JP2005027488A - Non-isolated step-down converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-isolated step-down converter capable of achieving the improvement of efficiency by expanding the duty of switching elements with a simple structure. <P>SOLUTION: A plurality of capacitors 3, 4 are connected in series between input terminals 13, 14 to divide an input voltage Vin. A switch circuit 15 is inserted between the capacitors 3, 4 and a choke coil 11. The switch circuit 15 supplies energy in sequence from each of the capacitors 3, 4 to the choke coil 11 while setting up the periods of sending out the energy of the choke coil 11 to the output side in between dead time periods TD when each of the capacitors 3, 4 are disconnected from the choke coil 11. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-isolated step-down converter used for point-of-load or the like.

  As a non-isolated step-down converter capable of responding rapidly to a sudden change in load, for example, as shown in Patent Document 1, two step-down converter circuits are connected in parallel to form a multi-phase converter. It is known that the phase of two step-down converter circuits is set to 180 ° so that the turn-on timing of the same switching frequency is shifted to speed up the response and reduce the ripple of the output voltage.

  FIG. 3 is an example of a multi-phase step-down converter incorporating such a plurality of step-down converter circuits. In the figure, reference numerals 1 and 2 denote input terminals to which an input voltage Vin is applied, and reference numeral 3 denotes an input smoothing capacitor for smoothing the DC input voltage Vin, which is connected between the input terminals 1 and 2. Reference numeral 5 denotes a step-down converter circuit for stepping down the smoothed input voltage Vin. Here, two step-down converter circuits 5a and 5b are connected in parallel. That is, the first step-down converter circuit 5a includes a rectifying first switch element 6a having one end connected to one input terminal 1, and the other end of the switch element 6a and the other input terminal 2. A second commutating switch element 7a for connecting one end and the other end; a choke coil 11a having one end connected to a common connection point of the switch elements 6a and 7a; and the other end of the choke coil 11a and the switch element 7a. The output smoothing capacitor 12 is connected between the other end. The second step-down converter circuit 5b includes a rectifying third switch element 6b having one end connected to the input terminal 1, and one end between the other end of the switch element 6b and the other input terminal 2. A commutating fourth switch element 7b for connecting the other end of the choke coil 11b, a choke coil 11b having one end connected to the connection point of the switch elements 6b and 7b, the other end of the choke coil 11b and the other end of the switch element 7a And a common output smoothing capacitor 12.

  Then, the switch elements 6a and 7a of the step-down converter circuit 5a and the switch elements 6b and 7b of the step-down converter circuit 5b are alternately turned on and off while having a phase of 180 ° by a control means (not shown), and the step-down converter The step-down output from the circuit 5 is output as a DC output voltage Vout between output terminals 13 and 14 connected between both ends of the output smoothing capacitor 12.

  FIG. 4 shows operation timing waveforms of the switch elements 6a and 7a and the switch elements 6b and 7b. Here, currents I6a and I6b flowing through the switch elements 6a and 6b and currents I7a and I7b flowing through the switch elements 7a and 7b are also shown. At the beginning of the period T1, the switch elements 6a and 7b are turned on, and the switch elements 6b and 7a are turned off. In step-down converter circuit 5a, energy is stored in choke coil 11a through switch element 6a. On the other hand, in another step-down converter circuit 5b, switch element 7b is on, so that energy released from choke coil 11b is reduced. A voltage lower than the input voltage Vin synthesized and smoothed by the output smoothing capacitor 12 is generated between the output terminals 13 and 14 as the output voltage Vout having a small ripple component. At this time, as shown in FIG. 4, the current I6a flowing through the switch element 6a rises with a relationship that energy is stored in the choke coil 11a, and the current I7b flowing through the switch element 7b releases energy from the choke coil 11b. (The current does not flow through the switch elements 6b and 7a).

  When it reaches the middle of the period T1, the switch element 7a is turned on instead of the switch element 6a being turned off, and the energy stored in the choke coil 11a of the step-down converter circuit 5a is released. Further, since the switch element 7b remains on, the energy stored in the choke coil 11b is continuously released, and an output voltage Vout having a small ripple component is generated between the output terminals 13 and 14. At this time, the current I7a flowing through the switch element 7a slopes down due to the release of energy from the choke coil 11a, and the current I7b flowing through the switch element 7b continues to slope down (current flows through the switch elements 6a and 6b). Absent).

  Next, in a period T2, the switch element 7b is turned off instead of the switch element 6b being turned on. Then, in the step-down converter circuit 5b, energy is stored in the choke coil 11b through the switch element 6b, and a voltage lower than the input voltage Vin is generated between the output terminals 13 and 14 as the output voltage Vout having a small ripple component. At this time, as shown in FIG. 4, the current I6b flowing through the switch element 6b rises and the current I7a flowing through the switch element 7a falls (current does not flow through the switch elements 6a and 7b).

When reaching the middle of the period T2, the switch element 7b is turned on instead of the switch element 6b being turned off, and the energy stored in the choke coil 11b is released. At this time, since the switching element 7a remains on, the energy stored in the choke coil 11a is continuously released, and an output voltage Vout having a small ripple component is generated between the output terminals 13 and 14. At this time, the current I7b flowing through the switch element 7b is tilted down because the energy is released from the choke coil 11b, and the current I7a flowing through the switch element 7a continues to tilt down (current flows through the switch elements 6a and 6b). Absent). And it returns to period T1 again and repeats the above-mentioned operation.
JP 2003-111396 A

  In the multi-phase step-down converter shown in FIG. 3, for example, when the input voltage Vin is DC5V and an output voltage of DC1.2V is to be taken out between the output terminals 13 and 14, Vout = D * Vin (D is the switch elements 6a and 6b). Therefore, the duty D of each switch element 6a, 6b is defined as 0.24 (a period of 24% with respect to one cycle in FIG. 4). However, it is generally known that a non-insulated step-down converter can increase efficiency when the duty D of the switch elements 6a and 6b on the rectifying side is wide. In the above circuit, the duty D is set to 0.24 or more. Since it could not be expanded, it was not possible to further improve the efficiency.

  Further, in the above circuit configuration, by reducing the inductance of the choke coils 11a and 11b per one by the plurality of step-down converter circuits 5a and 5b, the slope of the current flowing through the individual choke coils 11a and 11b is made steep. Responsiveness when load current changes suddenly is improved. However, for this reason, choke coils 11a and 11b must be provided in the step-down converter circuits 5a and 5b, respectively, and it is difficult to reduce the circuit size.

  In order to increase the duty of the switch element, for example, as shown in FIG. 5, a choke coil 11 constituting the step-down converter 5 is provided with a tap and one end of the switch element 7 is provided on the tap, or as shown in FIG. Thus, a method is known in which taps for dividing the number of turns are provided in the choke coils 11a and 11b, respectively, and one end of the switch elements 7a and 7b is provided in each of the taps. In this case, for example, in FIG. 5, assuming that the number of turns of the choke coil 11 is divided by n: 1 by a tap, the switch element 6 is turned on (n + 1 turn current flows) and the switch element 7 is turned on. (The current for one turn flows in) Since the inductance of each choke coil 11 is different, the desired output voltage Vout is taken out with the duty of the switch element 6 wider than that shown in FIG. Can do.

  However, in the above circuit configuration, unless the coupling of the choke coil 11 is made dense, noise is generated by the leakage inductance, and stress is applied to various components such as the switch element 6. In addition, in order to suppress this noise, it is necessary to connect an active clamp circuit in parallel to the commutation switch element 7 to absorb the back electromotive voltage caused by the leakage inductance, which further complicates the circuit configuration. It will be.

  An object of the present invention is to provide a non-insulated step-down converter capable of increasing the duty of a switch element with a simple configuration and achieving an improvement in efficiency.

  The non-isolated step-down converter according to claim 1 of the present invention is a non-isolated step-down converter that extracts a voltage lower than the input voltage by intermittently applying the input voltage to the choke coil, and between the input terminals to which the input voltage is applied. A plurality of charging / discharging means are connected in series, interposed between the charging / discharging means and the choke coil, while providing a period for sending the energy of the choke coil to the output side, from each of the charging / discharging means A switch circuit for sequentially supplying energy to the choke coil is provided.

  Further, the non-insulated step-down converter according to claim 2 of the present invention is provided separately from the first switch element that sequentially supplies energy from the charge / discharge means to the choke coil, and the first switch element, The switch circuit is configured by a second switch element that sends energy of the choke coil to the output side.

  According to the non-insulated step-down converter of claim 1 of the present invention, by connecting a plurality of charging / discharging means in series between the input terminals, a voltage lower than the input voltage is generated between both ends of each charging / discharging means. A voltage lower than the input voltage can be taken out by intermittently applying the voltage generated between both ends of the charging / discharging means from the charging / discharging means to the choke coil. Since the voltage applied to the choke coil is lower than the input voltage, the duty of the switch circuit can be increased when the same output voltage is taken out. In addition, since energy is supplied to the common choke coil from each charging / discharging unit, only one choke coil is required, and the duty of the switch element is substantially increased while the configuration is simple, and the efficiency is improved. Improvement can be achieved.

  According to the non-insulated step-down converter according to claim 2 of the present invention, the first switch element for sequentially supplying energy from each charging / discharging means to the choke coil, and the second switch element for sending the energy of the choke coil to the output side Are provided separately. Therefore, the second switch element can be operated independently of the operation of the first switch element, and a period for sending the choke coil energy to the output side can be ensured.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 and 2. In addition, about the thing which a structure overlaps with FIG. 3 of a prior art example, the same code | symbol is attached | subjected and the description is abbreviate | omitted as much as possible.

  In FIG. 1 showing the entire configuration of the circuit, in this embodiment, in order to divide the input voltage Vin on the input side of the step-down converter circuit 5, a capacitor 3 having the same capacity as charging / discharging means between the input terminals 1 and 2 is used. 4 series circuits are connected. Although the capacitors 3 and 4 are used here, a battery such as a secondary battery may be used.

  In addition to the choke coil 11 and the output smoothing capacitor 12, the step-down converter circuit 5 includes a switch circuit including a plurality of switch elements 6, 7, 8, and 9 between the series circuit of the capacitors 3 and 4 and the choke coil 11. Has 15. The switch circuit 15 has a switch element 6 inserted and connected to a voltage supply line extending from one end of the series circuit of the capacitors 3 and 4 to one end of the choke coil 11, and other than the capacitor 12 from the other end of the series circuit of the capacitors 3 and 4. The switch element 9 is inserted and connected to a reference voltage line that reaches the end, and the switch element 7 is connected between a connection point between the switch element 6 and one end of the choke coil 11 and a connection point between the switch element 9 and the other end of the capacitor 12. , 8 are connected to each other, and the connection point of the switch elements 7 and 8 is connected to the connection point of the capacitors 3 and 4. The switching elements 6 and 8 that supply the voltage V1 across the capacitor 3 to the choke coil 11 and the voltage V2 across the other capacitor 4 while providing a dead time period during which both the switching elements 6 and 9 are off. Are switched on and off alternately with a phase difference of 180 ° and the energy of the choke coil 11 is sent to the output side during the dead time period. In addition, a pulse drive signal is supplied to each of the switch elements 6 to 9 from a control means (not shown) so that both of the serially connected switch elements 7 and 8 that are also used are turned on.

  In the present embodiment, as indicated by the broken line in FIG. 1, a single switch element 10 is connected in parallel with the switch elements 7 and 8, and the switch elements 6 and 9 are both turned off during the dead time period. A pulse drive signal for turning on the switch element 10 may be supplied from the control means. In this case, the switch circuit 15 includes switch elements 6 to 9 as first switch elements for sequentially supplying energy from each of the capacitors 3 and 4 to one common choke coil 11, and these switch elements 6 to 9. Is provided separately, and is turned on when the switching elements 6 and 9 are turned off to disconnect the capacitors 3 and 4 from the choke coil 11, and one end of the choke coil 11 is short-circuited to the reference voltage line. And a second switch element 10 for sending 11 energy to the output side. When the switch element 10 is not connected, the energy stored in the choke coil 11 cannot be discharged without waste unless the switch elements 7 and 8 are turned on simultaneously during the dead time period when both the switch elements 6 and 9 are turned off. However, if the switch element 10 is connected, there is no need to request such a difficult control from the switch elements 7 and 8, and the period for sending the energy of the choke coil 11 to the output side is ensured. The energy stored in the choke coil 11 can be released without waste.

  Next, the operation of the above configuration will be described with reference to FIG. 2 showing the operation waveforms of the switch elements 6 to 10 and the current waveforms I6 and I9 of the switch elements 6 and 9.

  The switch elements 6 and 8 and the switch elements 7 and 9 are alternately turned on and off with a phase difference of 180 ° in one cycle. The phase difference is 120 ° when the switch elements 7 and 8 connected in series are three switch elements, and is 90 ° when the switch elements are four switch elements. Since the two capacitors 3 and 4 are connected in series between the input terminals 1 and 2, the capacitors 3 and 4 are charged and voltages V1 and V2 are generated between both ends thereof. These voltages V1 and V2 are half of the input voltage Vin (Vin / 2).

  First, the operation when the switch element 10 is not provided will be described. Until the middle of the period T1, the switch elements 6 and 8 are on and the switch elements 7 and 9 are off. As a result, both ends of one capacitor 3 are connected to both ends of a series circuit composed of the choke coil 11 and the output smoothing capacitor 12, so that energy is supplied from the capacitor 3 to the choke coil 11 and energy is stored in the choke coil 11. . At this time, the current I6 flowing into the choke coil 11 via the switch element 6 increases in inclination as shown in FIG.

  Then, when the period T1 elapses, for example, 96% (48% in one cycle), both the switch elements 6 and 9 are turned off, and a dead time period TD in which the energy supply from the capacitors 3 and 4 to the choke coil 11 is cut off is entered. To do. During this dead time period TD, the switch element 7 is turned on instead of the switch element 6 and both the switch elements 7 and 8 are turned on. Thereby, the energy stored in the choke coil 11 until then is released to the output side.

  In the next period T2, the switch element 6 is continuously turned off and the switch element 7 is turned on, but the switch element 8 is turned off. Instead, the switch element 9 is turned on and both ends of the other capacitor 4 are turned on. The switch elements 7 and 9 are connected to both ends of a series circuit composed of a choke coil 11 and an output smoothing capacitor 12. Therefore, energy is supplied from the capacitor 4 to the choke coil 11, and energy is stored in the choke coil 11. At this time, the current I7 flowing into the choke coil 11 via the switch element 9 increases in inclination as shown in FIG.

  When the period T2 elapses, for example, 96% (48% in one cycle), both the switch elements 6 and 9 are turned off again, and the dead time period TD in which the energy supply from the capacitors 3 and 4 to the choke coil 11 is interrupted. Transition. During this dead time period TD, the switch element 8 is turned on instead of the switch element 9, and both the switch elements 7 and 8 are turned on. Thereby, the energy stored in the choke coil 11 until then is released to the output side. By repeating the above operation, the output voltage Vout lower than the inter-terminal voltages V1 and V2 of the capacitors 3 and 4 can be taken out between the output terminals 13 and 14.

  Further, when the switch element 10 is provided, the switch element 10 is turned on during the dead time period TD. When the switch element 10 is turned on, the energy from the choke coil 11 is reliably sent to the output side using the switch element 10 as a commutation element, so that the switch elements 7 and 8 are at any timing during the dead time period TD. On and off may be switched.

  In the above series of operations, for example, when the input voltage Vin is DC 5 V and an output voltage of DC 1.2 V is to be taken out between the output terminals 13 and 14, the capacitors 3 and 4 which are substantial input voltages to the step-down converter circuit 5 are used. Since the inter-terminal voltages V1 and V2 are reduced to half of the original input voltage Vin, the duty D of each switch element 6 and 9 is expanded to 0.48 (a period of 48% with respect to one cycle in FIG. 3). To do. This is twice that of the conventional example shown in FIG. Therefore, the efficiency as the step-down converter circuit 5 can be greatly improved.

  Further, since the choke coil 11 sends the energy to the output side only 4% per cycle, the inductance value of the choke coil 11 can be reduced. Therefore, downsizing of the step-down converter circuit 5 can be realized, and the slope of the current flowing through the choke coil 11 is steep due to a small inductance value, and therefore the choke coil 11 flows when the load current changes suddenly. The current immediately follows, and a faster response can be realized.

  Further, if the duty D of the switch elements 6 and 9 is 0.5, the charging / discharging of energy by the choke coil 11 itself becomes unnecessary, so that the step-down converter circuit 5 without the choke coil 11 can be realized. . In this case, the output voltage Vout that can be taken out is half of the inter-terminal voltages V1 and V2 of the capacitors 3 and 4 (1/4 of the input voltage Vin).

  In addition, since the switch elements 6 and 8 and the switch elements 7 and 9 in the step-down converter circuit 5 repeat on and off operations with a phase difference of 180 °, compared to the step-down converter circuit controlled by one switch element, Therefore, a high-speed response to a change in the load connected between the output terminals 13 and 14 is possible.

  As described above, in this embodiment, in the non-insulated step-down converter that extracts a voltage lower than the input voltage Vin by intermittently applying the input voltage Vin to the choke coil 11, a plurality of capacitors 3 are connected between the input terminals 13 and 14. , 4 are connected in series, and the switch circuit 15 interposed between the capacitors 3 and 4 and the choke coil 11 is connected to the choke coil 11 during the dead time period TD for separating the capacitors 3 and 4 and the choke coil 11 from each other. While providing a period during which energy is sent to the output side, energy is sequentially supplied from the capacitors 3 and 4 to the choke coil 11.

  In this case, by connecting a plurality of capacitors 3 and 4 in series between the input terminals 13 and 14, a voltage lower than the input voltage is generated between both ends of the capacitors 3 and 4. By intermittently applying the voltage generated between both ends of the capacitors 3 and 4 to the choke coil 11 from the respective capacitors 3 and 4, voltages V1 and V2 lower than the input voltage Vin can be taken out. Since the voltage applied to the choke coil 11 is lower than the input voltage Vin, the duty of the switch circuit 15 can be increased when the same output voltage Vout is taken out. Further, since energy is supplied from the capacitors 3 and 4 to the common choke coil 11, only one choke coil 11 is required, and the duty of the switch elements 6 and 9 is substantially reduced while having a simple configuration. To improve efficiency.

  In the present embodiment, the first switch elements 6 to 9 for sequentially supplying energy from the capacitors 3 and 4 to the choke coil 11 and the first switch elements 6 to 9 are provided separately. A switch circuit 15 is constituted by the second switch element 10 that sends energy to the output side.

  In this case, first switch elements 6 to 9 for sequentially supplying energy from the capacitors 3 and 4 to the choke coil and a second switch element 10 for sending the energy of the choke coil to the output side are provided separately. . For this reason, the second switch element 10 can be operated independently of the operations of the first switch elements 6 to 9, and the period for sending the energy of the choke coil 11 to the output side can be ensured reliably.

  In addition, this invention is not limited to the said Example, A various deformation | transformation is possible. For example, each of the switch elements 6 to 10 may be composed of, for example, a MOS type FET or a transistor.

It is a circuit diagram which shows a preferable example of the non-insulation step-down converter in a present Example. FIG. 4 is a waveform diagram showing the operation of each switch element. It is a circuit diagram which shows an example of the conventional multiphase step-down converter. It is a timing diagram which shows an example of the drive waveform of each switch element same as the above. It is a circuit diagram which shows the example which expands the duty ratio of the conventional step-down converter. It is a circuit diagram which shows the example which expands the duty ratio of the conventional multiphase step-down converter.

Explanation of symbols

3, 4 Capacitor (charging / discharging means)
6-9 First switch element
10 Second switch element
11 Choke coil
15 Switch circuit

Claims (2)

In the non-insulated step-down converter that extracts a voltage lower than the input voltage by intermittently applying the input voltage to the choke coil,
A plurality of charging / discharging means are connected in series between input terminals to which the input voltage is applied,
A switch circuit that is interposed between the charging / discharging unit and the choke coil, and sequentially supplies energy from the charging / discharging unit to the choke coil while providing a period for sending the energy of the choke coil to the output side. A non-insulated step-down converter characterized by comprising: The switch circuit is provided separately from the first switch element for sequentially supplying energy to the choke coil from each of the charge / discharge means, and sends the energy of the choke coil to the output side. The non-insulated step-down converter according to claim 1, comprising: a second switch element.

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