JP2009005476A - Multi-output switching power supply unit for detecting each output current in each output choke coil and executing ocp protection in collectively configured section - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-output switching power supply unit capable of exhibiting an overcurrent protective function without providing an independent current detecting section in each output circuit and saving a space of the unit. <P>SOLUTION: Output currents Io1, Io2 of a main output circuit 11 and an output circuit 21 are monitored by current monitoring sections 55, 65 provided at the main output circuit 11 and the output circuit 21, and current detection signals proportional to the output currents Io1, Io2 are generated in the respective current monitoring sections 55, 65. The current detection signals are compared to a predetermined value by an overcurrent determination section 71 commonly arranged between the main output circuit 11 and the output circuit 21. When one of the current detection signals reaches the predetermined value, it is determined that either of the main output circuit 11 and the output circuit 21 is in an overcurrent state and an overcurrent generation signal is outputted, and a main control circuit 31 having received this signal controls the operation of an MOS-FET 4 so that the output currents Io1, Io2 are limited. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a multi-output switching power supply apparatus including a current detection unit that detects each output current in each output circuit.

  In general, a multi-output switching power supply apparatus includes a transformer formed by magnetically coupling a primary winding and a plurality of secondary windings, and an output rectifier circuit and an output for each secondary winding of the transformer. An output circuit consisting of a smoothing circuit is connected, and a predetermined DC output voltage is applied to the load from each output circuit by intermittently applying an input voltage to the primary winding of the transformer in accordance with the switching operation of the switching element. It is configured to supply. In each output circuit, the output voltage generated from the main main output circuit in particular is stabilized by the main control circuit that monitors this output voltage and feedback-controls the switching element, and other output circuits. The output voltage generated from is individually stabilized by each control circuit provided for each output circuit.

  On the other hand, such a switching power supply device includes a current detection unit that generates a current detection signal corresponding to the output current flowing through the load, and forcibly limits the output current when the current detection signal exceeds a predetermined voltage level. Overcurrent protection (OCP) function is provided.

  FIG. 2 shows a conventional example in which such a current detection circuit is applied to a multi-output switching power supply device. In these drawings, reference numerals 1 and 2 denote input terminals connected between both ends of the DC power source E. Between the input terminals 1 and 2, a primary winding 3A of the transformer 3 and a MOS type FET 4 which is a switching element are connected. A series circuit is connected.

  On the other hand, in the multi-output switching power supply device, the transformer 3 includes a plurality of secondary windings 3B and 3C according to the number of outputs. Here, assuming that two output voltages Vo1 and Vo2 are supplied to the respective loads Z1 and Z2, the main output circuit 11 connected to the secondary winding 3B and the secondary winding 3C are connected. And an output circuit 21. Of course, the number of secondary windings of the transformer 3 and the corresponding output circuits (main output circuit 11 and output circuit 21) may be three or more.

  The main output circuit 11 connected to the main secondary winding 3B is connected to the output rectifier circuit 14 composed of the rectifier diode 12 and the commutation diode 13 and the output terminal of the output rectifier circuit 14, and the choke coil 15 and the output The output smoothing circuit 17 is composed of a capacitor 16. Output terminals 18 and 19 to which a load Z1 can be connected are connected between both ends of the output capacitor 16 where the output voltage Vo1 is generated.

  An output circuit 21 connected to another secondary winding 3C is also connected to an output rectifier circuit 24 including a rectifier diode 22 and a commutation diode 23, and an output terminal of the output rectifier circuit 24. 25 and an output smoothing circuit 27 comprising an output capacitor 26. The output terminals 28 and 29 to which the load Z2 can be connected are connected between both ends of the output capacitor 26 where the output voltage Vo2 is generated. The output circuit 21 further includes a mag amplifier (saturable reactor) 30 inserted and connected between one end of the secondary winding 3 </ b> C and the input end of the output rectifier circuit 24. As is well known, the mag amplifier 30 functions as a magnetic switch for independently adjusting the output voltage Vo2 in the output circuit 21, and is switched by a reset current supplied from a sub-control circuit 32 described later.

  Note that, on the output side of the transformer 3, the negative voltage line connected to the output terminal 19 of the main output circuit 11 and the negative voltage line connected to the output terminal 29 of the output circuit 21 are both grounded and the same potential is maintained. Yes.

  In order to stabilize the output voltage Vo1 from the main output circuit 11, on the input (primary) side of the transformer 3, the output voltage Vo1 is monitored, and a pulse drive signal having a conduction width corresponding to the fluctuation of the output voltage Vo1 is provided. A main control circuit 31 for supplying the MOS type FET 4 is provided. The output circuit 21 also monitors the output voltage Vo2 and independently monitors the output voltage Vo2 in order to stabilize the output voltage Vo2 independently of the conduction width of the pulse drive signal supplied to the MOS FET 4. A mag-amplifier control circuit 32 that supplies a reset current commensurate with the fluctuation to the mag-amplifier 30 is provided on the output (secondary) side of the transformer 3.

  In a steady state, a pulse drive signal is supplied from the main control circuit 31 to the MOS FET 4, and the input voltage Vi from the DC power source E is intermittently applied to the primary winding 3 </ b> A of the transformer 3. Thus, in the main output circuit 11, when the MOS FET 4 is turned on, an induced voltage is generated in the secondary winding 3B of the transformer 3 so that the rectifier diode 12 is turned on and the commutation diode 13 is turned off. The voltage is supplied from the rectifier diode 12 through the choke coil 15 to the output capacitor 16 and the load Z1. Thereafter, when the MOS FET 4 is turned off, an induced voltage is generated in the secondary winding 3B of the transformer 3 so that the commutation diode 13 is turned on and the rectifier diode 12 is turned off. The energy stored in the capacitor 16 is supplied to the load Z1 connected to the main output circuit 11 through the commutation diode 13, so that a predetermined output voltage Vo1 is given across the load Z1.

  Here, the main control circuit 31 monitors the output voltage Vo1, and supplies the MOS FET 4 with a pulse drive signal having a conduction width corresponding to the fluctuation of the output voltage Vo1. The voltage feedback control by the main control circuit 31 stabilizes the output voltage Vo supplied from the main output circuit 11 to the load Z1.

  In the output circuit 21 other than the main output circuit 11, when the MOS type FET 4 is turned on, the induced voltage generated in the secondary winding 3C of the transformer 3 turns on the rectifier diode 22 and turns off the commutation diode 23. The induced voltage passes through the mag amplifier 30, the rectifier diode 22, and the choke coil 25 in order, and is supplied to the output capacitor 26 and the load Z2. Thereafter, when the MOS type FET 4 is turned off, the polarity of the induced voltage generated in the secondary winding 3C of the transformer 3 is reversed, and the commutation diode 23 is turned on and the rectifier diode 22 is turned off. Therefore, the energy previously stored in the choke coil 25 and the output capacitor 26 is supplied to the load Z2 connected to the output circuit 21 through the commutation diode 23. Here, the conduction angle of the rectangular wave AC from the secondary winding 3C converted by the transformer 3 is controlled by the mag-amplifier 30, and this is rectified and smoothed by the output circuit 21, thereby providing a predetermined output between both ends of the load Z2. A voltage Vo2 is applied.

  Further, the mag amplifier control circuit 32 monitors the output voltage Vo2, and causes the reset current to flow through the mag amplifier 30 when the output voltage Vo2 becomes higher than a predetermined value. The reset current for the mag amplifier 30 is controlled by the mag amplifier control circuit 32, so that the output voltage V02 is stabilized independently of the output circuit 21. As an output voltage control method for such a multi-output switching power supply device, an example in which a mag amplifier 30 is employed is known, for example, in Patent Document 1.

  In the circuit example shown in FIG. 2, the current transformer 35 is used as a current detector for detecting the current flowing through the load Z1, that is, the output current Io1 from the main output circuit 11, and the current flowing through the load Z2, that is, the output circuit 21. As a current detector for detecting the output current Io2 from the other current transformer 45, another current transformer 45 is used. Such a circuit configuration is known from Patent Document 2, for example.

  In the main output circuit 11, the primary winding 35 </ b> A of the current transformer 35 is inserted and connected between the negative output voltage line from the secondary winding 3 </ b> B of the transformer 3 to the output terminal 19. The current detection unit 36 amplifies the voltage generated across the secondary winding 35B of the current transformer 35. When the amplified current detection signal exceeds a predetermined voltage level, the current detection unit 36 An overcurrent generation signal is output to the main control circuit 31 on the input side of the transformer 3 via a signal transmission element 37 that is electrically insulated from the output side.

  In the output circuit 21, the primary winding 45 </ b> A of the current transformer 45 is inserted and connected between the negative output voltage line from the secondary winding 3 </ b> C of the transformer 3 to the output terminal 29. The current detection unit 46 amplifies the voltage generated between both ends of the secondary winding 45B of the current transformer 45. When the amplified current detection signal exceeds a predetermined voltage level, the current detection unit 46 outputs an overcurrent generation signal to the magamp control circuit 32. It is designed to output.

  With such a circuit configuration, the output terminals 18 and 19 of the main output circuit 11 are short-circuited or overloaded, and the output current I01 and the current flowing through the primary winding 35A of the current transformer 35 increase. When the generated current detection signal exceeds a predetermined voltage level, an overcurrent generation signal is output from the current detection unit 36 to the main control circuit 31. In response to this, the main control circuit 31 narrows the conduction width of the pulse drive signal to the MOS type FET 4 and forcibly limits the output current I01 from the main output circuit 11.

In addition, when the output terminals 28 and 29 of another output circuit 21 are short-circuited or overloaded, and the output current I02 and the current flowing through the primary winding 45A of the current transformer 45 increase, the current detection unit 46 When the generated current detection signal exceeds a predetermined voltage level, an overcurrent generation signal is output from the current detection unit 46 to the mag amplifier control circuit 32. In response to this, the mag-amp control circuit 31 controls the mag-amp 30 so that the mag-amp 30 is in a non-saturated (switch-off) state, whereby the output current I02 from the output circuit 21 is individually output by each output circuit 21. It can be forcibly restricted.
JP 2002-320383 A JP-A-2005-312203

  As described above, in the multi-output switching power supply device, the main output circuit 11 is provided with the current detection unit 36, and separately from the current detection unit 36, the other output circuit 21 has its own current detection unit 36. Provided. However, as the number of outputs increases, current detection units 36, 46,... Corresponding to the number of outputs are required, and the space of the apparatus cannot be saved.

  In the switching power supply described above, current transformers 35 and 45 and other shunt resistors are used as current detectors for detecting the output currents Io1 and Io2. However, the current transformers 35 and 45 and the shunt resistor must be selected in consideration of the winding diameter and rated power that satisfy the value of the output current Io, and the output currents Io1 and Io2 to be detected must be selected. The larger the value, the larger the component size proportionally. For this reason, it is necessary to secure a large part space, and it is impossible to save the space of the apparatus.

  Therefore, in view of the above problems, the present invention can operate an overcurrent protection function without providing a unique current detection unit in each output circuit, and can reduce the space of the device. The main object is to provide a power supply device.

  The invention of claim 1 includes a switching element, a transformer formed by magnetically coupling a primary winding and a plurality of secondary windings, and an output circuit connected to each of the secondary windings. The input voltage is intermittently applied to the primary winding of the transformer by switching of the switching element, and the voltage generated in each secondary winding of the transformer is rectified and smoothed by the respective output circuits to the load. In the multi-output switching power supply for supplying power, a current monitoring unit that is provided in each output circuit, monitors an output current flowing from the output circuit to the load, and generates a current detection signal proportional to the output current Provided in common to each of the output circuits, and when at least one of the current detection signals from the current monitoring units reaches a certain value or more, an overcurrent generation signal is generated. And overcurrent determination unit configured to force the overcurrent generation signal from the overcurrent determination unit is outputted, and a overcurrent protection unit that controls the operation of the switching element so as to limit the output current.

  According to a second aspect of the present invention, the output circuit comprises an output rectifier circuit that rectifies the voltage generated in the secondary winding of the transformer, and a choke coil that smoothes the voltage rectified by the output rectifier circuit. And supplying power to the load through the choke coil, and outputting an output current connected to the choke coil and flowing through the load as a voltage drop signal due to an internal resistance of the choke coil. The current monitoring unit is configured by a voltage drop detection circuit and an amplification circuit that amplifies a signal output from the voltage drop detection circuit and generates the current detection signal proportional to the output current.

  In the first aspect of the invention, the output current in each output circuit is monitored by a current monitoring unit provided for each output circuit, and a current detection signal proportional to the output current is generated by each current monitoring unit. These current detection signals are compared with a constant value by an overcurrent determination unit provided in common to each output circuit, and if one of the current detection signals reaches a certain value, one of the output circuits Is determined to be in an overcurrent state, an overcurrent generation signal is output, and the overcurrent protection unit receiving this signal controls the operation of the switching element so as to limit the output current.

  In this way, regardless of the number of output circuits, after generating the current detection signal, each output circuit does not have its own current detection unit, and the overcurrent determination unit and overcurrent protection common to each output circuit are provided. An appropriate overcurrent protection function can be operated by the unit, and the space of the apparatus can be saved.

  According to the second aspect of the present invention, in one or a plurality of output circuits, a voltage drop detection circuit is connected to the choke coil so that the output current flowing through the load is supplied to the amplifier circuit as a signal for the voltage drop due to the internal resistance of the choke coil. A current detection signal proportional to the output current can be generated from the amplifier circuit. In other words, without using any current transformer or shunt resistor as in the past, using the resistance of the choke coil that originally functions as an output smoothing circuit, just connecting the voltage drop detection circuit across this choke coil Thus, since the output current can be detected, even if the output current to be detected is a certain large value, the space saving of the apparatus can be easily realized. Also, by variably setting the amplification degree of each amplifier circuit, the overcurrent protection operating point in each output circuit can be easily set.

  Hereinafter, preferred embodiments of a switching power supply device according to the present invention will be described with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected to the location which is common in a prior art example, and description of the common part is abbreviate | omitted as much as possible in order to avoid duplication.

  FIG. 1 is a circuit configuration diagram showing one preferred embodiment of a switching power supply device. In this figure, a voltage drop detection circuit 51 for detecting a voltage drop across the choke coil 15 is provided in place of the current transformer 35, and similarly, the choke coil 25 is replaced with the current transformer 45. A voltage drop detection circuit 61 for detecting a voltage drop between both ends is provided. The voltage drop detection circuit 51 detects a voltage drop generated in this resistor in combination with a specific resistance component (not shown) included in the choke coil 15. Specifically, the voltage drop detection circuit 51 detects the voltage drop generated in this resistor. Is connected between both ends of the choke coil 15, and one end of the choke coil 15 connected to the output end of the output rectifier circuit 14 is connected to one end of the resistor 52. The other end of the resistor 52 and the capacitor The other ends of the choke coil 15 reaching the output terminal 18 are connected to the other end of the capacitor 53.

  Here, the choke coil 15 is inserted and connected to a positive output voltage line that generates a positive voltage with respect to the output terminal 19 and extends from the output terminal of the output rectifier circuit 14 to the output terminal 18. The choke coil 15 may be connected to the negative output voltage line extending from the output terminal of the output rectifier circuit 14 to the output terminal 19, and the voltage drop detection circuit 51 may be connected in parallel between both ends thereof.

  Similarly, the voltage drop detection circuit 61 detects a voltage drop generated in this resistor in combination with a specific resistance component (not shown) included in the choke coil 25. And one end of the choke coil 25 connected to the output end of the output rectifier circuit 24 is connected to one end of the resistor 62. The other end of the choke coil 25 reaching the output terminal 28 is connected to the other end of the capacitor 63.

  Here, the choke coil 25 is inserted and connected to a positive output voltage line that generates a positive voltage with respect to the output terminal 29 and extends from the output terminal of the output rectifier circuit 24 to the output terminal 28. The choke coil 25 may be connected to the negative output voltage line extending from the output terminal of the output rectifier circuit 24 to the output terminal 29, and the voltage drop detection circuit 61 may be connected in parallel between the both ends.

  The voltage drop detection circuit 51 generates an output current I01 flowing through the load Z1 between both ends of the capacitor 53 as a signal for a voltage drop due to the internal resistance of the choke coil 15, and the voltage drop detection circuit 61 The output current I02 flowing through Z2 is generated between both ends of the capacitor 63 as a signal for a voltage drop due to the internal resistance of the choke coil 25. A signal generated between both ends of the capacitor 53 is amplified by the amplifier circuit 54 and output as a current detection signal of the output current I01. Similarly, a signal generated between both ends of the capacitor 63 is amplified by another amplifier circuit 64 and output as a current detection signal of the output current I02. Here, the voltage drop detection circuit 51 and the amplification circuit 54 monitor the output current I01 flowing from the main output circuit 11 to the load Z1, and generate a current detection signal proportional to the output current I01. The voltage drop detection circuit 61 and the amplification circuit 64 monitor the output current I01 flowing from the main output circuit 11 to the load Z1 and generate a second current detection signal proportional to the output current I01. This corresponds to the current monitoring unit 65. One of these current monitoring units 55 and 65 is provided for each of the output circuits (the main output circuit 11 and the output circuit 21).

  On the other hand, 71 is an overcurrent determination unit that outputs an overcurrent generation signal when at least one of the current detection signals output from the amplifier circuits 54 and 64 reaches a predetermined value or more. Only one overcurrent determination unit 71 is provided regardless of the number of output circuits (the main output circuit 11 and the output circuit 21), and the current detection signals from the amplifier circuits 54 and 64 are used to prevent backflow. The comparator 72 applied to one common input terminal (here, a non-inverting input terminal) and the other input terminal (here, the inverting input terminal) of the comparator 72 are connected via the diodes 56 and 66. When the voltage level at the output terminal of the comparator 72 is inverted when at least one of the reference power supply 73 and the voltage level of each current detection signal reaches or exceeds the reference voltage generated by the reference power supply 73, the signal transmission element 37 is turned on. And an OCP (overcurrent protection) circuit 74 that outputs an overcurrent generation signal to the main control circuit 31. In response to the overcurrent generation signal from the overcurrent determination unit 71, the main control circuit 31 as the overcurrent protection unit controls the operation of the MOS FET 4 so as to limit the output currents Io1 and Io2. It has become.

  Next, the operation of the switching power supply device with the above configuration is as described above. A pulse drive signal is supplied from the main control circuit 31 to the MOS type FET 4, and the primary winding 3A of the transformer 3 is supplied from the DC power source E. The input voltage Vi is intermittently applied. Thereby, in the main output circuit 11, when the MOS type FET 4 is turned on, the rectifier diode 12 is turned on by the induced voltage generated in the secondary winding 3B of the transformer 3, while the commutation diode 13 is turned off. Is supplied from the rectifier diode 12 through the choke coil 15 to the output capacitor 16 and the load Z1. After that, when the MOS type FET 4 is turned off, an induced voltage having a reverse polarity is generated in the secondary winding 3B of the transformer 3 and the rectifier diode 12 is turned off while the commutation diode 13 is turned on. The energy stored in the coil 15 and the output capacitor 16 is supplied to the load Z1 through the commutation diode 13. By repeating such an operation, a predetermined output voltage Vo1 is generated between the output terminals 11 and 12, and this is applied across the load Z1.

  Similarly, in the other output circuit 21, when the MOS type FET 4 is turned on, the induced voltage generated in the secondary winding 3C of the transformer 3 turns on the rectifier diode 22, while the commutation diode 23 turns off. The induced voltage passes through the mag amplifier 30, the rectifier diode 22, and the choke coil 25 in order, and is supplied to the output capacitor 26 and the load Z2. After that, when the MOS type FET 4 is turned off, an induced voltage having a reverse polarity is generated in the secondary winding 3C of the transformer 3 and the rectifier diode 22 is turned off while the commutation diode 23 is turned on. The energy stored in the coil 25 and the output capacitor 26 is supplied to the load Z2 through the commutation diode 23. Here, the conduction angle of the rectangular wave AC from the secondary winding 3C converted by the transformer 3 is controlled by the mag-amplifier 30, and this is rectified and smoothed by the output circuit 21, thereby providing a predetermined output between both ends of the load Z2. A voltage Vo2 is applied.

  During the series of operations, the main output circuit 11 monitors the output voltage Vo1, and as the output voltage Vo1 decreases, the conduction width of the pulse drive signal supplied to the MOS-type FET 4 is increased. As it rises, so-called PWM control is performed to narrow the conduction width of the pulse drive signal. By such voltage feedback control of the main output circuit 11, the output voltage Vo is stabilized.

  Further, the mag amplifier control circuit 32 monitors the output voltage Vo2 from the output circuit 21, and causes a reset current to flow through the mag amplifier 30 when the output voltage Vo2 becomes higher than a predetermined value. The reset current for the mag amplifier 30 is controlled by the mag amplifier control circuit 32, so that the output voltage V02 is stabilized independently of the output circuit 21.

  In the main output circuit 11, energy is stored in the choke coil 15 during the ON period of the MOS FET 4, so that the output terminal of the output rectifier circuit 14 is connected to the other end of the choke coil 15 connected to the output terminal 18. A positive voltage is generated at one end of the connected choke coil 15. Therefore, in the voltage drop detection circuit 51, electric charge is stored in the capacitor 53 via the resistor 52, and the voltage across the capacitor 53 increases unilaterally.

  Eventually, when the MOS type FET 4 is in the OFF period, the energy stored in the choke coil 15 until then is sent to the load Z1 side, so that the negative electrode is connected to one end of the choke coil 15 with the other end of the choke coil 15 as a reference. Voltage is generated. When this happens, the capacitor 53 releases the charge stored so far, and the voltage across the capacitor 25 falls unilaterally. In other words, the voltage drop detection circuit 51 here charges and discharges the capacitor 25 using the voltage generated between both ends of the choke coil 15 in accordance with the ON / OFF operation of the MOS FET 4, and between the both ends of the capacitor 53. The voltage repeats rising and falling.

  Here, when the output current Io1 flowing through the load Z1 changes, the voltage drop of the internal resistance generated between both ends of the choke coil 15 changes due to the inherent internal resistance included in the choke coil 15. Therefore, the average value of the voltage across the capacitor 53 increases as the output current Io1 increases, and conversely decreases as the output current Io1 decreases, and the change in voltage drop due to the internal resistance of the choke coil 15 changes. Is output from the voltage drop detection unit 51 to the amplifier circuit 54 as a change in the voltage across the capacitor 53. The amplifier circuit 54 supplies a current detection signal obtained by amplifying the voltage across the capacitor 53 to the non-inverting input terminal of the comparator 72 through the diode 56.

  The same applies to the voltage drop detection circuit 61 connected to the choke coil 25 of the output circuit 21. That is, when the output current Io2 flowing through the load Z2 changes, the voltage drop of the internal resistance generated between both ends of the choke coil 25 changes due to the inherent internal resistance included in the choke coil 25. Therefore, the average value of the voltage across the capacitor 63 increases as the output current Io2 increases, and conversely decreases as the output current Io2 decreases, and the change in voltage drop due to the internal resistance of the choke coil 25 changes. Is output from the voltage drop detector 61 to the amplifier circuit 64 as a change in the voltage across the capacitor 63. The amplifier circuit 64 supplies a current detection signal obtained by amplifying the voltage across the capacitor 63 to the non-inverting input terminal of the comparator 72 through the diode 66.

  In the overcurrent determination unit 71, the current detection signals from the amplifier circuits 54 and 64 and the reference voltage of the reference power source 73 are compared by the comparator 72, and the voltage level of at least one current detection signal reaches or exceeds the reference voltage. Then, an overcurrent generation signal in which the voltage level at the output terminal of the comparator 72 is inverted (in this case, from L to H) is output. In response to this overcurrent generation signal, the output current Io can be forcibly limited by narrowing the conduction width of the pulse drive signal supplied to the MOS FET 4 by the main control circuit 31.

  As described above, in this embodiment, the MOS type FET 4 as a switching element, the transformer 3 formed by magnetically coupling the primary winding 3A and the plurality of secondary windings 3B and 3C, and the secondary winding The main output circuit 11 and the output circuit 21 serving as output circuits connected to each of 3B and 3C are provided, and the input voltage Vi is intermittently applied to the primary winding 3A of the transformer 3 by switching of the MOS type FET 4. In the multi-output switching power supply apparatus that rectifies and smoothes the voltages generated in the secondary windings 3B and 3C of the transformer 3 by the main output circuit 11 and the output circuit 21, respectively, and supplies power to the loads Z1 and Z2, An output current Io1 flowing from the main output circuit 11 to the load Z1 and an output current Io2 flowing from the output circuit 21 to the load Z2 are provided in each of the output circuit 11 and the output circuit 21. The current monitoring units 55 and 65 that generate current detection signals proportional to the output currents Io1 and Io2 and the main output circuit 11 and the output circuit 21 are provided in common. When at least one of the current detection signals reaches a certain value or more, an overcurrent determination unit 71 that outputs an overcurrent generation signal and an overcurrent generation signal are output from the overcurrent determination unit 71 And a main control circuit 31 as an overcurrent protection unit that controls the operation of the MOS type FET 4 so as to limit the output currents Io1 and Io2.

  Thus, the output currents Io1 and Io2 of the main output circuit 11 and the output circuit 21 are monitored by the current monitoring units 55 and 65 provided for each of the main output circuit 11 and the output circuit 21, and are proportional to the output currents Io1 and Io2. A current detection signal is generated by each of the current monitoring units 55 and 65. These current detection signals are compared with a constant value by an overcurrent determination unit 71 provided in common to the main output circuit 11 and the output circuit 21, and if one of the current detection signals reaches a constant value. Then, it is determined that one of the main output circuit 11 and the output circuit 21 is in an overcurrent state, and an overcurrent generation signal is output, and the main control circuit 31 receiving this signal limits the output currents Io1 and Io2. The operation of the MOS FET 4 is controlled.

  As described above, regardless of the number of output circuits (the main output circuit 11 and the output circuit 21), after generating the current detection signal, the main output circuit 11 is not provided with its own current detection unit in each output circuit. In addition, the overcurrent determination unit 71 and the main control circuit 31 common to the output circuit 21 can operate an appropriate overcurrent protection function, and the space of the apparatus can be saved.

  The main output circuit 11 and the output circuit 21 in this embodiment are rectified by output rectifier circuits 14 and 24 that rectify the voltage generated in the secondary windings 3B and 3C of the transformer 3, and the output rectifier circuits 14 and 24. Output smoothing circuits 17 and 27 having a choke coil for smoothing the voltage, and supplies power to the loads Z1 and Z2 through the choke coils 15 and 25, and is connected to the choke coils 15 and 25 to The voltage drop detection circuits 51 and 61 for outputting the output currents Io1 and Io2 flowing through Z1 and Z2 as signals of the voltage drop due to the internal resistances of the choke coils 15 and 25, and the voltage drop detection circuits 51 and 61 are output. The current monitoring unit includes amplification circuits 54 and 64 that amplify the signal and generate the current detection signal proportional to the output currents Io1 and Io2. Constitute a 5,65.

  In this way, by connecting the voltage drop detection circuits 51 and 61 to the choke coils 15 and 25 in one or more output circuits (main output circuit 11 and output circuit 21), the output current flowing through the load is , 25 are output to the amplifier circuits 54 and 64 as signals corresponding to voltage drops due to the internal resistances, and current detection signals proportional to the output currents Io1 and Io2 can be generated from the amplifier circuits 54 and 64. In other words, the current transformer or shunt resistor is not used at all, and the resistance of the choke coils 15 and 25 originally functioning as the output smoothing circuits 17 and 27 is used to connect the choke coils 15 and 25 between both ends. Since the output currents Io1 and Io2 can be detected simply by connecting the voltage drop detection circuits 51 and 61 to each other, even if the output currents Io1 and Io2 to be detected have a relatively large value, the space saving of the device can be easily realized. it can. In addition, the amplification degree of each of the amplifier circuits 54 and 64 is individually variably set, so that the main output circuit which is the respective output circuit is provided with the common overcurrent determination unit 71 and the main control circuit 31. 11 and the overcurrent protection operating point in the output circuit 21 can be set easily.

  In addition, a present Example is not limited to said each embodiment, A various deformation | transformation implementation is possible. For example, various semiconductor elements other than the MOS type FET 4 may be used as the main switching element, and the voltage drop detection circuits 51 and 61 are not limited to the circuit configuration shown in the embodiment. As the switching power supply device, for example, a center tap, half bridge, or full bridge type DC-DC converter other than the forward type may be applied.

It is a circuit diagram of the switching power supply device which detects each output current in each preferred embodiment of the present invention with each output choke coil and performs OCP protection in a collective component. It is a circuit diagram of the switching power supply device in a prior art example.

Explanation of symbols

3 Transformer 4 MOS type FET (Main switching element)
11 Main output circuit (output circuit)
14, 24 Output rectifier circuit 15, 25 Choke coil 17, 27 Output smoothing circuit 31 Main control circuit (overcurrent protection unit)
51, 61 Voltage drop detection circuit 55, 65 Current monitoring unit 54, 64 Amplifier circuit 71 Overcurrent determination unit Z1, Z2 Load

Claims (2)

A switching element, a transformer formed by magnetically coupling a primary winding and a plurality of secondary windings, and an output circuit connected to each of the secondary windings,
By switching the switching element, an input voltage is intermittently applied to the primary winding of the transformer, and the voltage generated in each secondary winding of the transformer is rectified and smoothed by the respective output circuits to power the load. In the multi-output switching power supply device that supplies
A current monitoring unit that is provided in each of the output circuits, monitors an output current flowing from the output circuit to the load, and generates a current detection signal proportional to the output current;
An overcurrent determination unit that is provided in common to each of the output circuits and outputs an overcurrent generation signal when at least one current detection signal reaches a predetermined value or more among the current detection signals from the current monitoring units. When,
A multi-output switching power supply apparatus comprising: an overcurrent protection unit that controls an operation of the switching element so as to limit the output current when an overcurrent generation signal is output from the overcurrent determination unit . The output circuit includes an output rectifier circuit that rectifies the voltage generated in the secondary winding of the transformer, and an output smoothing circuit that includes a choke coil that smoothes the voltage rectified by the output rectifier circuit. And supplying power to the load through
A voltage drop detection circuit connected to the choke coil and outputting an output current flowing through the load as a signal of a voltage drop due to an internal resistance of the choke coil;
2. The multiple current monitoring unit according to claim 1, wherein the current monitoring unit is configured by an amplification circuit that amplifies a signal output from the voltage drop detection circuit and generates the current detection signal proportional to the output current. Output switching power supply.

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