JP6528611B2 - Control circuit and switching power supply - Google Patents

Description

  The present invention relates to a control circuit that controls an output voltage and a switching power supply.

The switching power supply apparatus is known to have a soft start function for gradually raising the output voltage in order to prevent an inrush current at startup.
For example, in Patent Document 1 below, the capacitor voltage for soft start is charged to the same level as the triangular wave for PWM instantaneously from the start of start, thereby shortening the period from the start of start to the start of output voltage rise. .

  Further, in Patent Document 2 below, the period from the start of the start to the start of the rise of the output voltage is shortened by increasing the soft start voltage from the start of start to the rapid detection of the PWM pulse signal.

International Publication No. WO 2005/101629 JP, 2013-240159, A

  However, in these control methods, when a capacitor with a large capacitance is used in the control circuit of the switching power supply, it takes time until the voltage of the capacitor is charged from 0 V to the steady state value. It takes time for the voltage to reach the target value.

  The present invention has been made in view of the problems of the prior art, and it is an object of the present invention to provide a control circuit and a switching power supply in which an output voltage can reach a target value in a short time at startup.

  In order to solve the above problems, a control circuit according to the present invention includes a capacitive element, a switch element connected to the capacitive element, and an output voltage detection circuit, and the output voltage detection circuit is an output voltage of the switching power supply device. Is compared with a predetermined value, and when the output voltage is lower than the predetermined value, the switch element is shorted to charge the capacitive element, and when the output voltage is higher than the predetermined value, the switch element is opened.

  As a result, when using a capacitor with a large capacitance in the control circuit of the switching power supply, the switch element charges in a short time from 0 V to a steady-state value at start-up, so the time until the output voltage reaches the target value at start-up It does not cost.

  The control circuit according to the present invention includes a capacitive element, a switch element connected to the capacitive element, and an output voltage detection circuit, and the output voltage detection circuit shorts the switch element at startup of the switching power supply and starts the capacitive element. After charging, the output voltage of the switching power supply is compared with a predetermined value, and when the output voltage is high, the switch element is opened.

As a result, when using a capacitor with a large capacitance in the control circuit of the switching power supply, the switch element charges in a short time from 0 V to a steady-state value at start-up, so the time until the output voltage reaches the target value at start-up It does not cost. In addition, since the switch element is not short-circuited twice after the start-up period ends, the output voltage is reduced during steady-state operation and the switch element is not short-circuited to increase the output voltage ripple.
Therefore, since the predetermined value for comparing the output voltage can be set high, the capacitor voltage can be made close to the output voltage at the steady state value, and the time for the output voltage to reach the target value at startup can be obtained. It can be shortened.

  In the control circuit according to the present invention, the capacitive element may be connected to the output terminal of the switching power supply device. Thereby, the output voltage of the switching power supply can be stabilized by the capacitive element.

In the control circuit according to the present invention, the first resistor and the second resistor for dividing the output voltage of the switching power supply device, and the voltage divided by the first resistor and the second resistor are input to the first input terminal. And a control unit that controls the switching transistor based on an output signal of the comparator, wherein the reference voltage input to the second input terminal of the comparator is This is the first voltage when the output of the comparator is at the first level, the second voltage when the output of the comparator is at the second level, and the first resistor is the positive terminal of the output terminal of the switching power supply device. The capacitive element may be connected between the first input terminals of the comparator and in parallel with the first resistor.

  As a result, by rapidly charging the capacitive element connected in parallel to the voltage dividing resistor at the time of startup, it is possible to shorten the time until the output voltage reaches the target value at startup.

  In the control circuit according to the present invention, the first resistor and the second resistor for dividing the output voltage of the switching power supply device, and the voltage divided by the first resistor and the second resistor are input to the first input terminal. And a control unit for controlling the switching transistor based on the output voltage level of the error amplifier, and the capacitive element is the output terminal of the error amplifier and the first of the error amplifier. It may be inserted between the input terminals of.

  Thus, by rapidly charging the capacitive element for integration that feeds back the output of the error amplifier to the input at the time of start-up, it is possible to shorten the time until the output voltage reaches the target value at the time of start-up.

  In the control circuit according to the present invention, the output voltage detection circuit inputs the third and fourth resistors for dividing the output voltage of the switching power supply, the second comparator, and the reference voltage to the second comparator. A reference voltage source may be included.

  As a result, the time until the output voltage reaches the target value can be shortened at startup, and the output voltage detection circuit can be configured with a simple configuration.

  In the control circuit according to the present invention, the output voltage detection circuit may further include a flip flop circuit and a signal source connected to the flip flop circuit.

  As a result, the time until the output voltage reaches the target value can be shortened at startup, and the output voltage detection circuit can be configured with a simple configuration.

  According to the present invention, it is possible to provide a control circuit and a switching power supply in which an output voltage can reach a target value in a short time at startup.

FIG. 1 is a circuit diagram showing a configuration of a switching power supply device according to a first embodiment of the present invention. It is a circuit diagram showing composition of a switching power supply concerning a second embodiment of the present invention. It is a circuit diagram showing composition of a switching power supply concerning a third embodiment of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described. The subject matter of the present invention is not limited to the following embodiments. The constituent elements described below include those which can be easily conceived by those skilled in the art, and substantially the same ones, and the constituent elements can be combined appropriately.

  Embodiments of the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

(Embodiment 1)
FIG. 1 is a circuit diagram showing a configuration of a switching power supply device 1a according to a first embodiment of the present invention. As an example, the switching power supply device 1a shown in FIG. 1 has a pair of input terminals 2a and 2b (hereinafter, also referred to as "input terminal 2" when not particularly distinguished) and a pair of output terminals 3a and 3b (hereinafter, not particularly distinguished) The main circuit 4 and the control circuit 10a are also provided. The input voltage (DC voltage) V1 input to the input terminal 2 is converted to an output voltage (DC voltage) V2 and output from the output terminal 3 At the same time, the output voltage V2 is controlled to a predetermined target voltage. The switching power supply 1a inputs an input voltage V1 and an input current i1 to an input terminal 2 and outputs an output voltage V2 and a load current i2 from an output terminal 3.

  The main circuit 4 includes a switching transistor 5, a diode 6, a choke coil 7, and an output capacitor 8. As an example of the switching power supply device 1 a, it is configured by a circuit system of a buck converter, and converts an input voltage V1 input from the input terminal 2 into an output voltage V2 and outputs the output voltage V2 to the output terminal 3.

  In the control circuit 10a, the first resistor 20 and the second resistor 21 for dividing the output voltage V2 of the switching power supply device 1a, and the divided voltage Vn is inputted to the first inverting input terminal, and the second non-inverting input Based on a comparator 22 in which a reference voltage Vp is input to the terminal, a current detection circuit 9 for detecting a current iL flowing in the choke coil 7, an output signal Vco of the comparator 22 and a current value detected by the current detection circuit 9. And a control unit 30 that controls the switching transistor 5. The control circuit 10 a includes a first resistor 20 connected between the positive electrode 3 a of the output terminal and the first inverting input terminal of the comparator 22, and a capacitive element 11 connected in parallel to the first resistor 20. The common ground G of the control circuit 10a is connected to the negative electrode 3b of the output terminal. The voltage of each of the signals Vn, Vp, and Vco is a voltage based on the common ground G.

  The reference voltage Vp is the first high voltage VpH when the output Vco of the comparator 22 is the first high level, and the second low voltage when the output Vco of the comparator 22 is the second low level. It becomes VpL. The comparator 22 is a so-called hysteresis comparator, and as an example of a circuit configuration using this hysteresis comparator, the comparator 22, a resistor 23 connected between the output terminal of the comparator 22 and a noninverting input terminal, and a noninverting input A resistor 24 and a constant voltage source 25 connected in series between the terminal and the common ground G are provided.

  Next, the operation of the control circuit 10a will be described. When the voltage Vn obtained by dividing the output voltage V2 by resistance becomes lower than the second voltage VpL, the comparator output Vco becomes the first high level, and the control unit 30 starts driving the switching transistor 5, and the reference voltage is the first The voltage VpH of the The current of the choke coil 7 increases during the driving period of the switching transistor 5, and the current iL larger than the load current i2 is supplied from the choke coil 7 to the output capacitor 8 to charge the output capacitor 8 and output voltage V2 To rise. When the voltage Vn obtained by resistance-dividing the output voltage V2 becomes higher than the first voltage VpH, the comparator output Vco becomes a second low level, and the driving period is ended to become a pause period. At this time, the reference voltage is the second voltage VpL. Since the load current i2 is larger than the current iL from the choke coil 7 during the idle period, the output capacitor 8 is discharged to reduce the output voltage V2. When the voltage Vn obtained by dividing the output voltage V2 again by resistance becomes lower than the second voltage VpL, the driving period starts again, and the reference voltage becomes the first voltage VpH. By repeating this operation, the drive period and the idle period are controlled so that the resistance divided voltage Vn becomes a value between the first voltage VpH and the second voltage VpL, and the output voltage V2 is specified in advance. Control to the set target voltage.

  Furthermore, by connecting the capacitive element 11 to the first resistor 20, the voltage across the first resistor 20 is stabilized to a substantially constant value Vr1. As a result, the voltage Vn at the inverting input terminal of the comparator 22 becomes a value obtained by subtracting a constant Vr1 from the output voltage V2, so that the voltage ripple of Vn becomes equal to the voltage ripple of the output voltage V2. The control circuit 10a controls the drive period and the idle period so that Vn becomes a value between VpL and VpH, and controls the output voltage V2 to a predetermined target voltage. Therefore, the voltage ripple of Vn becomes equal to the difference VpH-VpL between the first voltage and the second voltage, and the magnitude of the voltage ripple of the output voltage V2 also becomes VpH-VpL.

  Further, by sufficiently increasing the capacitance of the capacitive element 11, Vr1 can be further stabilized, and static load fluctuation of the output voltage V2 can be reduced.

  However, when the capacitance of the capacitive element 11 is increased, it takes time for the voltage Vr1 across the capacitor 11 to be charged from 0 V at startup to a steady value. The steady-state value of Vr1 is Vr1 = V2 × R1 / (R1 + R2), where R1 is the resistance value of the first resistor 20 and R2 is the resistance value of the second resistor 21. At this time, the output voltage V2 is controlled to the target value Vp × (R1 + R2) / R2 such that Vn = V2−Vr1 becomes equal to Vp. Since Vn = V2−Vr1 is controlled to be equal to Vp even during a period when Vr1 at startup is lower than the steady value, V2 is lower than the target value. If the period in which Vr1 is lower than the steady value lasts for a long time at startup, the period during which the output voltage does not reach the target value at startup will continue for a long time.

  Charging of the capacitive element 11 at the time of start-up is performed along a path from the output terminal positive electrode 3a to the capacitive element 11 and the second resistor 21. The capacitance of the capacitive element 11 is large and the resistance value R2 of the second resistor 21 is large. It takes a long time to charge. Since the output voltage V2 is divided by the first resistor 20 and the second resistor 21, particularly when the output voltage V2 is high, it is necessary to suppress power consumption as a large resistance value of R1 and R2.

  Therefore, the switch element 12 connected in parallel to the second resistor 21 and the output voltage detection circuit 13 are provided in order to charge the capacitive element 11 at startup. The output voltage detection circuit 13 includes a comparator 14 that is a second comparator, a second reference voltage source 15 that inputs a reference voltage to the comparator 14, and a resistor 16 that is a third resistor that divides the output voltage V2. And the fourth resistor, the voltage source 15 is input to the non-inverting input terminal of the comparator 14, and the voltage obtained by dividing the output voltage V2 by the resistors 16 and 17 at the inverting input terminal of the comparator 14 Is input. The output terminal of the comparator 14 drives the switch element 12. The output voltage V2 of the switching power supply device 1a is compared with a predetermined value determined by the voltage division ratio of the resistors 16 and 17 and the voltage source 15 to short the switch element 12 when the output voltage V2 is low. The switch element 12 is opened when the output voltage V2 is high.

  Further, during a period in which the switch element 12 is shorted and the capacitive element 11 is charged rapidly, the output Vco of the comparator 22 is at the first high level, and the current value detected by the current detection circuit 9 is The control unit 30 controls the switching transistor 5 such that the set maximum value is obtained.

  Thereby, at the time of start-up when the output voltage V2 is lower than a predetermined value, charging of the capacitive element 11 is performed in a path passing from the output terminal positive electrode 3a to the capacitive element 11 and the switch element 12, and the capacitance of the capacitive element 11 is Even if it is large, it can be charged rapidly, so the time for the output voltage V2 to reach the target value can be shortened at startup.

Second Embodiment
FIG. 2 is a circuit diagram showing a configuration of a switching power supply 1b according to a second embodiment of the present invention. The switching power supply 1b shown in FIG. 2 differs from the switching power supply 1a according to the first embodiment of FIG. 1 in the configuration of the output voltage detection circuit 13. The output voltage detection circuit 13 b includes a comparator 14, a voltage source 15, a resistor 16 that divides the output voltage V 2, a resistor 17, an RS flip flop 18, and a signal source 19.

  The voltage obtained by dividing the output voltage V2 by the resistors 16 and 17 is input to the noninverting input terminal of the comparator 14, the voltage source 15 is input to the inverting input terminal of the comparator 14, and the output of the comparator 14 is RS Input to reset input terminal of flip flop 18. The signal source 19 is input to the set input terminal of the RS flip flop 18, and the output of the RS flip flop 18 drives the switch element 12. The signal source 19 sets the output of the RS flip flop 18 to high level by being high level only for a short period immediately after start-up. Therefore, the switch element 12 is short-circuited at start-up, and the capacitive element 11 is rapidly charged as in the first embodiment of FIG.

  Since the output voltage V2 is low at startup, the voltage obtained by dividing the output voltage V2 by the resistors 16 and 17 is lower than that of the voltage source 15, and the output of the comparator 14 is at the low level. When the output voltage V2 reaches a predetermined voltage, the voltage obtained by dividing the output voltage V2 by the resistors 16 and 17 becomes higher than that of the voltage source 15, and the output of the comparator 14 becomes high level. The output of the prop 18 is reset to low level, and the switch element 12 is open.

  Thereby, at the time of start-up when the output voltage V2 is lower than a predetermined value, charging of the capacitive element 11 is performed in a path passing from the output terminal positive electrode 3a to the capacitive element 11 and the switch element 12, and the capacitance of the capacitive element 11 is Even if it is large, it can be charged rapidly, so the time for the output voltage V2 to reach the target value can be shortened at startup.

  In addition, since the switch element 12 is not short-circuited twice after the start-up period ends, the output voltage ripple does not increase because the switch element 12 is short-circuited because the output voltage V2 decreases during steady operation. Therefore, since the predetermined value for comparing the output voltage V2 can be set high, the capacitor voltage Vr1 can be close to the output voltage at the steady state value, and the output voltage V2 reaches the target value at startup. Time can be shortened.

(Embodiment 3)
FIG. 3 is a circuit diagram showing the configuration of a switching power supply 1c according to a third embodiment of the present invention. The switching power supply 1c shown in FIG. 2 differs from the switching power supply 1b according to the second embodiment of FIG. 2 in the configuration of the control circuit 10c. A first resistor 20 and a second resistor 21 for dividing the output voltage V2 of the switching power supply device 1c, an error amplifier 26, a voltage source 25, a resistor 27, a capacitive element 11c, a current detection circuit 9, and a control unit 30c. , The switch element 12, and the output voltage detection circuit 13b similar to that of FIG.

  The voltage divided by the first resistor 20 and the second resistor 21 is input to the first input terminal which is the inverting input terminal of the error amplifier 26, and the voltage source 25 is supplied to the first input terminal which is the noninverting input terminal. The control unit 30 c controls the switching transistor 5 based on the output voltage level Va of the error amplifier 26 and the current value detected by the current detection circuit 9.

  Integration of the error between the output voltage V2 and the target voltage is performed by the resistor 27 and the capacitive element 11c connected between the output terminal of the error amplifier 26 and the inverting input terminal. When integration of a large time constant is performed, the capacitance of the capacitive element 11c becomes large.

  However, when the capacitance of the capacitive element 11c is increased, it takes time for the voltage V11 across the capacitor 11c to be charged from 0 V at startup to a steady value. The steady-state value of V11 is a value Va0−Vp obtained by subtracting the non-inverting input terminal voltage Vp of the error amplifier 26 from the output voltage level Va0 of the error amplifier 26 when the output voltage V2 is stabilized at the target voltage The charging current i11 of the capacitive element 11c is zero. At this time, assuming that the resistance value of the first resistor 20 is R1, the resistance value of the second resistor 21 is R2, and the resistance value of the resistor 27 is R3, the output voltage V2 is set to a target value Vp × (Vn is equal to Vp). It is controlled to R1 + R2) / R2.

  While V11 at startup is lower than the steady state value, V2 is lower than the target value. Since V11 is lower than the steady-state value, a current of i11 = (Va-Vp-V11) / R3 flows as the charging current i11 of the capacitive element 11c, and this current also flows to the second resistor 21, so the output voltage V2 is lower than the target value determined by the voltage division ratio by R1 * i11 = (Va-Vp-V11) R1 / R3. Because the capacitance of the capacitive element 11c is large, if a period in which V11 is lower than the steady value continues for a long time at startup, a period in which the output voltage V2 does not reach the target value for startup continues for a long time.

  Therefore, in order to shorten the charging period of the capacitive element 11c at the time of startup, the switch element 12 connected in parallel to the second resistor 21 and the output voltage detection circuit 13b are provided. As in the second embodiment of FIG. 2, the output voltage detection circuit 13b short-circuits the switch element 12 at the time of start-up to charge the capacitive element 11c, and when the output voltage V2 becomes higher than a predetermined voltage Open.

  Further, during a period in which the switch element 12 is short circuited to rapidly charge the capacitive element 11 c, the output Va of the error amplifier 26 is at a high voltage level, and the current value detected by the current detection circuit 9 is set. The control unit 30c controls the switching transistor 5 so as to obtain the maximum value.

  Thus, when the output voltage V2 is lower than a predetermined value, charging of the capacitive element 11c is performed from the output terminal of the error amplifier 26 through the capacitive element 11c and the switch element 12, and electrostatics of the capacitive element 11c are performed. Even when the capacity is large, the battery can be charged rapidly, so the time for the output voltage V2 to reach the target value can be shortened at startup.

  Although the output voltage detection circuit 13b of the third embodiment has been described as having the same configuration as the output voltage detection circuit 13b of the second embodiment, the output voltage detection circuit 13b may have the same configuration as the output voltage detection circuit 13 of the first embodiment. it can.

  As mentioned above, although the control circuit and switching power supply device of one embodiment of the present invention were explained, it is not limited to explanation of the above-mentioned embodiment, but various modification implementation is possible.

  For example, although the switching power supply device has been described by exemplifying a buck converter, the present invention is not limited to this, and can be applied to various switching power supply devices such as a forward converter and a push-pull converter.

DESCRIPTION OF SYMBOLS 1 ... Switching power supply device 2 ... Input terminal 3 ... Output terminal 4 ... Main circuit 5 of switching power supply device 5 ... Switching transistor 6 ... Diode 7 ... Choke coil 8 ... Output capacitor 9: Current detection circuit 10: Control circuit of switching power supply device 11: Capacitive element 12: Switch element 13: Output voltage detection circuit 14: Error amplifier 15: Voltage Source 16, 17, 20, 21, 23, 24, 27 ... Resistor 18 ... RS flip flop 19 ... Signal source 22 ... Comparator 26 ... Error amplifier 30 ... Control part

Claims (8)

A control circuit of the switching power supply,
A first resistor and a second resistor that divide an output voltage of the switching power supply device;
A comparator in which a voltage divided by the first resistor and the second resistor is input to a first input terminal and a reference voltage is input to a second input terminal;
A control unit that controls the switching transistor based on an output signal of the comparator;
A capacitive element connected in parallel to the first resistor connected between the positive electrode of the output terminal of the switching power supply and the first input terminal of the comparator ;
A switch element connected to the capacitive element;
Equipped with an output voltage detection circuit,
The reference voltage input to the second input terminal of the comparator is the first voltage when the output of the comparator is at the first level, and the reference voltage when the output of the comparator is at the second level The second voltage,
The output voltage detection circuit compares the output voltage of the switching power supply with a predetermined value, and when the output voltage is lower than the predetermined value, the switch element is shorted to charge the capacitive element, A control circuit characterized in that the switch element is opened when the output voltage is higher than the predetermined value. A control circuit of the switching power supply,
A first resistor and a second resistor that divide an output voltage of the switching power supply device;
A comparator in which a voltage divided by the first resistor and the second resistor is input to a first input terminal and a reference voltage is input to a second input terminal;
A control unit that controls the switching transistor based on an output signal of the comparator;
A capacitive element connected in parallel to the first resistor connected between the positive electrode of the output terminal of the switching power supply and the first input terminal of the comparator ;
A switch element connected to the capacitive element;
Equipped with an output voltage detection circuit,
The reference voltage input to the second input terminal of the comparator is the first voltage when the output of the comparator is at the first level, and the reference voltage when the output of the comparator is at the second level The second voltage,
The output voltage detection circuit shorts the switch element at the start of the switching power supply to charge the capacitive element, and the output voltage of the switching power supply is compared with a predetermined value, and the output voltage is the predetermined value. A control circuit characterized by opening the switch element if higher than the value of. The control circuit according to claim 1, wherein the capacitive element is connected to an output terminal of the switching power supply device. A control circuit of the switching power supply,
A first resistor and a second resistor that divide an output voltage of the switching power supply device;
An error amplifier in which a voltage divided by the first resistor and the second resistor is input to a first input terminal and a reference voltage is input to a second input terminal;
A control unit that controls the switching transistor based on the output voltage level of the error amplifier;
A capacitive element inserted between the output terminal of the error amplifier and the first input terminal of the error amplifier ;
A switch element connected to the capacitive element;
Equipped with an output voltage detection circuit,
The output voltage detection circuit compares the output voltage of the switching power supply with a predetermined value, and when the output voltage is lower than the predetermined value, the switch element is shorted to charge the capacitive element, A control circuit characterized in that the switch element is opened when the output voltage is higher than the predetermined value. A control circuit of the switching power supply,
A first resistor and a second resistor that divide an output voltage of the switching power supply device;
An error amplifier in which a voltage divided by the first resistor and the second resistor is input to a first input terminal and a reference voltage is input to a second input terminal;
A control unit that controls the switching transistor based on the output voltage level of the error amplifier;
A capacitive element inserted between the output terminal of the error amplifier and the first input terminal of the error amplifier ;
A switch element connected to the capacitive element;
Equipped with an output voltage detection circuit,
The output voltage detection circuit shorts the switch element at the start of the switching power supply to charge the capacitive element, and the output voltage of the switching power supply is compared with a predetermined value, and the output voltage is the predetermined value. A control circuit characterized by opening the switch element if higher than the value of.     The output voltage detection circuit includes a third resistor and a fourth resistor that divides an output voltage of the switching power supply device, a second comparator, and a reference voltage source that inputs a reference voltage to the second comparator. The control circuit according to any one of claims 1 to 5, characterized in that:     The control circuit according to claim 6, wherein the output voltage detection circuit further includes a flip flop circuit and a signal source connected to the flip flop circuit. A switching power supply device comprising the control circuit according to any one of claims 1 to 7.

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