Switching power supply circuit and switching power supply system

Abstract

To provide switching power supply circuits that stably operate even when they are connected in parallel.SOLUTION: A switching power supply circuit 100 comprises: a switching circuit 110 that is connected to an input power supply terminal 101 at an input node N1, and connected to an output power supply terminal 102 at an output node N2 via an output switch 140; a feedback circuit 120 that supplies feedback information F based on a voltage appearing at a control node N4 provided in parallel to the output node N2 of the switching circuit 110, to the switching circuit 110; and a start-up circuit 130 that turns on the output switch 140 after the lapse of a predetermined time from when the voltage appearing at the control node N4 exceeds a predetermined value. The switching circuit 110 adjusts the voltages appearing 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 that can adjust the relationship between the voltage appearing at the control node N4 and the feedback information F.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a switching power supply circuit and a switching power supply system including the same. [Background technology]

[0002] Patent Document 1 discloses a switching power supply system in which multiple switching power supply circuits are connected in parallel. The switching power supply system disclosed in Patent Document 1 synchronizes the restart timing of each switching power supply circuit by shorting the on / off control terminals of the PWM control ICs included in each switching power supply circuit. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2003-169471 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when multiple switching power supply circuits are connected in parallel, if there is a difference in output voltage between the switching power supply circuits, the switching power supply circuit with the higher output voltage may enter an overcurrent or overload state.For this reason, in the switching power supply system described in Patent Document 1, even if the switching power supply circuits are restarted simultaneously, an overcurrent or overload may occur in the switching power supply circuit with the higher output voltage, causing the switching operation to immediately stop.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a switching power supply circuit that operates stably even when connected in parallel, and a switching power supply system using the same. [Means for solving the problem]

[0006] A switching power supply circuit according to the present invention comprises a switching circuit having an input node connected to an input power supply terminal and an output node connected to the output power supply terminal via an output switch, a feedback circuit that feeds back information based on the voltage appearing at a control node provided in parallel with the output node to the switching circuit, and a start-up circuit that turns on the output switch after a predetermined time has elapsed since the voltage appearing at the control node exceeded a predetermined value, wherein the switching circuit adjusts the voltages appearing at the output node and the control node to predetermined levels based on the fed-back information, and the feedback circuit includes an adjustment mechanism that can adjust the relationship between the voltage appearing at the control node and the information.

[0007] According to the present invention, by using an adjustment mechanism that can adjust the relationship between the voltage appearing at a control node provided in parallel with the output node and the fed-back information, it is possible to adjust the level of the output voltage output from the output power supply terminal. As a result, when a switching power supply system is configured by connecting multiple switching power supply circuits in parallel, it is possible to prevent a phenomenon in which a specific switching power supply circuit preferentially enters an overcurrent state or an overload state.

[0008] In the present invention, the feedback circuit includes a voltage divider circuit that divides the voltage appearing at the control node, and the adjustment mechanism may be a variable resistor included in the voltage divider circuit, which makes it possible to easily adjust the level of the output voltage.

[0009] In the present invention, the switching circuit includes a transformer having a primary winding connected to an input node and a secondary winding connected to an output node and a control node, a switching element connected to the primary winding, and a switching control circuit that controls the switching element, and the switching control circuit may stop the switching operation of the switching element when it determines that the current flowing through the switching element is an overcurrent, thereby making it possible to resolve the overcurrent state.

[0010] In the present invention, the switching control circuit may stop the switching operation of the switching element when it determines that the information indicates an overload state, thereby making it possible to eliminate the overload state.

[0011] In the present invention, one end of the secondary winding 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 winding may be grounded, the output node may be grounded to ground via a first capacitor, and the control node may be grounded to ground via a second capacitor. In this case, the second diode may have a smaller maximum rating than the first diode, and the second capacitor may have a smaller capacitance than the first capacitor. With this configuration, a specified voltage can be stably output from the output power supply terminal regardless of the size of the load connected to the output power supply terminal.

[0012] A switching power supply system according to the present invention includes a plurality of the above-described switching power supply circuits, wherein the output power supply terminals included in each of the plurality of switching power supply circuits are short-circuited to each other, and the startup circuits included in each of the plurality of switching power supply circuits include startup control terminals that directly or indirectly control the output switches, and the startup control terminals included in each of the plurality of switching power supply circuits may be short-circuited to each other. This makes it possible to restart the plurality of switching power supply circuits simultaneously.

[0013] The switching power supply system according to the present invention may further include a plurality of power sources connected to the input power supply terminals of the plurality of switching power supply circuits, respectively, so that even if there is a difference in the levels of the input voltages supplied from the plurality of power sources, a specific switching power supply circuit will not preferentially enter an overcurrent or overload state. [Effects of the Invention]

[0014] 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 same. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram illustrating the configuration of a switching power supply system 10 according to one embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram of the switching power supply circuit 100. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0017] FIG. 1 is a block diagram illustrating the configuration of a switching power supply system 10 according to one embodiment of the present invention.

[0018] As shown in FIG. 1, a switching power supply system 10 according to this embodiment has a configuration 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 from which an output voltage Vout is output, and a startup control terminal 103. The output power supply terminals 102 included in each switching power supply circuit 100 are shorted to each other and connected in common to a load 12. The input power supply terminals 101 included in each switching power supply circuit 100 are connected to different power sources 11. The power sources 11 may be power pickup transformers that extract power by utilizing a magnetic field generated around a high-voltage power transmission line. The startup control terminals 103 included in each switching power supply circuit 100 are also shorted to each other.

[0019] FIG. 2 is a circuit diagram of the switching power supply circuit 100.

[0020] As shown in FIG. 2, the switching power supply circuit 100 includes a switching circuit 110, a feedback circuit 120, a start-up circuit 130, and an output switch 140. The switching circuit 110 includes a transformer T including a primary winding 111 and a secondary winding 112, a switching element 113 connected to one end of the primary winding 111, and a switching control circuit 114 that controls the switching element 113. The other end of the primary winding 111 forms an input node N1 of the switching circuit 110 and is connected to an input power supply terminal 101. An output node N3, which is one end of the secondary winding 112, is connected to an output node N2 via a diode 116 (first diode) and to a control node N4 via a diode 118 (second diode). The output node N2 is connected to the output power supply terminal 102 via an output switch 140. The other end of the secondary winding 112 is grounded via a ground node N6. The output node N2 is connected to the ground node N6 via a 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 a ground node N6 via a capacitor 119 (second capacitor).

[0021] 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 capacitance of capacitor 119 may be smaller than that of capacitor 117, and an electrolytic capacitor may be used for capacitor 117 and a multilayer ceramic capacitor may be used for capacitor 119.

[0022] The switching control circuit 114 is formed, for example, by a controller IC, and has a power supply node N11, a ground node N12, a control node N13, and feedback nodes N14 and N15. The switching control circuit 114 operates by a voltage supplied between the power supply node N11 and the ground node N12, and adjusts the voltage appearing at the output node N2 to a predetermined level by controlling the frequency and duty of a switching signal S output from the control node N13 based on feedback information F supplied to the feedback node N14. The switching element 113 to which the switching signal S is supplied is formed, for example, by an N-channel MOS transistor.

[0023] Furthermore, the current flowing through the switching element 113 is supplied to a feedback node N15 of the switching control circuit 114 via a resistor 115. The switching control circuit 114 monitors the current supplied to the feedback node N15, and if it determines that the current flowing through the switching element 113 is an overcurrent, it fixes the switching signal S to an inactive level (e.g., ground level) to stop the switching operation of the switching element 113. This makes it possible to prevent damage to the switching element 113 due to the overcurrent. Furthermore, if the switching control circuit 114 determines that the feedback information F indicates an overload state, it also fixes the switching signal S to an inactive level to stop the switching operation of the switching element 113. When the switching operation is stopped, the switching control circuit 114 is restarted and resumes the switching operation after a predetermined time.

[0024] The feedback circuit 120 generates feedback information F based on the voltage appearing at a control node N4 connected in parallel to the output node N2, and feeds this information back to the switching circuit 110. When the output switch 140 is on, the voltages appearing at the output node N2 and the control node N4 approximately match the output voltage Vout. The feedback circuit 120 includes fixed resistors 121 and 124, a variable resistor 122, a shunt regulator 123, a photodiode 125, and a phototransistor 126. The fixed resistor 121 and the variable resistor 122 are connected in series between the control node N4 and the anode of the shunt regulator 123 to form a voltage divider circuit, and the voltage at the connection point is supplied to the reference node of the shunt regulator 123. The fixed resistor 124 and the photodiode 125 are also connected in series between the control node N4 and the cathode of the shunt regulator 123. The photodiode 125 and the phototransistor 126 constitute a photocoupler, which plays a role in transmitting feedback information F from the secondary side to the primary side while ensuring insulation between the primary side and the secondary side.

[0025] The level of feedback information F varies not only depending on the voltage appearing at control node N4, which is equivalent to the voltage appearing at output node N2, but also on the voltage division ratio of a voltage divider circuit consisting of fixed resistor 121 and variable resistor 122. At the design stage, the voltage division ratio of the voltage divider circuit is determined so that the voltage appearing at output node N2 will be a predetermined level (e.g., 24 V). However, due to individual differences caused by manufacturing variations and the like, the voltage actually appearing at output node N2 may deviate from the predetermined level. Variable resistor 122 is an adjustment mechanism for eliminating such deviations. 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 adjusting the voltage appearing at output node N2 to a predetermined level (e.g., 24 V).

[0026] The startup circuit 130 includes fixed resistors 131 and 132, a timer IC 133, a capacitor 134, and an N-channel MOS transistor 135. The fixed resistors 131 and 132 are connected in series between a control node N4 and ground to form a voltage divider circuit, and the voltage at their junction is supplied to an input node N21 of the timer IC 133. When the voltage supplied to the input node N21 exceeds a predetermined value, the timer IC 133 outputs a high-level startup signal A from an output node N22 after a predetermined time has elapsed. The startup signal A is supplied to the gate electrode of a transistor 135. The transistor 135 is connected between the gate electrode of an output switch 140, which is a P-channel MOS transistor, and ground. Therefore, when the startup signal A is activated to a high level, the gate electrode of the P-channel MOS transistor that constitutes the output switch 140 is grounded, turning on the output switch 140. Therefore, the output switch 140 turns on after a predetermined time has elapsed since the voltage appearing at the control node N4 exceeded the predetermined 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.

[0027] The startup signal A is also supplied to the startup control terminal 103. As described above, the startup control terminal 103 is commonly connected among the multiple switching power supply circuits 100. Therefore, after the switching circuits 110 included in each of the multiple switching power supply circuits 100 are started, the startup signal A that is activated first is commonly supplied to each switching power supply circuit 100 via the startup control terminal 103. As a result, the output switches 140 included in each switching power supply circuit 100 are turned on almost simultaneously. Note that, although the startup signal A indirectly controls the output switch 140 via the transistor 135 in the example shown in FIG. 2, it may also be configured to directly control the output switch 140.

[0028] 1, a plurality of switching power supply circuits 100 having such a configuration 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 the switching power supply circuits 100 can be made approximately the same, preventing some of the switching power supply circuits 100 from entering an overload state.

[0029] Furthermore, if an overcurrent or overload state occurs in one switching power supply circuit 100, the switching operation of that switching power supply circuit 100 stops, and the output voltage Vout becomes zero. As a result, an overcurrent or overload state occurs in the remaining switching power supply circuits 100, and eventually, switching operation stops in all switching power supply circuits 100. Thereafter, the switching control circuit 114 restarts, causing the voltage of the output node N2 in each switching power supply circuit 100 to rise. Then, the start-up signal A is activated in the switching power supply circuit 100 whose output node N2 voltage reaches a predetermined value first, and this signal is supplied to the other switching power supply circuits 100, causing all switching power supply circuits 100 to start outputting power almost simultaneously. Therefore, an overcurrent or overload state does not occur in some switching power supply circuits 100 during startup.

[0030] 1, the switching power supply circuits 100 are connected to different power sources 11, and therefore the levels of the input voltages Vin input to the switching power supply circuits 100 do not necessarily match. Even under such conditions, the switching power supply system 10 according to this embodiment ensures that the levels of the output voltages Vout of the switching power supply circuits 100 are approximately the same, and therefore some of the switching power supply circuits 100 do not enter an overload state.

[0031] The output node N3 is one end of the secondary winding 112 of the transformer T, i.e., the anode of the diode 116. The level of the output node N3 is higher than the output node N2 by the forward voltage of the diode 116, and higher than the voltage level of the control node N4 by the forward voltage of the diode 118. However, since the levels of the output node N2 and the control node N4 are substantially linked to the output node N3, the control node N4 and the output node N2 can be considered to be substantially the same with respect to the operations of the feedback circuit 120 and the start-up circuit 130. For this reason, the start-up circuit 130 may be connected to the control node N4.

[0032] In this embodiment, the input node N5 of the feedback circuit 120 is connected to the control node N4 connected to the start-up circuit 130, rather than to 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 read correctly without being affected by the load 12 connected to the output power supply terminal 102, and the specified voltage can be output even when there is no load.

[0033] Ideally, the output node N2 is the desired destination for reading the feedback information F. If the control node N4 is used as the destination for reading the feedback information F, the loss in the diode 116 is not taken into consideration, and individual differences in the diodes 116 may cause variations in the output voltage level of each switching power supply circuit 100, potentially resulting in unstable operation during parallel operation. However, the output voltage level of the switching power supply circuit 100 is adjusted by adjusting the variable resistor 122 while monitoring the output voltage Vout appearing at the output power supply terminal 102, and the adjustment result is also reflected in the output node N2. Therefore, there is no problem in referring to the voltage of the control node N4 as the feedback information F.

[0034] Malfunction of the feedback circuit 120 caused by reading a voltage that flows back from another switching power supply circuit 100 during parallel operation can be prevented by inserting a diode between the output switch 140 and the output power supply terminal 102. However, in this embodiment, it is not necessary to mount such a diode, which is advantageous in terms of component costs, output efficiency, board size, etc.

[0035] The above describes a preferred embodiment of the present invention, but the present invention is not limited to the above embodiment, and various modifications are possible within the scope of the present invention, and it goes without saying that these modifications are also included within the scope of the present invention. [Explanation of symbols]

[0036] 10 Switching Power Supply System 11 Power source 12 Load 100 Switching power supply circuit 101 Input power terminal 102 Output power terminal 103 Start control terminal 110 Switching Circuit 111 Primary winding 112 Secondary winding 113 Switching element 114 Switching control circuit 115 Resistance 116 Diode (First Diode) 117 Capacitor (1st Capacitor) 118 Diode (Second Diode) 119 Capacitor (Second Capacitor) 120 Feedback Circuit 121,124 Fixed resistance 122 variable resistor 123 Shunt Regulator 125 photodiode 126 Phototransistor 130 Starter Circuit 131,132 Fixed resistance 133 Timer IC 134 Capacitor 135 transistors 140 Output Switch A Start signal F Feedback Information N1 input node N2,N3 output nodes N4 Control Node N5 input node N6 Ground Node N11 Power Node N12 Ground node N13 Control Node N14, N15 Feedback Nodes N21 input node N22 output node N23 Coordination Node S Switching signal T transformer Vin Input voltage Vout Output voltage

Claims

1. a switching circuit having an input node connected to an input power supply terminal and an output node connected via an output switch to an output power supply terminal; a feedback circuit that feeds back information based on a voltage appearing at a control node that is provided in parallel with the output node to the switching circuit; a start-up circuit that turns on the output switch after a predetermined time has elapsed since the voltage appearing at the control node exceeded a predetermined value; the switching circuit adjusts the voltages appearing at the output node and the control node to predetermined levels based on the fed-back 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 feedback circuit includes a voltage divider circuit that divides the voltage appearing at the control node; 2. The switching power supply circuit according to claim 1, wherein the adjusting mechanism is a variable resistor included in the voltage divider circuit.

3. the switching circuit includes a transformer including a primary winding connected to the input node and a secondary winding connected to the output node and the control node, a switching element connected to the primary winding, and a switching control circuit that controls the switching element; 2. The switching power supply circuit according to claim 1, wherein said switching control circuit stops a switching operation of said switching element when it is determined that the current flowing through said switching element is an overcurrent.

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

5. one end of the secondary winding is connected to the output node via a first diode and to the control node via a second diode; The other end of the secondary winding is grounded, the output node is connected to ground via a first capacitor; 4. The switching power supply circuit according to claim 3, wherein the control node is connected to ground via a second capacitor.

6. a plurality of switching power supply circuits according to any one of claims 1 to 5; the output power supply terminals included in each of the plurality of switching power supply circuits are short-circuited to each other, the startup circuit included in each of the plurality of switching power supply circuits includes a startup control terminal that directly or indirectly controls the output switch; The startup control terminals included in each of the plurality of switching power supply circuits are short-circuited to each other.

7. 7. The switching power supply system according to claim 6, further comprising a plurality of power sources connected to the input power supply terminals included in the plurality of switching power supply circuits, respectively.

Images