Switching power supply circuit and switching power supply system

Abstract

The invention provides a switching power supply circuit which operates stably even when connected in parallel. A switching power supply circuit (100) is provided with: a switching circuit (110) having an input node (N1) connected to an input power supply terminal (101) and an output node (N2) connected to an output power supply terminal (102) via an output switch (140); a feedback circuit (120) that supplies, to the switching circuit (110), feedback information (F) based on a voltage occurring at a control node (N4) provided in parallel with an output node (N2) of the switching circuit (110); and a start-up circuit that turns on the output switch (140) after the voltage occurring at the control node (N4) exceeds a predetermined value and a predetermined time has elapsed. The switching circuit (110) adjusts the voltage occurring at the output node (N2) and the control node (N4) to a predetermined level on the basis of the feedback information (F). The feedback circuit (120) includes an adjustment mechanism capable of adjusting the relationship between the voltage occurring at the control node (N4) and the feedback information (F).

Description

Technical Field

[0001] The present invention relates to a switching power supply circuit and a switching power supply system having the switching power supply circuit. Background Art

[0002] Patent Document 1 discloses a switching power supply system comprising multiple switching power supply circuits connected in parallel. The switching power supply system disclosed in Patent Document 1 synchronizes the restart timing of each switching power supply circuit by short-circuiting the on / off control terminals of the PWM control ICs included in each switching power supply circuit.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2003-169471 Summary of the Invention

[0006] Problems to be solved by the invention

[0007] However, when multiple switching power supply circuits are connected in parallel, if there is a difference in the output voltages of the switching power supply circuits, the switching power supply circuit with the higher output voltage may experience an overcurrent or overload condition. Therefore, in the switching power supply system described in Patent Document 1, even if all switching power supply circuits are restarted simultaneously, there is a possibility that an overcurrent or overload condition may occur in the switching power supply circuit with the higher output voltage, causing the switching operation to stop immediately.

[0008] Therefore, an object of the present invention is to provide a switching power supply circuit that operates stably even when connected in parallel, and a switching power supply system using the switching power supply circuit.

[0009] Technical solutions to solve problems

[0010] The present invention provides a switching power supply circuit comprising: a switching circuit having an input node connected to an input power supply terminal and an output node connected to an output power supply terminal via an output switch; a feedback circuit that feeds back information based on a voltage appearing at a control node provided in parallel with the output node to the switching circuit; and a startup circuit that turns on the output switch after a voltage appearing at the control node exceeds a specified value and a specified time has elapsed. The switching circuit adjusts the voltages appearing at the output node and the control node to specified levels based on the feedback information, and the feedback circuit includes an adjustment mechanism capable of adjusting the relationship between the voltage appearing at the control node and the information.

[0011] According to the present invention, by using an adjustment mechanism capable of adjusting the relationship between the voltage appearing at a control node connected in parallel with the output node and feedback information, the level of the output voltage outputted from the output power supply terminal can be adjusted. This prevents a particular switching power supply circuit from preferentially entering an overcurrent or overload state when a switching power supply system is constructed by connecting multiple switching power supply circuits in parallel.

[0012] In the present invention, the feedback circuit may include a voltage divider circuit for dividing the voltage appearing at the control node, and the adjustment mechanism may be formed by a variable resistor included in the voltage divider circuit.

[0013] In the present invention, the switching circuit may include a transformer, a switching element, and a switching control circuit, wherein the transformer includes a primary coil connected to an input node and a secondary coil connected to an output node and a control node, the switching element is connected to the primary coil, and the switching control circuit controls the switching element. When the switching control circuit determines that the current flowing through the switching element is an overcurrent, the switching control circuit stops the switching operation of the switching element. In this manner, the overcurrent condition can be eliminated.

[0014] In the present invention, when the switch control circuit determines that the information indicates an overload state, the switch control circuit may stop the switching operation of the switch element.

[0015] In the present invention, one end of the secondary coil may be connected to the output node via a first diode and to the control node via a second diode. The other end of the secondary coil may be grounded, the output node may be grounded via a first capacitor, and the control node may be grounded via a second capacitor. In this case, the maximum rating of the second diode may be smaller than that of the first diode, and the capacitance of the second capacitor may be smaller than that of the first capacitor. This configuration allows a predetermined voltage to be stably output from the output power terminal regardless of the size of the load connected to the output power terminal.

[0016] The present invention provides a switching power supply system comprising a plurality of the aforementioned switching power supply circuits, wherein the output power terminals of the plurality of switching power supply circuits are short-circuited with one another, and the startup circuits of the plurality of switching power supply circuits include startup control terminals that directly or indirectly control the output switches, wherein the startup control terminals of the plurality of switching power supply circuits are short-circuited with one another. This allows the plurality of switching power supply circuits to be restarted simultaneously.

[0017] The switching power supply system of the present invention may further include a plurality of power supplies connected to the input power terminals included in the plurality of switching power supply circuits. Thus, even when there is a difference in the input voltage levels supplied from the plurality of power supplies, a particular switching power supply circuit will not be preferentially overloaded or overcurrented.

[0018] Effects of the Invention

[0019] As described above, according to the present invention, it is possible to provide a switching power supply circuit that operates stably even when connected in parallel, and a switching power supply system using the switching power supply circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a block diagram for explaining the configuration of a switching power supply system 10 according to one embodiment of the present invention.

[0021] Figure 2 is a circuit diagram of the switching power supply circuit 100 . DETAILED DESCRIPTION

[0022] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0023] Figure 1 This is a block diagram for explaining the configuration of a switching power supply system 10 according to one embodiment of the present invention.

[0024] like Figure 1 As shown, the switching power supply system 10 of this embodiment has a structure in which a plurality of switching power supply circuits 100 are connected in parallel. Each switching power supply circuit 100 has an input power supply terminal 101 to which an input voltage Vin is supplied, an output power supply terminal 102 to which an output voltage Vout is output, and a start control terminal 103. The output power supply terminals 102 respectively included in each switching power supply circuit 100 are short-circuited with each other and connected to a load 12 in common. The input power supply terminals 101 respectively included in each switching power supply circuit 100 are connected to different power supplies 11. The power supply 11 may also be a power pickup transformer that extracts power by utilizing the magnetic field generated around a high-voltage transmission line. The start control terminals 103 respectively included in each switching power supply circuit 100 are also short-circuited with each other.

[0025] Figure 2 is a circuit diagram of the switching power supply circuit 100 .

[0026] like Figure 2As shown, switching power supply circuit 100 includes a switching circuit 110, a feedback circuit 120, a startup circuit 130, and an output switch 140. Switching circuit 110 includes a transformer T comprising a primary coil 111 and a secondary coil 112, a switching element 113 connected to one end of primary coil 111, and a switch control circuit 114 that controls switching element 113. The other end of primary coil 111 constitutes input node N1 of switching circuit 110 and is connected to input power supply terminal 101. Output node N3, which is one end of secondary coil 112, is connected to output node N2 via diode 116 (first diode) and to control node N4 via diode 118 (second diode). Output node N2 is connected to output power supply terminal 102 via output switch 140. The other end of secondary coil 112 is grounded via ground node N6. Output node N2 is connected to ground node N6 via capacitor 117 (first capacitor). The start-up circuit 130 is connected to a control node N4 provided in parallel with the output node N2 , and the control node N4 is connected to the ground node N6 via the capacitor 119 (second capacitor).

[0027] The characteristics of diode 118 may be the same as or different from those of diode 116. For example, the maximum rating of diode 118 may be smaller than that of diode 116. The characteristics of capacitor 119 may be the same as or different from those of capacitor 117. For example, the electrostatic capacitance of capacitor 119 may be smaller than that of capacitor 117. An electrolytic capacitor may be used for capacitor 117, and a multilayer ceramic capacitor may be used for capacitor 119.

[0028] Switch control circuit 114 is comprised of, for example, a controller IC and includes a power supply node N11, a ground node N12, a control node N13, and feedback nodes N14 and N15. Switch control circuit 114 operates based on the voltage supplied between power supply node N11 and ground node N12. It controls the frequency or duty cycle of switching signal S output from control node N13 based on feedback information F supplied to feedback node N14, thereby adjusting the voltage appearing at output node N2 to a predetermined level. Switch element 113, which supplies switching signal S, is comprised of, for example, an N-channel MOS transistor.

[0029] Furthermore, the current flowing through switching element 113 is supplied to feedback node N15 of switching control circuit 114 via resistor 115. Switching control circuit 114 monitors the current supplied to feedback node N15. If it determines that the current flowing through switching element 113 is overcurrent, it fixes switching signal S to an inactive level (e.g., ground level), thereby stopping the switching operation of switching element 113. This prevents damage to switching element 113 caused by overcurrent. Furthermore, if it determines that feedback information F indicates an overload state, switching control circuit 114 also fixes switching signal S to an inactive level, thereby stopping the switching operation of switching element 113. When switching operation stops, switching control circuit 114 restarts and resumes switching operation after a predetermined time.

[0030] Feedback circuit 120 generates feedback information F based on the voltage appearing at control node N4, which is connected in parallel with output node N2, and feeds this information back to switch circuit 110. When output switch 140 is on, the voltages appearing at output node N2 and control node N4 are substantially equal to output voltage Vout. Feedback circuit 120 includes fixed resistors 121 and 124, a variable resistor 122, a shunt regulator 123, a photodiode 125, and a phototransistor 126. Fixed resistor 121 and variable resistor 122 are connected in series between control node N4 and the anode of shunt regulator 123, forming a voltage divider circuit. The voltage at their connection point is supplied to the reference node of shunt regulator 123. Furthermore, fixed resistor 124 and photodiode 125 are connected in series between control node N4 and the cathode of shunt regulator 123. Photodiode 125 and phototransistor 126 form a photocoupler, which transmits feedback information F from the secondary side to the primary side while ensuring isolation between the primary and secondary sides.

[0031] The level of feedback information F varies not only based on the voltage appearing at control node N4, which is equivalent to the voltage appearing at output node N2, but also based on the voltage-dividing ratio of the voltage-dividing circuit formed by fixed resistor 121 and variable resistor 122. During the design phase, the voltage-dividing ratio of the voltage-dividing circuit is determined so that the voltage appearing at output node N2 reaches a predetermined level (e.g., 24V). However, due to individual differences caused by manufacturing variations, the actual voltage appearing at output node N2 may deviate from this predetermined level. Variable resistor 122 serves as an adjustment mechanism to eliminate this variation. By adjusting the resistance value of variable resistor 122, the relationship between the voltage appearing at control node N4 and feedback information F is fine-tuned after manufacturing, thereby aligning the voltage appearing at output node N2 with the predetermined level (e.g., 24V).

[0032] Startup circuit 130 includes fixed resistors 131 and 132, a timer IC 133, a capacitor 134, and an N-channel MOS transistor 135. Fixed resistors 131 and 132 are connected in series between control node N4 and ground, forming a voltage divider circuit. The voltage at their connection point is supplied to input node N21 of timer IC 133. When the voltage supplied to input node N21 exceeds a specified value, timer IC 133 outputs a high-level start signal A from output node N22 after a specified time has elapsed. Start signal A is supplied to the gate electrode of transistor 135. Transistor 135 is connected between the gate electrode of output switch 140, which is a P-channel MOS transistor, and ground. Therefore, when start signal A is activated to a high level, the gate electrode of the P-channel MOS transistor constituting output switch 140 is grounded, turning on output switch 140. Consequently, output switch 140 turns on after a specified time has elapsed after the voltage at control node N4 exceeds a specified value. Here, the predetermined time measured by the timer IC 133 can be adjusted by the capacitance of the capacitor 134 connected to the adjustment node N23 .

[0033] In addition, the start signal A is also supplied to the start control terminal 103. As described above, the start control terminal 103 is commonly connected between the plurality of switching power supply circuits 100. Therefore, after the switch circuits 110 included in the plurality of switching power supply circuits 100 are started, the first activated start signal A is commonly supplied to each switching power supply circuit 100 via the start control terminal 103. As a result, the output switches 140 included in each switching power supply circuit 100 are turned on substantially at the same time. Figure 2 In the example shown, the enable signal A indirectly controls the output switch 140 via the transistor 135 , but the output switch 140 may also be directly controlled.

[0034] like Figure 1 As shown, multiple switching power supply circuits 100 having this structure can be connected in parallel to form a switching power supply system 10. In this case, by adjusting the variable resistor 122, the output voltage levels of each switching power supply circuit 100 can be made substantially uniform, so that some switching power supply circuits 100 will not be overloaded.

[0035] Furthermore, if an overcurrent or overload condition occurs in a switching power supply circuit 100, switching in that switching power supply circuit 100 ceases, and the output voltage Vout reaches zero. Consequently, an overcurrent or overload condition also occurs in the remaining switching power supply circuits 100, ultimately halting switching in all switching power supply circuits 100. Subsequently, by restarting the switching control circuit 114, the voltage at the output node N2 in each switching power supply circuit 100 rises. Then, in the switching power supply circuit 100 whose output node N2 voltage reaches the specified value first, the start signal A becomes active, and this signal is supplied to the other switching power supply circuits 100, causing all switching power supply circuits 100 to begin outputting power substantially simultaneously. Therefore, an overcurrent or overload condition does not occur in some switching power supply circuits 100 during startup.

[0036] In addition, Figure 1 In the example shown, since each switching power supply circuit 100 is connected to a different power supply 11, the input voltage Vin to each switching power supply circuit 100 may not necessarily be the same level. Even under such conditions, the switching power supply system 10 of this embodiment maintains a substantially uniform level of output voltage Vout from each switching power supply circuit 100, preventing some switching power supply circuits 100 from becoming overloaded.

[0037] Output node N3 is one end of the secondary winding 112 of transformer T, i.e., the anode of diode 116. The voltage level of output node N3 is higher than that of output node N2 by the forward voltage (forward voltage drop) of diode 116, and higher than the voltage level of control node N4 by the forward voltage of diode 118. However, since the voltage levels of output node N2 and control node N4 are roughly linked to output node N3, the operation of feedback circuit 120 and startup circuit 130 can be considered to be roughly the same for control node N4 and output node N2. Therefore, startup circuit 130 can also be connected to control node N4.

[0038] In this embodiment, the input node N5 of the feedback circuit 120 is connected to the control node N4 connected to the startup circuit 130, not the output node N2 connected to the output power supply terminal 102 via the output switch 140. By connecting the input node N5 of the feedback circuit 120 to the control node N4, the output voltage Vout can be accurately read without being affected by the load 12 connected to the output power supply terminal 102. For example, a predetermined voltage can be output even when no load is present.

[0039] Originally, the feedback information F is desirably read from output node N2. If the feedback information F is read from control node N4, regardless of the losses in diode 116, individual differences in diode 116 could lead to variations in the output voltage levels of each switching power supply circuit 100, potentially leading to unstable operation during parallel operation. However, the output voltage level of the switching power supply circuit 100 is adjusted by adjusting variable resistor 122 while observing output voltage Vout at output power supply terminal 102, and the adjustment result is also reflected at output node N2. Therefore, there is no problem in referencing the voltage at control node N4 as feedback information F.

[0040] Inserting a diode between the output switch 140 and the output power supply terminal 102 can prevent malfunction of the feedback circuit 120 caused by reading a voltage flowing back from another switching power supply circuit 100 during parallel operation. However, in this embodiment, such a diode can be omitted, which is advantageous in terms of component cost, output efficiency, and substrate size.

[0041] While preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention, and such modifications are naturally encompassed within the scope of the present invention.

[0042] Description of Reference Numerals

[0043] 10Switching power supply system

[0044] 11 Power Supply

[0045] 12 loads

[0046] 100 switching power supply circuit

[0047] 101 input power terminal

[0048] 102 output power terminal

[0049] 103 start control terminal

[0050] 110 switch circuit

[0051] 111 primary coil

[0052] 112 secondary coil

[0053] 113 switching elements

[0054] 114 switch control circuit

[0055] 115 resistor

[0056] 116 diode (first diode)

[0057] 117 capacitor (first capacitor)

[0058] 118 diode (second diode)

[0059] 119 capacitor (second capacitor)

[0060] 120 feedback circuit

[0061] 121, 124 fixed resistors

[0062] 122 variable resistor

[0063] 123 shunt regulator

[0064] 125 photodiode

[0065] 126 phototransistors

[0066] 130 starting circuit

[0067] 131, 132 fixed resistors

[0068] 133 timer IC

[0069] 134 capacitors

[0070] 135 transistors

[0071] 140 output switch

[0072] AStart signal

[0073] Feedback Information

[0074] N1 input node

[0075] N2, N3 output nodes

[0076] N4 control node

[0077] N5 input node

[0078] N6 ground node

[0079] N11 power node

[0080] N12 ground node

[0081] N13 control node

[0082] N14, N15 feedback nodes

[0083] N21 input node

[0084] N22 output node

[0085] N23 adjustment node

[0086] S switch signal

[0087] T Transformer

[0088] Vin input voltage

[0089] Vout output voltage.

Claims

1. A switching power supply circuit comprising: a switch circuit having an input node connected to an input power supply terminal and an output node connected to an output power supply terminal via an output switch; a feedback circuit that feeds back information based on a voltage appearing at a control node provided in parallel with the output node to the switching circuit; as well as a startup circuit that turns on the output switch after a voltage appearing at the control node exceeds a specified value and a specified time has elapsed, The switching circuit adjusts the voltages appearing at the output node and the control node to predetermined levels based on the feedback information. The feedback circuit includes an adjustment mechanism capable of adjusting the relationship between the voltage appearing at the control node and the information.

2. The switching power supply circuit according to claim 1, wherein: The feedback circuit includes a voltage divider circuit for dividing the voltage appearing at the control node. The adjustment mechanism is formed by a variable resistor included in the voltage dividing circuit.

3. The switching power supply circuit according to claim 1, wherein: The switching circuit includes a transformer, a switching element, and a switching control circuit. The transformer includes a primary coil connected to the input node and a secondary coil connected to the output node and the control node. The switching element is connected to the primary coil. The switching control circuit controls the switching element. The switching control circuit stops the switching operation of the switching element when determining that the current flowing through the switching element is an overcurrent.

4. The switching power supply circuit according to claim 3, wherein: The switching control circuit stops the switching operation of the switching element when it is determined that the information indicates an overload state.

5. The switching power supply circuit according to claim 3, wherein: One end of the secondary coil is connected to the output node via a first diode and is connected to the control node via a second diode. The other end of the secondary coil is grounded. The output node is grounded via a first capacitor, The control node is connected to ground via a second capacitor.

6. A switching power supply system comprising a plurality of switching power supply circuits according to any one of claims 1 to 5, The output power terminals respectively included in the plurality of switching power supply circuits are short-circuited with each other, The startup circuits respectively included in the plurality of switching power supply circuits include startup control terminals for directly or indirectly controlling the output switches. The startup control terminals respectively included in the plurality of switching power supply circuits are short-circuited with each other.

7. The switching power supply system according to claim 6, wherein: The device further includes a plurality of power supplies connected to the input power supply terminals included in the plurality of switching power supply circuits, respectively.

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