JP4662992B2 - Inrush current reduction circuit and power supply device - Google Patents

Description

  The present invention relates to an inrush current reducing circuit that reduces an inrush current to a capacitor connected to a power input terminal of a load circuit, and a power supply apparatus that reduces the inrush current.

  The display device connected to the personal computer exchanges various signals with the personal computer and obtains power from the personal computer. Since the current that the personal computer can supply to the display device is limited, the maximum value is determined as the specification.

  However, in recent years, the functions and applications of personal computers have been expanded, and it has been demanded that television programs are received and DVDs (Digital Versatile Discs) are reproduced with full-fledged video and audio. In particular, it is necessary to stably supply a necessary current to the sound output circuit in order to reproduce a powerful sound with a wide dynamic range and enhance the sound effect. For this reason, the current required for the display device tends to increase, and the capacitor for stabilizing the voltage also tends to increase in the display device. As the capacity of the capacitor increases, the inrush current that flows from the personal computer to the display device increases.

Conventionally, in order to reduce the inrush current flowing into the load circuit, it has been proposed to use a plurality of timers and switching elements and connect the divided capacitors to the power supply line with a time difference (Patent Document 1).
JP 2000-175438 A

  In the case of the conventional method described above, the capacitor is divided, whereby the inrush current is dispersed, and the purpose can be achieved. However, since all the switching elements are turned on in a short time and all the capacitors are connected to the power supply circuit at the time when the load circuit is activated, all the capacitors are in a fully loaded operating state. Therefore, the specifications must be selected on the premise of full operation for all capacitors, which is disadvantageous in terms of cost reduction. If the capacitor specifications are lowered for cost reduction, the lifetime of the capacitor becomes a problem.

  The present invention has been made in view of the above-described problem, and reduces an inrush current to a capacitor in a load circuit or a power supply device, and can reduce an inrush current without shortening the life of the capacitor. And it aims at providing a power supply device.

  An inrush current reduction circuit according to the present invention is an inrush current reduction circuit for reducing an inrush current to a capacitor connected to a power input terminal of a load circuit, the load current detection circuit detecting a current flowing through the load circuit, A switching element that is turned on when a current detected by the load current detection circuit exceeds a threshold value or a change in current exceeds a threshold value, and the capacitor that is turned on when the switching element is turned on. And a second capacitor connected in parallel.

  Preferably, the switching element is controlled to be turned off when a current detected by the load current detection circuit does not exceed a threshold value or when a change amount of the current does not exceed a threshold value. When the element is turned off, the resistance connected in parallel to the second capacitor is substantially infinite, and the charge of the second capacitor is maintained.

  The load current detection circuit detects a current including a current flowing through an audio output circuit included in the load circuit, and the current exceeds a threshold due to an increase in an audio level in the audio output circuit. Sometimes, the switching element is turned on.

  The load current detection circuit detects a current including a current flowing through an inverter circuit having a variable duty ratio included in the load circuit. When the duty ratio in the inverter circuit approaches 50%, current is detected. When the amount of change exceeds a threshold value, the switching element is turned on.

  In addition, a plurality of switching elements each operating with a plurality of different threshold values are provided as the switching elements, and each switching element has a second capacitor connected in parallel with the capacitor when turned on. Is provided.

  Another embodiment of the inrush current reducing circuit according to the present invention is an inrush current reducing circuit for reducing an inrush current to a capacitor connected to a power input terminal of a load circuit, wherein the load detects a current flowing through the load circuit. A current detection resistor, a comparison circuit that outputs an ON signal when a voltage across the load current detection resistor exceeds a set value, a switching element that is turned ON when an ON signal is output from the comparison circuit, and And a second capacitor connected in parallel with the capacitor when the switching element is turned on.

  A power supply device according to the present invention is a power supply device that supplies a direct current to a load circuit, a capacitor for stabilizing the current supplied to the load circuit, and a load current that detects a current flowing through the load circuit A detection circuit, a switching element that is turned on when a current detected by the load current detection circuit exceeds a threshold value, or a change in current exceeds a threshold value, and when the switching element is turned on And a second capacitor connected in parallel with the capacitor.

  Preferably, the switching element is controlled to be turned off when a current detected by the load current detection circuit does not exceed a threshold value or when a change amount of the current does not exceed a threshold value. When the element is turned off, the resistance connected in parallel to the second capacitor is substantially infinite, and the charge of the second capacitor is maintained.

  According to the present invention, it is possible to reduce the inrush current to the capacitor in the load circuit and the power supply device, and to reduce the cost without shortening the life of the capacitor.

1 is a schematic circuit diagram of an electronic device provided with an inrush current reduction circuit according to the present invention. It is a figure which shows the example of operation | movement of an inrush current reduction circuit. It is a figure which shows the other example of operation | movement of an inrush current reduction circuit. It is a circuit diagram of the electronic device provided with the inrush current reduction circuit of the other example which concerns on this invention. It is a circuit diagram of the power supply device provided with the inrush current reduction circuit of the other example which concerns on this invention. It is a circuit diagram which shows the inrush current reduction circuit of another example.

  FIG. 1 is a schematic circuit diagram of an electronic device DK provided with an inrush current reducing circuit 5 according to the present invention, FIG. 2 is a diagram showing an example of the operation of the inrush current reducing circuit 5, and FIG. It is a figure which shows the other example of operation | movement.

  In FIG. 1, the circuit of the electronic device DK is provided with a protection circuit 11, a detection circuit 12, a load circuit 13, a switching element Q1, and two capacitors C1 and C2.

  The protection circuit 11 protects the circuit when the power supply line (including the load circuit 13) L1 of the electronic device DK is abnormal, or protects the power supply device that supplies power to the electronic device DK. is there. For example, the protection circuit 11 detects the current i flowing through the power supply line L1 and cuts off the connection between the power supply input terminal TM1 and the power supply line L1 when the current i exceeds a specified value. Further, the voltage e of the power supply line L1 is detected, and when the voltage e is out of the set range, the circuit is similarly cut off.

  The detection circuit 12 detects a current id flowing through the load circuit 13 or a change Δid of the current id flowing through the load circuit 13. In other words, the detection signal S1 is output when the current id exceeds the threshold value Th1 or when the change Δid exceeds the threshold value Th8.

  The load circuit 13 is an electronic circuit for realizing the original function of the electronic device DK. For example, when the electronic device DK is a display device, a lighting circuit, a control circuit, a synchronization circuit, a dimming circuit, a video circuit, a backlight circuit, etc. for performing display by LCD, PDP, CRT, etc. The load circuit 13 includes a sound output circuit for outputting sound from the speaker, a sound effect circuit, a sound quality adjustment circuit, a remote operation circuit, and other various circuits.

  The switching element Q1 is turned on when the detection signal S1 is turned on, that is, when the detection signal S1 is output. That is, the switching element Q1 is controlled to be turned off when the current id detected by the detection circuit 12 does not exceed the threshold Th1, or when the current change Δid does not exceed the threshold Th8. . By turning on the switching element Q1, the capacitor C2 is connected to the power supply line L1. As the switching element Q1, for example, a MOS FET, a bipolar transistor, a thyristor, an IC formed of them, a relay, or the like is used.

  The capacitor C1 is always connected to the power supply line L1. That is, it is indirectly connected to the power input terminal TM1 through the protection circuit 11. The capacitor C2 is connected to the power supply line L1 via the switching element Q1 as described above. When the switching element Q1 is turned on, the capacitor C2 is actually connected to the power supply line L1 and is in an operating state. That is, when the switching element Q1 is turned off, the resistance connected in parallel to the capacitor C2 is substantially infinite, and in this state, the charged charge of the capacitor C2 is almost maintained as it is.

  These capacitors C1 and C2 are intended to stabilize the power supply by suppressing fluctuations in the voltage in the power supply line L1, and are usually large-capacity aluminum electrolytic capacitors or the like. Capacitors C1 and C2 have the same capacitance, for example, 500 μF. That is, in this case, a capacitor having a capacity of 1000 μF is mounted as two capacitors C1 and C2 as the capacitor C for stabilizing the power supply.

  Since the capacitor C2 operates only when necessary as will be described later, the actual operation time is shorter than that of the capacitor C1. Therefore, the specification of the capacitor C2 can be selected lower than that of the capacitor C1. For example, when a capacitor C1 that can be used in a 105 ° C. environment is used for 1000 hours, a capacitor C2 that can be used in a 85 ° C. environment can be used.

  In FIG. 1, the detection circuit 12, the switching element Q <b> 1, and the capacitor C <b> 2 constitute an inrush current reduction circuit 5.

  Next, the operation of the inrush current reduction circuit 5 will be described.

  The power input terminal TM1 of the electronic device DK is connected to the power supply terminal of an appropriate device such as a personal computer. A power switch (not shown) is turned on to operate the electronic device DK. Such a power switch may be provided in the protection circuit 11 to connect or block between the power input terminal TM1 and the power line L1. Further, a power switch may be provided separately from the protection circuit 11 and the load circuit 13 to control the function and operation of the electronic device DK.

  As shown in FIG. 2, the inrush current it1 flows in the capacitor C1 at the time t1 when the power input terminal TM1 is connected to the power terminal or the power switch is turned on. Since the magnitude of the inrush current it1 depends on the capacitance of the capacitor C1, by setting the capacitor C1 to 500 μF, the magnitude of the inrush current it1 is about half that of 1000 μF. Thereafter, since the load circuit 13 operates normally, an idling current (load current id) flows due to the operation of the load circuit 13.

  Therefore, for example, the sound output circuit outputs a loud sound such as an explosion sound, so that the current id increases, and the increased current id is detected by the detection circuit 12. When the detected current id exceeds the threshold value Th1, the detection signal S1 is output.

  When the detection signal S1 is output, the switching element Q1 is turned on, and the capacitor C2 is connected to the power supply line L1. At that time t2, the inrush current it2 flows through the capacitor C2. Since the magnitude of the inrush current it2 depends on the capacitance of the capacitor C2, when the capacitor C2 is set to 500 μF, the inrush current it1 is the same as the inrush current it1 of the capacitor C1 or starts from a certain charge state, and is smaller than that. .

  While the current id of the load circuit 13 exceeds the threshold value Th1, the detection signal S1 is output. Therefore, during this period, the switching element Q1 is turned on and the capacitor C2 is in an operating state. When the current id becomes smaller than the threshold value Th1, the detection signal S1 is turned off, so that the switching element Q1 is turned off and the connection of the capacitor C2 is released.

  In this way, instead of one capacitor C originally connected to the power supply line L1, it is divided into two capacitors C1 and C2, and one capacitor C1 is always connected to the power supply line L1, and the other one Since the second capacitor C2 is connected when the current id increases, the inrush current it to the capacitor C is dispersed, and thereby the peak value (instantaneous maximum value) of the inrush current it is halved.

  In addition, since the inrush current it2 of the second capacitor C2 starts from a certain charge state, it becomes smaller than the inrush current it1 of the capacitor C1. Therefore, the peak value of the inrush current it can be further reduced as a whole by making the capacitance of the capacitor C2 larger than the capacitance of the capacitor C1.

  When the load circuit 13 includes an audio output circuit, the current id including the current flowing through the audio output circuit is detected by the detection circuit 12. Then, the switching element Q1 is turned on when the current id exceeds the threshold value Th1 due to the increase of the sound level in the sound output circuit. In this way, the capacitor C2 is connected and activated only when the load circuit 13 operates to a certain degree or more. Since the capacitor C2 is not activated when it is not necessary, the actual operating time of the capacitor C2 is reduced, and the capacitor C2 The lifespan of is extended. Therefore, the mounting cost of the capacitor C2 can be reduced.

  When the switching element Q1 is once turned on and then turned off, the voltage e of the power supply line L1 remains almost as it is in the capacitor C2, so that the inrush current it hardly flows when the switching element Q1 is turned on next time. Therefore, there is no substantial demerit due to repeated ON / OFF by the switching element Q1.

  Next, the operation when the load circuit 13 includes a backlight lighting circuit such as an LCD will be described. The backlight lighting circuit is lit by applying a square-wave voltage having a variable duty ratio to the arc tube and adjusting its luminance. For this purpose, an inverter circuit that outputs a square-wave voltage with a variable duty ratio is provided. When the duty ratio is 100%, a continuous current flows and the maximum luminance is obtained. In this case, there is no fluctuation of the current, and therefore it is not necessary to stabilize the power supply. Therefore, the capacitor C1 alone is sufficient.

  However, when the duty ratio becomes smaller than 100%, the luminance decreases accordingly, and the current becomes intermittent. That is, when the brightness is adjusted, the current becomes intermittent, and this appears as a fluctuation of the current. Therefore, it is necessary to connect the capacitor C2 to stabilize the power supply. When the duty ratio is 50%, the change Δid in the current id is the largest. Therefore, when the current change Δid exceeds the threshold Th8 due to the duty ratio approaching 50%, the detection circuit 12 detects this and outputs the detection signal S1. Specifically, centering on the case where the duty ratio is 50%, when the change is between the threshold value Th8H that is higher by α percentage and the threshold value Th8L that is lower by α percentage, The threshold value Th8 has been exceeded. "

  As shown in FIG. 3, the inrush current it1 flows through the capacitor C1 at the time t1 when the power is turned on. At the time point t2 when the backlight is turned on at a duty ratio of 100%, the current id is large (for example, about 2 A), but the change Δid is zero. Since the duty ratio is adjusted to be 50% at time t3, it is between the threshold Th8H and the threshold Th8L, and the change Δid exceeds the threshold Th8. Therefore, the detection signal S1 is output, the switching element Q1 is turned on, and the capacitor C2 is connected to the power supply line L1.

  When the duty ratio is further reduced at time t3, the change Δid does not exceed the threshold value Th8, the detection signal S1 is turned off, and the connection of the capacitor C2 is released.

  As described above, the detection circuit 12 detects the change Δid of the current id, and the switching element Q1 is controlled to be turned on when the change Δid exceeds the threshold Th8.

  Even when controlled in this way, the inrush current it to the capacitor C becomes small and the capacitor C2 becomes active only when the change Δid of the current id becomes large, so the actual operation time of the capacitor C2 is reduced. Thus, the cost of the capacitor C2 can be reduced.

  Next, another example inrush current reducing circuit 5B in the electronic device DK will be described.

  FIG. 4 is a schematic circuit diagram of an electronic device DK provided with an inrush current reducing circuit 5B according to another example of the present invention. In FIG. 4, parts having the same functions as those in FIG.

  In FIG. 4, a resistor Rk is provided as the detection circuit 12B, and a voltage drop of Ek (= Rk × id) is generated at both ends due to a current id flowing therethrough. Whether or not the voltage Ek exceeds a predetermined magnitude (threshold value Th1) is determined by a differential amplifier circuit including four resistors R1 to R4 and an operational amplifier Q11. When the current id exceeds the threshold value Th1, the output (detection signal) S1 of the operational amplifier Q11 becomes “H”. When the current id is equal to or less than the threshold value Th1, the output of the operational amplifier Q11 becomes “L”. Become. The switching element Q1 is turned on / off according to the detection signal S1, and the capacitor C2 is connected to or released from the power supply line L1.

  In the case of the inrush current reduction circuit 5B shown in FIG. 4, it is possible to detect the current id with a simple configuration and determine whether or not the magnitude exceeds the threshold value Th1.

  Next, an example of the power supply device 1 provided with the inrush current reduction circuit 5C will be described.

  FIG. 5 is a circuit diagram of the power supply device 1 provided with the inrush current reducing circuit 5C of another example according to the present invention.

  In FIG. 5, the power supply device 1 includes a protection circuit 21, an AC / DC converter 22, and an inrush current reduction circuit 5C.

  The protection circuit 21 is for protecting the circuit when the power supply device 1 has an abnormality. The protection circuit 21 is an overcurrent circuit breaker, a fuse, or the like. A power switch may be included.

  The AC / DC converter 22 converts the input AC voltage such as AC 100 volts or AC 200 volts into a predetermined DC voltage (for example, 5 volts, 9 volts, 12 volts, etc.). As the AC / DC converter 22, various known ones such as one using a power transformer and a rectifier or one using an inverter circuit can be adopted.

  Capacitors C1 and C2 are for stabilizing the power supply, and also serve as smoothing capacitors for reducing ripples. When an appropriate electronic device serving as a load is connected to the DC output terminal and an AC voltage is supplied to the power supply device 1, an inrush current first flows through the capacitor C1. When the current id flowing through the load is equal to or less than the threshold value Th1, the detection circuit 23 does not output the detection signal S1, so that the switching element Q1 is off and the capacitor C2 is not connected to the power supply line L1. When the current id flowing through the load exceeds the threshold Th1, the detection circuit 23 outputs a detection signal S1, the switching element Q1 is turned on, and the capacitor C2 is connected to the power supply line L1. At this time, an inrush current flows through the capacitor C2.

  Also in this power supply device 1, the capacitor C is divided into two capacitors C1 and C2, and since the second capacitor C2 is connected only when the current id increases, the inrush current to the capacitor is dispersed, The peak value is halved. Moreover, the actual operating time of the capacitor C2 is reduced.

  Next, another example of the inrush current reducing circuit 5D will be described.

  FIG. 6 is a circuit diagram showing an inrush current reducing circuit 5D of still another example.

  In the inrush current reduction circuit 5D shown in FIG. 6, the capacitor C is divided into three capacitors C1, C2, and C3 each having a capacity of one third. One capacitor C1 is always connected to the power supply line L1. The second capacitor C2 is connected when the current id exceeds the threshold Th1, and the third capacitor C3 is connected when the current id exceeds the threshold Th2 (Th2> Th1).

  That is, when the power supply is turned on, an inrush current flows through the capacitor C1, and thereafter, when the current id increases and exceeds the first threshold Th1, an inrush current flows through the second capacitor C2. When the current id increases and exceeds the second threshold Th2, an inrush current flows through the third capacitor C3.

  As described above, the inrush current to the capacitor C is distributed in three times, and the peak value of the inrush current can be further reduced.

  The capacitor C may be further divided, and the inrush current may be distributed four times, five times, six times, or seven times or more.

  In the above-described embodiment, the switching element can be configured to maintain the state once turned on. In this case, the timing of connecting each capacitor C is extended until the current id increases to the threshold value Th1.

  In addition, the protection circuit 11, the detection circuit 12, the load circuit 13, the inrush current reduction circuits 5, 5B, 5C, 5D, and the whole or each part of the power supply device 1, circuit configurations or circuit constants, types and specifications of capacitors and switching elements, etc. Can be appropriately changed in accordance with the gist of the present invention.

  INDUSTRIAL APPLICABILITY The present invention is used for reducing inrush current due to a capacitor in a display device that receives power supply from a computer body, and can also be used as a power supply device.

Claims (8)

An inrush current reduction circuit that reduces inrush current to the capacitor connected to the power input terminal of the load circuit,
A load current detection circuit for detecting a current flowing in the load circuit;
A switching element that is turned on when a current detected by the load current detection circuit exceeds a threshold value or when a change in current exceeds a threshold value;
A second capacitor connected in parallel with the capacitor when the switching element is turned on;
An inrush current reducing circuit comprising: The switching element is controlled to be turned off when the current detected by the load current detection circuit does not exceed the threshold value or when the change in current does not exceed the threshold value,
When the switching element is turned off, the resistance connected in parallel to the second capacitor is substantially infinite, and the charge of the second capacitor is maintained.
The inrush current reduction circuit according to claim 1. The load current detection circuit detects a current including a current flowing through an audio output circuit included in the load circuit,
The switching element is configured to be turned on when a current exceeds a threshold due to an increase in sound level in the sound output circuit.
The inrush current reducing circuit according to claim 1 or 2. The load current detection circuit detects a current including a current flowing through an inverter circuit having a variable duty ratio included in the load circuit,
When the duty ratio in the inverter circuit approaches 50%, the switching element is configured to be turned on when a change in current exceeds a threshold value.
The inrush current reducing circuit according to claim 1 or 2. As the switching element, there are provided a plurality of switching elements that respectively operate with a plurality of different threshold values,
For each switching element, a second capacitor is provided which is connected in parallel with the capacitor when turned on.
The inrush current reducing circuit according to any one of claims 1 to 4. An inrush current reduction circuit that reduces inrush current to the capacitor connected to the power input terminal of the load circuit,
A load current detection resistor for detecting a current flowing in the load circuit;
A comparison circuit that outputs an ON signal when the voltage across the load current detection resistor exceeds a set value;
A switching element that is turned on when an ON signal is output from the comparison circuit;
A second capacitor connected in parallel with the capacitor when the switching element is turned on;
An inrush current reducing circuit comprising: A power supply device for supplying a direct current to a load circuit,
A capacitor for stabilizing the current supplied to the load circuit;
A load current detection circuit for detecting a current flowing in the load circuit;
A switching element that is turned on when a current detected by the load current detection circuit exceeds a threshold value or when a change in current exceeds a threshold value;
A second capacitor connected in parallel with the capacitor when the switching element is turned on;
A power supply device comprising: The switching element is controlled to be turned off when the current detected by the load current detection circuit does not exceed the threshold value or when the change in current does not exceed the threshold value,
When the switching element is turned off, the resistance connected in parallel to the second capacitor is substantially infinite, and the charge of the second capacitor is maintained.
The power supply device according to claim 7.