Abstract:
A hall-effect switching system comprises a hall-effect switch, a voltage comparison module, and a resistance bypass module. The voltage comparison module compares a supply voltage and a reference voltage. The resistance bypass module selectively adjusts a voltage output to the hall-effect switch based on the comparison.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/109,631, filed on Oct. 30, 2008. The disclosure of the above application is incorporated herein by reference. 
     
    
     FIELD 
       [0002]    The present disclosure relates to hall-effect switching circuits and low voltage operation. 
       BACKGROUND 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Referring now to  FIG. 1 , a functional block diagram of a hall-effect switching circuit is shown. A hall-effect switch  100  switches between current states. The current states are based on changes of a magnetic field near the hall-effect switch  100 . One end of a sense resistance R 1  is connected to a low side of the hall-effect switch  100 . Another end of the sense resistance R 1  is connected to ground. A voltage V is measured across the sense resistance R 1  to determine the current state provided by the hall-effect switch  100 . 
         [0005]    One end of a supply resistance R 2  is connected to a high side of the hall-effect switch  100 . Another end of the supply resistance R 2  is connected to a voltage source, V s . A supply voltage across the supply resistance R 2  is determined by the voltage V s . 
       SUMMARY 
       [0006]    A hall-effect switching system comprises a hall-effect switch, a voltage comparison module, and a resistance bypass module. The voltage comparison module compares a supply voltage and a reference voltage. The resistance bypass module selectively adjusts a voltage output to the hall-effect switch based on the comparison. In further features, the voltage comparison module determines when the supply voltage is less than or equal to the reference voltage, and adjusts the voltage output based on the determination. In other features, the reference voltage is adjusted based on the comparison. 
         [0007]    In further features, the voltage comparison module determines when the supply voltage is greater than or equal to the adjusted reference voltage, and adjusts the voltage output based on the determination. In other features, the resistance bypass module increases the voltage output based on the comparison. In other features, the resistance bypass module includes a transistor and a resistance in parallel, and the transistor switches states based on the comparison. 
         [0008]    In further features, the resistance bypass module includes a second transistor that selectively biases the transistor based on the comparison. In still further features, the voltage comparison module includes an operational amplifier that selectively biases the second transistor based on the comparison. 
         [0009]    A hall-effect switching method comprises comparing a supply voltage and a reference voltage, and selectively adjusting a voltage output to a hall-effect switch based on the comparison. In further features, the hall-effect switching method further comprises determining when the supply voltage is less than or equal to the reference voltage, and adjusting the voltage output based on the determination. In other features, the hall-effect switching method further comprises adjusting the reference voltage based on the comparison. 
         [0010]    In further features, the hall-effect switching method further comprises determining when the supply voltage is greater than or equal to the adjusted reference voltage, and adjusting the voltage output based on the determination. In other features, the hall-effect switching method further comprises increasing the voltage output based on the comparison. In still other features, the hall-effect switching method further comprises switching states of a transistor that is connected in parallel with a resistance based on the comparison. 
         [0011]    In further features, the hall-effect switching method further comprises selectively biasing the transistor by switching states of a second transistor based on the comparison. In still further features, the hall-effect switching method further comprises adjusting an output of an operational amplifier based on the comparison, and selectively biasing the second transistor based on the output. 
         [0012]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0014]      FIG. 1  is a functional block diagram of a hall-effect switching circuit according to the principles of the prior art; 
           [0015]      FIG. 2  is a functional block diagram of a hall-effect switching circuit according to the principles of the present disclosure; 
           [0016]      FIG. 3  is an exemplary circuit schematic of a hall-effect switching circuit according to the principles of the present disclosure; 
           [0017]      FIG. 4   a  is an exemplary graphical depiction of voltage measurements of a hall-effect switching circuit according to the principles of the prior art; 
           [0018]      FIG. 4   b  is an exemplary graphical depiction of voltage measurements of a hall-effect switching circuit according to the principles of the present disclosure; and 
           [0019]      FIG. 5  is a flowchart depicting exemplary steps performed by a hall-effect switching circuit according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0021]    As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0022]    A hall-effect switching circuit may include a hall-effect switch, a voltage source, and resistances. The hall-effect switch changes current states based on changes of a magnetic field. The hall-effect switch switches between current states when the voltage across the hall-effect switch is greater than a minimum value. The minimum value depends on characteristics of the hall-effect switch. The voltage across the hall-effect switch depends on the values of the voltage source and the resistances connected to the hall-effect switch. 
         [0023]    If the voltage across the hall-effect switch is less than the minimum value, then the hall-effect switch will not switch between current states. The voltage provided by the voltage source in the present disclosure is compared to a reference voltage. If the voltage from the voltage source is not greater than the reference voltage, then the voltage across the hall-effect switch may be increased to enable operation of the hall-effect switch. 
         [0024]    Referring now to  FIG. 2 , a functional block diagram of a hall-effect switching circuit according to the principles of the present disclosure is shown. A voltage comparison module  200  compares a supply voltage V s  to a reference voltage (V reg ). When V s  is less than V reg , a resistance bypass module  202  may allow a higher voltage applied to a hall-effect switch  204 . For example only, the voltage comparison module  200  may trigger the resistance bypass module  202  when V s  is less than V reg . The resistance bypass module  202  may lower the resistance between V s  and the hall-effect switch  204 . 
         [0025]    The voltage across the hall-effect switch  204  increases based on the lowered resistance. The voltage across the hall-effect switch  204  may be increased so that the hall-effect switch  204  may switch between the current states. A voltage V is measured across a sense resistance R 1  to determine the current state provided by the hall-effect switch  204 . 
         [0026]    Referring now to  FIG. 3 , an exemplary circuit schematic of a hall-effect switching circuit according to the principles of the present disclosure is shown. The voltage comparison module  200  may include voltage dividers, an operational amplifier  300 , and resistances R 3 , R 4 , R 5 , R 6 , R 7 , R 8 , and R 9  to compare V s  and V reg . For example, V reg  may be divided by resistances R 3  and R 4  to generate a voltage V 1 . V s  may be divided by resistances R 5  and R 6  to generate a voltage V 2 . V 1  and V 2  may be compared by using other methods. 
         [0027]    The operational amplifier  300  receives V 1  as an input to a non-inverting terminal  302  and V 2  as an input to an inverting input terminal  304 . The operational amplifier  300  determines whether V 2  is greater than V 1 . An output voltage V 3  of the operational amplifier  300  is based on whether voltage V 2  is greater than V 1 . 
         [0028]    A resistance R 7  is connected between an output terminal  306  of the operational amplifier  300  and V s . A resistance R 8  is connected between the output terminal  306  and the non-inverting input terminal  302 . A resistance R 9  is connected between the output terminal  306  and a base terminal  308  of a bi-polar junction transistor (BJT)  310 . When the operational amplifier  300  determines that V 2  is less than or equal to V 1 , then V 3  is high. If V 2  is greater than V 1 , then V 3  is low. When V 3  is high, V 1  increases via feedback voltage across resistance R 8  (i.e. V 1  is adjusted based on V 3 ). In other implementations, V 1  may not be adjusted by V 3 . 
         [0029]    A resistance R 10  is connected between a collector terminal  312  of the BJT  310  and V s . An emitter terminal  314  of the BJT  310  is connected to ground. When V 3  is generated, the BJT  310  is forward biased and in a saturation mode. The voltage at the collector terminal  312  of the BJT  310  decreases. 
         [0030]    A p-channel metal-oxide-semiconductor field-effect transistor (MOSFET)  316  has a source terminal  318 , a drain terminal  320 , and a control terminal  322 . The MOSFET  316  is connected in parallel with R 2 . For example, the source terminal  318  is connected to V s  and the drain terminal  320  is connected to a high side of the hall-effect switch  204 . The control terminal  322  is connected to the collector terminal  312  of the BJT  310 . When the collector terminal  312  voltage is lowered, the MOSFET  316  becomes biased to an on state. Accordingly, a resistance between the source terminal  318  and the drain terminal  320  decreases significantly. 
         [0031]    When the resistance is lowered, R 2  is by-passed and the voltage supplied to the hall-effect switch  204  increases. In other words, the current will flow through the MOSFET  316  instead of the resistance R 2 . R 2  may be by-passed until V s  is greater than V reg , or until V 2  is greater than V 1 . The voltage V is measured across R 1  to determine the current state of the hall-effect switch  204 . 
         [0032]    Referring now to  FIG. 4   a,  an exemplary graphical depiction of voltage measurements of a hall-effect switching circuit according to the principles of the prior art is shown. A voltage supply line  400  depicts exemplary values of V s . As V s  changes, the voltage across the hall-effect switch  204  changes. A V H  line  402  shows exemplary values of the voltage across the hall-effect switch  204 . A disruption in the V H  line  402  occurs when the voltage across the hall-effect switch  204  drops below a minimum value. For example only, the disruption is shown to occur between roughly 200 ms and 400 ms. During the disruption, the hall-effect switch  204  does not switch between current states. 
         [0033]    Referring now to  FIG. 4   b,  an exemplary graphical depiction of voltage measurements of a hall-effect switching circuit according to the principles of the present disclosure is shown. A reference voltage line  404  depicts exemplary values of V 1 . A voltage supply line  406  represents exemplary possible values of V 2 . V 2  and V 1  are compared to determine whether voltage compensation is needed. 
         [0034]    When the voltage V 2  line  406  decreases below the reference voltage line  404 , a disruption occurs in a V H  line  408 . For example only, a starting point  410  shows that the voltage V 2  line  406  crosses the reference voltage line  404  at roughly 200 ms. The disruption is compensated for by V 3  going high during the period between the starting point  410  and an ending point  412 . 
         [0035]    At the starting point  410 , V 3  goes high because the voltage V 2  line  406  has dropped below the reference voltage line  404 . A voltage compensation line  414  represents exemplary values of V 3 . When V 3  is high, the V H  line  408  appears to not have a disruption because the voltage compensation line  414  fills in the missing portion of the V H  line  408 . V 3  continues to be high until the voltage V 2  line  406  is greater than the reference voltage line  404 . For example only, the voltage V 2  line  406  is greater than the reference voltage line  404  between the ending point  412  and a second starting point  416 . 
         [0036]    In  FIG. 4   b,  the reference voltage line  404  rises to a higher voltage when V 3  is high. Because the reference voltage line  404  rises to a higher voltage level when V 3  is high, the starting point  410  and the ending point  412  are at different voltage levels. In various implementations, the starting point  410  and the ending point  412  may be at the same voltage level. 
         [0037]    Referring now to  FIG. 5 , a flowchart depicting exemplary steps performed by a hall-effect switching circuit according to the principles of the present disclosure is shown. Control begins in step  500 . In step  500 , control receives the reference voltage. In step  502 , control receives the supply voltage. In step  504 , control determines whether the supply voltage is greater than the reference voltage. If the supply voltage is greater than the reference voltage, then control transfers to step  506 ; otherwise, control transfers to step  508 . 
         [0038]    In step  506 , control provides the supply voltage across the supply resistance. In step  508 , control bypasses the supply resistance. In step  510 , control measures the voltage across the sense resistance. 
         [0039]    Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.