KR100609139B1 - Buck Type Series Resonant Converter - Google Patents

Abstract

The present invention relates to a series resonant DC / DC converter having a step-down function, the configuration of which includes a DC power supply; A first bridge and a fourth switch of a full bridge to which anti-parallel diodes are connected, respectively; first and second switches connected in series with each other, and third and fourth switches are connected in parallel to both ends of the DC power supply, respectively. A switch unit for switching according to a switching control signal; A series resonator connected between a connection node of the first and second switches and a connection node of the third and fourth switches; A transformer including a primary coil and a secondary coil connected in series with the series resonator; A rectifier for rectifying the voltage output from the transformer; A smoothing capacitor that smoothes and outputs the voltage rectified by the rectifier; And the first to fourth switches and the anti-parallel diodes to periodically repeat a powering mode for storing energy in the series resonator unit and a free resonant mode for transferring the stored energy to the secondary side through the transformer. And a control unit controlling the switching time of the powering mode and the free resonance mode execution time according to the output voltage.

Full Bridge, Resonant Current, Series Resonance, DC / DC Converter, Rectifier

Description

Buck Type Series Resonant Converter}

1 is a circuit diagram of a DC / DC converter having a conventional step-down function.

2 is a circuit diagram of a series resonant DC / DC converter having a step-down function according to an embodiment of the present invention.

3A to 3D are diagrams for describing an operating state of a series resonant DC / DC converter having a step-down function according to the present invention.

4 is a view illustrating a switching period of a switch unit and a resonance period of a series resonator unit according to the present invention.

 Explanation of symbols on the main parts of the drawings

110: DC power supply 120: switch unit

130: DC resonator 140: transformer

150: rectifier 160: smoothing capacitor

170: control unit S1 to S4: full bridge switch

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC-DC (hereinafter referred to as DC / DC) converter, and in particular, a series resonance is achieved by turning on (T _ON ) / OFF (T _OFF ) a switch of a full bridge on the primary side of a transformer. A series resonant DC / DC converter having a step-down function of storing energy in a part and transferring the stored energy to the output terminal of the secondary side through the transformer.

DC / DC converters that convert DC voltages into DC voltages of different sizes are used in various fields. For example, a power supply that supplies power to a computer control board has a built-in DC / DC converter. Particularly in the controller design, when a DC voltage smaller than the basic input DC voltage is required, a DC / DC converter having a step-down function is used.

1 is a circuit diagram of a DC / DC converter having a conventional step-down function. Referring to FIG. 1, a switch S and an inductor L are connected in series to the (+) side of the DC power supply Vs, and the DC power supply (A) is connected at the connection node of the switch S and the inductor L. FIG. The diode D is connected in parallel with Vs). The switch S is turned on / off according to a switching signal of a controller (not shown) to switch the voltage of the DC power supply Vs to an output terminal. When the switch S is turned on, the current supplied by the DC power supply Vs is transferred to the output terminal through the inductor L. At this time, energy is accumulated in the inductor (L). Subsequently, when the switch S is turned off, the voltage Vo is output to the output terminal by the energy accumulated in the inductor L. The output voltage Vo is always equal to or less than the input voltage.

However, this conventional step-down DC / DC converter has a disadvantage in that the efficiency is poor due to the loss generated during switching.

The present invention has been proposed to solve the above-mentioned problems, and stores energy in a series resonator unit according to an on / off operation of a full bridge switch of a primary side of a transformer, and stores the energy of the stored primary side through a secondary side of the transformer. The purpose of the present invention is to provide a series resonant DC / DC converter having a step-down function that delivers a voltage lower than an input voltage to an output terminal while reducing switching loss.

A series resonant DC / DC converter having a step-down function of the present invention for achieving the above object is a direct current power source; First and second switches S1 to S4 of the full bridges having the anti-parallel diodes D1 to D4 connected thereto, respectively; Four switches (S3, S4) are respectively connected to both ends of the DC power supply in parallel, the switch unit for switching in accordance with a switching control signal; A series resonator connected between a connection node of the first and second switches S1 and S2 and a connection node of the third and fourth switches S3 and S4; A transformer including a primary coil and a secondary coil connected in series with the series resonator; A rectifier for rectifying the voltage output from the transformer; A smoothing capacitor that smoothes and outputs the voltage rectified by the rectifier; And the first to fourth switches S1 to S4 to periodically repeat a powering mode for storing energy in the series resonator unit and a free resonance mode for transferring the stored energy to the secondary side through the transformer. And controlling the switching time of the antiparallel diodes D1 to D4 to control the powering mode execution time and the free resonance mode execution time according to the output voltage.

In one embodiment of the present invention, the control unit controls the on / off switching of the set of the first and fourth switches and the other set of the second and third switches in a preset switching cycle for each group, wherein The controller controls on / off switching for each group when the resonance current of the series resonance unit is zero.

In one embodiment of the present invention, the control unit, each group of the second diode (D2) and the fourth switch (S4) and the other group of the second switch (S2) and the fourth diode (D4) for each group The on / off switching is controlled by a preset switching cycle, and the control unit turns on / off each of the groups alternately when the resonance current of the series resonator becomes zero.

In one embodiment of the present invention, the control unit controls the time to turn on / off of the first to fourth switches so that the resonance energy is stored in the series resonator, and also the on / off of the first to fourth switches Off is controlled to control the magnitude of the output voltage at the output stage.

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings. In describing the present invention, if it is determined that the detailed description of the related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

2 is a circuit diagram of a series resonant DC / DC converter having a step-down function according to an embodiment of the present invention. Referring to FIG. 2, the series resonant DC / DC converter of the present invention uses the first to fourth switches S1 to S4 of full bridges connected to the DC power supply 110 and the antiparallel diodes D1 to D4, respectively. The first and second switches S1 and S2 and the third and fourth switches S3 and S4 connected in series to each other are connected in parallel to both ends of the DC power supply 110, respectively. A series connected between the switch unit 120 switching according to SS1 to SS4, a connection node of the first and second switches S1 and S2, and a connection node of the third and fourth switches S3 and S4. A resonator 130, a transformer 140 including a primary coil and a secondary coil connected in series with the series resonator 130, a rectifier 150 rectifying a voltage output from the transformer 140, A smoothing capacitor 160 for smoothing and outputting the voltage rectified by the rectifier 150 and a powering mode for storing energy in the series resonator 130. By controlling the switching time of the first to fourth switches (S1 to S4) to periodically repeat the free resonant mode for transferring the stored energy to the secondary side through the transformer 140 And a controller 170 for controlling the powering mode execution time and the free resonance mode execution time according to the magnitude of the output voltage.

2, the present invention will be described in more detail. The DC power supply 110 supplies a DC voltage Vs (current) to a full bridge DC / DC converter.

The switch unit 120 includes first to fourth switches S1 to S4 having a full bridge structure to which the antiparallel diodes D1 to D4 are connected. The first to fourth switches S1 to S4 are turned on / off according to the switching signals SS1 to SS4 of the controller 170, and are connected to the primary side of the transformer 140 connected to the switches S1 to S4. Provide current. The antiparallel diodes D1 to D4 are connected between the emitters and the collectors of the switches S1 to S4, respectively. The first switch S1 and the second switch S2 are connected in series with each other, and the third switch S3 and the fourth switch S4 are connected in series with each other. In addition, the first and second switches S1 and S2 and the third and fourth switches S3 and S4 connected in series with each other are connected in parallel to both ends of the DC power supply 110, respectively. The switch unit 110 transfers the DC current provided from the DC power supply 110 to the series resonator 130 and the transformer 140 by the on / off switching control of the controller 170. As a result, energy is accumulated in the series resonator 130 and energy (or voltage) is transferred to the secondary side through the transformer 140.

The series resonator 130 is connected in series between a connection node of the first and second switches S1 and S2 and a connection node of the third and fourth switches S3 and S4. The energy received through the 120 is stored and configured to have a set resonance period. In addition, the series resonator 130 may emit the stored energy according to the switching operation of the switch unit 120.

The transformer 140 includes a primary coil and a secondary coil connected in series with the series resonator 130. The transformer 140 transmits the primary side energy to the secondary side according to the turns ratio of the primary coil and the secondary coil. In the present invention, the winding ratio is set to 1: 1, but is not limited thereto.

The rectifier 150 may be formed of bridge diodes D5 to D8 to rectify the voltage output from the transformer 140.

The smoothing capacitor 160 smoothes and outputs the voltage rectified by the rectifying unit 150.

The controller 170 periodically repeats a powering mode for storing energy in the series resonator 130 and a free resonant mode for transferring the stored energy to the secondary side through the transformer 140. The switching time of the first to fourth switches S1 to S4 is controlled to control the powering mode execution time and the free resonance mode execution time according to the output voltage. In detail, in the powering mode, the controller 170 may set one set of the first and fourth switches S1 and S4 and another set of the second and third switches S2 and S3 in a period set for each group. Turn on / off alternately. In this case, the controller 170 repeats the switching on / off for each group at the time when the resonance current of the series resonator 130 is zero for zero current switching (ZCS). . In the free resonant mode, the controller 170 may include one set of the second diode D2 and the fourth switch S4 and the other set of the second switch S2 and the fourth diode D4 for each group. Turn on / off alternately according to the set cycle. In this case, for zero current switching (ZCS), the on / off is repeated when the resonance current becomes zero.

As described above, in the series resonant DC / DC converter having the step-down function according to the present invention, the first to fourth switches S1 to S4 (each antiparallel diode D1 to D4 according to the switching control signal of the controller 170). In the powering mode, energy is accumulated in the DC resonator 130 so that a voltage is transmitted to the secondary side through the transformer 140 according to the winding ratio, and in the free resonance mode, No more energy is stored in the DC resonator 130, and the energy already stored in the DC resonator 130 is transferred to the secondary side through the transformer 140. At this time, since the energy of the DC resonator 130 is gradually reduced in the free resonant mode, the voltage output from the secondary side is reduced, and therefore, the output voltage Vo is smaller than the input voltage Vs. This is the step-down function is performed. The magnitude of the output voltage Vo may be controlled by switching control in the controller 170. That is, by controlling the switching time of the first to fourth switches S1 to S4 (including the antiparallel diodes D1 to D4) in the controller 170, a desired output voltage Vo may be obtained. .

3A to 3D are diagrams for describing an operating state of a series resonant DC / DC converter having a step-down function according to the present invention. 3A and 3B are current flow charts in a powering mode, and FIGS. 3C and 3D are current flow charts in a free resonance mode. More specifically, FIG. 3A illustrates a state in which the first and fourth switches S1 and S4 are turned on among the four full bridge switches S1 to S4 to which the anti-parallel diodes D1 to D4 on the primary side are connected. 2B is a flow chart of the second and third switches S2 and S3, and FIG. 3B shows the second and third switches S2 and S3 of the primary full bridge switches S1 to S4 turned on. In this state (in which the first and fourth switches S1 and S4 are turned off).

In addition, in FIG. 3C, a set of the second diode D2 and the fourth switch S4 on the primary side are turned on (at this time, the other set of the second switch S2 and the fourth diode D4 are turned off). 3d shows a state in which the other set of second switch S2 and the fourth diode D4 on the primary side are turned on (at this time, the set of second diode D2 and the fourth switch ( S4) is the current flow diagram in the OFF).

First, referring to FIG. 3A, in the powering mode, when the first and fourth switches S1 and S4 on the primary side are turned on and the second and third switches S2 and S3 are turned off, a DC power source The current supplied from 110 flows through the first switch S1, the series resonator 130, the primary coil Tr1 of the transformer 140, and the fourth switch S4. At this time, energy is accumulated in the series resonator 130 by the current, and voltage is induced in the secondary coil Tr2 by the voltage of the primary coil Tr1 of the transformer 140. Subsequently, the voltage induced on the secondary side of the transformer 140 is rectified by the rectifier 150, and the rectified voltage is smoothed by the smoothing capacitor 160 and then output as an output voltage Vo.

Subsequently, as shown in FIG. 3B, when the first and fourth switches S1 and S2 on the primary side are turned off and the second and third switches S2 and S3 are turned on, the DC power supply 110 turns on. The supplied current flows through the third switch S3, the primary coil Tr1 of the transformer 140, the series resonator 130, and the second switch S2. Also in this case, as in FIG. 3A, energy is accumulated in the series resonator 130 by the current, and energy is transferred to the secondary side through the transformer 140. However, the phase of the current is reversed from that of Fig. 3A. In addition, the voltage due to the energy transferred to the secondary side of the transformer 140 is rectified by the rectifier 150, the rectified voltage is smoothed by the smoothing capacitor 160, and then output to the output voltage Vo do.

As described above, in the powering mode, one set of the first and fourth switches S1 and S4 and another set of the second and third switches S2 and S3 repeatedly perform switching for each group, thereby performing the series resonance. While accumulating energy in the unit 130, energy is transferred to the secondary side through the transformer 140, and a predetermined voltage is supplied to the output terminal of the secondary side. In this case, when the control unit 170 switches and controls the first to fourth switches S1 to S4 for each group, the controller 170 alternately repeats when the resonant current of the series resonator 130 is zero. It is preferable to switch.

Next, the current flow in the free resonance mode will be described with reference to FIGS. 3C and 3D. As described above, in the free resonant mode, the second diode D2 and the fourth switch S4 on the primary side form one pair, and the second switch S2 and the fourth diode D4 form another pair. Alternately switched. First, as shown in FIG. 3C, when the second diode D2 and the fourth switch S4 are turned on, the current of the DC power supply 110 is supplied to the series resonator 130 and the transformer 140. No energy is accumulated in the series resonator 130. In this case, a current supplied from the series resonator 130 that has already accumulated energy in the powering mode flows through the transformer 140, the fourth switch S4, and the second diode D2. Through 140, the voltage of the primary side is transmitted to the secondary side according to the turns ratio. The voltage transferred to the secondary side is rectified by the rectifier 150, and then smoothed by the smoothing capacitor 160, and then output as an output voltage Vo.

Subsequently, when the second diode D2 and the fourth switch S4 are turned off and the second switch S2 and the fourth diode D4 are turned on according to the switching control of the controller 170, FIG. 3D. As shown in FIG. 2, current supplied from the series resonator 130 that has already accumulated energy in the powering mode flows through the second switch S2, the fourth diode D4, and the transformer 140. The voltage of the primary side is transmitted to the secondary side according to the turns ratio through the transformer 140. The voltage transferred to the secondary side is rectified by the rectifier 150, and then smoothed by the smoothing capacitor 160, and then output as an output voltage Vo.

As described above, in the free resonant mode illustrated in FIGS. 3C and 3D, the energy already stored in the series resonator 130 is gradually reduced, thereby decreasing the magnitude of the voltage transmitted to the output terminal through the transformer 140. Therefore, in the free resonance mode, the output voltage is equal to or smaller than the input voltage.

Here, in the free resonance mode, the detailed description of the present invention describes that the controller 170 controls the switching of the second and fourth switches S2 and S4 and the second and fourth diodes D2 and D4. As shown in FIG. 3C, when only the fourth switch S4 is turned on in the state in which the first to third switches S1 to S3 are turned off, the current caused by the energy stored in the series resonator 130 is transmitted. 140, the fourth switch S4 flows, and the current flows to the series resonator 130 due to the conduction of the second diode D2. As described above, the controller 170 describes that the on / off switching control is performed by using the second diode D2 and the fourth switch S4 as a pair, but this means that the second diode D2 is turned on. The conduction of the antiparallel diodes D1 to D4 may be implemented by controlling the first to fourth switches S1 to S4.

In addition, the controller 170 may control the switching of the first to fourth switches S1 to S4 to obtain a desired output voltage by appropriately controlling the operating time of the powering mode and the free resonant mode. In this way, the desired output voltage is determined according to the ratio of the operating time of the powering mode and the free resonance mode, where the duty ratio is defined as in Equation 1 below.

[Equation 1]

Duty ratio = Pt / (Pt + Rt)

Where Pt is the powering mode execution time and Rt is the free resonance mode execution time.

For example, as shown in Equation 1, the output time of the powering mode is increased for the output of the large voltage to increase the duty ratio relatively, and the execution time of the free resonance mode is increased for the output of the small voltage. Make the duty ratio relatively small. Here, the large voltage and the small voltage are each less than or equal to the input voltage.

As such, the controller 170 controls the switching of the first to fourth switches S1 to S4 (including the antiparallel diodes D1 to D4) of the full bridge, so that the voltage at the output terminal always exceeds the input voltage. Equal or smaller. Herein, the control unit 170 turns on / off the first and fourth switches S1 and S4 as a pair, and sets the second and third switches S2 and S3 as a different pair, for each group. By alternately turning on / off, energy is output to the series resonator 130 in the powering mode. In addition, the controller 170 alternately turns on / off the second set of diodes D2 and the fourth switch S4 and the second set of switches S2 and the fourth diode D4. In the free resonant mode, the voltage is transferred to the secondary side through the transformer 140 using energy accumulated in the series resonator 130. The switching periods of the first to fourth switches S1 to S4 for the powering mode and the switching periods of the second and fourth switches S2 and S4 and the diodes D2 and D4 for the free resonance mode are shown in FIG. 4. It demonstrates with reference to (a) and (b).

4A is a diagram for explaining the resonance period of the series resonance unit and the switching period of the switch unit of the present invention. Referring to FIG. 4A, the resonance current of the series resonator 130 is a square wave current. When the resonance current is zero, the first and fourth switches S1 and S4 are turned on and the second and third switches S2 and S3 are turned off. The circuit operation at this time is as described with reference to FIG. 3A. In addition, when the resonance current becomes zero again, the second and third switches S2 and S3 are turned on and the first and fourth switches S1 and S4 are turned off. The circuit operation at this time is as described with reference to FIG. 3B.

In addition, referring to FIG. 4B, when the resonance current of the series resonator 130 is zero, the set of the second diode D2 and the fourth switch S4 is turned on and the other one is turned on. The second switch S2 and the fourth diode D4 of the pair are turned off. The circuit operation at this time is as described with reference to FIG. 3C. In addition, when the resonance current becomes zero again, the second diode D2 and the fourth switch S4 are turned off and the second switch S2 and the fourth diode D4 are turned on. The circuit operation at this time is as described with reference to FIG. 3D.

As described above, the switches S1 to S4 (including the anti-parallel diodes D1 to D4) are divided into respective groups as described above, and thus the resonance period of the series resonator 130 may be adjusted. It is preferable to switch alternately in half.

As can be seen from the above, according to the switching control of the switches (S1 ~ S4) and the diodes (D2, D4) connected in anti-parallel to the second switch (S2) and the fourth switch (S4), respectively, The voltage is transmitted to the output terminal through 140, and the magnitude of the voltage is determined on the secondary side of the transformer 140 according to the execution time of the powering mode and the free resonance mode. In other words, when the execution time of the powering mode is extended, the output voltage (less than the input voltage) increases.

Furthermore, the voltage transferred to the secondary side through the transformer 140 is full-wave rectified by the rectifier 160, and the rectified voltage is smoothed by the smoothing capacitor 170 and then output.

Although the basic circuit diagram of the present invention is shown in FIG. 2, the circuit switching mode of the present invention can be configured in four modes as shown in FIGS. 3A to 3D. The first to fourth switches S1 to S4 of the full bridge are repeatedly operated on and off when the resonant current of the DC resonator is 0, and switching is always performed at half of the resonant period for optimal switching.

As described above, by switching the first to fourth switches of the full bridge to which the anti-parallel diodes are connected, and controlling the switching of the second and fourth diodes, a voltage lower than the input voltage can be output to the output terminal, and the switching By synchronizing the period with the resonant period, more reliable zero current switching (ZCS) can be guaranteed.

Here, it should be noted that in the detailed description and the drawings of the present invention, in the free resonant mode, the second diode D2 and the fourth switch S4 are grouped together, and the second switch S2 and the fourth diode D4 are used. Is alternately switched to another group to perform the free resonant mode, but this is only an example. Therefore, one of ordinary skill in the art to which the present invention pertains may refer to the above example and configure other switches for each group. For example, by combining the first diode D1 and the third switch S3 into one pair, the first switch S1 and the third diode D3 into another pair, and alternately switching each group, Free resonant mode could be implemented.

The detailed description and contents of the drawings described above are limited to the preferred embodiments of the present invention, and the present invention is not limited thereto. It will be possible to substitute, change or delete the component according to the present invention within the scope of the technical idea of the present invention. Therefore, the scope of the present invention should be determined by the appended claims rather than by the foregoing description and drawings.

Using the series resonant DC / DC converter having the step-down function of the present invention, it is possible to output a voltage lower than the input voltage at the output terminal while minimizing switching losses.

Further, according to the series resonant DC / DC converter of the present invention, more reliable zero current switching (ZCS) can be performed by using a series resonant circuit.

Claims (11)

DC power supply; First and second switches S1 to S4 of the full bridges having the anti-parallel diodes D1 to D4 connected thereto, respectively; Four switches (S3, S4) are respectively connected to both ends of the DC power supply in parallel, the switch unit for switching in accordance with a switching control signal; A series resonator connected between a connection node of the first and second switches S1 and S2 and a connection node of the third and fourth switches S3 and S4; A transformer including a primary coil and a secondary coil connected in series with the series resonator; A rectifier for rectifying the voltage output from the transformer; A smoothing capacitor that smoothes and outputs the voltage rectified by the rectifier; And The first to fourth switches S1 to S4 to periodically repeat a powering mode for storing energy in the series resonator unit and a free resonant mode for transferring the stored energy to the secondary side through the transformer. And a control unit controlling the switching time of the anti-parallel diodes D1 to D4 to control the powering mode execution time and the free resonance mode execution time according to the output voltage. Series resonant DC / DC converters. The method of claim 1, wherein the control unit, Controlling the on / off switching of one set of the first and fourth switches S1 and S4 and the other set of the second and third switches S2 and S3 at a predetermined switching period alternately for each group. A series resonant DC / DC converter having a step-down function. The method of claim 2, wherein the control unit, And a step-down function in which the first to fourth switches are alternately turned on and off at each time point when the resonance current of the series resonator becomes zero. The method of claim 1, wherein the control unit, The second diode D2 and the fourth switch S4 of one group and the second switch S2 and the fourth diode D4 of the other group are controlled on / off switching in a preset switching cycle for each group. A series resonant DC / DC converter having a step-down function, characterized in that. 5. The series resonant DC / DC converter having a step-down function according to claim 4, wherein the groups are alternately turned on / off when the resonance current of the series resonator becomes zero. The method of claim 1, wherein the control unit, Series resonant DC / DC converter having a step-down function, characterized in that for controlling the amount of resonant energy stored in the series resonator by controlling the time that the first to fourth switches (S1 ~ S4) on / off . The method of claim 1, wherein the control unit, The series resonant DC / DC converter having a step-down function, characterized in that for controlling the time of the output voltage of the output terminal by controlling the time that the first to fourth switches (S1 ~ S4) on / off. The method of claim 1, wherein the control unit, In the free resonant mode operation, the first diode D1 and the third switch S3 of the pair and the first switch S1 and the third diode D3 of the other group are set in advance and set in advance. A series resonant DC / DC converter having a step-down function, which controls on / off switching according to a switching cycle. The method of claim 8, wherein the control unit, And a step-down resonant DC / DC converter having a step-down function, which is alternately turned on / off at each time when the resonant current of the series resonator becomes zero. The method of claim 8, wherein the control unit, Series resonance having a step-down function, characterized in that by controlling the on / off switching of the first to fourth switches (S1 ~ S4) and the anti-parallel diodes (D1 ~ D4), the output voltage of the output terminal Type DC / DC converter. The method of claim 1, wherein the control unit, Series resonance having a step-down function characterized in that to control the magnitude of the output voltage of the output terminal by controlling the time that the first to fourth switches (S1 ~ S4) and the anti-parallel diodes (D1 ~ D4) on / off Type DC / DC converter.

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