Semiconductor device provided with feedback circuit including resistive element and capacitive element

The present invention provides a switching power supply circuit capable of stabilizing an output voltage as well as increasing a response speed of the output voltage by improving a phase margin of an open loop as a whole of the switching power supply circuit. The switching power supply circuit according to the present invention includes a resistor and a capacitor in addition to a configuration of a conventional switching power supply circuit. The resistor is connected between a node and the capacitor. The capacitor is connected between the resistor and another node. The resistor and the capacitor configure a phase compensation circuit. The phase compensation circuit has a cut-off frequency in accordance with a resonance frequency of an inductor and a capacitor by adjusting a resistance value of the resistor and a capacitance of the capacitor.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a semiconductor device. In particular, the present invention relates to a switching power supply circuit.

2. Description of the Background Art

In a switching power supply circuit as one of semiconductor devices, an error between a voltage obtained by division of an output voltage by a serial resistive element and a predetermined reference voltage is amplified with an error amplifier. On the basis of the error, On-Duty of a switching element is controlled with a PWM (Pulse Width Modulator) comparator, to keep an output voltage value constant. Thus, it is possible to obtain a desired direct current voltage from an input direct current voltage.

It is to be noted that conventional techniques regarding the switching power supply circuit are disclosed in, for example, Japanese Patent Application Laid-Open Nos. 2001-86740, 2003-52170 and 2004-80985.

As thus described, in the switching power supply circuit, an output voltage is fed back to the error amplifier to control the output voltage. Incidentally, in the switching power supply circuit, a low-pass filter circuit including an inductor and a capacitor is connected between an input terminal and an output terminal. Therefore, according to the configuration where the output voltage is fed back to the error amplifier, the aforementioned inductor and capacitor are included in the feedback loop. For this reason, there is a problem in that a phase of an open loop as a whole of the power supply circuit in a resonance frequency of the inductor and the capacitor changes by about 180°, which causes a phase margin to be lost, leading to oscillation of the circuit.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a semiconductor device capable of stabilizing an output voltage as well increasing a response speed of the output voltage by addition of a new feedback loop for improving a phase margin of an open loop as a whole of a switching power supply circuit.

According to a first aspect of the present invention, a semiconductor device includes an input terminal, an output terminal, a switching element, an output voltage detection circuit, a control circuit and a feedback circuit. The switching element is connected between the input terminal and the output terminal. The output voltage detection circuit detects an output voltage as a voltage of the output terminal. The control circuit is connected between a control electrode of the switching element and the output voltage detection circuit, and controls driving of the switching element on the basis of the output voltage detected by the output voltage detection circuit. The feedback circuit is connected between a first node as an output electrode of the switching element and a second node located between the output voltage detection circuit and the control circuit, and includes a resistive element and a capacitive element.

Thus, it is possible to improve a phase margin of the open loop as a whole of the switching power supply circuit.

A semiconductor device according to a second aspect of the present invention includes an input terminal, an output terminal, a switching element, an output voltage detection circuit, a control circuit and a feedback circuit. The switching element is connected between a first node located between the input terminal and the output terminal and a ground potential. The output voltage detection circuit detects an output voltage as a voltage of the output terminal. The control circuit is connected between a control electrode of the switching element and the output voltage detection circuit, and controls driving of the switching element on the basis of the output voltage detected by the output voltage detection circuit. The feedback circuit is connected between the control electrode and a second node located between the output voltage detection circuit and the control circuit, and includes a resistive element and a capacitive element.

Thus, it is possible to improve a phase margin of the open loop as a whole of the switching power supply circuit.

A semiconductor device according to a third aspect of the present invention includes an input terminal, an output terminal, a transformer, a switching element, an output voltage detection circuit, a control circuit and a feedback circuit. The transformer is connected between the input terminal and the output terminal. The switching element is connected to the transformer. The output voltage detection circuit detects an output voltage as a voltage of the output terminal. The control circuit is connected between a control electrode of the switching element and the output voltage detection circuit, and controls driving of the switching element on the basis of the output voltage detected by the output voltage detection circuit. The feedback circuit is connected between a first node located between the control electrode and the output voltage detection circuit and a second node located between the output voltage detection circuit and the control circuit, and includes a resistive element and a capacitive element.

Thus, it is possible to improve a phase margin of the open loop as a whole of the switching power supply circuit.

A semiconductor device according to a fourth aspect of the present invention includes an input terminal, an output terminal, a switching element, an output voltage detection circuit, a control circuit and a feedback circuit. The switching element is connected between the input terminal and the output terminal. The output voltage detection circuit detects an output voltage as a voltage of the output terminal. The control circuit is connected between a control electrode of the switching element and the output voltage detection circuit, and controls driving of the switching element on the basis of the output voltage detected by the output voltage detection circuit. The feedback circuit is connected between the control electrode and a node located between the output voltage detection circuit and the control circuit, and includes a resistive element and a capacitive element.

Thus, it is possible to improve a phase margin of the open loop as a whole of the switching power supply circuit.

A semiconductor device according to a fifth aspect of the present invention includes a first input terminal, a first output terminal, a first switching element, a first output voltage detection circuit, a first control circuit, a first feedback circuit, a second input terminal, a second output terminal, a second switching element, a second output voltage detection circuit, a second control circuit and a second feedback circuit. The first switching element is connected between the first input terminal and the first output terminal. The first output voltage detection circuit detects a first output voltage as a voltage of the first output terminal. The first control circuit is connected between a control electrode of the first switching element and the first output voltage detection circuit, and controls driving of the first switching element on the basis of the first output voltage detected by the first output voltage detection circuit. The first feedback circuit is connected between a first node as an output electrode of the first switching element and a second node located between the first output voltage detection circuit and the first control circuit, and includes a first resistive element and a first capacitive element. The second switching element is connected between a third node located between the second input terminal and the second output terminal and a ground potential. The second output voltage detection circuit detects a second output voltage as a voltage of the second output terminal. The second control circuit is connected between a control electrode of the second switching element and the second output voltage detection circuit, and controls driving of the second switching element on the basis of the second output voltage detected by the second output voltage detection circuit. The second feedback circuit is connected between the control electrode of the second switching element and a fourth node located between the second output voltage detection circuit and the second control circuit, and includes a second resistive element and a second capacitive element.

Thus, it is possible to improve a phase margin of the open loop as a whole of the switching power supply circuit.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The semiconductor device according to the present invention is applicable to various electronic devices, in particular, portable devices such as a digital steel camera (DSC) and a digital video camera (DVC), although not limited thereto, as a switching power supply with an input direct current voltage of the order of 1.5 to 4.2 V and an output direct current voltage of the order of −8 to +16 V.

In the following, embodiments of the semiconductor device according to the present invention will be specifically described by means of drawings, taking a switching power supply circuit as an example. It is to be noted that elements provided with the same one symbol in different drawings are equivalent or correspond to one another.

FIG. 1is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 2is a circuit diagram showing a configuration of a switching power supply circuit according to an embodiment of the present invention, corresponding toFIG. 1.FIGS. 1 and 2each show a step-down diode rectification switching power supply circuit.

Referring toFIG. 1, the conventional step-down diode rectification switching power supply circuit includes an input terminal1, an output terminal2, a terminal34, a PMOS transistor3a, a diode4a, an inductor5a(inductance L1), capacitors6,16,17(capacitances C1, C2, C3), resistors7,8,18(resistance values R1, R2, R3), an error amplifier9, a power supply10, a PWM comparator11, a triangular wave oscillator12, and a gate driver13a.

An input voltage VIN as a direct current voltage is inputted into the input terminal1. An output voltage VOUT as a direct current voltage is outputted from the output terminal2. A gate electrode of the PMOS transistor3ais connected to an output terminal of the gate driver13a, a source electrode thereof is connected to the input terminal1, and a drain electrode thereof is connected to a node N1a. An anode electrode of the diode4ais connected to a ground potential (reference potential of the circuit), and a cathode electrode thereof is connected to the node N1a.

The inductor5ais connected between the node N1a(the terminal34) and the output terminal2. The capacitor6is connected between the output terminal2and a ground potential. The resistor7is connected between the output terminal2and a node N2. The resistor8is connected between the node N2and a ground potential. The capacitor C2is connected between the output terminal2and the node N2, to constitute a phase compensation circuit14.

A first input terminal (minus side) of the error amplifier9is connected to the node N2, a second input terminal (plus side) thereof is connected to the power supply10, and an output terminal thereof is connected to a node N3. The power supply10is connected between the second input terminal of the error amplifier9and a ground potential, and outputs a predetermined reference voltage. The capacitor17is connected between the node N3and the resistor18. The resistor18is connected between the capacitor17and the node N2. The capacitor17and the resistor18constitute a phase compensation circuit15.

A first input terminal (plus side) of the PWM comparator11is connected to the node N3, a second input terminal (minus side) thereof is connected to the triangular wave oscillator12, and an output terminal thereof is connected to an input terminal of the gate driver13a. An output terminal of the gate driver13ais connected to the gate electrode of the PMOS transistor3a.

Referring toFIG. 2, similar to the conventional switching power supply circuit shown inFIG. 1, the switching power supply circuit according to this embodiment also includes an input terminal1, an output terminal2, a terminal34, a PMOS transistor3a, a diode4a, an inductor5a, capacitors6,16,17, resistors7,8,18, an error amplifier9, a power supply10, a PWM comparator11, a triangular wave oscillator12, and a gate driver13a. In addition to the configuration of the conventional switching power supply circuit, the switching power supply circuit according to this embodiment further includes a resistor20(resistance value R4) and a capacitor21(capacitance C4).

The resistor20is connected between the node N1aand the capacitor21. The capacitor21is connected between the resistor20and the node N2. The resistor20and the capacitor21constitute a phase compensation circuit19. The phase compensation circuit19improves a cut-off frequency of the open loop as a whole of the switching power circuit over a resonance frequency of the inductor5aand the capacitor6by adjusting the resistance value R4of the resistor20and the capacitance C4of the capacitor21. A feedback circuit, not including the inductor5aand the capacitor6but including a serial connection of the resistor20and the capacitor21is connected between a drain electrode of the PMOS transistor3aand a first input terminal of the error amplifier9, to increase a phase margin of an open loop as a whole of the switching power supply circuit. Namely, addition of the phase compensation circuit19leads to phase progression, thereby to alleviate a phase change made due to the inductor5aand the capacitor6.

In the node N2, a partial voltage appears, which is obtained by division of the output voltage VOUT by the resistance values R1, R2of the resistors7,8. Namely, the resistors7,8function as an output voltage detection circuit for detecting the output voltage VOUT.

The error amplifier9amplifies an error between the partial voltage of the node N2and the predetermined reference voltage inputted from the power supply10, to output an error signal. The PWM comparator11generates a pulse signal a pulse width of which is modulated according to the error signal inputted from the error amplifier9and a triangular wave signal inputted from the triangular wave oscillator12. The gate driver13acontrols drive of the PMOS transistor3a, which is a switching element, based upon the pulse signal inputted from the PWM comparator11. Thereby, the value of the output voltage VOUT is kept constant, to obtain a desired direct current voltage (VOUT) from the inputted direct current voltage (VIN). That is, the error amplifier9, the PWM comparator11, the power supply10, the triangular wave oscillator12and the gate driver13afunction as a control circuit for controlling switching of the PMOS transistor3abased upon the output voltage VOUT (strictly speaking, the partial voltage of the node N2) detected by the output voltage detection circuit including the resistors7,8.

FIG. 3is a block diagram functionally representing the switching power supply circuit shown inFIG. 2. InFIG. 3, the PMOS transistor3ashown inFIG. 2is represented as a switching element30. Further, the inductor5aand the capacitor6which are shown inFIG. 2are represented as a low-pass filter31. The resistors7,8which are shown inFIG. 2are represented as an output voltage detection circuit32. The error amplifier9, the PWM comparator11, the power supply10, the triangular wave oscillator12and the gate driver13awhich are shown inFIG. 2are represented as a control circuit33. It is to be noted that, inFIG. 3, the phase compensation circuits14,15which are shown inFIG. 2are not shown. InFIG. 3, a portion surrounded with a thick line35is a portion capable of integration as an IC. The input terminal1is connected to a direct current power supply36. The output terminal2is connected to a load37. The low-pass filter31is connected to a terminal34.

FIG. 4is an open loop Bode diagram regarding the conventional switching power supply circuit (conventional circuit) shown inFIG. 1and the switching power supply circuit of this embodiment (circuit in the present invention) shown inFIG. 2. In the conventional circuit, a phase margin in the resonance frequency of the inductor5aand the capacitor6is 6° or less. Namely, since the phase margin is small in the conventional circuit, it is likely that the output voltage VOUT oscillates due to an external parasitic LCR, and the output voltage VOUT is unstable. On the other hand, in the circuit in the present invention, the phase margin in the resonance frequency of the inductor5aand the capacitor6is about 52°, indicating significant improvement in phase margin as compared with the conventional circuit (see a region P inFIG. 4).

As shown inFIG. 2, according to the switching power supply circuit of this embodiment, the phase compensation circuit19including the serial connection of the resistor20and the capacitor21is connected between the drain electrode of the PMOS transistor3aand the first input terminal of the error amplifier9. Thereby, as apparent from the Bode diagram shown inFIG. 4, the phase margin of the open loop as a whole of the switching power supply circuit increases. This results in significant improvement in phase margin as compared with the conventional switching power supply circuit shown inFIG. 1, to allow stabilization of the output voltage VOUT as well as increase a response speed of the output voltage VOUT.

In the following, modifications of the present invention will be described. Also in all modifications described below, it is possible to obtain a similar effect to the switching power supply circuit according to the above-mentioned embodiment.

First Modification

FIG. 5is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 6is a circuit diagram showing a configuration of a switching power supply circuit according to a first modification of the present invention, corresponding toFIG. 5.FIGS. 5 and 6each show a step-down synchronous rectification switching power supply circuit.

In the conventional switching power supply circuit shown inFIG. 5, an NMOS transistor40aand a gate driver41aare provided in place of the diode4ain the conventional switching power supply circuit shown inFIG. 1. A gate electrode of the NMOS transistor40ais connected to an output terminal of the gate driver41a, a source electrode thereof is connected to a ground potential, and a drain electrode thereof is connected to a node N1a. An input terminal of the gate driver41ais connected to an output terminal of the PWM comparator11.

The switching power supply circuit according to the first modification of the present invention shown inFIG. 6includes a phase compensation circuit19including a resistance20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 5. As in the switching power supply circuit according to the embodiment of the present invention shown inFIG. 2, the resistor20is connected between the node N1aand the capacitor21, and the capacitor21is connected between the resistor20and a node N2.

Second Modification

FIG. 7is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 8is a circuit diagram showing a configuration of a switching power supply circuit according to a second modification of the present invention, corresponding toFIG. 7.FIGS. 7 and 8each show a step-up diode rectification switching power supply circuit.

Referring toFIG. 7, the conventional step-up diode rectification switching power supply circuit includes an NMOS transistor3b, a diode4b, an inductor5b, and a gate driver13b. Similar to the conventional switching power supply circuit shown inFIG. 1, this conventional switching power supply circuit also includes an input terminal1, an output terminal2, capacitors6,16,17, resistors7,8,18, an error amplifier9, a power supply10, a PWM comparator11, and a triangular wave oscillator12.

The inductor5bis connected between the input terminal1and a node N1b. A gate electrode of the NMOS transistor3bis connected to an output terminal of the gate driver13b, a source electrode thereof is connected to a ground potential, and a drain electrode thereof is connected to the node N1b. An input terminal of the gate driver13bis connected to an output terminal of the PWM comparator11. An anode electrode of the diode4bis connected to the node N1b, and a cathode electrode thereof is connected to the output terminal2.

The switching power supply circuit according to the second modification of the present invention shown inFIG. 8includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 7. The resistor20is connected between the gate electrode of the NMOS transistor3band the capacitor21, and the capacitor21is connected between the resistor20and a node N2.

Third Modification

FIG. 9is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 10is a circuit diagram showing a configuration of a switching power supply circuit according to a third modification of the present invention, corresponding toFIG. 9.FIGS. 9 and 10each show a step-up synchronous rectification switching power supply circuit.

In the conventional switching power supply circuit shown inFIG. 9, a PMOS transistor40band a gate driver41bare provided in place of the diode4bin the conventional switching power supply circuit shown inFIG. 7. A gate electrode of the PMOS transistor40bis connected to an output terminal of the gate driver41b, a source electrode thereof is connected to a node N1b, and a drain electrode thereof is connected to the output terminal2. An input terminal of the gate driver41bis connected to an output terminal of the PWM comparator11.

The switching power supply circuit according to the third modification of the present invention shown inFIG. 10includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 9. As in the switching power supply circuit according to the second modification of the present invention shown inFIG. 8, the resistor20is connected between the gate electrode of the NMOS transistor3band the capacitor21, and the capacitor21is connected between the resistor20and a node N2.

Fourth Modification

FIG. 11is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 12is a circuit diagram showing a configuration of a switching power supply circuit according to a fourth modification of the present invention, corresponding toFIG. 11.FIGS. 11 and 12each show a step-up/down diode rectification switching power supply circuit.

Referring toFIG. 11, similar to the conventional switching power supply circuit shown inFIG. 1, the conventional step-up/down diode rectification switching power supply circuit includes an input terminal1, an output terminal2, a PMOS transistor3a, a diode4a, an inductor5a, capacitors6,16,17, resistors7,8,18, an error amplifier9, a power supply10, a PWM comparator11, a triangular wave oscillator12, and the gate driver13a. Similar to the conventional switching power supply circuit shown inFIG. 7, this conventional switching power supply circuit in the fourth modification also includes an NMOS transistor3b, a diode4b, and a gate driver13b.

The switching power supply circuit according to the fourth modification of the present invention shown inFIG. 12includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 11. As in the switching power supply circuit according to the embodiment of the present invention shown inFIG. 2, the resistor20is connected between a node N1aand the capacitor21, and the capacitor21is connected between the resistor20and a node N2.

Fifth Modification

FIG. 13is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 14is a circuit diagram showing a configuration of a switching power supply circuit according to a fifth modification of the present invention, corresponding toFIG. 13.FIGS. 13 and 14each show a step-up/down synchronous rectification switching power supply circuit.

In the conventional switching power supply circuit shown inFIG. 13, an NMOS transistor40aand a gate driver41aare provided in place of the diode4ain the conventional switching power supply circuit shown inFIG. 11. Further, a PMOS transistor40band a gate driver41bare provided in place of the diode4bin the conventional switching power supply circuit shown inFIG. 11.

As in the conventional switching power supply circuit shown inFIG. 5, a gate electrode of the NMOS transistor40ais connected to an output terminal of the gate driver41a, a source electrode thereof is connected to a ground potential, and a drain electrode thereof is connected to a node N1a. An input terminal of the gate driver41ais connected to an output terminal of the PWM comparator11. Further, as in the conventional switching power supply circuit shown inFIG. 9, a gate electrode of the PMOS transistor40bis connected to an output terminal of the gate driver41b, a source electrode thereof is connected to a node N1b, and a drain electrode thereof is connected to the output terminal2. An input terminal of the gate driver41bis connected to the output terminal of the PWM comparator11.

The switching power supply circuit according to the fifth modification of the present invention shown inFIG. 14includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 13. As in the switching power supply circuit according to the fourth modification of the present invention shown inFIG. 12, the resistor20is connected between the node N1aand the capacitor21, and the capacitor21is connected between the resistor20and a node N2.

Sixth Modification

FIG. 15is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 16is a circuit diagram showing a configuration of a switching power supply circuit according to a sixth modification of the present invention, corresponding toFIG. 15.FIGS. 15 and 16each show a flyback-type switching power supply circuit.

Referring toFIG. 15, the conventional flyback-type switching power supply circuit includes a transformer5cand, similar to the conventional switching power supply circuit shown inFIG. 7, an input terminal1, an output terminal2, an NMOS transistor3b, a diode4b, a gate driver13b, capacitors6,16,17, resistors7,8,18, an error amplifier9, a power supply10, a PWM comparator11, and a triangular wave oscillator12. Namely, in the example of the conventional switching power supply circuit shown inFIG. 15, a transformer5cis provided in place of the inductor5bshown inFIG. 7.

The switching power supply circuit according to the sixth modification of the present invention shown inFIG. 16includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 15. The resistor20is connected between a node N1blocated between the gate electrode of the NMOS transistor3band the gate driver13band the capacitor21. The capacitor21is connected between the resistor20and a node N2.

Seventh Modification

FIG. 17is a circuit diagram showing a configuration of a conventional switching power supply circuit.FIG. 18is a circuit diagram showing a configuration of a switching power supply circuit according to a seventh modification of the present invention, corresponding toFIG. 17.FIGS. 17 and 18each show an inversion-type switching power supply circuit.

Referring toFIG. 17, the conventional inversion-type switching power supply circuit includes a PMOS transistor3c, an inductor5c, a diode4c, and a gate driver13c. Similar to the conventional switching power supply circuit shown inFIG. 1, this switching power supply circuit also includes an input terminal1, an output terminal2, capacitors6,16,17, resistors7,8,18, an error amplifier9, a power supply10, a PWM comparator11, and a triangular wave oscillator12.

A gate electrode of the PMOS transistor3cis connected to an output terminal of the gate driver13c, a drain electrode thereof is connected to the input terminal1, and a source electrode thereof is connected to a node N1c. An input terminal of the gate driver13cis connected to an output terminal of the PWM comparator11. An anode electrode of the diode4cis connected to the output terminal2, and a cathode electrode thereof is connected to the node N1c. The inductor5cis connected between the node N1cand a ground potential.

The switching power supply circuit according to the seventh modification of the present invention shown inFIG. 18includes a phase compensation circuit19including a resistor20and a capacitor21, in addition to the conventional switching power supply circuit shown inFIG. 17. The resistor20is connected between the gate electrode of the PMOS transistor3cand the capacitor21. The capacitor21is connected between the resistor20and a node N2.

Eighth Modification

FIG. 19is a circuit diagram showing a configuration of a switching power supply circuit according to an eighth modification of the present invention. The switching power supply circuit according to the eighth modification of the present invention is constituted such that the step-down synchronous rectification switching power supply circuit shown inFIG. 6and the step-up synchronous rectification switching power supply circuit shown inFIG. 10are mounted within the same one IC chip.

The step-down synchronous rectification switching power supply circuit includes an input terminal12, an output terminal22, a PMOS transistor3a, an NMOS transistor40a, an inductor5a, capacitors62,162,172,212, resistors72,82,182,202, an error amplifier92, a power supply10, a PWM comparator112, a triangular wave oscillator12, gate drivers13a,41a, a DTC (Dead Time Controller)50, an AND circuit512, and a control circuit522. The resistor202and the capacitor212constitute a phase compensation circuit192.

The step-up synchronous rectification switching power supply circuit includes an input terminal11, an output terminal21, an NMOS transistor3b, a PMOS transistor40b, an inductor5b, capacitors61,161,171,211, resistors71,81,181,201, an error amplifier91, a power supply10, a PWM comparator111, a triangular wave oscillator12, gate drivers13b,41b, a DTC50, an AND circuit511, and a control circuit521. The resistor201and the capacitor211constitute a phase compensation circuit191.

It is to be noted that the gate drivers13a,13b,41a,41bmay be switching elements such as MOS transistors or bipolar transistors.

Since connection relationships among each element in the circuit shown inFIG. 19are basically similar to those among each element in the circuits shown inFIGS. 6 and 10, specific descriptions thereof are omitted here. It is to be noted that the DTC50and the AND circuits511,512perform a control for periodically turning off the PMOS transistors3a,40band the NMOS transistors3b,40a. Further, the control circuit521performs a control for making the timing for switching on/off of the NMOS transistor3bdisagree with the timing for switching off/on of the PMOS transistor40b. Similarly, the control circuit522performs a control for making the timing for switching on/off of the PMOS transistor3adisagree with the timing for switching off/on of the NMOS transistor40a.

It is to be noted that, although the combination of the circuit shown inFIG. 6and the circuit shown inFIG. 10is described above, the combination is not limited thereto. It is possible to arbitrarily combine the circuits respectively shown inFIGS. 2,6,8,10,12,14,16and18.

Ninth Modification

FIG. 20is a circuit diagram showing a first configuration of a switching power supply circuit according to a ninth modification of the present invention, corresponding toFIG. 2. In the circuit shown inFIG. 20, the connection order of a resistor20and a capacitor21is opposite to that in the circuit shown inFIG. 2. Namely, in a phase compensation circuit19ashown inFIG. 20, the capacitor21is connected to a node N2through the resistor20. On the other hand, in the phase compensation circuit19shown inFIG. 2, the resistor20is connected to the node N2through the capacitor21.

FIG. 21is a circuit diagram showing a second configuration of a switching power supply circuit according to the ninth modification of the present invention, corresponding toFIG. 2. In the circuit shown inFIG. 21, resistors20a,20bare respectively connected to each side of a capacitor21. Namely, in a phase compensation circuit19bshown inFIG. 21, a resistor20ais connected to a node N2through the capacitor21and the resistor20b.

As thus described, the phase compensation circuit19ashown inFIG. 20or the phase compensation circuit19bshown inFIG. 21may be used in place of the phase compensation circuit19shown inFIG. 2. This applies to the phase compensation circuits19respectively shown inFIGS. 6,8,10,12,14,16and18, and the phase compensation circuits191,192shown inFIG. 19.

However, in cases including a case where a gate capacitor of a transistor constitutes a capacitor C4, a desirable configuration from the view point of enhancing surge withstand capability to protect the circuit is made by arrangement of a resistor R4and the capacitor21in this order seen from the input terminal1. Namely, the phase compensation circuits19shown inFIG. 2and the like and the phase compensation circuit19bshown inFIG. 21are preferred to the phase compensation circuit19ashown inFIG. 20.

First Embodiment

In the following, the step-down synchronous rectification switching power supply circuit shown inFIG. 6is taken as an example, and respective specific numeral values of the resistance values R3, R4of the resistors18,20, capacitances C1, C3, C4of the capacitances6,17,21, and the inductance L1of the inductor5awill be described.

Respective desirable ranges of the resistance value R4, the capacitances C1, C4and the inductance L1change according to a oscillation frequency of the triangular wave oscillator12. The oscillation frequency of the triangular wave oscillator12is in the range of 500 Hz to several MHz. In this case, the desirable range of the resistance value R4is from 10 to 1000 kΩ, the desirable range of the capacitance C1is from 1 to 100 μF, the desirable range of the capacitance C4is from 1 to 1000 pF, and the desirable range of the inductance L1is from 0.1 to 100 μH.

Specifically, when the oscillation frequency of the triangular wave oscillator12is 1 MHz, the desirable range of the resistance value R4is from 10 to several hundreds kΩ, and the desirable range of the capacitance C1is from 1 to several tens μF, the desirable range of the capacitance C4is from 1 to several hundreds pF, and the desirable range of the inductance L1is from 0.1 to several pH.

Further, the desirable range of the resistance value R3is from several to several tens kΩ, and the desirable range of the capacitance C3is from several to several tens pF. Therefore, a difference between the order (103to 104) of the resistance value R3and the order (104to 105) of the resistance value R4is within two digits, and a difference between the order (10−12to 10−11) of the capacitance C3and the order (10−12to 10−10) of the capacitance C4is within two digits.

When the resistance value R3and the capacitance C3become extremely small as compared with the resistance value R4and the capacitance C4, the effect due to the phase compensation circuit15cannot be obtained. Such a problem can be avoided by setting the resistance values R3, R4and the capacitances C3, C4such that the above-mentioned order differences are within two digits.

It is to be noted that, although specific numerical values of the resistance values R3, R4, the capacitances C1, C3, C4, and the inductances L1are described above taking the circuit shown inFIG. 6as an example, similar numerical values can be applied to the respective circuits shown inFIGS. 2,8,10,12,14,16,18and19.

Second Embodiment

FIG. 22is a top view schematically showing part of a layout pattern of an IC chip on which the switching power supply circuit according to the present invention is mounted. In a predetermined region of a silicon substrate100, an error amplifier9, resistors18,20, and capacitors17,21are formed.

Further,FIG. 23is a sectional view showing a cross-sectional structure of a portion of an IC chip shown inFIG. 22, where the resistor20and the capacitor21are formed. N-type wells101,102are partially formed within the top face of a P-type silicon substrate100. A P+-type impurity diffusion layer103which functions as the resistor20is partially formed within the top face of the well101. A gate insulating film104, made of silicon oxide or the like, is partially formed on the top face of the well102. A gate electrode105, made of polysilicon or the like, is formed on the gate insulating film104. The gate electrode105, the gate insulating film104, and the well102function as the capacitor21.