Switch controlled current sensing using a hall effect sensor

1. Field of the Invention

The present invention relates in general to the field of electronics, and more specifically to a system and method for sensing switch controlled currents using a Hall effect sensor.

2. Description of the Related Art

Electronic systems often detect signal values and utilize the values to perform other operations. Hall effect sensors (“Hall sensors”) are used in some contexts to detect signals. A Hall sensor generates a voltage corresponding to a magnetic field passing through the Hall sensor. An electrical current flowing through a conductor in proximity to a Hall sensor generates a magnetic field. The Hall sensor generates a voltage corresponding to the magnetic field generated by the current. Hall sensors generally have a low frequency noise component that is too large to allow detection of small changes in currents. For example, as explained subsequently in more detail, switching power converters that operate in continuous conduction mode (CCM) sense currents using a current sense circuit such as a resistor or a transformer.

FIG. 1A represents a power control system 100 , which includes switching power converter 102 . In at least one embodiment, switching power converter operates in a continuous conduction mode (CCM). In CCM, the inductor current i L does not go to zero during operation of switching power converter 102 . As subsequently described in more detail, in CCM operation, PFC and output voltage controller 114 senses controlled current i CC by sensing a voltage across resistor 109 . Voltage source 101 supplies an alternating current (AC) input voltage V IN to a full bridge diode rectifier 103 . The voltage source 101 is, for example, a public utility, and the AC voltage V IN is, for example, a 60 Hz/110 V line voltage in the United States of America or a 50 Hz/220 V line voltage in Europe. The rectifier 103 rectifies the input voltage V IN and supplies a rectified, time-varying, line input voltage V X to the switching power converter.

The switching power converter 102 includes at least two switching operations, i.e. controlling field effect transistor (FET) 108 to provide power factor correction and controlling FET 108 to provide regulation of link voltage V LINK . The goal of power factor correction technology is to make the switching power converter 102 appear resistive to the voltage source 101 so that the real power provided to switching power converter 102 is equal to the apparent power provided to switching power converter 102 . The inductor current i L ramps ‘up’ when FET 108 conducts, i.e. is “ON”. The inductor current i L ramps down when FET 108 is nonconductive, i.e. is “OFF”, and supplies current i L to recharge capacitor 106 . The time period during which inductor current i L ramps down is commonly referred to as the “inductor flyback time”. Diode 111 prevents reverse current flow into inductor 110 . In at least one embodiment, control signal CS 0 is a pulse width modulated signal, and FET 108 is an n-channel FET. In this embodiment, control signal CS 0 is a gate voltage of FET 108 , and FET 108 conducts when the pulse width of CS 0 is high. Thus, the ‘on-time’ of FET 108 is determined by the pulse width of control signal CS 0 . In at least one embodiment, the switching power converter 102 operates in CCM, i.e. ramp up time of the inductor current i L plus the inductor flyback time is greater than or equal to the period of the control signal CS 0 .

In at least one embodiment, switching power converter 102 boosts a 110-120 V rectified input voltage V X to a higher link voltage V LINK , such as 200-400V. Accordingly, FET 108 is fabricated to have a breakdown voltage sufficient to accommodate the controlled current i CCT and voltage drops across FET 108 associated with the high input voltage V X and higher link voltage V LINK . FET 108 is a high breakdown voltage device fabricated using a “high” voltage process. In at least one embodiment, FET 108 has a breakdown voltage greater than or equal to 30V and at least sufficient to accommodate operating characteristics of switching power converter 102 . In at least one embodiment, power factor correction (PFC) and output voltage controller 114 is an integrated circuit and is fabricated using a low voltage process that is insufficient to fabricate a switch with a sufficiently high breakdown voltage to control the controlled current i CCT . Thus, FET 108 is located external to PFC and output voltage controller 114 . As subsequently described in more detail, PFC and output voltage controller 114 generates a pulse width modulated control signal CS 0 to control conductivity of FET 108 . In at least one embodiment, FET 108 is a FET, and control signal CS 0 is a gate voltage.

Switching power converter 102 includes current sense resistor 109 . The switch controlled current i CC generates a sense voltage V SEN across current sense resistor 109 . The PFC and output voltage controller 114 receives the sense voltage V SEN . The resistance R of sense resistor 109 is known. The sense voltage V SEN is directly related to switch controlled current i CC via Ohm's law, i.e. V SEN =i CC ·R. “R” represents a resistance value of sense resistor 109 , and the value of R is a matter of design choice. In at least one embodiment, PFC and output voltage controller 114 utilizes the sense voltage V SEN and sensing two signals, namely, the line input voltage V X and the capacitor voltage/output voltage V LINK to generate the pulse width and duty cycle of control signal CS 0 .

Capacitor 106 supplies stored energy to load 112 . The capacitor 106 is sufficiently large so as to maintain a substantially constant output voltage V LINK , as established by PFC and output voltage controller 114 (as discussed in more detail below). The output voltage V LINK remains substantially constant during constant load conditions. However, as load conditions change, the output voltage V LINK changes. The switch state controller 114 responds to the changes in V LINK and adjusts the control signal CS 0 to restore a substantially constant output voltage as quickly as possible. The PFC and output voltage controller 114 includes a small capacitor 115 to filter any high frequency signals from the line input voltage V X .

The switch state controller 114 of power control system 100 controls FET 108 and, thus, controls power factor correction (PFC) and regulates output power of the switching power converter 102 . As previously stated, the goal of power factor correction technology is to make the switching power converter 102 appear resistive to the voltage source 101 . Thus, the switch state controller 114 attempts to control the inductor current i L so that the average inductor current i L is linearly and directly related to the line input voltage V X . A CCM PFC controller, model number UCC28019A, available from Texas Instruments, Inc., Texas, USA is an example of switch state controller 114 . The switch state controller 114 controls the pulse width (PW) and period (TT) of control signal CS 0 . To regulate the amount of energy transferred and maintain a power factor close to one, switch state controller 114 varies the period of control signal CS 0 so that the input current i L tracks the changes in input voltage V X and holds the output voltage V LINK constant. Thus, as the input voltage V X increases, switch state controller 114 increases the period TT of control signal CS 0 , and as the input voltage V X decreases, switch state controller 114 decreases the period of control signal CS 0 . At the same time, the pulse width PW of control signal CS 0 is adjusted to maintain a constant duty cycle (D) of control signal CS 0 , and, thus, hold the output voltage V LINK constant.

In at least one embodiment, the switch state controller 114 updates the control signal CS 0 at a frequency much greater than the frequency of input voltage V X . The frequency of input voltage V X is generally 50-60 Hz. The frequency 1/TT of control signal CS 0 is, for example, between 20 kHz and 130 kHz. Frequencies at or above 20 kHz avoid audio frequencies and frequencies at or below 130 kHz avoid significant switching inefficiencies while still maintaining good power factor, e.g. between 0.9 and 1, and an approximately constant output voltage V LINK .

Light emitting diodes (LEDs) are becoming particularly attractive as main stream light sources in part because of energy savings through high efficiency light output and environmental incentives such as the reduction of mercury. LEDs are semiconductor devices and are driven by direct current. The brightness (i.e. luminous intensity) of the LED approximately varies in direct proportion to the current flowing through the LED. Thus, increasing current supplied to an LED increases the brightness of the LED and decreasing current supplied to the LED dims the LED. Current can be modified by either directly reducing the direct current level to the LEDs or by reducing the average current through the LEDs through duty cycle modulation.

FIG. 1B depicts an LED driver system 150 . The LED driver system 150 includes a CCM, buck-based switching power converter 152 to provide a load voltage to switching LED system 154 . Voltage source 151 supplies the AC supply voltage V IN to a full, diode bridge rectifier 153 . The hold-up capacitor C 1 holds an approximately direct current (DC) link voltage V LINK across capacitor C 1 relative to a reference voltage V R . Link voltage V LINK is also the output voltage of power converter 152 and the input voltage for controller 156 . Input filter capacitor C 2 provides a high pass filter for high frequency components of the output voltage of rectifier 153 . A thermistor NTC 1 provides in-rush current protection for power converter 152 .

The controller 156 is, for example, a Supertex HV9915B integrated circuit controller available from Supertex, Inc. of Sunnyvale, Calif. The link voltage V LINK can vary from, for example, 8V to 450V. The controller 156 provides a gate drive signal from the GATE output node to the n-channel metal oxide semiconductor field effect transistor (MOSFET) Q 1 . Controller 156 modulates the gate drive signal, and thus, the conductivity of MOSFET Q 1 to provide a constant current to LED system 154 . Controller 156 modifies the average resistance of MOSFET Q 1 by varying a duty cycle of a pulse width modulated gate drive signal V GATE . Resistor R 1 and capacitor C 3 provide external connections for controller 156 to the ground reference.

Controller 156 generates and uses feedback to maintain a constant current i LED for LEDs 158 . Controller 156 receives a current feedback signal V fb representing a feedback voltage V fb sensed across sense resistor R 2 . The feedback voltage V fb is directly proportional to the LED current i LED in LEDs 158 . If the feedback voltage V fb exceeds a predetermined reference corresponding to a desired LED current, the controller 156 responds to the feedback voltage V fb by decreasing the duty cycle of gate drive signal V GATE to increase the average resistance of MOSFET Q 1 over time. If the feedback voltage V fb is less than a predetermined reference corresponding to the desired LED current, the controller 156 responds to the feedback voltage V fb by increasing the duty cycle of gate drive signal V GATE to decrease the average resistance of MOSFET Q 1 over time.

The LED system 154 includes a chain of one or more, serially connected LEDs 158 . When the MOSFET Q 1 is “on”, i.e. conductive, diode D 1 is reversed bias and, current i LED flows through the LEDs 158 and charges inductor L 1 . When the MOSFET Q 1 is “off”, i.e. nonconductive, the voltage across inductor L 1 changes polarity, and diode D 1 creates a current path for the LED current i LED . The inductor L 1 is chosen so as to store enough energy to maintain a constant current i LED when MOSFET Q 1 is “off”.

Sensing the controlled current through current sense circuit 109 ( FIG. 1A ) and the controlled LED current i LED through resistor R 2 ( FIG. 1B ) results in power loss and can be inaccurate.

In one embodiment of the present invention, an apparatus includes an integrated circuit. The integrated circuit includes a Hall sensor configured to sense a magnetic field of a controlled current. The integrated circuit also includes a controller coupled to the Hall sensor, wherein the controller is configured to receive information from the Hall sensor and to use the information to determine a time to cause a switch, which controls the controlled current, to conduct.

In another embodiment of the present invention, a method includes sensing a magnetic field of a controlled current using a Hall sensor and receiving information from the Hall sensor. The method further includes utilizing the information to determine a time to cause a switch, which controls the controlled current, to conduct.

In a further embodiment of the present invention, an apparatus includes means for sensing a magnetic field of a controlled current using a Hall sensor. The apparatus also includes means for receiving information from the Hall sensor, and means for utilizing the information to determine a time to cause a switch, which controls the controlled current, to conduct.

The present invention may be better understood, and its numerous objects, features and advantages made apparent to those skilled in the art by referencing the accompanying drawings. The use of the same reference number throughout the several figures designates a like or similar element.

FIG. 1A (labeled prior art) depicts an electronic system having a controller to control a switching power converter.

FIG. 1B (labeled prior art) depicts a switching light emitting diode (LED) driver system with LED current feedback.

FIGS. 2A , 2 B, 2 C, and 2 D each depict an electronic system that includes a Hall sensor in a controller to sense a magnetic field generated by a current controlled by the controller.

FIG. 3 depicts an embodiment of the controller for FIGS. 2A , 2 B, 2 C, and 2 D.

FIG. 4 depicts a flowchart showing an exemplary controlled current detection and switch control algorithm.

FIG. 5 depicts an exemplary Hall sensor voltage graph.

FIGS. 6A and 6B depict exemplary integrated circuit controllers that include Hall sensors.

FIG. 7 depicts an embodiment of the electronic system of FIG. 2 .

FIG. 8 depicts another embodiment of the electronic system of FIG. 2 .

FIG. 9 depicts a light source.

An electronic system includes a Hall sensor to sense a magnetic field of a controlled current. An average value of the current is controlled by controlling a switch. In at least one embodiment, a controller generates a duty cycle modulated switch control signal to control the switch. Increasing the duty cycle of the switch control signal increases the average value of the controlled current, and decreasing the duty cycle decreases the average value of the controlled current. The controller utilizes information from the Hall sensor about the magnetic field of the controlled current as feedback to control the controlled current. For example, if the information from the Hall sensor indicates the controlled current is too high relative to a target value, the controller decreases the duty cycle of the switch control signal. If the information from the Hall sensor indicates the controlled current is too low relative to the target value, the controller increases the duty cycle of the switch control signal.

In general, conventionally, low frequency noise of a Hall sensor prevents the Hall sensor from accurately sensing voltages related to small changes in current. In a switching power converter, in at least one embodiment, an average current in the switching power converter is controlled within +/−a few milliamps. Thus, conventionally, Hall sensors are not used in such applications because of the relatively large noise component of the Hall sensor. In at least one embodiment, a switching frequency f iCCT of the switch in the switching power converter corresponds to a frequency of pulses of the controlled current. The switching frequency f iCCT of the switch and, thus, the frequency of the controlled current is high relative to a frequency f N of the noise of the Hall sensor. For example, in at least one embodiment, f iCCT is at least 100 times larger than the noise frequency, i.e. f iCCT ≧100·f N . Because f iCCT >>f N , the Hall noise voltage is effectively constant during a single cycle of the controlled current. The controller can determine a difference between information from the Hall sensor that does not include a component associated with the controlled current to information that includes a component associated with the controlled current and effectively cancel out the Hall sensor noise since the Hall noise voltage is effectively constant during a pulse of the controlled current. For example, if while the Hall noise voltage is effectively constant, the information that does not include a component associated with the controlled current is a baseline voltage V HB and the information that includes the component associated with the controlled current is V HB +V ICCT , then the controller can determine V iCCT by subtraction, i.e. V iCCT =V HB −(V HB +V iCCT ). “V iCCT ” corresponds to a value of the controlled current. The controller can, thus, effectively cancel out the noise from the Hall sensor. The controller can then utilize the determined value V iCCT of the controlled current as feedback to generate the switch control signal to control the controlled current.

In at least one embodiment, the Hall sensor is positioned proximate to a signal path that conducts the controlled current and develops a voltage that includes a voltage component corresponding to the controlled current. A controller controls conductivity of a switch, and the switch controls the controlled current. Controlling conductivity of the switch controls the controlled current. The controller receives information either directly or indirectly from the Hall sensor corresponding to the controlled current and utilizes the information from the Hall sensor to control conductivity of the switch. In at least one embodiment, the controller generates a duty cycle modulated control signal to control the switch. In at least one embodiment, a pulse of the control signal causes the switch to turn “on”, i.e. conduct. In at least one embodiment, the switch can control the current for any purpose, including but not limited to providing power factor correction in a switching power converter and/or driving a load. The load can be any type of load including but not limited to, for example, a light emitting diode (LED) based light source.

In at least one embodiment, the electronic system includes a switching power converter operating in continuous conduction mode (CCM). The Hall sensor senses a magnetic field generated by a controlled current in the switch of the switching power converter and generates a sense signal corresponding to the controlled current. The controller utilizes the sense signal to provide, for example, power factor correction for the CCM switching power converter. In at least one embodiment, the switching power converter operates in discontinuous conduction mode (DCM), and the controller utilizes the sense signal to provide, for example, power factor correction for the DCM switching power converter.

In at least one embodiment, the electronic system includes a light source having one or more light emitting diodes (LEDs). The Hall sensor senses a magnetic field generated by a controlled current in the LEDs and generates a sense signal corresponding to the controlled current. The controller utilizes the sense signal to regulate current in the LEDs.

In at least one embodiment, the Hall sensor and the controller are at least part of an integrated circuit that is connected to a printed circuit board. The printed circuit board includes a signal path, referred to as a “signal trace”, that conducts the controlled current. In at least one embodiment, the Hall sensor is positioned proximate to the signal trace and develops a voltage that includes a voltage component corresponding to the controlled current.

In at least one embodiment, utilizing the Hall sensor to detect the controlled current i CCT is more accurate than using a sense resistor (such as sense resistor 109 ( FIG. 1 )) and dissipates less power than using the sense resistor.

FIG. 2A depicts an electronic system 200 that includes a controller 202 , and controller 202 generates a switch control signal CS 1 to control conductivity of switch 204 . As subsequently described in more detail, controller 202 includes a Hall sensor (HS) 203 to sense controlled current i CCT from load 210 . The controlled current i CCT into the switch 204 is routed via signal path 206 within close enough proximity to Hall sensor 203 to allow Hall sensor 203 to develop a voltage corresponding to a magnetic field generated by the controlled current i CCT . In at least one embodiment, the signal path 206 is actually connected to switch 204 . Signal path 206 is shown as broken without showing the actual connection to switch 204 or load 210 because the particular connection points is a matter of design choice. For example, signal path 206 could connect after switch 204 , before switch 204 , before load 210 , and so on. In at least one embodiment, the signal path 206 receives a mirrored copy of controlled current i CCT . The connection and routing of signal path 206 to conduct the controlled current i CCT are matters of design choice. Exemplary connection embodiments are subsequently described. Additionally, the number of turns around Hall sensor 203 is a matter of design choice. The solid line turn of signal path 206 indicates a single turn. The dashed line 207 indicates two or more turns of signal path 206 . As subsequently described in more detail, Hall sensor 203 develops a voltage corresponding to the controlled current i CCT . Controller 202 utilizes the voltage developed by Hall sensor 203 corresponding to the controlled current i CCT as feedback to generate a switch control signal to control the controlled current i CCT .

Electronic system 200 also includes a power source 208 to supply the controlled current i CCT to load 210 . Power source 208 can be any source of power, such as voltage source 101 or any power supply that supplies enough power for operation of load 210 . Load 210 can be any type of load that utilizes or supplies a switch controlled current i CCT . In at least one embodiment, load 210 includes one or more light emitting diodes (LEDs).

Controller 202 generates switch control signal CS 1 to control conductivity of current control switch 204 using, for example, duty cycle modulation. Switch 204 can be any type of switch that can be controlled by a switch control signal. In at least one embodiment, switch 204 is a field effect transistor (FET), and switch control signal CS 1 is a duty cycle modulated signal. In at least one embodiment, each pulse 212 of control signal CS 1 causes switch 204 to conduct. When each pulse ends, switch 204 is nonconductive. Turning switch 204 “on” and “off” in accordance with the duty cycle of switch control signal CS 1 establishes an average resistance of switch 204 . Since an average value of controlled current i CCT is directly related to the average resistance of switch 204 , the duty cycle of control signal CS 1 controls an average value of controlled current i CCT .

The Hall sensor 203 generates a voltage corresponding to a magnetic field of controlled current i CCT . Hall sensor 203 also produces a noise voltage component that can represent a significant component of the voltage generated by Hall sensor 203 . In at least one embodiment, the noise voltage of Hall sensor 203 has a relatively low frequency f N relative to a frequency f iCCT of switch control signal CS 1 . In at least one embodiment, the frequency f iCCT of switch control signal CS 1 is also the frequency of controlled current i CCT . As illustratively described in more detail below, in at least one embodiment, because f iCCT >>f N , controller 202 can sense a baseline noise voltage V HB of Hall sensor 203 (or obtain a representation of the baseline voltage V HB , such as an amplified baseline voltage V HB ) prior to sensing a signal voltage corresponding to the magnetic field of controlled current i CCT . In at least one embodiment, the frequency f iCCT is 100-1,000 times greater than the noise frequency f N . The frequency f iCCT of switch control signal CS 1 is a matter of design choice. In at least one embodiment, since the baseline noise voltage V HB remains effectively constant during a pulse of the higher frequency controlled current, controller 202 subsequently determines the voltage V ICCT corresponding to the magnetic field of the controlled current i CCT by subtracting the baseline noise V HB voltage of Hall sensor 203 from a Hall sensor output voltage V H representing V ICCT and V HB . Thus, controller 202 effectively cancels out the baseline noise voltage V HB of Hall sensor 203 . Since the controlled current i CCT corresponds to the voltage V ICCT corresponding to the magnetic field of the controlled current i CCT , controller 202 can determine a value of the controlled current i CCT . The dashed A-A line is a cross-section reference for controller 202 discussed subsequently with reference to FIG. 6A .

FIG. 2B depicts an electronic system 240 that includes a controller 242 to control power factor correction of a switching power converter 248 . As subsequently described in more detail, controller 242 includes a Hall sensor 203 to sense controlled current i CCT through switch 244 . The controlled current i CCT is routed via signal path 206 . Again, the particular connection points of signal path 206 to conduct controlled current i CCT in the switching power converter 248 or a representation of controlled current i CCT are not shown because they are a matter of design choice. As previously described, controller 242 utilizes the voltage developed by Hall sensor 203 corresponding to the controlled current i CCT to control controlled current i CCT .

Controller 242 generates control signal CS 2 to control conductivity of current control switch 244 . Switch 244 can be any type of switch that can be controlled by a switch control signal. In at least one embodiment, switch 244 is a field effect transistor (FET), and switch control signal CS 2 is a duty cycle modulated signal. In at least one embodiment, each pulse 214 of control signal CS 2 causes switch 244 to conduct. When each pulse ends, switch 244 is nonconductive. Thus, the duty cycle of control signal CS 2 controls an average value of controlled current i CCT through switch 244 . The particular methodology for generating control signal CS 2 using feedback from Hall sensor 203 is a matter of design choice.

Electronic system 240 also includes a voltage source 246 to provide a supply voltage to switching power converter 248 . In at least one embodiment, voltage source 246 is a public utility voltage source such as voltage supply 101 ( FIG. 1 ). Switching power converter 248 can be any type of switching power converter that provides a controlled current i CCT to load 250 . Switching power converter 248 can be any type of switching power converter, such as a boost-type, buck-type, or boost-buck type switching power converter. Load 250 can be any type of load, such as a light source that includes one or more LEDs.

FIG. 2C depicts electronic system 260 , which represents one embodiment of electronic system 240 ( FIG. 2B ). Electronic system 260 includes a switching power converter 261 , which represents one embodiment of switching power converter 248 ( FIG. 2B ). Electronic system 260 includes a printed circuit board (PCB) 262 , and controller 242 is attached to PCB 262 . Pins 263 and 264 of PCB 262 couple Hall sensor 203 to switch 244 . As subsequently described with reference to FIG. 6A , signal path 265 represents a printed circuit board trace routed within a close enough proximity to Hall sensor 203 to allow Hall sensor 203 to sense a magnetic field generated by controlled current i CCT . In at least one embodiment, controller 242 operates switching power converter 260 in CCM. In at least one embodiment, voltage source 266 is a public utility voltage source such as voltage supply 101 ( FIG. 1 ), and full-bridge diode rectifier 267 rectifies the input voltage V IN to generate an AC, rectified voltage V X . In at least one embodiment, using a sense signal from Hall sensor 203 indicating a value of controlled current i CCT and exemplary feedback signals V X and V LINK representing the rectified voltage V X and link voltage V LINK , the controller 242 generates switch control signal CS 2 to control switch 244 and provide power factor correction for switching power converter 261 . In at least one embodiment, switch control signal CS 2 also controls power factor correction and regulates link voltage V LINK in accordance with any conventional methodology and conventional controller, such as the CCM PFC controller, model number UCC28019A, available from Texas Instruments, Inc., Texas, USA.

FIG. 2D depicts an electronic system 270 that includes a controller 272 , and controller 272 generates a switch control signal CS 1 to control conductivity of switch 274 . As subsequently described in more detail, controller 272 includes a Hall sensor 203 to sense controlled current i CCT from load 280 . The controlled current i CCT is routed via signal path 206 . The signal path 206 is within sufficient proximity to Hall sensor 203 to allow the Hall sensor 203 to develop a voltage corresponding to a magnetic field generated by the controlled current i CCT . The connection and routing of signal path 206 to conduct the controlled current i CCT is a matter of design choice. Exemplary connection embodiments are described subsequently. As previously described, controller 272 utilizes the voltage developed by Hall sensor 203 as feedback corresponding to the controlled current i CCT to generate switch control signal CS 2 to control controlled current i CCT .

Load driver 278 can be any type of load driver that provides a controlled current i CCT to load 280 . In at least one embodiment, load driver 278 is a switching power converter, such as switching power converter 248 , and controller 272 also generates a switch control signal CS 2 to control switch 244 as described with reference to FIG. 2B . Load 210 can be, for example, any type of load utilizing a controlled current i CCT . In at least one embodiment, load 280 includes one or more light emitting diodes (LEDs).

Controller 272 generates control signal CS 1 to control conductivity of a current control switch 274 . Switch 274 can be any type of switch that can be controlled by a switch control signal. In at least one embodiment, switch 274 is a field effect transistor (FET), and switch control signal CS 2 is a duty cycle modulated signal. In at least one embodiment, each pulse 284 of control signal CS 2 causes switch 274 to conduct. When each pulse ends, switch 274 is nonconductive. Thus, the duty cycle of control signal CS 2 controls an average value of controlled current i CCT . The generation of control signal CS 2 is a matter of design choice. In at least one embodiment, controller 272 generates switch control signal CS 2 in the manner of generating a switch control signal illustratively described in U.S. patent application Ser. No. 11/864,366, entitled “Time-Based Control of a System having Integration Response,” inventor John L. Melanson, and filed on Sep. 28, 2007 (referred to herein as “Melanson I”). In at least one embodiment, controller 272 generates switch control signal CS 2 in the manner of generating a switch control signal illustratively described in U.S. patent application Ser. No. 12/415,830, entitled “Primary-Side Based Control Of Secondary-Side Current For An Isolation Transformer,” inventor John L. Melanson, and filed on Mar. 31, 2009 (referred to herein as “Melanson II”). Melanson I and II are incorporated by reference in their entireties.

As similarly described with reference to electronic system 200 ( FIG. 2A ), in at least one embodiment, the frequency f iCCT of switch control signal CS 1 , and, thus, the frequency of each pulse of controlled current i CCT , exceeds the frequency f N of the noise voltage of Hall sensor 203 by an amount sufficient to allow controllers 242 , 262 , and 272 to each effectively cancel out the noise voltage and determine a value of controlled current i CCT . For example, in at least one embodiment, each of controllers 242 , 262 , and 272 determines the voltage V ICCT corresponding to the magnetic field of the controlled current i CCT by subtracting a sensed baseline noise voltage V HB of Hall sensor 203 from a sensed voltage Hall sensor output voltage V H representing the voltage corresponding to the magnetic field V iCCT of the controlled current i CCT plus the baseline noise voltage V HB of Hall sensor 203 . Since the controlled current i CCT corresponds to the voltage corresponding to the magnetic field of the controlled current i CCT , each of controllers 242 , 262 , and 272 can determine a value of the controlled current i CCT .

FIG. 3 depicts controller 300 , which represents an exemplary embodiment of controllers 202 , 242 , and 272 . FIG. 4 depicts a flowchart showing an exemplary controlled current detection and switch control algorithm 400 utilized by controller 300 to determine a value associated with a controlled current and to use the value as feedback to generate a switch control signal to control the controlled current. FIG. 5 depicts an exemplary Hall sensor voltage graph 500 to illustrate how the controller effectively cancels out the Hall sensor baseline noise voltage V HB .

Because the Hall sensor 203 functions based upon a magnetic field of controlled current i CCT , the discussion no references FIG. 6A , which illustrates an exemplary placement of signal path 206 and a resulting magnetic field of the controlled current i CCT . Referring to FIG. 6A , FIG. 6A depicts an exemplary integrated circuit controller 600 that includes a Hall sensor 602 . Controller 600 represents one embodiment of controllers 202 , 242 , 272 , and 300 fabricated as an integrated circuit and located within an integrated circuit package 604 . The particular dimensions of controller 600 and Hall sensor 602 are a matter of design choice. The integrated circuit package 604 represents a cross-section of controller 202 along cross-sectional line A-A and includes exemplary leads 606 and 608 . The integrated circuit leads 606 and 608 connect controller 600 to a printed circuit board 610 . Signal path 612 represents an exemplary cross section of signal paths 206 , 265 , and 312 . Signal path 612 is a signal trace in printed circuit board 610 . “.X” and “.O” are appended to identifiers 612 to respectively indicate entry and exit points of controlled current i CCT in the cross-section of signal path 612 . When controlled current i CCT is flowing as indicated, controlled current i CCT generates a magnetic field B indicated by the concentric, dashed circles 614 . At the Hall sensor 602 , the direction of the magnetic field B is generally “up” as indicated by arrow 616 . Dimension d 0 represents a distance between the longitudinal centers of signal path 612 .O and Hall sensor 602 . Dimension d 1 represents a distance between longitudinal centers of signal path 612 .X and Hall sensor 602 . Dimension d 2 represents a distance between latitudinal centers of signal path 612 and Hall sensor 602 . The particular values for dimensions d 0 , d 1 , and d 2 are a matter of design choice. In at least one embodiment, d 0 =d 1 =d 2 =1 mm. In at least one embodiment, d 0 =d 1 =d 2 range from approximately 1 mm to several millimeters, such as 5 mm.

An exemplary operation of controller 300 is described with reference to FIGS. 3 , 4 , 5 , and 6 A. In at least one embodiment, the exemplary operation relates to controller 300 controlling switch 322 to control power factor correction in a switching power converter, such as switching power converter 248 , operating in continuous conduction mode. In at least one embodiment, the exemplary operation relates to controller 300 controlling switch 322 to control the controlled current i CCT in a load, such as load 280 .

Hall sensor 302 is an example of a Hall effect device. The particular design of Hall sensor 302 is a matter of design choice. Hall sensor 302 is, for example, fabricated from conductive material in a layer as part of an integrated circuit version of controller 300 . In some embodiments, Hall sensor 302 is a silicon diffusion layer, a doped silicon layer, or polysilicon. Hall sensor 302 has four connection tabs 304 , 306 , 308 , and 310 . Tab 304 is connected to a constant current source 311 , and tab 308 is connected to a reference, such as ground. Constant current source 311 supplies a current i H that flows through Hall sensor 302 . As controlled current i CCT flows through signal path 612 , a magnetic field B develops through the Hall sensor 302 as illustratively discussed in conjunction with FIG. 6A . The magnetic field B causes a separation of charge in Hall sensor 302 . The separation of charge causes a voltage V H + to develop at tap 310 and a voltage V H - to develop at tab 306 . Differential amplifier 314 amplifies the difference voltage V H +−V H − to generate Hall sensor output voltage V H . Thus, the Hall sensor output voltage V H equals V H +−V H −. The sensed Hall sensor output voltage V H is a function of the controlled current i CCT . The particular relationship between controlled current i CCT and Hall sensor output voltage V H is a function of various factors such as the material from which Hall sensor 203 is fabricated, the routing and configuration of magnetic field B, and so on. The particular function can be determined by a one of ordinary skill in the art using well-known techniques.

In at least one embodiment, signal path 612 has one turn as depicted in cross-section in FIG. 6A . However, signal path 612 can have any number of turns and any orientation. The number of turns and orientation of the turns is a matter of design choice. In at least one embodiment, signal path 612 includes multiple turns in different layers of PCB 610 to increase the strength of the magnetic field B of controlled current i CCT sensed by Hall sensor 302 . Additionally, signal path 312 can be routed through one or more layers of the controller 600 . In another embodiment, magnetic material is used with the signal path 612 to direct the magnetic field.

Routing of the signal path conducting controlled current i CCT is a matter of design choice. The signal path 612 FIG. 6B depicts another routing configuration for controlled current i CCT in an integrated circuit package 652 housing controller 600 . The integrated circuit package 652 also represents a cross-section of controller 202 ( FIG. 2 ) along cross-sectional line A-A and includes exemplary leads 654 and 656 . Wires 658 and 660 connect controller 600 to respective leads 654 and 656 . Leads 654 and 656 are part of a lead frame of integrated circuit package 652 that attach integrated circuit 652 to PCB 657 . Signal path 662 represents an exemplary cross section of signal paths 206 , 265 , and 312 . Signal path 662 is a signal trace located on top of lead 654 . “.X” and “.O” are appended to identifiers 662 to respectively indicate entry and exit points of controlled current i CCT in the cross-section of signal path 662 . When controlled current i CCT is flowing as indicated, controlled current i CCT generates a magnetic field B indicated by the concentric, dashed circles 664 . At the Hall sensor 602 , the direction of the magnetic field B is generally “up” as indicated by arrow 666 . The Hall sensor 602 generates a voltage proportional to the magnetic field of the controlled current i CCT in signal path 662 .

Referring to FIGS. 3 , 4 , and 5 , Hall sensor 302 produces a low frequency noise voltage 502 . The noise voltage 502 is shown as a dotted line during a pulse of controlled current i CCT , which occurs during time periods T A and T B . The actual Hall sensor output voltage V H is the solid line 504 , which includes the noise voltage 502 and the noise voltage 502 and the voltage V ICCT corresponding to the controlled current i CCT . Analog-to-digital converter (ADC) 316 converts the Hall sensor output voltage V H into a digital value V H (n). In at least one embodiment, processor 318 is digital signal processor or a mixed analog and digital signal processor. In at least one embodiment, the operations in controlled current detection and switch control algorithm 400 are stored as code in memory 320 . The particular configuration and operation of processor 318 is a matter of design choice. In at least one embodiment, processor 318 retrieves the code from memory 320 and performs the operations of controlled current detection and switch control algorithm 400 . In at least one embodiment, controlled current detection and switch control algorithm 400 is stored as firmware in a memory within processor 318 . In at least one embodiment, controlled current detection and switch control algorithm 400 is stored in an off-chip memory that is accessible to processor 318 . In at least one embodiment, processor 318 is configured as an analog device to perform operations in controlled current detection and switch control algorithm 400 .

Referring now to FIG. 4 , in operation 402 , processor 318 senses the Hall sensor output voltage V H at time t 0 (i.e. prior to turning current control switch “on”) to obtain a baseline Hall sensor noise voltage V HB . Because the frequency f N of the Hall baseline noise voltage V HB is much larger than the frequency f iCCT of switch control signal CS 1 , the Hall baseline voltage V HB remains relatively constant during time period T A . Time t 0 corresponds to a time prior to generating switch control signal CS 1 to turn switch 322 “on”, i.e. cause switch 322 to conduct. Switch 322 represents one embodiment of switches 204 , 244 , and 274 .

In operation 404 , processor 318 generates a pulse of control signal CS 1 at time t 1 , which causes switch 322 to conduct and the controlled current i CCT to increase. The particular methodology for generating control signal CS 1 is a matter of design choice. In at least one embodiment, each period of control signal CS 1 is constant, as, for example, described in Melanson I and II (“periods” are described in terms of switch states in Melanson I).

The time lapse between times t 0 and t 1 is a matter of design choice. In at least one embodiment, the time lapse between times t 1 −t 0 is minimized to establish a baseline noise voltage V HB that is approximately unchanged between times t 0 and t 2 . In operation 406 , processor 318 samples the Hall sensor output voltage V H at time t 1 to determine an initial voltage value V 0 of the Hall sensor voltage Hall sensor output voltage V H . The initial value V 0 represents the Hall baseline noise voltage V HB plus the voltage V ICCT corresponding to the controlled current i CCT at the beginning of the pulse of switch control signal CS 1 . The initial value of the controlled current i CCT at time t 1 is a function of V 0 −V HB , since V 0 =V HB +V ICCT . As previously discussed, determination of the initial value of the controlled current i CCT from V 0 −V HB is a well-known function based on the material make-up of the Hall sensor 203 , the number of turns of signal path 206 , and distances d 0 , d 1 , and d 2 ( FIG. 6A ), and so on.

As the controlled current i CCT increases, the strength of the magnetic field B increases, and, thus, the voltage V ICCT component of the Hall sensor output voltage V H also increases as shown by arrow 506 . However, since the noise frequency f N of Hall sensor 304 is much less than the frequency f iCCT of the switch control signal CS 1 , the baseline noise voltage V HB remains relatively constant during period T A . Processor 318 continues to sample the Hall sensor output voltage V H to determine when the Hall sensor output voltage V H has increased from the initial voltage V 0 to the target voltage V TARGET . The particular sampling frequency of the Hall sensor output voltage V H is a matter of design choice. In at least one embodiment, the sampling frequency is high enough to determine approximately when the Hall sensor output voltage V H has increased from the initial voltage V 0 to the target voltage V TARGET .

Operation 408 determines whether the Hall sensor output voltage V H has increased from the initial voltage V 0 by a target voltage V TARGET . In at least one embodiment, the target voltage V TARGET is directly related to the controlled current i CCT . The particular target voltage V TARGET depends on, for example, a desired average controlled current. For example, in at least one embodiment, the initial voltage V 0 represents 350 mA, the target voltage V TARGET represents 50 mA, and the peak voltage V 1 represents 400 mA, so that the average controlled current equals 400 mA.

In at least one embodiment, to determine if the Hall sensor output voltage V H equals the initial voltage V 0 +V TARGET , between times t 1 and t 2 operation 408 subtracts the initial voltage V 0 from a sampled Hall sensor output voltage V H to determine if the sampled Hall sensor output voltage V H has increased from the initial voltage V 0 by an amount equal to the target voltage V TARGET . The frequency f iCCT of switch control signal CS 1 is large relative to the frequency f N of Hall voltage noise 502 . For example, in at least one embodiment, the frequency of switch control signal CS 1 is approximately 100 kHz, and the frequency of the Hall voltage noise 502 is approximately 100 Hz. So, the Hall voltage noise 502 remains approximately constant between times t 1 and t 3 . Thus, subtracting the initial sampled Hall sensor voltage V 0 corresponding to the leading edge of switch control signal CS 1 at time t 1 from the current sample of Hall sensor output voltage V H represents the change V Δ in the voltage V ICCT corresponding to the controlled current i CCT , i.e. V H =V 0 +V Δ .

If the Hall sensor output voltage V H does not equal the initial voltage V 0 +V TARGET , in operation 410 , processor 318 continues generating a pulse of switch control signal CS 1 to keep switch 322 “on”. Thus, the controlled current i CCT continues to increase causing the Hall sensor output voltage V H to increase. Operation 410 returns to operation 408 , and processor 318 continues to sense the Hall sensor output voltage V H . If in operation 408 processor 318 determines that V Δ =V TARGET , operation 412 determines the time t 2 at which V Δ =V TARGET .

In operation 414 , processor 318 determines the time t 3 at which to cease generating the pulse of control signal CS 1 and, thus, turn switch 322 “off”. In at least one embodiment, the switch 322 turn “off” time t 3 is set so that times t 3 −t 2 =t 2 −t 1 . Time period T A equals times t 2 −t 1 , and time period T B equals times t 3 −t 2 . Thus, in at least one embodiment, processor 318 sets the time period T A during which the Hall sensor output voltage V H rises from the baseline voltage V 0 to the target voltage V TARGET V 0 to be the same or approximately the same as the time period T B during which the Hall sensor output voltage V H rises from the target voltage V TARGET +V 0 to a peak voltage V 1 .

In operation 416 , processor 318 ends the pulse of control signal Cs 1 , thus, turning switch 322 “off”. When switch 322 is “off”, the controlled current i CCT continues to decrease. Operation 402 restarts controlled current detection and switch control algorithm 400 at the beginning of period TT 1 for control signal CS1 and continues for each consecutive period.

As previously discussed, the connection and routing of signal paths 206 , 265 , and 312 , which conduct embodiments of the controlled current i CCT , are a matter of design choice. FIGS. 7 and 8 depict respective, exemplary embodiments of electronic system 200 and routing of signal paths to conduct controlled current i CCT into a proximal relationship with Hall sensor 203 , thus, allowing Hall sensor 203 to generate a voltage in response to the magnetic field of the controlled current i CCT .

Referring to FIG. 7 , electronic system 700 represents one embodiment of electronic system 200 . In electronic system 700 , load driver 208 and controller 202 are attached to a printed circuit board 702 . N-channel metal oxide semiconductor field effect transistor (MOSFET) 704 represents an embodiment of switch 212 . Signal trace 706 represents an embodiment of signal trace 206 . Signal trace 706 is in series with a source of MOSFET 704 and a reference voltage connection 708 to allow Hall sensor 203 to sense the magnetic field of the controlled current i CCT in signal trace 706 .

Referring to FIG. 8 , electronic system 800 represents one embodiment of electronic system 200 . In electronic system 800 , load driver 208 and controller 202 are attached to a printed circuit board 802 . Signal trace 804 represents an embodiment of signal trace 206 . Signal trace 804 is in series with a drain of MOSFET 704 to allow Hall sensor 203 to sense the magnetic field of the controlled current i CCT in signal trace 704 .

The routings, connections, and configurations of a signal path to allow Hall sensor 203 to sense the magnetic field generated by the controlled current i CCT are virtually limitless and are a matter of design choice.

FIG. 9 depicts a light source 900 , which represents one embodiment of load 210 . Light source 900 includes one or more LEDs 902 and exemplary peripheral circuitry including a capacitor 904 connected across the LEDs 902 , and series connected diode 906 and inductor 908 connected in parallel with capacitor 904 and LEDs 902 .

Thus, an electronic system includes a Hall sensor to sense a controlled current, and a controller receives information either directly or indirectly from the Hall sensor corresponding to the controlled current and utilizes the information from the Hall sensor to control conductivity of a switch. In at least one embodiment, controlling conductivity of the switch controls a drive current for a load. In at least one embodiment, utilizing the Hall sensor to detect the controlled current i CCT is more accurate than using a sense resistor (such as sense resistor 109 ( FIG. 1 )) and dissipates less power than using the sense resistor.

Although the present invention has been described in detail, it should be understood that various changes, substitutions and alterations can be made hereto without departing from the spirit and scope of the invention as defined by the appended claims. For example, in at least one embodiment, the controlled current sensed by the Hall sensor 203 is representative of an actual controlled current i CCT but is not the current flowing through the load. For example, in at least one embodiment, a current mirror can be used to mirror the controlled current i CCT and the controlled current sensed by the Hall sensor 203 is the mirrored current.