JP2017077068A - Power supply circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a power supply circuit that can operate normally with simple circuitry.SOLUTION: A plurality of detectors 2 are provided correspondingly to a plurality of constant voltage power supplies 1, and each detector has a voltage dividing resistor for dividing the output voltage of a corresponding constant voltage power supply 1, and a transistor generating a state voltage indicating the state of the output voltage based on the divided output voltage. A plurality of resistors 3 are connected between the plurality of detectors 2 and one junction 6, a pull-up resistor 4 is connected between a second power supply and the junction 6, and a short circuit detector 52 detects at least one short circuit of the plurality of constant voltage power supplies 1, based on the voltage of the junction 6.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a power supply circuit that supplies a voltage to an internal circuit such as a home appliance, and more particularly to a power supply circuit that stops the supply of voltage when an output of the power supply circuit is short-circuited.

  Home appliances such as television receivers are provided with a plurality of constant voltage power supplies for operating an internal circuit, and a constant voltage regulator or the like is used for each constant voltage power supply. Each constant-voltage power supply may cause a short circuit on the output side due to an unexpected cause such as a circuit failure. If such a short circuit occurs, a malfunction may occur in the circuit due to heating of the regulator due to a load short circuit. .

  For such a problem, for example, a short circuit protection circuit for a power supply circuit as in Patent Document 1 has been proposed. The short-circuit protection circuit includes a detection circuit that uses an output of a specific constant voltage power supply among a plurality of constant voltage power supplies as a voltage for controlling another constant voltage power supply, and detects an output voltage of each constant voltage power supply. . Then, the output of the detection circuit is connected by an OR circuit, the control terminal of the regulator that is the source of control is turned off based on the output of the OR circuit, and the supply of the reference voltage of each constant voltage power supply is stopped, thereby the regulator Stop the output of.

JP 2005-190264 A

  According to the technique of Patent Document 1, the function is effective in a certain circuit configuration. However, in a circuit configuration in which the output voltage of the power supply circuit is higher than the voltage input to the emitter of the short circuit detection transistor, the Zener diode connected to the base of the short circuit detection transistor is useless. In other words, such a circuit configuration is equivalent to a circuit without a Zener diode, and the voltage at which the short circuit detection of the output voltage is constant. As a result, for example, when the output voltage is V1-Vbe or less (V1: emitter voltage of the short-circuit detection transistor, Vbe: saturation voltage between the base and emitter of the short-circuit detection transistor), the short-circuit detection transistor is turned on. However, there is a problem that it is impossible to determine and design how many volts the output voltage of the power supply circuit should be lowered to operate the protection circuit.

  Further, when the output voltage is higher than V1, for example, when the output voltage exceeds the reverse bias between the base and the emitter of the short-circuit detection transistor, there is a problem that the circuit configuration of Patent Document 1 does not operate normally. Further, when the integrated constant voltage power source that controls the short circuit protection is used as a circuit power source in the same manner as other constant voltage power sources, there is a problem that the short circuit protection of the integrated constant voltage power source cannot be realized with the circuit configuration of Patent Document 1.

  Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to provide a power supply circuit that has a simple circuit configuration and can operate normally.

  A power supply circuit according to the present invention is provided corresponding to a plurality of constant voltage power supplies each generating a predetermined output voltage based on a voltage supplied from a first power supply, and the plurality of constant voltage power supplies, A plurality of detection circuits each including a voltage dividing resistor that divides the output voltage of the constant voltage power supply to which each corresponds, and a transistor that generates a state voltage indicating the state of the output voltage based on the divided output voltage A plurality of resistors connected between the plurality of detection circuits and one connection point, a pull-up resistor connected between a second power supply and the connection point, and a voltage at the connection point. A short-circuit detecting unit that detects at least one short circuit of the plurality of constant-voltage power sources, and supply of voltage from the first power source to the plurality of constant-voltage power sources when the short-circuit detecting unit detects a short circuit. And a control unit to stop

  The present invention is provided corresponding to a plurality of constant voltage power supplies, each of which shows a voltage dividing resistor for dividing the output voltage of the corresponding constant voltage power supply, and the state of the output voltage based on the divided output voltage A plurality of detection circuits having a transistor for generating a state voltage; a plurality of resistors connected between the plurality of detection circuits and the one connection point; and a pull connected between the second power supply and the connection point. And a short-circuit detection unit that detects at least one short-circuit of the plurality of constant voltage power sources based on the voltage at the connection point. As a result, a power supply circuit having a simple circuit configuration and capable of operating normally can be realized.

1 is a block diagram illustrating a configuration of a power supply circuit according to a first embodiment. FIG. 3 is a circuit diagram showing a partial configuration of the power supply circuit according to the first embodiment. 3 is a circuit diagram showing an equivalent circuit corresponding to a part of the power supply circuit according to Embodiment 1. FIG. 3 is a circuit diagram showing an equivalent circuit corresponding to a part of the power supply circuit according to Embodiment 1. FIG. 3 is a flowchart showing the operation of the power supply circuit according to the first embodiment.

<Embodiment 1>
FIG. 1 is a block diagram showing a configuration of a power supply circuit according to Embodiment 1 of the present invention. Although the power supply circuit according to the first embodiment includes the power supply circuit unit 100 and the short circuit detection protection circuit 200, the power supply circuit unit 100 may be provided outside the power supply circuit.

  The power supply circuit unit 100 includes a main power supply 101 that is a first power supply and a standby power supply 102 that is a second power supply.

  The short circuit detection protection circuit 200 includes a plurality of constant voltage power supplies 1 (constant voltage power supplies 11, 12, 13), a plurality of detection circuits 2 (detection circuits 21, 22, 23), and a plurality of resistors 3 (resistors 31, 32). 33), a pull-up resistor 4 and a microcomputer (microcomputer) 5.

  In the first embodiment, the number of constant voltage power supply systems, the number of constant voltage power supplies 1, the detection circuit 2, and the resistance 3 are set to three according to the number of loads 300. However, this is only an example, and the number of each of these elements is not limited to three.

  The microcomputer 5 can control the constant voltage power supplies 11, 12, and 13 and the main power supply 101 in an integrated manner. In the first embodiment, the microcomputer 5 has an ADC input terminal 51, and the ADC input terminal 51 corresponds to one connection point 6 to be described later.

  Further, the microcomputer 5 as a processing circuit reads out and executes a program (software, firmware, or a combination thereof) stored in a memory or the like (not shown), whereby the function of the short-circuit detection unit 52 and the function of the control unit 53 are detected. And are realized. That is, the power supply circuit stores a program that, when executed by the microcomputer 5, results in the operation (step) of the short-circuit detection unit 52 and the operation (step) of the control unit 53 being executed as a result. Provide memory.

  Here, the memory corresponds to, for example, a nonvolatile or volatile semiconductor memory such as RAM, ROM, flash memory, EPROM, or EEPROM, a magnetic disk, a flexible disk, an optical disk, a compact disk, a mini disk, a DVD, or the like. To do. Further, instead of the short-circuit detection unit 52 and the control unit 53 that operate according to the software program, the short-circuit detection unit 52 and the control unit 53 may be realized by a signal processing circuit that realizes the operation by an electrical circuit of hardware. The processing circuit may be realized by combining software and hardware.

  Next, an outline of the short circuit detection protection circuit 200 will be described. When the main power supply voltage Vm is supplied from the main power supply 101 of the power supply circuit unit 100, the constant voltage power supplies 11, 12, 13 of the short-circuit detection protection circuit 200 use the main power supply voltage Vm as predetermined output voltages V1, V2, and so on. By converting to V3, the output voltages V1, V2, and V3 are supplied to the load 300 (loads 301, 302, and 303).

  In the short-circuit detection protection circuit 200, the outputs of the detection circuits 21, 22, and 23 connected to the outputs of the constant voltage power supplies 11, 12, and 13 are input to the connection point 6 through the resistors 31, 32, and 33, respectively. At the same time, the voltage of the standby power supply 102 is input to the connection point 6 via the pull-up resistor 4, whereby a voltage is generated at the connection point 6. Hereinafter, the voltage at the connection point 6 will be described as “coupling voltage”.

  The short circuit detector 52 detects at least one short circuit of the constant voltage power supplies 11, 12, and 13 based on the combined voltage (voltage at the connection point 6). When the occurrence of a short circuit is detected, the control unit 53 turns off the main power supply 101 and stops supplying the main power supply voltage Vm to the constant voltage power supplies 11, 12, and 13. By performing such a stop, the internal circuit can be protected.

  Next, each component will be described in detail.

  The main power supply 101 supplies the main power supply voltage Vm to the constant voltage power supplies 11, 12, and 13. The standby power supply 102 is a separate system from the main power supply 101, and supplies the standby power supply voltage Vs for starting (operating) the microcomputer 5 (the short-circuit detection unit 52 and the control unit 53) to the microcomputer 5 and the like. In the first embodiment, when the short-circuit detection protection circuit 200 is connected to the main power supply 101, the standby power supply voltage Vs is supplied from the standby power supply 102 to the microcomputer 5 or the like.

  The constant voltage power supplies 11, 12, and 13 generate predetermined output voltages V 1, V 2, and V 3 based on the main power supply voltage Vm supplied from the main power supply 101. By supplying the output voltages V1, V2, and V3 to the loads 301, 302, and 303, respectively, the loads 301, 302, and 303 can be driven.

  The detection circuits 21, 22, and 23 are provided corresponding to the constant voltage power supplies 11, 12, and 13. Here, FIG. 2 is a circuit diagram showing the connections among the components of the detection circuits 21, 22, 23, the resistors 31, 32, 33, the pull-up resistor 4, and the microcomputer 5 having the ADC input terminal 51. is there. Hereinafter, the components of the detection circuits 21, 22, and 23 will be described in detail with reference to FIG.

  The detection circuit 21 includes voltage dividing resistors 21a and 21b and a transistor 21c. The voltage dividing resistors 21a and 21b of the detection circuit 21 divide (resistor-divide) the output voltage V1 of the corresponding constant voltage power supply 11 and input it to the base of the transistor 21c. When there is no abnormality such as a short circuit in the load 91, the resistance value is designed so that a base current that can sufficiently saturate between the collector and the emitter of the transistor 21c flows. In a state where the base current is sufficiently saturated and flows, the collector of the transistor 21c has substantially the same voltage as the emitter. However, even in this state, the collector-emitter saturation voltage Vce remains.

  According to such a configuration, when there is no abnormality such as a short circuit in the load 91 and the divided output voltage V1 is sufficiently high, the transistor 21c is turned on, and the voltage between the collector and the emitter is the on voltage ( = Saturation voltage Vce). On the other hand, when there is an abnormality such as a short circuit in the load 91 and the divided output voltage V1 is low, the transistor 21c is turned off, and the collector-emitter off voltage (≠ saturation voltage Vce). In this way, the transistor 21c generates a state voltage (on voltage or off voltage) indicating the state of the output voltage V1 based on the divided output voltage V1.

  The detection circuit 21 has been described above. The detection circuits 22 and 23 are configured in the same manner as the detection circuit 21. That is, the detection circuit 22 includes voltage dividing resistors 22a and 22b and a transistor 22c similar to the voltage dividing resistors 21a and 21b and the transistor 21c, and the detection circuit 23 is similar to the voltage dividing resistors 21a and 21b and the transistor 21c. Voltage dividing resistors 23a and 23b and a transistor 23c.

  The resistors 31, 32 and 33 are connected between the detection circuits 21, 22 and 23 and the connection point 6. The pull-up resistor 4 is connected between the standby power supply 102 and the connection point 6. According to such a configuration, the combined voltage Vi is generated by combining the state voltage generated by the detection circuits 21, 22 and 23 and the standby power supply voltage Vs of the standby power supply 102 at the connection point 6. The For this reason, the coupling voltage Vi is applied to the ADC input terminal 51 which is the connection point 6.

  Here, the combined voltage Vi [V] in a state where all the constant voltage power supplies 11, 12, and 13 are operating normally is expressed by the following equation (1). In the following equation (1), Ra is the resistance value [Ω] of the pull-up resistor 4, and Rb is the resistance value [Ω] of the resistors 31, 32, and 33. FIG. 3 shows an equivalent circuit in this state.

  Assuming that a short circuit occurs in the load 91 and the output voltage V1 of the constant voltage power supply 11 decreases, a case where the system of the load 91 is completely short-circuited is assumed. In this case, since the output voltage V1 is almost 0, the transistor 21c is cut off. In this state, since the detection circuit 2 in the on state is reduced from three systems to two systems, the coupling voltage Vi applied to the ADC input terminal 51 increases. The coupling voltage Vi [V] in this state is expressed by the following equation (2). FIG. 4 shows an equivalent circuit in this state.

  As can be seen from the above, the logical OR of the abnormality related to the system of the constant voltage power supplies 11, 12, 13 is reflected in the combined voltage Vi.

  In view of this, the short circuit detection unit 52 is configured to detect at least one short circuit of the constant voltage power supplies 11, 12, and 13 based on the combined voltage Vi. In the first embodiment, the analog combined voltage Vi is converted into a digital signal by the ADC input terminal 51 which is an analog-digital conversion circuit, and the short-circuit detection unit 52 performs the above-described detection based on the digital signal.

  The control unit 53 stops the supply of the main power supply voltage Vm from the main power supply 101 to the constant voltage power supplies 11, 12, and 13 when the short circuit detection unit 52 detects a short circuit. Thereby, the protection operation is realized.

<Operation>
FIG. 5 is a flowchart showing the operation of the power supply circuit according to the first embodiment. Hereinafter, the operation of the power supply circuit will be described with reference to FIG. As a premise, the standby power supply voltage Vs from the standby power supply 102 is supplied to the microcomputer 5 in order to start the microcomputer 5 before the following operation is performed.

  In step S1, the microcomputer 5 that has started the operation turns on the main power supply 101 in accordance with an instruction from a device control microcomputer (not shown) in order to put the device in an operating state. As a result, the main power supply voltage Vm from the main power supply 101 is supplied to the constant voltage power supplies 11, 12 and 13.

  In step S <b> 2, the microcomputer 5 issues an instruction to turn on the output voltage of the constant voltage power supply 1 and causes the constant voltage power supply 1 to output the output voltages V <b> 1, V <b> 2, V <b> 3. The main power supply voltage Vm is supplied to the constant voltage power supply 1 even if there is no instruction from the microcomputer 5, for example, when there is no restriction on the load 300, depending on the required specifications of the load 300 connected in the subsequent stage. In some cases, the constant voltage power supply 1 may be automatically activated, or the output voltage of the constant voltage power supply 1 may be turned on.

  In step S3, the microcomputer 5 reads data obtained by converting the analog coupling voltage Vi at normal time and abnormal time into a digital value from a storage device (not shown), and stores the data in advance in a memory (not shown) as an initial value. . Here, the normal coupling voltage Vi in the data is determined on the basis of the coupling voltage Vi shown in the equation (1), and the abnormal coupling voltage Vi in the data is the coupling voltage shown in the equation (2). It is determined based on Vi. In view of the fact that there is some variation in the output voltage of the constant voltage power supply 1 and that it is desirable to be able to perform the protection operation as soon as possible when the output voltage deviates from the normal time. The input voltage range is determined.

  In step S4, after turning on the constant voltage power supply 1, the microcomputer 5 performs polling for periodically reading the coupling voltage Vi (more precisely, its digital value) at the ADC input terminal 51.

  In step S5, the short-circuit detection unit 52 of the microcomputer 5 compares the combined voltage Vi read in step S4 (more precisely, its digital value) with the data stored in step S3, and constant voltage power supplies 11, 12 , 13 is detected whether it is short-circuited.

  Here, in the first embodiment, the ADC input terminal 51 is used as the input terminal of the microcomputer 5 to which the coupling voltage Vi is input. This contributes to making each detection circuit 2 as simple as possible and reducing the number of semiconductor components. However, in the configuration according to the first embodiment in which the plurality of detection circuits 2 are connected to the ADC input terminal 51 via the plurality of resistors 3, the number of detection circuits 2 cannot be increased (for example, infinite). .

  Hereinafter, this reason will be described. For example, assuming that one of the n constant voltage power supplies 1 is short-circuited, the number of resistors 3 connected to the ground side as viewed from the ADC input terminal 51 changes from n to (n−1). The variation of the coupling voltage Vi at the ADC input terminal 51 due to this change decreases as the value of n increases. For this reason, when the value of n is large, even if one constant voltage power supply 1 is short-circuited, the combined voltage Vi does not operate normally from the normal operation voltage range used as the initial value described above. Without moving into the voltage range, the voltage remains in the normal operation voltage range, and short circuit detection is no longer possible. For this reason, in the configuration according to the first embodiment, the number of detection circuits 2 cannot be increased (for example, infinite).

  Actually, the number of constant voltage power supplies 1 and detection circuits 2 is the resolution of AD conversion of the ADC input terminal 51 of the microcomputer 5, the tolerance of the resistor 3 and the pull-up resistor 4, the power supply stability of the standby power supply 102, etc. It will be designed in consideration of. For example, if the number of digital quantization bits of the microcomputer 5 is 8 bits, a tolerance class F resistor is used for each resistor 3, and the voltage fluctuation of the standby power supply 102 is 3.3V ± 5%, the maximum Thus, a calculation result is obtained that the eight constant voltage power supplies 1 and the detection circuit 2 can be connected.

  Return the story to the operation of FIG. If the short circuit state is detected in step S5, the process proceeds to step S6. If the short circuit state is not detected (when the normal state is detected), the process returns to step S4.

  In step S6, when the microcomputer 5 detects a short circuit, the control of the main power supply 101 is turned off and the output of the main power supply voltage Vm is stopped. As a result, it is possible to stop not only the power supply line of the system in which the short circuit has occurred in the constant voltage power supply 1, but also the power supply lines of all the systems. Thereafter, the operation of FIG.

<Summary>
According to the power supply circuit according to the first embodiment as described above, the state of the output voltage of the plurality of constant voltage power supplies 1 can be transferred to the input terminal of the microcomputer 5 without being converted into the open collectors of the transistors and coupled. Can be connected. Accordingly, the number of semiconductor components used in the short-circuit detection protection circuit 200 can be reduced as compared with the conventional one.

  The output voltage (short circuit detection start voltage) indicating the state of the output voltage of each constant voltage power supply 1 can be determined by resistance division connected to the bases of the transistors 21c, 22c, and 23c. Therefore, it can be designed according to the requirements of the individual constant voltage circuits and the requirements of the load circuits connected thereto, how many volts the voltage of each constant voltage power supply 1 is detected to detect a short circuit. Therefore, a power circuit that can operate normally can be realized.

  Further, in a device having a plurality of constant voltage power supplies 1, when a load short circuit occurs in any one of the constant voltage power supply 1 systems, the collector current of the transistor decreases and the transistor is out of the switching operation region. Here, in the first embodiment, the program of the microcomputer 5 is such that the coupling voltage formed by coupling the collector of the transistor with a resistor, that is, the coupling voltage applied to the ADC input terminal 51 of the microcomputer 5 deviates from the normal value. Designed. For this reason, an abnormal short circuit of the load circuit can be detected.

  Further, in the first embodiment, since the microcomputer 5 has an output terminal for controlling on / off of the main power supply 101, power supply to each constant voltage power supply 1 is stopped when the main power supply 101 is turned off when a short circuit is detected. . At this time, if the resistance values of the plurality of resistors 3 are made different from each other, the change in the coupling voltage varies depending on the short-circuited system. Can be detected. In addition, according to such a configuration, the shorted path can be held in the memory, and the system in which the short circuit has occurred can be determined.

  Since the standby power supply 102 that supplies the standby power supply voltage Vs for operating the microcomputer 5 is a separate system from the main power supply 101, the microcomputer 5 itself even if the supply of the main power supply 101 is stopped. This does not affect the control operation.

  By configuring the power supply circuit short circuit detection protection circuit as described above, the power supply can be normally protected with a simple circuit configuration. In addition, the cost of parts can be reduced, and the cost of the power supply circuit can be reduced.

  In the present invention, the embodiments can be appropriately modified and omitted within the scope of the invention.

  1, 11, 12, 13 constant voltage power supply, 2, 21, 22, 23 detection circuit, 21a, 21b, 22a, 22b, 23a, 23b voltage dividing resistor, 21c, 22c, 23c transistor, 3, 31, 32, 33 Resistor, 4 Pull-up resistor, 5 Microcomputer, 6 Connection point, 51 ADC input terminal, 52 Short circuit detection unit, 53 Control unit, 101 Main power supply, 102 Standby power supply

Claims (4)

A plurality of constant voltage power sources each generating a predetermined output voltage based on the voltage supplied from the first power source;
A voltage dividing resistor provided for the plurality of constant voltage power supplies, each of which divides the output voltage of the corresponding constant voltage power supply, and indicates the state of the output voltage based on the divided output voltage A plurality of detection circuits having transistors for generating a state voltage;
A plurality of resistors connected between the plurality of detection circuits and one connection point;
A pull-up resistor connected between a second power source and the connection point;
Based on the voltage at the connection point, a short-circuit detection unit that detects at least one short-circuit of the plurality of constant voltage power sources,
A power supply circuit comprising: a control unit that stops supply of a voltage from the first power supply to the plurality of constant voltage power supplies when the short circuit detection unit detects a short circuit. The power supply circuit according to claim 1,
An analog-to-digital conversion circuit that converts the voltage at the connection point in analog form into a digital signal;
The short circuit detection unit is a power supply circuit that performs the detection based on the digital signal. The power supply circuit according to claim 1 or 2,
The short circuit detection unit and the control unit are power supply circuits realized by executing a program of a microcomputer. The power supply circuit according to any one of claims 1 to 3,
The power supply circuit, wherein the second power supply is a separate system from the first power supply, and supplies a power supply voltage for operating the short-circuit detection unit and the control unit.

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