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USOO5854519A Ulllted States Patent [19] [11] Patent Number: 5,854,519 Gershen et al. [45] Date of Patent: Dec. 29, 1998

[54] ASYMMETRICAL AC TRIGGER [56] References Cited SIMULATION U.S. PATENT DOCUMENTS

[75] Inventors: Bernard J. Gershen, Centerport; 4,006,368 2/1977 Ichikawa ...... 327/457 Alfred J. Lombardi, La Grangeville; 4,914,327 4/1990 Dekker ...... 327/457 YevgenyEdward JISha?r, Krajci, Jamaica Franklin Estates, Square; an of 5,668,496 9/1997 GershenRebordosa Ct 8.1...... 327/452 NY Primary Examiner—Richard T. Elms [73] AS _ L M f C I Attorney, Agent, or Firm—Paul J. Sutton s1gnee: eviton anu acturing 0., nc., Little Neck, NY. [57] ABSTRACT The present invention teaches a dimmer Which incorporates [21] Appl- NO-I 821,748 an alternating current (AC) trigger Which exhibits asym [22] F1led. _ Mar 20 1997 metrlcai 1 e 1 ectr1cai 1 c h aracter1st1cs.i ' Th‘1s e 1.1m1natest i h e un d e ' ' ’ sirable snap on hysteresis effect associated With conven R l t d U.S. A l - t - D t tional dimmers utilizing symmetrical AC triggers such as e a e pp lea Ion a a diacs and silicon bilateral sWitches (SBS). One embodiment [63] Continuation of Ser_ No_ 1837459’ Jam 18’ 1994’ Pat NO_ of the present invention utilizes a Zener diode to create the 5,619,081' asymmetry. Dunng one polarity of the AC source, the

6 breakover voltage of the trigger is increased 9 forcing the [51] Int. Cl...... H01H 47/00 trigger to breakover at a time later in the AC Cycle than it [52] _ 307/125; 327/457 Would otherWise have With a symmetric trigger. This com [58] Field of Search ...... 307/112, 113, pensates for Charge dumping of the phase Control Capacitor 307/116, 125, 129, 139, 140, 157, 315/194, into the gate of the triac Which Would otherWise cause the 199, 299, 361, 362, DIG. 2, 323/265, 273, snap on hysteresis effect. 282, 284, 300, 905, 327/419, 438, 447, 452, 455, 457 6 Claims, 4 Drawing Sheets

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. IF| N $5 AC SOURCE \14 '. 5:? S‘I 56 l_ QUADRAC 5,854,519 1 2 ASYMMETRICAL AC TRIGGER components or using AC triggers having asymmetrical elec SIMULATION trical characteristics. The resulting devices, hoWever, are not believed to be commercially available and having to add a This Application is a continuation of US. patent appli number of components to a phase control circuit design to cation Ser. No. 08/183,459 ?led Jan. 18, 1994 and now US. achieve the effect of an AC trigger increases its cost and Pat. No. 5,619,081 issued Apr. 8, 1997. complexity. The result has been a long felt need for a solution to this BACKGROUND OF THE INVENTION problem that is simple and effective, and yet costs very little The present invention relates generally to the ?eld of in terms of component cost and circuit complexity. electric light dimmers and controls, and more particularly to a system for controlling and eliminating undesirable char SUMMARY OF THE INVENTION acteristics associated With conventional electric light Aprimary object of the present invention is to provide an dimmers, such as What is knoWn as snap on hysteresis AC trigger having asymmetrical electrical characteristics so effects. as to eliminate the snap on hysteresis effect. 15 Conventional loW cost light dimmers of the type a con Another object of the present invention is to provide such sumer might purchase from his or her local hardWare or an AC trigger Which is relatively inexpensive. mass merchandising store presently exhibit an undesirable Yet another object of the present invention is to provide an characteristic Which Will herein be referred to as the snap on hysteresis effect. This effect manifests itself in the operation AC trigger Which is simple and relatively easy to incorporate of a dimmer by causing the lamp to Which the dimmer is into circuits. connected (such as an incandescent electric light bulb) to Other objects and features of the invention Will be pointed turn on at an initial brightness level someWhat and often out in the folloWing description and claims and illustrated in signi?cantly higher than the minimum brightness level the accompanying draWings, Which disclose, by Way of achievable. This effect is both unexpected and undesirable. example, the principles of the invention, and the best modes Typically, dimmer designs today incorporate semiconduc 25 presently contemplated for carrying them out. tor devices that perform the dimming function, and comprise BRIEF DESCRIPTION OF THE DRAWINGS an AC sWitch and a trigger control circuit to control the AC sWitch. Conventional trigger circuits employ diacs con In the draWings in Which similar elements are given nected to the gate of a triac Which acts as the AC sWitch to similar reference characters: turn the triac on and turn off. Aphase shift circuit used With FIG. 1 is a circuit diagram of a conventional dimmer of the diac determines Where in the half cycle of the AC voltage the type found in the prior art; supply Wave the triac ?res, thereby determining the duration FIG. 1A is a graph illustrating typical electrical charac of time current ?oWs through the lamp Which, in turn, teristics of a symmetrical trigger as found in the prior art; determines its brightness. A typical phase control circuit of the type presently being sold by Leviton Manufacturing Co., 35 FIG. 2 is a circuit diagram of a dimmer constructed according to the concepts of the present invention; Inc. of Little Neck, NY, for example, utiliZes a trigger that exhibits symmetrical electrical characteristics during both FIG. 2A is a graph illustrating the electrical characteristics positive and negative half cycles of the AC voltage. Due to of the dimmer of FIG. 2; characteristics of the triac, hoWever, the phase control circuit FIG. 3 is a circuit diagram of a further embodiment of a exhibits asymmetrical electrical characteristics When con dimmer constructed according to the concepts of the present trolling the gate of a triac. The end result is that the triac invention; triggers earlier in the half cycle than it Would otherWise have FIG. 4 is a circuit diagram of yet another embodiment of and at a higher than minimum brightness level. Auser, When a dimmer constructed according to the concepts of the confronted With the higher than desired brightness level, Will 45 present invention; back off the control (turn the control knob, for example, in FIG. 5 is a circuit diagram of still another embodiment of the dimming direction) to achieve brightness levels closer to a dimmer constructed according to the concepts of the the minimum achievable level. present invention. In addition to the undesirable higher initial brightness level of the lamp, another draWback of the snap on effect is DETAILED DESCRIPTION OF THE that if poWer is interrupted and the brightness Was backed off INVENTION after initial turn on, and thereafter the poWer Was restored, In order to provide,the reader With a more complete the light might not come on at all. Furthermore, if the phase understanding of the present invention and an appreciation control circuit utiliZes a series of stepped resistances instead of its advantages, a description of a preferred embodiment of of a potentiometer, it is not possible With such conventional 55 the present invention in a typical operating environment is devices to reach relatively loWer brightness level. presented beloW. Prior art attempts to solve this snap on hysteresis problem ShoWn in FIG. 1 is a schematic shoWing a conventional have included utiliZing tWo circuits to control the ?ring of triac phase control circuit as found in the prior art and used the triac, rather than a single circuit. The ?rst such circuit extensively in dimming and other applications such as motor controls the timing (i.e. brightness) of ?ring, While the speed controls. The characteristics of its symmetrical trigger second circuit controls the charge dumping of the capacitor are shoWn in FIG. 1A. Conventional loW cost dimmers into the gate of the triac. DraWbacks With this prior art typically employ this type of circuit. It suffers, hoWever, approach include an increase in cost and added complexity from a feature called snap on hysteresis. At the start of a of the overall circuitry. positive half cycle, assuming the dimmer shoWn in FIG. 1 is Another attempted solution to the snap on hysteresis 65 energiZed, and the potentiometer 16 is set to maximum problem is to use an asymmetrical trigger in the phase resistance, the load 12, typically a lamp, Will be off. This is control circuit. This can be done using a number of discrete because the peak voltage across the capacitor 18 does not 5,854,519 3 4 exceed the symmetrical trigger or diac 20 breakover voltage metrical trigger causes the SBS 36 and the triac 38 to trigger VB. As the resistance of potentiometer 16 is reduced, a point later in the AC cycle than it Would have With a symmetrical Will be reached Where the capacitor 18 voltage exceeds the trigger, thereby causing the elimination of the undesirable diac 20 breakover voltage VB. When the diac 20 breaks over, snap on hysteresis effect. charge from the capacitor 18 ?oWs into the gate of the triac In an alternative embodiment of the present invention, an 22 to turn it on. At the same time, the capacitor 18 voltage approach is used in conjunction With a conventional sym drops to a value less positive than before the reduction in metric diac 46, as shoWn in FIG. 4. As With the design charge. As shoWn in FIG. 1A, the symmetrical trigger or diac utiliZing the SBS 36, the requirement here is that the Zener 20 exhibits negative resistance as it starts conducting more 44 breakdoWn voltage equal the difference the breakover current. Thus, as the triac starts conducting, the voltage and maintaining voltage of the diac 46. The operation of the across the diac 20 drops. This alloWs more charge to How device of FIG. 4 is substantially similar to that described from the capacitor 18 into the gate of the triac 22. At this With respect to the SBS 36. point, during the folloWing negative half cycle of the AC In yet another embodiment of the present invention, the source 14, the diac 20 breakover voltage-VB is reached desired result is achieved utiliZing a quadrac semiconductor sooner because the capacitor 18 has a reduction in maximum 15 positive voltage due to its loss of charge in the positive half device 56, as shoWn in FIG. 5. The quadrac consists of a triac With a diac connected in series With the gate of the triac. cycle. The result is that subsequent diac 20 trigger or The operation of the device of FIG. 5 is substantially the breakover points, both positive and negative, occur earlier same as described above With respect to the SBS 36 of FIG. than the diac 20 breakover point of the very ?rst half cycle. 3. Triggering the diac 20 sooner in the AC cycle causes the light to turn on at a higher voltage. This results in the light The same bene?ts Which have been described above 12 being brighter than that Which the ?rst half cycle Would utiliZing dimming circuits as examples of the environment have provided. In order for a user to dim the light, the for the present invention may also be achieved using a triac potentiometer 16 resistance must be increased. It is unde based motor speed control Which uses a circuit similar to that of a dimmer. sirable to require a user to reduce brightness after turning on 25 the light. While there have been shoWn and described and pointed The solution of this problem afforded by the present out the fundamental novel features of the invention as invention is to provide an asymmetrical trigger or diac. FIG. applied to the preferred embodiment, it Will be understood 2 shoWs a block diagram of a dimmer 58 incorporating an that various omissions and substitutions and changes of the asymmetrical trigger 10 connected betWeen the phase con form and details of the device illustrated and its operation trol circuit consisting of potentiometer 24 and capacitor 26 may be made by those skilled in the art, Without departing and a triac 28. The trigger characteristics of the asymmetri from the sprit of the invention. cal trigger 10 are shoWn in FIG. 2A. FIGS. 3 to 5 shoW The embodiments of the invention in Which an exclusive alternative applications of the asymmetrical trigger 10 in property or privilege is claimed are de?ned as folloWs: dimming circuits. What is claimed is: Referring to FIG. 2A, in one polarity, the breakover 1. A dimmer comprising: voltage VB1 is the same as in a symmetrical diac. In the other a) sWitching means having ?rst and second terminals and polarity, hoWever, the breakover voltage VB2 is increased by a gate terminal; said ?rst terminal connected to one side the same amount as the voltage difference betWeen break of a load; said second terminal connected to a source of over and maintenance in the ?rst polarity, VB1_VM. The AC voltage; said sWitching means operable to change result is that even though the capacitor 26 voltage is reduced from a state of high impedance to a state of loW during the ?rst half cycle, it must charge to the higher impedance upon the application of suf?cient current to breakover voltage, thus maintaining the brightness level of said gate terminal causing current to How through said the ?rst half cycle. load; Since an asymmetrical trigger device as a single compo 45 b) a conductor coupled betWeen the other side of said load nent is not available, its characteristics have been simulated and said source of AC voltage; With the present invention. This has been done using a Zener c) symmetrical trigger means having third and fourth diode 34 in series With a silicon bilateral sWitch (SBS) 36, terminals, said symmetrical trigger means fourth ter as shoWn in FIG. 3. The Zener breakdoWn voltage is chosen minal coupled to said gate terminal of said sWitching to be the difference betWeen the breakover and maintaining means for preventing said sWitching means from voltage of the SBS. Assume initially the capacitor 32 is fully changing state until suf?cient voltage appears across discharged, With the potentiometer 30 near its maximum said third and fourth terminals of said symmetrical setting, the capacitor 32 begins charging. When the capacitor trigger means; said symmetrical trigger means exhib 32 voltage reaches the breakover voltage of the SBS 36, it iting negative impedance characteristic upon breakover starts conducting and current ?oWs through the Zener 34, 55 and having similar breakover points during both posi Which is forWard biased, into the gate of the triac, turning it tive and negative half cycles of a source of AC voltage; on. Ass current ?oWs into the gate of the triac 38, the voltage d) phase control means coupled betWeen said one side of across the SBS 36 drops to its maintaining voltage due to its said load, said source of AC voltage and to an output negative impedance characteristics. As in the case of a diac terminal; and trigger, this causes additional charge to be removed from e) asymmetrical trigger means connected betWeen said capacitor 32. In the folloWing half cycle the Zener 34 is noW output terminal of said phase control means and said reverse biased and Will not conduct until its breakdown third terminal of said symmetrical trigger means, said voltage is reached. The Zener 34 breakdoWn voltage, symmetrical trigger means operable to compensate for hoWever, is chosen to be the difference betWeen the break charge depletion in said phase control means caused by over and maintaining voltage of the SBS 36. Therefore, the 65 said symmetrical trigger means; said asymmetrical capacitor 32 must charge an additional amount; the value of trigger means effective to change state asymmetrically the Zener 34 breakdoWn voltage. Thus, utiliZing an asym during each half cycle of said AC voltage. 5,854,519 5 6 2. A dimmer, as de?ned in claim 1, wherein said phase 3. A dimmer, as de?ned in claim 1, Wherein said asym control means further comprises: metrical trigger means includes a silicon bilateral sWitch. a) potentiometer means having a ?fth and siXth terminal, 4. A dimmer, as de?ned in claim 1, Wherein said asym said ?fth terminal coupled to said one side of said load metrical trigger means includes a diac. to control the current ?oWing to said load from said 5 5. A dimmer, as de?ned in claim 1, Wherein said asym source of AC voltage; metrical trigger means includes a quadrac Wherein a diac of b) a capacitor having seventh and eighth terminals, said said quadrac comprises said symmetrical trigger means. eighth terminal connected to said source of AC voltage; 6. A dimmer, as de?ned in claim 1, Wherein said asym and said seventh terminal of said capacitor coupled to metrical trigger means includes a Zener breakdown diode. said siXth terminal of said potentiometer and to said 10 asymmetrical trigger means. * * * * *