Switching power supply units, switch control devices, and industrial equipment

Abstract

This switching power supply device comprises a switching element and a control unit. The control unit comprises: a current source circuit; a voltage source circuit; a PWM signal generation circuit; a capacitor having a first end connected to the current source circuit and a second end connected to the PWM signal generation circuit; a unidirectional conductive element that is provided between the first end of the capacitor and the voltage source circuit and allows only the passage of current flowing from the capacitor toward the voltage source circuit; and a comparison circuit that compares the voltage generated at the first end of the capacitor and a voltage based on the output voltage of the switching power supply device and uses the result of comparison as a basis to control the switching element.

Description

Technical Field

[0001] The invention disclosed in this specification relates to a switching power supply device, a switch control device, and industrial equipment.

Background Art

[0002] Conventionally, a switching power supply device that performs maximum on-duty control has been developed (see, for example, Patent Document 1).

[0003] Particularly in a switching power supply device using a transformer, maximum on-duty control is a very important technology to prevent transformer saturation.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In Patent Document 1, the specific configuration of the maximum duty control circuit that performs maximum on-duty control is not disclosed. In order to reduce the cost of the switching power supply device, it is necessary to realize maximum on-duty control at a low cost.

Means for Solving the Problems

[0006] A switching power supply device disclosed herein comprises a switching element and a control unit configured to control the on / off state of the switching element, wherein the control unit comprises a current source circuit configured to output a predetermined current, a voltage source circuit configured to output a predetermined voltage, a PWM signal generation circuit configured to output a PWM signal, a capacitor whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit, a unidirectional conductive element provided between the first end of the capacitor and the voltage source circuit and configured to allow current to flow only from the capacitor to the voltage source circuit, and a comparison circuit configured to compare the voltage generated at the first end of the capacitor with a voltage based on the output voltage of the switching power supply device and to control the switching element based on the result of the comparison.

[0007] The switch control device disclosed herein is configured to control the on / off state of a switching element provided in a switching power supply device, and comprises: a current source circuit configured to output a predetermined current; a voltage source circuit configured to output a predetermined voltage; a PWM signal generation circuit configured to output a PWM signal; a capacitor whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit; a unidirectional conductive element provided between the first end of the capacitor and the voltage source circuit, configured to allow current to flow only from the capacitor to the voltage source circuit; and a comparison circuit configured to compare the voltage generated at the first end of the capacitor with a voltage based on the output voltage of the switching power supply device, and to control the switching element based on the result of the comparison.

[0008] The industrial equipment disclosed herein comprises a switching power supply or a switch control device having the above configuration. [Effects of the Invention]

[0009] According to the inventions disclosed herein, maximum on-duty control can be achieved at low cost. [Brief explanation of the drawing]

[0010] [Figure 1] Figure 1 shows a schematic configuration of a switching power supply device according to the first embodiment. [Figure 2] Figure 2 shows a first configuration example of a switching power supply device according to the first embodiment. [Figure 3] Figure 3 shows a second configuration example of the switching power supply device according to the first embodiment. [Figure 4] Figure 4 shows the waveforms of the voltages at each part of the switching power supply shown in Figure 2. [Figure 5] Figure 5 shows a schematic configuration of a switching power supply according to the second embodiment. [Figure 6] Figure 6 shows an example configuration of a digital PWM signal generation circuit. [Figure 7] Figure 7 is a diagram illustrating the operation of the digital PWM signal generation circuit shown in Figure 6. [Figure 8] Figure 8 shows a schematic configuration of industrial equipment. [Modes for carrying out the invention]

[0011] In this specification, a MOS field-effect transistor refers to a field-effect transistor whose gate structure consists of at least three layers: "a layer made of a conductor or a semiconductor such as polysilicon with low resistance," "an insulating layer," and "a P-type, N-type, or intrinsic semiconductor layer." In other words, the gate structure of a MOS field-effect transistor is not limited to a three-layer structure of metal, oxide, and semiconductor.

[0012] In this specification, a specified current refers to a current that is constant under ideal conditions, and in reality, it is a current that may fluctuate slightly due to temperature changes, etc.

[0013] In this specification, a predetermined voltage means 、 a voltage that is constant in an ideal state and can actually vary slightly due to temperature changes or the like.

[0014] In this specification, a reference voltage means 、 a voltage that is constant in an ideal state and can actually vary slightly due to temperature changes or the like.

[0015] <First Embodiment> FIG. 1 is a diagram showing a schematic configuration of a switching power supply device according to the first embodiment. A switching power supply device 1 (hereinafter referred to as "switching power supply device 1") according to the first embodiment is a power supply device that converts an input voltage Vi generated by an input power supply VIN1 into an output voltage Vo and outputs the output voltage Vo. The switching power supply device 1 includes a power circuit PW1 and a control unit CNT1.

[0016] The power circuit PW1 includes a transformer T1, a switching element TR1, a rectifying element D1, a freewheeling element D2, an output choke coil LO, and an output capacitor CO. The transformer T1 includes a primary winding N1 and a secondary winding N2. In this embodiment, an N-channel MOS field effect transistor is used as the switching element TR1, but the switching element TR1 is not limited to an N-channel MOS field effect transistor. The switching element TR1 may be, for example, a bipolar transistor. Also, in this embodiment, diodes are used as the rectifying element D1 and the freewheeling element D2, but each of the rectifying element D1 and the freewheeling element D2 is not limited to a diode. Each of the rectifying element D1 and the freewheeling element D2 may be, for example, a synchronous rectifying element.

[0017] The first end of the primary winding N1 is connected to the positive electrode of the input power supply VIN1. The second end of the primary winding N1 is connected to the drain of the switching element TR1. The source of the switching element TR1 is connected to the negative electrode of the input power supply VIN1.

[0018] The first end of the secondary winding N2 is connected to the cathode of the reflux element D2 and the first end of the output choke coil LO. The second end of the output choke coil LO is connected to the first end of the output capacitor CO. The second end of the secondary winding N2 is connected to the cathode of the rectifying element D1. The anode of the rectifying element D1 is connected to the anode of the reflux element D2, the second end of the output capacitor CO, and the ground potential. An output voltage Vo is generated across the output capacitor CO.

[0019] In this embodiment, the power circuit PW1 is a single-ended forward converter. In the power circuit PW1 which is a single-ended forward converter, when the switching element TR1 is turned on, current is supplied to the load LD through the rectifying element D1 and the output choke coil LO, and when the switching element TR1 is turned off, the energy stored in the output choke coil LO is released and current is supplied to the load LD through the reflux element D2.

[0020] Note that since the single-ended forward converter is merely an example, the power circuit PW1 may have a circuit form other than single-ended forward. Also, the power circuit PW1 may be configured without a transformer.

[0021] The control unit CNT1 includes a current source circuit IS1, a voltage source circuit VS1, a unidirectional conduction element U1, a PWM (Pulse Width Modulation) signal generation circuit PM1, an output voltage control signal generation circuit VFB1, a timing capacitor CT1, and a comparison circuit CP1. The control unit CNT1 is configured to control the switching element TR1. In other words, the control unit CNT1 is a switch control device configured to control the on / off of the switching element TR1. The output voltage control signal generation circuit VFB1 includes an error amplifier EA1 and a reference voltage source circuit VR1. Note that the output voltage control signal generation circuit VFB1 may have a circuit configuration other than that shown in FIG. 1, for example, a circuit configuration including a photocoupler.

[0022] The output voltage Vo is supplied to the inverting input terminal of the error amplifier EA1. The positive terminal of the reference voltage source circuit VR1 is connected to the non-inverting input terminal of the error amplifier EA1. The negative terminal of the reference voltage source circuit VR1 is connected to ground potential.

[0023] The output terminal of the error amplifier EA1 is connected to the non-inverting input terminal of the comparator circuit CP1.

[0024] A voltage for driving the current source circuit IS1 is applied to the first terminal of the current source circuit IS1. The second terminal of the current source circuit IS1 is connected to the first terminal of the unidirectional conducting element U1, the first terminal of the timing capacitor CT1, and the inverting input terminal of the comparator circuit CP1.

[0025] The second terminal of the unidirectional conductive element U1 is connected to the positive terminal of the voltage source circuit VS1. The negative terminal of the voltage source circuit VS1 is connected to ground potential.

[0026] The second terminal of the timing capacitor CT1 is connected to the PWM signal generation circuit PM1.

[0027] The current source circuit IS1 is configured to output a predetermined current Is.

[0028] The voltage source circuit VS1 is configured to output a predetermined voltage Vs. The voltage source circuit VS1 outputs a predetermined voltage Vs such that the sum obtained by adding the predetermined voltage Vs and the forward voltage Vu of the unidirectional conducting element U1 is greater than the maximum value Vfb_max of the output voltage control signal Vfb, which will be described later.

[0029] The PWM signal generation circuit PM1 is configured to output a PWM signal Vp. The PWM signal generation circuit PM1 supplies the PWM signal Vp to the second terminal of the timing capacitor CT1.

[0030] The timing capacitor CT1 generates a slope-shaped charging voltage Vct by charging (integrating) a predetermined current Is. Therefore, an added voltage Vadd, which is the sum of the PWM signal Vp and the charging voltage Vct, is generated at the first terminal of the timing capacitor CT1.

[0031] The unidirectional conducting element U1 is configured to allow current to flow only from the timing capacitor CT1 to the voltage source circuit VS1. In other words, when the summing voltage Vadd is greater than a predetermined voltage Vs, current flows through the unidirectional conducting element U1 and the timing capacitor CT1 discharges.

[0032] The output voltage control signal generation circuit VFB1 is configured to generate an output voltage control signal Vfb, which is a voltage based on the output voltage Vo. The error amplifier EA1 is configured to output the output voltage control signal Vfb, which is an error signal between the output voltage Vo and the reference voltage Vr output from the reference voltage source circuit VR1.

[0033] The comparator circuit CP1 is configured to compare the summing voltage Vadd with the output voltage control signal Vfb and control the switching element TR1 based on the result of this comparison. Specifically, if the summing voltage Vadd is greater than the output voltage control signal Vfb, the output signal Vgs of the comparator circuit CP1 becomes LOW, and the switching element TR1 turns off. On the other hand, if the summing voltage Vadd is less than the output voltage control signal Vfb, the output signal Vgs of the comparator circuit CP1 becomes HIGH, and the switching element TR1 turns on.

[0034] Figure 2 shows a first configuration example of the switching power supply device 1. In the first configuration example shown in Figure 2, the unidirectional conducting element U1 is a diode whose anode is connected to the first terminal of the timing capacitor CT1 and whose cathode is connected to the voltage source circuit VS1. According to the first configuration example shown in Figure 2, the unidirectional conducting element U1 can be realized without any special control.

[0035] In the first configuration example shown in Figure 2, the current source circuit IS1 is a resistive element. By making the current source circuit IS1 a resistive element, the configuration of the current source circuit IS1 can be simplified.

[0036] In the first configuration example shown in Figure 2, the power supply voltage of the control unit CNT1 is a predetermined voltage Vs. Specifically, the predetermined voltage Vs is supplied to the PWM signal generation circuit PM1, the first terminal of the current source circuit IS1, the power supply terminal of the comparator circuit CP1, and the power supply terminal of the error amplifier EA1. This makes it easy to make the sum obtained by adding the predetermined voltage Vs and the forward voltage Vu of the unidirectional conduction element U1 greater than the maximum value Vfb_max of the output voltage control signal Vfb.

[0037] Figure 3 shows a second configuration example of the switching power supply 1. In the second configuration example shown in Figure 3, the unidirectional conducting element U1 is a synchronous rectifier element that turns on and off in response to the PWM signal Vp. As the synchronous rectifier element, a MOS field-effect transistor or the like, which has a lower forward high voltage than a diode, can be used. Therefore, according to the second configuration example shown in Figure 3, the on-resistance of the unidirectional conducting element U1 can be reduced, thereby increasing efficiency.

[0038] In the second configuration example shown in Figure 3, the current source circuit IS1 is a resistive element. By making the current source circuit IS1 a resistive element, the configuration of the current source circuit IS1 can be simplified.

[0039] Furthermore, in the second configuration example shown in Figure 3, the power supply voltage of the control unit CNT1 is a predetermined voltage Vs. Specifically, the predetermined voltage Vs is supplied to the PWM signal generation circuit PM1, the first terminal of the current source circuit IS1, the power supply terminal of the comparator circuit CP1, and the power supply terminal of the error amplifier EA1. This makes it easy to make the sum obtained by adding the predetermined voltage Vs and the forward voltage Vu of the unidirectional conduction element U1 greater than the maximum value Vfb_max of the output voltage control signal Vfb.

[0040] Figure 4 shows the waveforms of the voltages at each part of the switching power supply unit 1 shown in Figure 2. In Figure 4, the waveforms of the output signal Vgs of the comparator circuit CP1, a predetermined voltage Vs, the output voltage control signal Vfb, the summing voltage Vadd, the charging voltage Vct, and the PWM signal Vp are illustrated. In Figure 4, the horizontal axis represents time, and the vertical axis represents voltage values. V1 in Figure 4 is the value of the predetermined voltage Vs.

[0041] Figure 4 shows the waveforms of various voltages when the current flowing through the load LD suddenly increases at timing t1, causing the output voltage Vo to temporarily decrease.

[0042] In Figure 4, during the period before timing t1, the pulse width W1 of the output signal Vgs of the comparator circuit CP1 is determined by the output voltage control signal Vfb and the summing voltage Vadd. On the other hand, in the period after timing t1 in Figure 4, the pulse width W2 of the output signal Vgs of the comparator circuit CP1 is determined by the LOW level period of the PWM signal Vp. In other words, the maximum on-duty cycle of the switching element is the same as the off-duty cycle of the PWM signal Vp and is limited by the off-duty cycle of the PWM signal Vp.

[0043] According to the switching power supply unit 1, the switching element Tr1 can be directly controlled by the output signal Vgs of the comparator circuit CP1 in both cases: when the switching element Tr1 is driven at its maximum on-duty cycle (after timing t1 in Figure 4) and when the switching element Tr1 is not driven at its maximum on-duty cycle (before timing t1 in Figure 4). Therefore, the number of components in the switching power supply unit 1 can be reduced, and maximum on-duty cycle control can be achieved at a low cost.

[0044] The on-duty cycle of the PWM signal Vp is set to be greater than or equal to the first duty cycle duty 1 so that the output voltage Vo can satisfy the target output voltage Vt, and less than the second duty cycle duty 2 so that the transformer T1 does not saturate. The first duty cycle duty 1 and the second duty cycle duty 2 can be determined as follows. Here, n1 is the number of turns of the primary winding N1, n2 is the number of turns of the secondary winding N2, Vi is the input voltage, Vt is the target output voltage, Bm is the maximum magnetic flux density of the core of the transformer T1, Ae is the effective cross-sectional area of ​​the core of the transformer T1, and T is the switching period of the switching element Tr1. duty 1 ≤ duty <duty2 duty1 = (n2 / n1) · Vt / Vi duty2 = (Bm·n1·Ae) / (Vi·T)

[0045] <Second Embodiment> Figure 5 shows a schematic configuration of the switching power supply unit 2 according to the second embodiment. The switching power supply unit 2 according to the second embodiment (hereinafter referred to as "switching power supply unit 2") is a power supply unit that converts the input voltage Vi generated by the input power supply VIN1 into an output voltage Vo and outputs the output voltage Vo. Switching power supply unit 2 It comprises a power circuit PW1 and a control unit CNT2.

[0046] The control unit CNT2 includes a digital processor DP1 and a memory unit M1, and differs from the control unit CNT1 in the first embodiment in that it includes a digital PWM signal generation circuit DPM1, which is a PWM signal generation circuit that performs digital processing, instead of the analog PWM signal generation circuit PM1. In all other respects, it is the same as the control unit CNT1 in the first embodiment. The control unit CNT2 is configured to control the switching element TR1, similar to the control unit CNT1. In other words, the control unit CNT2 is a switch control device configured to control the on / off state of the switching element TR1, similar to the control unit CNT1.

[0047] Therefore, the specific examples and modifications described in the first embodiment can also be applied to the switching power supply device 2.

[0048] The memory unit M1 is configured to pre-store information INF_Vt, which is the target output voltage Vt. For example, a register, non-volatile memory, etc., can be used as the memory unit M1.

[0049] The digital processor DP1 is configured to set the pulse width of the PWM signal Vp based on the input voltage Vi information INF_Vi and the target output voltage Vt information INF_Vt stored in the memory unit M1. For example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), etc., can be used as the digital processor DP1. The input voltage Vi information INF_Vi is supplied to the digital processor DP1 from an input voltage detection unit (not shown) configured to detect the input voltage Vi and generate digital data of the input voltage Vi information INF_Vi from the detection result.

[0050] In switching power supply unit 2, the accuracy of the PWM signal Vp is improved compared to switching power supply unit 1, thus improving the accuracy of maximum on-duty control. Therefore, in switching power supply unit 2, it is possible to reduce the size of the core of transformer T1, thus enabling miniaturization of transformer T1.

[0051] Figure 6 shows an example configuration of a digital PWM signal generation circuit DPM1. The digital PWM signal generation circuit DPM1 shown in Figure 6 comprises a clock generation circuit 11, a counter 12, a first determination circuit 13, a second determination circuit 14, and an output circuit 15.

[0052] The clock generation circuit 11 is configured to output a clock.

[0053] The counter 12 is configured to update its count value based on the clock generated by the clock generation circuit 11. Specifically, the count value is incremented by one for each clock cycle.

[0054] The first determination circuit 13 is configured to determine the relationship between the count value of the counter 12 and a first setpoint for setting the period of the PWM signal Vp supplied from the digital processor DP1. Specifically, the first determination circuit 13 determines whether the count value of the counter 12 has reached the first setpoint. If the count value of the counter 12 has reached the first setpoint, the first determination circuit 13 outputs a HIGH level signal. If the count value of the counter 12 has not reached the first setpoint, the first determination circuit 13 outputs a LOW level signal.

[0055] The second determination circuit 14 is configured to determine the relationship between the count value of the counter 12 and a second setpoint for setting the pulse width of the PWM signal Vp supplied from the digital processor DP1. Specifically, the second determination circuit 14 determines whether the count value of the counter 12 has reached the second setpoint. If the count value of the counter 12 has reached the second setpoint, the second determination circuit 14 outputs a HIGH level signal. If the count value of the counter 12 has not reached the second setpoint, the second determination circuit 14 outputs a LOW level signal.

[0056] The output circuit 15 is configured to generate a PWM signal Vp based on the output signal of the first determination circuit 13, which indicates the determination result of the first determination circuit 13, and the output signal of the second determination circuit 14, which indicates the determination result of the second determination circuit 14. In the configuration example shown in Figure 6, an RS flip-flop is used as the output circuit 15. The output signal of the first determination circuit 13 is supplied to the set terminal (S terminal) of the RS flip-flop, and the output signal of the second determination circuit 14 is supplied to the reset terminal (R terminal) of the RS flip-flop. Then, the PWM signal Vp is output from the output terminal (Q terminal) of the RS flip-flop.

[0057] The output signal of the first determination circuit 13 is also used as a reset signal to reset the counter 12. When the output signal of the first determination circuit 13 becomes HIGH level, the counter 12 resets its count value.

[0058] According to the configuration example shown in Figure 6, the period and pulse width of the PWM signal Vp can be arbitrarily set without the need for multiple counters. Because multiple counters are not required, the digital PWM signal generation circuit DPM1 can be made lower cost and smaller.

[0059] Figure 7 is a diagram illustrating the operation of the digital PWM signal generation circuit DPM1 shown in Figure 6. In Figure 7, the period of the PWM signal Vp is set to 1000 clock cycles, and the pulse width of the PWM signal Vp is set to 700 clock cycles. Therefore, in the example shown in Figure 7, the maximum on-duty cycle of the switching element TR1 is 70%.

[0060] As described in the first embodiment, the on-duty cycle of the PWM signal Vp should be set to a first duty cycle of duty 1 or greater so that the output voltage Vo can satisfy the target output voltage Vt, and to a second duty cycle of duty 2 or less so that the transformer T1 does not saturate.

[0061] <Examples of application> The devices or equipment on which the above-described switching power supply 1 or switching power supply 2 is installed are not limited. In other words, the above-described switching power supply 1 or switching power supply 2 may be installed in industrial equipment, for example, or in consumer electronics.

[0062] The switching power supply unit 1 is mounted on, for example, the industrial equipment 3 shown in Figure 8. In other words, the industrial equipment 3 is equipped with the switching power supply unit 1. Each of the DC / DC converters 1A to 1C, described later, is a switching power supply unit 1.

[0063] The number of electronic circuits and DC / DC converters in the configuration shown in Figure 8 is merely an example. For example, a configuration different from that shown in Figure 8 may be made in which electronic circuit 3B is omitted and the number of electronic circuits and DC / DC converters are equal. The industrial equipment 3 shown in Figure 8 comprises an input terminal 3A, DC / DC converters 1A to 1C, and electronic circuits 3B to 3E. An input voltage Vi, which is a DC voltage, is supplied to input terminal 3A. The input voltage Vi is supplied to electronic circuit 3B and DC / DC converters 1A to 1C. Electronic circuit 3B uses the input voltage Vi as its power supply voltage. DC / DC converter 1A converts the input voltage Vi into a DC voltage V1 with a different value from the input voltage Vi, and supplies the DC voltage V1 to electronic circuit 3C. Electronic circuit 3C uses the DC voltage V1 as its power supply voltage. DC / DC converter 1B converts the input voltage Vi into a DC voltage V2 with a different value from the input voltage Vi, and supplies the DC voltage V2 to electronic circuit 3D. Electronic circuit 3D uses DC voltage V2 as its power supply voltage. DC / DC converter 1C converts the input voltage Vi into DC voltage V3, which has a different value from the input voltage Vi, and supplies DC voltage V3 to electronic circuit 3E. Electronic circuit 3E uses DC voltage V3 as its power supply voltage. Industrial equipment 3 shown in Figure 8 is a wireless base station for a mobile phone network, and electronic circuits 3B to 3E, such as antenna circuits, conversion circuits that convert high-frequency signals to intermediate-frequency signals or baseband signals, FPGAs (Field Programmable Gate Arrays), etc., are mounted on industrial equipment 3.

[0064] Other examples of industrial equipment besides wireless base stations for mobile phone networks include medical equipment and robots installed in production facilities.

[0065] <Points to note> The configuration of the present invention can be modified in various ways, in addition to the embodiments described above, without departing from the spirit of the invention. The embodiments described above should be considered in all respects to be illustrative and not restrictive, and the technical scope of the present invention is indicated by the claims, not by the description of the embodiments described above, and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0066] The switching power supply devices (1, 2) described above are switching power supply devices comprising a switching element (TR1) and control units (CNT1, CNT2) configured to control the on / off state of the switching element, wherein the control unit comprises a current source circuit (IS1) configured to output a predetermined current, a voltage source circuit (VS1) configured to output a predetermined voltage, PWM signal generation circuits (PM1, DPM1) configured to output a PWM signal, a capacitor (CT1) whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit, a unidirectional conductive element (U1) provided between the first end of the capacitor and the voltage source circuit and configured to allow only current flowing from the capacitor to the voltage source circuit, and a comparison circuit (CP1) configured to compare the voltage generated at the first end of the capacitor with a voltage based on the output voltage of the switching power supply device and to control the switching element based on the result of the comparison (first configuration).

[0067] According to the first configuration of the switching power supply described above, the switching elements can be directly controlled by the output signal of the comparator circuit, both when the switching elements are driven at their maximum on-duty cycle and when they are not driven at their maximum on-duty cycle. Therefore, the number of components in the switching power supply can be reduced, and maximum on-duty control can be achieved at a low cost.

[0068] The switching power supply in the first configuration described above may also be configured in a second configuration in which the unidirectional conducting element is a diode whose anode is connected to the first end of the capacitor and whose cathode is connected to the voltage source circuit.

[0069] According to the switching power supply device of the second configuration described above, a unidirectional conductive element can be realized without performing any special control.

[0070] The switching power supply device of the first configuration described above may also have a configuration in which the unidirectional conducting element is a synchronous rectifier element that turns on and off in accordance with the PWM signal (third configuration).

[0071] According to the third configuration of the switching power supply described above, the on-resistance of the unidirectional conductive element can be reduced, thereby increasing efficiency.

[0072] In any of the first to third configurations described above, the switching power supply device may also have a configuration in which the power supply voltage of the control unit is the predetermined voltage (fourth configuration).

[0073] According to the fourth configuration of the switching power supply described above, it becomes easy to make the sum obtained by adding a predetermined voltage and the forward voltage of the unidirectional conducting element greater than the maximum value of the voltage based on the output voltage of the switching power supply, which is compared in the comparator circuit with the voltage generated at the first terminal of the capacitor.

[0074] A switching power supply according to any of the first to fourth configurations described above may also have a fifth configuration in which the control unit further comprises a digital processor (DP1) configured to set the period and pulse width of the PWM signal based on information about the input voltage of the switching power supply and information about the target output voltage of the switching power supply.

[0075] According to the fifth configuration of the switching power supply described above, the PWM signal is generated by digital processing, improving the accuracy of the PWM signal, and thus improving the accuracy of maximum on-duty control.

[0076] The switching power supply in the fifth configuration described above includes, in which the PWM signal generation circuit comprises a clock generation circuit (11) configured to output a clock, a counter (12) configured to update a count value based on the clock, a first determination circuit (13) configured to determine the relationship between the count value and a first setting value for setting the period of the PWM signal supplied from the digital processor, a second determination circuit (14) configured to determine the relationship between the count value and a second setting value for setting the pulse width of the PWM signal supplied from the digital processor, and an output circuit (15) configured to generate the PWM signal based on the determination result of the first determination circuit and the determination result of the second determination circuit, wherein the counter may be configured to reset the count value based on the determination result of the first determination circuit (sixth configuration).

[0077] According to the sixth configuration of the switching power supply described above, it is not necessary to provide multiple counters in the PWM signal generation circuit, thus enabling cost reduction and miniaturization of the PWM signal generation circuit.

[0078] A switching power supply in any of the above configurations 1 to 6 may also have a configuration (7th configuration) in which the sum obtained by adding the predetermined voltage and the forward voltage of the unidirectional conducting element is greater than the maximum value of the voltage based on the output voltage of the switching power supply that is compared with the voltage generated at the first end of the capacitor in the comparison circuit.

[0079] According to the seventh configuration of the switching power supply described above, it is possible to reliably provide a period during which the switching element is turned off.

[0080] The switch control devices (CNT1, CNT2) described above are switch control devices configured to control the on / off state of switching elements provided in a switching power supply device, and comprise a current source circuit (IS1) configured to output a predetermined current, a voltage source circuit (VS1) configured to output a predetermined voltage, PWM signal generation circuits (PM1, DPM1) configured to output a PWM signal, a capacitor (CT1) whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit, a unidirectional conductive element (U1) provided between the first end of the capacitor and the voltage source circuit and configured to allow current to flow only from the capacitor to the voltage source circuit, and a comparison circuit (CP1) configured to compare the voltage generated at the first end of the capacitor with the voltage based on the output voltage of the switching power supply device and to control the switching element based on the result of the comparison (eighth configuration).

[0081] According to the eighth configuration of the switch control device described above, maximum on-duty control of the switching power supply can be achieved at a low cost.

[0082] The industrial equipment (3) described above is configured to include a switching power supply device with any of the configurations described in the first to seventh above, or a switch control device with the configuration described in the eighth above (the ninth configuration).

[0083] According to the industrial equipment of the ninth configuration described above, maximum on-duty control of the switching power supply can be achieved at low cost. [Explanation of Symbols]

[0084] 1. Switching power supply according to the first embodiment 1A~1C DC / DC converter 2. Switching power supply according to the second embodiment 3 Industrial Equipment 3A Input Terminal 3B~3E Electronic circuit 11. Clock generation circuit 12 counters 13 First judgment circuit 14 Second judgment circuit 15 RS Flip-Flops CNT1, CNT2 control unit CO output capacitor CP1 comparison circuit CT1 Timing Capacitor D1 Rectifier element D2 Refrigeration element DP1 Digital Processor DPM1 Digital PWM Signal Generator Circuit EA1 Error Amplifier IS1 current source circuit LD load LO output choke coil M1 storage section N1 Primary winding N2 secondary winding PM1 PWM signal generation circuit PW1 Power Circuit T1 Transformer TR1 switching element U1 Unidirectional conductive element VFB1 Output Voltage Control Signal Generator Circuit VIN1 Input Power Supply VR1 Reference Voltage Source Circuit VS1 Voltage Source Circuit

Claims

1. Switching element and A control unit configured to control the on / off state of the switching element, A switching power supply device comprising, The control unit, A current source circuit configured to output a predetermined current, A voltage source circuit configured to output a predetermined voltage, A PWM signal generation circuit configured to output a PWM signal, A capacitor whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit, A unidirectional conductive element is provided between the first end of the capacitor and the voltage source circuit, and is configured to allow current to flow only from the capacitor to the voltage source circuit. A comparison circuit is configured to compare the voltage generated at the first end of the capacitor with the voltage based on the output voltage of the switching power supply, and to control the switching element based on the result of the comparison. A switching power supply unit equipped with the following features.

2. The switching power supply device according to claim 1, wherein the unidirectional conducting element is a diode whose anode is connected to the first end of the capacitor and whose cathode is connected to the voltage source circuit.

3. The switching power supply device according to claim 1, wherein the unidirectional conducting element is a synchronous rectifier element that turns on and off in accordance with the PWM signal.

4. The switching power supply device according to claim 1, wherein the power supply voltage of the control unit is the predetermined voltage.

5. The switching power supply according to claim 1, further comprising a digital processor configured to set the period and pulse width of the PWM signal based on information about the input voltage of the switching power supply and information about the target output voltage of the switching power supply.

6. The PWM signal generation circuit is A clock generation circuit configured to output a clock, A counter configured to update its count value based on the aforementioned clock, A first determination circuit configured to determine the relationship between the count value and a first set value for setting the period of the PWM signal supplied from the digital processor, A second determination circuit is configured to determine the relationship between the count value and a second setting value for setting the pulse width of the PWM signal supplied from the digital processor, An output circuit configured to generate the PWM signal based on the determination result of the first determination circuit and the determination result of the second determination circuit, Equipped with, The switching power supply device according to claim 5, wherein the counter resets the count value based on the determination result of the first determination circuit.

7. The switching power supply according to claim 1, wherein the sum obtained by adding the predetermined voltage and the forward voltage of the unidirectional conducting element is greater than the maximum value of the voltage based on the output voltage of the switching power supply, which is compared in the comparison circuit with the voltage generated at the first end of the capacitor.

8. A switch control device configured to control the on / off state of a switching element provided in a switching power supply device, A current source circuit configured to output a predetermined current, A voltage source circuit configured to output a predetermined voltage, A PWM signal generation circuit configured to output a PWM signal, A capacitor whose first end is connected to the current source circuit and whose second end is connected to the PWM signal generation circuit, A unidirectional conductive element is provided between the first end of the capacitor and the voltage source circuit, and is configured to allow current to flow only from the capacitor to the voltage source circuit. A comparison circuit is configured to compare the voltage generated at the first end of the capacitor with the voltage based on the output voltage of the switching power supply, and to control the switching element based on the result of the comparison. A switch control device equipped with the following features.

9. Industrial equipment comprising a switching power supply device according to claim 1 or a switch control device according to claim 8.

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