Abstract:
The present invention is a voltage conditioner and switching device applied to alternating current relays. An electronic circuit and direct current (DC) relay to overcome material, mechanical, physical, and construction variations of electromechanical alternating current (AC) relays is disclosed.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates generally to a circuit and apparatus for switching an alternating current (AC) relay at predetermined voltage levels with assured repeatability and precision. 
     2. The Prior Art 
     Electromechanical relays with solenoid coils are characterized by a pickup voltage, the voltage at which the solenoid pulls in and energizes the contacts, and a dropout voltage at which the solenoid drops out and de-energizes the contacts. The pickup and dropout voltage for alternating current (AC) relays varies significantly from relay to relay when made by the same manufacturer with even greater differences for relays made by different manufacturers. These differences are due to limitations of control over materials, the size of the relays and assembly techniques. 
     These limitations are minimal and electrically controllable for direct current (DC) relays. Direct current relays, however, are limited in general applications and cannot be substituted for alternating current relay applications. This invention exploits the controllability and precision of direct current relays and amplifies and transfers the qualities to alternating current relays. 
     There are several patents that disclose various apparatus and methods for controlling relays. 
     Graff et al. U.S. Pat. No. 5,267,120 discloses a device whereby a micro-controller measures and then adjusts a time delay in order for the contacts to make at a predetermined point on a sinusoidal waveform. 
     Hancock, U.S. Pat. No. 4,389,691 discloses an arc suppression device for protecting contacts against excessive wear due to arcing. 
     Doneghue, U.S. Pat. No. 5,905,422 discloses mechanical means for adjusting the travel distance of the armature of an electromechanical relay to meet the response time parameters. 
     Brodetsky, U.S. Pat. No. 5,528,120 discloses a field adjustable electronic potential relay for a starting circuit for single-phase motors. 
     Moan, U.S. Pat. No. 5,633,540 discloses a surge resistant relay switching circuit where the electromechanical relay contacts are protected from inrush currents by placing a TRIAC in series with the switching contacts which blocks current flow until after the contacts are closed. 
     Lillemo et al, U.S. Pat. No. 5,283,706 discloses a switching circuit whereby a solid state switch forces contacts of an electromechanical relay to open or close at the moment the sine wave crosses at zero in order to prevent arcing and overheating of the contacts. 
     It therefore is an object of the present invention to provide a device for energizing or de-energizing any alternating current relay at precise pre-determined voltage levels. 
     It is another object of this invention to provide a device for energizing or de-energizing a solid state switching device capable of switching a current and/or voltage load larger than the current and/or voltage capabilities of the direct current relay contacts. 
     BRIEF DESCRIPTION OF THE INVENTION 
     The present invention is a voltage conditioner and switching device applied to alternating current relays. The present invention is distinguished over the prior art in general and these patents in particular by a simple rectifier circuit which by fixed resistor selection and capacitor filtering determine the precise energizing voltage of a direct current relay. The direct current relay contacts can then energize or de-energize an alternating current relay at consistently the same voltage level regardless of manufacturing material or assembly technique differences. A solid state switching device such as a MOSFET, TRIAC, SCR or other device may be triggered by the direct current relay if the alternating current relay solenoid amperage and/or voltage requirements exceed the direct current relay contact ratings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING FIGURES 
     FIG. 1A, FIG. 1B, FIG.  2  and FIG. 3 are schematic diagrams of embodiments of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Those of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons. 
     Referring to FIG. 1A, a schematic diagram of an illustrative first embodiment of the present invention is shown. When alternating current (AC) voltage  10  is applied at terminals  20  and  30 , AC current passes through resistor  40  and is converted to half-wave-rectified direct current (DC) after passing through diode  50 . Capacitor  60  minimizes the ripple of the half-wave-rectified direct current and applies a DC voltage (indicated by the arrow at reference numeral  70 ) to the solenoid  80  of direct current relay  90 . If AC voltage  10  increases, the solenoid voltage  70  increases proportionately and when AC voltage  10  reaches a predetermined high voltage level, then the solenoid DC voltage  70  will energize and close the normally-open (NO) set of contacts. This applies AC energizing voltage  100  to the solenoid  110  of AC relay  120  through the closed contacts and closes the normally-open set of contacts  130 . Load  140  is therefore connected to voltage  150  at a precise voltage level at terminals  20  and  30  as the voltage is increasing. 
     Referring to FIG. 1B, it should be understood that if solenoid  110  of AC relay  120  is connected to the normally closed (NC) set of contacts of DC relay  90  which energizes solenoid  110  of AC relay  120 , then the load  140  is disconnected from voltage  150  at a precise high voltage level at terminals  20  and  30  as the voltage is increasing. 
     It should be further understood, referring to FIG. 1A, that when AC voltage  10  is applied and relay RDC is immediately energized, then resistor  40  can be selected such that as the AC voltage  10  is decreasing, the solenoid voltage decreases proportionately and AC voltage  10  reaches a predetermined low voltage level, then the solenoid DC voltage  70  will de-energize and open the normally open set of contacts. This disconnects AC energizing voltage  100  to the solenoid  110  of AC relay  120  and opens the contacts  130 . Load  140  is therefore disconnected to voltage  150  at a precise decreasing voltage level at terminals  20  and  30 . 
     It should also be understood, referring to FIG. 1B, that if solenoid  110  of AC relay  120  is connected to the normally closed (NC) contact of DC relay  90  which energizes solenoid  110  of AC relay  120 , then the load  140  is connected to voltage  150  at a precise high voltage level at terminals  20  and  30  as the voltage is decreasing. 
     In summary, the invention will energize or de-energize a load at a precise voltage as the voltage increases and will energize or de-energize a load at a precise voltage as the voltage decrease. The precise AC voltage  10  at terminals  20  and  30 , which energizes DC relay  90  can be altered by the selection of the resistance value of resistor  40 . 
     Voltage  10  can be in the range between 110V and 460V. Solenoid  80  is rated for 48V DC and therefore, a “Voltage Drop” resistor  40  is required. For example, if Voltage  10  is 110V, then resistor  40  may have a value of 12 k ohms to drop voltage 70 to 48V. The diode  50  half-wave-rectifies the AC voltage to DC voltage and the capacitor  60  acts as a filter to smooth a “pulsating” DC voltage. The value of capacitor  60  could be from 2 microfarads (MFD) to 100 MFD depending on how much filtering (smoothing) is required depending on the selection of RDC. 
     Referring to FIG. 2, a schematic diagram of an illustrative second embodiment is show. The function of this embodiment is the same as in FIG. 1, except that a solid state switching device  160  such as a MOSFET, TRIAC, SCR is triggered to conduct current and energize AC relay  170  when the solenoid voltage and/or current requirements are not compatible with the contact ratings of DC relay  175 . 
     Referring to FIG. 3, a schematic diagram of an illustrative third embodiment is shown. The function of this embodiment is the same as in FIG. 2, except that the load  180  may be switched directly with solid state switch  190  if that design is preferred. 
     A typical application would see the device for instance connected between the 110V plug and a computer. Referring to FIG. 1, resistor  40  is selected such that if the voltage at the plug goes above 125V, the computer is disconnected and a warning device is turned on. Voltage  100  could be again 110V to 460V depending on application and the warning device, (Load  140  e.g., a light bulb, buzzer, telephone dialer) may only be 12V or 24V or 460V (Voltage  150 ). The invention is flexible in application because it could be used to start the same chain of events if the voltage  10  went below for example 90V. In short, the invention can be used to sense many different voltages  10  over or under, and can turn on or off many different voltages  100  and  150  depending on the selection of resistor  40  and connections to the contacts of the DC relay  90  or the AC relay  120 . 
     It will be appreciated by those skilled in the art that the present invention can be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore considered in all respects to be illustrative and not restrictive. The scope of the invention is indicated by the appended claims rather than the foregoing description, and all changes that come within the meaning and range and equivalence thereof are intended to be embraced therein.