JPH11187649A - Synchronous dc-to-dc converter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a synchronous DC-to-DC converter of relatively a simple circuit constitution and moreover is possible of high-speed operation. SOLUTION: When a main switching element 1 is turned on, the signal of a logical value 'high' is outputted from a fourth comparator 18, and an RSFF (set reset flip flop) 22 is reset, and the gate of a switching element 6 for commutation is put in such a condition that the logical value is low, so that the switching element 6 for commutation is turned off. On the other hand, when the main switching element 1 is turned off, the signal of the logical value which is high is outputted from a third comparator 17, and the RSFF 22 is set, and the gate of the switching element 6 for commutation is put in such condition that the logical value is high, so the switching element 6 for commutation is turned off, and the main switching element 1 and the switching element 6 for commutation are alternately turned on and turned off.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DC / DC converter for converting a DC voltage, and more particularly to an improvement of a so-called synchronous DC / DC converter.

[0002]

2. Description of the Related Art Conventionally, as this type of DC / DC converter, for example, there is one as shown in FIG. The asynchronous DC / DC converter shown in FIG. 3 has a main switching element (FIG. 3) to which an input DC voltage Vcc is applied.
In FIG. 4, “Q1” 31 is turned on (hereinafter, referred to as “on”) or cut off (hereinafter, “off”).
That. ), The main switching element 31
(In FIG. 3 and FIG. 4, "L1"
The AC voltage that is excited by the commutation diode 32 is rectified by a commutation diode (denoted as “D1” in FIGS. 3 and 4) 33 and a smoothing capacitor (denoted as “C1” in FIGS. 3 and 4) 34. And a load (FIG. 3)
4 is described as “LOAD” in FIG. 4).

In this asynchronous DC / DC converter, a resistor connected in series between the output terminal 35 and the ground (denoted as "R1" in FIGS. 3 and 4).
A so-called divided voltage having a magnitude corresponding to the output voltage is obtained from a connection point of the resistor 37 and a resistor (denoted as “R2” in FIGS. 3 and 4).
9 is compared with the reference voltage Vs. Further, a comparison result of the comparator 39 and an output of an oscillator (denoted as “OSC” in FIGS. 3 and 4) 41 that outputs a signal of a predetermined frequency are compared by the comparator 42, and based on the comparison result of the comparator 42. The DC voltage converted to a predetermined voltage is output from the output terminal 35 by the on / off control of the main switching element 31.

In an asynchronous DC / DC converter, when the main switching element 31 is off, the coil 32
Is grounded via a commutating diode 33. At this time, it is desirable that the input side of the coil 32 be completely grounded so that the excited current becomes zero.
Actually, a potential difference is generated by a voltage drop in the forward direction of the commutation diode 33, and the voltage is not completely grounded. Therefore, the asynchronous DC / DC converter is
There is a problem that the so-called power conversion efficiency is deteriorated by the voltage drop generated in the commutation diode 33.

In order to solve the above problem and improve the power conversion efficiency, for example, a synchronous DC / DC converter having a configuration as shown in FIG. 4 has been proposed. This synchronous DC / DC converter includes a commutation switching element (indicated as “Q2” in FIG. 4) 43 connected in parallel with the commutation diode 33 and having a lower forward voltage than the commutation diode 33. .
In the synchronous DC / DC converter, the main switching element 31 and the switching element 43 for commutation are alternately turned on and off by a logic circuit (denoted as “LOG” in FIG. The input side is grounded via a switching element 43 for commutation to improve power conversion efficiency.

[0006]

In the latter synchronous DC / DC converter, the logic circuit 4
4, the main switching element 31 and the commutation switching element 43 are turned on and off alternately. However, in the operation of the logic circuit 44, the main switching element 31 and the commutation switching element 43 are simultaneously turned on. A state cannot be completely avoided. This synchronous D
In the C / DC converter, the main switching element 31
And the switching element 43 for commutation are simultaneously turned on, the voltage Vcc on the output side of the main switching element 31
Flows as it is to the ground side via the commutating switching element 43, and the two switching elements 3
There is a disadvantage that the output voltage drops to near the instantaneous zero v for a short time in which the operations of the steps 1 and 43 overlap.

Therefore, in order to prevent the main switching element 31 and the commutation switching element 43 from being turned on at the same time, conventionally, for example, in the logic circuit 44, a pulse faster than the operating frequency of the oscillator 41 is used. By generating a fixed delay time and using this delay time, a time sequence is created in which the main switching element 31 and the switching element 43 for commutation do not simultaneously turn on. Has also been done.

However, as described above, a certain delay time is generated by a pulse faster than the operating frequency of the oscillator 41, and the timing at which the main switching element 31 and the commutation switching element 43 are simultaneously turned on is determined. If a configuration is made to create a time sequence that does not occur, the configuration of the circuit becomes complicated and the cost of the device is increased. In addition, since a certain delay time is generated to prevent the main switching element 31 and the commutation switching element 43 from being turned on at the same time, the high-speed operation of the circuit is reduced by the delay time. Has a new problem that limits are imposed.

The present invention has been made in view of the above circumstances, and has as its object to provide a synchronous DC / DC converter having a relatively simple circuit configuration and capable of operating at high speed. is there. Another object of the present invention is to use a circuit that requires a time sequence such that a delay time is provided in the operation timing of both elements so that the main switching element and the commutation switching element are not simultaneously turned on. Another object of the present invention is to provide a synchronous DC / DC converter with good power conversion efficiency and relatively low cost.

[0010]

According to a first aspect of the present invention, there is provided a synchronous DC / DC converter, wherein a main switching element and a coil are directly connected between an input terminal and an output terminal, and the main switching device is connected to the main switching device. A switching element for commutation is provided between a connection point between the element and the coil and ground, and the main switching element and the switching element for commutation are alternately turned on and off, and a predetermined direct current is applied to the output terminal. Synchronous DC /
A DC converter, comprising: a commutation switching element control unit that controls an operation of the commutation switching element based on a voltage at a connection point between the main switching element and the coil and a voltage at the output terminal. It is.

In particular, the commutating switching element control means includes an input-side voltage dividing means for dividing the voltage at the connection point between the main switching element and the coil, and an output-side voltage dividing means for dividing the output voltage at the output end into two different voltages. A voltage dividing means for comparing a divided voltage obtained by the input-side voltage dividing means with one of two divided voltages obtained by the output-side voltage dividing means having a higher voltage value; (1) compares the divided voltage obtained by the input-side voltage dividing means with the other divided voltage having a lower voltage value among the two divided voltages obtained by the output-side voltage dividing means. While the second comparator is set by the output signal of the first comparator,
It is preferable that the reset signal be reset by an output signal of the second comparator, and the output signal be provided with a set / reset flip-flop used for controlling the operation of the commutation switching element.

In this configuration, the voltages on the input side and the output side of the coil are detected by the input-side voltage dividing means and the output-side voltage dividing means, respectively, and the divided voltages by the first and second comparators are detected. Based on the comparison result, the switching element for commutation is controlled to be turned on / off via a set / reset flip-flop. That is,
When the main switching element is turned on, the circuit constant is set so that the divided voltage on the input side of the coil is larger than the divided voltage on the output side of the coil, and the first comparator Is configured to output a signal of a logical value Low and a signal of a logical value High from the second comparator. As a result, the set / reset flip-flop is reset, and the signal of the logical value Low is applied to the switching element for commutation. As a result, the switching element for commutation is turned off. On the other hand, when the main switching element is turned off, the switching element for commutation is turned on, contrary to the above, and when the main switching element is turned on, after all, When the commutating switching element is reliably turned off and the main switching element is turned off,
Since the commutation switching elements can be reliably turned on and each of them can be controlled, and unlike the related art, there is no need to provide a configuration for setting a delay time by a time sequence, so that a high-speed operation and an efficient synchronous DC / DC can be performed. A converter will be provided.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. The members, arrangements, and the like described below do not limit the present invention, and can be variously modified within the scope of the present invention. First, a first circuit configuration example of the synchronous DC / DC converter according to the embodiment of the present invention will be described with reference to FIG. This synchronous DC / DC converter has a main switching element (denoted as "Q1" in FIGS. 1 and 2) to which a predetermined DC voltage Vcc is applied.
It has. Here, an N-channel MOS FET transistor is used as the main switching element 1. On the output side of the main switching element 1, a coil (denoted as "L1" in FIGS. 1 and 2) 2 is connected in series, and this coil 2 is connected to a load (FIG. And "LOAD" in FIG. 2).

The input side of the coil 2 has a cathode of a commutation diode (denoted as "D1" in FIGS. 1 and 2) 5 and a commutation switching element (FIGS. 1 and 2).
, Are connected to one end of a commutation diode 5, and the other ends of the commutation diode 5 and the commutation switching element 6 are grounded. Here, as the commutation switching element 6, an N-channel MOS FET transistor is used. Further, a smoothing capacitor (FIG. 1) is connected to the output side of the coil 2.
And a first resistor (in FIGS. 1 and 2) connected in series with one end of a “C1” 7 to detect a so-called divided voltage having a magnitude corresponding to the output voltage. 8 and a second resistor (see FIGS. 1 and 2).
In FIG. 9, one end of the first resistor 8 is connected to each other, and the other end of the smoothing capacitor 7 and the other end of the second resistor 9 are connected to each other. Both are grounded.

A connection point between the first resistor 8 and the second resistor 9 is connected to an inverting input terminal of a first comparator 10, and a predetermined non-inverting input terminal of the first comparator 10 The reference voltage Vs is applied and the output terminal 3
Are compared with the reference voltage Vs by the first and second resistors 8 and 9 corresponding to the magnitude of the output voltage at the reference voltage Vs, and the comparison result is input to the inverting input terminal of the second comparator 13. It has become so. The output terminal of the second comparator 13 is the main switching element 1.
The output stage of an oscillator (denoted as “OSC” in FIGS. 1 and 2) 12 that outputs a predetermined frequency signal is connected to the non-inverting input terminal.
On and off control of the main switching element 1 is performed based on the comparison result of the second comparator 13, and a predetermined DC voltage is output from the output terminal 3 to the load 4.

The components described above are basically the same as those of the prior art. However, in the first circuit configuration example, the voltages on the input side and the output side of the coil 2 are further detected. A commutation switching element control circuit 14 for controlling on / off of the commutation switching element 6 is provided. That is, the commutation switching element control circuit 14 is a third resistor ("R3" in FIGS. 1 and 2) which constitutes an input-side voltage dividing means connected in series to detect the voltage on the input side of the coil 2. ) 15 and a fourth resistor (denoted as “R4” in FIGS. 1 and 2) 16
One end of the third resistor 15 is connected to the input side of the coil 2, and the other end of the fourth resistor 16 is grounded.

The connection point between the third resistor 15 and the fourth resistor 16 is connected to the inverting input terminal of the third comparator 17 and the non-inverting input terminal of the fourth comparator 18, respectively. , A divided voltage corresponding to the voltage on the input side of the coil 2 is applied. A fifth resistor 19 (indicated as “R5” in FIGS. 1 and 2) and a sixth resistor which are connected in series and constitute an output-side voltage dividing means are provided on the output side of the coil 2. 1 and 2, a seventh resistor (indicated as “R7” in FIGS. 1 and 2) 21, and a fifth resistor 19. Is connected to the output side of the coil 2, while the other end of the seventh resistor 21 is grounded. A connection point between the fifth resistor 19 and the sixth resistor 20 is connected to a third comparator 17 as a first comparator.
The sixth resistor 20 is connected to the non-inverting input terminal of the
The connection point between the second resistor and the seventh resistor 21 is connected to an inverting input terminal of a fourth comparator 18 as a second comparator.

An output terminal of the third comparator 17 is connected to a set terminal of a set / reset flip-flop (hereinafter, referred to as “RSFF”) 22 having a known / well-known circuit configuration. 4 comparators 18
Is connected to the reset terminal of the RSFF 22. The output terminal of the RSFF 22 is connected to the gate of the switching element 6 for commutation.
According to the output of the SFF 22, the commutation switching element 6
Are driven on and off.

Next, the operation in the above configuration is shown in FIG.
This will be described with reference to FIG. First, when the main switching element 1 is turned on, the voltage at the point A on the input side of the coil 2 rises to a value substantially equal to the input voltage Vcc. Then this A
The voltage at the point is divided by the third and fourth resistors 15 and 16 provided for detecting the voltage on the input side of the coil 2, and the voltage of the third and fourth resistors 15 and 16 is changed. At the connection point, a divided voltage determined by the resistance ratio of the third and fourth resistors 15 and 16 corresponding to the voltage at point A is generated.
The divided voltage generated at the connection point between the third and fourth resistors 15 and 16 is applied to the inverting input terminal of the third comparator 17 and the non-inverting input terminal of the fourth comparator 18, respectively.

On the other hand, in this case, the voltage on the output side of the coil 2 is lower than the voltage at the point A by the voltage drop of the coil 2. The voltage on the output side of the coil 2 is divided by the fifth to seventh resistors 19 to 21, and the divided voltage at the connection point of the fifth and sixth resistors 19 and 20 becomes the third voltage. The divided voltage at the connection point of the sixth and seventh resistors 20 and 21 is supplied to the non-inverting input terminal of the comparator 17 and the inverting input terminal of the fourth comparator 18.
Each will be applied.

Here, the third and fourth resistors 15,
16 and the fifth and sixth resistors 19, 2
The resistance values of the third and fourth resistors 15, 16 and the fifth to seventh resistors 19 to 21 are set in advance so as to be larger than the divided voltage at the connection point of 0. Therefore, when the divided voltage is applied to the third and fourth comparators 17 and 18 as described above, the third comparator 17 outputs an output signal corresponding to the logical value Low from the fourth comparator 17 From 18, an output signal corresponding to the logical value High is output.

As a result, the RSFF 22 is reset by the output signal of the fourth comparator 18 and its output Q
Becomes a logical value Low state, which is applied to the gate of the commutation switching element 6, so that the commutation switching element 6 is turned off.

Next, when the main switching element 1 is turned off, the voltage at the input side of the point A of the coil 2 is lowered toward the forward voltage V _F of the commutation diode 5. On the other hand, the voltage at the point A on the input side of the coil 2 is the forward voltage V
_While falling toward _F , the voltage at the output side of the coil 2 differs from the voltage change at the point A on the input side due to the action of the coil 2 and changes slowly without dropping sharply. The divided voltage at the connection point between the fourth resistors 15 and 16 is the divided voltage at the connection point between the fifth resistor 19 and the sixth resistor 20 and the sixth resistor 20 and the seventh resistor. 2
Instantaneously lower than the divided voltage at the node 1;
As a result, the logical value Hi is output from the third comparator 17.
The output signal corresponding to gh and the output signal corresponding to the logical value Low are output from the fourth comparator 18, respectively, and the output Q of the RSFF 22 becomes the state of the logical value High. Thus, commutation switching element 6 is turned on, the voltage at the point A, a state close to a lower substantially ground potential than the forward voltage V _F of the above.

By repeating the operation associated with the ON / OFF operation of the main switching element 1 as described above, the output voltage determined by the magnitudes of the resistance values of the first resistor 8 and the second resistor 9 but it is supplied from the output terminal 3 to the load 4, while the main switching element 1 is off, so that the reduction of the prior art such as the power conversion efficiency due to the forward voltage V _F is left is reliably avoided . The on / off control of the main switching element 1 is basically the same as the conventional one, and is omitted in the above description of the operation.
Here, to explain roughly, first, the output voltage is equal to the first voltage.
And the voltage divided by the second resistors 8 and 9
, And is compared with a reference voltage Vs. When the divided voltage by the first and second resistors 8 and 9 is equal to or lower than the reference voltage Vs,
A signal corresponding to the logical value High is output from the first comparator 10, and is compared with a signal from the oscillator 12 in the second comparator 13. As a result, the main switching element 1 is turned on / off. ing.

The threshold values and input ranges of the third comparator 17 and the fourth comparator 18 are determined by the third and fourth resistors 15 and 16 and the fifth to seventh resistors 19
It can be adjusted as appropriate by changing the values of .about.21. Also, by setting the threshold value when the switching element 6 for commutation is turned on near the input voltage Vcc and the threshold value when the switching element 6 is turned off near ground voltage, respectively, the switching element 6 for commutation is set. It is possible to obtain a timing that can be quickly turned on / off.

Next, a second circuit configuration example will be described with reference to FIG. Note that the same components as those in the circuit configuration example shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. Hereinafter, different points will be mainly described. In this second circuit configuration example, the synchronous DC /
The DC converter includes a resistor for obtaining a divided voltage for the first comparator 10 and a third and fourth comparator 1
The circuit is simplified by sharing with a resistor for obtaining a divided voltage for 7 and 18.

That is, specifically, on the output side of the coil 2, between the output-side end of the coil 2 and the ground,
Instead of the first and second resistors 8 and 9 and the fifth to seventh resistors 19 to 21 in the circuit configuration example shown in FIG. 1, eighth to eleventh resistors 23 to 26 are used. Are connected in series. A connection point between the eighth resistor 23 and the ninth resistor 24 is connected to a non-inverting input terminal of the third comparator 17 and a connection point between the ninth resistor 24 and the tenth resistor 25 is provided. Are connected to the inverting input terminal of the first comparator 10, and the connection point between the tenth resistor 25 and the eleventh resistor 26 is connected to the inverting input terminal of the fourth comparator 18.

The eighth to eleventh resistors 2
The resistance values of 3 to 26 are the same as those of the comparators 10, 17, and 17 described in the description of the operation of the circuit configuration example shown in FIG.
18 are set so that 18 operations can be obtained. Therefore, the circuit operation is basically the same as that in the case of the first circuit configuration example shown in FIG. 1 described above, and the description thereof will not be repeated here.

In this second circuit configuration example, the main switching element control means is realized by the first comparator 10, the second comparator 13, and the oscillator 12, and the eighth to eleventh resistors 23 to 26 realizes the output voltage dividing means and the output voltage dividing means for controlling the main switching element.

In the above-described embodiment of the present invention,
The case where an N-channel MOS FET transistor is used as the main switching element 1 and the commutation switching element 6 has been described. However, the present invention is not limited to this, and other MOS FETs or bipolar elements may be used. A configuration in which an FET element and a bipolar element are combined may be used, and the same operation can be obtained in any case. Further, the main switching element 1 and the commutation switching element 6 may be configured such that n-stage FET elements are connected in series or in parallel, or n-stage bipolar elements are connected in series or in parallel. However, basically the same operation can be obtained.

Further, in the above-described embodiment of the present invention, a resistor is used as a voltage dividing means for detecting a voltage at a connection point A between the main switching element 1 and the coil 2 and an output voltage. A similar operation can be obtained even if the voltage is divided using the so-called on-resistance. Further, the same applies to a case where a voltage dividing means is configured by combining a resistor and an FET element or a resistor and a bipolar element.

The power of the control circuit for controlling the commutation switching element 6 may be supplied from either the input voltage Vcc or the output voltage.
Further, the same operation can be obtained by switching from supplying the input voltage Vcc at the time of startup and supplying the output voltage thereafter.

[0033]

As described above, according to the present invention,
Use a circuit that requires the creation of a special time sequence as in the past, by configuring the operation of the commutation switching element based on the voltage on the input side of the coil and the output voltage. And a synchronous DC / DC converter capable of ensuring that the main switching element and the commutation switching element are alternately turned on and off alternately, has a relatively simple circuit configuration, and can operate at high speed. Is what you can do.

[Brief description of the drawings]

FIG. 1 shows a synchronous DC / DC according to an embodiment of the present invention.
FIG. 2 is a circuit diagram illustrating a first circuit configuration example of a converter.

FIG. 2 shows a synchronous DC / DC according to an embodiment of the present invention.
FIG. 6 is a circuit diagram illustrating a second circuit configuration example of the converter.

FIG. 3 is a circuit diagram showing a circuit configuration example of a conventional asynchronous DC / DC converter.

FIG. 4 is a circuit diagram showing a circuit configuration example of a conventional synchronous DC / DC converter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Main switching element 2 ... Coil 5 ... Commutation diode 6 ... Commutation switching element 10 ... First comparator 13 ... Second comparator 14 ... Commutation switching element control circuit 17 ... Third comparator 18 ... Fourth Comparator 22 ... RSFF

Claims (4)

[Claims] 1. A main switching element and a coil are directly connected between an input terminal and an output terminal, and a commutation switching element is provided between a connection point between the main switching element and the coil and ground. A synchronous DC / DC converter configured such that the main switching element and the commutation switching element are alternately turned on and off, and a predetermined DC output voltage is obtained at the output terminal. A synchronous switching element control means for controlling the operation of the commutating switching element based on a voltage at a connection point between the main switching element and the coil and a voltage at the output terminal. Type DC /
DC converter. The commutating switching element control means includes an input-side voltage dividing means for dividing a voltage at a connection point between the main switching element and the coil, and an output-side voltage dividing means for dividing an output voltage at an output terminal into two different voltages. A voltage dividing means for comparing a divided voltage obtained by the input-side voltage dividing means with one of the two divided voltages obtained by the output-side voltage dividing means having a higher voltage value; The comparator of claim 1 compares the divided voltage obtained by the input-side voltage dividing means with the other divided voltage having a lower voltage value among the two divided voltages obtained by the output-side voltage dividing means. A second comparator, which is set by the output signal of the first comparator, and is reset by the output signal of the second comparator, and the output signal is the operation of the switching element for commutation. Set library used for control Synchronous DC / DC converter according to claim 1, characterized by being provided with the Tsu preparative flip-flop. 3. The input-side voltage dividing means and the output-side voltage dividing means,
3. The synchronous DC / DC converter according to claim 2, wherein the synchronous DC / DC converter comprises a plurality of resistors provided separately and connected in series. 4. A main switching element control means for controlling an operation of a main switching element, and an output voltage dividing means for controlling a main switching element for dividing an output voltage, wherein the main switching element control means comprises: The operation of the main switching element is controlled based on the divided voltage of the switching element control output voltage dividing means, and the main switching element control output voltage dividing means is composed of a plurality of resistors connected in series. And
3. The synchronous DC / DC converter according to claim 2, wherein the plurality of resistors connected in series also serve as output-side voltage dividing means.