Patent Grant
7906916
1. Field of the Invention
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.
2. Description of the Related Art
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.
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.
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.
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.
According to an embodiment of the present invention, a load control device with an adjustable high-end trim 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 for reducing the high-end trim of the load control device from a first level to a second level lower than the first level, where the user-accessible actuator has substantially no affect upon the low-end trim of the load control device. 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 for generating a firing voltage signal. The triggering circuit is operable to control the semiconductor switch in response to the firing voltage signal. The user-accessible actuator comprises a mechanical switch. The timing circuit further comprises a first resistor, a capacitor coupled to the first resistor and operable to conduct a charging current from the power source through the first resistor such that the firing voltage signal is produced across the capacitor, and a transient voltage suppressor coupled in series electrical connection with the mechanical switch, where the series combination of the transient voltage suppressor and the mechanical switch is coupled in parallel electrical connection with the first resistor.
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.
Other features and advantages of the present invention will become apparent from the following description of the invention that refers to the accompanying drawings.
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.
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.
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.
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).
The timing circuit 120 includes a resistor R1 connected to the junction of the choke L1 and a first main lead of the triac 110, and a capacitor C1 connected between the resistor R1 and the junction of the dimmed hot terminal 106 and a second main lead of the triac 110. Preferably, the resistor R1 has a resistance of 5.6 kΩ and the capacitor C1 has a capacitance of 0.1 μF. A wiper lead (or adjustable arm) of a potentiometer R2 is connected to the junction of the resistor R1 and the capacitor C1. The potentiometer R2 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 R2 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.
A second lead of the potentiometer R2 is connected to a first lead of a transient voltage suppressor Z1 and a first lead of a resistor R3, which preferably has a resistance of 31.6 kΩ. The transient voltage suppressor Z1 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 Z1 preferably has a breakover voltage VZ of about 33.3V. The transient voltage suppressor Z1 has a second lead connected to a first lead of a resistor R4, which preferably has a resistance of 100Ω. The second lead of the resistor R4 is coupled to the first lead of a normally open single-pole single-throw switch S2. The switch S2 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 S2 is connected to a second lead of the resistor R3. The junction of the second lead of the switch S2, the second lead of the resistor R3, and a first lead of a capacitor C2 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 C2 is connected to the junction of a second lead of the capacitor C1, 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.
In operation, the timing circuit 120 sets a firing voltage, which is the voltage across the capacitor C2, for turning on the triac 110 after a selected phase angle in each line voltage half-cycle. The charging time of the capacitor C2 is varied in response to a change in the resistance of the potentiometer R2 to change the selected phase angle at which the triac 110 begins conducting. The capacitor C2 preferably has a capacitance of 0.1 μF.
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 VBR (for example 30V), and will conduct current to and from the triac control lead only when the firing voltage on the capacitor C2 exceeds substantially the breakover voltage VBR 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.
When the switch S2 is closed, the dimmer switch 10 operates in the normal mode with the nominal high-end trim level. While the potentiometer R2 is at the minimum resistance and the switch S2 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 VBR of the diac 130, during a first period of time, i.e., at a first rate. Accordingly, the capacitor C2 charges for the first period of time before the diac 130 fires.
In contrast, when the switch S2 is open, the dimmer switch 10 operates in the energy saver mode with the reduced high-end trim level. While the potentiometer R2 is at the minimum resistance and the switch S2 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 C2 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.
When switch S2 is closed, the series combination of the transient voltage suppressor Z1 and the resistor R4 is connected in parallel with the resistor R3. When the voltage developed across the resistor R3 exceeds substantially the breakover voltage VZ of the transient voltage suppressor Z1, the transient voltage suppressor Z1 conducts. Resistor R3 is then effectively short-circuited (since the resistance of resistor R4 is substantially small, i.e., 100Ω, compared to resistor R3). The total resistance in the charging path of the capacitor C2 is reduced, thereby shortening the time required for the capacitor C2 to charge to the breakover voltage VBR of the diac 130. Thus, the triac 110 begins conducting earlier than it would if the switch S2 were open, thereby raising the high-end trim to a higher level than when the switch S2 is open, i.e., with the nominal high-end trim level.
When the diac 130 fires, the voltage across the diac decreases to a breakback voltage VBB, 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 C2 decreases to substantially the breakback voltage VBB 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 Z1, the resistor R4, and the switch S2 increases by this difference, i.e., approximately five volts. The resistor R4 operates to protect the transient voltage suppressor Z1 by limiting the current that is conducted through the transient voltage suppressor at this time. Note that the resistor R4 is not an essential part. Alternatively, a transient voltage suppressor having a greater current rating could be used.
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 S2 is closed, and the reduced high-end trim level when the switch S2 is open. The low-end trim is not affected by the state of the switch S2 because, at low-end, the value of the resistance of the potentiometer R2 is sufficiently high so that the charging current through the capacitor C2 remains sufficiently small so that the voltage developed across the resistor R3 never exceeds the breakover voltage VZ of the transient voltage suppressor Z1.
When the multi-position switch S2′ is in position D, the dimmer switch 300 operates at the nominal high-end trim level (as with the dimmer switch 10 of
When the switch S2″ is in a first position, the potentiometer R2 is simply coupled in series with the resistor R3. When the switch S2″ is in a second position, the current-limiting circuit 550 is coupled in series between the potentiometer R2 and the resistor R3. As a voltage develops across the current-limiting circuit 550, current flows through the resistor R7 (which preferably has a resistance of 33 kΩ) and into the base of the transistor Q1, such that a limited current ILIMIT flows through the main leads of the transistor. The shunt diode Z3 preferably has a shunt connection coupled to the emitter of the transistor Q1 to limit the magnitude of the limited current ILIMIT. The magnitude of the limited current ILIMIT is determined by the reference voltage of the shunt diode Z3 and the resistance of the resistor R8. Preferably, the shunt diode Z3 has a reference voltage of 1.8V and the resistor R8 has a resistance of 392Ω.
When the switch S2″ is in the second position, the limited current ILIMIT causes the capacitor C2 to charge at a slower rate than when the switch S2″ is in the first position. Therefore, the triac 110 begins conducting at a later time than when the switch S2″ is in the first position. Accordingly, the dimmer switch 500 operates at the nominal high-end trim level when the switch S2″ is in the first position, and at the reduced high-end trim level when the switch S2″ is in the second position.
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.
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.
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| Number | Date | Country | |
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| Number | Date | Country | |
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