JP6067443B2 - Power protection circuit - Google Patents

Description

  The present invention relates to a power supply protection circuit.

  In an electronic device that is supplied with power from a DC power source such as an AC / DC converter or a battery, when the positive side of the DC power source is connected to the negative side of the electronic device and the negative side of the DC power source is connected to the positive side of the electronic device A diode for preventing reverse connection has been widely used to prevent failure of electronic equipment (during reverse power connection). However, since a forward voltage drop exists in the diode, in an electronic device that requires a large current, the power consumption of the diode, which is the product of the voltage corresponding to the voltage drop and the current flowing in the reverse connection prevention diode, is low. This may increase the power consumption of the entire electronic device and reduce power efficiency.

  Also, if the power supply wiring from the DC power supply to the electronic device is long, or if the time change of the power consumption in the electronic device is large, the fluctuation of the DC voltage applied to the electronic device will become so large that it cannot be ignored. A smoothing capacitor may be used. When the power is turned on with no electric charge in the smoothing capacitor, a large current (hereinafter referred to as “rush current”) flows instantaneously to charge the smoothing capacitor. When a high current flows, the fuse that cuts off the input current may be blown, and it is necessary to suppress the inrush current.

  For example, in the prior art, an apparatus using an electromagnetic connector with a low voltage drop has been proposed in order to prevent a failure of a device when a power supply is reversely connected (see Patent Document 1 below).

Japanese Patent Laid-Open No. 9-331694 (FIG. 2)

  However, in the prior art disclosed in Patent Document 1, since the electromagnetic connector is configured to open and close the mechanical contact, the contact life is often short, and the circuit configuration tends to increase in size. was there.

  The present invention has been made in view of the above, and obtains a power supply protection circuit capable of downsizing a circuit while performing protection when a DC power supply is reversely connected and suppressing inrush current when the DC power supply is turned on. For the purpose.

In order to solve the above-described problems and achieve the object, the present invention includes a capacitor having one end connected to the positive side terminal of the DC power source and the other end of the capacitor without passing through the negative side terminal of the DC power source. A resistor connected to one end, the other end connected to the minus terminal, a first MOSFET connected in parallel to the resistor, and the minus terminal of the DC power source and the resistor. A second MOSFET; and a drive control unit that receives power from the DC power supply and controls ON / OFF of the first MOSFET and the second MOSFET. The first MOSFET and the second MOSFET are turned off until a predetermined time has elapsed from the activation of the control unit, and after the predetermined time has elapsed, the first MOSFET and the second MOSFET The ON signal for the second MOSFET to the ON state and transmits to said second MOSFET and said first MOSFET.

  According to the present invention, since the MOSFET of the semiconductor switch is used for circuit protection at the time of reverse connection, the circuit can be reduced in size while performing protection at the time of reverse connection of the DC power supply and suppressing the inrush current when the DC power supply is turned on. There is an effect that it can be achieved.

FIG. 1 is a configuration diagram of a power protection circuit according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating a path of a current that flows when the external switch changes from the OFF state to the ON state. FIG. 3 is a time-series chart showing the operation of the power protection circuit according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a path of a current that flows when the inrush current suppression MOSFET and the power supply reverse connection protection MOSFET are turned on. FIG. 5 is a configuration diagram of a power protection circuit according to Embodiment 2 of the present invention. FIG. 6 is a configuration diagram of a power protection circuit according to Embodiment 3 of the present invention.

  Embodiments of a power protection circuit according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

Embodiment 1 FIG.
FIG. 1 is a configuration diagram of a power protection circuit according to Embodiment 1 of the present invention. FIG. 2 is a diagram illustrating a path of a current that flows when the external switch changes from the OFF state to the ON state. FIG. 3 is a time-series chart showing the operation of the power protection circuit according to Embodiment 1 of the present invention. FIG. 4 is a diagram illustrating a path of a current that flows when the inrush current suppression MOSFET and the power supply reverse connection protection MOSFET are turned on.

  The power source protection circuit 20 shown in FIG. 1 mainly includes a capacitor 3 that smoothes the DC voltage from the DC power source 1 and suppresses fluctuations in the input voltage to the load side circuit 11, and an inrush current when the DC power source is turned on. A resistor 4 for suppressing, an inrush current suppressing MOSFET 5 connected in parallel to the resistor 4, and a MOSFET 6 for protecting the DC / DC converter circuit 10 by cutting a reverse current when the DC power source 1 is reversely connected A drive circuit 8 for ON / OFF control of the MOSFET 5 and the MOSFET 6, a control circuit 9 for outputting a control signal for operating the drive circuit 8, and a DC / DC converter 10 for supplying power to the drive circuit 8 and the control circuit 9. It is comprised. The drive circuit 8, the control circuit 9, and the DC / DC converter 10 constitute a drive control unit 21 that receives ON / OFF control of the MOSFET 5 and the MOSFET 6 upon receiving power from the DC power supply 1.

  The illustrated MOSFET 5 and MOSFET 6 are n-channel MOSFETs as an example. The body diode 5a parasitic between the drain and source of the MOSFET 5 has an anode connected to the source and a cathode connected to the drain. The body diode 6a parasitic between the drain and source of the MOSFET 6 has an anode connected to the source and a cathode connected to the drain.

  An external switch 2 is provided between the input plus terminal of the DC power source 1 and the capacitor 3, and the capacitor 3 is provided so that one end can be connected to the input plus terminal of the DC power source 1 via the external switch 2 and the other end. Is connected to the connection end of the drain of the MOSFET 5 and the resistor 4.

  MOSFET 6 has a source connected to the connection end of the source of MOSFET 5 and resistor 4, and a drain connected to the input minus terminal of DC power supply 1. The drive circuit 8 and the control circuit 9 are supplied with power from the DC / DC converter 10, and the control signal from the drive circuit 8 is input to the gates of the MOSFET 5 and the MOSFET 6.

  The operation will be described below. As shown in FIG. 1, when the external switch 2 is in the OFF state, the capacitor 3 is not sufficiently charged. In addition, when the external switch 2 is in the OFF state, the DC / DC converter 10 is not supplied with power from the DC power supply 1, so that the drive circuit 8 and the control circuit 9 do not operate and the MOSFET 5 and the MOSFET 6 are in the OFF state.

  When the power supply protection circuit 20 is normally connected to the DC power supply 1 (when not reversely connected), when the external switch 2 is turned ON, as shown in FIG. Current supplied to the DC / DC converter 10 (that is, inrush current) flows in the order of the external switch 2, the capacitor 3, the resistor 4, the body diode 6 a of the MOSFET 6, and the DC power supply 1.

  FIG. 2 shows a current path I1a charged in the capacitor 3 and a current path I2a for supplying power to the DC / DC converter 10. In the illustrated example, since the MOSFET 5 and the MOSFET 6 are in the OFF state, the magnitude of the current charged in the capacitor 3 is suppressed by flowing through the resistor 4. That is, the magnitude of the inrush current when the power is turned on in a state where the capacitor 3 is not charged is suppressed.

  Next, the operation when the external switch 2 is turned on will be described with reference to FIG. When the external switch 2 is turned on (time t1), an inrush current (current I3) flows through the capacitor 3, and the capacitor 3 is charged, whereby the voltage V3 across the capacitor 3 increases with time. The DC / DC converter 10 starts from the time when charging of the capacitor 3 is started (time t1) until the capacitor 3 is sufficiently charged (for example, at the time t2 in the illustrated example), and the drive circuit 8 The control circuit 9 is supplied with power from the DC / DC converter 10.

  When the control circuit 9 is activated by the power supplied from the DC / DC converter 10, the control circuit 9 elapses, for example, after the DC / DC converter 10 is activated (time t <b> 2) until the capacitor 3 is sufficiently charged. When this occurs (time t3), an ON signal is transmitted to the drive circuit 8.

  The time for which the capacitor 3 is sufficiently charged is equal to, for example, the time constant obtained by the product of the capacitance of the capacitor 3 and the value of the resistor 4, and this time constant is set in the control circuit 9 as the time T for transmitting the ON signal. Has been. When the driving circuit 8 receives an ON signal output from the control circuit 9 when the time T has elapsed, the MOSFET 5 and the MOSFET 6 are turned on. The time T set in the control circuit 9 is not limited to the time constant obtained by the product of the capacitance of the capacitor 3 and the value of the resistor 4, and may be a time longer than the time constant.

  FIG. 4 shows a path I1b of a current discharged from the capacitor 3 when the MOSFET 5 and the MOSFET 6 are turned on by the ON signal from the control circuit 9. Since the MOSFET 5 and the MOSFET 6 are in the ON state, the current discharged from the capacitor 3 flows in the order of the capacitor 3, the MOSFET 5, the MOSFET 6, and the DC power source 1. That is, since the current discharged from the capacitor 3 does not flow through the resistor 4 and the body diode 6a of the MOSFET 6, useless power loss does not occur.

  Next, the operation when the DC power supply 1 is reversely connected to the power supply protection circuit 20 (when the power supply is reversely connected) will be described. As shown in FIG. 1, when the external switch 2 is in the OFF state and the power supply reverse connection is performed, and then the external switch 2 is turned on, the body diode 6a of the MOSFET 6 is reverse to the direction in which the power supply current flows. Connected to polarity. Therefore, current passage to the DC / DC converter 10 and the load side circuit 11 can be prevented.

  As described above, the power supply protection circuit 20 according to the present embodiment includes the capacitor 3 connected to the positive terminal of the DC power supply 1, the resistor 4 connected in series to the capacitor 3, and the resistor 4 in parallel. The first MOSFET (MOSFET 5) to be connected, the second MOSFET (MOSFET 6) connected between the negative terminal of the DC power source 1 and the resistor 4, and the power supplied from the DC power source 1 receive the first MOSFET. A drive control unit 21 (DC / DC converter 10, control circuit 9, and drive circuit 8) that controls ON / OFF of the first MOSFET and the second MOSFET. The first MOSFET and the second MOSFET are turned off until a predetermined time has elapsed from the start-up, and after the predetermined time has elapsed, the first MOSFET and the second MOSFET It is configured to a T to ON state. With this configuration, it is possible to simultaneously realize the suppression of the inrush current and the circuit protection during the reverse connection of the power source with a simple circuit configuration without using a mechanism for opening and closing the mechanical contact by the electromagnetic connector. In addition, by using the MOSFET 6 of the semiconductor switch instead of the conventional diode for circuit protection at the time of reverse connection, the circuit can be reduced in size, the circuit life can be greatly extended, and the power loss in the steady state can be reduced. Can be suppressed.

Embodiment 2. FIG.
FIG. 5 is a configuration diagram of a power protection circuit according to Embodiment 2 of the present invention. The difference from the first embodiment is that a resistance dividing circuit 7 is connected in parallel to the capacitor 3. Hereinafter, the same parts as those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The resistance dividing circuit 7 divides the voltage V3 across the capacitor 3, and the divided voltage value is input to the control circuit 9 as the charging voltage value 7a of the capacitor 3. Based on this charging voltage value 7a, the control circuit 9 detects the charging voltage of the capacitor 3, and the control circuit 9 generates and outputs an ON signal to the drive circuit 8 at an arbitrary timing according to the charging voltage of the capacitor 3. More specifically, a predetermined voltage value is set in the control circuit 9 in advance, and this predetermined voltage value is defined by, for example, a lower limit value of the voltage at which the DC / DC converter 10 can continue to operate. . The control circuit 9 does not transmit an ON signal to the drive circuit 8 until the charging voltage value 7a of the capacitor 3 detected by the resistance dividing circuit 7 exceeds a predetermined voltage value, and the value of the charging voltage value 7a is a predetermined voltage value. When ON is exceeded, an ON signal is transmitted. Since the control circuit 9 according to the second embodiment is configured as described above, it is not necessary to set the time T for transmitting the ON signal to the drive circuit 8.

  Further, in the configuration of the second embodiment, since the charging voltage of the capacitor 3 can be detected by the resistance dividing circuit 7, for example, when the external switch 2 is in the ON state, the external switch 2 is in the OFF state for a short time due to some factor. Even when the operation returns to the ON state again, the magnitude of the inrush current can be suppressed. That is, when the external switch 2 in the ON state is in the OFF state for a short time, the charging voltage value 7a decreases, and when the charging voltage value 7a falls below a predetermined voltage value set in the control circuit 9 in advance, The control circuit 9 stops transmission of the ON signal to the drive circuit 8. Thereafter, when the external switch 2 returns to the ON state again, the control circuit 9 does not transmit an ON signal until the charge voltage value 7a exceeds a predetermined voltage value. Therefore, when the external switch 2 is turned ON. Inrush current is suppressed by the resistor 4.

  When the charging voltage value 7a exceeds a predetermined voltage value, an ON signal is transmitted from the control circuit 9 to the drive circuit 8.

  As described above, the power supply protection circuit 20 according to the present embodiment is connected to the capacitor 3 in parallel and detects a voltage value (charging voltage value 7a) applied to the capacitor 3 (resistance dividing circuit). 7), the drive control unit 21 turns off the MOSFET 5 and the MOSFET 6 until the voltage value detected by the voltage detection unit exceeds a predetermined voltage value, and the voltage value exceeds the predetermined voltage value. Later, the MOSFET 5 and the MOSFET 6 are configured to be turned on. With this configuration, in addition to the effect of the first embodiment, the magnitude of the inrush current can be suppressed even when the external switch 2 repeats ON / OFF for a short time due to some factor.

Embodiment 3 FIG.
FIG. 6 is a configuration diagram of a power protection circuit according to Embodiment 3 of the present invention. The difference from the second embodiment is that the control circuit 9 is configured to detect a decrease in capacity due to the life of the capacitor 3 and to output a signal 9 a for notifying the user of the life of the capacitor 3. Hereinafter, the same parts as those of the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  When the external switch 2 is turned on while the capacitor 3 is not charged, the control circuit 9 is activated after the DC / DC converter 10 is activated. The control circuit 9 according to the third embodiment measures the time from when the control circuit 9 is activated until the charging voltage value 7a falls below a predetermined voltage value, and this measurement time and a predetermined value set in the control circuit 9 in advance. Is compared with the time. The predetermined time is defined by the lifetime of the capacitor 3, for example. As a result of this comparison, when the measurement time is longer than the predetermined time, the control circuit 9 detects a decrease in capacity due to the life of the capacitor 3, and the control circuit 9 outputs a signal 9a for informing the user of the life of the capacitor 3. . The signal 9a is transmitted to, for example, a display device (not shown) provided outside the power protection circuit 20, and the display device that has received the signal 9a displays a warning message that prompts that the life of the capacitor 3 is approaching, for example. Is called.

  As described above, in the power supply protection circuit 20 according to the present embodiment, the drive control unit 21 detects a decrease in the capacity of the capacitor 3 based on the charging voltage value 7a detected by the resistance dividing circuit 7, and It is configured to generate and output a signal (information display signal 9a) for informing the capacity reduction. With this configuration, in addition to the effects of the second embodiment, the user can know that the life of the capacitor 3 is approaching, and the normal operation of the power supply protection circuit 20 can be maintained by replacing the capacitor 3. it can.

  Note that at least one of the MOSFET 5 and the MOSFET 6 used in the power supply protection circuit 20 according to the first to third embodiments may be formed of a wide band gap semiconductor such as GaN (gallium nitride), SiC (silicon carbide), or diamond. Good. A wide band gap semiconductor has a higher heat resistance temperature, dielectric breakdown strength, thermal conductivity, and the like than a Si (silicon) semiconductor, and has a short-circuit withstand capability expressed by a current square time product lower than that of a Si semiconductor. Therefore, by adopting a wide band gap semiconductor for at least one of the MOSFET 5 and the MOSFET 6, the peak of the inrush current can be suppressed, and the power protection circuit 20 having a low ON resistance can be realized without being restricted by the short-circuit withstand capability. Can do.

  Further, the embodiment of the present invention shows an example of the contents of the present invention, and can be combined with another known technique, and a part thereof is not deviated from the gist of the present invention. Of course, it is possible to change the configuration such as omission.

  As described above, the present invention can be applied to a power supply protection circuit, and in particular, it is possible to reduce the size of the circuit while performing protection when the DC power supply is reversely connected and suppressing inrush current when the DC power supply is turned on. It is useful as an invention.

1 DC power supply, 2 external switch, 3 capacitor, 4 resistor, 5 and 6 MOSFET, 5a and 6a body diode, 7 resistance dividing circuit, 7a charge voltage value, 8 drive circuit, 9 control circuit, 9a signal, 10 DC / DC Converter, 11 load side circuit, 20 power protection circuit, 21 drive control unit.

Claims (5)

A capacitor having one end connected to the positive terminal of the DC power supply;
One end is connected to the other end of the capacitor without going through the negative terminal of the DC power supply, and the other end is connected to the negative terminal,
A first MOSFET connected in parallel to the resistor;
A second MOSFET connected between the negative terminal of the DC power source and the resistor;
A drive control unit that performs ON / OFF control of the first MOSFET and the second MOSFET in response to power supply from the DC power supply;
With
The drive control unit turns off the first MOSFET and the second MOSFET until a predetermined time elapses from activation of the drive control unit, and after the predetermined time elapses, A power supply protection circuit , wherein an ON signal for turning on the second MOSFET is transmitted to the first MOSFET and the second MOSFET . A capacitor having one end connected to the positive terminal of the DC power supply;
One end is connected to the other end of the capacitor without going through the negative terminal of the DC power supply, and the other end is connected to the negative terminal,
A first MOSFET connected in parallel to the resistor;
A second MOSFET connected between the negative terminal of the DC power source and the resistor;
A drive control unit that performs ON / OFF control of the first MOSFET and the second MOSFET in response to power supply from the DC power supply;
A voltage detector connected in parallel to the capacitor to detect the value of the voltage applied to the capacitor;
With
The drive control unit turns off the first MOSFET and the second MOSFET until the voltage value detected by the voltage detection unit exceeds a predetermined voltage value, and the voltage value is a predetermined value. After the voltage value is exceeded, an ON signal for turning on the first MOSFET and the second MOSFET is transmitted to the first MOSFET and the second MOSFET. .   The drive control unit detects a decrease in the capacitance of the capacitor based on a voltage value detected by the voltage detection unit, and generates and outputs a signal for informing the decrease in the capacitance of the capacitor. The power supply protection circuit according to claim 2.   4. The power supply protection circuit according to claim 1, wherein at least one of the first MOSFET and the second MOSFET is configured by a wide band gap semiconductor. 5.   The power supply protection circuit according to claim 4, wherein the wide band gap semiconductor is formed of a semiconductor using silicon carbide or a gallium nitride material.

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