JP5584463B2 - Switching regulator control circuit, power supply device using the same, and electronic equipment - Google Patents

Description

  The present invention relates to a switching regulator.

  In recent electronic devices such as mobile phones and PDAs (Personal Digital Assistants), devices that require a power supply voltage higher or lower than the battery voltage are mounted. In order to supply an appropriate power supply voltage to such a device, a step-up, step-down or step-up / step-down switching regulator is used.

  A pulse width modulation (PWM) method is used as a method for controlling on / off of the switching element of the switching regulator. In the PWM method, the output voltage of the switching regulator is compared with a reference voltage corresponding to a target value, and the pulse width of the drive signal for the switching element is changed so that the error voltage is minimized. The output voltage is kept constant by changing the ON time when the switching element is turned on, that is, the duty ratio.

  A load driving capability of a general PWM switching regulator is determined according to an inductance value and a switching frequency. The inductance value of the inductor decreases as the current flowing through the inductor (coil current) increases. Therefore, it is necessary to select a large inductor so as to ensure a necessary inductance value at the maximum load (maximum coil current). Large inductors are expensive and have a large mounting area.

  The present invention has been made in view of these problems, and one of the exemplary purposes of an aspect thereof is to reduce the size of an inductor of a switching regulator.

  One embodiment of the present invention relates to a control circuit for driving a switching transistor of a switching regulator. This control circuit is a pulse width modulator that generates a pulse width modulation signal that instructs on / off of a switching transistor, and the duty ratio of the pulse width modulation signal is based on a feedback voltage corresponding to the output voltage of the switching regulator. According to the pulse width modulator that adjusts to match the voltage, the driver circuit that drives the switching transistor based on the pulse width modulation signal, and the coil current flowing through the inductor of the switching regulator, the larger the coil current, the more the pulse width modulation signal A frequency control unit that controls the pulse width modulator so that the frequency of the signal becomes higher.

  In a state where a large coil current flows during heavy load, the inductance value of the inductor decreases. Therefore, a decrease in inductance value can be compensated for by increasing the switching frequency under heavy load. That is, since the inductance value of the inductor can be reduced as compared with the conventional case, the size of the inductor can be reduced.

  The pulse width modulator compares an error amplifier that generates an error signal according to the error between the feedback voltage and the reference voltage, an oscillator that generates a triangular wave periodic signal, the periodic signal and the error signal, and according to the comparison result. And a comparator for generating a pulse width modulation signal. The frequency control unit may control the oscillation frequency of the oscillator.

  The pulse width modulator includes first and second resistors provided in series between an output terminal of the switching regulator and a fixed voltage terminal, and a first capacitor connected in parallel with the first resistor, and the output voltage of the switching regulator. A feedback circuit that generates a feedback voltage, a hysteresis comparator that receives the feedback voltage at its first input terminal and a reference voltage at its second input terminal, and between the output terminal and the first input terminal of the hysteresis comparator A third resistor and a second capacitor provided in series with each other. The frequency control unit may control at least one of a resistance value of the third resistor, a capacitance value of the first capacitor, a capacitance value of the second capacitor, and a hysteresis width of the hysteresis comparator.

  Another embodiment of the present invention is also a control circuit. This control circuit is a pulse width modulator that generates a pulse width modulation signal that instructs on / off of a switching transistor, and the duty ratio of the pulse width modulation signal is based on a feedback voltage corresponding to the output voltage of the switching regulator. A pulse width modulator that adjusts to match the voltage; and a driver circuit that drives the switching transistor based on the pulse width modulation signal. The pulse width modulator includes first and second resistors provided in series between an output terminal of the switching regulator and a fixed voltage terminal, and a first capacitor connected in parallel with the first resistor, and the output voltage of the switching regulator. A feedback circuit that generates a feedback voltage, a hysteresis comparator that receives the feedback voltage at its first input terminal and a reference voltage at its second input terminal, and between the output terminal and the first input terminal of the hysteresis comparator A third resistor and a second capacitor provided in series with each other, and at least one of a resistance value of the third resistor, a capacitance value of the first capacitor, a capacitance value of the second capacitor, and a hysteresis width of the hysteresis comparator, and a pulse width A frequency hopping controller that hops the frequency of the modulation signal.

  According to this aspect, since the spectrum is dispersed and the intensity peak value is reduced, it is easy to take measures against EMI (Electro Magnet Interference).

  The frequency hopping control unit may switch the frequency of the pulse width modulation signal for each period of the pulse width modulation signal.

  The switching regulator is a synchronous rectification type including a synchronous rectification transistor, and the frequency hopping control unit performs a pulse width modulation signal according to the timing when the switching transistor is turned off from the state where the switching transistor is on and the synchronous rectification transistor is off. The frequency may be switched.

  Yet another embodiment of the present invention is also a control circuit. This control circuit is a pulse width modulator that generates a pulse width modulation signal that instructs on / off of a switching transistor, and the duty ratio of the pulse width modulation signal is based on a feedback voltage corresponding to the output voltage of the switching regulator. A pulse width modulator that adjusts to match the voltage; and a driver circuit that drives the switching transistor based on the pulse width modulation signal. The pulse width modulator includes first and second resistors provided in series between an output terminal of the switching regulator and a fixed voltage terminal, and a first capacitor connected in parallel with the first resistor, and the output voltage of the switching regulator. A feedback circuit that generates a feedback voltage, a hysteresis comparator that receives the feedback voltage at its first input terminal, an impedance circuit that receives a reference voltage and inputs it to the second input terminal of the hysteresis comparator, and an output of the hysteresis comparator And an inverter that inverts a pulse signal having a logic level corresponding to the second signal, and a third resistor and a second capacitor provided in series between the output terminal of the inverter and the second input terminal of the hysteresis comparator.

  According to this aspect, the loop gain of the DC feedback can be independently controlled by the feedback circuit, and the frequency feedback can be independently controlled by the third resistor, the second capacitor, and the inverter.

The control circuit of an aspect may further include a constant voltage circuit that supplies a stabilized constant voltage to the hysteresis comparator.
In a pulse width modulator using a hysteresis comparator, the gain of the hysteresis comparator changes according to the power supply voltage to the hysteresis comparator, which adversely affects the stability of the output voltage of the switching regulator. According to this aspect, since the power supply voltage for the hysteresis comparator is stabilized, the output voltage of the switching regulator can be stabilized.

  Yet another embodiment of the present invention is a power supply device. This apparatus includes the control circuit according to any one of the above-described aspects.

  Yet another embodiment of the present invention is an electronic device. This electronic apparatus includes the above-described power supply device.

  Note that any combination of the above-described constituent elements, and those in which the constituent elements and expressions of the present invention are mutually replaced between methods, apparatuses, systems, and the like are also effective as an aspect of the present invention.

  According to an aspect of the present invention, the inductor of the switching regulator can be reduced in size.

It is a circuit diagram which shows the structure of the switching regulator which concerns on 1st Embodiment. 2A shows the relationship between the coil current and the inductance value of the inductor, and FIG. 2B shows the relationship between the coil current and the oscillation frequency of the oscillator. It is a circuit diagram which shows the structure of the switching regulator which concerns on 2nd Embodiment. It is a figure which shows the relationship between the output voltage of the DC / DC converter using a hysteresis comparator, and the power supply voltage with respect to a hysteresis comparator. It is a circuit diagram which shows the structure of the switching regulator which concerns on 3rd Embodiment. 6A and 6B are circuit diagrams showing the configuration of the switching regulator according to the modification of FIG. It is a circuit diagram which shows the structure of the switching regulator which concerns on 4th Embodiment.

  The present invention will be described below based on preferred embodiments with reference to the drawings. The same or equivalent components, members, and processes shown in the drawings are denoted by the same reference numerals, and repeated descriptions are omitted as appropriate. The embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

In this specification, “the state in which the member A is connected to the member B” means that the member A and the member B are electrically connected in addition to the case where the member A and the member B are physically directly connected. It includes the case of being indirectly connected through another member that does not affect the connection state.
Similarly, “the state in which the member C is provided between the member A and the member B” refers to the case where the member A and the member C or the member B and the member C are directly connected, as well as an electrical condition. It includes the case of being indirectly connected through another member that does not affect the connection state.

(First embodiment)
FIG. 1 is a circuit diagram showing a configuration of a switching regulator (power supply device) 4 according to the first embodiment. The switching regulator 4 is a step-down switching regulator that receives a power supply voltage (input voltage) Vdd, steps down it, generates a stabilized output voltage Vout, and supplies the output voltage Vout to the load 2. The power supply voltage Vdd is supplied from a battery or an external power supply.

  The switching regulator 4 is mounted on electronic devices such as a mobile phone terminal, a digital camera, a digital video camera, and a portable audio player together with loads such as a DSP (Digital Signal Processor), a liquid crystal driver, and an audio circuit.

  The switching regulator 4 includes a control circuit 100, an inductor L1, and an output capacitor Co. Although the switching transistor M1 and the synchronous rectification transistor M2 are incorporated in the control circuit 100, they may be discrete elements provided outside the control circuit 100.

  The circuit topology of the switching transistor M1, the synchronous rectification transistor M2, the inductor L1, and the output capacitor Co is the same as that of a general synchronous rectification switching regulator.

  The control circuit 100 drives the switching transistor M1 and the synchronous rectification transistor M2 based on the feedback voltage Vfb corresponding to the output voltage Vout, and stabilizes the output voltage Vout to a desired level.

The control circuit 100 includes a power supply terminal P1, a ground terminal P2, a switching terminal P3, and a feedback terminal P4. A power supply voltage Vdd is input to the power supply terminal P1, and a ground voltage _VGND is supplied to the ground terminal P2. The switching terminal P3 is a terminal for outputting the potential SWOUT at the connection point between the switching transistor M1 and the synchronous rectification transistor M2 to the inductor L1. The output voltage Vout is fed back to the feedback terminal P4.

  The control circuit 100 includes a pulse width modulator 10, a driver 20, and a frequency control unit 30 in addition to the switching transistor M1 and the synchronous rectification transistor M2.

The pulse width modulator 10 generates a pulse width modulation (PWM) signal S _PWM that instructs on / off of the switching transistor M1 and the synchronous rectification transistor M2. The pulse width modulator 10 adjusts the duty ratio of the PWM signal S _{PWM so} that the feedback voltage Vfb corresponding to the output voltage Vout of the switching regulator matches the reference voltage Vref.

  The pulse width modulator 10 includes a first resistor R1, a second resistor R2, an error amplifier 12, an oscillator 14, and a PWM comparator 16. The first resistor R1 and the second resistor R2 form a feedback circuit 18 and divide the output voltage Vout to generate a feedback voltage Vfb.

The error amplifier 12 generates an error signal Verr corresponding to the error between the feedback voltage Vfb and the reference voltage Vref. The oscillator 14 generates a triangular wave periodic signal Vosc. The PWM comparator 16 compares the periodic signal Vosc and the error signal Verr, and generates a PWM signal S _PWM having a level corresponding to the comparison result.

The driver 20 drives the switching transistors M1 and M2 based on the PWM signal _SPWM . The assignment of the level of the PWM signal S _PWM and the on / off state of each transistor is arbitrary, but in this embodiment, the low level of the PWM signal S _PWM is on for the switching transistor M1 and off for the synchronous rectification transistor M2. The high level corresponds to the switching transistor M1 being turned off and the synchronous rectification transistor M2 being turned on. A dead time in which the switching transistor M1 and the synchronous rectification transistor M2 are simultaneously turned off is provided for each level transition of the PWM signal _SPWM .

Frequency control unit 30, in response to the coil current _{I L1} flowing to inductor L1 of the switching regulator 4, as the coil current _{I L1} is large, the pulse width modulator 10 so that the frequency of the PWM signal _{S PWM} is high, more specifically The oscillator 14 is controlled.

A current I _M1 corresponding to the coil current I _L1 flows through the switching transistor M1. Therefore, the frequency control unit 30 controls the frequency of the PWM signal S _PWM based on the current I _M1 flowing through the switching transistor M1. For example, a resistance element may be provided in series with the switching transistor M1, and a voltage drop generated in the resistance element may be used as a signal indicating the coil current _IL1 . When the current I _M1 flowing through the switching transistor M1 is used, it is not necessary to acquire a signal indicating the load current Iout from the outside of the control circuit 100. Therefore, the circuit configuration can be simplified and the circuit can be downsized.

The coil current I _L1 may be directly monitored instead of the current I _M1 flowing through the switching transistor M1. In this case, a current detection element such as a resistor may be inserted between the inductor L1 and the switching terminal P3 or between the inductor L1 and the output capacitor Co. Or load current Iout which flows into load 2 also becomes a value according to coil current _IL1 . Therefore, the frequency control unit 30 may control the frequency based on a signal indicating the load current Iout itself.

The above is the configuration of the switching regulator 4. Next, the operation will be described.
2A shows the relationship between the coil current I _L1 and the inductance value of the inductor L1, and FIG. 2B shows the relationship between the coil current I _L1 and the oscillation frequency of the oscillator 14.

As the load current Iout increases, that is, as the coil current _IL1 increases, the inductance value of the inductor L1 decreases. This means that the capability of the switching regulator 4 is reduced. The frequency control unit 30 increases the oscillation frequency fosc of the oscillator 14 and increases the frequency of the PWM signal S _{PWM as} the load current Iout increases.

When the frequency of the PWM signal S _PWM increases, the switching frequency of the switching transistor M1 and the synchronous rectification transistor M2 increases. As a result, a decrease in the inductance value of the inductor L1 accompanying an increase in the load current Iout can be canceled, and a decrease in the capability of the switching regulator 4 can be suppressed.

As shown in (I) of FIG. 2B, the frequency fosc may be continuously controlled according to the coil current _IL1 , and as shown in (II), the frequency fosc is changed to the coil current _IL1 . You may control in steps according to it. (I) has higher efficiency than (II), and (II) has better circuit stability than (I). Therefore, how to set the frequency-current characteristics may be determined in consideration of efficiency and circuit stability.

  The advantage of this switching regulator 4 becomes clear by comparison with a switching regulator having a constant frequency fosc. In a switching regulator with a constant frequency, the inductor L1 is selected so that the load can be driven at the maximum load current Iout_max, that is, in a state where the inductance value of the inductor L1 is small. The inductor L1 thus selected is large. On the other hand, according to the switching regulator 4 of FIG. 1, since the decrease in the inductance value accompanying the increase in the load current Iout is compensated by the frequency control, it is possible to use a coil having a smaller inductance value than the conventional one. This leads to cost reduction and miniaturization of the circuit.

(Second Embodiment)
FIG. 3 is a circuit diagram showing a configuration of the switching regulator 4a according to the second embodiment. The switching regulator 4 in FIG. 1 is a separately excited DC / DC converter using an oscillator, whereas the switching regulator 4a in FIG. 3 is a self-excited type using a hysteresis comparator.

  The pulse width modulator 10a of the control circuit 100a includes a feedback circuit 18a, a hysteresis comparator 22, a second capacitor C2, and a third resistor R3.

  The first resistor R1 and the second resistor R2 are provided in series between the output terminal of the switching regulator 4a and the ground terminal. The first capacitor C1 is connected in parallel with the first resistor R1. The feedback circuit 18a divides the output voltage Vout of the switching regulator 4a to generate a feedback voltage Vfb.

  A hysteresis width is set in the hysteresis comparator 22. The hysteresis comparator 22 receives the feedback voltage Vfb at its first input terminal (−) and receives the reference voltage Vref at its second input terminal (+).

  The third resistor R3 and the second capacitor C2 are provided in series between the output terminal of the hysteresis comparator 22 and the first input terminal (−).

According to this pulse width modulator 10a, a PWM signal _SPWM is generated that goes low when the output voltage Vout reaches a certain upper threshold value and goes high when the output voltage Vout falls to a certain lower threshold value. The

Frequency of the oscillation frequency, i.e. the PWM signal _{S PWM} pulse width modulator 10a is determined by the hysteresis width which is set to the second capacitor C2 and the third resistor R3 and the hysteresis comparator 22. Specifically, the smaller the resistance value of the third resistor R3, the capacitance value of the second capacitor C2, and the hysteresis width of the hysteresis comparator 22, the higher the oscillation frequency fosc.

Therefore, the frequency control unit 30a controls the resistance value of the third resistor R3 according to the coil current _IL1 . The third resistor R3 is a variable resistor, and the resistance value can be switched stepwise or continuously. The frequency controller 30a decreases the resistance value of the third resistor R3 and increases the oscillation frequency fosc as the coil current _IL1 increases.

  Instead of the resistance value of the third resistor R3, the capacitance value of the second capacitor C2 may be switched as a variable capacitor, the hysteresis width of the hysteresis comparator 22 may be switched, or a combination thereof may be used.

  According to the switching regulator 4a of FIG. 3, the same effect as the switching regulator 4 of FIG. 1 can be obtained.

The control circuit 100a in FIG. 3 further includes a constant voltage circuit 50. Constant voltage circuit 50 receives the power supply voltage Vdd, and supplies the power supply terminal of the hysteresis comparator 22 generates a voltage V _REG stabilized it.

The present inventors have studied a self-excited DC / DC comparator using a hysteresis comparator, and have come to recognize the following problems. In this DC / DC converter, the amplitude of the PWM signal S _PWM changes according to the power supply voltage to the hysteresis comparator 22. Thus, if with respect to the hysteresis comparator 22 to supply the power supply voltage Vdd from the external direct power supply voltage Vdd is increased the higher the PWM signal _{S PWM} high level, the PWM signal _{S PWM} high enough supply voltage Vdd is low The level is lowered.

FIG. 4 is a diagram illustrating a relationship between the output voltage Vout of the DC / DC converter using the hysteresis comparator and the power supply voltage Vdd_CMP with respect to the hysteresis comparator. As shown in FIG. 4, when the power supply voltage Vdd_CMP for the hysteresis comparator increases, the output voltage Vout of the switching regulator 4 also increases accordingly. Therefore, a constant voltage circuit 50 is provided, and the output voltage Vout is stabilized as shown by the broken line in FIG. 4 by supplying the stabilized voltage _VREG to the hysteresis comparator 22 regardless of the fluctuation of the power supply voltage Vdd. Can do.

  The constant voltage circuit 50 of FIG. 3 can be suitably combined with the switching regulator 4 of FIGS. 5 and 7 using the hysteresis comparator 22, and these are also included in the embodiments of the present invention.

(Third embodiment)
FIG. 5 is a circuit diagram showing a configuration of a switching regulator 4b according to the third embodiment. The control circuit 100b of FIG. 5 includes a frequency hopping control unit 32 in addition to or instead of the frequency control unit 30 of FIG.

The frequency hopping control unit 32 switches the frequency of the PWM signal S _PWM at a predetermined cycle. The predetermined cycle is a cycle of the PWM signal S _PWM . The frequency hopping control unit 32 receives a PWM signal _SPWM or a pulse signal having a level corresponding to the PWM signal _SPWM . Frequency hopping controller 32, in response to the PWM signal _{S PWM} edge switches the frequency of the PWM signal _{S PWM.} In order to switch the frequency, the resistance value of the third resistor R3 may be switched. Alternatively, the capacitance value of the second capacitor C2 and the hysteresis width of the hysteresis comparator 22 may be switched.

  The frequency may be switched in three stages around a certain reference frequency. Specifically, when the reference frequency is 6 MHz, it may be switched at about ± 200 kHz.

It is desirable to change the frequency randomly. The frequency hopping control unit 32 is a random number generator and has a table that holds pseudo-random numerical values. In this table, three numbers from 0 to 2 are stored pseudo-randomly. Then, the frequency hopping control unit 32 sequentially refers to the values in the table for each edge of the PWM signal S _PWM , and sets the resistance value of the third resistor R3 according to the value. For example, the values 0, 1, and 2 correspond to 5.8 MHz, 6 MHz, and 6.2 MHz, respectively.

The frequency hopping control unit 32 outputs the PWM signal S _PWM in accordance with the timing when the switching transistor M1 is turned off from the state where the switching transistor M1 is on and the synchronous rectification transistor M2 is off, that is, the negative edge timing of the PWM signal _SPWM. Change the frequency. Since the predetermined period after the negative edge of the PWM signal S _PWM is a dead time, the frequency can be switched without impairing the stability of the circuit.
In a variant, it may be switched to the frequency at the timing of the positive edge of the PWM signal _{S PWM.}

Alternatively, it may be switched to the frequency at the timing of both positive and negative edges of the PWM signal S _PWM. In this case, for each half cycle of the PWM signal _{S PWM,} frequency is switched.

The above is the configuration of the switching regulator 4b in FIG. Next, the operation will be described. In the switching regulator 4b of FIG. 5, for each cycle of the PWM signal _{S PWM,} the frequency is switched. Therefore, the spectrum of noise generated by the switching regulator 4b can be diffused, and it becomes easy to take measures against EMI.

For example, in the switching regulator as shown in FIG. 1, in order to perform the same processing, it is necessary to add a dedicated logic circuit for switching the oscillation frequency of the oscillator, and there is a problem that the circuit scale increases. On the other hand, according to the switching regulator 4b of FIG. 5, since it In other cut resistance of the third resistor R3 in response to the PWM signal S _PWM edges, without increasing the circuit scale, realizing frequency hopping it can.

When the delay circuit 24 is provided between the hysteresis comparator 22 and the driver 20, the frequency hopping control unit 32 may control the delay amount of the delay circuit 24 instead of the control of the third resistor R3 and the second capacitor C2. Good. Also in this case, the frequency of the PWM signal S _PWM can be hopped.

  The frequency hopping technique described in the third embodiment can be suitably combined with the switching regulator 4 of FIGS. 3 and 7 using the hysteresis comparator 22.

  6A and 6B are circuit diagrams showing the configuration of the switching regulator according to the modification of FIG. The switching regulator 4c in FIG. 6A includes an operational amplifier 23 and a fifth resistor R5 in addition to the switching regulator 4b in FIG. The operational amplifier 23 amplifies the error between the feedback voltage Vfb and the reference voltage Vref. The fifth resistor R <b> 5 is provided between the output terminal of the operational amplifier 23 and the inverting input terminal of the hysteresis comparator 22. According to the configuration of FIG. 6A, the feedback gain can be adjusted by the resistance value of the fifth resistor R5. In FIG. 6A, the capacitance value of the capacitor C2 may be controlled in order to control and hop the frequency.

In the switching regulator 4 d of FIG. 6B, the output terminal of the operational amplifier 23 is connected to the first input terminal (−) of the hysteresis comparator 22. The second capacitor C2 and the third resistor R3 are provided between the output terminal of the hysteresis comparator 22 and the second input terminal (+). The impedance circuit 19 is connected to the non-inverting input terminal (+) of the hysteresis comparator 22. The impedance circuit 19 includes a third capacitor C3 and a fourth resistor R4. A voltage Vref ′ obtained by dividing the reference voltage Vref and the PWM signal S _PWM by the two impedance circuits 19 and 21 is input to the second input terminal (+) of the hysteresis comparator 22, which corresponds to the feedback voltage Vfb. Feedback is applied to match the output signal of the operational amplifier 23. In FIG. 6B, in order to control and hop the frequency, the capacitance values of the capacitors C2 and C3 or the resistance values of the resistors R3 and R4 may be controlled.

(Fourth embodiment)
The switching regulator of FIG. 3 and FIG. 5, the frequency of the PWM signal _{S PWM} is defined by the capacitor C1, C2, R1, R2, R3. At the same time, these circuit constants define the gain of the feedback loop for stabilizing the output voltage Vout. Therefore, there is a problem that increasing the frequency of the PWM signal S _PWM is not compatible with increasing the loop gain. In the fourth embodiment, a technique for solving this problem will be described. FIG. 7 is a circuit diagram showing a configuration of a switching regulator 4e according to the fourth embodiment.

  The pulse width modulator 10e includes a feedback circuit 18a, a hysteresis comparator 22, an impedance circuit 19, a second capacitor C2, and a third resistor R3.

  The impedance circuit 19 receives the reference voltage Vref and inputs it to the second input terminal (+) of the hysteresis comparator 22. The impedance circuit 19 includes a fourth resistor R4 and a third capacitor C3.

The inverter (buffer) 26 inverts a pulse signal having a logic level corresponding to the output S _PWM of the hysteresis comparator 22. The second capacitor C2 and the third resistor R3 are provided in series between the output terminal of the inverter 26 and the second input terminal (+) of the hysteresis comparator 22.

Instead of the PWM signal _SPWM , the inverter 26 may receive the gate signal of the switching transistor M1 or the signal of the switching terminal P3.

A voltage Vref ′ obtained by dividing the reference voltage Vref and the PWM signal S _PWM by the two impedance circuits 19 and 21 is input to the second input terminal (+) of the hysteresis comparator 22, which matches the feedback voltage Vfb. So take feedback. In this circuit, the loop gain of the DC feedback is determined by the feedback circuit 18a, and the oscillation frequency is defined by the impedance circuits 21 and 19.

  That is, since the oscillation frequency and the feedback loop gain can be designed independently, a high frequency and a high gain can be achieved at the same time.

  The pulse width modulator 10e shown in FIG. 7 can be suitably combined with the switching regulator 4 shown in FIG. 3 or 5 using the hysteresis comparator 22.

  Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate the principles and applications of the present invention, and the embodiments are defined in the claims. Many variations and modifications of the arrangement are permitted without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 2 ... Load, 4 ... Switching regulator, Co ... Output capacitor, L1 ... Inductor, 10 ... Pulse width modulator, 12 ... Error amplifier, 14 ... Oscillator, 16 ... PWM comparator, 18 ... Feedback circuit, 19 ... Impedance circuit, 20 DESCRIPTION OF SYMBOLS ... Driver, 22 ... Hysteresis comparator, 24 ... Delay circuit, 26 ... Inverter, M1 ... Switching transistor, M2 ... Synchronous rectification transistor, 30 ... Frequency control part, 32 ... Frequency hopping control part, 50 ... Constant voltage circuit, 100 ... Control circuit, P1 ... power supply terminal, P2 ... ground terminal, P3 ... switching terminal, P4 ... feedback terminal, R1 ... first resistor, R2 ... second resistor, R3 ... third resistor, R4 ... fourth resistor, C1 ... first 1 capacitor, C2... Second capacitor, C3.

Claims (9)

A control circuit for driving a switching transistor of a switching regulator,
A pulse width modulator that generates a pulse width modulation signal that instructs on / off of the switching transistor, wherein a duty ratio of the pulse width modulation signal is a feedback voltage according to an output voltage of the switching regulator as a reference voltage. A pulse width modulator that adjusts to match,
A driver circuit for driving the switching transistor based on the pulse width modulation signal;
According to the coil current flowing through the inductor of the switching regulator, a frequency control unit that controls the pulse width modulator so that the frequency of the pulse width modulation signal increases as the coil current increases;
With
The pulse width modulator is
A first capacitor connected in parallel with the first resistor; and a first capacitor connected in parallel between the output terminal of the switching regulator and the fixed voltage terminal; and dividing the output voltage of the switching regulator. A feedback circuit for generating the feedback voltage;
A hysteresis comparator that receives the feedback voltage at its first input terminal and a reference voltage at its second input terminal;
A third resistor and a second capacitor provided in series between the output terminal of the hysteresis comparator and the first input terminal;
Including
Wherein the frequency control unit, the third resistor of the resistance value, a capacitance value of the first capacitor, the capacitance value of the second capacitor, system you characterized your control at least one of hysteresis width of said hysteresis comparator circuit. A control circuit for driving a switching transistor of a switching regulator,
A pulse width modulator that generates a pulse width modulation signal that instructs on / off of the switching transistor, wherein a duty ratio of the pulse width modulation signal is a feedback voltage according to an output voltage of the switching regulator as a reference voltage. A pulse width modulator that adjusts to match,
A driver circuit for driving the switching transistor based on the pulse width modulation signal;
A frequency hopping controller that switches the frequency of the pulse width modulation signal at a predetermined period;
With
The pulse width modulator is
A first capacitor connected in parallel with the first resistor; and a first capacitor connected in parallel between the output terminal of the switching regulator and the fixed voltage terminal; and dividing the output voltage of the switching regulator. A feedback circuit for generating the feedback voltage;
A hysteresis comparator that receives the feedback voltage at its first input terminal and a reference voltage at its second input terminal;
A third resistor and a second capacitor provided in series between the output terminal of the hysteresis comparator and the first input terminal;
Including
The frequency hopping control unit controls at least one of a resistance value of the third resistor, a capacitance value of the first capacitor, a capacitance value of the second capacitor, and a hysteresis width of the hysteresis comparator, and controls the pulse width modulation signal. A control circuit characterized by switching the frequency. A delay circuit provided between the pulse width modulator and the driver circuit;
The control circuit according to claim 2 , wherein the frequency hopping control unit controls a delay amount of the delay circuit to switch a frequency of the pulse width modulation signal. The control circuit according to claim 2, wherein the frequency hopping control unit switches the frequency of the pulse width modulation signal for each period of the pulse width modulation signal. The switching regulator is a synchronous rectification type including a synchronous rectification transistor,
The frequency hopping control unit switches the frequency of the pulse width modulation signal from a state where the switching transistor is on and the synchronous rectification transistor is off according to a timing when the switching transistor is turned off. Item 5. The control circuit according to Item 4 . A control circuit for driving a switching transistor of a switching regulator,
A pulse width modulator that generates a pulse width modulation signal that instructs on / off of the switching transistor, wherein a duty ratio of the pulse width modulation signal is a feedback voltage according to an output voltage of the switching regulator as a reference voltage. A pulse width modulator that adjusts to match,
A driver circuit for driving the switching transistor based on the pulse width modulation signal;
With
The pulse width modulator is
A first capacitor connected in parallel with the first resistor; and a first capacitor connected in parallel between the output terminal of the switching regulator and the fixed voltage terminal; and dividing the output voltage of the switching regulator. A feedback circuit for generating the feedback voltage;
A hysteresis comparator that receives the feedback voltage at its first input terminal;
An impedance circuit for receiving a reference voltage and inputting the reference voltage to the second input terminal of the hysteresis comparator;
An inverter for inverting a pulse signal having a logic level according to the output of the hysteresis comparator;
A third resistor and a second capacitor provided in series between the output terminal of the inverter and the second input terminal of the hysteresis comparator;
A control circuit comprising: Control circuit according to any one of claims 1 to 6, characterized by further comprising a constant voltage circuit for supplying a constant voltage stabilized against the hysteresis comparator. Power supply, characterized in that it comprises a control circuit according to any one of claims 1 to 7. An electronic apparatus comprising the power supply device according to claim 8 .

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