Abstract:
An apparatus and process are provided for regulating the voltage across a resistive or inductive load by phase angle control of the applied load voltage. Instantaneous load voltage is compared with a preset reference value to control the phase angle of the applied load voltage by means of rms voltage approximation feedback control. A visual display can be provided to assist the user in establishing the preset reference value.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/403,958, filed Aug. 16, 2002. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a line voltage regulator that regulates the voltage across a load by phase angle control. 
     BACKGROUND OF THE INVENTION 
     Line voltage regulators are used to control the voltage applied to a load. A phase angle control technique can be used to adjust the effective voltage applied across the load by phase shifting the gate pulses of switching devices used in the voltage adjusting circuit. The present invention provides a means of adjusting the effective voltage applied to a load based upon fluctuations in a supply line voltage. 
     BRIEF SUMMARY OF THE INVENTION 
     In one aspect, the present invention is an apparatus for, and method of, regulating the effective voltage across a load by phase angle control of the supply line voltage based upon fluctuations in the supply line. 
     Other aspects of the invention are set forth in this specification and the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For the purpose of illustrating the invention, there is shown in the drawings a form that is presently preferred; it being understood, however, that this invention is not limited to the precise arrangements and instrumentalities shown. 
     FIG. 1 is a schematic diagram of one example of the line voltage regulator circuit of the present invention. 
     FIG. 2 is a schematic diagram of one example of a power supply circuit that can be used with a line voltage regulator of the present invention. 
     FIG. 3 is a schematic diagram of one example of a visual display that can be used with a line voltage regulator of the present invention. 
     FIG. 4 is a parts lists for the components shown in the schematic diagrams in FIG. 1, FIG.  2  and FIG.  3 . 
     FIG. 5 is a partial schematic diagram of another example of the line voltage regulator circuit of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like numerals indicate like elements, there is shown in the drawings, one example of the line voltage regulator of the present invention. FIG. 4 is a parts lists for components used in the schematics shown in FIG.  1  through FIG.  3 . 
     The line voltage regulator of the present invention can be used with resistive or inductive loads. In this non-limiting example, the load is referred to as a resistive heater load R load . Referring to FIG. 1, load R load  is connected between neutral input power terminal (PWR N) of the power supply shown in FIG. 2 and a first terminal J 2  (TRIAC  2 ) of TRIAC Q 5 . The second terminal J 1  (TRIAC  1 ) of TRIAC Q 5  is connected to the high voltage input terminal of the power supply. The high voltage connection is either 120-volts ac (J 7 ) or 240-volts ac (J 5 ) in FIG. 2 as further described below. 
     Triac Q 5  controls the effective voltage (and power) applied to load R load  by a phase angle control technique. The phase angle control circuit comprises optoisolator U 6 , silicon controlled rectifier Q 2 , transistor Q 4 , diodes D 7 , D 8  and D 9 , and associated resistors and capacitors as illustrated in FIG.  1 . 
     The primary of transformer T 2  is connected across the terminals of load R load . The voltage on the secondary of transformer T 2  represents a proportional ac value of the voltage applied across load R load . This proportional voltage is rectified by diodes D 1  and D 12 , and passed through a Root Mean Square (RMS) voltage approximation filter  12  comprising circuit elements resistor R 32 , capacitor C 22 , resistor R 35 , and resistor R 10 . The output of the RMS voltage approximation filter is a dc signal proportional to the RMS value of the voltage applied to load R load  and allows the line voltage regulator to maintain constant power to load R load . In this non-limiting example of the invention, the phase angle control range is from 50 percent to 100 percent voltage (or power), which corresponds to 90 degrees to approximately zero degrees phase angle control, respectively. In this non-limiting example, with supply power of 60 Hertz, the resistance of resistor R 32  is selected as approximately one-third of the combined resistance values of resistor R 10  and resistor R 35 , and the impedance of capacitor C 22  at 60 Hertz is selected as approximately one-tenth of the resistance of R 32 . The output of the RMS voltage approximation filter can be across resistor R 35 , resistor R 10 , or the series combination of resistors R 35  and R 10 . In this example of the invention, resistors R 32  and R 35  form a voltage divider with resistor R 10  to supply a suitable output voltage level. 
     The output voltage from the RMS voltage approximation filter is amplified by op amp U 1 D to output a feedback signal. Op amp U 1 A compares the feedback signal with a setpoint signal from potentiometer R 2 . The resistance range of potentiometer R 2  is selected so that the phase control circuitry allows a percentage range of utility line voltage to be applied across load R load . For example, potentiometer R 2  may be adjustably set so that the applied voltage across load R load  ranges from 50 percent to 100 percent of utility line voltage. The user adjusts the setting of potentiometer R 2  to the desired setpoint for a regulated percentage of utility line voltage. In this non-limiting example of the invention, potentiometer R 1  is used to limit the range of potentiometer R 2  to accommodate applications wherein the nominal utility line voltage is either 120-volts or 240-volts. If the setpoint signal is greater than the feedback signal, op amp U 1 A will output an increased TRIAC Q 5  gate drive signal to optoisolator U 6  to advance the phase angle of the effective voltage applied to load R load . If the setpoint signal is less than the feedback signal, op amp U 1 A will output a decreased TRIAC Q 5  gate drive signal to optoisolator U 6  to retard the phase angle of the effective voltage to load R load . Consequently a constant effective voltage will be applied across load R load  for a given setpoint regardless of utility line voltage fluctuations. 
     The feedback signal can also optionally be supplied to a line voltage display indicator, such as digital voltmeter U 2  and associated components shown in FIG. 1 to provide a visual display of the instantaneous effective voltage across load R load  on suitable display elements such as LED segmented display digits DS 1 , DS 2  and DS 3  as shown in FIG. 3 or a colored LED bar display. The user can make use of the visual display for initially setting potentiometer R 1  to achieve a desired regulated voltage value, or make other adjustments. 
     An optional process control switch (not shown in the figures) may be connected between terminals J 3  (ROT SW) and J 4  (ROT SW) in FIG. 1 to inhibit the application of voltage across load R load  unless the process control switch shorts terminal J 3  to terminal J 4 . The process control switch may be any type of switch suitable for a particular process application. For example, if the process requires rotation of a component before voltage is applied to load R load , a Hall effect rotation sensor or centrifugal switch can be used. In other applications, a proximity switch may be appropriate for sensing the presence of a material to be heated by load R load  before voltage is applied to the heater load. In other applications not requiring the optional process control switch, the associated circuitry may be omitted or a jumper can be installed between terminals J 3  and J 4 . 
     FIG. 2 illustrates one example of a power supply circuit that can be used with the line voltage regulator of the present invention. In this non-limiting example, supply line voltage, or utility power, is either nominal single phase 120-volts or 240-volts, and is provided between terminals J 7  (120V) and J 6  (PWR N), or terminals J 5  (240V) and J 6  (PWR N), respectively. Components are as identified in the parts list shown in FIG.  4 . Unregulated 10-volts dc (V+), regulated 5-volts dc for analog circuitry (5V), regulated 5-volts dc for digital circuitry (5VD), regulated 4.3-volts dc for display circuitry (4V3) and negative 5-volts dc (−5V) is provided by the power supply to various connections in the control circuitry as shown in FIG.  1 . 
     FIG.  1  through FIG. 4, in combination with the modifications shown in FIG. 5, illustrate another example of the line voltage regulator circuit of the present invention. In this example of the invention, a monolithic RMS approximation filter is used in lieu of the discrete elements for RMS approximation filter  12  in the previous example of the invention. In FIG. 5, the non-limiting monolithic RMS approximation filter is ANALOG DEVICES Part No. AD736 (available from Analog Devices, Inc., Norwood, Mass.) and is designated U 7  in FIG.  5 . Components within the dashed lines are different from those in the previous example of the invention to accommodate the input and output characteristics of device U 7 . Outside of the dashed lines, circuitry is generally the same as that in the previous example of the invention. 
     The foregoing examples do not limit the scope of the disclosed invention. The scope of the disclosed invention is further set forth in the appended claims.