JP2007151381A - Dc-dc converter and control circuit thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC-DC converter, having linear relationship between an error signal and an output DC voltage, and facilitating the stabilization design of a feedback system, in a DC-DC converter, having the non-linear relationship between a duty ratio and the output DC voltage. <P>SOLUTION: The DC-DC converter comprises an error amplification circuit for generating an error signal, obtained by amplifying the error between output and a desired value; an oscillation circuit for generating a triangular wave signal having an amplitude corresponding to the error signal; and a comparison circuit for comparing a reference signal having a prescribed value with the triangular wave signal to turn on and off a switching element. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a DC-DC converter that repeatedly stores and discharges energy to and from an inductor by an on / off operation of a switch element and converts a DC input voltage to a target output voltage, and a control circuit therefor.

  In a power supply circuit that inputs an input DC voltage from an input DC power supply and outputs an output DC voltage serving as a power supply voltage for various electronic circuits, for example, when outputting an output DC voltage that is larger than the input DC voltage, a boost converter is used.

  As a general boost converter and its control circuit, a configuration as shown in FIG. 9 is known. The first conventional boost converter and its control circuit will be described below with reference to FIG. In FIG. 9, 1 is an input DC power source such as a battery, 2 is an inductor, 3 is a switching element made of a MOSFET, 4 is a rectifying means made of a diode, 5 is a smoothing means made of a capacitor, and 30 is a control circuit. The inductor 2 and the switch element 3 are connected in series, and this series circuit is connected in parallel with the input DC power supply 1. The rectifying means 4 is connected to the connection point between the inductor 2 and the switch element 3, the output of the rectifying means 4 is smoothed by the smoothing means 5, and the output DC voltage Vo is output. The inductor 2, the switching element 3, the rectifying means 4 and the smoothing means 5 constitute a boost converter. The control circuit 30 detects the output DC voltage, supplies a drive signal DR to the switch element 3, and performs on / off control thereof.

  The control circuit 30 includes an error amplification circuit 31, an oscillation circuit 32, and a comparator 33. The error amplifying circuit 31 detects the output DC voltage Vo and generates an error signal Ve obtained by amplifying an error from the target value. The error signal Ve decreases when the output DC voltage Vo is higher than the target value, and increases when the output DC voltage Vo is lower than the target value. The oscillation circuit 32 generates a triangular wave signal Vt that increases or decreases at a predetermined cycle. Let Et be the width of vibration of the triangular wave signal Vt. The comparator 33 compares the triangular wave signal Vt and the error signal Ve, and generates a drive signal DR that becomes H level when the error signal Ve is large.

  FIG. 10 is an operation waveform diagram of each part of the control circuit 30 and shows the triangular wave signal Vt, the error signal Ve, and the drive signal DR. The pulse width of the drive signal DR, that is, the ON time of the switch element increases as the error signal Ve increases.

  In FIG. 9, when the switch element 3 is on, the input DC voltage Vi is applied to the inductor 2, a current flows from the input DC power source 1 through the inductor 2 to the switch element 3, and energy is supplied to the inductor 2. Accumulated. Next, when the switch element 3 is off, a differential voltage (Vi−Vo) between the output DC voltage Vo and the input DC voltage Vi is applied to the inductor 2, and the rectifying means is supplied from the input DC power supply 1 through the inductor 2. The current flows to 4 and the energy stored in the inductor 2 is released. When the ratio (referred to as duty ratio) of the ON time (pulse width of the drive signal DR) to one switching period (period of the triangular wave signal Vt) of the switch element 3 is D, the output DC voltage Vo is Vo = Vi / (1 -D). The duty ratio D increases as the error signal Ve increases. That is, the duty ratio D is adjusted by the control circuit 30 so that the output DC voltage Vo becomes the target value.

For example, Patent Document 1 discloses a control circuit with improved versatility by using a clock signal instead of the triangular wave signal Vt of the control circuit 30 of the conventional boost converter as described above.
Hereinafter, as a second conventional example, a boost converter and its control circuit disclosed in Patent Document 1 will be described with reference to FIG. In FIG. 11, the configuration of the step-up converter including the input DC power source 1, the inductor 2, the switch element 3, the rectifying means 4, and the smoothing means 5 is the same as that of FIG. A control circuit 40 detects an output DC voltage, supplies a drive signal DR to the switch element 3, and performs on / off control thereof.

  The control circuit 40 includes an error amplification circuit 41, an oscillation circuit 42, a constant current source circuit 43, a capacitor 44, a comparator 45, a latch circuit 46, and a transistor 47. The error amplifying circuit 41 detects the output DC voltage Vo and generates an error signal Ve obtained by amplifying an error from the target value. The error signal Ve decreases when the output DC voltage Vo is higher than the target value, and increases when the output DC voltage Vo is lower than the target value. The oscillation circuit 42 generates a clock signal Vck having a predetermined cycle and sets the latch circuit 46. The constant current source circuit 43 outputs a constant current Io and charges the capacitor 44. The capacitance of the capacitor 44 is C4. The comparator 45 compares the error signal Ve with the charging voltage V4 of the capacitor 44. When the charging voltage of the capacitor 44 exceeds the error signal Ve, the comparator 45 outputs a high level and resets the latch circuit 46. The output Q of the latch circuit 46 is high when the latch circuit 46 is set, and generates a drive signal DR that is low when the latch circuit 46 is reset. The drive signal DR is input to the gate of the switch element 3, and the switch element 3 is turned on when it is at a high level, and is turned off when it is at a low level. On the other hand, the inverted output QB of the latch circuit 46 drives the transistor 47, and the capacitor 44 is short-circuited and discharged while the drive signal DR is at a low level, that is, when the switch element 3 is off.

FIG. 12 is an operation waveform diagram of each part of the control circuit 40, showing the clock signal Vck, the error signal Ve, the charging voltage V4 of the capacitor 44, the reset signal R to the latch circuit 46, and the drive signal DR. The pulse width of the drive signal DR, that is, the ON time of the switch element 3 increases as the error signal Ve increases.
Japanese Patent Laid-Open No. 5-76169

In the conventional boost converter configured as described above, the error signal Ve and the duty ratio D have a linear relationship, but the relationship between the duty ratio D and the output DC voltage Vo is Vo = Vi / (1-D). And is non-linear.
For example, in the case of the first conventional boost converter and its control circuit 30 shown in FIG. 9, if the triangular wave signal Vt increases or decreases from 0 to Et for simplification, the duty ratio D depends on the error signal Ve. D = Ve / Et. Therefore, the output DC voltage Vo is expressed by the following formula (1).

Vo = Vi / (1-D) = Vi · Et / (Et−Ve) (1)

That is, as the error signal Ve increases, the way of increasing the output DC voltage Vo (∂Vo / 誤差 Ve) increases.
On the other hand, in the case of the second conventional step-up converter and its control circuit 40, the ON time Ton of the switch element 3 is determined by using Ton = Ve · C4 using the error signal Ve, the capacitance C4 of the capacitor 44 and the constant current Io. / Io. When the period of the clock signal Vck, that is, the switching period is Ts, the duty ratio D is D = Ton / Ts, and therefore the output DC voltage Vo is expressed by the following equation (2).

Vo = Vi · Ts / (Ts−Ton)
= Vi · Ts / (Ts−Ve · C4 / Io) (2)

  Therefore, the point that (∂Vo / ∂Ve) increases as the error signal Ve increases is the same as in the first conventional example. This indicates that as the output DC voltage Vo becomes larger than the input DC voltage Vi, the output DC voltage Vo greatly fluctuates with respect to slight fluctuations in the error signal Ve, and there is a problem that the output DC voltage Vo tends to become unstable. .

  In the present invention, for example, in a DC-DC converter in which the relationship between the duty ratio D and the output DC voltage Vo is nonlinear, such as a boost converter, the relationship between the error signal Ve and the output DC voltage Vo is linear, and the feedback system is stabilized. It is an object of the present invention to provide a DC-DC converter and a control circuit for the same.

  In order to achieve the above object, a DC-DC converter according to a first aspect of the present invention includes a switching element that repeatedly turns on and off, stores energy from an input during an on period of the switching element, and an off period of the switching element. A DC-DC converter having an inductor for discharging energy to an output, an error amplification circuit for generating an error signal obtained by amplifying an error between the output and a target value, and a triangular wave signal having an amplitude corresponding to the error signal. An oscillation circuit to be generated, and a comparison circuit that compares a reference signal having a predetermined value with the triangular wave signal to generate a drive signal for turning on and off the switch element.

  A DC-DC converter according to a second aspect of the present invention is configured such that, in the DC-DC converter according to the first aspect, the oscillation circuit generates a triangular wave signal having an amplitude proportional to the magnitude of the error signal. Have.

  A DC-DC converter according to a third aspect of the present invention is the DC-DC converter according to the second aspect, wherein the oscillation circuit outputs a current proportional to the magnitude of the error signal; A clock signal generator that generates a clock signal having a frequency of: a discharge switch that is turned on and off according to the clock signal; a capacitor that is charged by the current source circuit and discharged by the discharge switch; It has a configuration that is a charge / discharge voltage waveform of the capacitor.

  According to a fourth aspect of the present invention, in the DC-DC converter according to the first aspect, the comparison circuit compares the reference signal having a magnitude corresponding to the input voltage with the triangular wave signal. Have

  A DC-DC converter according to a fifth aspect of the present invention is the DC-DC converter according to the first aspect, wherein the comparison circuit decreases from a level higher than the predetermined value toward the predetermined value over time from a level at the time of startup. The reference signal and the triangular wave signal are compared.

  A control circuit for a DC-DC converter according to a sixth aspect of the present invention includes a switch element that repeatedly turns on and off, stores energy from the input during the on period of the switch element, and releases energy to the output during the off period of the switch element. A control circuit for use in a DC-DC converter having an inductor that generates an error signal obtained by amplifying an error between an output and a target value; and an amplitude corresponding to the error signal. And an oscillation circuit that generates a triangular wave signal, and a comparison circuit that compares a reference signal having a predetermined value with the triangular wave signal to generate a drive signal for turning on and off the switch element.

  A control circuit for a DC-DC converter according to a seventh aspect of the present invention is the control circuit for a DC-DC converter according to the sixth aspect, wherein the oscillation circuit has a triangular wave having an amplitude proportional to the magnitude of the error signal. It has a configuration for generating a signal.

  A control circuit for a DC-DC converter according to an eighth aspect of the present invention is the control circuit for a DC-DC converter according to the seventh aspect, wherein the oscillation circuit outputs a current proportional to the magnitude of the error signal. A current source circuit; a clock signal generator that generates a clock signal having a predetermined frequency; a discharge switch that is turned on and off according to the clock signal; and a capacitor that is charged by the current source circuit and discharged by the discharge switch. The triangular wave signal is a charge / discharge voltage waveform of the capacitor.

  A control circuit for a DC-DC converter according to a ninth aspect of the present invention is the control circuit for a DC-DC converter according to the sixth aspect, wherein the comparison circuit includes a reference signal having a magnitude corresponding to an input voltage and the reference signal. It has a configuration for comparing triangular wave signals.

  A control circuit for a DC-DC converter according to a tenth aspect of the present invention is the control circuit for a DC-DC converter according to the sixth aspect, in which the comparison circuit is changed over time from a level greater than the predetermined value at startup. A reference signal that decreases toward a predetermined value is compared with the triangular wave signal.

  The DC-DC converter and the control circuit thereof according to the present invention include an error signal obtained by amplifying an error between the output DC voltage and the target value in a DC-DC converter in which the relationship between the duty ratio and the output DC voltage is nonlinear, such as a boost converter. In addition to the effect that the output DC voltage relationship can be made linear and the operation is stable even at a high duty ratio, the stabilization design of the feedback system is facilitated. In addition, the maximum duty ratio is set and the maximum duty ratio is determined by the input voltage. Correction and soft start setting are also easy.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a DC-DC converter and a control circuit thereof according to the invention will be described with reference to the accompanying drawings.

<< First Embodiment >>
FIG. 1 is a circuit diagram showing the configuration of a DC-DC converter and its control circuit according to the first embodiment of the present invention.
As shown in FIG. 1, an input DC power source 1 such as a battery is connected to one end of an inductor 2, one end of a switch element 3 formed of a MOSFET at the other end of the inductor 2, and rectification formed of a diode. One end of the means 4 is connected. The other end of the switch element 3 is grounded. The other end of the rectifying means 4 is connected to the other end of the smoothing means 5 composed of a capacitor whose one end is grounded. Further, the other end of the rectifying means 4 serves as an output end and is connected to the control circuit 10. As described above, the inductor 2 and the switch element 3 are connected in series, and this series circuit is connected in parallel with the input DC power supply 1. The rectifying means 4 is connected to the connection point between the inductor 2 and the switch element 3, the output of the rectifying means 4 is smoothed by the smoothing means 5, and the output DC voltage Vo is output. The inductor 2, the switching element 3, the rectifying means 4 and the smoothing means 5 constitute a boost converter. The control circuit 10 detects the output DC voltage, supplies the drive signal DR to the switch element 3, and performs on / off control thereof.

  In FIG. 1, a control circuit 10 includes an error amplifier circuit 11 that generates an error signal Ve obtained by amplifying an error between the output DC voltage Vo and a target value, and an oscillation circuit that generates a triangular wave signal Vt having the level of the error signal Ve as an amplitude. 12, a voltage source circuit 13 that generates a reference signal Vr, and a comparison circuit 14 that compares the triangular wave signal Vt with the reference signal Vr and outputs a drive signal DR that turns on and off the switch element 3.

  In FIG. 1, an oscillation circuit 12 includes a capacitor 120, a constant current source circuit 121 that charges the capacitor 120 with a constant current I1, and a constant current source circuit 122 that discharges the capacitor 120 with a constant current I2 (I2 <I1). A comparator 123 that compares the voltage of the capacitor 120 with the error signal Ve, a comparator 124 that compares the voltage of the capacitor 120 with the ground potential, and a latch circuit 125 to which the outputs of the comparator 123 and the comparator 124 are input. And a switch 126 for turning on and off the charging current of the capacitor 120 with the output of the latch circuit 125. As will be described later, the voltage of the capacitor 120 has a triangular wave shape and is output as a triangular wave signal Vt.

  The operation of the boost converter will be described below. When the switch element 3 is on, the input DC voltage Vi is applied to the inductor 2, current flows from the input DC power source 1 through the inductor 2 to the switch element 3, and energy is stored in the inductor 2. Next, when the switch element 3 is off, a differential voltage (Vi−Vo) between the input DC voltage Vi and the output DC voltage Vo is applied to the inductor 2, and the rectifying means is supplied from the input DC power supply 1 through the inductor 2. The current flows to 4 and the energy stored in the inductor 2 is released. When the ratio (referred to as duty ratio) of the ON time (pulse width of the drive signal DR) to one switching period (period of the triangular wave signal Vt) of the switch element 3 is D, the output DC voltage Vo is Vo = Vi / (1 -D). As will be described below with reference to FIGS. 1 and 2, the control circuit 10 detects the output DC voltage Vo and adjusts the duty ratio D so that the output DC voltage Vo becomes a target value.

  FIG. 2 is an operation waveform diagram of each part of the control circuit 10 and shows the error signal Ve, the triangular wave signal Vt, the reference signal Vr, and the drive signal DR. In FIG. 1, the error signal Ve generated by the error amplifying circuit 11 rises when the output DC voltage Vo is lower than the target value, and falls when the output DC voltage Vo is higher than the target value. The error signal Ve is compared with the triangular wave signal Vt which is the voltage of the capacitor 120 by the comparator 123. When the output Q of the latch circuit 125 is at a high level, the switch 126 is on, so that the capacitor 120 is charged with a constant current (I1-I2). When the voltage of the capacitor 120 (triangular wave signal Vt) rises and reaches the error signal Ve, the comparator 123 inverts the output to high level and resets the latch circuit 125. When the output Q of the latch circuit 125 becomes low level, the switch 126 is turned off, so that the capacitor 120 is discharged with the constant current I2. The voltage of the capacitor 120 (triangular wave signal Vt) is lower than the error signal Ve, and the output of the comparator 123 is at a low level. When the voltage of the capacitor 120 (triangular wave signal Vt) falls to the ground potential, the comparator 124 inverts the output to a high level and sets the latch circuit 125. When the output Q of the latch circuit 125 becomes high level, the switch 126 is turned on, so that the capacitor 120 is charged with a constant current (I1-I2). By repeating the above operation, the voltage of the capacitor 120 (triangular wave signal Vt) becomes a triangular wave signal that increases or decreases between the ground potential and the error signal Ve as shown in FIG. Assuming that the capacitance of the capacitor 120 is C1 and I1 = 2 × I2 for simplification, the period Ts of the triangular wave signal Vt is expressed by Ts = C1 · Ve / I1.

The triangular wave signal Vt is compared with the reference signal Vr by the comparison circuit 14. When the triangular wave signal Vt is higher than the reference signal Vr, the drive signal DR becomes high level. Since the pulse width of the drive signal DR, that is, the ON time Ton of the switch element 3 is Ton = Ts · (1−Vr / Ve), the duty ratio D is expressed by the following equation (3).

D = Ton / Ts = 1−Vr / Ve (3)

  That is, the duty ratio D increases as the error signal Ve increases as shown in FIG. On the other hand, the output DC voltage Vo is expressed by Vo = Vi / (1-D). For example, when the output DC voltage Vo is lower than the target value, the error signal Ve increases, and accordingly, the duty ratio D increases and the output DC voltage Vo is adjusted to the target value.

  In the control circuit of the DC-DC converter according to the first embodiment of the present invention, in the steady state where the output DC voltage Vo is stabilized, the relationship of the following formulas (4) and (5) is established.

Vo = Vi / (1-D) = Vi · Ve / Vr (4)
∂Vo / ∂Ve = Vi / Vr (5)

As described above, the relationship between the error signal Ve and the output DC voltage Vo is linear, and the rate of change (∂Vo / ∂Ve) of the output DC voltage Vo due to the error signal Ve does not depend on the level of the error signal Ve. The stabilization design of the system becomes easy.
Further, as shown in Expression (3), since the duty ratio D is determined from the error signal Ve and the reference signal Vr, the maximum duty ratio Dmax can be set by the maximum value of the error signal Ve and the reference signal Vr.

<< Second Embodiment >>
FIG. 3 is a circuit diagram showing the configuration of the DC-DC converter and its control circuit according to the second embodiment of the present invention. In FIG. 3, the same reference numerals are given to the same functions and configurations as those of the DC-DC converter and its control circuit according to the first embodiment shown in FIG. 1, and the description thereof is omitted. The difference from the configuration of the first embodiment in FIG. 1 is the configuration of the control circuit. In the second embodiment, the control circuit 20 is used to distinguish it from the configuration of FIG.

  In FIG. 3, the control circuit 20 generates an error signal Ve that amplifies an error between the output DC voltage Vo and a target value, and an oscillation circuit 22 that generates a triangular wave signal Vt having the amplitude of the error signal Ve. The voltage source circuit 23 that generates the reference signal Vr, and the comparison circuit 24 that compares the triangular wave signal Vt with the reference signal Vr and outputs the drive signal DR for turning on and off the switch element 3 are provided.

  In FIG. 3, the oscillation circuit 22 includes a capacitor 220, a current source circuit 221 that receives the error signal Ve and charges the capacitor 220 with a current Ie proportional to the error signal Ve, and a clock that outputs a clock signal Vck at a predetermined frequency. The circuit 222 includes a switch 223 that is driven by the clock signal Vck and discharges the voltage of the capacitor 220 to the ground potential. Further, it is assumed that the ON time Td during which the clock signal Vck is at a high level is set to be short enough to short-circuit the capacitor 220. As will be described later, the voltage of the capacitor 220 has a triangular wave shape and is output as a triangular wave signal Vt.

  The operation of the DC-DC converter of the second embodiment and its control circuit 20 will be described below with reference to FIGS. FIG. 4 is an operation waveform diagram of each part of the control circuit 20, and shows the clock signal Vck, the triangular wave signal Vt, the reference signal Vr, and the drive signal DR. In FIG. 3, the error signal Ve generated by the error amplifying circuit 21 increases when the output DC voltage Vo is lower than the target value, and decreases when the output DC voltage Vo is higher than the target value. The current source circuit 221 outputs a current Ie proportional to the error signal Ve to charge the capacitor 220. When the clock signal Vck is at a high level, the switch 223 is in an on state, and the voltage Vt of the capacitor 220 is short-circuited to the ground potential. Since the voltage Vt of the capacitor 220 is lower than the reference signal Vr, the output of the comparison circuit 24, that is, the drive signal DR is at a low level. When the clock signal Vck becomes low level, the switch 223 is turned off, so that the capacitor 220 is charged with the current Ie. When the voltage of the capacitor 220 (triangular wave signal Vt) increases and reaches the reference signal Vr, the comparison circuit 24 inverts the drive signal DR to a high level and turns on the switch element 3. Charging of the capacitor 220 continues until the clock signal Vck becomes high level. When the clock signal Vck becomes a high level, the switch 223 is turned on to short-circuit and discharge the voltage Vt of the capacitor 220 to the ground potential. The voltage Vt of the capacitor 220 becomes lower than the reference signal Vr, and the comparison circuit 24 inverts the drive signal DR to a low level and turns off the switch element 3. By repeating the above operation, the voltage waveform of the capacitor 220 becomes a triangular wave signal Vt that increases or decreases between the ground potential and the peak voltage Vp as shown in FIG.

  Assume that the cycle of the clock signal Vck is Ts, the on-time Td of the clock signal Vck is negligible compared to the cycle Ts, the capacitance of the capacitor 220 is C2, and the resistance value of the current source circuit 221 is Re. When Ie = Ve / Re, the peak voltage Vp of the triangular wave signal Vt is expressed by the following equation (6).

Vp = (Ts−Td) · Ie / C2
≒ Ts ・ Ve / (C2 ・ Re) (6)

  The triangular wave signal Vt is compared with the reference signal Vr by the comparison circuit 24. When the triangular wave signal Vt is higher than the reference signal Vr, the drive signal DR becomes high level. The pulse width of the drive signal DR, that is, the ON time Ton of the switch element 3 is expressed by the following equation (7).

Ton = (Ts−Td) · (1−Vr / Vp)
≒ Ts-Vr ・ C2 ・ Re / Ve (7)

  Therefore, the duty ratio D is expressed by the following equation (8).

D = Ton / Ts
= 1− (C2 · Re / Ts) · (Vr / Ve) (8)

  That is, the duty ratio D increases as the peak voltage Vp increases in proportion to the error signal Ve, as shown in FIG. On the other hand, the output DC voltage Vo is expressed by Vo = Vi / (1-D). For example, when the output DC voltage Vo is lower than the target value, the error signal Ve increases, and accordingly, the duty ratio D increases and the output DC voltage Vo is adjusted to the target value.

  In the control circuit in the DC-DC converter according to the second embodiment of the present invention, in the steady state where the output DC voltage Vo is stabilized, the relationship of the following formulas (9) and (10) is established.

Vo = Vi / (1-D)
= Vi · Ve · Ts / (Vr · C2 · Re) (9)
∂Vo / ∂Ve = Vi · Ts / (Vr · C2 · Re) (10)

As described above, the relationship between the error signal Ve and the output DC voltage Vo is linear, and the rate of change (∂Vo / ∂Ve) of the output DC voltage Vo due to the error signal Ve does not depend on the level of the error signal Ve. The stabilization design of the system becomes easy. It has been shown that the control circuit of the DC-DC converter of the second embodiment can be configured to switch in synchronization with the clock signal Vck.
In this embodiment, for simplicity of explanation, the clock signal Vck has a narrow pulse width that can be ignored with respect to the switching period. However, the clock signal Vck is limited to such a shape. It is not a thing. For example, when the DC-DC converter according to the second embodiment is desired to operate in synchronization with a clock signal having a predetermined pulse width, the capacitor 220 is connected to the ground potential in synchronization with the rising edge of the clock signal. Short-circuit discharge.

  Further, as shown in Expression (8), since the duty ratio D is determined from the error signal Ve and the reference signal Vr, the maximum duty ratio Dmax can be set by the maximum value of the error signal Ve and the reference signal Vr.

<< Third Embodiment >>
FIG. 5 is a circuit diagram showing the configuration of a DC-DC converter and its control circuit according to a third embodiment of the present invention. In FIG. 5, the same functions and configurations as those of the DC-DC converter and its control circuit according to the second embodiment shown in FIG. The difference from the configuration of the second embodiment in FIG. 3 is the configuration of the control circuit. In order to distinguish it from the configuration in FIG. 3, the control circuit 20A is used in the third embodiment.

  In the control circuit 20A shown in FIG. 5, the error amplifier circuit 21, the oscillation circuit 22, and the comparison circuit 24 have the same configuration as the control circuit 20 shown in FIG. The difference is that a voltage source circuit 23A including a series circuit of a resistor 230 and a resistor 231 is used instead of the voltage source circuit 23 that generates the reference signal Vr shown in FIG. The voltage source circuit 23A compares the input DC voltage Vi by resistance division with the triangular wave signal Vt in the comparison circuit 24 as the reference signal Vr. Assuming that the resistance division ratio by the resistors 230 and 231 is α, the relationship between the reference signal Vr and the input DC voltage Vi is expressed by the following equation (11).

  Vr = α · Vi (11)

  In the DC-DC converter according to the third embodiment, except for the relationship represented by the equation (11), the operation of the boost converter and the control circuit is the same as the operation of the DC-DC converter according to the second embodiment and the control circuit thereof. The same. Substituting equation (11) into equations (8) through (10) yields the following relational equations (12) through (14).

D = 1− (C2 · Re / Ts) · (α · Vi / Ve) (12)
Vo = Vi / (1-D)
= Ve · Ts / (α · C2 · Re) (13)
∂Vo / ∂Ve = Ts / (α · C2 · Re) (14)

  As described above, the relationship between the error signal Ve and the output DC voltage Vo is linear, and the rate of change of the output DC voltage Vo due to the error signal Ve (電 圧 Vo / ∂Ve) does not depend on the level of the error signal Ve. In addition, it does not depend on the input DC voltage Vi. As a result, the error signal Ve hardly fluctuates in a normal stabilization operation. The error amplifying circuit 21 that generates the error signal Ve has a narrow output dynamic range, so that the design can be facilitated.

  Further, as shown in Expression (12), since the duty ratio D is determined from the error signal Ve and the input DC voltage Vi, the maximum duty ratio Dmax can be set by the maximum value of the error signal Ve and the input DC voltage Vi. That is, the higher the input DC voltage Vi, the smaller the maximum duty ratio Dmax. The magnetic energy stored in the inductor 2 is proportional to the product of the applied voltage and the applied time. This voltage time product is maximized during a transition such as when the maximum input is applied, and is Vimax × Dmax × Ts. If the maximum duty ratio Dmax is constant, this value is unnecessarily large as compared with the normal operation, which causes the shape of the inductor 2 to increase. By setting the maximum duty ratio Dmax to be smaller as the input DC voltage Vi is higher as described above, the upper limit of the magnetic energy stored in the inductor 2 can be suppressed, and the inductor 2 can be downsized. To do.

<< Fourth Embodiment >>
FIG. 6 is a circuit diagram showing the configuration of a DC-DC converter and its control circuit according to the fourth embodiment of the present invention. In FIG. 6, the same functions and configurations as those of the DC-DC converter and its control circuit according to the third embodiment shown in FIG. The difference from the third embodiment of FIG. 5 is the configuration of the control circuit. In order to distinguish it from the configuration of FIG. 5, the control circuit 20B is used in the fourth embodiment.

  In the control circuit 20B shown in FIG. 6, the error amplification circuit 21, the oscillation circuit 22, and the comparison circuit 24 have the same configuration as the control circuit 20 shown in FIG. A difference is that a voltage source circuit 23B including a series circuit of a resistor 230 and a resistor 231 and a capacitor 232 connected in parallel with the resistor 230 is used instead of the voltage source circuit 23A of FIG. . By this voltage source circuit 23B, the voltage obtained by resistance-dividing the input DC voltage Vi is compared with the triangular wave signal Vt in the comparison circuit 24 as the reference signal Vr. In normal operation, if the resistance division ratio of the resistor 230 and the resistor 231 is α, Vr = α · Vi, Vo = Ve · Ts / (α · C2 · Re), ∂Vo / ∂Ve = Ts / The relational expression (α · C2 · Re) is obtained, and the relationship between the error signal Ve and the output DC voltage Vo is linear. The rate of change of the output DC voltage Vo due to the error signal Ve (∂Vo / ∂Ve) does not depend on the level of the error signal Ve, as in the boost converter according to the third embodiment shown in FIG.

The DC-DC converter and its control circuit according to the fourth embodiment of the present invention operate differently from the DC-DC converter according to the third embodiment and its control circuit shown in FIG. , At startup. FIG. 7 is an operation waveform diagram of each part of the control circuit 20B at the time of activation, and shows the clock signal Vck, the triangular wave signal Vt, the reference signal Vr, and the drive signal DR. Assuming that the capacitor 232 has no charge at the time of startup, immediately after the input DC voltage Vi is input, the potential of the resistor 231, that is, the level of the reference signal Vr is large and is close to the input voltage. For this reason, the pulse width of the drive signal DR, which is a comparison result with the triangular wave signal Vt, is reduced. As time passes, the capacitor 232 is charged, and the level of the reference signal Vr gradually decreases. For this reason, the pulse width of the drive signal DR gradually increases.
As described above, the DC-DC converter and its control circuit according to the fourth embodiment of the present invention also have an effect that soft start can be easily set.

<< Fifth Embodiment >>
In the first to fourth embodiments described above, the boost converter is used as the DC-DC converter. However, the present invention is not limited to the boost converter. FIG. 8 is a circuit configuration diagram of a DC-DC converter and its control circuit according to the fifth embodiment of the present invention. In FIG. 8, reference numeral 1 denotes an input DC power supply, which is constituted by a circuit such as a battery or rectifying and smoothing a commercial AC voltage, and outputs an input DC voltage Vi. Reference numeral 6 denotes a transformer having a primary winding 61 connected to the input DC power source 1 and a secondary winding 62. A turns ratio of the number of turns N1 of the primary winding 61 of the transformer 6 and the number of turns N2 of the secondary winding 62 is n (= N2 / N1). Reference numeral 7 denotes a switching element formed of a MOSFET, which is connected to the primary winding 61 and applies an input DC voltage to the primary winding 61 when turned on. Reference numeral 8 is a rectifying means constituted by a diode, and reference numeral 9 is a smoothing means constituted by a capacitor. The rectifying means 8 and the smoothing means 9 are connected to the secondary winding 62 and a voltage generated in the secondary winding 62. Is rectified and smoothed to output an output DC voltage Vo. The transformer 6, the switch element 7, the rectifying means 8, and the smoothing means 9 constitute a flyback converter. Reference numeral 100 denotes a control circuit that detects the output DC voltage Vo, supplies a drive signal DR to the switch element 7, and performs on / off control thereof.

  In FIG. 8, a control circuit 100 includes an error amplifier circuit 101 that generates an error signal Ve obtained by amplifying an error between the output DC voltage Vo and a target value, and an oscillation circuit 102 that generates a triangular wave signal Vt having an amplitude of the error signal Ve. The voltage source circuit 103 that generates the reference signal Vr, and the comparison circuit 104 that compares the triangular wave signal Vt with the reference signal Vr and outputs the drive signal DR for turning on and off the switch element 7 are included. The error amplifier circuit 101 outputs an error amplifier 111 for comparing and amplifying the output DC voltage Vo and the target value, a photodiode 112 connected to the output of the error amplifier 111, and a current corresponding to the amount of light emitted from the photodiode 112. And a resistor 114 that converts the current of the phototransistor 113 into an error signal Ve. When the output DC voltage Vo is to be larger than the target value, the error amplifier 111 increases the current flowing through the photodiode 112 and increases the light emission amount of the photodiode 112. As a result, the current of the phototransistor 113 also increases and the error signal Ve increases. Further, the oscillation circuit 102 illustrated in FIG. 8 has the same configuration as the oscillation circuit 12 illustrated in FIG.

  The operation of the flyback converter will be described below. When the switch element 7 is on, the input DC voltage Vi is applied to the primary winding 61 of the transformer 6, and current flows from the input DC power source 1 to the primary winding 61 and the switch element 7, and energy is transferred to the transformer 6. Is accumulated. When the switch element 7 is turned off, the voltages of the primary winding 61 and the secondary winding 62 of the transformer 6 are inverted, and a current flows from the secondary winding 62 to the output through the rectifier 8 and is stored in the transformer 6. The released energy is released. Assuming that the ratio (referred to as duty ratio) of the on-time (pulse width of the drive signal DR) to one switching period (period of the triangular wave signal Vt) of the switch element 7 is D, the output DC voltage Vo is Vo = Vi · n · It is represented by D / (1-D). The control circuit 100 detects the output DC voltage Vo and adjusts the duty ratio D so that the output DC voltage Vo becomes a target value.

  The error signal Ve generated by the error amplifier circuit 101 increases when the output DC voltage Vo is lower than the target value, and decreases when the output DC voltage Vo is higher than the target value. The error signal Ve is compared with the voltage of the capacitor 120 (triangular wave signal Vt) by the comparator 123. When the output Q of the latch circuit 125 is at a high level, the switch 126 is on, so that the capacitor 120 is charged with a constant current (I1-I2). When the voltage of the capacitor 120 (triangular wave signal Vt) rises and reaches the error signal Ve, the comparator 123 inverts the output to high level and resets the latch circuit 125. When the output Q of the latch circuit 125 becomes low level, the switch 126 is turned off, so that the capacitor 120 is discharged with the constant current I2. The voltage of the capacitor 120 (triangular wave signal Vt) is lower than the error signal Ve, and the output of the comparator 123 is at a low level. When the voltage of the capacitor 120 (triangular wave signal Vt) falls to the ground potential, the comparator 124 inverts the output to a high level and sets the latch circuit 125. When the output Q of the latch circuit 125 becomes high level, the switch 126 is turned on, so that the capacitor 120 is charged with a constant current (I1-I2). By repeating the above operation, the voltage of the capacitor 120 (triangular wave signal Vt) becomes a triangular wave signal that increases or decreases between the error signal Ve from the ground potential. Assuming that the capacitance of the capacitor 120 is C1 and I1 = 2 × I2 for simplification, the period Ts of the triangular wave signal Vt is expressed by Ts = C1 · Ve / I1.

The triangular wave signal Vt is compared with the reference signal Vr by the comparison circuit 104. When the triangular wave signal Vt is higher than the reference signal Vr, the drive signal DR becomes high level. Since the pulse width of the drive signal DR, that is, the ON time Ton of the switch element 3 is Ton = Ts · (1−Vr / Ve), the duty ratio D is D = Ton / Ts = 1−Vr / Ve, And increases as the error signal Ve increases. On the other hand, the output DC voltage Vo is expressed by Vo = Vi · n · D / (1-D). For example, when the output DC voltage Vo is lower than the target value, the error signal Ve increases, and accordingly, the duty ratio D is increased, and the output DC voltage Vo is adjusted to the target value.
In the steady state where the output DC voltage Vo is stabilized, the relationship of the following formulas (15) and (16) is established.

Vo = Vi · n · D / (1-D)
= N · Vi · (Ve−Vr) / Vr (15)
∂Vo / ∂Ve = n · Vi / Vr (16)

  As described above, the present invention can be applied not only to a boost converter but also to a flyback converter using a transformer. The relationship between the error signal Ve and the output DC voltage Vo is linear, and the rate of change (∂Vo / ∂ Ve) does not depend on the level of the error signal Ve. In the present invention, the maximum duty ratio Dmax can be set by the maximum value of the error signal Ve and the reference signal Vr. In the fifth embodiment, the control circuit for the DC-DC converter according to the first embodiment of the present invention is applied to an insulating flyback converter. However, the second to fourth embodiments have been described. The control circuit of the DC-DC converter can be similarly applied to an insulating flyback converter, and has the same effect. In addition to the flyback converter, the DC-DC converter and its control circuit of the present invention can be applied to a buck-boost converter including an inverting converter and a SEPIC (Single-Ended Primary Inductance Converter). It is possible and has the same effect.

  In each of the above-described embodiments, a device constituted by a DC-DC converter that outputs a DC output voltage with respect to a DC input voltage and its control circuit has been described. In the configuration, the DC-DC converter may include a control circuit.

  The present invention is useful for a DC-DC converter that outputs a DC output voltage with respect to a DC input voltage and a control circuit thereof.

1 is a circuit diagram showing a configuration of a DC-DC converter and a control circuit thereof according to a first embodiment of the present invention. Operation waveform diagram of each part of the control circuit in the DC-DC converter according to the first embodiment of the present invention The circuit diagram which shows the structure of the DC-DC converter of 2nd Embodiment which concerns on this invention, and its control circuit. Operation waveform diagram of each part of the control circuit in the DC-DC converter of the second embodiment according to the present invention The circuit diagram which shows the structure of the DC-DC converter of 3rd Embodiment which concerns on this invention, and its control circuit. The circuit diagram which shows the structure of the DC-DC converter of 4th Embodiment concerning this invention, and its control circuit Operation waveform diagram of each part of the control circuit in the DC-DC converter of the fourth embodiment according to the present invention The circuit diagram which shows the structure of the DC-DC converter of the 5th Embodiment concerning this invention, and its control circuit Circuit diagram showing the configuration of a conventional boost converter and its control circuit Operation waveform diagram of each part of the control circuit of the conventional boost converter shown in FIG. Circuit diagram showing the configuration of a conventional boost converter and its control circuit Operation waveform diagram of each part of the control circuit of the conventional boost converter shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Input DC power supply 2 Inductor 3 Switch element 4 Rectification means 5 Smoothing means 10 Control circuit 11 Error amplification circuit 12 Oscillation circuit 13 Voltage source circuit 120 Capacitor 121 Constant current source circuit 122 Constant current source circuit 123 Comparator 124 Comparator 125 Latch circuit 126 switch

Claims (10)

A DC-DC converter having a switch element that repeatedly turns on and off, and an inductor that stores energy from an input during an on period of the switch element and releases energy to an output during an off period of the switch element,
An error amplification circuit for generating an error signal obtained by amplifying an error between the output and the target value;
An oscillation circuit for generating a triangular wave signal having an amplitude corresponding to the error signal;
A comparison circuit that compares a reference signal having a predetermined value with the triangular wave signal to generate a drive signal for turning on and off the switch element;
A DC-DC converter.   2. The DC-DC converter according to claim 1, wherein the oscillation circuit generates a triangular wave signal having an amplitude proportional to the magnitude of the error signal. The oscillation circuit is
A current source circuit that outputs a current proportional to the magnitude of the error signal;
A clock signal generator for generating a clock signal having a predetermined frequency;
A discharge switch that turns on and off according to the clock signal;
A capacitor charged by the current source circuit and discharged by the discharge switch;
3. The DC-DC converter according to claim 2, wherein the triangular wave signal is a charge / discharge voltage waveform of the capacitor.   2. The DC-DC converter according to claim 1, wherein the comparison circuit compares a reference signal having a magnitude corresponding to an input voltage with the triangular wave signal.   2. The DC-DC converter according to claim 1, wherein the comparison circuit compares the triangular wave signal with a reference signal that gradually decreases from a level greater than the predetermined value toward the predetermined value at the time of activation. A control circuit used for a DC-DC converter having a switching element that repeatedly turns on and off, and an inductor that stores energy from an input during an on period of the switching element and releases energy to an output during an off period of the switching element. ,
An error amplification circuit for generating an error signal obtained by amplifying an error between the output and the target value;
An oscillation circuit for generating a triangular wave signal having an amplitude corresponding to the error signal;
A comparison circuit that compares a reference signal having a predetermined value with the triangular wave signal to generate a drive signal for turning on and off the switch element;
A control circuit for a DC-DC converter.   7. The control circuit for a DC-DC converter according to claim 6, wherein the oscillation circuit generates a triangular wave signal having an amplitude proportional to the magnitude of the error signal. The oscillation circuit is
A current source circuit that outputs a current proportional to the magnitude of the error signal;
A clock signal generator for generating a clock signal having a predetermined frequency;
A discharge switch that turns on and off according to the clock signal;
A capacitor charged by the current source circuit and discharged by the discharge switch;
8. The DC-DC converter control circuit according to claim 7, wherein the triangular wave signal is a charge / discharge voltage waveform of the capacitor.   7. The control circuit for a DC-DC converter according to claim 6, wherein the comparison circuit compares the triangular signal with a reference signal having a magnitude corresponding to an input voltage.   7. The control of the DC-DC converter according to claim 6, wherein the comparison circuit compares the triangular wave signal with a reference signal that gradually decreases from a level greater than the predetermined value toward the predetermined value at startup. circuit.

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