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 EdwardYevgeny 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 LOAD 5 AC SOURCE 56 QUADRAC U.S. Patent Dec. 29, 1998 Sheet 1 of4 5,854,519 —>°_ LOAD \12 16 SYMMETFHCAL AC SOURCE x14 - TRIGGERKI £592 l>| __ \20 >c T“. FIG. 1 (PRIOR ART) -V ‘B I :V VB FIG. 1A (PRIOR ART) U.S. Patent Dec. 29, 1998 Sheet 2 of4 5,854,519 _ _ _ _ _ _ — _ _ _ _ _l —>°- LOAD i “12 I I I 24 l I F28 | AC SOURCE “1 4 I ASYMMETRICAL | | IGGER um I : 7%“26 | l )0 '_ _ _ _DLMM_I§R_ _ _ _| FIG. 2 5‘8 1-1 V51 VM . l I V‘ :v : B2 FIG. 2A U.S. Patent Dec. 29, 1998 Sheet 3 of4 5,854,519 ——+<>— LOAD \12 g- I: so _______ __ 538 AC SOURCEXM , I I __ I_B4_____3§I 10 >0 T32. FIG.3 OAD x12 0 _______ __ F48 AC SOURCENM . i m g I / '44 46 >0 T42. U.S. Patent Dec. 29, 1998 Sheet 4 0f 4 5,854,519 ‘——> °- LOAD . 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.