Patent Publication Number: US-2020295541-A1

Title: Resettable relay control for micro power distribution blocks

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application claims the benefit of U.S. Provisional Patent Application No. 62/594,094, filed Dec. 4, 2017, which is incorporated by reference. 
    
    
     BACKGROUND 
     Power distribution blocks are provided in electricity supply systems that take an electrical power feed and distributes the feed to subsidiary circuits, while providing a protective fuse for the subsidiary circuits in a common enclosure. The fuse serves as an overcurrent protection when current provided via a power distribution block exceeds a limit. Power distribution blocks are used in various applications and come in different current ratings. The current ratings specify a maximum total current draw that the power distribution block can handle before its fuse blows. 
     SUMMARY 
     Embodiments of the disclosure provide a micro power distribution block for operation in a high temperature environment. The micro power distribution block includes: an enclosure; a connector, the connector comprising a power input terminal, a power output terminal, a ground terminal, and a reset terminal; and a circuit member disposed within the enclosure and operatively connected to the connector. The circuit member includes: a relay coupled to the power input terminal, the relay configured to switch between an ON state and an OFF state, wherein the relay allows power flow from the power input terminal through the relay in the ON state and prevents power flow from the power input terminal through the relay in the OFF state; a feedback sensor configured to sense power flow through the relay in the ON state; and a control circuit configured to: (a) generate a relay control signal for switching the relay from the ON state to the OFF state based on a magnitude of the sensed power flow, and (b) receive a reset signal, via the reset terminal, for switching the relay from the OFF state to the ON state. 
     Embodiments of the disclosure provide a method for distributing power to a load by a micro power distribution block comprising: (a) receiving a power input via a connector of the micro power distribution block, the power input received via a power input terminal of the connector and powering a circuit member of the micro power distribution block; (b) sensing, via a feedback sensor of the circuit member, power flow from the power input terminal through a relay of the circuit member; (c) determining, via a control circuit of the circuit member, whether a magnitude of the sensed power flow exceeds a power threshold; (d) in response to said determining that the power threshold is exceeded, generating, by the control circuit, a relay control signal for switching the relay from the ON state to the OFF state; (e) receiving a reset signal via the connector, the reset signal received via a reset terminal of the connector; and (f) in response to receiving the reset signal, switching, via the control circuit, the relay from the OFF state to the ON state, wherein the relay allows power flow from the power input terminal through the relay in the ON state and prevents power flow from the power input terminal through the relay in the OFF state. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a micro power distribution block (μPDB) according to an embodiment of the disclosure; 
         FIG. 2  is a block diagram illustrating components in a μPDB according to an embodiment of the disclosure; 
         FIG. 3  is a schematic of a μPDB according to an embodiment of the disclosure; 
         FIG. 4  is a printed circuit board layout of a IμPDB according to an embodiment of the disclosure; and 
         FIG. 5  is a flow diagram for operating a μPDB according to an embodiment of the disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The present disclosure generally relates to an electrical relay controls and, more specifically, to a settable field effect transistor-based relay typically used in a vehicle. In general, relays of this type are suitable for use in vehicle systems including junction distribution blocks, power distribution modules (PDM) or power distribution blocks (PDB), and other body control systems. These systems typically employ a wire harness to connect the various body and control systems throughout the vehicle. Without loss of generality, micro power distribution blocks will be used in describing various embodiments of the disclosure. 
     Power distribution blocks (PDB) are enclosures or boxes that typically contain fuses and relays. Conventional PDBs are designed for specific current ratings demanded by specific applications. Each application requires the selection of a specific type or size of fuse to use in the sealed box. Selecting a desired fuse size for the application limits applicability of a manufactured PDB. For example, a PDB having a current rating of 20 A cannot be used in an application requiring a current rating of 60 A, so when an application&#39;s specification changes, the PDB may have to be replaced to meet the new specification. Furthermore, during use, once a fuse blows, the blown fuse must be replaced. Still further, fuses and fuse terminals may add a significant amount of heat to a PDB design, thus limiting how much current each unit can carry as well as acceptable physical locations of the PDB in an application. 
     Embodiments of the disclosure provide a sealed micro power distribution block (μPDB) with a resettable relay. The resettable relay allows resetting of the μPDB once the current limit is reached. Compared to conventional PDBs, the sealed μPDB with the resettable relay does not have a fuse, so once reset, the sealed μPDB can be reused. Furthermore, the resettable relay of the μPDB can be programmed for use in various applications since a desired fuse size is not hardware dependent. One μPDB design can be used for various applications and a programmed current rating can determine when the relay trips, preventing power from being supplied to downstream electrical loads. Further, a μPDB programmed for an application requiring a current rating of 20 A can be repurposed for use in an application requiring 60 A by reprogramming it for 60 A. 
     Embodiments of the disclosure provide a sealed μPDB that is programmable for various current limits. An advantage of the programmable sealed μPDB design is that it reduces required inventory and changes in printed circuit board layouts. The same sealed μPDB design can be used in various applications requiring different current ratings, thus there is no need for an organization or user to maintain multiple sealed μPDB designs, each having different fuse ratings. 
     A sealed μPDB can be used in harsh environments like an automobile&#39;s engine compartment. The engine compartment can get very hot, reaching temperatures of from −40° C. to 110° C. As such, opening a sealed μPDB to replace a fuse may be impractical since tampering with the sealing element of the μPDB can compromise its quality, rendering the iμPDB unable to fully protect its electronics from environmental elements. Furthermore, even if the fuse were to be replaced, it would require replacing the blown fuse and resealing the μPDB. Sealed μPDBs are typically discarded and replaced once their fuses blow. Embodiments of the disclosure provide an alternative to the options of discarding the sealed μPDB or replacing the fuse within the sealed uPDB by providing a resettable sealed μPDB that can be programmed for various current ratings. A design for a resettable sealed μPDB which is programmable can be scaled to various applications, and once a current limit is reached, the same sealed μPDB can be reset and reused without the need to tamper with the protective covering and seals of the sealed μPDB. The cost associated with using a resettable μPDB is less than the cost of replacing a sealed μPDB or replacing a fuse within the sealed μPDB. Sealed μPDBs according to embodiments of the disclosure operate within a temp range of −40° C. to 110° C., in wet or dry environments, and in many automotive vibration environments. They are resistive to typical chemicals found in the automotive environments. 
       FIG. 1  illustrates a μPDB  100  for operation in a high temperature environment according to an embodiment of the disclosure. The PDB  100  includes a rear cover  102 , a circuit member such as a printed circuit board (PCB)  104 , and an interconnect component such as connector  114 . The rear cover  102  has a cavity  112  with an opening for receiving the PCB  104 . In some embodiments, the rear cover  102  can include channels or slots  118  along sidewalls  116  of the rear cover  102  that are configured to slidingly receive, support, and secure the PCB  104  within the rear cover  102 . Other manners of mounting the PCB  104  within the rear cover  102  are contemplated. 
     The connector  114  includes a flange  110  with a shroud  106  extending therefrom. A plurality of electrically conductive terminals or contacts  108  are mounted on the connector  114  with a mating end of each terminal disposed within the shroud  106 . Mounting ends (not shown) of each terminal  108  are electrically connected to the PCB  104 . 
     The flange  110  is configured in a manner that substantially matches the opening of the rear cover  102  such that the rear cover  102  and the flange  110  define an enclosure that can be readily sealed. In an embodiment, an adhesive or glue may be applied between the rear cover  102  and the shroud  106 . Further, the terminals  108  may extend through the connector  114  in a sealed manner so that the PCB  104  is fully sealed within the enclosure formed by the combination of the rear cover  102  and flange  110  to prevent liquids or other substances from reaching the electronic components and circuitry within the cavity. Electrical connections to the PCB  104  are provided via the mating portions of the terminals  108  disposed within the shroud  106 . Examples of materials used in μPDBs according to embodiments of the disclosure include plastic materials such as polybutylene terephthalate (PBT). PCB  104  can be made with high temperature FR4 materials. In an embodiment, the adhesive includes a sealant that bods two plastic components. 
       FIG. 2  is a block diagram illustrating components associated with a PCB  200  of a μPDB according to an embodiment of the disclosure.  FIG. 2  illustrates components mounted on or disposed in, e.g., PCB  104 . The PCB  200  can include access to a power source  202 . Access to the power source  202  can be provided via terminals of a connector, e.g., the connector  114 . The terminals for access to the power source  202  may be a power input terminal and a ground terminal. 
     The PCB  200  further includes a relay  204  coupled to the power source  202 . The relay  204  switches between an ON state and an OFF state. The relay  204  allows power flow from the power source  202  through the relay  204  in the ON state and prevents power flow from the power input terminal through the relay  204  in the OFF state. Examples of relay  204  include single pole single throw (SPST), single pole double throw (SPDT), H bridge, and twin relays. Attachment methods may include thru hole and SMT design. 
     The PCB  200  further includes a feedback sensor  206  that senses power flow through the relay  204  in the ON state. The feedback sensor  206  essentially senses power flow through the relay  204  to the load  208 . Access to the load  208  can be provided via a power output terminal of the connector. The feedback sensor  206  can sense a current flowing through the relay  204  and/or a voltage drop across its terminals and provide the sensed current flow or the voltage drop a measure of the power flow through the relay  204  since power is directly proportional to both voltage and current. The feedback sensor  206  can be an electrical, thermal or optical sensor that sends a feedback signal to a control circuit  220  for switching states of the relay  204 . 
     The PCB  200  further includes the control circuit  220  for switching the relay  204  between the ON state and the OFF state. In an embodiment, the control circuit is a microcontroller or a microprocessor that receives a reset signal  214  and/or a magnitude of the sensed power flow from the feedback sensor  206  and generates a relay control signal for switching the relay  204  between the ON state and the OFF state. The relay control signal switches the relay  204  from the ON state to the OFF state when the magnitude of the sensed power flow exceeds a target threshold. The relay control signal switches the relay  204  from the OFF state to the ON state when the reset signal  214  is asserted. 
     In an embodiment where the control circuit includes a microcontroller or a microprocessor, the control signal can generate an error code whenever the relay  204  switches from the ON state to the OFF state. The microcontroller may be a local interconnect network (LIN) chip or a control area network (CAN) chip in an automobile or in an automotive environment. The LIN or CAN chip can provide the error code to other systems in the automobile whenever the relay  204  switches to the OFF state. 
     In an embodiment, the control circuit  220  for switching the relay  204  includes a programmable set point  218 , a feedback control circuit  210 , a resettable latch  212 , and a relay control circuit  216 . The programmable set point  218  can be a resistor ladder controlled via switches for generating a target threshold voltage as the target threshold. The programmable set point  218  can be set of current sources combined via switches for generating a target threshold current as the target threshold. The programmable set point  218  can be a microcontroller with a digital to analog converter for providing the target threshold directly to the feedback control circuit  210 . 
     The feedback control circuit  210  compares the sensed power flow from the feedback sensor  206  and the target threshold from the programmable set point  218  to determine whether the sensed power flow exceeds the target threshold. The feedback control circuit  210  generates an OFF signal for turning OFF the relay when the target threshold is exceeded. 
     The resettable latch  212  latches the OFF signal and provides the latched OFF signal to the relay control circuit  216 . The relay control circuit  216  generates the relay control signal for switching the relay  204  from the ON state to the OFF state based on receiving the latched OFF signal from the latch  212 . 
     After the relay  204  is in the OFF state, the conditions that generated the OFF signal in the feedback control circuit  210  are no longer present, and the feedback sensor  206  senses zero current. The OFF signal from the feedback control circuit  210  is no longer asserted when zero current is flowing through the relay  204 , but the resettable latch  212  still has an asserted latched OFF signal, so the relay  204  will remain in the OFF state. The reset signal  214 , when asserted, resets the latch  212  so that the latched OFF signal is de-asserted. Once the latch  212  is reset, the relay control circuit  216  generates the relay control signal for switching the relay  204  from the OFF state to the ON state. 
     In some embodiments, the relay  204  and the relay control circuit  216  can be replaced with a FET. The FET can receive from the resettable latch  212  control signal for switching from an ON state to an OFF state and vice versa. In the OFF state, the FET operates in a similar manner as a relay, preventing power flow to the load  208 , and in the ON state, the FET allows power flow to the load  208 . 
       FIG. 3  is a schematic of a PCB  300  of a μPDB according to an embodiment of the disclosure.  FIG. 3  illustrates a schematic of, e.g., the PCB  104 . The PCB  300  can include a connector  322  for input/output communication and also for power access and provision. The connector  322  serves to electrically connect the PCB to other electrical components outside the PCB. The connector  322  can provide terminals for, e.g., a reset signal  314 , a power in (V CC )  302 , a ground (GND)  320 , and a power out to a load  308 . In some embodiments, the connector  322  provides a signal for programming a target threshold for the control circuitry. 
     The PCB  300  can include a relay  304 , which is an example of the relay  204 . The relay  304  can be modeled as a double pole single throw (DPST) switch controlled by a magnetic coil. When current flows through the magnetic coil, the DPST switch (hence the relay  304 ) is in an ON state, allowing power flow from the power in  302  terminal to circuit components downstream. When current does not flow through the magnetic coil, the DPST switch (hence the relay  304 ) is in an OFF state, preventing power flow from the power in  302  terminal to the circuit components downstream. 
     The PCB  300  can include a resistor R SENSE    306  for sensing a current flow through the relay  304 . The R SENSE    306  is an example of the feedback sensor  206 . The R SENSE    306  is connected between the relay  304  and the power out to the load  308 , thus current flow through the R SENSE    306  is the current supplied to the load. 
     The feedback control circuit  310  is included in the PCB  300 . The feedback control circuit  310  includes a feedback amplifier  332  and a comparator  334 . The feedback amplifier  332  determines a magnitude of a voltage difference across R SENSE    306  and amplifies this magnitude. In an embodiment, the feedback amplifier  332  is a difference amplifier that is temperature stable. The comparator  334  compares the amplified magnitude with the target threshold to determine whether the target threshold is exceeded by the amplified magnitude. 
     In an embodiment, the target threshold is generated by a set point circuit  318  which includes a resistive divider including resistors R 1    328 , R 2    326 , R 3    324  and a Zener diode D 1    330 . R 3    324  serves a protective role, bearing an excess voltage drop between V CC  and the voltage drop across D 1    330 . D 1    330  provides a stable voltage across the series combination of R 1    328  and R 2    326 . R 1    328  and R 2    326  implement a voltage divider such that the target threshold is a voltage drop across R 1    328 . Table 1 shows different R 1    328  and R 2    326  combinations for setting different target thresholds in an example design using the PCB layout of  FIG. 4 . In an embodiment, D 1    330  is automotive grade and temperature stable. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                   
                   
                 Current 
                   
                   
               
               
                   
                 Current 
                 mv out 
                 V out   
                 for 
                 R 1   
                   
               
               
                 Combination 
                 Output 
                 (TP4) 
                 (TP1) 
                 R 1 &amp;R 2   
                 (Ohms) 
                 R 2 (Ohms) 
               
               
                   
               
             
            
               
                 1 
                 20 
                 20 
                 1.01 
                 0.506 mA 
                   2k 
                 8.06k 
               
               
                 2 
                 30 
                 30 
                 1.53 
                 0.511 mA 
                   3k 
                 6.98k 
               
               
                 3 
                 40 
                 40 
                 2.04 
                 0.508 mA 
                 4.02k 
                 6.04k 
               
               
                 4 
                 50 
                 50 
                 2.53 
                 0.511 mA 
                 4.99k 
                 4.99k 
               
               
                 5 
                 60 
                 60 
                 3.04 
                 0.508 mA 
                 6.04k 
                 4.02k 
               
               
                   
               
            
           
         
       
     
     The comparator  334  of the feedback control circuit  310  determines whether the amplified voltage across R SENSE    306  exceeds the target threshold, and when it does, then the comparator  334  asserts a relay control signal for switching the relay  304  to the OFF state. The relay control signal, when asserted, is latched by the latch  312 . In the example provided in Table 1, the resistance values of R 1  and R 2  (R 1    328  and R 2    326 ) are chosen to determine the target threshold. The voltage (TP 4 ) is the voltage across R SENSE    306 , and the voltage across R 1  (TP 1 ) is the voltage presented at the input of the comparator  334 . The voltage (TP 1 ) indicates the target threshold, and when the voltage (TP 4 ) is amplified and compared, the relay control signal is asserted once the target threshold is reached. In Table 1, it can be inferred that the feedback amplifier  332  provides a  50 X gain to the voltage (TP 4 ) across R SENSE    306 . 
     In an embodiment, the latch  312  is an S-R latch with an S input, an R input, a Q output, and a Q-bar output. When both the S input and the R input are de-asserted, the S-R latch is in a hold state; when the S input is asserted, the S-R latch is in a set state, and when the R input is asserted, the S-R latch is in a reset state. By asserting the relay control signal connected to the S input of the S-R latch, the S input is asserted while the R input is de-asserted, thus the latch  312  is in a set state. 
     The Q-bar output of the S-R latch controls a relay control circuit  316 . The relay control circuit  316  includes a transistor M 1    336  that is either in an ON transistor state or an OFF transistor state based on the Q-bar output. When the latch  312  is in the set state, then Q-bar output controls M 1    336  to switch to an OFF transistor state, disabling current flow through M 1    336 . The lack of current flow through M 1    336  results in no voltage drop across resistor R 4    338 , which indicates no voltage difference applied to the magnetic coils of the relay  304  and, therefore, the relay  304  switches from the ON state to the OFF state. 
     When the relay  304  is in the OFF state, R SENSE    306  no longer has current flowing through it which causes the amplifier  332  to provide an amplified voltage substantially lower than the target threshold. Therefore, the comparator  334  de-asserts the relay control signal and the S-R latch then has an input combination where both the S and R inputs are de-asserted, placing the S-R latch in a hold state. That is, although the relay control signal is de-asserted, the S-R latch maintains the previous Q-bar output, therefore, M 1    336  remains in an OFF transistor state and the relay  304  remains in an OFF state. 
     M 1    336  can be placed in the ON transistor state, enabling current flow through M 1    336 , by asserting the reset signal  314 . The reset signal  314  is an input to the R input of the S-R latch, thus when the R input is asserted, the S-R latch is reset, and the Q-bar output controls M 1    336  to switch to the ON transistor state. In the ON transistor state, there is a current flow through R 4    338 , thus a voltage difference provided to the magnetic coil of the relay  304 , and the relay  304  switches from the OFF state to the ON state. After some time, the reset signal  314  is de-asserted, so both the S and R inputs of the S-R latch are de-asserted, putting the S-R latch in a hold state. 
     Although described with an S-R latch, other types of latches can be used, e.g., a J-K latch. The Q-bar output of the S-R latch is used for controlling the M 1    336 , but based on transistor type or logic circuit, the Q output may be used in other embodiments. The M 1    336  can be a p-type field effect transistor (FET) or an n-type FET, and an enhancement mode FET or a depletion mode FET. R SENSE    306  is chosen to be as small as possible. 
       FIG. 5  is a flow diagram  500  for operating a PCB of a PDB according to an embodiment of the disclosure. At  502 , the PCB receives a reset signal for turning ON a relay. The reset signal is asserted then de-asserted, thus can be viewed as a reset pulse. 
     At  504 , the PCB monitors current through the relay to determine whether the current exceeds a target current threshold. The target current threshold can be programmable to indicate a maximum tolerable current allowed to flow through the relay. The PCB monitors the current via a feedback sensor according to embodiments of the disclosure. 
     At  506 , when the current flowing through the relay exceeds the target current threshold, the PCB generates a set signal to turn OFF the relay. Once the relay is turned OFF, the set signal is de-asserted, but the relay remains in the OFF state. This behavior can be achieved with a latch that captures the set signal being asserted and turns OFF the relay based on the set signal being asserted. 
     At  508 , the PCB waits for the reset signal or pulse in order to turn ON the relay. That is, once the set signal is latched, causing the relay to turn OFF, the reset signal is the only signal that can turn the relay back ON. 
     Embodiments of the disclosure provide a PDB with a resettable power relay. The resettable relay can trip at various reset points, e.g., between the range of 10 A to 40 A. The μPDB can be reset by cycling the power provided to components on the PCB of the μPDB or by toggling a reset signal input of the PCB. The μPDB exhibits high thermal performance via high current relays, sturdy PCB materials and terminal/connector designs. The μPDB is sealed to an IP67K rating, thus providing protection against environmental factors such as liquids and solids. The μPDB can vary input voltage from 7 V to 14 V with little to no effect on control electronics, thus making the μPDB compatible with automotive applications. A FET control in relay coil path relaxes thermal or high current requirements. 
     Embodiments of the disclosure provide a μPDB that can be used for automotive applications. μPDBs utilized in the automotive world must pass various environmental tests. Load conditions, i.e., resistive, capacitive or inductive, vibration testing under elevated temperatures, humidity, salt spray, thermal shock, current and voltage cycling, are requirements for functional performance of μPDBs. Due to potential high currents, good contact interface design, in a sealed environment, are necessary. Because of the electronic components, electromagnetic compatibility (EMC) requirements are also necessary. Embodiments of the disclosure provide advantages within harsh automotive environments by using a feedback loop to sense current provided to electric loads and stop the current flow when a limit is reached. Current flow is prevented until a reset signal is received by the μPDB, therefore, the μPDB does not toggle back and forth between an ON and OFF states due to the feedback loop. 
     All references, including publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
     The use of the terms “a” and “an” and “the” and “at least one” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The use of the term “at least one” followed by a list of one or more items (for example, “at least one of A and B”) is to be construed to mean one item selected from the listed items (A or B) or any combination of two or more of the listed items (A and B), unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
     Preferred embodiments of this invention are described herein, including the best mode known to the inventors for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventors expect skilled artisans to employ such variations as appropriate, and the inventors intend for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.