The present invention relates to a DC-DC converter, and particularly to a DC-DC converter applicable to a multi-output DC-DC converter capable of outputting plural different output voltage.
The DC-DC converter has a function of increasing and decreasing a DC voltage to output it. Such a DC-DC converter includes a multi-output DC-DC converter having a plurality of output circuits to output plural different output voltage. In the multi-output DC-DC converter performing multi-output in a DC-DC converter using a transformer, a plurality of output circuits are made up of a plurality of secondary side windings and a plurality of secondary side rectifying circuit of the transformer.
A conventional multi-output DC-DC converter detects output voltage of one output circuit in a plurality of output circuits, and controls a conduction ratio of a primary side switching element of the transformer so that the output voltage becomes a target value, thereby controlling output voltage of one output circuit described above. In the meanwhile, output voltage of the other output circuit, that is to say, the output voltage which is not directly controlled is roughly calculated using a turn ratio of the transformer to the output voltage which is directly controlled. A technique of a multi-output DC-DC converter is also proposed in Patent Document 1.
The output voltage which is not directly controlled in the multi-output DC-DC converter fluctuates depending on a load and input voltage in each output circuit, thus can be hardly adjusted accurately. In the meanwhile, in the technique of Patent Document 1, each output circuit can be adjusted in some degree.
However, in the technique of Patent Document 1, energy accumulated in a secondary side inductor provided individually from the transformer is taken out only as needed using a secondary side switching element. In such a configuration, a magnetic component, whose number corresponds to the number of outputs, such as an inductor having a relatively large area, needs to be mounted to a converter. Thus, the multi-output DC-DC converter mounted at low cost or high density can be hardly achieved.
The present invention therefore has been made to solve the above problems, and it is an object of the present invention to provide a technique capable of achieving a multi-output DC-DC converter mounted at low cost or high density.
A DC-DC converter according to the present invention includes: a transformer including a primary winding, at least one secondary winding, and a tertiary winding; a first circuit connected to the primary winding and the tertiary winding; and at least one second circuit connected to the at least one secondary winding, wherein the first circuit includes: a first switching element converting a predetermined DC voltage into an AC voltage, and supplies the AC voltage to the primary winding; and a main control device controlling a conduction ratio of the first switching element based on an electrical power of the tertiary winding, the second circuit includes an individual control device selectively accumulating and taking out an electrical power in the secondary winding corresponding to the second circuit based on the electrical power taken out from the secondary winding, and the second circuit converts an AC voltage of the secondary winding corresponding to the second circuit into a DC voltage.
According to the present invention, the individual control device of the second circuit selectively accumulates and takes out an electrical power in the secondary winding corresponding to the second circuit based on the electrical power taken out from the secondary winding. According to such a configuration, the multi-output DC-DC converter mounted at low cost or high density can be achieved.
These and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
The transformer 4 includes a primary winding 41, at least one secondary winding 42 having a secondary side excitation inductance, and a bias winding 43 which is a tertiary winding. In the present embodiment 1, at least one secondary winding 42 is secondary windings 42a and 42b, however, the number of secondary windings 42 is not limited thereto.
The first circuit 11 is connected to a DC power source 19, the primary winding 41, and the bias winding 43. The first circuit 11 in
The switching element 12 converts a predetermined DC voltage being input from the DC power source 19 into an AC voltage under control of main control device 15, and supplies the AC voltage (electrical power) to the primary winding 41. A semiconductor switching element, for example, is applied to the switching element 12.
The rectifying circuit 13 converts the AC voltage of the electrical power taken out from the bias winding 43 into the DC voltage, and supplies the DC voltage to terminals Vcc, FB, and GND of main control device 15. Voltage between both ends of the current detection resistance 14 increases when the current in the primary winding 41 increases. This voltage between both ends is detected by main control device 15 via terminals CLM and GND.
The main control device 15 controls a conduction ratio of the switching element 12, that is to say, a ratio of conduction time of a pulse drive signal based on the electrical power of the bias winding 43. The electrical power of the bias winding 43 herein indicates voltage being input via the rectifying circuit 13, for example.
The second circuit 21 is described next. Each second circuit 21 is connected to the secondary winding 42, and includes an individual control device 22 individually controlling the second circuit 21, a capacitor 23, and a pair of output terminals 24. In the example in
The individual control device 22a takes out the electrical power (energy) from the secondary winding 42a corresponding to the second circuit 21a. Then, the individual control device 22a selectively accumulates and takes out (consumes) the electrical power in the secondary winding 42a based on the electrical power which has been taken out. The individual control device 22a performs feedback in this manner, thus the voltage being output from the output terminal 24a is brought close to a target value which is preset in the second circuit 21a.
Similarly, the individual control device 22b takes out the electrical power from the secondary winding 42b corresponding to the second circuit 21b, and selectively accumulates and takes out the electrical power in the secondary winding 42b based on the electrical power which has been taken out.
Terminals pin 1 to pin 5 in
The power supply rectifying circuit 51 converts the electrical power being input from the secondary winding 42 to the terminal pin 1 into an electrical power necessary for operations of the differential amplifier circuit 52, the error signal detection circuit 53, and the gate drive circuit 54, and supplies the converted electrical power thereto. Voltage (differential output) of a pair of wirings between the individual control device 22 and the capacitor 23 in
The error signal detection circuit 53 generates an error signal based on a comparison between the voltage amplified in the differential amplifier circuit 52 and predetermined voltage (bandgap reference). The gate drive circuit 54 outputs a signal for reducing the difference between the amplified voltage and the bandgap reference to a gate terminal of the switching element 55 based on the error signal generated in the error signal detection circuit 53. The signal is input to the gate terminal of the switching element 55, thus an on state an off state of the switching element 55, that is to say, a conduction ratio of the switching element 55 is controlled.
A source terminal which is one end of the switching element 55 is connected to one end of the secondary winding in
The individual control device 22 having the above configuration selectively performs switching of the switching element 55 from the on state to the off state and switching of the element 55 from the off state to the on state based on the electrical power taken out from the secondary winding 42 when current flows in a forward direction of the diode 56. The individual control device 22 controls such a switching, that is to say, the conduction ratio of the switching element 55, thereby selectively accumulating and taking out the electrical power in the secondary winding 42.
The second circuit 21 in
The error signal detection circuit 53 in
The configuration of the individual control device 22 is not limited to that described above. For example, in the individual control device 22, the switching element 55 and the diode 56 may be replaced with the other circuit having a function similar thereto. It is also applicable that the number of pins of the individual control device 22 is increased to externally mount a circuit element constituting the individual control device 22 and the number of circuit elements in the individual control device 22 is thereby reduced. In
The first related DC-DC converter includes at least one fourth circuit 61 in place of at least one second circuit 21. At least one fourth circuit 61 in
The fourth circuit 61a is connected to the secondary winding 42a, and includes a rectifying circuit 62a, a DC-DC converter integrated circuit (IC) 63a, a secondary side inductor 64a, pressure dividing resistances 65a and 66a, a capacitor 67a, and a pair of output terminals 68a. Similarly, the fourth circuit 61b is connected to the secondary winding 42b, and includes a rectifying circuit 62b, a DC-DC converter IC 63b, a secondary side inductor 64b, pressure dividing resistances 65b and 66b, a capacitor 67b, and a pair of output terminals 68b. Constituent elements of the fourth circuit 61a are described hereinafter, and constituent elements of the fourth circuit 61b are similar to those in the description hereinafter.
The secondary side inductor 64a is provided individually from the secondary winding 42a corresponding to the fourth circuit 61a. The voltage of the secondary winding 42a is output to the secondary side inductor 64a via the DC-DC converter IC 63a, and the secondary side inductor 64a accumulates the electrical power taken out from the secondary winding 42a. The DC-DC converter IC 63a selectively accumulates and takes out (consumes) the electrical power in the secondary side inductor 64a based on the electrical power taken out from the secondary side inductor 64a. That is to say, the DC-DC converter IC63a controls a conduction ratio of a switching element provided inside the DC-DC converter IC 63a but not shown in the drawings based on the electrical power taken out from the secondary side inductor 64a.
The fourth circuit 61a converts the AC voltage of the secondary side inductor 64a into the DC voltage by controlling the conduction ratio of the switching element in the DC-DC converter IC 63a and by the capacitor 67a, for example, and outputs the DC voltage from the pair of output terminals 24. According to the above configuration, the DC-DC converter IC 63a performs the feedback on the electrical power taken out from the secondary side inductor 64a, thus the fourth circuit 61a can output the DC voltage brought close to the target value of the fourth circuit 61a from the pair of output terminals 68a.
The DC-DC converter IC and the secondary side inductor described above are generally necessary for each output circuit to bring each output voltage of the plurality of fourth circuits 61 which are the plurality of output circuits close to each target value different from each other in the first related DC-DC converter in
In the meanwhile, in the DC-DC converter in
As described above, in the present embodiment 1, the individual control device 22 controls a timing of switching the switching element 55 from the on state to the off state or from the off state to the on state based on a comparison between the differential output and a bandgap reference when current flows in the diode 56 so that the output voltage of the output terminal 24b is brought close to the preset target value.
Herein, if the energy accumulated in the secondary winding 42 is too much in relation to output load, the output voltage of the second circuit 21 increases, thus there may be a case where the output voltage of the second circuit 21 is hardly brought close to the target value only by controlling the individual control device 22. Thus, when the main control device 15 detects increase in voltage of the bias winding 43 in accordance with the increase in the output voltage, the main control device 15 reduces the conduction ratio of the switching element 12 and reduces electrical power supplied to the primary winding 41. When the main control device 15 detects increase in voltage between both ends of the current detection resistance 14 in accordance with the increase in the output voltage, the main control device 15 reduces the conduction ratio of the switching element 12 and reduces electrical power supplied to the primary winding 41. In the manner described above, the excess energy accumulated in the secondary winding 42 can be reduced.
In the meanwhile, if the energy accumulated in the secondary winding 42 is too little in relation to output load, the output voltage of the second circuit 21 decreases, thus there may be a case where the output voltage of the second circuit 21 is hardly brought close to the target value only by controlling the individual control device 22. Thus, when the main control device 15 detects decrease in voltage of the bias winding 43 in accordance with the decrease in the output voltage or decrease in voltage between both ends of the current detection resistance 14, the main control device 15 increases the conduction ratio of the switching element 12 and increases an electrical power supplied to the primary winding 41. Accordingly, shortfall of the energy accumulated in the secondary winding 42 can be compensated.
A configuration of the DC-DC converter in
As described hereinafter, the DC-DC converter including the feedback circuit 76 according to the present embodiment 2 can have a higher accuracy of the output voltage than the DC-DC converter which does not include the feedback circuit 76 according to the embodiment 1.
The third circuit 71 is connected to a secondary winding 42c, and includes a diode 72, a capacitor 73, and a pair of output terminals 74. The third circuit 71 converts an AC voltage of the secondary winding 42c corresponding to the third circuit 71 into a DC voltage using the diode 72 and the capacitor 73, for example, and outputs the DC voltage from the pair of output terminals 74.
The feedback circuit 76 is a circuit stabilizing an output from the pair of output terminals 74 of the third circuit 71. The feedback circuit 76 is provided between the third circuit 71 and the first circuit 11, and is connected to the third circuit 71 and the first circuit 11.
The feedback circuit 76 in
The pressure dividing resistances 76a and 76b divide the output voltage of the pair of output terminals 74. The shunt regulator 76c functions as a comparator comparing a detection signal, that is to say, a partial pressure of the output voltage obtained in a connection point between the voltage dividing resistances 76a and 76b with an internal reference power source, and amplifying a comparison result thereof.
The photo coupler 76d transmits a feedback signal based on the comparison result in the shunt regulator 76c to the primary side first circuit 11 of the transformer 4 with the feedback signal electrically isolated from the first circuit 11. That is to say, the photo coupler 76d transmits the feedback signal which is a signal corresponding to a fluctuation of the output voltage corresponding to the third circuit 71 to the first circuit 11. The main control device 15 of the first circuit 11 controls the conduction ratio of the switching element 12 based on the feedback signal isolated and transmitted by the photo coupler 76d and the voltage of the bias winding 43. The resistances 76e, 76f, and 76g, and the capacitor 76h are elements for adjusting a control parameter.
A configuration of the second related DC-DC converter in
In the meanwhile, in the DC-DC converter in
As described above, in the present embodiment 2, the individual control device 22 controls a timing of switching the switching element 55 from the on state to the off state or from the off state to the on state based on a comparison between the differential output and a bandgap reference when current flows in the diode 56 so that the output voltage of the output terminal 24b is brought close to the preset target value.
Herein, if the energy accumulated in the secondary winding 42 is too much in relation to output load, the output voltage of the second circuit 21 increases, thus there may be a case where the output voltage of the second circuit 21 is hardly brought close to the target value only by controlling the individual control device 22. Thus, when the main control device 15 detects increase in voltage of the bias winding 43 in accordance with the increase in the output voltage, the main control device 15 reduces the conduction ratio of the switching element 12 and reduces electrical power supplied to the primary winding 41. When the main control device 15 detects the feedback signal indicating increase in the output voltage of the third circuit 71, the main control device 15 reduces the conduction ratio of the switching element 12 and reduces electrical power supplied to the primary winding 41. In the manner described above, the excess energy accumulated in the secondary winding 42 can be reduced.
In the meanwhile, if the energy accumulated in the secondary winding 42 is too little in relation to output load, the output voltage of the second circuit 21 decreases, thus there may be a case where the output voltage of the second circuit 21 is hardly brought close to the target value only by controlling the individual control device 22. Thus, when the main control device 15 detects decrease in voltage of the bias winding 43 in accordance with the decrease in the output voltage or the feedback signal indicating decrease in the output voltage of the third circuit 71, the main control device 15 increases the conduction ratio of the switching element 12 and increases an electrical power supplied to the primary winding 41. Accordingly, shortfall of the energy accumulated in the secondary winding 42 can be compensated.
A configuration of the third related DC-DC converter in
The third circuit 71a is connected to the secondary winding 42a, and includes a diode 72a, a capacitor 73a, and a pair of output terminals 74a similar to the diode 72, the capacitor 73, and the pair of output terminals 74 in
The third circuit 71b is connected to the secondary winding 42b, and includes a diode 72b, a capacitor 73b, and a pair of output terminals 74b similar to the diode 72, the capacitor 73, and the pair of output terminals 74 in
The third circuit 71c is connected to the secondary winding 42c, and includes a diode 72c, a capacitor 73c, and a pair of output terminals 74c similar to the diode 72, the capacitor 73, and the pair of output terminals 74 in
In the third related DC-DC converter in
In the meanwhile, output voltage of the third circuits 71a and 71b other than the third circuit 71c, that is to say, output voltage which is not directly controlled is roughly calculated using a turn ratio of the transformer to the output voltage of the third circuit 71c, that is to say, the output voltage which is directly controlled. However, the output voltage of the output circuit which is not directly controlled in the multi-output DC-DC converter fluctuates depending on a load of the controlled output circuit and on a load and input voltage in each output circuit. The output voltage of the output circuit which is not directly controlled is hardly adjusted accurately.
The output voltage which is not directly controlled is generally adjusted by various parameters such as a change in the number of turns of the transformer 4, a change in a primary side inductance value of the transformer 4, an addition of the power control resistances 78a and 78b and the power consumption resistances 79a and 79b to each winding, an order of turns of the transformer 4, and a change in a turn position of the winding, for example. However, it is difficult to adjust the output voltage by reason that there are various parameters. There is a problem that a redesign and a readjustment, for example, need to be performed by changing a transformer, adding an insulating tape, changing a varnish impregnation condition, and changing a manufacturer (material) of a transformer core, for example.
Considered is a configuration that a low dropout (LDO) regulator or a three-terminal regulator is provided in the third circuits 71a and 71b which are not directly controlled to simplify the adjustment of the output voltage of the configuration in
In contrast, according to the present embodiment 2, highly accurate output voltage having fine regulation characteristics can be obtained in each output circuit of the multi output DC-DC converter. A magnetic component can be gathered in one transformer 4, thus a multi-output DC-DC converter mounted at low cost and high density can be achieved. A flyback transformer often used in a multi-output DC-DC converter can be easily designed, thus a development period and a manufacturing period can be reduced.
The LDO regulator or the three-terminal regulator is not used in the DC-DC converter according to the present embodiment 2, thus a range of voltage and current which can be handled by the DC-DC converter can be relatively expanded. In addition, an inductor having a large inductance value is necessary when a new DC-DC converter is used for output to handle large current, however, according to the present embodiment 2, such a large-size component needs not be added. In the present embodiment 2, a MOSFET performs an operation similar to a behavior of a synchronous rectification, thus reduction in power consumption can be expected compared with a configuration of using a general power control resistance and a power consumption resistance, for example.
The DC-DC converter according to the embodiment 1 (
The DC-DC converter according to the embodiment 2 (
A configuration of the DC-DC converter in
Herein, the diode 56 generally tends to generate larger heat than the switching element 55 due to a forward loss. In view of this, the terminal pin 6 lead from the connection point of the switching element 55 and the diode 56 is provided in
A configuration of the DC-DC converter in
The individual control device 27a further includes terminals pin 3′ to pin 5′ similar to the terminals pin 3 to pin 5 of the individual control device 22a. A connection point of the terminal pin 3 and the terminal pin 4 and the terminal pin 2 are connected to an output Vout1 via a capacitor. The connection point of the terminal pin 3 and the terminal pin 4 and a connection point of the terminal pin 3′ and the terminal pin 4′ are connected to an output Vout1′ via a capacitor. That is to say, the individual control device 27a includes two outputs (the output Vout1 and the output Vout1′). The individual control device 27a according to the present embodiment 3 is configured to control the two outputs (the output Vout1 and the output Vout1′).
A configuration on a side of the individual control device 22b is similar to that on a side of the individual control device 22b in the embodiment 1, and the connection point of the terminal pin 3 and the terminal pin 4 and the terminal pin 2 of the individual control device 22b are connected to an output Vout2 via a capacitor.
According to the present invention, each embodiment and each modification example can be arbitrarily combined, or each embodiment and each modification example can be appropriately varied or omitted within the scope of the invention.
The present invention has been shown and described in detail, the foregoing description is in all aspects illustrative, thus the present invention is not limited thereto. It is therefore understood that numerous modification examples can be devised without departing from the scope of the invention.
4 transformer, 11 first circuit, 12, 55 switching element, 15 main control device, 21, 21a, 21b second circuit, 22, 22a, 22b, 26, 26a, 26b, 27a individual control device, 41 primary winding, 42, 42a, 42b secondary winding, 43 bias winding, 56, 57, 57a, 57b diode, 61, 61a, 61b fourth circuit, 63a, 63b DC-DC converter IC, 64a, 64b inductor, 71 third circuit, 76d photo coupler.
Number | Date | Country | Kind |
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2018-236026 | Dec 2018 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2019/048437 | 12/11/2019 | WO | 00 |