Abstract:
A dimmer switch has a user adjustable high-end trim. The dimmer switch includes a bidirectional semiconductor switch, such as a triac, for controlling the amount of power delivered from a source of alternating current power to a lighting load, such as an electric lamp. A user-adjustable timing circuit controls the conduction time of the triac from a minimum time to a maximum time. The maximum possible conduction time of the triac is the high-end trim. The minimum possible conduction time of the triac is the low-end trim. The timing circuit includes a user-accessible switch that allows a user to reduce the high-end trim from a first nominal level to a second reduced level, lower than the first level, without substantially affecting the low-end trim. The switch allows a user to switch a transient voltage suppressor into and out of parallel connection with a resistor that is part of an RC timing circuit for the triac. The dimmer switch advantageously uses less energy and the lifetime of the lamp is extended when the second reduced level of the high-end trim is selected.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims priority from commonly-assigned U.S. Provisional Patent Application Ser. No. 60/812,337, filed Jun. 8, 2006, entitled DIMMER WITH ADJUSTABLE HIGH-END TRIM, the entire disclosure of which is hereby incorporated by reference. 
     
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to load control devices for controlling the amount of power delivered to an electrical load, specifically a dimmer switch that controls the intensity of a lighting load. More particularly, the invention relates to a dimmer switch having a user-accessible switch for adjusting a high-end trim of the dimmer switch. 
         [0004]    2. Description of the Related Art 
         [0005]    A conventional wall-mounted load control device is mounted to a standard electrical wall box and is coupled between a source of alternating-current (AC) power (typically 50 or 60 Hz line voltage AC mains) and an electrical load. Standard load control devices, such as dimmers and dimmer switches, use one or more semiconductor switches, typically bidirectional semiconductor switches, such as triacs or field effect transistors (FETs), to control the current delivered to the load, and thus, the intensity of the light provided by the lighting load. The semiconductor switch is typically coupled in series between the source and the lighting load. Using a phase-control dimming technique, the dimmer renders the semiconductor switch conductive for a portion of each line half-cycle to provide power to the lighting load, and renders the semiconductor switch non-conductive for the other portion of the line half-cycle to disconnect power from the load. The ratio of the on-time, during which the semiconductor switch is conductive, to the off-time, during which the semiconductor switch is non-conductive, determines the intensity of the light produced by the lighting load. 
         [0006]    Wall-mounted dimmer switches typically include a user interface having a means for adjusting the light intensity of the load, such as a linear slider, a rotary knob, or a rocker switch. Dimmer switches also typically include a button or switch that allows for toggling of the load from off (i.e., no power is conducted to the load) to on (i.e., power is conducted to the load), and vice versa. 
         [0007]    Many people desire to save energy. One way to save energy in a dimmer is to adjust the high-end trim of the dimmer to limit the maximum amount of power that the dimmer will deliver to the lighting load. The high-end trim is the maximum amount of power that a dimmer is capable of delivering to a lighting load. The high-end trim is determined by the maximum possible on-time of the semiconductor switch. In contrast, the low-end trim is the minimum amount of power that a dimmer is capable of delivering to a lighting load, when the dimmer is on. The low-end trim is determined by the minimum possible on-time of the semiconductor switch when the semiconductor switch is conducting. 
         [0008]    Prior art dimmer switches typically have fixed high-end trims and provide no user-accessible means for a user to be able to change the high-end trim. This is especially true of two-wire analog dimmer switches. There is, therefore, a need for a simple, low-cost, two-wire, analog dimmer having a user-accessible means for selecting a lower high-end trim. 
       SUMMARY OF THE INVENTION 
       [0009]    In one embodiment of the present invention, a load control device with an adjustable high-end trim comprises a user-accessible means for reducing the high-end trim of the load control device from a first level to a second level lower than the first level, the user-accessible means for reducing having substantially no affect upon the low-end trim of the load control device. 
         [0010]    According to another embodiment of the present invention, a load control device for controlling the amount of power delivered to an electrical load from an AC power source comprises a semiconductor switch, a triggering circuit, a timing circuit, and a user-accessible adjustment actuator. The semiconductor switch is operable to be coupled in series electrical connection between the source and the load. The semiconductor switch has a control input for controlling the semiconductor switch. The triggering circuit renders the semiconductor switch conductive each half-cycle of the AC voltage source. The timing circuit is coupled in parallel electrical connection with the semiconductor switch. The timing circuit has an output for providing a firing voltage signal. The triggering circuit is coupled to the output of the timing circuit and is operable to control the semiconductor switch in response to the firing voltage signal. The timing circuit further comprises a first circuit for causing the firing voltage signal to increase from substantially zero volts to a predetermined voltage in a first amount of time such that the semiconductor switch is rendered conductive at a first time each half-cycle of the AC voltage source, and a second circuit for causing the firing voltage signal to increase from substantially zero volts to the predetermined voltage in a second amount of time such that the semiconductor switch is rendered conductive at a second time each half-cycle of the AC voltage source. The user-accessible adjustment actuator is coupled to the timing circuit for selectively causing the semiconductor switch to be rendered conductive at either the first time or the second time each half-cycle of the AC voltage source. 
         [0011]    The present invention further provides a timing circuit for allowing the adjustment of a high-end trim of a load control device. The timing circuit is operable to generate a firing voltage signal and the load control device is operable to control the amount of power delivered to an electrical load from an AC power source in response to the firing voltage signal. The timing circuit comprises a capacitor operable to conduct a charging current from the power source such that the firing voltage signal is produced across the capacitor, a first circuit for causing the firing voltage signal to increase from substantially zero volts to a predetermined voltage in a first amount of time, and a second circuit for causing the firing voltage signal to increase from substantially zero volts to the predetermined voltage in a second amount of time greater than the first amount of time. 
         [0012]    In addition, the present invention provides a method of adjusting a high-end trim of a load control device for controlling the amount of power delivered to an electrical load. The method comprises the steps of: (1) controlling the amount of power delivered to the electrical load to a first high-end trim level; (2) actuating a user-accessible high-end trim adjustment actuator; and (3) controlling the amount of power delivered to the electrical load to a second high-end trim level different from the first in response to the step of actuating. 
         [0013]    Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a perspective view of the user interface of a dimmer switch having an adjustable high-end trim; 
           [0015]      FIG. 2  is another perspective view of the user interface of  FIG. 1 ; 
           [0016]      FIG. 3  is a simplified schematic diagram of the dimmer switch of  FIG. 1  according to a first embodiment of the present invention; 
           [0017]      FIG. 4  is a plot of the power delivered to a lighting load controlled by the dimmer switch of  FIG. 1  versus the position of a slider actuator of the dimmer switch when operated in a normal mode and an energy saver mode; 
           [0018]      FIG. 5  is a simplified electrical schematic diagram of a dimmer switch according to a second embodiment of the present invention; 
           [0019]      FIG. 6  is a simplified electrical schematic diagram of a dimmer switch according to a third embodiment of the present invention; 
           [0020]      FIG. 7  is a simplified electrical schematic diagram of a dimmer switch according to a fourth embodiment of the present invention; 
           [0021]      FIG. 8  is a simplified electrical schematic diagram of a dimmer switch according to a fifth embodiment of the present invention; 
           [0022]      FIG. 9  is a perspective view of the user interface of a dimmer switch having adjustable high-end trim according to a sixth embodiment of the present invention; 
           [0023]      FIG. 10  is another perspective view of the user interface of  FIG. 9 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    The foregoing summary, as well as the following detailed description of the preferred embodiments, is better understood when read in conjunction with the appended drawings. For the purposes of illustrating the invention, there is shown in the drawings an embodiment that is presently preferred, in which like numerals represent similar parts throughout the several views of the drawings, it being understood, however, that the invention is not limited to the specific methods and instrumentalities disclosed. 
         [0025]      FIG. 1  and  FIG. 2  are perspective views of the user interface of a dimmer switch  10  having adjustable high-end trim. The dimmer switch  10  includes a rocker switch  12 , a slider actuator  14  (i.e., an intensity adjustment actuator), and a user-accessible high-end trim adjustment actuator  16 . The slider actuator  14  allows for turning on and off a connected lighting load, such as an electric lamp (e.g., a lighting load  108  shown in  FIG. 3 ). The slider actuator  14  allows for adjusting the lighting level of the lighting load  108  from a minimum lighting level (i.e., the low-end trim level) to a maximum lighting level (i.e., the high-end trim level). The dimmer switch  10  also includes a bezel  18  attached to a front surface  20  of a mounting yoke  22  and a printed circuit board  24  mounted inside the dimmer switch  10 . The bezel  18  is adapted to be received in an opening of a faceplate (not shown). 
         [0026]    The high-end trim adjustment switch allows a user to change the dimmer switch  10  between a normal operating mode and an energy saver mode. When the dimmer switch  10  is in the normal operating mode, the high-end trim is set at a nominal high-end trim level. When the dimmer switch  10  is in the energy saver mode, the high-end trim is set at a reduced high-end trim level. Accordingly, the dimmer switch  10  uses less energy and the lifetime of the lamp is extended when the dimmer switch is in the energy saver mode. 
         [0027]    The high-end trim adjustment actuator  16  is coupled to a mechanical switch  26  mounted on the printed circuit board  24  via a coupling member  28 . The mechanical switch  26  includes an actuation knob  30 , which is received in a notch in the coupling member. Accordingly, the high-end trim adjustment actuator  16  is provided through an opening  32  of the mounting yoke  22 , such that the user is able to change the high-end trim from the user interface of the dimmer switch  10 . Preferably, the adjustment actuator  16  is located such that the adjustment actuator cannot be seen when the faceplate is mounted to the dimmer switch  10 , but can be accessed when the faceplate is removed. 
         [0028]      FIG. 3  is a simplified electrical schematic diagram of the dimmer switch  10  according to a first embodiment of the present invention. The dimmer switch  10  includes a hot terminal  102  that is connected to an AC power source  104 , and a dimmed hot terminal  106  that is connected to a lighting load  108 , such as an electric lamp. The dimmer switch  10  includes a switch S 1  connected to the hot terminal  102 , a choke L 1  connected in series with the switch S 1 , and a triac  110  connected in series between the choke L 1  and the dimmed hot terminal  106 . The triac  110  may alternatively be replaced by any suitable bidirectional switch, such as, for example, a field-effect transistor (FET) or an insulated gate bipolar junction transistor (IGBT) in a rectifier bridge, two FETs in anti-series connection, two IGBTs in anti-series connection, or a pair of silicon-controlled rectifiers. The switch S 1  is the electrical representation of the rocker switch  12  of the user interface of the dimmer switch  10 . When the switch S 1  is open, no power is delivered to the lighting load  108 . When the switch S 1  is closed, the dimmer switch  10  is operable to control the amount of power delivered to the lighting load  108 . The choke L 1  operates as an electromagnetic interference (EMI) filter. 
         [0029]    A timing circuit  120  is connected in parallel with the main leads of the triac  110 . A diac  130  is connected in series between an output of the timing circuit  120  and a control lead (i.e., a gate) of the triac  110 . The diac  130  may alternatively be replaced by any suitable triggering circuit or triggering device, such as, for example, a silicon bilateral switch (SBS). 
         [0030]    The timing circuit  120  includes a resistor R 1  connected to the junction of the choke L 1  and a first main lead of the triac  110 , and a capacitor C 1  connected between the resistor R 1  and the junction of the dimmed hot terminal  106  and a second main lead of the triac  110 . Preferably, the resistor R 1  has a resistance of 5.6 kΩ and the capacitor C 1  has a capacitance of 0.1° F. A wiper lead (or adjustable arm) of a potentiometer R 2  is connected to the junction of the resistor R 1  and the capacitor C 1 . The potentiometer R 2  preferably has a value that can be varied from a minimum resistance (e.g., approximately 0Ω) up to a maximum value of about 300 kΩ. The potentiometer R 2  is coupled to the slider actuator  14  and allows a user to adjust the light intensity level of the attached lighting load from the minimum light intensity level to the maximum light intensity level. 
         [0031]    A second lead of the potentiometer R 2  is connected to a first lead of a transient voltage suppressor Z 1  and a first lead of a resistor R 3 , which preferably has a resistance of 31.6 kΩ. The transient voltage suppressor Z 1  may comprise, for example, a pair of Zener diodes connected in series in reverse order or a TransZorb® transient voltage suppressor (manufactured by Vishay Intertechnology). The transient voltage suppressor Z 1  preferably has a breakover voltage V Z  of about 33.3V. The transient voltage suppressor Z 1  has a second lead connected to a first lead of a resistor R 4 , which preferably has a resistance of 100Ω. The second lead of the resistor R 4  is coupled to the first lead of a normally open single-pole single-throw switch S 2 . The switch S 2  is the electrical representation of the user-accessible mechanical switch  26 , which is actuated by the high-end trim adjustment actuator  16 . A second lead of the switch S 2  is connected to a second lead of the resistor R 3 . The junction of the second lead of the switch S 2 , the second lead of the resistor R 3 , and a first lead of a capacitor C 2  comprises an output of the timing circuit  120  that is connected to a first lead of the diac  130 . A second lead of the capacitor C 2  is connected to the junction of a second lead of the capacitor C 1 , the second main lead of the triac  110 , and the dimmed hot terminal  106 . A second lead of the diac  130  is connected to the control lead of the triac  110 . 
         [0032]    In operation, the timing circuit  120  sets a firing voltage, which is the voltage across the capacitor C 2 , for turning on the triac  110  after a selected phase angle in each line voltage half-cycle. The charging time of the capacitor C 2  is varied in response to a change in the resistance of the potentiometer R 2  to change the selected phase angle at which the triac  110  begins conducting. The capacitor C 2  preferably has a capacitance of 0.1 μF. 
         [0033]    The diac  130  is in series with the control lead of the triac  110  and is used as a triggering device. The diac  130  has a breakover voltage V BR  (for example 30V), and will conduct current to and from the triac control lead only when the firing voltage on the capacitor C 2  exceeds substantially the breakover voltage V BR  of the diac  130 . A gate current flows into the control lead of the triac  110  during the positive half-cycles of the line voltage and out of the control lead of the triac  110  during the negative half-cycles. 
         [0034]    When the switch S 2  is closed, the dimmer switch  10  operates in the normal mode with the nominal high-end trim level. While the potentiometer R 2  is at the minimum resistance and the switch S 2  is closed, the firing voltage at the output of the timing circuit  120  increases from substantially zero volts to a predetermined voltage, i.e., the breakover voltage V BR  of the diac  130 , during a first period of time, i.e., at a first rate. Accordingly, the capacitor C 2  charges for the first period of time before the diac  130  fires. 
         [0035]    In contrast, when the switch S 2  is open, the dimmer switch  10  operates in the energy saver mode with the reduced high-end trim level. While the potentiometer R 2  is at the minimum resistance and the switch S 2  is closed, the firing voltage at the output of the timing circuit  120  increases from substantially zero volts to the predetermined voltage during a second period of time, i.e., at a second rate. Accordingly, the capacitor C 2  charges for the second period of time before the diac  130  fires. In both the normal mode and the energy saver mode, the user of the dimmer switch  10  may change the firing angle via the slider actuator  14  to decrease the amount of power delivered to the lighting load  108 . 
         [0036]    When switch S 2  is closed, the series combination of the transient voltage suppressor Z 1  and the resistor R 4  is connected in parallel with the resistor R 3 . When the voltage developed across the resistor R 3  exceeds substantially the breakover voltage V Z  of the transient voltage suppressor Z 1 , the transient voltage suppressor Z 1  conducts. Resistor R 3  is then effectively short-circuited (since the resistance of resistor R 4  is substantially small, i.e., 100Ω, compared to resistor R 3 ). The total resistance in the charging path of the capacitor C 2  is reduced, thereby shortening the time required for the capacitor C 2  to charge to the breakover voltage V BR  of the diac  130 . Thus, the triac  110  begins conducting earlier than it would if the switch S 2  were open, thereby raising the high-end trim to a higher level than when the switch S 2  is open, i.e., with the nominal high-end trim level. 
         [0037]    When the diac  130  fires, the voltage across the diac decreases to a breakback voltage V BB , e.g., 25V. Since the voltage between the control input and the second main lead of the triac  110  is substantially zero volts, the voltage across the capacitor C 2  decreases to substantially the breakback voltage V BB  of the diac  130 , i.e., decreases by approximately five (5) volts. As a result, the voltage across the series combination of the transient voltage suppressor Z 1 , the resistor R 4 , and the switch S 2  increases by this difference, i.e., approximately five volts. The resistor R 4  operates to protect the transient voltage suppressor Z 1  by limiting the current that is conducted through the transient voltage suppressor at this time. Note that the resistor R 4  is not an essential part. Alternatively, a transient voltage suppressor having a greater current rating could be used. 
         [0038]    Accordingly, the dimmer switch  10  has a user-accessible adjustable high-end trim that is adjustable between the nominal high-end trim level when the switch S 2  is closed, and the reduced high-end trim level when the switch S 2  is open. The low-end trim is not affected by the state of the switch S 2  because, at low-end, the value of the resistance of the potentiometer R 2  is sufficiently high so that the charging current through the capacitor C 2  remains sufficiently small so that the voltage developed across the resistor R 3  never exceeds the breakover voltage V Z  of the transient voltage suppressor Z 1 . 
         [0039]      FIG. 4  is a plot of the power delivered to the lighting load  108  versus the position of a slider actuator  14  of the dimmer switch  10  when operated in the normal mode and the energy saver mode. When the dimmer switch  10  is operated in the energy saver mode, the power delivered to the lighting load  108  at 100% (i.e., at high-end) is less than the power delivered to the lighting load at high-end when the dimmer switch is in the normal mode. As shown by  FIG. 4 , the power delivered to the lighting load  108  at 0% (i.e., at low-end) is substantially the same when the dimmer switch is operating in the energy saver mode and the normal mode. 
         [0040]      FIG. 5  is a simplified electrical schematic diagram of a dimmer switch  200  according to a second embodiment of the present invention. Rather than including the switch S 2 , the dimmer switch  200  comprises a potentiometer R 5  for adjusting the high-end trim. The potentiometer R 5  has a wiper lead that is connected to the second lead of the resistor R 4  and a second lead connected to the junction of the resistor R 3 , the capacitor C 2 , and the diac  130 . Preferably, potentiometer R 5  comprises an adjustment member, such as a slider control or a rotary knob, which is provided in an opening in the yoke  22  or between the bezel  18  and the yoke  22  (e.g., the opening  32  shown in  FIGS. 1 and 2 ). The potentiometer R 5  preferably has a value that can be varied from a minimum resistance (e.g., approximately 0Ω) up to a maximum value of about 1 MΩ. When the resistance of the potentiometer R 5  is substantially 0Ω, the dimmer  200  operates at the first nominal high-end trim level (as does the dimmer  10  of  FIG. 3  when the switch S 2  is closed). As the resistance of the potentiometer R 5  is increased, the current through the series combination of the transient voltage suppressor Z 1 , the resistor R 4 , and the potentiometer R 5  decreases. Thus, the adjustable high-end trim of the dimmer  200  continuously decreases as the resistance of the potentiometer R 5  is increased (and vice versa). When the potentiometer R 5  is at the maximum resistance, the adjustable high-end trim is at a minimum reduced high-end trim level. 
         [0041]      FIG. 6  is a simplified electrical schematic diagram of a dimmer switch  300  according to a third embodiment of the present invention. The dimmer switch  300  comprises a multi-position switch S 2 ′, having four (4) positions A, B, C, D. Three resistors R 6 A, R 6 B, R 6 C are coupled between the transient voltage suppressor Z 1  and the multi-position switch S 2 ′. The transient voltage suppressor Z 1  is coupled in series with the first resistor R 6 A, the second resistor R 6 B, and the third resistor R 6 C when the switch S 2 ′ is in the first position A, the second position B, and the third position C, respectively. When the switch S 2 ′ is in the fourth position D, the series combination of the transient voltage suppressor Z 1  and the resistor R 4  is simply coupled in parallel with the resistor R 3 . The first resistor R 6 A has a first resistance, for example, 63 kΩ. The second resistor R 6 B has a second resistance, smaller than the first resistance, for example, 56 kΩ. The third resistor R 6 C has a third resistance, smaller than the second resistance, for example, 45 kΩ. The fourth resistor R 4  has a fourth resistance smaller than the third resistance. 
         [0042]    When the multi-position switch S 2 ′ is in position D, the dimmer switch  300  operates at the nominal high-end trim level (as with the dimmer switch  10  of  FIG. 3  when the switch S 2  is closed). When the multi-position switch S 2 ′ is in position C, the dimmer switch  300  operates at a first reduced high-end trim level, which is less than the nominal high-end trim level. When the multi-position switch S 2 ′ is in position B, the dimmer switch  300  operates at a second reduced high-end trim level, which is less than the first reduced high-end trim level. When the multi-position switch S 2 ′ is in position A, the dimmer switch  300  operates at a third and minimum reduced high-end trim level, which is less than the second reduced high-end trim level. 
         [0043]      FIG. 7  is a simplified electrical schematic diagram of a dimmer switch  400  according to a fourth embodiment of the present invention. The dimmer switch  400  comprises three separate transient voltage suppressors Z 2 A, Z 2 B, Z 2 C coupled in series with each of the resistors R 6 A, R 6 B, R 6 C, respectively. Like the dimmer switch  300  of  FIG. 6 , the dimmer switch  400  operates at the nominal high-end trim level when the multi-position switch S 2 ′ is in position D. When the multi-position switch S 2 ′ is in positions A, B, C, the dimmer switch  400  operates at one of a plurality of reduced high-end trim levels. Each of the plurality of reduced high-end trim levels is determined by the breakover voltage V Z  of the transient voltage suppressor Z 2 A, Z 2 B, Z 2 C and the resistance of the resistor R 6 A, R 6 B, R 6 C that are coupled in series with the respective switch position A, B, C. The first transient voltage suppressor Z 2 A has, for example, a breakover voltage V Z  of 60V. The second transient voltage suppressor Z 2 B has, for example, a breakover voltage V Z  of 51 V. The third transient voltage suppressor Z 3 A has, for example, a breakover voltage V Z  of 42V. 
         [0044]      FIG. 8  is a simplified electrical schematic diagram of a dimmer switch  500  according to a fifth embodiment of the present invention. The dimmer switch  500  comprises a single-pole double-throw (SPDT) switch S 2 ″ and a current-limiting circuit  550 . The SPDT switch S 2 ″ has a movable contact coupled to the resistor R 3  and two fixed contacts coupled to the potentiometer R 2  and the current limiting circuit  550 . The current-limiting circuit  550  comprises an NPN bipolar junction transistor Q 1 , two resistors R 7 , R 8  and a shunt regulator zener diode Z 3 . 
         [0045]    When the switch S 2 ″ is in a first position, the potentiometer R 2  is simply coupled in series with the resistor R 3 . When the switch S 2 ″ is in a second position, the current-limiting circuit  550  is coupled in series between the potentiometer R 2  and the resistor R 3 . As a voltage develops across the current-limiting circuit  550 , current flows through the resistor R 7  (which preferably has a resistance of 33 kΩ) and into the base of the transistor Q 1 , such that a limited current I LIMIT  flows through the main leads of the transistor. The shunt diode Z 3  preferably has a shunt connection coupled to the emitter of the transistor Q 1  to limit the magnitude of the limited current I LIMIT . The magnitude of the limited current I LIMIT  is determined by the reference voltage of the shunt diode Z 3  and the resistance of the resistor R 8 . Preferably, the shunt diode Z 3  has a reference voltage of 1.8V and the resistor R 8  has a resistance of 392Ω. 
         [0046]    When the switch S 2 ″ is in the second position, the limited current I LIMIT  causes the capacitor C 2  to charge at a slower rate than when the switch S 2 ″ is in the first position. Therefore, the triac  110  begins conducting at a later time than when the switch S 2 ″ is in the first position. Accordingly, the dimmer switch  500  operates at the nominal high-end trim level when the switch S 2 ″ is in the first position, and at the reduced high-end trim level when the switch S 2 ″ is in the second position. 
         [0047]      FIG. 9  and  FIG. 10  are perspective views of the user interface of a dimmer switch  600  having adjustable high-end trim according to a sixth embodiment of the present invention. The dimmer switch  600  includes a high-end trim adjustment actuator  610 , which is provided in an opening  620  of the mounting yoke  22 . Since the high-end trim adjustment actuator  610  comprises simply a mechanical switch  630  mounted to the printed circuit board  24 , the coupling member  28  of the dimmer switch  10  (shown in  FIGS. 1 and 2 ) is not required. Note that the mechanical switch  630  may comprise any of the switches S 2 , S 1 ′, or S 2 ″ (of  FIGS. 3 ,  6 ,  7 , and  8 ). The adjustment actuator  610  is located such that the adjustment actuator cannot be seen when a faceplate is mounted to the dimmer switch  600 , but can be accessed when the faceplate is removed. 
         [0048]    Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein, but only by the appended claims.