Patent Publication Number: US-2022229454-A1

Title: Voltage regulator and in-vehicle backup power supply

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is the U.S. national stage of PCT/JP2020/017929 filed on Apr. 27, 2020, which claims priority of Japanese Patent Application No. JP 2019-091924 filed on May 15, 2019, the contents of which are incorporated herein. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates to a voltage regulator and an in-vehicle backup power supply. 
     BACKGROUND 
     In the protection system disclosed in JP 2005-198439A, a gate voltage of an external FET is controlled by an operational amplifier to which a reference voltage is input, and an output of the external FET is connected using resistance division. When the midpoint of the resistance division is input to the operational amplifier, feedback is added and a desired voltage is output. 
     A voltage regulator such as a linear regulator has a function of outputting a predetermined output voltage according to an input voltage. However, when an overcurrent occurs on the output side, it is desirable to interrupt such a function and forcibly stop the output. In this regard, in the technique disclosed in JP 2005-198439A, whether or not a short-circuit failure has occurred is determined using a comparator, and when the output of the LDO output voltage falls below a predetermined voltage, it is deemed that a short-circuit has occurred, and protection is performed by shutting down the LDO. However, in the technique that requires an operational amplifier and a comparator as in JP 2005-198439A, there is a concern that the circuit scale will become complex. 
     Therefore, an object of the present invention is to provide a configuration capable of realizing a voltage regulator or an in-vehicle backup power supply capable of forcibly stopping an output when an output current exceeds a reference, while keeping the circuit scale from being complex. 
     SUMMARY 
     A voltage regulator according to an embodiment of the present disclosure is a voltage regulator configured to receive an input voltage based on power supplied via a first conductive path, and output an output voltage to a second conductive path, the voltage regulator including: a switch including a control terminal, and provided between the first conductive path and the second conductive path; a first resistor portion having one end electrically connected to the first conductive path and another end electrically connected to the switch; a PNP-type first transistor having a base electrically connected to a conductive path between the first resistor portion and the switch directly or via a resistor; a second resistor portion having one end electrically connected to the first conductive path and another end electrically connected to an emitter of the first transistor; a third resistor portion having one end electrically connected to the conductive path between the first resistor portion and the switch, and another end electrically connected to a collector of the first transistor; an NPN-type second transistor; a ground-side resistor portion having one end electrically connected to an emitter of the second transistor and another end electrically connected to the ground; a Zener diode having an anode electrically connected to a conductive path between the emitter of the second transistor and the ground-side resistor portion, and a cathode electrically connected to the second conductive path; and a control unit configured to apply an operating voltage to a base of the second transistor, wherein the collector of the first transistor is electrically connected to a collector of the second transistor and the control terminal, electricity flows through the second transistor in the operating state in which the control unit applies the operating voltage to the base of the second transistor; the Zener diode sets, in the operating state, a voltage of the second conductive path to a voltage corresponding to a voltage across the Zener diode; a current corresponding to an addition value obtained by adding a value of a current flowing through the second resistor portion in the operating state, a value of a current flowing through the third resistor portion in the operating state, and a value of a current flowing through the Zener diode in the operating state flows through the ground-side resistor portion, and the control unit stops the output of the operating voltage when a voltage of the second conductive path is lower than or equal to a threshold value. 
     An in-vehicle backup power supply according to the present disclosure, including: a power storage unit electrically connected to the above first conductive path; and the above voltage regulator, wherein the control unit applies the operating voltage to the base of the second transistor in response to establishment of a backup condition. 
     Advantageous Effects of Invention 
     According to the present disclosure, it is possible to realize a voltage regulator or an in-vehicle backup power supply capable of forcibly stopping an output when an output current exceeds a reference, while keeping a circuit scale from being complex. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a configuration of a voltage regulator according to an embodiment. 
         FIG. 2  is an explanatory diagram illustrating, in association with each other, a graph showing a relationship between an output current and voltages, a graph showing a relationship between an output current and currents, and a graph showing a relationship between an output current and an output voltage in the voltage regulator according to the embodiment. 
         FIG. 3  is a block diagram illustrating an electrical configuration of an in-vehicle power supply system in which the voltage regulator according to the embodiment is applied to a discharge circuit. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
     First, embodiments of the present disclosure will be listed and described. 
     In a voltage regulator according to an embodiment of the present disclosure, the collector of the first transistor is electrically connected to the collector of the second transistor and the control terminal. Electricity flows through the second transistor in the operating state in which the control unit applies an operating voltage to the base of the second transistor. The Zener diode sets the voltage of the second conductive path to a voltage corresponding to the voltage across the Zener diode in the above-described operating state. A current corresponding to an addition value obtained by adding a value of a current flowing through the second resistor portion in the operating state, a value of a current flowing through the third resistor portion in the operating state, and a value of a current flowing through the Zener diode in the operating state flows through the ground-side resistor portion. Then, the control unit stops the output of the operating voltage when the voltage of the second conductive path is lower than or equal to a threshold value. 
     The voltage regulator having the above-described configuration can achieve a configuration in which the output can be forcibly stopped when the output current flowing through the second conductive path exceeds a reference, while keeping a circuit scale from being complex. In particular, main elements other than the control unit can be mainly constituted by passive elements, which is highly advantageous in simplifying and miniaturizing a circuit. 
     An in-vehicle backup power supply according to an embodiment of the present disclosure is configured to include the voltage regulator described above, and thus can be a power supply having the same effects as those of the voltage regulator described above. 
     It is desirable that the above-described voltage regulator has the following actions and operations. 
     It is desirable that when the second transistor is in a non-electricity-flowing state, no current flows through the third resistor portion, and when the second transistor is in an electricity-flowing state, a third current corresponding to a potential difference between one end of the switch on the first resistor portion side and the control terminal flows through the third resistor portion. It is desirable that the switch is turned on when the third current flows. It is desirable that the voltage at the other end of the first resistor portion is set to a value corresponding to the current flowing through the switch by interposing the first resistor portion between the first conductive path and the switch. It is desirable that the emitter of the first transistor is connected to the first conductive path via the second resistor portion, and the base of the first transistor is electrically connected to the conductive path between the first resistor portion and the switch directly or via another member, so that a current flows through the first transistor when the first current flowing through the first resistor portion exceeds a predetermined value, and the second current flows through the second resistor portion. It is desirable that when the first current flowing through the first resistor portion is lower than or equal to the predetermined value, no current flows through the first transistor, and the second current does not flow through the second resistor portion. It is desirable that when the second transistor is in the electricity-flowing state, the emitter voltage of the second transistor is a fixed value that is based on the base voltage and the base-emitter voltage of the second transistor. It is desirable that a fixed current that is based on the emitter voltage of the second transistor and the resistance value of the ground-side resistor portion flows through the ground-side resistor portion. It is desirable that the value of the fixed current is a value corresponding to the sum of the value of the second current, the value of the third current, and the value of the current flowing through the Zener diode from the cathode side to the anode side. It is desirable that the current flowing through the Zener diode from the cathode side to the anode side decreases in accordance with an increase in the second current. Further, it is desirable that the Zener diode does not break down when the current flowing from the cathode side to the anode side of the Zener diode is lower than or equal to a predetermined current value (that is, when the voltage applied to the second conductive path is lower than or equal to a predetermined value). It is desirable that when a current flows from the cathode side to the anode side in the Zener diode, the voltage applied to the second conductive path has a value corresponding to the sum of the voltage across the Zener diode and the emitter voltage of the second transistor. In such a configuration, it is desirable that the control unit stops the output of the operating voltage when the voltage of the second conductive path is lower than or equal to the threshold value, and in response to this, the second transistor is operated so as to be in a non-electricity-flowing state and the switch is operated so as to be in an off state. According to such a configuration, most or all of the elements other than the control unit can be configured by passive elements, which is advantageous in terms of keeping the circuit scale from being complex and reducing the cost. 
     Specific examples of a voltage regulator and an in-vehicle backup power supply according to the present disclosure will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but defined by the scope of the claims, and is intended to include all modifications within the meaning and scope equivalent to the scope of the claims. 
     The voltage regulator of the present disclosure will be described with reference to  FIGS. 1 and 2 . A voltage regulator  10  shown in  FIG. 1  has a configuration in which an input voltage is input based on power that is supplied via a first conductive path  91 , and an output voltage is output to a second conductive path  92 . The voltage regulator  10  includes a switch  21 , a resistor (first resistor portion)  31 , a resistor (second resistor portion)  32 , a resistor (third resistor portion)  33 , a resistor  34 , a resistor (ground-side resistor portion)  37 , a transistor (first transistor)  41 , a transistor (second transistor)  42 , a Zener diode  51 , and a control unit  60 . 
     The switch  21  is configured as a P-channel MOSFET. The switch  21  is provided between the first conductive path  91  and the second conductive path  92 . The source of the switch  21  is electrically connected to a third conductive path  93 . The source of the switch  21  and the third conductive path  93  have the same potential. The drain of the switch  21  is electrically connected to the second conductive path  92 . 
     The drain of the switch  21  and the second conductive path  92  have the same potential. The gate (control terminal) of the switch  21  is electrically connected to the collector of the transistor  41  described later, the other end of the resistor  33 , and the collector of the transistor  42 . The gate of the switch  21 , the collector of the transistor  41 , the other end of the resistor  33 , and the collector of the transistor  42  have the same potential. 
     The resistor  31  is provided between the first conductive path  91  and the third conductive path  93 . One end of the resistor  31  is electrically connected to the first conductive path  91 . The one end of the resistor  31  and the first conductive path  91  have the same potential. The other end of the resistor  31  is electrically connected to the source of the switch  21  via the third conductive path  93 . The other end of the resistor  31  and the third conductive path  93  have the same potential. 
     The resistor  32  is provided between the first conductive path  91  and the transistor  41 . One end of the resistor  32  is electrically connected to the first conductive path  91 . The other end of the resistor  32  is electrically connected to the emitter of the transistor  41 . The other end of the resistor  32  and the emitter of the transistor  41  have the same potential. 
     The resistor  33  is provided between the first conductive path  91  and the transistor  41 . One end of the resistor  33  is electrically connected to the third conductive path  93 . The one end of the resistor  33  and the third conductive path  93  have the same potential. The other end of the resistor  33  is electrically connected to the collector of the transistor  41 , the collector of the transistor  42 , and the gate of the switch  21 . 
     The resistor  34  is provided between the third conductive path  93  and the transistor  41 . One end of the resistor  34  is electrically connected to the third conductive path  93 . The one end of the resistor  34  and the third conductive path  93  have the same potential. The other end of the resistor  34  is electrically connected to the base of the transistor  41 . The other end of the resistor  34  and the base of the transistor  41  have the same potential. 
     The transistor  41  is configured as a PNP-type bipolar transistor. The base of the transistor  41  is electrically connected to the other end of the resistor  34 . The emitter of the transistor  41  is electrically connected to the other end of the resistor  32 . The collector of the transistor  41  is electrically connected to the other end of the resistor  33 , the collector of the transistor  42 , and the gate of the switch  21 . 
     The transistor  42  is configured as an NPN-type bipolar transistor. The base of the transistor  42  is electrically connected to the other end of a resistor  35  described later and one end of a resistor  36 . The base of the transistor  42 , the other end of the resistor  35 , and the one end of the resistor  36  have the same potential. The collector of the transistor  42  is electrically connected to the collector of the transistor  41 , the other end of the resistor  33 , and the gate of the switch  21 . The emitter of the transistor  42  is electrically connected to one end of the resistor  37  described later and the anode of the Zener diode  51 . The emitter of the transistor  42 , the one end of the resistor  37 , and the anode of the Zener diode  51  have the same potential. The transistor  42  is in an electricity-flowing state in the operating state in which the control unit  60  described later applies an operating voltage to the base thereof. 
     The control unit  60  functions to apply an operating voltage to the base of the transistor  42 . The control unit  60  includes a control circuit  61 , the resistor  35 , and the resistor  36 . When the voltage of the second conductive path  92  is lower than or equal to a threshold voltage described later, the control unit  60  stops the output of the operating voltage. The control circuit  61  is configured as, for example, a microcomputer, and includes a memory such as a CPU, a ROM, or a RAM. The control circuit  61  operates, for example, on the basis of electric power supplied from a power supply, and can operate on power that is supplied from a backup power supply even when the supply of power from the power supply is stopped. The control circuit  61  applies an operating voltage to the base of the transistor  42  via the resistor  35 . The control circuit  61  has a function of detecting an output voltage of the second conductive path  92 . 
     The resistor  35  is provided between the control circuit  61  and the transistor  42 . One end of the resistor  35  is electrically connected to an output terminal of the control circuit  61 . The one end of the resistor  35  and the output terminal of the control circuit  61  have the same potential. The other end of the resistor  35  is electrically connected to one end of the resistor  36  and the base of the transistor  42 . 
     The resistor  36  is provided between the resistor  35  and the ground. The one end of the resistor  36  is electrically connected to the other end of the resistor  35  and the base of the transistor  42 . The other end of the resistor  36  is electrically connected to the ground, and has the ground potential. 
     The resistor  37  is provided between the transistor  42  and the ground. One end of the resistor  37  is electrically connected to the emitter of the transistor  42  and the anode of the Zener diode  51 . The other end of the resistor  37  is electrically connected to the ground, and has the ground potential. When the transistor  42  is in the operating state, a current corresponding to an addition value obtained by adding the value of the current flowing through the resistor  32 , the value of the current flowing through the resistor  33 , and the value of the current flowing through the Zener diode  51  described later flows through the resistor  37 . 
     The Zener diode  51  is provided between the second conductive path  92  and the resistor  37 . The anode of the Zener diode  51  is electrically connected to a conductive path between the emitter of the transistor  42  and the one end of the resistor  37 . The cathode of the Zener diode  51  is electrically connected to the second conductive path  92 . The cathode of the Zener diode  51  and the second conductive path  92  have the same potential. The Zener diode  51  sets the voltage of the second conductive path  92  to a voltage corresponding to the voltage across the second conductive path  92  when the transistor  42  is in the operating state. 
     Next, overcurrent detection control performed by the voltage regulator  10  will be described. 
     The control unit  60  applies an operating voltage having a voltage value Vcc to the base of the transistor  42 . As a result, the transistor  42  is in an electricity-flowing state, and a current flows from the collector to the emitter. The voltage value Vout of the output voltage output from the voltage regulator  10  to the second conductive path  92  is expressed by V 7 +Vz, which is the sum of the voltage value V 7  of the voltage across the resistor  37  and the Zener voltage Vz of the Zener diode  51 . Further, when the resistance value of the resistor  35  is R 5 , the resistance value of the resistor  36  is R 6 , and the voltage value of the base-emitter voltage of the transistor  42  is Vbe, the voltage value V 7  is expressed by V 7 =Vcc×R 6 /(R 5 +R 6 )−Vbe. Therefore, the voltage value Vout is expressed by Vout=V 7 +Vz=Vcc×R 6 /(R 5 +R 6 )−Vbe+Vz. 
     When a ground fault or the like occurs on the second conductive path  92 , the output current flowing through the second conductive path  92  increases. Here, when the voltage value of the power supply voltage is V and the voltage value of the voltage applied to the third conductive path  93  is Vs, the voltage value of the voltage across the resistor  31  is expressed by V-Vs. As the output current increases, Vs decreases and V-Vs increases as shown in  FIG. 2 . At the timing when the output current is Ia shown in  FIG. 2 , when V-Vs is approximately the voltage value Vbe of the base-emitter voltage of the transistor  41 , the collector current having the current value I 2  starts flowing through the transistor  41 . 
     When the current value of the current flowing through the resistor  37  is I 7 , the current value of the current flowing through the resistor  33  is I 3 , and the current value of the current flowing through the Zener diode  51  is Iz, the current value I 7  is expressed by I 7 =I 2 +I 3 +Iz. I 7  is set to a certain value based on Vcc, R 5 , and R 6  according to the characteristics of the transistor  42 . I 3  is constant because the magnitude of the gate-source voltage of the switch  21  does not substantially change. For this reason, according to the relationship I 7 =I 2 +I 3 +Iz, when I 2  increases, Iz decreases. When Iz decreases, Vz decreases. The control unit  60  detects that the voltage value Vout of the output voltage of the second conductive path  92  is lower than or equal to a threshold value (for example, a value smaller than a value Vout 1  of the output voltage by which the transistor  41  is in the electricity-flowing state as shown in  FIG. 2 ), and stops the output of the operating voltage. In this manner, the voltage regulator  10  can detect an overcurrent flowing through the second conductive path  92  and stop the operation. 
     Next, an in-vehicle power supply system  100  (hereinafter also referred to as a power supply system  100 ) to which an in-vehicle backup power supply (hereinafter also referred to as a backup power supply) of the present disclosure is applied will be described with reference to  FIG. 3 . A power supply system  100  shown in  FIG. 3  includes an in-vehicle power supply unit  101  (hereinafter also referred to as a power supply unit  101 ), a backup power supply  110 , a load  103 , and a charging circuit  105 , and is configured as a system capable of supplying power to the load  103 . The backup power supply  110  includes an in-vehicle power storage unit  102  (hereinafter also referred to as a power storage unit  102 ), a control unit  60 , and a discharge circuit  106 . 
     The power supply unit  101  functions as a main power supply. The power storage unit  102  functions as a backup power supply, and serves as a power supply source when power supply from the power supply unit  101  is stopped. The power storage unit  102  is electrically connected to the first conductive path  91 . The charging circuit  105  is a circuit that performs a charging operation of charging the power storage unit  102  based on power that is supplied from the power supply unit  101 . The discharge circuit  106  is a circuit that performs a discharge operation of discharging power stored in the power storage unit  102 . The discharge circuit  106  is electrically connected to the first conductive path  91  and the second conductive path  92 . The discharge circuit  106  and the control unit  60  constitute the voltage regulator  10 . 
     The discharge circuit  106  receives, from the control unit  60 , a discharge instruction signal instructing that the power storage unit  102  be discharged or a discharge stop signal instructing that discharge of the power storage unit  102  be stopped, and performs a discharge operation of passing a discharge current from the power storage unit  102  to the load  103  and a cutoff operation of cutting off the discharge current. The control unit  60  transmits a discharge instruction signal in response to the establishment of a backup condition. In other words, the control unit  60  applies an operating voltage to the base of the transistor  42 . Here, a backup condition is established, for example, when the voltage of the conductive path  191  falls to a predetermined threshold value or lower. 
     When the discharge circuit  106  receives a discharge instruction signal from the control unit  60 , the discharge circuit  106  performs a step-down operation using the voltage of the first conductive path  91  to which the output voltage of the power storage unit  102  is applied as an input voltage, and performs a discharge operation so as to apply a changed output voltage to the second conductive path  92  on the output side. When the discharge circuit  106  receives a discharge stop signal from the control unit  60 , the discharge circuit  106  stops such a discharge operation, and performs a cutoff operation so as to bring a portion between the second conductive path  92  and the power storage unit  102  into a non-conductive state. When the discharge circuit  106  is performing the discharge operation, the output current (discharge current) output from the discharge circuit  106  is supplied to the load  103 . 
     When a ground fault or the like occurs on a conductive path (the second conductive path  92  or the like) between the discharge circuit  106  and the load  103 , the voltage regulator  10  can detect an overcurrent and stop the discharge operation of the discharge circuit  106 . 
     As described above, in the voltage regulator  10  of the present disclosure, the collector of the transistor  41  is electrically connected to the collector of the transistor  42  and the gate of the switch  21 . The transistor  42  is in the electricity-flowing state, during the operating state in which the control unit  60  applies an operating voltage to the base of the transistor  42 . The Zener diode  51  sets the voltage of the second conductive path  92  to a voltage corresponding to the voltage across the Zener diode  51  in the above-described operating state. A current corresponding to an addition value obtained by adding the value of the current flowing through the resistor  32  in the operating state, the value of the current flowing through the resistor  33  in the operating state, and the value of the current flowing through the Zener diode  51  in the operating state flows through the resistor  37 . When the voltage of the second conductive path  92  is lower than or equal to a threshold value, the control unit  60  stops the output of the operating voltage. 
     With this configuration, it is possible to realize a configuration in which the output can be forcibly stopped when the output current flowing through the second conductive path  92  exceeds the reference, while keeping the circuit scale from being complex. In particular, main elements other than the control unit  60  can be mainly constituted by passive elements, which is highly advantageous in simplifying and miniaturizing a circuit. 
     In the voltage regulator  10  of the present disclosure, the following actions and operations occur. 
     First, when the transistor  42  is in a non-electricity-flowing state, no current flows through the resistor  33 , and when the transistor  42  is in an electricity-flowing state, a third current corresponding to a potential difference between one end of the switch  21  on the resistor  31  side and the gate of the switch  21  flows through the resistor  33 . When the third current flows, the switch  21  is turned on. Because the resistor  31  is interposed between the first conductive path  91  and the switch  21 , the voltage at the other end of the resistor  31  is set to a value corresponding to the current flowing through the switch  21 . The emitter of the transistor  41  is connected to the first conductive path  91  via the resistor  32 , and the base of the transistor  41  is electrically connected to the third conductive path  93  between the resistor  31  and the switch  21  directly or via another member. With this configuration, a current flows through the transistor  41  when the first current flowing through the resistor  31  exceeds a predetermined value, and the second current flows through the resistor  32 . When the first current flowing through the resistor  31  is lower than or equal to a predetermined value, no current flows through the transistor  41 , and the second current does not flow through the resistor  32 . When the transistor  42  is in an electricity-flowing state, the emitter voltage of the transistor  42  is a fixed value that is based on the base voltage and the base-emitter voltage of the transistor  42 . A fixed current based on the emitter voltage of the transistor  42  and the resistance value of the resistor  37  flows through the resistor  37 . The value of the fixed current is a value corresponding to the sum of the value of the above second current, the value of the above third current, and the value of the current flowing through the Zener diode  51  from the cathode side to the anode side. The current flowing through the Zener diode  51  from the cathode side to the anode side decreases in accordance with an increase in the second current. Further, the Zener diode  51  does not break down when the current flowing from the cathode side to the anode side of the Zener diode  51  is lower than or equal to a predetermined current value (that is, when the voltage applied to the second conductive path  92  is lower than or equal to a predetermined value). When a current flows from the cathode side to the anode side in the Zener diode  51 , the voltage applied to the second conductive path  92  has a value corresponding to the sum of the voltage across the Zener diode  51  and the emitter voltage of the transistor  42 . In such a configuration, when the voltage of the second conductive path  92  is lower than or equal to a threshold value, the control unit  60  stops the output of the operating voltage. In response to this, the transistor  42  is in the non-electricity-flowing state and the switch  21  turns to an off state. According to such a configuration, most or all of the elements other than the control unit  60  can be configured by passive elements, which is advantageous in terms of suppressing the circuit scale and reducing the cost. 
     Other Embodiments of the Present Disclosure 
     It should be understood that the embodiments disclosed herein are illustrative and non-restrictive in every respect. The following embodiments can be adopted, for example. 
     In the embodiment, the voltage value Vout of the output voltage can be adjusted to a desired value by changing the resistance values of the resistors  35  and  36  to any values and changing the value of the voltage applied from the control unit  60  to the base of the transistor  42 . 
     In the embodiment, the base of the transistor  41  is electrically connected to the other end of the resistor  34 . However, the base of the transistor  41  may also be directly electrically connected to the third conductive path  93  without being interposed by the resistor  34 .