JP2017123740A - Switching power supply - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply capable of avoiding an unstable operation even in a case where an AC input voltage is increased or in a case where a DC output voltage is reduced.SOLUTION: A switching power supply 1b converts an AC voltage into a DC voltage by a switching operation of a switching circuit 3b, and steps up the DC voltage. The switching power supply comprises: a relay contact 41a for on/off-controlling the supply of the AC voltage to the switching circuit 3b; a PTC element 42b connected between both ends of the relay contact 41a; and a controller 7 that on/off-controls the relay contact 41a. The controller 7 on/off-controls the relay contact 41a depending on a magnitude of a difference between a magnitude of the DC voltage stepped up by the switching circuit 3b, and an amplitude of the AC voltage at one end or the other end of the relay contact 41a.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a switching power supply including a switching circuit that converts an AC voltage into a DC voltage and boosts the voltage by a switching operation using a switching element.

  In recent years, inverters are frequently used in motor drive units of electrical appliances such as air conditioners and washing machines. The DC voltage input to the inverter is generated by, for example, rectifying an AC voltage from a commercial power supply with a rectifier and boosting the rectified DC voltage with a switching power supply. In order to improve the power factor for the commercial power supply, a PFC (Power Factor Correction) circuit is applied to the switching power supply.

  In general, a switching power supply using a PWM method is likely to become unstable when a pulse width is narrowed. For example, Patent Document 1 discloses that a PWM type flyback type switching circuit has an extremely narrow ON pulse width at a light load and a high input voltage, resulting in reduced efficiency and unstable operation. It is listed as an issue.

  Similarly, the boost type PFC circuit is likely to be unstable in operation at a high input voltage. For example, in Patent Document 2, when the input voltage from the AC power supply is high in a power factor improving switching regulator, the error signal of the error amplifier is smaller than the case where the input voltage is low, and is easily affected by noise. Therefore, it is described that the operation state becomes unstable. Non-Patent Document 1 describes that when the PFC circuit is at a high input voltage and a light load, the gain becomes too high and the operation becomes unstable, and the ripple voltage of the output voltage may increase.

  As described above, a step-up switching power supply including a switching regulator tends to become unstable when the voltage difference between the input voltage and the output voltage is small, and operates with this voltage difference appropriately increased. It is preferable to make it.

JP 2001-78450 A JP-A-5-219728

Nobuhito Sugawara, Yukihiro Yaguchi, Kazunori Matsumoto, “3rd Generation Critical Mode PFC Control IC“ FA1A00 Series ””, Fuji Electric Technical Report, 2014, vol87, no. 4, P263-267

  However, depending on the application of the switching power supply, there may be a restriction in securing the above voltage difference. For example, when a DC voltage boosted by a switching power supply is input to an inverter of an air conditioner, a high-frequency leakage current flows through the refrigerant between the motor winding of the compressor and the case in synchronization with the PWM output of the inverter. Therefore, the input voltage of the inverter that affects the amplitude of the PWM output of the inverter cannot be increased more than necessary. For this reason, when the voltage of the commercial power source input to the switching power source rises, the above voltage difference cannot be secured, and the operation of the switching power source may become unstable.

  The present invention has been made in view of such circumstances, and an object thereof is to avoid unstable operation even when the AC input voltage increases or the DC output voltage decreases. It is an object of the present invention to provide a switching power supply that can be used.

  A switching power supply according to an aspect of the present invention is a switching power supply that converts an AC voltage into a DC voltage by a switching operation by the switching circuit and boosts the voltage, and a switch that turns on and off the supply of the AC voltage to the switching circuit; A resistor connected between both ends, and a controller for controlling on / off of the switch according to the difference between the magnitude of the DC voltage boosted by the switching circuit and the amplitude of the AC voltage at one end or the other end of the switch It is characterized by providing.

  In the switching power supply according to an aspect of the present invention, the resistor may be a PTC element having a positive resistance temperature coefficient.

  In the switching power supply according to an aspect of the present invention, the control unit turns off the switch when the difference is smaller than a first voltage, and after turning off the switch, the difference exceeds the first voltage. When the voltage is larger than the voltage, the switch may be turned on.

  In the switching power supply according to one aspect of the present invention, a series circuit of a second resistor and a second switch is connected in parallel to the resistor, and the control unit has the difference when the switch is turned off. The second switch may be turned off according to the difference within a range smaller than the second voltage.

  In the switching power supply according to one aspect of the present invention, a parallel circuit of a third resistor and a third switch is connected in series to the resistor, and the control unit has the difference when the switch is turned off. The third switch may be turned off according to the difference within a range smaller than the second voltage.

  A switching power supply according to an aspect of the present invention includes a second switching circuit that steps down a DC voltage from the switching circuit, a fourth switch that turns on and off the supply of the DC voltage to the second switching circuit, When the DC voltage from the switching circuit is lower than a predetermined threshold, a drive circuit that turns off the fourth switch may be provided.

  In the switching power supply according to one aspect of the present invention, the drive circuit includes a voltage dividing circuit that divides a DC voltage from the switching circuit, and the fourth switch is turned on based on the divided voltage of the voltage dividing circuit. It may be turned off.

  In the switching power supply according to one aspect of the present invention, the fourth switch may be a relay contact of a relay that is driven by applying the divided voltage to a relay coil.

According to the above, the switch is switched from on to off while the difference between the magnitude of the DC voltage output from the switching circuit and the amplitude of the AC voltage from the outside changes from large to small, and the input side of the switching circuit A resistor is inserted into the switching circuit, thereby reducing the AC voltage input to the switching circuit.
Therefore, even when the AC input voltage increases or the DC output voltage decreases, it is possible to ensure the necessary voltage difference between the input and output of the switching circuit and avoid unstable operation. Become.

It is a circuit diagram which shows the structure of the switching power supply which concerns on Embodiment 1 of this invention. It is a circuit diagram which shows the structure of the switching power supply which concerns on Embodiment 2 of this invention. It is a flowchart which shows the process sequence of CPU which controls ON / OFF of a relay contact with the switching power supply which concerns on Embodiment 2 of this invention. It is a flowchart which shows the process sequence of CPU which concerns on the subroutine of a voltage difference calculation. It is a circuit diagram which shows the structure of the switching power supply which concerns on Embodiment 3 of this invention. It is a flowchart which shows the process sequence of CPU which controls ON / OFF of a relay contact with the switching power supply which concerns on Embodiment 3 of this invention. It is a circuit diagram which shows the structure of the switching power supply which concerns on Embodiment 4 of this invention. It is a block diagram which shows the structure of the switching power supply which concerns on Embodiment 5 of this invention. It is a block diagram which shows the structure of the switching power supply which concerns on Embodiment 6 of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.
(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 1 of the present invention. In the figure, reference numeral 1a denotes a switching power supply. The switching power supply 1a includes a switching circuit 3a that converts an AC voltage from the AC power supply 2 into a DC voltage and boosts the voltage, and a relay contact that turns on and off the supply of the AC voltage to the switching circuit 3a ( A relay 41 having a switch 41a) and a resistor 42a connected in parallel between both ends of the relay contact 41a. However, a power switch for opening and closing the connection between the AC power supply 2 and the switching power supply 1a is not shown.

  The switching power supply 1a also includes diodes 51 and 52 that rectify the AC voltage of the AC power supply 2, a peak hold circuit 53 that holds the amplitude (crest value) of the pulsating voltage rectified by the diodes 51 and 52, and a relay 41. The control part 6 which controls the drive of this is provided. When the control unit 6 controls the drive of the relay 41, the ON / OFF of the relay contact 41a is indirectly controlled. The switching circuit 3a is a so-called semi-bridgeless PFC circuit. A DC voltage that is an output voltage of the switching circuit 3 a is supplied to an external inverter circuit 21 that drives the AC motor 22.

  The switching circuit 3a has inductors L1 and L2 to which an AC voltage supplied via a parallel circuit of a resistor 42a and a relay contact 41 is applied to one end, and a drain connected to the other end of each of the inductors L1 and L2. N-channel MOSFETs (Metal Oxide Semiconductor Field Effect Transistors: hereinafter referred to simply as FETs) Q1a, Q2a, diodes D1, D2 having anodes connected to the other ends of the inductors L1, L2, and FETs Q1a, Q2a, respectively. And a PFC control circuit IC1a for controlling on / off.

  One end of each of the inductors L1 and L2 is connected to the cathodes of the diodes D3 and D4 and the anodes of the diodes D5 and D6 that rectify the AC voltage input to the switching circuit 3a. The anodes of the diodes D3 and D4 are connected to the ground potential in order to link the potential of the AC voltage of the AC power supply 2 and the ground potential. The pulsating voltage rectified by the diodes D5 and D6 is divided by a series circuit of resistors R3 and R4 and input to the PFC control circuit IC1a.

  The gates of the FETs Q1a and Q2a are connected to the PFC control circuit IC1a. The sources of the FETs Q1a and Q2a are connected to the other ends of the resistors R1 and R2 whose one ends are connected to the ground potential and the PFC control circuit IC1a. The resistors R1 and R2 are for detecting the drain currents of the FETs Q1a and Q2a, respectively.

  The cathodes of the diodes D1 and D2 are connected to the smoothing capacitor C1, and the voltage across the smoothing capacitor C1 becomes the output voltage of the switching circuit 3a, that is, the output voltage of the switching power supply 1a. The output voltage of the switching circuit 3a is divided by the voltage dividing circuit of the resistors R5 and R6 and input to the PFC control circuit IC1a. Since the on / off control of the FETs Q1a and Q2a by the PFC control circuit IC1a, that is, PFC control is known per se, its description is omitted.

  In the relay 41, the relay contact 41a is a normally open contact (NO = Normally Open Contact), and one end of the relay coil 41b is connected to the 12V power source and the cathode of the surge absorbing diode 41c. The other end of the relay coil 41b is connected to the anode of the diode 41c and the collector of an NPN transistor 41d with a common emitter. When the transistor 41d is turned on, the relay coil 41b is excited (that is, the relay 41 is driven), the relay contact 41a is turned on, and both ends of the resistor 42a are short-circuited.

  The control unit 6 outputs a voltage proportional to the difference between the magnitude of the voltage from the peak hold circuit 53, that is, the amplitude of the AC voltage from the AC power supply 2, and the magnitude of the DC voltage from the switching circuit 3a. 61 and a comparator 66 that compares the output voltage of the differential amplifier 61 and the voltage of the reference voltage source 67. When the output voltage of the comparator 66 becomes high level, a base current flows to the transistor 41d via the resistor 41e, and the transistor 41d is turned on.

  In the differential amplifier 61, a resistor 62 is connected between the inverting input terminal and the output terminal, and the voltage from the peak hold circuit 53 is applied to the inverting input terminal via the resistor 63. In the differential amplifier 61, a resistor 64 is further connected between the non-inverting input terminal and the ground potential, and the output voltage of the switching circuit 3a is applied to the non-inverting input terminal via the resistor 65. Here, for simplicity, the resistance values of the resistors 64 and 65 are the same as the resistance values of the resistors 62 and 63, respectively. Thereby, the differential amplifier 61 calculates the difference between the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage from the AC power supply 2 as “(resistance value of the resistors 62, 4) / (resistors 63, A resistance value of 65) "is amplified. Usually, this magnification is sufficiently smaller than 1.

  In the comparator 66, a resistor 68 is connected between the non-inverting input terminal and the output terminal, and the voltage from the differential amplifier 61 is applied to the non-inverting input terminal via the resistor 69. With this configuration, the comparator 66 has a hysteresis characteristic. Here, for the sake of simplicity, the resistance value of the resistor 69 is set to the same value as the resistance value of the resistor 68. In this case, the hysteresis width in the comparator 66, that is, the voltage difference between the upper threshold value and the lower threshold value is represented by “(Vh−Vl) / (resistance value of the resistors 68 and 69)”. However, Vh and Vl are output voltages on the high side and low side of the comparator 66, respectively. The voltage difference between the upper threshold value or the lower threshold value in the comparator 66 and the voltage of the reference voltage source 67 is half of the hysteresis width.

  Here, it is assumed that the switching circuit 3a operates stably when the magnitude of the DC voltage from the switching circuit 3a is larger than the amplitude of the AC voltage input to the switching circuit 3a by the first voltage or more. According to this assumption, when the magnitude of the DC voltage from the switching circuit 3a is larger than the amplitude of the AC voltage from the AC power supply 2 by the first voltage (or the second voltage), the output voltage of the differential amplifier 61 is the comparator. It is assumed that the threshold value is adjusted to match the lower threshold value (or the upper threshold value) of 66. The second voltage is a voltage exceeding the first voltage.

  In the above configuration, when the power switch (not shown) is turned on and the AC power supply 2 is connected to the switching power supply 1a, the relay contact 41a is off until the relay 41 is driven. A resistor 42a is inserted into the resistor 42a. After that, when a power supply voltage (not shown) (for example, +5 V) is supplied to the control unit 6 and the PFC control circuit IC1a and PFC control is started, the magnitude of the DC voltage from the switching circuit 3a is the AC voltage from the AC power supply 2. The output voltage of the differential amplifier 61 is lower than the lower threshold value in the comparator 66 until the voltage amplitude becomes larger than the first voltage. Therefore, the output voltage of the comparator 66 is at a low level, and since the transistor 41d is off, the relay 41 is not driven and the relay contact 41a is kept off.

  Thereafter, the magnitude of the DC voltage from the switching circuit 3a becomes higher than the amplitude of the AC voltage from the AC power supply 2, and the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage from the AC power supply 2 are Is greater than the second voltage, the output voltage of the differential amplifier 61 exceeds the upper threshold value of the comparator 66. As a result, the output voltage of the comparator 66 becomes high level and the transistor 41d is turned on, so that the relay 41 is driven and the resistor 42a is bypassed by the relay contact 41a. The state where the insertion of the resistor 42a is released in this way is defined as a reference state of the switching power supply 1a.

  When the difference between the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage from the AC power supply 2 becomes smaller than the first voltage in the switching power supply 1a in the reference state, the output voltage of the differential amplifier 61 Falls below the lower threshold value of the comparator 66, the output voltage of the comparator 66 becomes low level. As a result, the transistor 41d is turned off, the drive of the relay 41 is released, and the bypass of the resistor 42a by the relay contact 41a is released (that is, the resistor 42a is inserted). By inserting the resistor 42a on the input side of the switching circuit 3a, the magnitude of the DC voltage from the switching circuit 3a becomes greater than the amplitude of the AC voltage input to the switching circuit 3a by at least the first voltage, The switching circuit 3a operates stably.

  After that, when the difference between the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage from the AC power supply 2 becomes larger than the second voltage, the output voltage of the differential amplifier 61 becomes the upper threshold value of the comparator 66. The output voltage of the comparator 66 becomes high level. Thereby, the transistor 41d is turned on to drive the relay 41, and the resistor 42a is bypassed by the relay contact 41a (that is, the insertion of the resistor 42a is released). Even when the insertion of the resistor 42a is released and the reference state is restored, the difference between the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage input to the switching circuit 3a is greater than the first voltage. Great probability. Therefore, the driving of the relay 41 is prevented from being repeated in a short period.

  In the above-described first embodiment, the amplitude of the pulsating voltage rectified by the diodes 51 and 52 in the peak hold circuit 53 (that is, the AC voltage on the AC power supply 2 side (one end side) of the relay contact 41a). The amplitude of the AC voltage on the switching circuit 3a side (the other end side) of the relay contact 41a may be held. However, in this case, when the relay contact 41a is controlled to be turned off and the resistor 42a is inserted on the input side of the switching circuit 3a, the amplitude of the AC voltage input to the differential amplifier 61 is a voltage drop in the resistor 42a. Note that it drops by minutes. That is, since the difference between the magnitude of the DC voltage from the switching circuit 3a and the amplitude of the AC voltage on the switching circuit 3a side of the relay contact 41a increases by the voltage drop in the resistor 42a, the relay contact 41a is controlled to be off. It is necessary to increase the hysteresis width in the comparator 66 so that the output voltage of the differential amplifier 61 does not exceed the upper threshold value of the comparator 66 immediately after.

(Embodiment 2)
In the first embodiment, the switching circuit 3a directly switches the AC voltage from the AC power source 2 to convert it into a DC voltage, and the control unit 6 configured by a hardware circuit controls the on / off of the relay contact 41a. Met. In contrast, in the second embodiment, the switching circuit 3b switches the pulsating voltage rectified by the diode bridge DB1 to convert it into a DC voltage, and the control unit 7 having the CPU 71 controls the on / off of the relay contact 41a. It is. Below, it demonstrates centering on a different point from Embodiment 1, the same code | symbol is attached | subjected to the location corresponding to Embodiment 1, and the description is simplified or abbreviate | omitted.

  FIG. 2 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 2 of the present invention. In the figure, reference numeral 1b denotes a switching power source. The switching power source 1b converts the AC voltage from the AC power source 2 into a DC voltage and boosts it, and a relay contact 41a that turns on and off the supply of the AC voltage to the switching circuit 3b. And a PTC element (corresponding to a resistor) 42b having a positive resistance temperature characteristic connected in parallel between both ends of the relay contact 41a. The switching circuit 3b is an interleaved PFC circuit, but may be a non-interleaved PFC circuit or a general boost type switching circuit that does not perform PFC control. In the latter case, a pulsating voltage from a diode bridge DB1 described later is smoothed by a capacitor.

  The switching power supply 1b also includes a peak hold circuit 53 that holds the amplitude of the pulsating voltage rectified by the diode bridge DB1, a series circuit of resistors 54 and 55 that divides the voltage from the peak hold circuit 53, and a switching circuit. A series circuit of resistors 56 and 57 that divide the output voltage of 3b and a control unit 7 that controls driving of the relay 41 are provided.

  In the switching circuit 3b, a diode bridge DB1 that rectifies an AC voltage supplied from the AC power supply 2 through a parallel circuit of the relay contact 41a and the PTC element 42b, and a pulsating voltage from the diode bridge DB1 are applied to one end of each. Inductors L1 and L2, IGBTs (Insulated Gate Bipolar Transistors) Q1b and Q2b having collectors connected to the other ends of the inductors L1 and L2, and diodes D1 and D1 having anodes connected to the other ends of the inductors L1 and L2, respectively. D2 and a PFC control circuit IC1b for controlling on / off of each of the IGBTs Q1b and Q2b.

  The pulsating voltage from the diode bridge DB1 is divided by a series circuit of resistors R3 and R4 and input to the PFC control circuit IC1b. The gates of the IGBTs Q1b and Q21b are connected to the PFC control circuit IC1b. The emitters of the IGBTs Q1b and Q21b are connected to the other ends of the resistors R1 and R2 whose one ends are connected to the ground potential and the PFC control circuit IC1b. Resistors R1 and R2 are for detecting the collector currents of IGBTs Q1b and Q2b, respectively.

  The cathodes of the diodes D1 and D2 are connected to the smoothing capacitor C1, and the voltage across the smoothing capacitor C1 becomes the output voltage of the switching circuit 3b, that is, the output voltage of the switching power supply 1b. The output voltage of the switching circuit 3b is divided by the voltage dividing circuit of the resistors R5 and R6 and input to the PFC control circuit IC1b. The on / off control of the IGBTs Q1b and Q2b by the PFC control circuit IC1b, that is, the PFC control by the interleave method is known per se, and the description thereof is omitted.

  The control unit 7 is a microcomputer having a CPU (Central Processing Unit) 71. The CPU 71 includes a ROM (Read Only Memory) 72 for storing information such as programs, a RAM (Random Access Memory) 73 for storing temporarily generated information, a timer 74 for measuring time, and an input / output for inputting / outputting signals. A port (I / O) 75 and an A / D converter 76 for converting an analog voltage into a digital value are connected to each other by a bus. One port in the input / output port 75 is connected to the base of the transistor 41d through the resistor 41e.

  The A / D converter 76 generates a pulsating current from the diode bridge DB1 based on the voltage divided by the series circuit of the resistors 54 and 55 and the voltage divided by the series circuit of the resistors 56 and 57, respectively. The amplitude of the voltage and the magnitude of the DC voltage from the switching circuit 3b are detected as digital values. Since the amplitude of the pulsating voltage from the diode bridge DB1 is equivalent to the amplitude of the AC voltage input to the switching circuit 3b if the voltage drop in the diode bridge DB1 is ignored, the A / D converter 76 includes the switching circuit. It can be said that the magnitude of the DC voltage output from 3b and the amplitude of the AC voltage input to the switching circuit 3b are detected.

  In the above configuration, when the power switch (not shown) is turned on and the AC power supply 2 is connected to the switching power supply 1b, the relay contact 41a is off until the relay 41 is driven. The PTC element 42b is inserted into the. Since the resistance value of the PTC element 42b increases as the temperature rises due to Joule heat, the PTC element 42b autonomously limits the alternating current flowing into the switching circuit 3b. Thereafter, a power supply voltage (not shown) (for example, + 5V) is supplied to the PFC control circuit IC1b and the control unit 7 to start PFC control, and the CPU 71 in the control unit 7 starts to operate.

  In the initialization process, the CPU 71 clears a later-described resistance flag to 0, and outputs a low level signal from one port in the input / output port 75. In this case, since the transistor 41d is kept off and the relay 41 is not driven, the relay contact 41a is kept off. That is, the PTC element 42b is continuously inserted on the input side of the switching circuit 3b.

  Thereafter, when an appropriate time elapses and the output voltage of the switching circuit 3 b reaches the target voltage, the CPU 71 outputs a high level signal from one port of the input / output port 75. Thereby, the transistor 41d is turned on, the relay 41 is driven, and the PTC element 42b is bypassed by the relay contact 41a. Thereafter, the CPU 71 detects the magnitude of the DC voltage output from the switching circuit 3b and the amplitude of the AC voltage input to the switching circuit 3b in time series by the A / D converter 76, and the difference between the detection results. ON / OFF of relay contact 41a is controlled based on the size of

Below, operation | movement of the control part 7 mentioned above is demonstrated using the flowchart which shows it.
FIG. 3 is a flowchart showing a processing procedure of the CPU 71 for controlling on / off of the relay contact 41a by the switching power supply 1b according to the second embodiment of the present invention. FIG. 4 shows a processing procedure of the CPU 71 according to a voltage difference calculation subroutine. It is a flowchart which shows. The process shown in FIG. 3 is started at a constant cycle, for example. The start cycle is preferably longer than the sum of the response time of the relay 41 and the response time between the input and output of the switching circuit 3b. The resistance flag in the figure indicates that the PTC element 42b is inserted on the input side of the switching circuit 3b, and its initial value is zero. In the following, it is assumed that the relay 41 is in a driven state.

  When the process of FIG. 3 is started, the CPU 71 calls a subroutine related to voltage difference calculation (S11). When returning from the subroutine, the CPU 71 determines whether or not the resistance flag is set to 1, that is, whether or not the PTC element 42b is inserted on the input side of the switching circuit 3b (S12). When the resistance flag is not set to 1 (S12: NO), the CPU 71 determines whether or not the voltage difference as a return value of the subroutine is smaller than the first voltage (S13).

  When the voltage difference is smaller than the first voltage (S13: YES), the CPU 71 releases the drive of the relay 41 and controls the relay contact 41a to be turned off (S14), and then sets the resistance flag to 1 (S15). The process of FIG. 3 is terminated. On the other hand, when the voltage difference is not smaller than the first voltage (S13: NO), the CPU 71 ends the process of FIG. 3 without executing any special process.

  If the resistance flag is set to 1 in step S12 (S12: YES), the CPU 71 determines whether or not the voltage difference that is the return value of the subroutine is larger than the second voltage (S16). When the voltage difference is larger than the second voltage (S16: YES), the CPU 71 drives the relay 41 to turn on the relay contact 41a (S17), and then clears the resistance flag to 0 (S18). Terminate the process. On the other hand, when the voltage difference is not greater than the second voltage (S16: NO), the CPU 71 ends the process of FIG. 3 without executing any special process.

  Turning to FIG. 4, when a subroutine relating to voltage difference calculation is called, the CPU 71 causes the A / D converter 76 to detect the amplitude of the pulsating voltage from the diode bridge DB1, that is, the AC voltage input to the switching circuit 3b. Amplitude (denoted as input voltage in the figure) is detected (S21). Thereafter, the CPU 71 detects the magnitude of the DC voltage (denoted as output voltage in the figure) from the switching circuit 3b by the A / D converter 76 (S22), and determines the amplitude of the AC voltage from the magnitude of the DC voltage. The voltage difference is calculated by subtraction (S23), and the process returns to the called routine. The return value in this case is a voltage difference.

  In the second embodiment, the peak hold circuit 53 holds the amplitude of the pulsating voltage from the diode bridge DB1 (that is, the amplitude of the AC voltage on the switching circuit 3b side of the relay contact 41a). Similarly to the first embodiment, the amplitude of the AC voltage on the AC power supply 2 side of the relay contact 41a may be maintained. Alternatively, the effective value of the AC voltage on the AC power supply 2 side may be detected by hardware, and the detected effective value may be multiplied by √2 by processing by the CPU 71 to calculate the AC voltage amplitude.

  On the other hand, in the second embodiment, when the relay contact 41a is controlled to be turned off and the PTC element 42b is inserted on the input side of the switching circuit 3b, the amplitude of the pulsating voltage from the diode bridge DB1 is PTC element. Note that it drops by the voltage drop at 42b. That is, since the difference between the magnitude of the DC voltage from the switching circuit 3b and the amplitude of the pulsating voltage from the diode bridge DB1 increases by the voltage drop in the PTC element 42b, immediately after the relay contact 41a is controlled to be turned off, The second voltage needs to be sufficiently larger than the first voltage so that the voltage difference is not determined to be larger than the second voltage.

As described above, according to the first embodiment (or 2), the AC voltage supplied to the switching circuit 3a (or 3b) is switched through the parallel circuit of the resistor 42a (or PTC element 42b) and the relay contact 41a. It is converted into a DC voltage and boosted by operation. The controller 6 (or 7) is configured so that the difference between the magnitude of the DC voltage boosted by the switching circuit 3a (or 3b) and the amplitude of the AC voltage at one end or the other end of the parallel circuit is greater than the first voltage. The relay contact 41a is controlled from on to off while changing to a small state, and the relay contact 41a is controlled from off to on while changing from a state smaller than the second voltage to a large state.
As a result, the relay contact 41a is switched from on to off while the difference between the magnitude of the DC voltage output from the switching circuit 3a (or 3b) and the amplitude of the AC voltage from the AC power supply 2 changes from large to small. Thus, the resistor 42a (or PTC element 42b) is inserted on the input side of the switching circuit 3a (or 3b), whereby the AC voltage input to the switching circuit 3a (or 3b) is lowered.
Therefore, even when the AC input voltage increases or the DC output voltage decreases, the necessary voltage difference is secured between the input and output of the switching circuit 3a (or 3b) to avoid unstable operation. It becomes possible to do.

Further, according to the first embodiment (or 2), when the above-described difference is smaller than the predetermined first voltage, the control unit 6 (or 7) controls the relay contact 41a to be turned off and the resistor 42a (or PTC). The bypass of the element 42b) is released, and then the control unit 6 (or 7) controls the relay contact 41a to be turned on when the above-mentioned difference rises from the first voltage and becomes larger than the predetermined second voltage. Bypass the resistor 42a (or the PTC element 42b).
Therefore, it becomes possible to insert the resistor 42a (or PTC element 42b) on the input side of the switching circuit 3a (or 3b) when the above-described difference becomes smaller than the predetermined first voltage. And when the above-mentioned difference becomes larger than a 2nd voltage, it becomes possible to cancel | release insertion of the resistor 42a (or PTC element 42b).

  Furthermore, according to the second embodiment, since the resistor connected in parallel to the relay contact 41a is the PTC element 42b having a positive resistance temperature coefficient, the relay contact 41a is turned off when the switching circuit 3b rises. By configuring, it becomes possible to autonomously limit the input current to the switching circuit 3b.

(Embodiment 3)
In the second embodiment, one resistor (PTC element 42b) is connected in parallel to the relay contact 41a, whereas in the third embodiment, the resistor 42c and the resistor 43 are connected to the relay contact 41a. And a series circuit of relay contacts 44a are connected in parallel. Below, it demonstrates centering on a different point from Embodiment 2, the same code | symbol is attached | subjected to the location corresponding to Embodiment 1 and 2, and the description is simplified or abbreviate | omitted.

  FIG. 5 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 3 of the present invention. In the figure, reference numeral 1c denotes a switching power source. The switching power source 1c converts the AC voltage from the AC power source 2 into a DC voltage and boosts it, and a relay contact 41a that turns on and off the supply of the AC voltage to the switching circuit 3b. A relay 41 having a relay contact 41a, a resistor 42c connected in parallel between both ends of the relay contact 41a, a relay 44 further connected in parallel to the relay contact 41a, and having a relay contact (corresponding to a second switch) 44a; And a series circuit including a resistor (corresponding to a second resistor) 43. The number of the series circuits connected in parallel to the relay contact 41a is not limited to 1, and may be 2 or more. The switching power supply 1 c also includes a peak hold circuit 53, a series circuit of resistors 54 and 55, a series circuit of resistors 56 and 57, and a control unit 7.

  In the relay 44, the relay contact 44a is a normally closed contact (NO = Normally Closed Contact), and one end of the relay coil 44b is connected to the 12V power source and the cathode of the surge absorbing diode 44c. The other end of the relay coil 44b is connected to the anode of a diode 44c and the collector of an NPN transistor 44d with a common emitter. The base of the transistor 44d is connected to another port in the input / output port 75 through the resistor 44e. When a low level signal is applied to the resistor 44e from another port in the input / output port 75, the transistor 44d is turned off and the excitation of the relay coil 44b is released (ie, the drive of the relay 44 is released). Thereby, the relay contact 44a is turned on, and the resistor 43 is connected in parallel to the resistor 42c.

  In the above configuration, when a power switch (not shown) is turned on and the AC power supply 2 is connected to the switching power supply 1c, the relay contact 41a is off and the relay contact 44a is on until the relays 41 and 44 are driven. Therefore, a parallel circuit of the resistor 42c and the resistor 43 is inserted on the input side of the switching circuit 3b. Thereafter, a power supply voltage (not shown) (for example, + 5V) is supplied to the PFC control circuit IC1b and the control unit 7 to start PFC control, and the CPU 71 in the control unit 7 starts to operate.

  In the initialization process, the CPU 71 clears a resistance flag, which will be described later, to 0, and outputs a low level signal from one port and the other port in the input / output port 75. In this case, since the transistors 41d and 44d are kept off and the relays 41 and 44 are not driven, the relay contacts 41a and 44a are kept off and on, respectively. That is, the parallel circuit of the resistors 42c and 43 continues to be inserted on the input side of the switching circuit 3b.

  Thereafter, when an appropriate time elapses and the output voltage of the switching circuit 3 b reaches the target voltage, the CPU 71 outputs a high level signal from one port of the input / output port 75. Thereby, the transistor 41d is turned on, the relay 41 is driven, and the parallel circuit of the resistors 42c and 43 is bypassed by the relay contact 41a. Thereafter, the CPU 71 detects the magnitude of the DC voltage output from the switching circuit 3b and the amplitude of the AC voltage input to the switching circuit 3b in time series by the A / D converter 76, and the difference between the detection results. The relay contacts 41a and 44a are controlled to be turned on / off based on the size of the.

Below, operation | movement of the control part 7 mentioned above is demonstrated using the flowchart which shows it.
FIG. 6 is a flowchart showing a processing procedure of the CPU 71 for controlling on / off of the relay contacts 41a and 44a in the switching power supply 1c according to the third embodiment of the present invention. The process shown in FIG. 6 is started at a constant cycle, for example. The start cycle is preferably longer than the sum of the response time of the relays 41 and 44 and the response time between the input and output of the switching circuit 3b.

  The resistance flag in the figure indicates that at least the resistor 42c is inserted on the input side of the switching circuit 3b, and the initial value is zero. The relay 41 is in a driven state, and the relay 44 is not driven. Therefore, both relay contacts 41a and 44a are on. In the figure, N represents the number of series circuits including the relay 44 and the resistor 43, and m represents the number of relay contacts 44a that are controlled to be off among the relay contacts 44a included in the N series circuits. . The initial value of m is 0. The N resistors 43 included in the N series circuits preferably have different resistance values.

  The processing from step S31 to S38 shown in FIG. 6 is the same as the processing from step S11 to S18 shown in FIG. 3 of the first embodiment, except that the branch destination in step S36 is different. A part of the description is omitted. In FIG. 6, the relay contact 44a is referred to as a second relay contact.

  When the processing of FIG. 6 is activated, the CPU 71 calls a subroutine relating to voltage difference calculation (S31), determines whether the resistance flag is set to 1 (S32), and according to the determination result. It is determined whether the voltage difference between the return values is smaller than the first voltage (S33) or whether the voltage difference is larger than the second voltage (S36).

  When the resistance flag is not set to 1 (S32: NO) and the voltage difference is smaller than the first voltage (S33: YES), the CPU 71 releases the drive of the relay 41 and controls the relay contact 41a to be turned off. (S34). Thereby, the parallel circuit of the resistors 42c and 43 is inserted on the input side of the switching circuit 3b.

  On the other hand, when the resistance flag is set to 1 (S32: YES) and the voltage difference is not larger than the second voltage (S36: NO), the CPU 71 determines that the voltage difference of the return value of the subroutine is again from the first voltage. It is determined whether or not it has become smaller (S41). When the voltage difference is not smaller than the first voltage (S41: NO), the CPU 71 ends the process of FIG. 6 without controlling the relay contact 44a to be turned off.

  When the voltage difference between the return values becomes smaller than the first voltage again (S41: YES), the CPU 71 determines whether or not m is N in order to determine whether or not all the relay contacts 44a are controlled to be turned off. Is determined (S42). When m is N (S42: YES), that is, when all the relay contacts 44a are already controlled to be turned off, the CPU 71 ends the process of FIG. 6 as it is.

  On the other hand, when m is not N (S42: NO), the CPU 71 increments m by 1 (S43), and then controls the m-th relay contact 44a (second relay contact) to be off ( S44) The processing of FIG. By the process of step S44, the number of resistors 43 connected in parallel to the resistor 42c is reduced by one, the combined resistance of the resistors inserted on the input side of the switching circuit 3b is increased, and input to the switching circuit 3b. The AC voltage generated is further reduced.

  If the voltage difference between the return values is larger than the second voltage in step S36 (S36: YES), the CPU 71 controls the relay contact 41a to be on (S37), and then clears the resistance flag to 0 (S38). Thereafter, the CPU 71 releases the drive of all the relays 44 and controls all the relay contacts 44 (second relay contacts) to be turned on (S39), initializes m to 0 (S40), and performs the process of FIG. Exit. By the processing from step S37 to S40, the relay contact 41 and all the relay contacts 44a return to the state when the processing of FIG. 6 is first activated.

  In the above-described third embodiment, the peak hold circuit 53 holds the amplitude of the pulsating voltage from the diode bridge DB1 (that is, the amplitude of the AC voltage on the switching circuit 3b side of the relay contact 41a). Similarly to the first embodiment, the amplitude of the AC voltage on the AC power supply 2 side of the relay contact 41a may be maintained. In this case, after the relay contact 41a is controlled to be turned off, the output current from the switching circuit 3b is detected, or the rotational speed of the AC motor 22 is detected, and further off based on the detected output current or rotational speed. The number of relay contacts 44a to be controlled can be determined. Based on the difference between the magnitude of the DC voltage from the switching circuit 3b and the amplitude of the AC voltage on the AC power supply 2 side of the relay contact 41a, the number of relay contacts 44a to be further turned off may be determined.

  In contrast, in the third embodiment, when the relay contact 41a is controlled to be turned off and a parallel circuit including the resistor 42c and all the resistors 43 is inserted on the input side of the switching circuit 3b, the diode bridge DB1. Note that the amplitude of the pulsating voltage from is reduced by the voltage drop in the parallel circuit. That is, since the difference between the magnitude of the DC voltage from the switching circuit 3b and the amplitude of the pulsating voltage from the diode bridge DB1 increases by the voltage drop in the parallel circuit, immediately after the relay contact 41a is controlled to be turned off, The second voltage needs to be sufficiently larger than the first voltage so that the voltage difference is not determined to be larger than the second voltage.

As described above, according to the third embodiment, when the relay contact 41a is controlled to be turned off due to the difference being smaller than the first voltage, one or more series circuits of the resistor 43 and the relay contact 44a are provided. For the parallel circuit of the circuit connected in parallel and the resistor 42c, the relay contact 44a is sequentially turned off in accordance with the above difference within a range where the above difference is smaller than the second voltage.
Accordingly, by configuring the relay contact 44a to be on when the relay contact 41a is controlled to be turned off, the relay contact 41a is first controlled to be turned off in response to the decrease in the difference, and then the relay contact 44a is turned on. Since it is controlled to be off, the parallel resistance of the resistor 42c and the one or more resistors 43 can be increased stepwise.

(Embodiment 4)
In the third embodiment, a circuit in which one or a plurality of series circuits of the resistor 43 and the relay contact 44a are connected in parallel is connected in parallel to the resistor 42c, whereas in the fourth embodiment, the resistor 45 and In this configuration, one or more parallel circuits of relay contacts 46a are connected in series to a resistor 42d. Below, it demonstrates centering on a different point from Embodiment 3, the same code | symbol is attached | subjected to the location corresponding to Embodiment 1 to 3, and the description is simplified or abbreviate | omitted.

  FIG. 7 is a circuit diagram showing a configuration of a switching power supply according to Embodiment 4 of the present invention. In the figure, 1d is a switching power supply, and the switching power supply 1d is connected in parallel to the switching circuit 3b, a relay 41 having a relay contact 41a, and the relay contact 41a, and a relay contact (corresponding to a third switch) 46a. A parallel circuit including a relay 46 and a resistor (corresponding to a third resistor) 45 and a series circuit of a resistor 42d. The number of the parallel circuits connected in series to the resistor 42d is not limited to 1 and may be 2 or more. The switching power supply 1d also includes a peak hold circuit 53, a series circuit of resistors 54 and 55, a series circuit of resistors 56 and 57, and a control unit 7.

  In the relay 46, the relay contact 46a is a normally closed contact, and one end of the relay coil 46b is connected to the 12V power source and the cathode of the surge absorbing diode 46c. The other end of the relay coil 46b is connected to the anode of a diode 46c and the collector of an NPN transistor 46d with a common emitter. The base of the transistor 46d is connected to the other port in the input / output port 75 through the resistor 46e. When a low level signal is applied to the resistor 46e from another port in the input / output port 75, the transistor 46d is turned off and the excitation of the relay coil 46b is released (ie, the drive of the relay 46 is released). As a result, the relay contact 46a is turned on and the resistor 45 is bypassed.

  In the above configuration, when a power switch (not shown) is turned on and the AC power supply 2 is connected to the switching power supply 1d, the relay contact 41a is off and the relay contact 46a is on until the relays 41 and 46 are driven. Therefore, the resistor 42d is inserted on the input side of the switching circuit 3b. Thereafter, a power supply voltage (not shown) (for example, + 5V) is supplied to the PFC control circuit IC1b and the control unit 7 to start PFC control, and the CPU 71 in the control unit 7 starts to operate.

  In the initialization process, the CPU 71 clears the resistance flag to 0, and outputs a low level signal from one port and the other port in the input / output port 75. In this case, since the transistors 41d and 46d are kept off and the relays 41 and 46 are not driven, the relay contacts 41a and 44a are kept off and on, respectively. That is, the resistor 42d continues to be inserted on the input side of the switching circuit 3b.

  Thereafter, when an appropriate time elapses and the output voltage of the switching circuit 3 b reaches the target voltage, the CPU 71 outputs a high level signal from one port of the input / output port 75. Thereby, the transistor 41d is turned on, the relay 41 is driven, and the resistor 42d is bypassed by the relay contact 41a. Thereafter, the CPU 71 detects the magnitude of the DC voltage output from the switching circuit 3b and the amplitude of the AC voltage input to the switching circuit 3b in time series by the A / D converter 76, and the difference between the detection results. The relay contacts 41a and 44a are controlled to be turned on / off based on the size of the.

  Since the flowchart showing the operation of the control unit 7 described above is formally similar to that shown in FIG. 6 in the third embodiment, only the main points will be described with reference to FIG. The second relay contact is read as the third relay contact. Here, N represents the number of parallel circuits including the relay 46 and the resistor 45, and m represents the number of relay contacts 46a that are controlled to be off among the relay contacts 46a included in the N parallel circuits. . The initial value of m is 0. The N resistors 45 included in the N series circuits preferably have different resistance values.

  When the processing of FIG. 6 is activated, the CPU 71 calls a subroutine relating to voltage difference calculation (S31), determines whether the resistance flag is set to 1 (S32), and according to the determination result. It is determined whether the voltage difference between the return values is smaller than the first voltage (S33) or whether the voltage difference is larger than the second voltage (S36).

  When the resistance flag is not set to 1 (S32: NO) and the voltage difference is smaller than the first voltage (S33: YES), the CPU 71 releases the drive of the relay 41 and controls the relay contact 41a to be turned off. (S34). Thereby, the resistor 42d is inserted on the input side of the switching circuit 3b.

  On the other hand, when the resistance flag is set to 1 (S32: YES) and the voltage difference is not larger than the second voltage (S36: NO), the CPU 71 determines that the voltage difference of the return value of the subroutine is again from the first voltage. It is determined whether or not it has become smaller (S41). When the voltage difference is not smaller than the first voltage (S41: NO), the CPU 71 ends the process of FIG. 6 without controlling the relay contact 46a to be turned off.

  When the voltage difference between the return values becomes smaller than the first voltage again (S41: YES), the CPU 71 determines whether m is N in order to determine whether or not all the relay contacts 46a are controlled to be turned off. Is determined (S42). When m is N (S42: YES), that is, when all the relay contacts 46a are already controlled to be turned off, the CPU 71 ends the process of FIG. 6 as it is.

  On the other hand, when m is not N (S42: NO), the CPU 71 increments m by 1 (S43), and then controls the m-th relay contact 46a (third relay contact) to be off ( S44) The processing of FIG. By the processing in step S44, the number of resistors 45 connected in series to the resistor 42d is increased by 1, and the combined resistance of the resistors inserted on the input side of the switching circuit 3b is increased, and input to the switching circuit 3b. The AC voltage generated is further reduced.

  If the voltage difference between the return values is larger than the second voltage in step S36 (S36: YES), the CPU 71 controls the relay contact 41a to be on (S37), and then clears the resistance flag to 0 (S38). Thereafter, the CPU 71 releases the drive of all the relays 46 and controls all the relay contacts 46a (third relay contacts) to be turned on (S39), initializes m to 0 (S40), and performs the process of FIG. Exit. By the processing from step S37 to S40, the relay contact 41 and all the relay contacts 46a are returned to the state when the processing in FIG. 6 is first activated.

  In the above-described fourth embodiment, the peak hold circuit 53 holds the amplitude of the pulsating voltage from the diode bridge DB1 (that is, the amplitude of the AC voltage on the switching circuit 3b side of the relay contact 41a). Similarly to the first embodiment, the amplitude of the AC voltage on the AC power supply 2 side of the relay contact 41a may be maintained. In this case, after the relay contact 41a is controlled to be turned off, the output current from the switching circuit 3b is detected, or the rotational speed of the AC motor 22 is detected, and further off based on the detected output current or rotational speed. The number of relay contacts 46a to be controlled can be determined. Based on the difference between the magnitude of the DC voltage from the switching circuit 3b and the amplitude of the AC voltage on the AC power supply 2 side of the relay contact 41a, the number of relay contacts 46a to be further turned off may be determined.

  On the other hand, in the fourth embodiment, when the relay contact 41a is controlled to be turned off and the resistor 42d is inserted on the input side of the switching circuit 3b, the amplitude of the pulsating voltage from the diode bridge DB1 is the resistor. Note that it drops by the voltage drop at 42d. That is, since the difference between the magnitude of the DC voltage from the switching circuit 3b and the amplitude of the pulsating voltage from the diode bridge DB1 increases by the voltage drop in the resistor 42d, immediately after the relay contact 41a is controlled to be turned off, The second voltage needs to be sufficiently larger than the first voltage so that the voltage difference is not determined to be larger than the second voltage.

As described above, according to the fourth embodiment, when the relay contact 41a is controlled to be turned off because the difference is smaller than the first voltage, one or more parallel circuits of the resistor 45 and the relay contact 46a are provided. With respect to the series circuit of the circuit connected in series and the resistor 42d, the relay contact 46a is sequentially turned off according to the above difference within a range where the above difference is smaller than the second voltage.
Accordingly, by configuring the relay contact 46a to be on when the relay contact 41a is controlled to be turned off, the relay contact 41a is first controlled to be turned off in response to the decrease in the difference, and then the relay contact 46a is turned on. Since the control is turned off, the series resistance of the resistor 42d and the one or more resistors 45 can be increased stepwise.

(Embodiment 5)
Each of the first, second, third, and fourth embodiments is provided with switching circuits 3a and 3b that convert the AC voltage from the AC power source 2 into a DC voltage and step up the voltage, whereas the fifth embodiment is a switching circuit. The present embodiment further includes another switching circuit that steps down the DC voltage boosted by the circuit 3a or 3b and outputs a low-voltage DC voltage.

  Generally, when a serious abnormality is detected in the control circuit or control IC of the power supply device, the control circuit or control IC may be in a so-called latch protected state and stop operating. Such a state continues until the power supply voltage supplied to the control circuit or the control IC is sufficiently lowered and the internal latch circuit is reset.

  On the other hand, when the input voltage of the power supply device is a DC voltage smoothed by a capacitor, the charge remains in the capacitor even after the upper power supply device or commercial power supply for charging the capacitor is turned off. The actual situation is that the power supply voltage of the control circuit or control IC does not decrease for a long time.

  On the other hand, Japanese Patent Laid-Open No. 2006-166561 (hereinafter referred to as “Publication 1”) is a power supply device that performs a latch protection operation when an overcurrent occurs, and detects a secondary overcurrent by a latch release time reduction circuit. In this case, a technique for discharging the charge of the smoothing capacitor on the input side with a discharge resistor is disclosed. Japanese Patent Laying-Open No. 2014-64376 (hereinafter referred to as “Publication 2”) discloses a technique for discharging charges accumulated in a capacitor that supplies a control voltage to a control circuit by a latch signal generated during a latch protection operation. ing.

  However, when it is not detected that the control circuit or the control IC is in the latch protection state, the techniques disclosed in the publications 1 and 2 cannot be applied. In such a power supply device, for example, when a power outage occurs in a host power supply device or commercial power supply, depending on the power outage time, the relationship between the terminals of the control circuit or the control IC is disrupted and the latch protection state is established, and power is restored. However, there is a problem that the control circuit or the control IC does not operate.

  The switching power supply according to Embodiment 5 of the present invention makes it possible to prevent latch protection from occurring in other switching circuits even when the input AC voltage is cut off for a short time. Is.

  FIG. 8 is a block diagram showing a configuration of a switching power supply according to Embodiment 5 of the present invention. In the figure, reference numeral 100a denotes a switching power supply. The switching power supply 100a is a switching circuit (first circuit) for stepping down a DC voltage from the switching power supply 1a (or 1b, 1c, or 1d) and the switching circuit 3a (or 3b). 8) and a relay 91 having a relay contact (corresponding to a fourth switch) 91a for turning on and off the supply of DC voltage to the switching circuit 8.

  The switching circuit 8 switches the voltage applied to the primary coil of the step-down transformer T81 and the step-down transformer T81 to which the DC voltage from the switching circuit 3a (or 3b) is applied to one end of the primary coil via the relay contact 91a. And a step-down control circuit IC81 having a built-in FET.

  In the step-down transformer T81, one end of the secondary coil is connected to the ground potential, and the other end of the secondary coil and the tap are connected to the anodes of the diodes D81 and 82, respectively. Capacitors C81 and C82 are connected between the cathodes of the diodes D81 and 82 and the ground potential.

  The step-down control circuit IC81 includes a D terminal and an S terminal to which the drain and source of the built-in FET are connected, a VIN terminal for supplying current to the internal control circuit, and a VDD that is a reference voltage terminal for the internal circuit power supply. A terminal and an FB terminal for inputting a feedback signal.

  Each of the VIN terminal and the D terminal is connected to one end and the other end of the primary coil of the step-down transformer T81. The S terminal is connected to the ground potential. A stabilization capacitor C83 is connected between the VDD terminal and the ground potential, and a series circuit of a diode D83 and a resistor R8 is connected to the cathode of the diode D81 in a direction in which current flows from the diode D81. It is connected. The feedback circuit 81 is connected between the FB terminal and the cathode of the diode D82, and the filter 82 is connected between the FB terminal and the ground potential.

  In the relay 91, the relay contact 91a is a normally open contact, and one end of the relay coil 91b is connected to the ground potential. The other end of the relay coil 91b is connected to a voltage dividing point of a voltage dividing circuit (corresponding to a drive circuit) composed of resistors 92 and 93 that divide a DC voltage from the switching circuit 3a (or 3b).

  In the above-described configuration, + 15V and + 5V are output from the cathodes of the diodes D81 and 82 by the switching operation by the FET built in the step-down control circuit IC81. The step-down control circuit IC81 stops the transmission of a signal for turning on and off the built-in FET when the current flowing into the VDD terminal reaches a certain value. This state is a so-called latch-protected state and does not recover until the DC voltage applied to the VIN terminal is cut off.

  Such a latch protection state is, for example, when the AC power supply 2 is momentarily interrupted or when a power switch (not shown) connected to the AC power supply 2 is turned on and off in a short time, the switching circuit 3a (or 3b May occur when the voltage at the VIN terminal rises again before the voltage at the VIN terminal is sufficiently lowered.

  On the other hand, the fifth embodiment has a configuration in which the supply of the DC voltage to the switching circuit 8 is promptly stopped when the DC voltage from the switching circuit 3a (or 3b) drops below a certain voltage. That is, when the DC voltage from the switching circuit 3a (or 3b) becomes lower than a predetermined threshold, the exciting current of the relay coil 91b decreases, the drive of the relay 91 is released, and the relay contact 91a is turned off.

  The voltage value that can be the predetermined threshold is lower than the lower limit value of the DC voltage that is output when the switching circuit 3a (or 3b) is operating normally, and the switching circuit 3a (or 3b) temporarily stops operating. In the process of restarting after that, unless the DC voltage input to the switching circuit 8 is further reduced, the step-down control circuit IC81 has a voltage value higher than the lower limit value of the voltage that does not fall into the latch protection state. When the DC voltage from the switching circuit 3a (or 3b) falls below the threshold as described above, the supply of the DC voltage to the switching circuit 8 is stopped, and then the supply of the DC voltage to the switching circuit 8 is resumed. Even when the switching is performed, the operation is resumed from the state in which the switching circuit 8 is normally reset.

As described above, according to the fifth embodiment, the divided voltage of the voltage dividing circuit composed of the resistors 92 and 93 is applied to the relay coil 91b of the relay 91, whereby a DC voltage is supplied to the switching circuit 8. The
Accordingly, the supply of the DC voltage to the switching circuit 8 can be turned on / off by the hardware circuit without intervention of software.

(Embodiment 6)
In the fifth embodiment, the relay 91 is driven by directly exciting the relay coil 91b of the relay 91 with the divided voltage of the voltage dividing circuit composed of the resistors 92 and 93, so that the switching power supply is connected via the relay contact 91a. In contrast to the configuration in which a DC voltage is supplied to 8, the sixth embodiment is a configuration in which a DC voltage is supplied to the switching power supply 8 via an FET that is turned on and off based on the divided voltage of the voltage dividing circuit.

  FIG. 9 is a block diagram showing a configuration of a switching power supply according to Embodiment 6 of the present invention. In the figure, reference numeral 100b denotes a switching power source. The switching power source 100b is a switching power source 1a (or any one of 1b, 1c, 1d), a switching circuit 8, and a P for turning on / off the supply of a DC voltage to the switching circuit 8. A channel-type FET (corresponding to a fourth switch) 94, and a series circuit of a Zener diode 95 and a resistor 96 connected between the connection point of the resistors 92 and 93 and the ground potential.

  In the FET 94, a DC voltage from the switching circuit 3a (or 3b) is applied to the source, and a DC voltage is supplied to the switching circuit 8 from the drain. A resistor 94 a is connected between the source and gate of the FET 94. The gate of the FET 94 is connected to the collector of an NPN-type grounded transistor 94c via a resistor 94b. The base of the transistor 94c is connected to the connection point of the anode of the Zener diode 95 and the resistor 96 via the resistor 94d. The resistors 92, 93, 94a, 94d, 96, the diode 95, and the transistor 94c correspond to a drive circuit.

  In the above-described configuration, when the DC voltage from the switching circuit 3a (or 3b) becomes lower than a predetermined threshold value, the divided voltage of the voltage dividing circuit composed of the resistors 92 and 93 is changed to the Zener voltage of the Zener diode 95 as a transistor. The transistor 94c is turned on when the voltage becomes higher than the voltage obtained by adding the voltage between the base and emitter of 94c. As a result, the FET 94 is turned off and the supply of the DC voltage to the switching circuit 8 is stopped. Therefore, even when the supply of the DC voltage to the switching circuit 8 is resumed, the switching circuit 8 is reset. Resume operation from state.

As described above, according to the fifth or sixth embodiment, when the DC voltage from the switching circuit 3a (or 3b) is lower than the predetermined threshold, the switching circuit 8 that steps down the DC voltage from the switching circuit 3a (or 3b). Turn off the DC voltage supply to the.
Accordingly, when the DC voltage from the switching circuit 3a (or 3b) is lower than a predetermined threshold, the supply of the DC voltage to the switching circuit 8 is actively stopped, so that the step-down control circuit IC81 enters a latch protection state. Can be prevented.

Further, according to the fifth or sixth embodiment, the relay contact 91a (or FET 94) is based on the voltage obtained by dividing the DC voltage from the switching circuit 3a (or 3b) by the voltage dividing circuit including the resistors 92 and 93. Turn off.
Therefore, by selecting the voltage dividing ratio of the voltage dividing circuit, the relay contact 91a (or FET 94) can be turned off when the DC voltage from the switching circuit 3a (or 3b) becomes lower than a predetermined threshold. .

  Furthermore, according to the sixth embodiment, since it is not necessary to directly drive the relay coil 91b with the divided voltage of the voltage dividing circuit composed of the resistors 92 and 93, the resistance compared to the case of the fifth embodiment. The resistance values of the devices 92 and 93 can be increased, and the power consumption of the drive circuit for the FET 94 can be greatly reduced.

  The embodiment disclosed this time is to be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims. In addition, the technical features described in each embodiment can be combined with each other.

  Regarding the above embodiment, the following additional notes are disclosed.

  The switching power supply according to one aspect of the present invention is the switching power supply (1a or 1b) that converts an AC voltage into a DC voltage by a switching operation by the switching circuit (3a or 3b) and boosts the voltage. The switch (41a) for turning on / off the supply of AC voltage to the switch, the resistor (42a or 42b) connected between both ends of the switch (41a), and the DC voltage boosted by the switching circuit (3a or 3b) And a control unit (6 or 7) for controlling on / off of the switch (41a) according to the difference between the magnitude and the amplitude of the AC voltage at one end or the other end of the switch (41a). .

In the present application, the AC voltage supplied to the switching circuit via the parallel circuit of the resistor and the switch is converted into a DC voltage by a switching operation and boosted. The controller turns on the switch while the difference between the magnitude of the DC voltage boosted by the switching circuit and the amplitude of the AC voltage at one or the other end of the parallel circuit changes from large to small (or from small to large). Control from off to on (or off to on).
As a result, the switch is switched from ON to OFF while the difference between the magnitude of the DC voltage output from the switching circuit and the amplitude of the AC voltage from the outside changes from large to small, and a resistance is applied to the input side of the switching circuit. A vessel is inserted.

  The switching power supply according to one aspect of the present invention is characterized in that the resistor (42b) is a PTC element having a positive resistance temperature coefficient.

In this application, when the above-mentioned difference is smaller than a predetermined first voltage, the switch is turned off to release the bypass of the resistor, and then the above-mentioned difference rises above the first voltage and reaches the predetermined voltage. When the voltage exceeds the second voltage, the switch is turned on to bypass the resistor.
Thereby, when the above-mentioned difference becomes smaller than the predetermined first voltage, a resistor is inserted on the input side of the switching circuit. And when the above-mentioned difference becomes larger than a 2nd voltage, insertion of a resistor is cancelled | released.

  In the switching power supply according to an aspect of the present invention, the controller (6 or 7) turns off the switch (41a) when the difference is smaller than the first voltage, and turns off the switch (41a). The switch (41a) is turned on when the difference is larger than a second voltage exceeding the first voltage.

  In the present application, since the resistor is a PTC element having a positive resistance temperature coefficient, when the switch is configured to be off at the time of startup of the switching circuit, the input current to the switching circuit is autonomously Limited.

  In the switching power supply according to one aspect of the present invention, a series circuit of a second resistor (43) and a second switch (44a) is connected in parallel to the resistor (42c), and the control unit (7 ), When the switch (41a) is turned off, the second switch (44a) is turned off according to the difference within a range where the difference is smaller than the second voltage.

In the present application, when the switch is controlled to be turned off because the difference is smaller than the first voltage, the second resistor and the series circuit of the second switch and the parallel circuit of the resistor, The second switch is controlled to be turned off according to the above difference within a range where the above difference is smaller than the second voltage.
Accordingly, when the second switch is turned on when the switch is controlled to be turned off, the switch is first controlled to be turned off in accordance with the decrease in the difference, and then the second switch is turned off. Therefore, the parallel resistance of the resistor and the second resistor increases stepwise.

  In the switching power supply according to one aspect of the present invention, a parallel circuit of a third resistor (45) and a third switch (46a) is connected in series to the resistor (42d), and the control unit (7 ), When the switch (41a) is turned off, the third switch (46a) is turned off according to the difference within a range where the difference is smaller than the second voltage.

In the present application, when the switch is controlled to be turned off because the difference is smaller than the first voltage, the second resistor and the parallel circuit of the second switch and the series circuit of the resistor, The second switch is controlled to be turned off according to the above difference within a range where the above difference is smaller than the second voltage.
Accordingly, when the second switch is turned on when the switch is controlled to be turned off, the switch is first controlled to be turned off in accordance with the decrease in the difference, and then the second switch is turned off. Therefore, the series resistance of the resistor and the second resistor increases stepwise.

  A switching power supply according to an aspect of the present invention includes a second switching circuit (8) that steps down a DC voltage from the switching circuit (3a or 3b), and a DC voltage to the second switching circuit (8). A fourth switch (91a or 94) for turning on / off the supply and a drive circuit for turning off the fourth switch (91a or 94) when the DC voltage from the switching circuit (3a or 3b) is lower than a predetermined threshold value It is characterized by providing.

In the present application, when the DC voltage from the switching circuit is lower than a predetermined threshold, the supply of the DC voltage to the second switching circuit that steps down the DC voltage from the switching circuit is turned off.
Thus, when the DC voltage from the switching circuit becomes lower than a predetermined threshold, the operation of the second switching circuit is actively stopped.

  In the switching power supply according to one aspect of the present invention, the drive circuit includes a voltage dividing circuit (92, 93) that divides a DC voltage from the switching circuit (3a or 3b). 93), the fourth switch (91a or 94) is turned off based on the divided voltage.

In the present application, the fourth switch is turned off based on the voltage obtained by dividing the DC voltage from the switching circuit by the voltage dividing circuit.
Thereby, the voltage dividing ratio of the voltage dividing circuit is selected so that the fourth switch is turned off when the DC voltage from the switching circuit becomes lower than the predetermined threshold value.

  In the switching power supply according to one aspect of the present invention, the fourth switch (91a) is a relay contact of a relay (91) driven by applying the divided voltage to the relay coil (91b). And

In the present application, the DC voltage is supplied to the second switching circuit by applying the divided voltage of the voltage dividing circuit to the relay coil of the relay.
Thereby, the supply of the DC voltage to the second switching circuit is turned on / off by the hardware circuit.

1a, 1b, 1c, 1d, 100a, 100b Switching power supply 2 AC power supply 21 Inverter circuit 22 AC motor 3a, 3b Switching circuit DB1 Diode bridge 41, 44, 46 Relay 41a, 44a, 46a Relay contact 42a, 42c, 42d, 43 45 Resistor 42b PTC element 53 Peak hold circuit 6 Control unit 61 Differential amplifier 66 Comparator 7 Control unit 71 CPU
72 ROM
75 I / O port 76 A / D converter 8 Switching circuit IC81 Step-down control circuit 91 Relay 91a Relay contact 92, 93 Resistor

Claims (8)

In a switching power supply that boosts by converting AC voltage to DC voltage by switching operation by a switching circuit
A switch for turning on and off the supply of an alternating voltage to the switching circuit;
A resistor connected across the switch;
A switching power supply comprising: a control unit that controls on / off of the switch according to a difference between a magnitude of a DC voltage boosted by the switching circuit and an amplitude of an AC voltage at one end or the other end of the switch. .   The switching power supply according to claim 1, wherein the resistor is a PTC element having a positive resistance temperature coefficient.   The control unit turns off the switch when the difference is smaller than a first voltage, and turns on the switch when the difference is larger than a second voltage exceeding the first voltage after turning off the switch. The switching power supply according to claim 1 or 2. A series circuit of a second resistor and a second switch is connected in parallel to the resistor,
The switching power supply according to claim 3, wherein when the switch is turned off, the control unit turns off the second switch in accordance with the difference within a range where the difference is smaller than the second voltage. . A parallel circuit of a third resistor and a third switch is connected in series to the resistor,
The said control part turns off the said 3rd switch according to the said difference within the range in which the said difference is smaller than the said 2nd voltage, when the said switch is turned off. The Claim 3 or 4 characterized by the above-mentioned. Switching power supply. A second switching circuit for stepping down a DC voltage from the switching circuit;
A fourth switch for turning on and off the supply of a DC voltage to the second switching circuit;
The switching power supply according to any one of claims 1 to 5, further comprising: a drive circuit that turns off the fourth switch when a DC voltage from the switching circuit is lower than a predetermined threshold value. The drive circuit is
A voltage dividing circuit for dividing a DC voltage from the switching circuit;
The switching power supply according to claim 6, wherein the fourth switch is turned off based on a divided voltage of the voltage dividing circuit. The switching power supply according to claim 7, wherein the fourth switch is a relay contact of a relay that is driven by applying the divided voltage to a relay coil.

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