Patent US3868546 - LIGHT DIMMING SYSTEM FOR CONTROLLING

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LIGHT DIMMING SYSTEM FOR CONTROLLING lamp load 8. An illustrative lamp dimmer is disclosed

BRIGHTNESS AND RATE OF CHANGE OF in co-pending application, Ser. No. 168,317, filed Au

BRIGHTNESS OF LIGHTS gust 2, 1971, now U.S. Pat. No. 3,733,528 granted May

15 1973

BACKGROUND OF THE INVENTION , '.' .. . . t. .

5 The lamp dimmer 4 functions in response to voltage

This invention relates to light dimming systems and signals from a field effect transistor 54 which is coupled

to control units for such systems capable of controlling to the lamp dimmer by conductor 28. A common con

the brightness and the rate of change of brightness of ductor 32 couples the lamp dimmer 4 with a plurality

a lamp or lamps connected to the system. of separate remote control units 16, 20, ... , and 24

Conventional systems for controlling the rate of 10 which are coupled in parallel with one another by conchange of brightness of lights (i.e., the rate at which the ductors 32, 56, 60 and 62. A direct current voltage brightness level is increased or decreased) typically in- source 51 provides direct current operating voltage via elude either a manually operated potentiometer or a a positive terminal 52 connected to conductor 60 and motor-driven potentiometer. With a light dimming sys- via a negative terminal 53 connected to common contem utilizing a manually operated potentiometer, it is 15 ductor 32, for energizing the control units 16, 20, . . . difficult to obtain smooth and even transitions between > and 24. Although only three control units are shown, brightness levels because of the dependency upon the more or less could be provided as desired by the system steadiness of the human operator. Light dimming sys- user Each of the contro, units fa identicai in constructems utilizing motor-driven potentiometers overcome tion and includes two control knobs> an "on- button this problem, but such systems are relatively bulky and 20 and ^ „off„ ... For ... contro, unit u m_ costly. Further, such systems are subject to fairly rapid dudeg a sprjng loaded pushbutton switch 36 for «turn. wear because of the frequent mechanical movement. jng Qn„ the contro, unjt ,6 a spring ,oaded pushbutton

It is an object of the present invention to provide a switch 40 for tumi off the contro, unit 16 and a]so

compact and inexpensive light dimming system for con- {he other contro] unhs> a rotatable control knob 44 for

troll.ng the brightness level of lights and the rate of 25 setti the bd htness or intensit ,eve, of the ,am ,oad

chang.ng the brightness level. 8 and a rotatable eontrol knob 48 for setti the rate

It is another object of the present invention to pro- at which ^ bri htness for the , load 8 is tQ be

vide such a system having a relatively long and useful ... from ^ ^ ^ ^ ^ a ^

,'. .... ., ,. . c .. . . .. . in greater or less than the previous level. Each of the conIt is still another object of the present invention to JU f . .. . ,, . , , .. . . , .,

., . . .i .. .... . . . • ■ trol units may be used independently to control the

provide a control unit for a light dimming system which .... j . c , r. . .. ,

• ■ . , . ♦ i u «u • u* i i *i- u. brightness and rate of change of brightness of the lamp

is adapted to control change of brightness level of light . = _ ,. ... e . , .v

, .• „ . ... . • • *u r _ ♦ l°a(l 8 regardless of the previous settings of any of the

automatically and without requiring the use of a motor. , 6 , v 6 J

, i i- i.^ J- • . u ■ u- i ether control units.

The need for light dimming systems having multiple . . , ,

contro! units has been discussed in J. C. Johnson, U.S. 35 t A caPacltorJ>4 '"^connects conductors 56 and 32 Pat. No. 3,697,821, issued Oct. 10, 1972. A system is for stonng a charge and for thereby supplying a voltage there disclosed which includes a plurality of separate to the f,ate ^ctrode of the field effect transistor 54 for remote control units for individually and independently controlling the voltage at the source electrode 57 of the controlling the operation of a common lamp dimmer fleld efffct transistor and thus the voltage supplied via unit, each remote control unit being capable of turning 40 the conductor 28 to the lamp dimmer 4. The lamp dimoff and turning on the lamp dimmer unit and of control- mer 4'in response .to the voltage on conductor 28, conling the brightness of the lamps independently of the trols the brightness of the lamp load 8. The voltage previous setting or condition of any of the other remote across the capacitor 64 is determined by the control control units. In this system, the brightness level is con- unlts 16> 20, ... , and 24 as will be more particularly trollable but not the rate of changing the brightness described later.

level (other than manually). The operation of control unit 24 will now be deIt is a further object of the present invention to pro- scribed, it being understood that the other control units vide a new and improved control unit for a light dim- 16> 20,..., operate in the same fashion. The control ming system which may be connected in parallel with unit 24 includes a spring-loaded normally open switch one or more other such control units to individually 0 66 for turning on the control unit 24 and a similar and independently control both the brightness and the spring-loaded normally open switch 68 for turning off rate of change of brightness of lights. or disabling the control unit 24 and any other control

unit which may not have been turned off. The switch

BRIEF DESCRIPTION OF THE DRAWINGS 66 is connected to the gate electrode of a unilateral

The above and other objects and advantages of the 55 semiconductor triode switch 70 of the type known as

present invention will become more apparent from the a silicon-controlled rectifier (SCR). The cathode of the

following detailed description presented in connection SCR 70 is connected to the common conductor 32 in

with the accompanying drawing which shows a light terconnecting all the control units to the lamp dimmer

dimming system having a plurality of control units in 6Q 4. The anode of the SCR 70 is connected to the junc

accordance with the present invention. tion interconnecting a capacitor 72 and a resistor 74.

r. A rrs Ccodidti^m When the switch 66 is momentarily closed in response

DETAILED DESCRIPTION t0 the depression of a corresponding "on" pushbutton

The system shown in the drawing includes a master of the control unit 24, current flows from the direct lamp dimmer unit 4 for controlling the brightness level 65 current source 51 via a resistor 76, the switch 66 and of a lamp or lamps included in a lamp load 8. The lamp a resistor 78 to the conductor 32. Current is also supdimmer 4 controls the root-mean-square (R.M.S.) plied to the gate electrode of the SCR 70 and this turns value of current flow from an A.C. source 12 to the on or renders conductive the SCR.

When the SCR 70 is conductive, its internal anodeto-cathode impedance is very small. When turned on, the SCR 70 remains conductive until the voltage between its anode and cathode is reduced to practically zero or is reversed in polarity. With the SCR 70 con- 5 ductive and the switch 66 opened following its momentary closure, the commutating capacitor 72 charges up to a direct current voltage level corresponding to the direct current voltage difference between the junction of resistor 76 and switch 66 (which is B+) and the junc- 10 tion between resistor 74 and the SCR 70 (which is near B—, i.e., near the potential of conductor 32.)

Turning on the SCR 70 causes direct current to flow from the terminal 52 via a resistor 80, an indicator lamp 82, (which is energized to provide a visual indica- 15 tion that the control unit is on) the resistor 74, and the SCR 70 to the conductor 32. A voltage drop is thus developed across the resistor 80 causing a PNP-type transistor 84 to be biased into saturation so that current also flows via the transistor 84 through the resistor of 20 a potentiometer 86 to the conductor 32. The flow of current through the resistor of the potentiometer 86 establishes a voltage at the tap of the potentiometer and it is this voltage which ultimately determines the brightness level of the lamp load 8. The tap of the potentiom- 25 eter 86 is mechanically coupled to a corresponding control knob for setting the brightness level in accordance with the operation to be described hereafter.

Turning on the transistor 84 also causes current to flow from the collector of the transistor through a vari- 30 able resistor 88 to the control terminal 90 of an operational transconductance amplifier (OTA) 92. the adjustable element of the variable resistor 88 is mechanically coupled to a corresponding control knob for controlling the rate of changing the brightness level of the 35 lamp load 8 as will be described hereafter.

The OTA 92 is similar to a conventional operational amplifier in that it includes the usual two differential input terminals 91 and 93, but also differs therefrom in that it includes a control terminal 90. One of the differ- 4^ ential input terminals 93 of the OTA 92 is connected via a diode 94 and a resistor 96 to the tap of the potentiometer 86. The other differential input terminal 91 is connected via a diode 98 and a resistor 100 to the source electrode 57 of the field effect transistor 54. The output terminal of the OTA 92 is connected to the capacitor 64 and to the gate electrode of the field effect transistor 54.

The OTA 92 operates to generate an output current 5Q which is proportional to the transconductance of the OTA and the voltage difference at the OTA's two differential input terminals. The transconductance of the OTA 92, in turn, is determined by the current supplied to the control terminal 90. The voltage difference at ^ the two differential input terminals of the OTA 92 also determines the polarity of the output current of the OTA. When the voltages at the two differential input terminals 91 and 93 are equal, then the output current is zero. The OTA 92 might illustratively comprise one 6Q of the OTA's described in RCA publication "RCA Solid State Data Book Series," Application Notes, SSD-202, 1972, pages 223 et seq.

The output current from OTA 92 either charges or discharges the capacitor 64, depending upon the polar- 65 ity of the current. The rate of charging and discharging the capacitor 64 can thus be controlled by controlling the application of current to the control terminal 90,

which, in turn, is controlled by the setting of the variable resistor 88. As long as there is a voltage difference at the input terminals 91 and 93 of the OTA 92 and current is being supplied to control terminal 90, the capacitor 64 will continue to charge or discharge, depending on the polarity of the output current of the OTA. If the polarity is positive, the capacitor 64 will continue to charge, causing the voltage thereacross to increase and the voltage at the source electrode 57 and thus at the differential input terminal 91 to increase until the voltage at terminal 91 is equal to the voltage at differential input terminal 93. The voltage at terminal 93 is, of course, established by the setting of the tap of the potentiometer 86. If the polarity of the output current of the OTA 92 is negative, then the converse operation occurs. Thus the setting of the tap of the potentiometer 86 determines the voltage across the capacitor 64 and the setting of the variable resistor 88 determines the rate of change of the voltage across the capacitor. As already indicated, the voltage across the capacitor 64 controls the voltage at the source electrode 57 of the field effect transistor 54 to thereby control the voltage supplied to the lamp dimmer 4.

The employment of the OTA 92 in the configuration of the drawing provides an advantage over other types of circuitry because of its ability to generate currents of low magnitude. Because of this, the charge or discharge time of the capacitor 64 can be made longer than would otherwise be possible so that the elapsed time of changing the brightness of the lamp load 8 can similarly be made longer. This is desirable in lamp dimming systems.

The field effect transistor 54 is provided for purposes of isolation. Some current is required for the differential input 91 of the OTA 92 and if this input were coupled directly to the capacitor 64, it would adversely affect the rate of charge or discharge of the capacitor. Because the gate electrode of a field effect transistor does not draw current by coupling the gate electrode to the capacitor 64, no charge is drained from the capacitor 64 by the differential input 91 in the course of charging and discharging the capacitor. The current needed by the differential input 91 is obtained via conductor 60 from the terminal 52 of the voltage source 51.

The control unit 24 is turned off, i.e., disabled from affecting the voltage across the capacitor 64 by momentarily closing an "off" switch 68. Prior to closing the switch 68, when the control unit 24 is on so that the SCR 70 is conducting, the left-hand plate of the capacitor 72 is at a potential of B+ and the right-hand plate is at near B— potential of conductor 32. When the switch 68 is closed, the potential of the left-hand plate of the capacitor 72 is brought to near B— potential causing the right-hand plate to be momentarily brought to a negative potential below the potential of the lefthand plate. The voltage at the cathode of the SCR 70 is thus momentarily made more positive than the voltage at the anode thereof thereby disabling or rendering the SCR 70 non-conductive. With the SCR 70 nonconductive, no current flows via the resistor 80 so that the transistor 84 is turned off. This, in turn, results in the termination of current flow via the variable resistor 88 to the control terminal 90 of the OTA 92 so that the OTA is effectively turned off. The control unit 24 is thereby disabled or turned off until the "on" switch 66 is again closed.

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Patente

LIGHT DIMMING SYSTEM FOR CONTROLLING