JP2011199973A - Switching regulator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching regulator of hysteretic control that prevents malfunction due to noise, without degrading response when a load is rapidly changed.SOLUTION: The switching regulator switch-controls a switch element (1) to step down an input voltage and generates an output voltage. The regulator includes a pseudo ripple generator (6) that generates a target voltage obtained by superimposing a voltage that makes a predetermined time change each time the switch element (1) is turned off on a given reference voltage, a feedback circuit (7) that cuts a high-frequency component contained in the output voltage to generate a feedback voltage, a comparator (8) that compares the feedback voltage with the target voltage, and a certain time trigger circuit (9) that, when the output of the comparator (8) makes a predetermined logical change, makes the output active for a certain time. The switch element (1) performs a switching operation according to the output of the certain time trigger circuit (9).

Description

  The present invention relates to a power supply circuit that supplies a DC voltage to various electronic devices, and more particularly to a step-down switching regulator.

  Generally, a switching regulator is used as a power supply circuit for many electronic devices because it can efficiently convert power. In particular, in a portable device using a battery as an input voltage source, control such as timely changing the power supplied to the electronic circuit according to the usage state is performed in order to enable long-term use. Therefore, there is a need for a switching regulator that responds quickly to changes in usage conditions.

  As a switching regulator capable of high-speed response, there is a ripple regulator as shown in FIG. FIG. 14 shows operation waveforms of the regulator. When the switch element 1 is on, the charging current of the output capacitor 4 flowing through the inductor 3 having the input voltage Vin applied to the input terminal increases, and the output voltage Vout is reduced by the voltage drop at the equivalent series resistance of the output capacitor 4. To rise. When the output voltage Vout reaches the upper limit threshold set in the hysteresis comparator 8, the output of the hysteresis comparator 8 is inverted, the switch element 1 is turned off, and the switch element 2 is turned on. When the switch element 2 is on, the charging current of the output capacitor 4 flowing through the inductor 3 whose input terminal is grounded decreases, and the output voltage Vout decreases due to the voltage drop at the equivalent series resistance of the output capacitor 4. When the output voltage Vout reaches the lower limit threshold set in the hysteresis comparator 8, the output of the hysteresis comparator 8 is inverted, the switch element 2 is turned off, and the switch element 1 is turned on. By repeating the above operation, the switching elements 1 and 2 are controlled using the hysteresis comparator 8 so that the output voltage Vout increases and decreases within a predetermined range. Therefore, no phase compensation is required when an error amplifier is used in the feedback system, the response speed of the feedback system is determined by the response speed of the hysteresis comparator 8, and the response performance as a switching regulator is not the feedback system but the inductor 3 or The output capacitor 8 is bound.

  Thus, the control method using the hysteresis comparator in the feedback system is called hysteresis control or hysteretic control, and can respond at high speed on the principle of operation. On the other hand, in order to prevent malfunction due to the hysteresis comparator responding to surge voltages such as switching noise, the hysteresis width of the hysteresis comparator, that is, the increase / decrease width of the output voltage Vout must be increased. There is a problem that the output ripple voltage increases.

  Therefore, as shown in FIG. 15, the output voltage Vout is compared with the pseudo ripple voltage Vref1 by comparing the pseudo ripple voltage Vref1 obtained by superimposing the voltage having the reverse waveform with the output ripple on the reference voltage Vref with the output voltage Vout. A method of turning on the switch element 1 for a certain period of time has been devised. The switching regulator achieves stable control characteristics without increasing the actual output ripple voltage by giving the pseudo ripple voltage Vref1 sufficient amplitude (see, for example, Patent Document 1).

US Pat. No. 7,202,642

  In the switching regulator having the conventional configuration described above, if the amplitude of the pseudo ripple waveform voltage of the pseudo ripple generator 6 is made larger than the noise of the output voltage Vout, malfunction due to the comparator 8 responding to the noise can be prevented. However, when the amplitude of the pseudo ripple waveform voltage is increased, when the load 5 changes rapidly, the response is delayed because the output voltage Vout does not respond unless the output voltage Vout changes more than the amplitude of the lamp voltage. In view of the problem, an object of the present invention is to provide a hysteretic control switching regulator that prevents malfunction due to noise without deteriorating the response when the load suddenly changes.

  In order to solve the above problems, the present invention has taken the following measures. That is, a switching regulator that performs switching control of a switch element to step down an input voltage to generate an output voltage, and superimposes a voltage that changes for a predetermined time each time the switch element is turned off on a given reference voltage. A pseudo ripple generator for generating a target voltage, a feedback circuit for generating a feedback voltage by cutting a high-frequency component included in the output voltage, a comparator for comparing the target voltage and the feedback voltage, and the comparator And a constant time trigger circuit that activates the output for a predetermined time when the output of the output of the switch has a predetermined logic change, and the switching element performs a switching operation according to the output of the trigger circuit for the predetermined time.

  According to the present invention, it is possible to prevent malfunction due to noise of the output voltage without deteriorating the response when the load suddenly changes.

FIG. 1 is a circuit configuration diagram of the switching regulator according to the first embodiment. FIG. 2 is an operation waveform diagram of the regulator of FIG. FIG. 3 is a circuit configuration diagram of the switching regulator according to the second embodiment. FIG. 4 is a graph showing gain frequency characteristics of the feedback circuit of FIG. FIG. 5 is a circuit configuration diagram of a switching regulator with a compensation circuit. FIG. 6 is a graph showing gain frequency characteristics of the feedback circuit of FIG. FIG. 7 is a circuit configuration diagram of a switching regulator according to the third embodiment. FIG. 8 is a graph showing gain frequency characteristics of the feedback circuit of FIG. FIG. 9 is a circuit configuration diagram of a switching regulator according to the fourth embodiment. FIG. 10 is a graph showing gain frequency characteristics of the feedback circuit of FIG. FIG. 11 is a circuit configuration diagram of a switching regulator according to the fifth embodiment. FIG. 12 is a graph showing gain frequency characteristics of the feedback circuit of FIG. FIG. 13 is a circuit configuration diagram of a conventional ripple regulator. FIG. 14 is an operation waveform diagram of the regulator of FIG. FIG. 15 is a circuit configuration diagram of a conventional switching regulator using a pseudo ripple voltage.

(First embodiment)
FIG. 1 shows a circuit configuration of a switching regulator according to the first embodiment. The switch elements 1 and 2 and the inductor 3 constitute a power stage. The switch elements 1 and 2 are alternately switched according to drive signals having opposite logics. By switching the switch elements 1 and 2 alternately, a pulse waveform having the peak value of the input DC voltage Vin is applied to the input terminal of the inductor 3. An output capacitor 4 is connected to the output terminal of the inductor 3 that is the output of the power stage, the pulse waveform applied to the inductor 3 is averaged, and the DC output voltage Vout is supplied to the load 5.

  The feedback circuit 7 detects the output voltage Vout and removes noise components. Here, the filter characteristic of the feedback circuit 7 needs to be at least a first-order LPF which does not attenuate the phase of the switching frequency or rotate the phase. This is because the ripple of the output voltage Vout cannot be detected correctly and stable control characteristics cannot be obtained if there is an attenuation or phase shift of the switching frequency component.

  The output of the feedback circuit 7 is applied to the negative input terminal of the comparator 8 as a feedback voltage Vfb. A target voltage Vref <b> 1 is applied to the positive input terminal of the comparator 8. The pseudo ripple generator 6 generates a target voltage Vref1 by superimposing a voltage (pseudo ripple waveform voltage) that changes for a predetermined time every time the switch element 1 is turned off on the reference voltage Vref. The output of the comparator 8 becomes a trigger signal of the trigger circuit 9 for a predetermined time. The constant time trigger circuit 9 makes the output active (H level) for a fixed time when the output of the comparator 8 becomes H level. The output of the trigger circuit 9 for a certain time becomes a drive signal for the switch elements 1 and 2.

  FIG. 2 shows operation waveforms of the switching regulator according to the present embodiment. When the switch element 1 is on and the switch element 2 is off, the target voltage Vref1 has a negative slope, and when the switch element 1 is off and the switch element 2 is on, the target voltage Vref1 has a positive slope. When the feedback voltage Vfb becomes lower than the target voltage Vref1, the comparator 8 outputs a trigger signal to the trigger circuit 9 for a predetermined time. The fixed time trigger circuit 9 outputs a drive signal for turning on the switch element 1 for a fixed on time Ton.

  With the configuration and operation as described above, the switching regulator according to the present embodiment can prevent the malfunction due to the noise of the output voltage Vout by removing the noise of the output voltage Vout by the feedback circuit 7.

  Note that the ripple regulator of FIG. 13 provides the same effect as described above by providing the feedback circuit 7. When synchronous rectification is not required, a diode may be used instead of the switch element 2.

(Second Embodiment)
FIG. 3 shows a circuit configuration of the switching regulator according to the second embodiment. The schematic configuration of the switching regulator according to this embodiment is the same as that of the first embodiment. The feedback circuit 7 includes resistance elements 71 and 72 connected in series between the output voltage Vout and the ground, and a capacitor 77 connected between the connection point of these resistance elements and the ground. The feedback circuit 7 detects the output voltage Vout by resistance division of the resistance elements 71 and 72 and removes high frequency noise of the output voltage Vout by a primary LPF by the resistance elements 71 and 72 and the capacitor 77. FIG. 4 shows the gain frequency characteristic of the feedback circuit 7. The feedback circuit 7 removes high-frequency noise from the output voltage Vout so as not to affect the switching frequency component, and feeds it back to the comparator 8, thereby stably controlling the output voltage Vout of the switching regulator and outputting the output voltage. It is possible to prevent malfunction due to high frequency noise of Vout.

(Third embodiment)
In the configuration of the switching regulator according to the second embodiment, even if the capacitor 77 is omitted, the parasitic LPF is actually configured by the parasitic capacitor and the resistance elements 71 and 72 in parallel with the feedback voltage Vfb. Furthermore, the resistance elements 71 and 72 tend to be set to a high resistance value due to the recent demand for low power consumption. For this reason, if the cutoff frequency of the parasitic LPF becomes lower than the switching frequency, the ripple of the output voltage Vout cannot be detected correctly, and stable control characteristics cannot be obtained. Therefore, by connecting the capacitor 75 in parallel to the resistance element 71 as shown in FIG. 5, the gain in the switching frequency region can be compensated and the output voltage Vout can be stably controlled. Note that the capacitor 77 'in the figure is a parasitic capacitor. FIG. 6 shows gain frequency characteristics of the feedback circuit 7. A zero point by the capacitor 75 is set in a lower frequency region than the cutoff frequency by the parasitic capacitor 77 ′, and a gain at the switching frequency can be obtained.

  However, since such a compensation circuit increases the overall high frequency gain, there is also a problem of inducing a malfunction due to high frequency noise. The switching regulator according to the third embodiment is for solving such a problem.

  FIG. 7 shows a circuit configuration of a switching regulator according to the third embodiment. The schematic configuration of the switching regulator according to this embodiment is the same as that of the first embodiment. The feedback circuit 7 includes resistance elements 71, 72, 73 connected in series between the output voltage Vout and the ground, and a capacitor 75 connected in parallel to the resistance element 72. The capacitor 75 may be connected in parallel to the resistance element 71. The feedback circuit 7 detects the output voltage Vout by resistance division of the resistance elements 71, 72, and 73. The voltage at the connection point of the resistance elements 72 and 73 becomes the feedback voltage Vfb. The filter characteristic of the feedback circuit 7 has two poles and one zero point as shown in FIG. 8 when the parasitic capacitor 77 'is taken into consideration. That is, according to the present embodiment, by adding one pole to the filter characteristic of FIG. 6 to obtain a filter characteristic having two poles and one zero point, the compensation circuit as described above increases the high frequency gain. Can be eliminated, and malfunction due to high frequency noise can be prevented.

(Fourth embodiment)
FIG. 9 shows a circuit configuration of a switching regulator according to the fourth embodiment. The schematic configuration of the switching regulator according to this embodiment is the same as that of the first embodiment. The feedback circuit 7 includes resistance elements 71, 72, 73, 74 connected in series between the output voltage Vout and the ground, a capacitor 75 connected in parallel to the resistance element 72, and a capacitor 76 connected in parallel to the resistance element 73. It has. The capacitor 75 may be connected in parallel to the resistance element 71. The capacitor 76 may be connected in parallel to the resistance element 74. The feedback circuit 7 detects the output voltage Vout by resistance division of the resistance elements 71, 72, 73, and 74. The voltage at the connection point of the resistance elements 72 and 73 becomes the feedback voltage Vfb. Here, each resistance is set such that one pole and one zero point formed by the resistance elements 71 and 72 and the capacitor 75 are offset by one pole and one zero point formed by the resistance elements 73 and 74 and the capacitor 76. The characteristic values of the element and each capacitor are adjusted.

  FIG. 10 shows the gain frequency characteristic of the feedback circuit 7. When the resistance values of these resistance elements are increased in order to reduce the current flowing through the resistance elements 71, 72, 73, 74, the impedance of the feedback circuit 7 will increase if the capacitors 75, 76 are not provided, and the parasitic capacitor 77 '. The cutoff frequency of the parasitic LPF constituted by the above may be lower than the switching frequency, and the operation of the switching regulator may become unstable. On the other hand, by providing the capacitors 75 and 76, the impedance of the feedback circuit 7 becomes sufficiently low, and the cutoff frequency of the parasitic LPF can be increased. By adjusting the characteristics of the parasitic LPF so as not to affect the component of the switching frequency, it is possible to stably control the output voltage Vout and prevent malfunction due to high frequency noise of the output voltage Vout.

(Fifth embodiment)
FIG. 11 shows a circuit configuration of a switching regulator according to the fifth embodiment. The schematic configuration of the switching regulator according to this embodiment is the same as that of the first embodiment. The feedback circuit 7 of the switching regulator according to this embodiment is obtained by adding a twin T-type notch filter 78 between the output voltage Vout and the resistance element 71 in the feedback circuit 7 of the switching regulator according to the second embodiment. . The twin T-type notch filter 78 functions as a BEF. Here, the reject center frequency of the BEF is adjusted to be close to the frequency of the switching noise. The capacitor 77 may be omitted.

  FIG. 12 shows the gain frequency characteristic of the feedback circuit 7. Switching noise is effectively removed by the twin T-type notch filter 78. Thereby, it is possible to stably control the output voltage Vout and to effectively prevent malfunction due to high frequency noise of the output voltage Vout.

  The switching regulator according to the present invention can prevent malfunction due to noise in the output voltage without deteriorating the response when the load suddenly changes, and thus requires a high-speed response and supplies a DC voltage to various electronic devices. This is useful for a step-down power supply circuit.

DESCRIPTION OF SYMBOLS 1 Switch element 2 Switch element 6 Pseudo ripple generator 7 Feedback circuit 71 Resistance element (1st resistance element)
72 resistance element (second resistance element)
73 resistance element (third resistance element)
74 resistance element (fourth resistance element)
75 Capacitor 76 Capacitor 77 Capacitor 78 Twin T-type Notch Filter 8 Comparator 9 Trigger Circuit for a Fixed Time

Claims (5)

A switching regulator that performs switching control of a switch element to step down an input voltage and generate an output voltage,
A pseudo ripple generator that generates a target voltage in which a voltage that changes for a predetermined time each time the switching element is turned off to a given reference voltage;
A feedback circuit that generates a feedback voltage by cutting a high-frequency component contained in the output voltage;
A comparator for comparing the target voltage and the feedback voltage;
A fixed time trigger circuit that activates the output for a fixed time when the output of the comparator has a predetermined logic change;
The switching regulator performs a switching operation according to an output of the trigger circuit for a predetermined time. The switching regulator of claim 1,
The feedback circuit includes:
First and second resistance elements connected in series between the output voltage and ground;
A capacitor connected between a connection point of the first and second resistance elements and a ground;
A switching regulator that outputs the feedback voltage from a connection point of the first and second resistance elements. The switching regulator of claim 1,
The feedback circuit includes:
A twin T-type notch filter to which the output voltage is input;
First and second resistance elements connected in series between the output of the twin T-type notch filter and the ground;
A switching regulator that outputs the feedback voltage from a connection point of the first and second resistance elements. The switching regulator of claim 1,
The feedback circuit includes:
First, second and third resistance elements connected in series between the output voltage and ground;
A capacitor connected in parallel to one of the first and second resistance elements,
A switching regulator that outputs the feedback voltage from a connection point of the second and third resistance elements. The switching regulator of claim 4,
The feedback circuit includes:
A fourth resistance element connected between the third resistance element and the ground;
A switching regulator comprising: a capacitor connected in parallel to one of the third and fourth resistance elements.

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