JP7515375B2 - Power supply circuit - Google Patents

Description

This disclosure relates to a power supply circuit.

A conventional inrush current prevention circuit includes a main switch, a limiting resistor, contacts, and a smoothing circuit. The smoothing circuit includes a capacitor, an inductance, etc. The output of the smoothing circuit is connected to a DC/DC converter. The contacts are connected in parallel with the limiting resistor. Power is supplied to the conventional inrush current prevention circuit from a power source via the main switch.

In the initial state, the contacts are open. Therefore, when the main switch is changed from the off state to the on state, an inrush current flows through the smoothing circuit via the limiting resistor, and the inrush current is limited by the limiting resistor. When the contacts are closed after a certain delay time, both ends of the limiting resistor are short-circuited (see, for example, Patent Document 1).

Japanese Patent Application Laid-Open No. 58-49081

In conventional inrush current prevention circuits such as those described above, a relatively large inrush current flows through the limiting resistor, so the limiting resistor needs to have a large rated power. The larger the rated power of the resistor, the larger the resistor size becomes. Therefore, conventional inrush current prevention circuits need a relatively large limiting resistor, which causes the circuit to become larger.

This disclosure has been made to solve the above problems, and aims to provide a power supply circuit that can reduce inrush current while preventing the circuit from becoming too large.

The power supply circuit according to the present disclosure includes a first capacitor connected between a first power supply line and a second power supply line, a second capacitor, a switch connected in series to the second capacitor, and a control unit that controls opening and closing of the switch, the second capacitor and the switch being connected in parallel to the first capacitor between the first power supply line and the second power supply line, and the control unit keeps the switch open until a first time has elapsed since the start of the supply of power from a power source connected to the first power supply line and the second power supply line, and closes the switch after the first time has elapsed.

The power supply circuit disclosed herein can reduce inrush current while preventing the circuit from becoming too large.

1 is a circuit diagram showing a power supply circuit according to a first embodiment; 2 is a timing chart showing the operation of the power supply circuit of FIG. 1 . FIG. 11 is a circuit diagram showing a power supply circuit according to a second embodiment. 4 is a timing chart showing the operation of the power supply circuit of FIG. 3 . FIG. 11 is a circuit diagram showing a power supply circuit according to a third embodiment.

Hereinafter, embodiments will be described with reference to the drawings.
Embodiment 1.
Fig. 1 is a circuit diagram showing a power supply circuit according to embodiment 1. As shown in Fig. 1, a power supply circuit 10 includes a first power supply line 11, a second power supply line 12, a first capacitor 13, a second capacitor 14, a first switch 15, and a control unit 16.

The first power supply line 11 is a high-potential power supply line. The second power supply line 12 is a low-potential power supply line. The second power supply line 12 is a GND line.

The first capacitor 13 is connected between the first power supply line 11 and the second power supply line 12. The capacitance of the first capacitor 13 is C1. The second capacitor 14 and the first switch 15 are connected in parallel to the first capacitor 13 between the first power supply line 11 and the second power supply line 12. The first switch 15 is connected in series to the second capacitor 14. The capacitance of the second capacitor 14 is C2. The capacitance C1 of the first capacitor 13 is smaller than the capacitance C2 of the second capacitor 14.

The first capacitor 13 and the second capacitor 14 are smoothing capacitors. The first capacitor 13 and the second capacitor 14 reduce the ripple that occurs between the first power supply line 11 and the second power supply line 12. The larger the capacity of the capacitor, the larger the ripple that can be reduced. Therefore, the second capacitor 14 can reduce a larger ripple than the first capacitor 13.

The control unit 16 controls the opening and closing of the first switch 15. More specifically, the control unit 16 generates a control signal for opening and closing the first switch 15, and inputs the control signal to the first switch 15. The first switch 15 is open when the voltage of the control signal is less than a first voltage _Vth , and is closed when the voltage of the control signal is equal to or greater than the first voltage _Vth .

Therefore, the capacitance of the smoothing capacitors in the entire power supply circuit 10 is C1 when the voltage of the control signal is less than the first voltage _Vth , and is (C1+C2) when the voltage of the control signal is equal to or greater than the first voltage _Vth .

A positive terminal of a DC power supply 22 is connected to one end of the first power supply line 11 via a main switch 23 and a reverse connection prevention diode 21. One end of a load 90 is connected to the other end of the first power supply line 11. The other end of the load 90 is grounded to GND. The load 90 is an FA (Factory Automation) device, a home appliance, or the like. A negative terminal of the DC power supply 22 is connected to one end of the second power supply line 12. The other end of the second power supply line 12 is grounded to GND. The power supply voltage of the DC power supply 22 is _Vp .

Fig. 2 is a timing chart showing the operation of the power supply circuit 10 of Fig. 1. Fig. 2 shows the input current I _IN , the input voltage V _IN , the control voltage V _SW , the first capacitor current I _C1 , the second capacitor current I _C2 , and the load current I _LOAD .

The input current I _IN is a current flowing through the DC power supply 22. The input voltage V _IN is a potential difference between the first power supply line 11 and the second power supply line 12 on the DC power supply 22 side. The control voltage V _SW is an input voltage of a control signal to the first switch 15. The first capacitor current I _C1 is a current flowing through the first capacitor 13. The second capacitor current I _C2 is a current flowing through the second capacitor 14. The load current I _LOAD is a current flowing through the load 90.

At time t10, the main switch 23 is closed and power supply from the DC power supply 22 to the power supply circuit 10 begins. Therefore, the input voltage V _IN rises from 0 V at time t10, and then reaches the power supply voltage V _P .

Furthermore, at time t10, a first inrush current I _rush1 begins to flow through the first capacitor 13 in order to charge the first capacitor 13. The first inrush current I _rush1 is a peak that appears in the first capacitor current _IC1 . Since the capacitance C1 of the first capacitor 13 is set to a value smaller than the capacitance C2 of the second capacitor 14, charging of the first capacitor 13 is completed relatively quickly. Therefore, the period during which the first inrush current I _rush1 occurs is relatively short.

At time t10, the control unit 16 opens the first switch 15. Therefore, at time t10, no current flows through the second capacitor 14. In other words, the second capacitor current I _C2 is zero.

When power begins to be supplied to the load 90 at time t10, the load 90 enters a low-load state. The low-load state is a state in which the load 90, which is an FA device or a home appliance, is in a standby state. For example, if the load 90 is an FA device, the low-load state corresponds to a state in which a reset circuit and a control circuit for stopping erroneous output are operating. If the load 90 is a home appliance, the low-load state corresponds to a state in which a standby circuit for accepting remote control operations is operating.

In the light load state, the load current _ILOAD is relatively small, and the ripple is also relatively small. The capacitance C1 of the first capacitor 13 is selected to have a value that can sufficiently reduce the ripple in the light load state.

Time t11 is the time when the control voltage V _SW becomes equal to or higher than the first voltage V _th . Therefore, at time t11, the control unit 16 closes the first switch 15. Time t11 is also the time after the first time has elapsed since time t10. The first time is a period shorter than the period from time t10 to time t11.

For example, the first time period is defined as the time required for the first inrush current I _rush1 to become equal to or less than the first current I _th . In the first embodiment, the first current I _th is defined as zero. The first time period is preset in the control unit 16 based on the capacitance C1 of the first capacitor 13.

At time t11, the second inrush current I _rush2 begins to flow through the second capacitor 14 to charge the second capacitor 14. The second inrush current I _rush2 is a peak that appears in the second capacitor current I _C2 .

Time t12 is the time when the second inrush current I _rush2 becomes substantially zero. In other words, time t12 is the time when charging of the second capacitor 14 is completed.

Time t13 is the time when the state of the load 90 transitions from the small load state to the full load state. The full load state is, for example, a state in which the FA device or home appliance serving as the load 90 operates at rated output. In the full load state, the load current _ILOAD is relatively large, and the ripple is also relatively large. A value capable of sufficiently reducing the ripple in the full load state is selected as the capacitance C2 of the second capacitor 14.

In this way, the control unit 16 determines time t11 in consideration of the period until the first inrush current I _rush1 becomes zero, the period (t12-t11) during which the second inrush current I _rush2 is occurring, and time t13 when the state of the load 90 transitions from a light load state to a full load state. More specifically, time t11 is preset so that it is a time after the time when the first inrush current I _rush1 becomes zero, and so that the period from time t11 to time t13 is longer than the period during which the second inrush current I _rush2 is occurring.

The input current I _IN corresponds to the sum of the first capacitor current _IC1 , the second capacitor current _IC2 , and the load current I _LOAD . Note that in Fig. 2, the polarity of the input current I _IN is opposite to the polarities of the first capacitor current _IC1 , the second capacitor current _IC2 , and the load current I _LOAD .

As described above, according to the power supply circuit 10 of the first embodiment, the first capacitor 13 and the second capacitor 14 are connected in parallel between the first power supply line 11 and the second power supply line 12. Furthermore, the first switch 15 is connected in series to the second capacitor 14.

The control unit 16 of the power supply circuit 10 closes the first switch 15 and causes the second inrush current I _rush2 to flow through the second capacitor 14 during the period from when the first inrush current I _rush1 becomes zero until the state of the load 90 transitions from the light load state to the full load state.

As a result, the period during which the first inrush current I _rush1 flows through the first capacitor 13 and the period during which the second inrush current I _rush2 flows through the second capacitor 14 are separated into different periods. This makes it possible to reduce the inrush current per unit time. In other words, it is possible to prevent an excessive current from flowing through the power supply circuit 10.

Therefore, in the power supply circuit 10, there is no need to provide a current limiting resistor in the path through which the inrush current flows. A resistor with a large rated power is required as a current limiting resistor. Therefore, the size of the current limiting resistor is large compared to other circuit components. Therefore, with the power supply circuit 10, which does not require a current limiting resistor, it is possible to reduce the inrush current while preventing the circuit from becoming larger.

In addition, since the power supply circuit 10 does not require a resistor for current limiting, there is no risk of voltage drop caused by a resistor for current limiting.

Furthermore, the first time period is the time required for the first inrush current I _rush1 to become equal to or less than the first current I _th . Therefore, the control unit 16 closes the first switch 15 after the first inrush current I _rush1 becomes equal to or less than the first current I _th . This separates the first inrush current I _rush1 and the second inrush current I _rush2 from each other. This makes it possible to reduce the inrush current flowing through the power supply circuit 10.

Furthermore, when the first current _Ith is set to zero, the first inrush current _Irush1 and the second inrush current _Irush2 are more clearly separated and do not overlap with each other, thereby making it possible to further reduce the inrush current flowing through the power supply circuit 10.

Furthermore, the larger the load current _ILOAD , the larger the capacitance required of the smoothing capacitor. On the other hand, the larger the capacitance of the capacitor, the larger the inrush current. However, as described above, in a light load state, the load current _ILOAD is relatively small, so the capacitance C1 of the first capacitor 13 can be made smaller than the capacitance C2 of the second capacitor 14. Therefore, in the power supply circuit 10, the first inrush current _Irush1 can be made small.

The high-potential terminal of the DC power supply 22 is connected to the first power supply line 11 via a reverse connection prevention diode 21. The low-potential terminal of the DC power supply 22 is connected to the second power supply line 12. Therefore, the power supply circuit 10 can more reliably supply power from the DC power supply 22 to the load 90.

In the first embodiment, the control unit 16 has preset the first time based on the capacitance C1 of the first capacitor 13. However, the power supply circuit 10 may further include a current detection circuit for detecting the first capacitor current I _C1 , and the control unit 16 may close the first switch 15 after the time when the detected first inrush current I _rush1 becomes equal to or less than the first current.

In addition, in the first embodiment, the first time is shorter than the period from time t10 to time t11, but it may be equal to the period from time t10 to time t11.

Embodiment 2.
Fig. 3 is a circuit diagram showing a power supply circuit according to embodiment 2. As shown in Fig. 3, the power supply circuit 10A includes a first power supply line 11, a second power supply line 12, a first capacitor 13, a second capacitor 14, a first switch 15, and a control unit 16. The first switch 15 is an n-channel MOSFET (Metal Oxide Semiconductor Field Effect Transistor).

The power supply circuit 10A further includes a pull-down resistor 24, a first dividing resistor 25, and a second dividing resistor 26. The resistance values of the first dividing resistor 25 and the second dividing resistor 26 are R1 and R2, respectively. The resistance value of the pull-down resistor 24 is R8.

The control unit 16 has a first input resistor 161, a second input resistor 162, a first transistor 163, a first series resistor 164, a second transistor 165, a second series resistor 166, an adjustment resistor 167, and an adjustment capacitor 168.

The resistance values of the first input resistor 161, the second input resistor 162, the first series resistor 164, the second series resistor 166, and the adjustment resistor 167 are R3, R4, R5, R6, and R7, respectively. The potential Vd between the first dividing resistor 25 and the second dividing resistor 26 is determined by the resistance values R1, R2, R3, and R4. In other words, the potential Vd is determined by the voltage division ratio between the first power supply line 11 and the second power supply line 12. The voltage division ratio is preset so that the potential Vd is equal to or greater than the second voltage.

The capacitance of the adjustment capacitor 168 is C3. The first transistor 163 is an npn bipolar transistor. The second transistor 165 is a pnp bipolar transistor.

The first transistor 163 is off when the potential Vd is less than the second voltage, and is on when the potential Vd is equal to or greater than the second voltage. The second transistor 165 is off when the first transistor 163 is off, and is on when the first transistor 163 is on.

The adjustment resistor 167 and the adjustment capacitor 168 determine the time constant of the control voltage V _SW . The adjustment resistor 167 and the adjustment capacitor 168 form a time constant circuit of the control unit 16. The time constant of the time constant circuit is determined by a resistance value R7 and a capacitance C3.

The other configurations in embodiment 2 are the same as those in embodiment 1.

Fig. 4 is a timing chart showing the operation of the power supply circuit 10A in Fig. 3. As shown in Fig. 4, at time t20, the main switch 23 is closed and the power supply voltage _Vp is applied between the first power supply line 11 and the second power supply line 12. From time t20, the first inrush current _Irush1 starts to flow through the first capacitor 13.

Furthermore, when the power supply voltage _Vp is applied between the first power supply line 11 and the second power supply line 12, the potential Vd between the first dividing resistor 25 and the second dividing resistor 26 becomes equal to or higher than the second voltage, so that the first transistor 163 is turned on and the second transistor 165 is also turned on.

The control voltage V _SW of the first switch 15 starts to rise from 0 V in accordance with the time constant of the time constant circuit of the control unit 16, and reaches the first voltage V _th at time t21. When the control voltage V _SW reaches the first voltage V _th , the first switch 15 is closed. Thus, in the second embodiment, the first time is the time until the voltage input to the gate of the first switch 15 becomes equal to or higher than the first voltage V _th .

Then, at time t21, the second inrush current I _rush2 begins to flow through the second capacitor 14. At time t22, the second inrush current I _rush2 becomes zero. Furthermore, at time t23, the state of the load 90 transitions from the light load state to the full load state.

In this way, according to the power supply circuit 10A of the second embodiment, the control unit 16 can be easily realized using a few transistors, resistors, and capacitors, so that the inrush current can be reduced while preventing the circuit from becoming too large.

As described above, the first switch 15 is an n-channel MOSFET, and the first time period is the time period required for the control voltage V _SW to the n-channel MOSFET to reach or exceed the first voltage V _th . This makes it possible to easily realize the power supply circuit 10A.

The control unit 16 also generates a signal that controls the opening and closing of the first switch 15 based on a voltage determined by the voltage division ratio between the first power supply line 11 and the second power supply line 12. This allows the power supply circuit 10A to be simplified.

In addition, in the first and second embodiments, the other end of the first power supply line 11 may be connected to the load 90 via a DC/DC converter.

In the first and second embodiments, time t11 and time t21 are times after the first inrush current I _rush1 becomes zero. However, time t11 and time t21 may be times after the first inrush current I _rush1 has dropped to a certain degree from its peak value. In other words, in Figs. 2 and 4, the tail portion of the first inrush current I _rush1 and the tail portion of the second inrush current I _rush2 may overlap in the time axis direction. That is, the first current I _th may not be zero, but may be a value greater than zero. What is important is that the peak of the first inrush current I _rush1 and the peak of the second inrush current I _rush2 can be separated from each other.

Embodiment 3.
Fig. 5 is a circuit diagram showing a power supply circuit according to embodiment 3. As shown in Fig. 5, the power supply circuit 10B includes a first power supply line 11, a second power supply line 12, a first capacitor 13, a second capacitor 14, a first switch 15, a control unit 16, a switching control unit 34, and a second switch 35. The power supply circuit 10B further includes a primary side diode 36, a primary side capacitor 37, a primary side resistor 38, a transformer 39, a secondary side diode 41, a secondary side capacitor 42, a feedback circuit 43, a first insulation circuit 44, and a second insulation circuit 45.

In addition, in the power supply circuit 10B, an AC power supply 32 is connected between the first power supply line 11 and the second power supply line 12 via a main switch 33 and a diode bridge 31.

In the power supply circuit 10B, it is assumed that the control signal input to the control unit 16 is supplied from another circuit, for example, a microcomputer (not shown) present on the secondary side. The microcomputer is, for example, a microcomputer in an FA device including a load 90.

The control unit 16 inputs a signal from the microcomputer via the second insulation circuit 45. The control unit 16 controls the opening and closing of the first switch 15 based on the signal from the microcomputer. The configuration of the control unit 16 is the same as the configuration of the control unit 16 in the second embodiment. However, the resistance value R7 of the adjustment resistor 167 and the capacitance C3 of the adjustment capacitor 168 are different from those in the second embodiment.

The feedback circuit 43 inputs the output voltage of the secondary diode 41. The feedback circuit 43 transmits data corresponding to the output voltage of the secondary diode 41 to the switching control unit 34 via the first insulation circuit 44. The switching control unit 34 changes the switching frequency, modulation pulse width, etc. based on the data corresponding to the output voltage of the secondary diode 41.

The other configurations in embodiment 3 are the same as those in embodiment 1.

The switching control unit 34 controls the opening and closing of the second switch 35 based on a signal sent from the feedback circuit 43. The second switch 35 may be, for example, an n-channel MOSFET.

The transformer 39 is a transformer in which the polarity of the primary winding and the polarity of the secondary winding are opposite to each other. The secondary side diode 41 is a rectifier diode for rectifying the current flowing on the secondary side. The secondary side capacitor 42 is a smoothing capacitor for smoothing the voltage on the secondary side. The capacitance of the secondary side capacitor 42 is C5.

The second switch 35, the transformer 39, the secondary side diode 41, and the secondary side capacitor 42 constitute a flyback type DC/DC converter. When the second switch 35 is closed, a current flows through the primary side winding of the transformer 39, and energy is stored in the transformer 39. When the second switch 35 is opened, the energy stored in the transformer 39 is output from the secondary side winding through the secondary side diode 41.

The primary side diode 36, the primary side capacitor 37, and the primary side resistor 38 form a snubber circuit. The snubber circuit suppresses the surge voltage that occurs in the second switch 35 when the second switch 35 is switched. The capacitance of the primary side capacitor 37 is C4. The resistance value of the primary side resistor 38 is R9.

In general, the ripple voltage of the input capacitor C _IN of a power supply circuit is calculated by the following formula (1). The input capacitor C _IN corresponds to the smoothing capacitor of the power supply circuit 10B. As can be seen from formula (1), the ripple voltage ΔV _IN increases as the output current I _OUT increases. The output current I _OUT corresponds to the load current I _LOAD of the power supply circuit 10B. f _OSC is the switching frequency of the second switch 35.

Therefore, the larger the output current I _OUT is, the larger the capacitance of the input capacitor C _IN must be. In other words, the larger the output current I _OUT is, the larger the inrush current of the input capacitor C _IN is.

In the power supply circuit 10B of the third embodiment, the AC power supply 32 is connected between the first power supply line 11 and the second power supply line 12 via a diode bridge 31. In this way, the power supply circuit 10B is applicable to the AC power supply 32.

The power supply circuit 10B of the third embodiment can also be applied to a DC power supply, and the power supply circuit 10 of the first embodiment and the power supply circuit 10A of the second embodiment can both be applied to an AC power supply.

In addition, according to the power supply circuit 10B, the opening and closing of the first switch 15 is controlled based on a signal from the microcomputer. The microcomputer also serves as the microcomputer of the FA equipment, etc., so that the inrush current can be reduced while preventing the circuit from becoming large.

In the third embodiment, the first capacitor 13 and the second capacitor 14 are provided on the primary side, but they may be provided on the secondary side. In other words, the secondary side capacitor 42 may be divided into two parallel capacitors, and a switch may be connected in series to one of the divided capacitors. This switch corresponds to the first switch 15, and opening and closing is controlled by the control unit 16.

In addition, in the third embodiment, the control unit 16 may control the opening and closing of the first switch 15 based on a signal from a reset circuit (not shown) on the load 90 side. The reset circuit is a circuit for resetting the microcomputer to an initial state when the power supply is started. In this way, the opening and closing of the first switch 15 is controlled based on a signal from the reset circuit, so that the inrush current can be reliably reduced at startup and when recovering from a momentary power outage.

The first switch 15 and the second switch 35 are not limited to n-channel MOSFETs. The first switch 15 and the second switch 35 may be IGBTs (Insulated Gate Bipolar Transistors). The first switch 15 and the second switch 35 may be semiconductor switches made of materials such as SiC (Silicon Carbide) and GaN (Gallium Nitride).

In addition, in embodiment 3, the microcontroller may be a microcontroller in a home appliance.

In the first to third embodiments, the capacitance C1 of the first capacitor 13 is set to a value smaller than the capacitance C2 of the second capacitor 14, but the capacitance C1 may be set to a value equal to the capacitance C2. Furthermore, the capacitance C1 may be set to a value larger than the capacitance C2. In short, the values of the capacitances C1 and C2 may be any values that can sufficiently reduce the ripple.

Also, multiple series circuits, each consisting of a second capacitor 14 and a first switch 15, may be provided in parallel with each other, and the first switches 15 of each series circuit may be closed in sequence over time. This can further reduce the inrush current per unit time.

10, 10A, 10B power supply circuit, 11 first power supply line, 12 second power supply line, 13 first capacitor, 14 second capacitor, 15 first switch (switch), 16 control unit, 21 reverse connection prevention diode, 22 DC power supply (power supply), 31 diode bridge, 32 AC power supply (power supply), 90 load.

Claims (8)

a first capacitor connected between the first power supply line and the second power supply line;
A second capacitor,
a switch connected in series to the second capacitor; and a control unit that controls opening and closing of the switch,
the second capacitor and the switch are connected in parallel to the first capacitor between the first power supply line and the second power supply line,
the control unit keeps the switch open until a first time has elapsed since a power supply from a power source connected to the first power line and the second power line has started, and closes the switch after the first time has elapsed ;
The first time period is a time period required for an inrush current flowing through the first capacitor to become equal to or less than a first current.
Power supply circuit. a first capacitor connected between the first power supply line and the second power supply line;
A second capacitor,
a switch connected in series with the second capacitor; and
A control unit for controlling the opening and closing of the switch
Equipped with
the second capacitor and the switch are connected in parallel to the first capacitor between the first power supply line and the second power supply line,
the control unit keeps the switch open until a first time has elapsed since a power supply from a power source connected to the first power line and the second power line has started, and closes the switch after the first time has elapsed;
the switch is a transistor having a gate;
The voltage input to the gate increases over time,
the switch is closed when a voltage input to the gate is equal to or greater than a first voltage;
The first time period is a time period required for an inrush current flowing through the first capacitor to become equal to or less than a first current and for a voltage input to the gate to become equal to or greater than the first voltage .
Power supply circuit. The power supply circuit according to claim 1 , wherein the capacitance of the first capacitor is smaller than the capacitance of the second capacitor. 4. The power supply circuit according to claim 1, wherein the power supply is a DC power supply, a high-potential terminal of the DC power supply is connected to the first power supply line via a reverse connection prevention diode, and a low-potential terminal of the DC power supply is connected to the second power supply line. The power supply circuit according to claim 1 , wherein the power supply is an AC power supply and is connected between the first power supply line and the second power supply line via a diode bridge. 6. The power supply circuit according to claim 1, wherein the control unit generates a signal that controls opening and closing of the switch based on a voltage determined by a voltage division ratio between the first power supply line and the second power supply line. The power supply circuit according to claim 1 , wherein the control unit controls opening and closing of the switch based on a signal from a reset circuit. The power supply circuit according to claim 1 , wherein the control unit controls opening and closing of the switch based on a signal from a microcomputer.