US3299320A - Dimmer for a plurality of discharge lamps - Google Patents

Description

17, I M'AM'ORU KURATA :3, 299;320

DIMMER FOR A PLURALITY 01 DISCHARGE LAMPS Filed Oct. 28; 1965 2 Sheets-Sheet 1 I Freq/- F I e HH MHN NH Hn N I HV INVENTOR.

Q BY

9 MAMOF'QU KURATA 3,299,320

DIMMER FOR A PLURALITY DISCHARGE LAMPS Filed Oct. 28, 1963 2 Sheets-Sheet 2 Wl V I NVEN TOR.

BY 9 8 A cw United States Patent 3,299,320 DIMMER FOR A PLURALITY OF DISCHARGE LAMPS Mamoru Kurata, Kawasaki-sin, Japan, assignor to Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan, a corporation of Japan Filed Oct. 28, 1963, Ser. No. 319,288 Claims priority, application Japan, Oct. 31, 1962,

1 Claim. (Cl. 315-210) This invention relates to a dimmer or illumination control device for discharge lamps and the like.

Present time dimmers for discharge lamps are usually comprised'by a conduction controller including at least one semiconductor such as a silicon controlled rectifier element and a gatesignal generator for providing a gate signal, usually in the form of an electric pulse, to the gate electrode of said rectifier element. For dimmers designed to control a relatively large number of discharge lamps, the gate signal generator is required to produce a gate pulse of large magnitude. Generally the gate signal generator includes a pulse generator or oscillator and a gate transformer connected between said pulse generator and the gate electrode of said semiconductor rectifier element. In order to produce a large gate pulse from the secondary winding of the gate transformer the resist ance in series with the primary winding thereof should be decreased. Then the resultant impedance of the circuit of the primary winding becomes inductive and if a silicon controlled rectifier element is involved in series with the primary winding it becomes difiicult .to turn off this rectifier element. In other words, the pulse generator can not generate a satisfactory pulse and hence the discharge lamp can not be controlled in the desired manner.

It is an object of this invention to eliminate the abovementioned defect.

Further object of this invention is to provide a pulse generator of large power which can efiiciently control semiconductor dimmer. While the specification con-' clu-des with the claim particularly pointing out and distinctly claiming the subject matter which is regardedas this invention, it is believed that the invention will be better understood from the following description taken in connection with the accompanying drawing, in which FIG. 1 shows a connection diagram of a prior dimmer for discharge lamps;

FIG. 2 shows waveforms of various components of the dimmer shown in FIG. 1 and FIG. 3 shows a connection diagram of a dimmer for discharge lamps constructed in accordance with this invention.

Before describing this invention in detail an example of a prior art dimmer will be described hereunder by referring to FIG. 1. A ocnduction controller including a pair of parallel connected semiconductors, such as silicon controlled rectifier elements SCR and SCR of opposite polarities is connected between a source of alternating current represented by input terminals t and t and a suitable step-up autotransformer T the secondary side thereof being connected to a discharge lamp PL. Filaments of the discharge lamp are energized by separate filament transformer T The gate signal generating circuit 2 generally includes a full wave bridge rectifier 1 comprised by four diodes D D D and D Input terminals of the bridge rectifier are connected across said terminals t and t and a series circuit including a resistor R the primary winding L of a gate transformer T and a silicon controlled rectifier SCR poled as shown in FIG. 1, and another series circuit including a resistor R and a Zener diode Z D 3,299,320 Patented Jan. 17, 196? ice poled as shown, 'are connectedin parallel across the'out-' put terminals A and B of the bridge rectifier. "A resistor R is connected across said primary winding L The anode. of the Zener diodeis connected to one base. electrode B of a unijunction transistor UJ T through a resistbr R while the cathode of the Zener diode'is connectedt o secondary windings the other base "electrode B of 'the unijunctiont'ransistor through a resistor R to 'con'stitutea relaxation oscillator; The junctionbetween the base electrode B and there}. sistorR is ocnnected to the gate electrode of the silicon controlled'rectifier SCR In parallel with'the Zener diode ZD is connected a seriescircuit comprising a ,re-' sistor R a"variable resistorjVR' and a condenser' 'p, the junction between the variable resistor VR and the condenser C vbeing'connected to the emitter electrode. E of the unijunction transistor UJT, [Secondarywi ndings Lg and "L fof the transformer T are respe'c tively cori nected across the gate and cathode electrodes of the silicon controlled rectifier ,elrnents SCR and SC R and diodes D and D are respectively cormected'across said- The magnitudeofthe output voltage of the fullwave rectifier 1 at the righthand terminal of the resistor .R is made constant by'the action of the" ZenerdiodeZjD and is then utilized to charge the condenser C through resistors R and V R. When the'terminalvoltage'of the condenser C exceeds'a predetermined value the unijuric tion transistor UJT will conduct momentarilyto produce a pulse, as shown by'FIG. 2b,. across the resistorfR Thus, it will be seen'that thephaseof this pulse is de termined by the time constant of a circuit including resistors R VR and the condenserC so tat it can beflsuitably varied by the adjustment 'of the VariabIe resiStorVRJ The gatesignal generating"circuit Zoperatesas follows: A Alternating current voltage supplied to input terminals t and I is rectified by the full wave rectifier 1'to produce a pulsating voltage as shown by FIG. 2a across output terminals A and B. As-sta-ted above the relaxation oscillator comprising the unijunctidn transistor UJT 'acts to produce a pulse signal 1 as shown by FIGI Zbywhich 2c. As a result a. voltagefindicated FbY FIGi Zd will be induced in the secondary win-dingsL andL of the gate transformerT As is well known in the art the silicon controlled rectifier elements SCR and SCR of the conduction controller are rendered conductive when the gate voltage a induced in the secondary windings L and L exceeds their threshold value. Since their conduction period during successive half cycles is determined by the phase of the pulse b shown in FIG. 2 the current supplied to the discharge lam-p PL can be easily controlled by varying the variable resistor VR.

It is obvious that dimmers adapted to control many discharge lamps and the like loads require semiconductor controlled rectifier elements of large capacity so that large gate signals should be generated to operate these rectifier elements. To meet this requirement it is necessary to reduce the magnitude of the resistance R connected in series with the primary winding L of the gate transformer T to increase the voltage induced in its secondary windings.

Decrease in the magnitude of said resistor R however, will make inductive the resultant impedance of the circuit including R R L and SCR It was found that the silicon controlled rectifier SCR connected in series with the primary winding often fails to cut-off its current owing to such inductive impedance, thus providing unsatisfactory illuminating control.

' This invention contemplates to eliminate the abovement-ioned defect by substituting a diode for the resistor R whichis connected in parallel with the primary winding L of the gate ,transforn'i'erTi.

gMore particularly, as shown in FIG. 3, a diode D is'connectedacross the primary winding L of the gate transformer with the polarity indicated. Thus, when it is intended to change the silicon controlled rectifier from conductive state to non-conductive state the current which tends to flow through the primary winding L by the action of saidinc-reased inductive impedance is by-passed through the diode D, so thatthe silicon controlled rectifier elementSCR is positively rendered non-condud tive." h Q Since other components of FIG. 3 are quite identical with those designated by thesame reference characters in FIG. 1, description thereof is believed unnecessary. Thus, even in large dimmers for energizing relatively large number or lamps, by merely substituting a simple diode D; for a resistor R connected across the primary winding of a gate transformer T of the prior gate signal generating circuit 2 it is possible to provide" sufficiently large gate pulses for the controlled rectifier elements contained in the, conduction controller, thus assuring positive operation of the dimmer.

'1 Although in-the above described embodiment there has been shown a conduction. controller comprising a pair of parallel'conne'cted silicon controlled rectifier elements of opposite,polarities, it will-be understood to those skilled in the art that the conduction controller may comprise four diodes. connected in a bridge and one silicon controlled rectifier element connected between diagonals of the bridge. t v

While the invention has been explained by describing a particularemb-odiment thereof, it will be apparent that improvements and modifications may be made without departing from the scope of the invention as defined in the appended claim.

Whatis claimed is: I A dimmer circuit comprising a plurality of discharge lamps, a source of alternating current, a conduction controller including a first silicon controlled rectifier element con- -nected-between said source of alternating current and said'dis'chargelam-ps, and a gate signal generator adapted to supply a gate signal to said first silicon controlled rectifier element,- said gate signal generator including 4 a rectifier to rectify the alternating current voltage of said source, a pulse oscillator for generating electric pulses comprising a unijunction transistor supplied with the output of said rectifier, a circuit connected across the output terminals of said rectifier :and including in series a primary winding of a gate transformer,

a resistor of relatively low value compared to the impedance of said primary winding, and a second silicon controlled seniiconduct-or rectifier element,

. said electric pulses being applied tothe gate electrode of said second silicon controlled rectifier element to repetitively trigger and cu-t-ofl said second silicon controlled rectifier element mean-sto supply the output of a secondary winding of said gate transformer to the gate electrode of said first silicon con-trolled rectifier element of d said conduction controller,

and a diode means of polarity opposite to that of said second silicon controlled rectifier element and connected in parallel with said primary of said gate transformer and in series with said second silicon controlled rectifier element for passing therethroughthe current which tends to flow through said primary winding due to its inductive impedance when said second silicon controlled rectifier element is cut-off in response to a pulse from said pulse oscillator, thereby causing a positive cut-01f action.

References Cited by the Examiner UNITED STATES PATENTS 2,914,683 11/1959 Terry -307-88.5 3,113,241 12/1963 Yonushka 3l5200 3,131,309 4/1964 Blocher 30788.5 3,140,423 7/1964 Roberts et a1, 315201 OTHER REFERENCES Article entitled, A Survey of Some Circuit Applications of the Silicon Controlled Switch and Silicon Controlled Rectifier found in the December 1959 issue of Solid State Products, Inc., Bulletin D420-02, pp. 7, 8, 9, 22, 23 and 24.

I.B.M. Technical Disclosure Bulletin, vol. 5, September 1962, p. 55.

JOHN W. HUCKERT, Primary Examiner. A. M. LESNIAK, Assistant Examiner.

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