Abstract:
In high-current electrical devices protected by fuses, additional performance data besides whether or not a fuse is blown is useful for diagnostics, repair, and preventing emerging failures from reaching a level that damages the device. An intelligent fuse-holder includes a built-in current sensor. The current sensor signals are passed through an A/D converter and analyzed by a microcontroller. Through an interface, a user can program the fuse-holder to periodically degauss the current sensor coil to improve performance or turn the sensor power off to conserve power. The user may also control various I/O signals carrying information about the fuse, the intelligent electronics, or the host board on which the fuse-holder is mounted.

Description:
BACKGROUND 
       [0001]    Many circuits fabricated on printed circuit boards (PCBs) benefit from a board-mounted fuse to protect the components from damage by power surges and other overcurrent conditions. However, conventional DIN and panel-mounted fuse-holders do not easily plug into a PCB. There are PCB-mounted fuse clips for a wide variety of fuses such as ¼AG, 5×20 mm, and automotive. 
         [0002]    However, neither these simple fuse clips nor the non-PCB-compatible fuse holders include capabilities for measuring currents and using a microcontroller to calculate leakage current, saving power, and monitoring various external conditions that affect performance of the host board. Instead, designers must mount separate components on the host board to perform these functions. All these functions are related to energy efficiency, performance optimization, and damage prevention for the host board, which are useful in a wide variety of circuits. Building them into the host board separately takes design time and uses up space on the host board. 
         [0003]    In addition, many conventional open-loop current sensors experience signal drift when operated over wide temperature ranges. Host boards that must operate in non-climate-controlled environments, such as those in remote communications or energy stations, often experience wide temperature ranges. To cope with these situations, designers need to include temperature-compensation circuits, which further increase design cost and use up more of the limited available space on the host board. 
         [0004]    Therefore, a need exists for a next-generation fuse-holder that can accurately measure host-board current under a wide range of ambient conditions, alert users when important operating conditions change, and save power. Such a device would be even more useful if the functions were programmable to meet the monitoring needs of various types of host boards operating under various conditions. 
       BRIEF SUMMARY 
       [0005]    A need exists for a fuse-holder adapted to monitor current circulating on a host board. The Intelligent Fuse Holder (IFH) includes Hall-effect current sensors that interface to a microcontroller. A need exists for a fuse-holder adapted to monitor leakage current in the host board. The IFH includes dual current inputs and dual current outputs to collect the measurements necessary for calculating leakage current, and a microcontroller with instructions for automatically performing the calculations. 
         [0006]    A need exists for maintaining the accuracy of the current sensors in the fuse-holder over extended operating time. The IFH includes a degauss coil which improves sensor performance by periodically neutralizing magnetic field build-up during operation. 
         [0007]    A need exists for a fuse-holder that can alert users to a failure or problem that affects the current through the fuse. The IFH includes alerting components controlled by the microcontroller to communicate information to a user. The alerting components may be indicators, such as LEDs, on an easily visible surface of the IFH. They may also include audible signals or other signals transmitted through wires or over the air to a user&#39;s receiving device (such as a computer or mobile receiving device). 
         [0008]    A need exists for a current-monitoring fuse-holder that is adaptable to a wide range of circuits and consumes only as much power as is necessary to perform the needed functions on the particular type of host board where it is used. The IFH microcontroller includes a built-in A/D converter and multiplexer unit, a programmable gain amplifier (PGA), a temperature sensor, programmable digital I/O and two digital-to-analog converters (DAC). The microcontroller scans and records the current sensor output by turning the sensor power on, degaussing the sensors to ensure accurate sensing, reading the sensor outputs, turning sensor power off when the measurement is complete, and recording the temperature from a temperature sensor that may be built-in. It will perform this measurement cycle at a user-programmable rate to minimize the power consumed by the current monitoring function. In addition, the IFH includes several high-current/high-voltage pins (the number depending on the current load and pin rating) and several low voltage pins to carry power or signals, as well as several programming pins for programming the microcontroller; all of these features enhance the IFH&#39;s versatility and adaptability. 
         [0009]    A need exists for an intelligent fuse-holder that is compatible with existing standards. The IFH can operate through a standard serial interface (such as RS485) and utilize a standard protocol (such as Modbus) to allow the user to read both Hall-effect current sensors, control one or more I/O signals which may be used for alarm/warning indications, and set other user parameters. The IFH also mates to a host board via a PCB-mount socket, making it easy to install, remove and replace. 
         [0010]    A need exists to minimize resulting waste and down-time after a fuse failure. When a fuse blows, the IFH can be quickly and safely removed or the fuse can be quickly ejected and replaced. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]      FIG. 1  is a conceptual diagram of the outside of the IFH showing an example of the indicators and connections. 
           [0012]      FIG. 2  is a functional diagram of one embodiment of an IFH. 
           [0013]      FIGS. 3   a - 3   c  show an approach to enabling IFHs to read protocol addresses based on the locations of the IFHs on the host board. 
           [0014]      FIG.4  is an example flowchart of a microcontroller process in a preferred embodiment. 
           [0015]      FIGS. 5   a - 5   c  illustrate example layouts of a fuse module, a programming module, and the manner in which the two modules connect to each other. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    The IFH communicates failures (such as blown fuses) and sub-failure problems (such as overcurrents that do not blow the fuse or temperatures exceeding a prescribed range) without requiring the user to apply test probes or otherwise disturb the host board. Multiple IFHs may be used on a single host board. The fuse and fuse-holder electronics are contained in a compact insulated housing that plugs into the host board via one or more convenient connectors. Indicators on the most easily visible surface of the housing change their appearance to indicate failures or problems. Alerts about failures or problems may also be sent to a user&#39;s receiving device (e.g. computer, mobile phone, personal digital organizer). 
         [0017]      FIG. 1  is a conceptual diagram of one possible insulated housing for a preferred embodiment of the IFH. The housing may be made of plastic by an inexpensive, convenient method such as injection molding, but other insulating materials and manufacturing methods may also be used. The housing&#39;s connection surface  100  includes the operating connections to the host board. Connection features on connection surface  100  include high current/ high voltage connectors  102   a - d  and low-voltage power/signal pins  103 . High-current/high-voltage connectors  102   a  and  102   c  connect to the source current, while high-current/high-voltage connectors  102   b  and  102   d  connect to the return current. Power/signal pins  103  may be built into a PCB-compatible connector  101 , which may be a standard part or a custom design. Multiple IFHs may be mounted on a single host board. Other features are flexible in where they may be placed. 
         [0018]    Alerting indicators  104  may be programmed to respond to conditions such as a blown fuse, excessive ground-fault current, or extreme temperature. If alerting indicators  104  are visual indicators, they are preferably placed where they can be easily seen while the board is operating. Here they are shown on the top, but other embodiments may mount them on a side surface of the IFH for boards that are more easily viewed edge-on during operation. If alerting indicators  104  send an audible signal, they need not be placed in an easily visible location. If alerting indicators  104  send signals to an electronic receiver, they may be placed anywhere where the signal will not be obstructed or interfere with host board operation. Fuse hatch lid  105 , through which the fuse (omitted from this view for drawing clarity) is installed and replaced, and fuse ejector  106  that allows a user to open fuse hatch lid  105  and manually or mechanically eject a fuse, are preferably placed where a user can easily and safely reach them. Recessed programming port  107 , which is only connected when the functions are being programmed, is shown on a side surface in the example figure but may be in any convenient location. For instance, in applications where programming should take place only when the IFH is disconnected, or only in a lab or factory rather than in the field, programming port  107  could be located on connection surface  100  to prevent mistaken access during operation. Where programming or retrieval of stored data will be done by a separate device while the IFH operates, the programming port may be located on an accessible surface but protected from accidental contact. Alternatively, power/signal port  201  could be adapted to handle the programming signals, enabling the IFH to be programmed by or through the host board. 
         [0019]      FIG. 2  is a functional diagram of one IFH embodiment. The IFH receives power and signals from the host board through power/signal port  201 . Power/signal port  201  may carry, among other things: 
         [0020]    1. Power for microcontroller logic 
         [0021]    2. Power for degauss circuit 
         [0022]    3. Signal/power ground 
         [0023]    4. Serial interface signals 
         [0024]    5. Bus protocol address 
         [0025]    Incoming power goes through voltage regulator  218 , which adapts the supply voltage to an optimal range for powering microcontroller  220 . Reset signal  225  and address signal  226  go directly to microcontroller  220  from power/signal port  201 . Communication signal  221  passes to and from microcontroller  220  through a communications module, shown here as transceiver  211  but also realizable as a separate transmitter and receiver. Microcontroller  220  also receives programming signals  227  through programming port  207  when a designer or user programs operating code and parameters into the IFH. Depending on its configuration, programming port  207  can simply accept input code from an external programming device, or also allow retrieval of stored data by an external device. Alternatively, power/signal port  201  could be adapted to handle the programming signals, enabling the IFH to be programmed by or through the host board. 
         [0026]    Source-current sensor  212   a  measures source current in the host board and sends source-current measurement  222   a  to microcontroller  220 . Return-current sensor  212   a  measures return current in the host board and sends return-current measurement  222   b  to microcontroller  220 . (Neither the host board nor the high-current connections are shown in this figure). Differential measurement  222   c  is a comparison of measurements  222   a  and  222   b  calculated by microcontroller  220 . If  222   a  and  222   b  are different in magnitude, the host board is leaking current to ground and the difference between them is nonzero. Enhancements may include averaging several current measurements, correcting the current measurement using temperature data if available, and detecting trends in current over time. This system can also detect the arcing that occurs in some defective fuses. Optionally, the system can generate a particular alert when the fluctuation characteristic of an arcing fuse is detected. 
         [0027]    One problem endemic to Hall-effect current sensors is that magnetic fields build up around the coil, affecting the sensed-current reading and decreasing its accuracy. To solve this problem, microcontroller  220 &#39;s digital output includes degauss controls  223 , which causes degauss circuit  213  to generate degauss pulses  233   a  and  233   b.  The degauss pulses  233   a  and  233   b  remove any built-up magnetic fields from the coils of current sensors  212   a  and  212   b,  respectively. Preferably, the degauss coils may be operated by a single double-capacity degauss circuit to reduce the component count. Degauss cycles may be generated either periodically or when triggered by a predetermined signal or calculation result. After delivering the degauss pulse(s), degauss circuit  213  deactivates so normal operation can continue. A delay may be built in between degaussing and measuring current to prevent any tail-end effects of the degauss pulse from affecting the measurements. 
         [0028]    To compensate for any signal drift of the current sensors with temperature, microcontroller  220  may also collect data from a temperature sensor, either built-in or external. A stored look-up table of temperatures and corresponding compensation values can be used to adjust the reading taken from the current sensor. 
         [0029]    When a predetermined triggering event occurs, such as a blown fuse, ground fault, overcurrent, or undercurrent, microcontroller  220  sends alerting signals  224  to activate the corresponding alerting indicators  204 . Temperature sensor  236  may optionally also trigger an alert when the temperature varies outside a predetermined optimal operating range, via microcontroller  220 &#39;s accessing stored the minimum and maximum operating temperatures from a look-up table and comparing them to the most recently measured temperature. The alerts enable a user to immediately identify a problem without connecting test equipment to the host board, saving a significant fraction of potential down-time and reducing operating costs. The alerting indicators can be visual indicators (for example, LEDs or small displays) built into the IFH housing, audio alarms built into the IFH or the host board, or messages from internal transceiver  211  or an external transceiver on the host board to a user&#39;s computer, phone, or mobile receiving device. Optionally, a wireless transceiver may be used. 
         [0030]    In a preferred embodiment, the alerting functions are fully programmable in the operating protocol through programming port  207 ; for instance, the user could program an alert to be triggered when the fuse has experienced current greater than 12.8A more than 10 times. More alerting options are possible when multiple IFHs are used on the same host board or connected host boards and their transceivers  211  can communicate with each other. For instance, the user could program microcontroller  220  to send an alert when the programmed IFH&#39;s current is low compared to other IFHs in an assembly. 
         [0031]    Power saving is important to the operation of many host boards. Therefore, the IFH should use only as much power as necessary to perform its intended function. To save power, microcontroller  220  can command the current sensors to turn on for a measurement and off after a measurement using optional power-save mode signals  228   a  and  228   b.  This can reduce the power required by as much as 50%. Reset signal  225  may be used for entering and exiting power-save mode as well as powering the entire IFH up and down. 
         [0032]      FIG. 2   b  is a detail schematic of some of the subcomponents that may either be built into or connected to microcontroller  220 . An A/D converter (ADC)  231  with a multiplexer  232  and programmable gain amplifier (PGA)  233 , is preferably built into microcontroller  220 , but may be a separate component. The negative side of each differential amplifier  237   a  and  237   b  receiving measurements from a current sensor  212   a  or  212   b  is preferably connected to an external voltage divider  235 . The voltage divider may use the same voltage source as the current sensors. Temperature measurement signals from a temperature sensor  236  may be input to multiplexer  232  as well as current measurement signals coming through differential amplifiers  237   a  and  237   b.  A voltage reference for ADC  231  may be built into microcontroller  220  or external. In some situations, an external reference voltage may be more accurate. Here, either external voltage reference  234   x  or internal voltage reference  234 n may be selected by setting switch  238 . 
         [0033]    The analog inputs to ADC  231  may be either single-ended or differential. Differential analog inputs are preferred because they increase accuracy. Differential A/D enables automatic compensation of current-sensor output variations resulting from variations in supplied power. Differential A/D also rejects common noise from both signal and power sources. 
         [0034]    The serial interfaces for the programming port and operating power/signal port are preferably efficient and industry-standard. For example, a J-tag or ICP may be suitable for the programming port, depending on the particular functions desired. Optionally using an RS485 serial interface for the power/signal port enables interconnection of multiple IFHs on a single half-duplex communication line, so that the IFHs can communicate and compare data to identify and locate host-board problems. Preferably, the power/signal port serial interface supports a single baud rate of at least 1200 bps and operates under a convenient protocol, such as Modbus (an open-source protocol that is widely used in process control) or DNP. The protocol is primarily chosen for its ability to support desired IFH functions. The functions can include:
       1. Changing the rate at which the IFH current sensors take measurements   2. Changing the Excessive Ground Current alerting threshold   3. Requesting minimum, maximum, or average current-sensor readings since last scan   4. Initiating current-sensor calibrations   5. Requesting IFH serial number and other manufacturing data   6. Requesting the version identifier for the IFH firmware currently running on the microcontroller   7. Initiating and changing triggering conditions for user-defined alerts   8. Testing the functionality of alerts or surge-protection features       
 
         [0043]    In enhanced versions, retrieving identification and other data from chips on the host board through an interface such as I2c, SPI, or I-wire. 
         [0044]    Implementation of some protocols (including Modbus) requires that each IFH have a protocol address. Any method of assigning addresses may be used. However, on a host board with multiple IFHs, localized problems can be quickly located for faster repair and reduced downtime if the IFH addresses are based on IFH location on the host board and are retrievable without disrupting IFH operation. If each of the IFH host board connectors has a unique address pinout, the IFHs can use this to “read” their locations directly off the host board. With this capability, the IFHs may be replaced or interchanged randomly and still always have addresses based on their location on the host board. 
         [0045]      FIGS. 3   a - 3   c  illustrate one possible approach to a host board conferring location-based addresses to multiple IFHs through the pinout configuration of individual IFH connectors. For clarity, only the parts of the connectors dedicated to address detection are shown. 
         [0046]      FIG. 3   a  shows part of a power/signal connector  301  and part of a microcontroller  320  in an IFH. In this example, five channels BA 1 -BA 5  in power/signal connector  301  are dedicated to address detection. If each channel carries 1 bit of data, this configuration allows 2 5 =32 different addresses. (More or fewer addresses may be enabled by other configurations). Each IFH address channel BA 1 -BA 5  has a dedicated input/output point in microcontroller  320 , which includes a weak pull-up on each BAx signal. 
         [0047]      FIG. 3   b  shows examples of address-readable connector pinouts on the host board. At various locations  350   a - 350   c  on the host board are mating connectors  351   a - c,  which mate with IFH power-signal connectors configured like connector  301  in  FIG. 3   a.  Mating connector  351   a  at host-board location  350   a  has all the BA 1 -BA 5  pinout connections grounded (board address 0). Mating connector  351   b  at location  350   b  has BA 1  floating and BA 2 -BA 5  grounded (board address 1). Mating connector  351   a  at host-board location  350   a  has all the BA 1 -BA 5  pinout connections floating (board address 31). 
         [0048]      FIG. 3   c  is an example flowchart of the process by which the IFHs recognize their location-based addresses. When the host board is powered on, the microcontroller ( 320  in  FIG. 3   a ) reads BA 1 -BA 5  applying a weak pull-up, assigns zero to grounded signals and 1 to floating signals and computes the binary value, then adds 1 to the resulting decimal-converted value to determine the protocol address. Thus the IFH connected to connector  351   a  in  FIG. 3   b  would have protocol address 001, the IFH connected to connector  351   b  would have protocol address 002, and the IFH connected to connector  351   b  would have protocol address 032. This eliminates the need to pre-program IFH addresses, and thereby the need to mark and sort IFHs to ensure positioning them on the host board according to those addresses. Therefore, even if an IFH must be immediately replaced with another one when a fuse blows and the blown fuse replaced offline, the new IFH will automatically have the same location-based address as the replaced one. 
         [0049]      FIG. 4  is an example flowchart of a microcontroller process in a preferred embodiment that includes power saving. At programmed intervals, (or, in enhanced versions, responsive to triggering signals from the host board that come through the communications port), the microcontroller turns on and, if necessary, degausses the current sensors. The microcontroller then sends “measure” commands to the current sensors (and optionally a temperature sensor) and analyzes the signals (optionally taking several measurements and averaging them). If a current leakage (ground fault) condition is detected from the measurements (when the difference between the source and return currents exceeds the predetermined threshold), the microcontroller activates the ground-fault alerting indicator. Optionally, the microcontroller can store successive measurements and measure trends, or store a history of alerts, for performance reporting. The data can be retrieved through the programming port (if the programming port is optionally configured for user interface), sent from the transceiver to a remote receiver, or accesses through part of the host board with a communications connection to the IFH. When a measurement is complete, the current sensors (and optionally other components) are deactivated to save power until the next measurement occasion. 
         [0050]    In one embodiment, the IFH circuitry is divided into two modules. The division can be advantageous when, for example, the circuits are fabricated on PCBs; the blocks can be arranged on separate PCBs, which can be stacked or placed side-by-side inside the housing to save lateral space if the host board has components that do not fit under the bottom of the IFH housing. Analog board layout techniques help insure accuracy such as ground planes, short traces, ferrite beads etc. One possible division is into a fuse module and a programming module. 
         [0051]      FIG. 5   a  is an example diagram of a fuse module. Some of the components and connections are omitted for clarity. The fuse module includes the fuse  508  removably mounted in fuse mount  568 . Fuse mount  568 , shown here as a simple pair of fuse clips, may also be part of a spring-loaded fuse ejector. High-current connectors  502   a  and  502   b,  illustrated for the example here as quick-connect tabs, both connect to the source or the return current of the host board (not shown). The current travels through high-current traces  562   a  and  562   b  to jumper  572   a,  where the current passes through Hall-effect current sensor  512   a  to be measured. Degauss coils  582   a  are included to degauss current sensor  512   a.  To save space while allowing high-current traces  561   a  and  561   b  to be wide enough to carry the high current, high-current connectors  502   a  and  502   b  are mounted on the back of the fuse-module board in this example. Main power/signal connector  501  is also mounted on the fuse module in this example, to connect with a mating connector on the host board (not shown). Connector  501  delivers its power and signals to interface connector  561  as well as to any components on the fuse module that use the power and signals. Mechanically thick parts such as connector  501 , fuse  508 , current sensor  512   a,  and degauss capacitor  563   a  are arranged for non-interference with thick parts on the programming module. The exception is interface connector  561 , which lines up with its mating interface connector on the programming module. Various other electronics, including surface-mount components, may be arranged in the remaining space according to analog layout principles. Preferably, to minimize module size and maximize high-current trace width, any components that take up space on both sides of the board are located close to the center or near the fuse edge of this board. 
         [0052]      FIG. 5   b  is an example a programming module; for clarity, only some of the components and traces are shown. In this example, programming port  507  (which will be recessed in the housing to protect it during operation), microprocessor  520 , and alerting indicators  504  are located on the programming module. This enables some programming functions and tests to be performed on the programming module in isolation, using fixtures rather than needing the entire IFH to be assembled. High-current connectors  502   c  and  502   d  connect to the return or the source current of the host board (not shown), whichever current is not engaged by the fuse module. The current travels through high-current traces  562   c  and  562   d  to jumper  572   b,  where the current passes through Hall-effect current sensor  512   b  to be measured. Degauss coils  582   a  are included to degauss current sensor  512   a.  To save space while allowing high-current traces  561   a  and  561   b  to be wide enough to carry the high current, high-current connectors  502   a  and  502   b  are mounted on the back of the fuse-module board in this example. In the programming module, locating the high-current/high-voltage traces on the back of the module serves to isolate them from the low-voltage traces (not shown) carrying sensitive signals to and from programming port  507 . Mating power/signal interface connector  571  mates with interface connector  561  on the fuse module. In this example, connector  571  carries power and signals from the fuse module to components using them on the programming module. 
         [0053]      FIG. 5   c  is an exploded view showing how the fuse module and programming module of this example are connected together. Interface connector  561  mates with mating interface connector  571 . High-current connectors  502   a - d,  and their connected traces (not shown in this view) are on the outside surfaces of the assembly, and the bulky, mechanically vulnerable parts of each module are between the boards. Standoffs (not shown) can be added for mechanical ruggedness and electrical isolation of the parts from the respective modules that face each other when the IFH is assembled. 
         [0054]    Multiple other configurations are possible. For instance, if accessing the fuse in a direction perpendicular to the fuse module is more important than having the indicators reside on the programming module for feedback while programming or debugging, the indicators can be mounted beside the fuse on the fuse module and part of the programming-module board may be cut away for unobstructed access to the fuse. 
         [0055]    Only the claims, rather than the specification, abstract, or drawings, are intended to limit the scope of the subject matter of this document.