JP2012016241A - Dc-dc converter and electronic apparatus using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a DC-DC converter capable of realizing the stable operation, low ripple voltage characteristics, and high-speed response characteristics at the time of a sudden load change and to achieve high electric power conversion efficiency.SOLUTION: A DC-DC converter includes: a comparator 16 that compares a reference voltage Vref with a voltage Vfb2 obtained by adding an AC voltage component Vsensel changing at the same phase depending on an AC current component of a coil current IL to a feedback voltage Vfb1 proportional to an output DC voltage Vout; a driver driving circuit 15 that on-off controls alternately an output transistor FET1 and a rectification transistor FET2 on the basis of an output signal of a comparison result of the comparator 16; and a current sense circuit (output transistor current sense circuit 17 and rectification transistor current sense circuit 18) that generates a voltage Vsensel including the AC voltage component changing at the same phase depending on the AC current component of the coil current IL by using a current proportional to a current flowed by the output transistor FET1 and the rectification transistor FET2.

Description

  The present invention relates to a technology of a DC-DC converter (DC-DC regulator, switching regulator) that converts an input DC voltage into a stable output DC voltage, and more particularly, stable operation, low ripple voltage characteristics, and load in the DC-DC converter. The present invention relates to a technique that enables a high-speed response characteristic at the time of sudden change and is suitable for achieving high power conversion efficiency.

  A DC-DC converter that converts an input DC voltage into a stable output DC voltage is widely used in electronic devices such as computer devices and car navigation devices. Examples of the DC-DC converter include Patent Documents 1-5. As described above, there is a DC-DC converter having a configuration in which an output transistor and a rectifying element (rectifying transistor) are alternately turned on and off according to a comparison result between a feedback voltage proportional to the output DC voltage and a reference voltage.

  FIG. 1 shows a voltage-controlled DC-DC converter circuit having such a configuration. In the example of FIG. 1, the output transistor FET1, the rectifying transistor FET2, the coil L, and the output capacitor COUT are shown, and the configuration of the step-down converter is shown.

  Switching (on / off) is controlled by the synchronous rectification method by the output transistor FET1 and the rectifying transistor FET2 connected between the input terminal VIN and the ground potential.

  When the current flowing through the coil L is continuous, an output voltage Vout substantially proportional to the duty ratio of the output transistor FET1 (ratio of on-time to switching period) is obtained.

  The resistors R1 to R3, the capacitors C1 and C2, the reference voltage generator 11 and the error amplifier 13 constitute an error amplification circuit, the feedback voltage Vfb obtained by dividing the output voltage Vout by the resistors R1 and R3, and the reference voltage generator 11 The error amplifier 13 amplifies an error with respect to the reference voltage Vref.

  The PWM comparator 14 compares the error signal voltage Verr amplified by the error amplifier circuit with the triangular wave signal voltage Vramp from the triangular wave generator 12, and generates a PWM signal for controlling the duty based on the comparison result.

  In response to the PWM signal, the driver drive circuit 15 alternately controls the output transistor FET1 and the rectifying transistor FET2 on and off.

  As a result, the error signal voltage Verr output from the error amplifier 13 increases the duty ratio of the output transistor FET1 when the feedback voltage Vfb is smaller than the reference voltage Vref. The output voltage Vout is controlled by controlling the duty ratio to decrease.

  In such a voltage-controlled DC-DC converter circuit, phase compensation is indispensable for stabilizing the voltage-controlled DC-DC converter circuit, which is a negative feedback circuit, because of a phase delay caused by the coil L and the output capacitor COUT. Become.

  In general phase compensation, the phase delay caused by the coil L and the output capacitor COUT is caused by connecting the capacitor C1 between the output terminal VOUT and the node N1 to which the feedback voltage Vfb is generated and the resistors R1 and R3 are connected. The amplifier 13 is configured as a transconductance amplifier, and a resistor R2 and a capacitor C2 are connected in series between the output node N2 and the ground potential to set the loop gain at a high frequency low.

  However, when sufficient stability is obtained by such a phase compensation technique, the loop gain in the high frequency range of the error amplifier is set low, which causes a problem that high-speed response becomes difficult.

  In addition, when only the above-described phase compensation is used, if the fluctuation ranges of the input voltage Vin, the output voltage Vout, and the load ROUT of the DC-DC converter are set wide, there is a problem that sufficient stability and responsiveness cannot be obtained. There is also.

  As a circuit for overcoming the drawbacks of such a voltage control type DC-DC converter circuit, a comparator control type DC-DC converter circuit as shown in FIG. 2 is known.

  This comparator control method is also called a ripple control method, a bang-bang control method, a hysteresis control method, a D-Cap mode control method, or the like.

  In the example of FIG. 2, the output transistor FET1, the rectifying transistor FET2, the coil L, and the output capacitor COUT are configured as a step-down converter, and the output transistor FET1 and the rectifying transistor FET2 connected between the input terminal VIN and the ground potential. Thus, the switching control is performed by the synchronous rectification method.

  The resistors R1 and R3, the capacitor C1, the reference voltage generator 11 and the comparator 16 constitute a comparison circuit. The feedback voltage Vfb obtained by dividing the output voltage Vout by the resistors R1 and R3 and the reference voltage Vref from the reference voltage generator 11 are used. Comparison is made by the comparator 16.

  When the output voltage Vout decreases and the feedback voltage Vfb becomes lower than the reference voltage Vref, the comparator 16 outputs a high level signal, and the driver driving circuit turns on the output transistor FET1 and turns off the rectifying transistor FET2.

  As a result, a current is supplied from the input terminal VIN to the load via the coil L, and the output voltage Vout increases. When the output voltage Vout rises and the feedback voltage Vfb becomes higher than the reference voltage Vref, the comparator 16 outputs a low level signal, and the driver drive circuit turns off the output transistor FET1 and turns on the rectifier transistor FET2.

  The energy stored in the coil L is supplied to the load via the rectifying transistor FET2, but the current flowing through the coil L gradually decreases as the energy is released, and the output voltage Vout of the DC-DC converter also gradually increases. Go down.

  Thereafter, when the output voltage Vout decreases and the feedback voltage Vfb falls below the reference voltage Vref, the comparator 16 outputs a high level signal again, and the driver drive circuit turns on the output transistor FET1 and turns on the rectifier transistor FET2. The operation of turning off is repeated.

  When the output transistor FET1 is turned on and the rectifying transistor FET2 is turned off, a voltage of (Vin−Vout) is applied to the coil L, so that the current flowing through the coil L increases linearly.

  Further, when the output transistor FET1 is turned off and the rectifying transistor FET2 is turned on, a voltage of Vout having a polarity opposite to that described above is applied to the coil L, so that the current flowing through the coil L decreases linearly.

  That is, the current flowing through the coil L includes a triangular wave AC current component.

  When this triangular wave AC current component flows into the equivalent series resistance ESR of the output capacitor COUT, an AC voltage component similar to the AC current component is generated in the output voltage Vout, and the output voltage Vout is divided by the feedback resistors R1 and R3. An AC voltage component is also generated in the feedback voltage Vfb obtained in this way.

  In the comparator control method, the negative feedback control is performed so that the feedback voltage Vfb on which the AC voltage component that fluctuates according to the AC current component of the current flowing through the coil L is superimposed and the reference voltage Vref are compared and the two voltages are equal. The output voltage Vout is controlled.

  As described above, in the comparator control system, the comparator 16 directly compares the feedback voltage Vfb and the reference voltage Vref and immediately controls on / off of the output transistor FET1 and the rectifier transistor FET2. Is no longer necessary, and a high-speed response is possible.

  However, even in such a comparator control type DC-DC converter circuit, there arises a problem that switching control becomes unstable if a phase delay is caused by the coil L and the output capacitor COUT.

  In particular, as the equivalent series resistance ESR of the output capacitor COUT decreases, the above-described phase delay increases and the AC voltage component of the output voltage Vout also decreases, so that an appropriate amount of AC voltage component is superimposed on the feedback voltage Vfb. The switching control becomes unstable such that subharmonic oscillation occurs even in a steady state.

  Therefore, the capacitor C1 is connected between the node N1 to which the resistors R1 and R3 that generate the output terminal VOUT and the feedback voltage Vfb are connected, the phase delayed by the coil L and the output capacitor COUT is returned, and the feedback voltage Vfb is restored. A technique for increasing the superimposed AC voltage component is conceivable.

  However, if this is still insufficient, it is necessary to increase the AC voltage component itself generated in the output voltage Vout.

  As described above, as a technique for increasing the AC voltage component of the output voltage Vout, it is conceivable to increase the equivalent series resistance ESR of the output capacitor COUT. However, increasing the AC voltage component of the output voltage Vout This is not desirable because the so-called ripple voltage of the voltage Vout increases and the power conversion efficiency of the DC-DC converter decreases.

  In Patent Document 4, by inserting a sense resistor between the coil and the output terminal, an AC voltage similar to the AC current component of the current flowing in the coil is output to the node between the coil and the inserted sense resistor. There has been proposed a comparator-controlled DC-DC converter circuit that generates a voltage in which components are added and adds only the AC voltage component to a feedback voltage.

  With this DC-DC converter circuit, even when a capacitor with a small equivalent series resistance ESR is used as the output capacitor COUT, it is possible to stabilize the switching control of the DC-DC converter circuit and achieve a high-speed response. It has become.

  Patent Document 4 proposes a circuit in which a resistor and a capacitor are connected in series in parallel with a coil without using a sense resistor. This proposed DC-DC converter circuit also stabilizes the switching control of the DC-DC converter circuit even when a capacitor with a small equivalent series resistance ESR is used as the output capacitor COUT under certain conditions, It is possible to respond.

  However, the two DC-DC converter circuits proposed in Patent Document 4 have the following problems.

  First, in the case of a circuit in which a sense resistor is inserted between the coil and the output terminal, inserting the sense resistor is equivalent to reducing the quality factor Q of the coil, and the power conversion efficiency of the DC-DC converter. There is a problem that decreases.

  Next, in the case of a circuit in which a resistor and a capacitor are connected in series in parallel with the coil, there is no problem that the power conversion efficiency is reduced as described above, but the condition for correctly detecting the coil current is the coil inductance. And the DC resistance component, the resistance value of the resistor, and the capacitance value of the capacitor, the coil current cannot be detected correctly for an arbitrary coil.

  In addition, if the resistance value of the resistor and the capacitance value of the capacitor are small, the RC time constant becomes small, and the amplitude of the detected AC voltage component becomes too large. Therefore, the amplitude of the AC voltage component added to the feedback voltage is also large. There is a problem that the actual output voltage DC level becomes too large, and the deviation from the original output voltage DC level, which is determined by the reference voltage, becomes large.

  In order to solve such a problem, the RC time constant may be increased by increasing the resistance value and the capacitance value. However, in consideration of the switching frequency, a resistor having a large resistance value or a capacitor having a large capacitance value is used as a semiconductor. It may be difficult to form on a chip.

  In such a case, it is necessary to externally attach resistors and capacitors with discrete components. As a result, problems such as an increase in board area and an increase in component mounting costs arise, which is not desirable.

  Problems to be solved are as follows: (a) The technology for stabilizing the operation of the conventional voltage control type DC-DC converter by phase compensation makes it difficult to respond at high speed, and the input voltage, the output voltage, and the load resistance When the fluctuation range is set wide, sufficient stability and responsiveness cannot be obtained. (B) Even in the conventional comparator control type DC-DC converter, when the phase delay is caused by the coil and the output capacitor, the switching control is performed. It becomes unstable, especially when the series equivalent resistance of the output capacitor is small, low-frequency oscillation occurs even in the steady state, and switching control becomes unstable, and it occurs in the output voltage to cope with this If the AC voltage component is increased, the rip voltage of the output voltage will increase, making it impossible to maintain the low ripple voltage characteristics and reducing the power conversion efficiency. (C) In order to cope with this, in the technique (Patent Document 4) in which a sense resistor is inserted between the coil and the output terminal, the quality factor of the coil is reduced and the power conversion efficiency is reduced. (D) In the technique in which a resistor and a capacitor are connected in series in parallel with the coil in order not to reduce the power conversion efficiency, the coil current cannot be correctly detected for an arbitrary coil and the DC level shift of the output voltage is not possible. (E) If the resistance value and the capacitance value are increased in order to solve this problem, it becomes difficult to form on the semiconductor chip, and if it is externally attached, the substrate area increases. And an increase in component mounting costs.

  An object of the present invention is to solve these problems of the prior art, to enable stable operation, low ripple voltage characteristics, and high-speed response characteristics at the time of sudden load change in a DC-DC converter, and to achieve high power conversion efficiency. It is possible.

  In order to achieve the above object, as shown in FIG. 3, the DC-DC converter of the present invention is (1) a DC-DC converter that converts an input DC voltage into a stable output DC voltage, and an output DC voltage Vout. A comparator (comparison circuit) 16 that compares a reference voltage Vref with a voltage Vfb2 obtained by adding an AC voltage component Vsensel that varies in phase according to the AC current component of the coil current IL to a feedback voltage Vfb1 proportional to The driver drive circuit 15 that alternately controls the output transistor FET1 and the rectifier element (rectifier transistor FET2) on and off based on the output signal that is the result of the comparison, and an AC that varies in phase according to the AC current component of the coil current IL The voltage Vsensel including the voltage component is output from the output transistor FET1 and the rectifier element (rectifier transistor). The current sense circuit (output transistor current sense circuit 17 which generates with a current proportional to the current static FET2) shed, characterized in that a rectification transistor current sensing circuit 18). (2) The current sense circuit generates a voltage including an AC voltage component that varies in phase according to the AC current component of the coil current IL, using a current proportional to the current that the output transistor FET1 flows. An AC voltage component that varies in phase according to the AC current component of the coil current is included using a current proportional to the current flowing through the voltage generation circuit (output transistor current sense circuit 17) and the rectifier element (rectifier transistor FET2). Of the voltages generated by the second voltage generation circuit (rectifier transistor current sense circuit 18) for generating a voltage and the first and second voltage generation circuits (output transistor current sense circuit 17, rectifier transistor current sense circuit 18) , A low-pass filter circuit (LPF19) that extracts only a voltage component that varies according to the AC current component of the coil current IL. The a, a voltage component extracted by a low pass filter circuit (LPF 19), characterized in that it added to the feedback voltage Vfb1 proportional to the output DC voltage Vout. (3) The current sense circuit (output transistor current sense circuit 17 and rectifier transistor current sense circuit 18) outputs only the AC voltage component out of the voltage component extracted by the low pass filter circuit (LPF 19) as output DC. An AC adding circuit 20 for adding to a feedback voltage proportional to the voltage is provided. (4) Furthermore, as shown in FIG. 6, in the DC-DC converter of the present invention, a voltage Vref2 obtained by adding an AC voltage component Vsensea that fluctuates in reverse phase according to the AC current component of the coil current to the reference voltage Vref; The comparator (comparator circuit) 16 that compares the feedback voltage Vfb proportional to the output DC voltage Vout and the output transistor FET1 and the rectifier element (rectifier transistor FET2) alternately based on the output signal that is the comparison result of the comparator 16 The driver drive circuit 15 that performs on / off control and the voltage Vsensea that includes an AC voltage component that varies in reverse phase according to the AC current component of the coil current are proportional to the current that the output transistor FET1 and the rectifier element (rectifier transistor FET2) flow. Current sense circuit generated using current (output transistor current sensor Circuit 17, and characterized in that a rectification transistor current sense circuit 18). (5) The current sense circuit generates a voltage including an AC voltage component that fluctuates in a reverse phase according to the AC current component of the coil current, using a current proportional to the current flowing through the output transistor FET1. Using a current proportional to the current flowing through the voltage generation circuit (output transistor current sensing circuit 17) and the rectifying element (rectifying transistor FET2), an AC voltage component that varies in reverse phase according to the AC current component of the coil current is included. Of the voltages generated by the second voltage generation circuit (rectifier transistor current sense circuit 18) for generating a voltage and the first and second voltage generation circuits (output transistor current sense circuit 17, rectifier transistor current sense circuit 18) And a low-pass filter circuit (LPF 19) that extracts only a voltage component that varies according to the AC current component of the coil current. Pass filter circuit and the extracted voltage component in (LPF 19), characterized by adding to the reference voltage Vref. (6) Further, the current sense circuit has an inverting amplifier circuit 22 for inverting and amplifying the voltage extracted by the low pass filter circuit (LPF 19). (7) Further, the current sense circuit has an AC addition circuit 20 that adds only the AC voltage component of the output voltage of the inverting amplification circuit 22 to the reference voltage Vref. (8) Moreover, the electronic device of this invention was equipped with the DC-DC converter in any one of above-mentioned (1)-(7).

  According to the present invention, an arbitrary coil that fluctuates in accordance with the AC current component of the coil current without reducing the power conversion efficiency of the DC-DC converter or requiring a discrete external component. By generating an amplitude voltage and adding only an AC voltage component of the generated voltage to the feedback voltage or reference voltage in an arbitrary amount, it is stable even when a capacitor with a small equivalent series resistance is used as the output capacitor. Switching control is possible. For example, (A) a voltage including a voltage component that fluctuates according to the AC current component of the coil current is generated using a current that is proportional to the current flowing between the output transistor and the rectifying element, and thus a resistor that directly detects the coil current. There is no need to use. Therefore, high power conversion efficiency can be maintained. (B) Further, since an appropriate AC voltage component can be generated even for a coil having an arbitrary inductance, the voltage at both ends of the coil that can obtain an appropriate AC voltage component only for a certain inductance coil is integrated. Technology that is superior in versatility compared to the technology to be used. (C) Since only the AC voltage component that varies in phase according to the AC current component of the coil current can be added to the feedback voltage, the equivalent series resistance of the output capacitor is small, and the AC current component of the coil current included in the output voltage Even when the AC voltage component that fluctuates according to the output voltage is reduced, the output voltage can be controlled by stable switching control. (D) Since a voltage including a voltage component that varies according to the AC current component of the coil current is generated using a current proportional to the current flowing between the output transistor and the rectifier element, a resistor that directly detects the coil current is generated. There is no need to use it. Therefore, high power conversion efficiency can be maintained. (4) Further, since an appropriate AC voltage component can be generated even for a coil having an arbitrary inductance, the voltage at both ends of the coil which can obtain an appropriate AC voltage component only for a coil having a certain inductance is integrated. Technology that is superior in versatility compared to this technology. (E) Since only the AC voltage component that varies in the opposite phase according to the AC current component of the coil current can be added to the reference voltage, the equivalent series resistance of the output capacitor is small, and the AC current of the coil current included in the output voltage Even when the AC voltage component that varies depending on the component is reduced, the output voltage can be controlled by stable switching control.

It is a block diagram which shows the circuit structural example of the conventional voltage control system DC-DC converter. It is a block diagram which shows the circuit structural example of the conventional comparator control system DC-DC converter. It is a block diagram which shows the 1st circuit structural example of the DC-DC converter which concerns on this invention. It is explanatory drawing which shows transition of the voltage waveform produced | generated in the DC-DC converter of FIG. FIG. 4 is a block diagram showing a detailed configuration of an output transistor current sensing circuit, a rectifying transistor current sensing circuit, a low pass filter circuit, and an AC adding circuit in FIG. 3. It is a block diagram which shows the 2nd circuit structural example of the DC-DC converter which concerns on this invention. It is explanatory drawing which shows transition of the voltage waveform produced | generated in the DC-DC converter of FIG. FIG. 7 is a block diagram showing a detailed configuration of an output transistor current sensing circuit, a rectifying transistor current sensing circuit, a low pass filter circuit, an inverting circuit, and an AC adding circuit in FIG. 6.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings. FIG. 3 shows a circuit for explaining the first principle of the DC-DC converter of the present invention used in an electronic device such as a computer device or a car navigation device, and is a step-down type that is switched and controlled by a synchronous rectification method. The configuration of the comparator control type DC-DC converter circuit is shown as an example.

  Resistors R1 and R3 and capacitor C1 generate first feedback voltage Vfb1 at node N1 from output voltage Vout. The first feedback voltage Vfb1 is derived from the output voltage Vout obtained by returning the phase delay between the coil L and the output capacitor COUT by the resistor R1 and the capacitor C1 to the DC voltage component determined by the voltage dividing ratio of the resistors R1 and R3 from the output voltage Vout. Is a voltage obtained by adding the AC voltage components.

  The output transistor current sense circuit 17 supplies a current proportional to the current flowing through the output transistor FET1 (for example, 1 / 10,000 of the current flowing through the output transistor FET1), and the rectifier transistor current sense circuit 18 is proportional to the current flowing through the rectifier transistor FET2. Current (for example, 1/10000 of the current flowing through the rectifying transistor FET2) is passed.

  The current that flows through the output transistor current sense circuit 17 flows into the ground potential via the sense resistor RSENSE, and the current that flows through the rectifier transistor current sense circuit 18 flows out of the ground potential through the sense resistor RSENSE.

  Here, since the current flowing through the output transistor FET1 and the current flowing through the rectifying transistor FET2 are equal to the current flowing through the coil L, the current flowing through the output transistor current sensing circuit 17 and the rectifying transistor current sensing circuit 18 are respectively represented by the coil L. The current is proportional to the current flowing through

  Therefore, the current IL flowing through the coil L and the voltage Vsense of the node N3 have waveforms as shown in FIG. 4A, and the voltage Vsense of the node N3 varies depending on the AC current component of the current IL flowing through the coil L. Voltage component to be included.

  The LPF 19 is a low-pass filter that extracts only the voltage component that fluctuates according to the AC current component flowing through the coil L from the voltage Vsense of the node N3. The output voltage Vsensel of the LPF 19 is shown in FIG. The waveform is as shown.

  The AC adder circuit 20 adds only the AC voltage component of the output voltage Vsensel of the LPF 19 to the first feedback voltage Vfb1, and generates the second feedback voltage Vfb2 as shown in FIG. 4C at the node N2. .

  The comparator 16 compares the second feedback voltage Vfb2 with the reference voltage Vref from the reference voltage generator 11.

  When the second feedback voltage Vfb2 becomes lower than the reference voltage Vref, the comparator 16 outputs a high level signal, and the driver driving circuit turns on the output transistor FET1 and turns off the rectifying transistor FET2.

  As a result, the current supplied from the input terminal VIN to the load via the coil L increases, and the output voltage Vout increases.

  Accordingly, the first feedback voltage Vfb1 rises as the output voltage Vout rises, and the second feedback voltage Vfb2 adds the AC voltage component that rises as the current flowing through the coil L increases to the first feedback voltage Vfb1. It further rises above the first feedback voltage Vfb1.

  When the second feedback voltage Vfb2 becomes higher than the reference voltage Vref, the comparator 16 outputs a low level signal, and the driver drive circuit turns off the output transistor FET1 and turns on the rectification transistor FET2.

  As a result, the energy stored in the coil L is supplied to the load via the rectifying transistor FET2, but the current flowing through the coil L decreases as the energy is released, and the output voltage Vout also decreases.

  Therefore, the first feedback voltage Vfb1 decreases as the output voltage Vout decreases, and the second feedback voltage Vfb2 adds the AC voltage component that decreases as the current flowing through the coil L decreases to the first feedback voltage Vfb1. It further falls below the first feedback voltage Vfb1.

  Thereafter, when the second feedback voltage Vfb2 becomes lower than the reference voltage Vref, the operation of the comparator 16 again outputting a high level signal and the driver driving circuit turning on the output transistor FET1 and turning off the rectifying transistor FET2 is repeated. .

  By the above operation, the second feedback voltage Vfb2 on which only the AC voltage component that varies in phase according to the AC current component flowing in the coil L is superimposed is compared with the reference voltage Vref, and negative feedback is made so that both voltages are equal. Since the control works, the output voltage Vout is controlled.

  According to the circuit for explaining the first principle of the present invention, the voltage Vsensel which fluctuates according to the AC current component flowing in the coil L with respect to the coil having an arbitrary inductance without using the resistor for directly detecting the coil current. Can be generated.

  Further, since the second feedback voltage Vfb2 can be generated by adding only the AC voltage component of the voltage Vsensel to the first feedback voltage Vfb1 generated from the output voltage Vout, the second feedback voltage Vfb2 is compared with the reference voltage Vref. The output voltage Vout can be controlled by stable and stable switching control.

  Even when the equivalent series resistance ESR of the output capacitor COUT is small and the AC voltage component that fluctuates according to the AC current component flowing in the coil L included in the output voltage Vout is reduced, the coil L is applied to the second feedback voltage Vfb2. Since an appropriate amount of AC voltage component that varies in phase according to the AC current component flowing in the AC phase can be added, the output voltage Vout can be controlled by stable switching control.

  FIG. 5 shows a circuit diagram of an embodiment embodying the first principle of the present invention shown in FIG.

  The circuit 117 is a specific example of the output transistor current sense circuit 17.

  A sense output transistor FET3 having a common gate and source with the output transistor FET1 is provided, and the drain voltage of the sense output transistor FET3 is controlled to be equal to the drain voltage of the output transistor FET1 by the transistor FET5 and the operational amplifier 21. The

  If the ratio between the channel width and the channel length (hereinafter referred to as W / L) of the output transistor FET1 and the sense output transistor FET3 is set to be m: n (m> n), the current flowing through the sense output transistor FET3 is changed to the output transistor. It can be set to n / m of the current flowing through the FET 1.

  Since this is equal to the current flowing through the output transistor FET1 and the current flowing through the coil L, the current flowing through the sense output transistor FET3 can be set to n / m of the current flowing through the coil L.

  Further, since the current flowing through the sense output transistor FET3 flows into the ground potential via the sense resistor RSENSE, the voltage Vsense of the node N3 varies according to the increase in the current flowing through the coil L when the output transistor FET1 is turned on. Voltage component to be included.

  A voltage that varies according to an increase in the current flowing through the coil L when the output transistor FET1 is turned on by arbitrarily adjusting the W / L ratio of the output transistor FET1 and the sense output transistor FET3 and the resistance value of the sense resistor RSENSE. It is possible to arbitrarily set the slope and amplitude of Vsense.

  The circuit 118 is a specific example of the rectifying transistor current sensing circuit 18. A sense output transistor FET4 having a common gate and drain with the rectifying transistor FET2 is provided.

  If the W / L of the rectifying transistor FET2 and the sense rectifying transistor FET4 is set to be m: n (m> n), the current flowing through the sense rectifying transistor FET4 is set to n / m of the current flowing through the rectifying transistor FET2. be able to.

  Since the current flowing through the rectifying transistor FET2 is equal to the current flowing through the coil L, this means that the current flowing through the sense rectifying transistor FET4 can be set to n / m of the current flowing through the coil L.

  In addition, since the current flowing through the sense rectifier transistor FET4 flows out from the ground potential via the sense resistor RSENSE, the voltage Vsense generated at the node N3 increases as the current flowing through the coil L decreases when the rectifier transistor FET2 is turned on. Voltage component to be included.

  A voltage that varies according to a decrease in the current flowing through the coil L when the rectifier transistor FET2 is turned on by arbitrarily adjusting the W / L ratio of the rectifier transistor FET2 and the sense rectifier transistor FET4 and the resistance value of the sense resistor RSENSE. It is possible to arbitrarily set the slope and amplitude of Vsense.

  However, if the amplitude of the voltage Vsense of the node N3 is excessively increased, the difference between the source voltages of the rectification transistor FET2 and the sense rectification transistor FET4 increases, so that the current flowing through the sense rectification transistor FET4 is increased between the rectification transistor FET2 and the sense rectification transistor FET4. Note that the current does not correspond to the W / L ratio.

  The circuit 119 is a specific example of the LPF 19 and the AC addition circuit 20. An RC low pass filter is configured by the resistor R4 and the capacitor C3, and the cutoff frequency of the output transistor allows only the voltage component that fluctuates according to the AC current component flowing in the coil L out of the voltage Vsense of the node N3. It is set to cut off a voltage component that changes sharply when the FET1 and the rectifying transistor FET2 are turned on and off.

  Therefore, a voltage Vsensel that varies according to the AC current component flowing in the coil L is generated at the node N4 to which the resistor R4 and the capacitor C3 are connected.

  In addition, since the capacitor C3 constituting the low pass filter is connected between the node N1 and the node N3, it acts as an AC adding circuit, and only the AC voltage component of the voltage Vsensel of the node N3 is applied to the node N1. to add.

  That is, an AC voltage component that varies according to an AC current component flowing through the coil L is added to the feedback voltage Vfb from the output voltage Vout determined by the resistors R1 and R3 and the capacitor C1.

  When the impedance of the node N1 is sufficiently smaller than the resistance value of the resistor R4, the cutoff frequency of the RC low pass filter is arbitrarily set by adjusting the resistance value of the resistor R4 and the capacitance value of the capacitor C3. By adjusting the impedance of the node N1 and the capacitance value of C3, it is possible to arbitrarily set the amount of the AC voltage component of the voltage Vsensel added to the feedback voltage Vfb by the AC adding circuit.

  FIG. 6 is a circuit diagram illustrating the second principle of the present invention. FIG. 3 is a principle circuit diagram illustrating a configuration of a step-down comparator control type DC-DC converter circuit that is switching-controlled by a synchronous rectification method.

  Resistors R1 and R3 and capacitor C1 generate feedback voltage Vfb at node N1 from output voltage Vout.

  The feedback voltage Vfb is an AC voltage from the output voltage Vout obtained by returning the phase lag at the coil L and the output capacitor COUT by the resistor R1 and the capacitor C1 to a DC voltage component determined by the voltage dividing ratio of the resistors R1 and R3 from the output voltage Vout. The voltage is the sum of the voltage components.

  The output transistor current sense circuit 17 supplies a current proportional to the current flowing through the output transistor FET1 (for example, 1 / 10,000 of the current flowing through the output transistor FET1), and the rectifier transistor current sense circuit 18 is proportional to the current flowing through the rectifier transistor FET2. Current (for example, 1/10000 of the current flowing through the rectifying transistor FET2) is passed.

  The current that flows through the output transistor current sense circuit 17 flows into the ground potential via the sense resistor RSENSE, and the current that flows through the rectifier transistor current sense circuit 18 flows out of the ground potential through the sense resistor RSENSE.

  Here, since the current flowing through the output transistor FET1 and the current flowing through the rectifying transistor FET2 are equal to the current flowing through the coil L, the current flowing through the output transistor current sensing circuit 17 and the rectifying transistor current sensing circuit 18 are respectively represented by the coil L. The current is proportional to the current flowing through

  Therefore, the current IL flowing through the coil L and the voltage Vsense of the node N3 have waveforms as shown in FIG. 7A, and the voltage Vsense of the node N3 varies according to the AC current component of the current flowing through the coil L. The voltage component will be included.

  The LPF 19 is a low-pass filter that extracts only the voltage component that varies according to the AC current component flowing through the coil L from the voltage Vsense of the node N3. The output voltage Vsensel of the LPF 19 is shown in FIG. The waveform is as shown.

  The inverting amplifier circuit 22 is a circuit that inverts and amplifies the output voltage Vsensel of the LPF 19 and outputs the waveform, and the output voltage Vsensea has a waveform as shown in FIG.

  The AC adding circuit 20 adds only the AC voltage component of the output voltage Vsensea of the inverting amplifier circuit to the reference voltage Vref from the reference voltage generator 11, and a second reference voltage Vref2 as shown in FIG. Generate to N2.

  The comparator 16 compares the feedback voltage Vfb with the second reference voltage Vref2. When the feedback voltage Vfb becomes lower than the second reference voltage Vref2, the comparator 16 outputs a high level signal, and the driver driving circuit turns on the output transistor FET1 and turns off the rectifying transistor FET2.

  As a result, the current supplied from the input terminal VIN to the load via the coil L increases, and the output voltage Vout increases.

  Therefore, the feedback voltage Vfb rises as the output voltage Vout rises, and the second reference voltage Vref2 falls by adding the AC voltage component that falls as the current flowing through the coil L is added to the reference voltage Vref.

  When the feedback voltage Vfb becomes higher than the second reference voltage Vref2, the comparator 16 outputs a low level signal, and the driver drive circuit turns off the output transistor FET1 and turns on the rectifying transistor FET2.

  As a result, the energy stored in the coil L is supplied to the load via the rectifying transistor FET2, but the current flowing through the coil L decreases as the energy is released, and the output voltage Vout also decreases.

  Therefore, the feedback voltage Vfb decreases as the output voltage Vout decreases, and the second reference voltage Vref2 increases by adding the AC voltage component that increases as the current flowing through the coil L increases to the reference voltage Vref.

  Thereafter, when the feedback voltage Vfb becomes lower than the second reference voltage Vref2, the operation of the comparator 16 again outputting a high level signal and the driver driving circuit turning on the output transistor FET1 and turning off the rectifying transistor FET2 is repeated. .

  By the above operation, the feedback voltage Vfb is compared with the second reference voltage Vref2 on which only the AC voltage component that varies in the opposite phase according to the AC current component flowing in the coil L is compared, and the negative voltage is set so that both voltages are equal. Since feedback control works, the output voltage Vout is controlled.

  According to the circuit for explaining the second principle, a voltage that varies in reverse phase according to the AC current component flowing in the coil L with respect to a coil having an arbitrary inductance without using a resistor that directly detects the coil current. Vsensea can be generated.

  Further, since the second reference voltage Vref2 obtained by adding only the AC voltage component of the voltage Vsensea to the reference voltage Vref from the reference voltage generator 11 can be generated, the second reference voltage Vref2 and the feedback voltage Vfb are compared and stabilized. The output voltage Vout can be controlled by the switching control.

  Even when the equivalent series resistance ESR of the output capacitor COUT is small and the AC voltage component that fluctuates according to the AC current component of the coil L included in the output voltage Vout is reduced, the second reference voltage Vref2 is applied to the coil L. Since an appropriate amount of AC voltage component that varies in reverse phase according to the flowing AC current component can be added, the output voltage Vout can be controlled by stable switching control.

  FIG. 8 shows a circuit diagram of an embodiment embodying the second principle of the present invention shown in FIG.

  The circuit 117 is a specific example of the output transistor current sense circuit 17. A sense output transistor FET3 having a common gate and source with the output transistor FET1 is provided, and the drain voltage of the sense output transistor FET3 is controlled to be equal to the drain voltage of the output transistor FET1 by the transistor FET5 and the operational amplifier 21. The

  If the ratio between the channel width and the channel length (hereinafter referred to as W / L) of the output transistor FET1 and the sense output transistor FET3 is set to be m: n (m> n), the current flowing through the sense output transistor FET3 is changed to the output transistor. It can be set to n / m of the current flowing through the FET 1.

  Since this is equal to the current flowing through the output transistor FET1 and the current flowing through the coil L, the current flowing through the sense output transistor FET3 can be set to n / m of the current flowing through the coil L.

  Further, since the current flowing through the sense output transistor FET3 flows into the ground potential via the sense resistor RSENSE, the voltage Vsense of the node N3 varies according to the increase in the current flowing through the coil L when the output transistor FET1 is turned on. Voltage component to be included.

  A voltage that varies according to an increase in the current flowing through the coil L when the output transistor FET1 is turned on by arbitrarily adjusting the W / L ratio of the output transistor FET1 and the sense output transistor FET3 and the resistance value of the sense resistor RSENSE. It is possible to arbitrarily set the slope and amplitude of Vsense.

  Circuit 118 is a specific example of rectifying transistor current sensing circuit 18. A sense output transistor FET4 having a common gate and drain with the rectifying transistor FET2 is provided.

  If the W / L of the rectifying transistor FET2 and the sense rectifying transistor FET4 is set to be m: n (m> n), the current flowing through the sense rectifying transistor FET4 is set to n / m of the current flowing through the rectifying transistor FET2. be able to.

  Since the current flowing through the rectifying transistor FET2 is equal to the current flowing through the coil L, this means that the current flowing through the sense rectifying transistor FET4 can be set to n / m of the current flowing through the coil L.

  Further, since the current flowing through the sense rectifier transistor FET4 flows out from the ground potential via the sense resistor RSENSE, the voltage Vsense generated at the node N3 varies according to the decrease in the current flowing through the coil L when the rectifier transistor FET2 is turned on. A voltage component is included.

  A voltage that varies according to a decrease in the current flowing through the coil L when the rectifier transistor FET2 is turned on by arbitrarily adjusting the W / L ratio of the rectifier transistor FET2 and the sense rectifier transistor FET4 and the resistance value of the sense resistor RSENSE. It is possible to arbitrarily set the slope and amplitude of Vsense.

  However, if the amplitude of the voltage Vsense of the node N3 is excessively increased, the difference between the source voltages of the rectification transistor FET2 and the sense rectification transistor FET4 increases, so that the current flowing through the sense rectification transistor FET4 is increased between the rectification transistor FET2 and the sense rectification transistor FET4. Note that the current does not correspond to the W / L ratio.

  The circuit 119 is a specific example of the LPF 19. An RC low pass filter is formed by the resistor R4 and the capacitor C3. The cut-off frequency of the voltage Vsense of the node N3 passes only the voltage component that varies according to the AC current component flowing in the coil L, and outputs It is set to cut off a voltage component that changes sharply when the transistor FET1 and the rectifying transistor FET2 are turned on and off.

  Therefore, a voltage Vsensel that varies according to the AC current component flowing in the coil L is generated at the node N4 to which the resistor R4 and the capacitor C3 are connected.

  The circuit 122 is a specific example of the inverting amplifier 22. A resistor R5 is connected between the node N4 and the inverting input of the operational amplifier, a reference voltage source E1 is connected between the non-inverting input of the operational amplifier and the ground potential, and between the output of the operational amplifier and the inverting input. A resistor 6 is connected. The relationship between the voltage Vsensel at the node N4 and the voltage Vsensea at the output node N5 of the operational amplifier is expressed by the following equation where the output voltage of the reference voltage source E1 is Vref3.

Vsensea
= Vref3- (Vsensel-Vref3) * R6 / R5
= Vref3 * (R5-R6) / R5-Vsensel * R6 / R5

  From the above equation, it can be seen that the voltage Vsensea at the node N5 is inverted by R6 / R5 times with the voltage Vref3 × (R5−R6) / R5 as a reference level.

  Here, if the resistance ratio of the resistors R5 and R6 and the output voltage Vref3 of the reference voltage source are not set so that Vsensea is always positive with respect to any value of the voltage Vsensel of the node N4, the voltage Vsensea of the node N5 is distorted. It should be noted that this will occur.

  The circuit 120 is a specific example of the AC addition circuit 20. The resistor R2 and the capacitor C2 are included. The resistor R2 is connected between the node N2 and the reference voltage generator 11, and the capacitor C2 is connected between the node N5 and the node N2.

  For the reference voltage Vref from the reference voltage generator 11, it acts as a low-pass filter that passes only the DC voltage component to the node N2, and for the voltage Vsensea of the node N5, only the AC voltage component is applied to the node N2. Acts as a high pass filter to pass.

  Therefore, the second reference voltage Vref2 generated at the node N2 is a voltage obtained by adding the reference voltage Vref from the reference voltage generator 11 and the AC voltage component of the voltage Vsensea at the node N5.

  Note that the cutoff frequency of the RC low pass filter of the circuit 119 can be arbitrarily set by adjusting the resistance value of the resistor R4 and the capacitance value of the capacitor C3.

  Further, by adjusting the resistance values of the resistors R5 and R6 and the voltage value of the output voltage Vref3 of the reference voltage source E1, the inversion amplification factor and the reference level of the circuit 122 can be arbitrarily set.

  Furthermore, by adjusting the resistance value of the resistor R2 and the capacitance value of the capacitor C2, it is possible to arbitrarily set the amount by which the circuit 120 adds the AC voltage component.

  As described above with reference to FIGS. 3 to 8, the DC-DC converter of the present example is a DC-DC that converts an input DC voltage into a stable output DC voltage, for example, as shown in FIGS. 3 and 5. A reference voltage Vref is compared with a reference voltage Vref, which is a DC converter, which is obtained by adding an AC voltage component Vsensel that varies in phase according to the AC current component of the coil current IL to a feedback voltage Vfb1 proportional to the output DC voltage Vout. Based on the comparator 16 and the output signal that is the comparison result of the comparator 16, the driver drive circuit 15 that alternately controls the output transistor FET1 and the rectifying transistor FET2 on and off, and the in-phase according to the AC current component of the coil current IL A voltage Vsensel including a varying AC voltage component is converted into an output transistor FET1 and a rectifying transistor. ET2 current sense circuit generated using a current proportional to the current is flowing (output transistor current sense circuit 17, rectification transistor current sense circuit 18) and the the provided configuration.

  As described above, the voltage including the voltage component that fluctuates according to the AC current component of the coil current is generated using the current proportional to the current flowing through the output transistor FET1 and the rectifying transistor FET2, and thus the coil current is directly detected. There is no need to use resistors. Thereby, high power conversion efficiency can be maintained. In addition, since an appropriate AC voltage component can be generated even for a coil having an arbitrary inductance, a technique for integrating the voltages at both ends of the coil, which can obtain an appropriate AC voltage component only for a certain inductance coil, and Compared to this, it is possible to provide a technology with superior versatility.

  3 and 5 includes an AC voltage component that varies in phase according to the AC current component of the coil current IL, using a current proportional to the current flowing through the output transistor FET1. The output transistor current sensing circuit 17 that generates a voltage and a rectification transistor that generates a voltage including an AC voltage component that varies in phase according to the AC current component of the coil current, using a current proportional to the current that the rectification transistor FET2 flows. Low-pass that extracts only the voltage component that varies according to the AC current component of the coil current IL out of the voltage generated by the current sense circuit 18 and the output transistor current sense circuit 17 and the rectifying transistor current sense circuit 18 • Extraction with the filter circuit (LPF19) and this low-pass filter circuit (LPF19) Among a voltage component, only the AC voltage component, a structure having an AC adding circuit 20 for adding the feedback voltage Vfb1 proportional to the output DC voltage Vout.

  In this way, in the DC-DC converter circuit of this example, only the AC voltage component that varies in phase according to the AC current component of the coil current can be added to the feedback voltage, so that the equivalent series resistance of the output capacitor is small and the output Even when the AC voltage component that varies according to the AC current component of the coil current included in the voltage is reduced, the output voltage can be controlled by stable switching control.

  Further, as shown in FIGS. 6 and 8, the DC-DC converter circuit of the present example includes a voltage Vref2 obtained by adding an AC voltage component Vsensea that varies in a reverse phase according to the AC current component of the coil current to the reference voltage Vref. , A comparator 16 that compares the feedback voltage Vfb proportional to the output DC voltage Vout, and a driver driving circuit that alternately controls on / off of the output transistor FET1 and the rectifying transistor FET2 based on an output signal that is a comparison result of the comparator 16 15 and a current sense circuit that generates a voltage Vsensea including an AC voltage component that varies in an opposite phase according to the AC current component of the coil current, using a current proportional to the current flowing through the output transistor FET1 and the rectifying transistor FET2 (output) Transistor current sense circuit 17, rectifier transistor current sensor Scan circuit 18) a configuration in which a.

  As described above, also in the DC-DC converter circuits of FIGS. 6 and 8, the voltage including the voltage component that fluctuates according to the AC current component of the coil current is proportional to the current that flows through the output transistor FET1 and the rectifying transistor FET2. Since the current is generated using the current, it is not necessary to use a resistor that directly detects the coil current. Thereby, high power conversion efficiency can be maintained. In addition, since an appropriate AC voltage component can be generated even for a coil having an arbitrary inductance, a technique for integrating the voltages at both ends of the coil, which can obtain an appropriate AC voltage component only for a certain inductance coil, and Compared to this, it is possible to provide a technology with superior versatility.

  6 and 8 includes an AC voltage component that varies in reverse phase according to the AC current component of the coil current, using a current proportional to the current flowing through the output transistor FET1. The output transistor current sensing circuit 17 that generates the voltage and the current that is proportional to the current that the rectifying transistor FET2 passes, and the rectification that generates the voltage including the AC voltage component that varies in the opposite phase according to the AC current component of the coil current. Low-pass that extracts only the voltage component that varies according to the AC current component of the coil current out of the voltages generated by the transistor current sense circuit 18 and the output transistor current sense circuit 17 and the rectifier transistor current sense circuit 18 -The electricity extracted by the filter circuit (LPF19) and the low-pass filter circuit (LPF19) And an inverting amplifier circuit 22 and outputs the inverted and amplified, of the output voltage of the inverting amplifier circuit 22, only the AC voltage component, is configured to have an AC adding circuit 20 for adding the reference voltage Vref.

  Thus, in the DC-DC converter circuit of this example, only the AC voltage component that varies in the opposite phase according to the AC current component of the coil current can be added to the reference voltage, so the equivalent series resistance of the output capacitor is small, Even when the AC voltage component that varies according to the AC current component of the coil current included in the output voltage is reduced, the output voltage can be controlled by stable switching control.

  As described above, according to the DC-DC converter of this example, the power conversion efficiency of the DC-DC converter is not reduced, and no discrete external component is required. A voltage with an arbitrary amplitude that varies according to the AC current component is generated, and only the AC voltage component of the generated voltage is added to the feedback voltage or the reference voltage by an arbitrary amount. Even when used as an output capacitor, stable switching control can be performed.

  In addition, this invention is not limited to the example demonstrated using FIGS. 3-8, In the range which does not deviate from the summary, various changes are possible. For example, in this example, a synchronous rectification type DC-DC converter is used as an example, but a diode may be used as the rectifying element. In that case, if the rectifier transistor FET2 is replaced with a rectifier diode, the sense rectifier transistor FET4 is replaced with a sense rectifier diode, and the junction area ratio between the rectifier diode and the sense rectifier diode is m: n (m> n), sense rectification is performed. The current flowing through the diode can be set to n / m of the current flowing through the rectifier diode.

  In the above-described embodiment of the present example, the case where the AC voltage component Vsensel similar to the AC current component flowing in the coil L is generated with reference to the ground potential is taken as an example, but the input terminal VIN may be used as a reference. .

  Furthermore, in the embodiment described above, the switching frequency is variable depending on conditions such as the input voltage Vin, the output voltage Vout, and the load. However, the present invention can also be applied to a comparator control type DC-DC converter control circuit with the switching frequency fixed. .

  Alternatively, the present invention can also be applied to a hysteresis comparator control type DC-DC converter control circuit in which the comparator 16 has hysteresis characteristics to prevent erroneous switching due to noise of the input voltage.

  That is, the present invention is widely applicable to various comparator control type DC-DC converter control circuits.

  11: reference voltage generator, 12: triangular wave generator, 13: error amplifier, 14: PWM comparator, 15: driver driving circuit, 16: comparator, 17: output transistor current sensing circuit, 18: rectifying transistor current sensing circuit, 19 : LPF (low pass filter), 20: AC adder circuit, 21: operational amplifier, 22: inverting amplifier circuit, 117: circuit (output transistor current sense circuit), 118: circuit (rectifier transistor current sense circuit), 119 : Circuit (LPF), 120: Circuit (AC addition circuit), 122: Circuit (inverting amplifier circuit), C1, C2, C3: Capacitor, COUT: Output capacitor, E1: Reference voltage source, ESR: Equivalent series resistance, FET1 : Output transistor, FET2: Rectifier transistor, FET3: Sense output transistor , FET4: sense rectifier transistor, FET5: transistor, IL: current (coil), L: coil, N1, N2, N3, N4, N5: node, R1, R2, R3, R4, R5, R6: resistor, ROUT: Load, RSENSE: sense resistor, Verr: error signal voltage, Vfb: feedback voltage, Vfb1: first feedback voltage, Vfb2: second feedback voltage, Vramp: triangular wave signal voltage, Vref: reference voltage, Vref2: second reference voltage, Vref3: output voltage of the reference voltage source E1, Vin: input voltage, VIN: input terminal, Vout: output voltage, VOUT: output terminal, Vsense: voltage of node 3, Vsensel: output voltage of LPF, Vsensea: inverting amplifier circuit 22 Output voltage.

JP-A-10-225105 JP 2000-287439 A JP 2000-32744 A JP 2007-174772 A JP 2010-35316 A

Claims (8)

A DC-DC converter that converts an input DC voltage to a stable output DC voltage,
A comparison circuit that compares a voltage obtained by adding an AC voltage component that varies in phase according to an AC current component of a coil current to a feedback voltage proportional to the output DC voltage, and a reference voltage;
A driver driving circuit for alternately turning on and off the output transistor and the rectifying element based on an output signal that is a comparison result of the comparison circuit;
A current sense circuit that generates a voltage including an AC voltage component that varies in phase according to an AC current component of the coil current using a current proportional to a current that flows through the output transistor and the rectifier element; DC-DC converter characterized. The DC-DC converter according to claim 1,
The current sense circuit is
A first voltage generation circuit that generates a voltage including an AC voltage component that varies in phase according to an AC current component of the coil current, using a current proportional to a current that the output transistor flows;
A second voltage generation circuit that generates a voltage including an AC voltage component that varies in phase according to an AC current component of the coil current, using a current proportional to a current that the rectifying element flows;
A low-pass filter circuit that extracts only a voltage component that varies in accordance with an AC current component of the coil current among the voltages generated by the first and second voltage generation circuits;
A DC-DC converter, wherein the voltage component extracted by the low-pass filter circuit is added to a feedback voltage proportional to the output DC voltage. The DC-DC converter according to claim 2, wherein
The current sense circuit is
A DC-DC converter comprising an AC adding circuit for adding only an AC voltage component of voltage components extracted by the low-pass filter circuit to a feedback voltage proportional to the output DC voltage. A DC-DC converter that converts an input DC voltage to a stable output DC voltage,
A comparison circuit that compares a reference voltage with a voltage obtained by adding an AC voltage component that varies in reverse phase according to the AC current component of the coil current, and a feedback voltage proportional to the output DC voltage;
A driver driving circuit for alternately turning on and off the output transistor and the rectifying element based on an output signal that is a comparison result of the comparison circuit;
A current sense circuit that generates a voltage including an AC voltage component that varies in an opposite phase according to an AC current component of the coil current, using a current proportional to a current flowing through the output transistor and the rectifier element; DC-DC converter characterized by this. The DC-DC converter according to claim 4, wherein
The current sense circuit is
A first voltage generation circuit that generates a voltage including an AC voltage component that varies in reverse phase according to an AC current component of the coil current, using a current proportional to a current that the output transistor flows;
A second voltage generation circuit that generates a voltage including an AC voltage component that varies in reverse phase according to an AC current component of the coil current, using a current proportional to a current that the rectifying element flows;
A low-pass filter circuit that extracts only a voltage component that varies in accordance with an AC current component of the coil current among the voltages generated by the first and second voltage generation circuits;
A DC-DC converter characterized in that the voltage component extracted by the low-pass filter circuit is added to the reference voltage. The DC-DC converter according to claim 5, wherein
The current sense circuit is
A DC-DC converter comprising an inverting amplifier circuit that inverts and amplifies the voltage extracted by the low-pass filter circuit. The DC-DC converter according to claim 6, wherein
The current sense circuit is
A DC-DC converter comprising an AC addition circuit for adding only an AC voltage component of the output voltage of the inverting amplifier circuit to the reference voltage.   An electronic apparatus comprising the DC-DC converter according to any one of claims 1 to 7.

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