1 through 3

, a power supply


14


provides an input voltage to the module


10


that in turn supplies voltage to a single coil solenoid


16


. As shown in

FIGS. 1



a


through


3




a


, a power supply


14


provides an input voltage to the module


10


that in turn supplies voltage to a double coil solenoid


18


.





FIG. 1

shows a single coil solenoid


16


having a solenoid plunger


20


where no voltage has been supplied to the solenoid. In

FIG. 2

, a predetermined voltage has been applied to the solenoid


16


, thereby causing the solenoid plunger


20


to retract as shown by arrow


22


. In

FIG. 3

, the solenoid plunger


20


is in the hold mode and a predetermined pulse width modulated voltage is applied to the solenoid coil assembly.

FIGS. 1



a


-


3




a


are similar to

FIG. 1-3

, except that a double coil solenoid


18


is shown.




The voltage and current are carried from the power source


14


through wires


24


,


26


and


28


. Wire


24


is the positive input, wire


26


is the auxiliary positive input and wire


28


is the negative input. The module


10


has two or three output connections, depending upon whether it is to be attached to a single coil (

FIGS. 1-3

) or a double coil (

FIGS. 1



a


-


3




a


) solenoid. In a single coil application output connections


30


and


32


are utilized. Output


30


is the ground or neutral output. In a typical solenoid application, the wire connected to output


30


is black. Connection


32


is the working voltage and hold voltage connection that supplies a predetermined voltage to the solenoid


16


. In common solenoid applications, the wire connected to connection


32


is white. For double solenoid applications, a third output is present. Additional wire


34


is the “hold” voltage wire. In common applications, the wire connected to output


34


is red.




The solenoid control circuit


10


shown in

FIG. 4

ultimately controls the voltage supplied to the coil of a single coil solenoid


16


. An identical solenoid control circuit


10


shown in

FIG. 5

controls the voltage supplied to the coils of a dual or two-coil solenoid


18


. The only appreciable difference between the circuit shown in FIG.


4


and the circuit shown in

FIG. 5

is the provision of output connection


34


in FIG.


5


. The amount of voltage and form of the voltage supplied to the solenoid is controlled by the circuit


10


. For purposes of illustration only, the circuit set forth below will be described to receive power from a twelve (12) volt power source such as a lead-acid battery. It is to be understood that the output of a lead-acid battery and its supporting charging system in engine installations can vary from between approximately eight (8) volts to approximately sixteen (16) volts. Furthermore, it is to be expressly understood that this circuit, being universal in nature, can be used as presented in a twenty-four (24) volt installation and further more could be adapted for use with other voltage sources and voltage levels.




Referring now to

FIG. 4

, input voltage is supplied to the circuit


10


at lines


24


,


26


and


28


. A constant 12-volt positive input is supplied by a battery or other power source


14


at line


24


. A constant 12-volt negative input is supplied by the battery or other power source


14


at line


28


. An auxiliary 12-volt positive input is also supplied at line


26


to the circuit


10


line switch S


1


is energized. For example, switch S


1


may be energized by an ignition switch being turned to the “on” position, by a signal received from a remote operator station, or by receiving a signal from a outside source (i.e. receiving a signal from the engine to which the solenoid is attached).




Z


5


, a zener diode type transient voltage suppressor is connected in between the two primary power inputs, lines


24


and


28


. Z


5


serves dual purposes. When the primary power source


14


is connected and polarity is proper, Z


5


functions as a transient voltage protection device. Should abnormalities occur in the primary power source


14


, Z


5


will limit positive voltage excursions to approximately forty eight (


48


) volts thereby protecting other components in the circuit


10


. Devices within the family of components that Z


5


comes from are available in a broad variety of voltage ratings. Z


5


is sized so as to have considerable maximum forward current capability so that it might perform its second function which is to protect the circuit


10


from reverse polarity connection to power source


14


.




It is recommended that a fuse


40


be installed in the wiring between the positive battery output and line


24


. In the preferred embodiment, the fuse


40


is a 10 or 12 amp slow blow fuse. In combination with fuse


40


, transient absorption zener diode Z


5


also performs the function of reverse voltage protection. In the event that the installer connects module


10


to power source


14


in an incorrect manner, transient absorptions zener diode Z


5


will go into forward conduction and thereby clamp the negative battery voltage down to approximately one (1) volt to protect the circuit


10


from damage. At the same time the transient absorption zener diode Z


5


is performing its voltage clamping function, fuse


40


will blow thereby cutting off all voltage to the module


10


. Z


5


is located physically very close to the power source input terminals so as to minimize heat on the traces of the circuit board under such a fault condition.




Similar functionality can be achieved through use of a lower current capacity transient voltage suppression device in conjunction with a standard rectifier diode connected with a cathode to line


24


and an anode to line


28


. The present embodiment is preferred in that it reduces the number of components and circuit board space consumption while at the same time providing a robust level of transient energy protection.




The 12-volt positive auxiliary input line


26


supplies a positive voltage into the circuit


10


when activated by switch S


1


. The combination of resistor R


1


and zener diode Z


1


protects the circuit


10


from an over-voltage condition or reverse polarity connection on line


26


. Capacitor C


1


provides a small amount of energy storage so that if there is a brief current or voltage interruption in line


24


, the capacitor will maintain the line.




The combination of resistor R


8


, resistor R


10


, transistor Q


4


, zener diode Z


4


and resistor R


9


form a low voltage supply protection circuit


50


. If the voltage in the circuit


10


falls to a low level, which can cause damage to the MOSFET transistors Q


2


and Q


3


due to inadequate gate drive voltage, the low voltage supply circuit


50


will shut off the circuit


10


until a higher voltage level is achieved. MOSFET transistors Q


2


and Q


3


, discussed in detail below, must be supplied with a minimum gate to source voltage. If supplied with a voltage that is less than the minimum required gate to source voltage, the MOSFET transistors Q


2


and Q


3


will act as linear amplifiers, not as switches as required. U


1


:B, also discussed in detail below, is the driver for MOSFET transistors Q


2


and Q


3


. The low voltage supply circuit


50


will turn U


1


:B off if the voltage falls below the minimum level of approximately 8 volts.




The primary power source negative input line


28


provides a ground to the circuit


10


. This a common ground for the entire circuit (as shown in the schematic) and is also the ground reference for VCC or the controlled voltage. Referring back to the description of zener diode Z


1


, it will be appreciated that VCC will never exceed the voltage rating of Z


1


.




A 556 CMOS chip having 14 pins is shown at U


1


:A and U


1


:B. The chip performs two distinct functions. It acts as both an a-stable multi-vibrator constantly toggling between an on and off stage and as a one shot or mono-stable multi-vibrator. Both functions will be discussed below.




As will become evident during the following discussion, voltage is not supplied to the coil assembly of the coil


16


until the MOSFET transistors Q


2


and Q


3


have been energized. Without being energized, the coil


16


is not connected to ground. U


1


:B is the driver that provides current to the gates of the MOSFET transistors Q


2


and Q


3


.




U


1


:B in conjunction with R


4


, R


5


, D


2


and C


3


comprises an a-stable multi-vibrator. In the absence of Q


1


, or with Q


1


in a non-conducting state, U


1


:B's output continuously toggles between the on and off state. When full power is required at solenoid


16


(i.e. during the “pull-in” or work period), the U


1


:A output turns on the base of transistor Q


1


. This in turn shunts capacitor C


3


and thus forces a low voltage condition at the “trigger” pin (pin


8


) of U


1


:B which forces U


1


:B to its “on” state. With U


1


:B stalled in its “on” state, MOSFET transistors Q


2


and Q


3


are in full conduction providing a path of continuous current flow to solenoid


16


. The path of current flow is from the positive terminal of the power source


14


, through the solenoid


16


, through Q


2


and Q


3


, and back to the negative terminal of the power source


14


. With this uninterrupted supply of voltage, solenoid


16


performs its work of retracting or “pulling in” its plunger


20


as illustrated in FIGS.


2


/


2




a.






U


1


:A in conjunction with R


2


and C


2


comprises a monostable multi-vibrator or “oneshot” device. Its preset on time determines the solenoid “pull in” or work period. Prior to closing switch S


1


, VCC is zero. C


2


is initially at zero or discharged. When switch S


1


is turned on, C


2


charges through R


2


toward the VCC maximum level (i.e. approximately 12 volts). Capacitor C


2


acts as the timer for the predetermined solenoid work period. When the voltage on C


2


is less than one-third (⅓) VCC, the output pin


5


of U


1


:A chip is on. When the voltage on C


2


reaches two-thirds (⅔) VCC, U


1


:A output at pin


5


turns off. U


1


:A output, when “on”, directs current through R


3


and biases Q


1


on. At the two-thirds VCC level on C


2


, the output is turned off, yet capacitor C


2


continues to charge to VCC level and then stays at the VCC level. As an aside, when VCC is removed (i.e. the circuit is de-energized) C


2


discharges over time.




The “pull in” period lasts for a predetermined period of time. In circuit


10


, the “pull-in” period is approximately one-half second. After the “pull in” period has expired, U


1


:B operates as an a-stable multi-vibrator to supply a pulse width modulated voltage to the solenoid


16


. Resistor R


4


, resistor R


5


and capacitor C


3


set the frequency and duty cycle of the pulse width modulated voltage. Rectifier diode D


2


is provided to allow the circuit


10


to operate at less than fifty percent (50%) duty cycle. When the output of U


1


:B is off or conducting to ground. D


2


prevents current flow from C


3


through R


4


to U


1


:B output pin


9


.




As stated above, U


1


:B functions as the driver that provides current to the gates of MOSFET transistors Q


2


and Q


3


. When the output of U


1


:B is high, capacitor C


3


is charging. When the charge on capacitor C


3


equals two-thirds VCC, U


1


:B turns on a discharge path through resistor R


5


and pin


13


. At the same time, U


1


:B turns its output to the off state. This is accomplished within the CMOS chip by tying the output to ground through an internal transistor.




Capacitor C


3


continues to discharge until its output equals one-third VCC. At this point, U


1


:B turns its output back on and turns its discharge path off. It will be appreciated that capacitor C


3


and resistor R


5


control the off time while the combination of capacitor C


3


, resistor R


4


and diode D


2


control the on time. The ratio of resistor R


4


as compared to resistor R


5


sets the duty cycle. Capacitor C


3


controls the frequency of the pulse width modulated signal. The U


1


:B output is on as C


3


charges between one-third VCC and two-thirds VCC; U


1


:B output is off as C


3


discharges from two-thirds (⅔) to one-third (⅓) VCC. Resistor R


6


and resistor R


7


balance the MOSFET transistors Q


2


and Q


3


to make sure each transistor is doing approximately the same work as the other.




C


4


functions as a random noise bypass device for any unwanted noise to prevent noise from affecting the 556 timer. It should be noted that C


4


is tied to both control outputs. C


5


functions as a bypass device for high frequency noise on VCC. Z


2


is simply a precautionary element in the circuit. It protects the gates of Q


2


and Q


3


against damage from voltage transients. Z


3


is a transient voltage protection device. It protects Q


2


and Q


3


from static and unexpected high voltage input at solenoid connection point


30


. For example, a static charge generated by the installer of the controller or solenoid.




In the preferred embodiment, the pull time generated from R


2


and C


2


is approximately one-half (½) second. By changing the value of R


2


and C


2


, the work or pull time can be varied widely, but for typical applications the time is generally in the range of 0.1 seconds to 3 seconds.




D


3


is a Schottky diode. It provides a path for continuous current to flow through the solenoid coil or coils


16


/


18


each time Q


2


and Q


3


switch from their conducting state to their non-conducting state (i.e. on and off). A Schottky diode is chosen as the freewheeling diode in the present invention predominately for two reasons: reduced power dissipation in the diode itself and improved magnetic drive in the solenoid


16


under reduced voltage operating conditions.




Both cited benefits derive from the lower forward voltage drop exhibited by the Schottky device. In a typical high energy solenoid application, continuous coil current when the solenoid is holding a load in position is of a magnitude of several amps. Whereas an appropriately sized standard fast recovery rectifier might exhibit a forward voltage drop of about one (1) volt, a similarly sized Schottky diode would exhibit a forward drop of approximately one-half (0.5) volts. This means that at a given current level, the Schottky device is dissipating about one-half the power and thereby generating one-half the heat output as compared to the standard device. If both devices are constructed using the same mechanical structure (i.e. a JEDEC TO-220 package) and implying the package will exhibit the same thermal resistance junction to ambient, then the temperature rise of Schottky device will be one-half that of the standard fast recovery diode. This ultimately allows the use of a smaller device or a reduction or elimination of heat sink provisions when using the Schottky diode. The net result includes, among other benefits, lower cost and a smaller end product.




In regard to improved magnetic drive in the solenoid


16


under reduced voltage the following analysis illustrates the point. In the case of the preferred embodiment 10 described herein, the pulse width modulated duty cycle in the continuous hold mode is thirteen percent (13%). This means that the power MOSFETs within the module


10


connects the solenoid coil to the supply voltage source


14


thirteen percent (13%) of the time. Ignoring conduction losses, the voltage across the coil equals supply voltage during that time. The polarity of the impressed voltage is such that it reverse biases the freewheeling diode to a non-conducting state. The remaining eighty seven percent (87%) of the time, the power MOSFETs are switched off thereby disconnecting the solenoid


16


from the primary voltage source


14


. When this occurs, coil current declines resulting in magnetic field collapse around the solenoid coil. This in turn causes a reversal of the voltage across the coil. This reverse polarity voltage rises in magnitude until it reaches a value sufficient to forward bias the freewheeling diode, bringing it into conduction. Once forward biased into conduction, the diode allows maintenance of current in the solenoid coil. The current path is localized to the coil and the freewheeling diode. During this time the voltage across the solenoid coil equals the forward voltage drop of the freewheeling diode; but, polarity is the inverse of that present when the MOSFETs are conducting.




Assuming the power source


14


is a twelve volt battery (that may reduce in voltage depending upon battery load and the supportive charging system), the following situations occur.




Standard diode, battery supply at 12 volts:




Vcoil=12V (Vsupply)×0.13(13% on time)−1.0V (Vf diode)×0.87(87% off time)=0.69 volts (average)




Schottky diode, battery supply at 12 volts:




Vcoil=12V (Vsupply)×0.13(13% on time)−0.5 V (Vf diode)×0.87 (87% off time)=1.125 volts (average)




Standard diode, battery supply reduced to 8 volts:




Vcoil=8V (Vsupply)×0.13(13% on time)−1.0V (Vf diode)×0.87 (87% off time)=0.170 volts (average) Schottky diode, battery supply reduce to 8 volts:




Vcoil=8V (Vsupply)×0.13 (13% on time)−0.5 V (Vf diode)×0.87 (87% off time)=0.605 volts (average)




where Vcoil is the voltage supplied to the solenoid coil; Vsupply is the supply voltage; and Vf is the forward voltage drop of the diode.




The thirteen percent (13%) duty cycle is chosen to provide the best all around performance of the module


10


across it's full specified operating range of 8 to 30 volts. The above calculations show that the use of the Schottky diode at D


3


provides far superior performance in respect to maintaining voltage to the solenoid coil under reduced operating voltage conditions. The solenoid's hold strength is directly related to the average voltage supplied to the coil. Therefore, it maintains acceptable performance much longer with a faltering voltage supply when a Schottky diode is used at D


3


.




The following is a list of exemplary components that may be used in the circuits illustrated in

FIGS. 4 and 5

. These components are merely exemplary and other components could be utilized or readily substituted without departing from the scope of the present invention.




Exemplary Components




Resistors




R


1


510 Ohms, 2 watt




R


2


226 kOhms, ¼ watt




R


3


30.1 kOhms, ¼ watt




R


4


13.0 kOhms, ¼ watt




R


5


100 kOhms, ¼ watt




R


6


46.4 Ohms, ¼ watt




R


7


46.4 Ohms, ¼ watt




R


8


4.12 kOhms, ¼ watt




R


9


100 kOhms, ¼ watt




R


10


39.2 kOhms, ¼ watt




Capacitors




C


1


2.2 micro F, 25 volt




C


2


2.2 micro F, 25 volt




C


3


0.01 micro F, 50 volt




C


4


0.01 micro F, 50 volt




C


5


0.01 micro F, 50 volt




Diodes




Z


1


Zener Diode, 12 volt, 1 watt




Z


2


Zener Diode, 15 volt, ½ watt




Z


3


Transorb, 600 watt unidirectional, 34 volt min VBR, 49.9 volt max clamp




Z


4


Zener Diode, 6.2 volt, ½ watt




Z


5


Zener Diode 5000 watt unidirectional, 33.3 volt min VBR, 48.4 volt max clamp




Transistors




Q


1


40 volt, 500 ma




Q


2


Power MOSFET, 55 volt, 64 amp, 0.016 ohm, RDS (on), 140 watt




Q


3


Power MOSFET, 55 volt, 64 amp, 0.016 ohm, RDS (on), 140 watt




Q


4


Tansistor, NPN, 40 volt, 500 ma




Rectifier Diodes




D


2


0.2 amp, 250 volt




D


3


Schottky rectifier, 20 amp, 45 volt




Integrated Circuits




U


1


:A/U


1


:B CMOS 556 IC Dual Timer, 14 pin DIP




While the invention has been described in conjunction with a specific embodiment, it is to be understood that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. For example, without departing from the invention, the CMOS 556 IC Dual Timer could be replaced with two (2) CMOS 555 timers. Accordingly, this invention is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the following claims. As another example, the effect of the mono-stable and a-stable multi-vibrations could be duplicated using a digital micro-controller in place of the 556 timer and related resistors and capacitors. As yet another example a single more robust power MOSFET could be used to replace the two power MOSFETs (Q


2


and Q


3


).



Claims
  • 1. An electric circuit for controlling a solenoid, the circuit comprising:a first voltage control means for providing a first electrical voltage to the solenoid for a predetermined time period; the first means being connected to the solenoid; a second voltage control means for providing a second electrical voltage to the solenoid; the second means being connected to the solenoid; and the second voltage being a pulse width modulated voltage.
  • 2. The circuit of claim 1 wherein the second means further includes a free wheeling diode for maintaining current flow through the solenoid thereby maintaining a magnetic field around the coil when the pulse width modulation voltage cycles off.
  • 3. The circuit of claim 2 wherein the free wheeling diode is a Schottky diode.
  • 4. The circuit of claim 1 further comprising transient voltage suppressing means for protecting said circuit from an over voltage condition;the transient voltage suppressing means being connected to the solenoid.
  • 5. The circuit of claim 4 wherein the transient voltage suppressing means is a transient absorption zener diode.
  • 6. The circuit of claim 1 further including a first, a second and a third output connection, said first and second output connections being adaptable for connection to a single coil solenoid and said first, second and third connections being adaptable for connection to a double coil solenoid.
  • 7. The circuit of claim 1 further including resistor means and capacitor means, said resistor and capacitor means being connected to said circuit and wherein the predetermined time period is determined by said capacitor and resistor means.
  • 8. The circuit of claim 1 further including reverse polarity protection means associated with said first and second voltage control means for opening an external protective fuse wired in series with said circuit in the event that input polarity to said circuit is reversed.
  • 9. The circuit means of claim 1 further including low voltage protection means associated with said first and second voltage control means for disabling said first and second voltage control means when inadequate input voltage is supplied to said circuit.
  • 10. The circuit of claim 1 further including an input voltage source, the input voltage source being in the range of 8 volts to 30 volts.
  • 11. The circuit of claim 10 wherein the input voltage source is 12 volts.
  • 12. The circuit of claim 10 wherein the input voltage source is 24 volts.
  • 13. The circuit claim of claim 1 further including an auxiliary control input for supplying an auxiliary control input signal to said circuit;said auxiliary control input signal providing the low current control signal to exercise complete on and off control of said circuit; and said auxiliary control connection being connected to said circuit.
  • 14. A solenoid control circuit connected to a solenoid and a voltage supply source, said circuit comprising:at least one switching means; a semi-conductor means for providing a mono-stable and an a-stable signal to said switching means; said semi-conductor means being connected to said switching means; said switching means being connected to said solenoid; said mono-stable signal supplying a constant voltage to said solenoid for a predetermined time period; and said a-stable signal providing a pulse width modulated voltage to said solenoid at the expiration of the predetermined time period.
  • 15. The circuit of claim 14 further including a free wheeling diode for maintaining a continuous current through the solenoid after the predetermined time period;the free wheeling diode being connected to the switching means.
  • 16. The circuit of claim 14 wherein the free wheeling diode is a Schottky diode.
  • 17. The circuit of claim 14 further comprising transient voltage suppressing means for protecting said circuit from an over voltage condition.
  • 18. The circuit of claim 17 wherein the transient voltage suppressing means is a transient absorption zener diode.
  • 19. The circuit of claim 14 further including a first, a second and a third output connection, said first and second output connections being adaptable for connection to a single coil solenoid and said first, second and third connections being adaptable for connection to a double coil solenoid.
  • 20. The circuit of claim 14 further including resistor means and capacitor means, said resistor and capacitor means being connected to said circuit and wherein the predetermined time period is determined by said capacitor and resistor means.
  • 21. The circuit of claim 14 further including reverse polarity protection means associated with said voltage supply source for opening a supply fuse in the event that said circuit is reversely connected to said voltage supply source.
  • 22. The circuit of claim 21 further including low voltage protection means associated with said semi-conductor means for disabling said semi-conductor means when inadequate input voltage is supplied to said circuit.
  • 23. The circuit of claim 14 further including an auxiliary control input for supplying an auxiliary control input signal to said circuit;said auxiliary control input signal providing the low current control signal to exercise complete on and off control of said circuit; and said auxiliary control connection being connected to said circuit.
  • 24. A system for controlling the voltage applied to a solenoid, the system comprising:a voltage supply source; a voltage control means capable of supplying a pre-determined mono-stable signal to said switching means and an a-stable signal to said switching means for producing a constant voltage output and a pulse width modulated voltage output, said voltage control means being connected to said voltage supply source; at least one switching means, said switching means being connected to said voltage control means and to said solenoid.
  • 25. The system of claim 24 further including a free wheeling diode, the free wheeling diode being connected to said switching means.
  • 26. The system of claim 25 wherein the free wheeling diode is a Schottky diode.
US Referenced Citations (18)
Number Name Date Kind
4295177 Woodhouse et al. Oct 1981
4384213 Bogel May 1983
4620259 Oshizawa Oct 1986
4620260 Oshizawa et al. Oct 1986
4661766 Hoffman et al. Apr 1987
4949215 Studtmann et al. Aug 1990
4964014 Boe et al. Oct 1990
5255152 Estes, III et al. Oct 1993
5489831 Harris Feb 1996
5546268 Hurley et al. Aug 1996
5621603 Adamec et al. Apr 1997
5647387 Tsutsui Jul 1997
5703748 Fulks et al. Dec 1997
5703750 Kim et al. Dec 1997
5748431 Goodnight et al. May 1998
5754386 Barbour et al. May 1998
5757605 Furukawa May 1998
5861746 Ensten Jan 1999