Switching regulator

Abstract

To provide a switching regulator with a slow start circuit capable of generating reference voltage which gradually increases without requiring a frequency dividing circuit for frequency-dividing a high frequency clock signal.SOLUTION: A slow start circuit is configured of a comparator 70, a counter 50, and a slow-start reference voltage circuit 60, and achieves a slow start function so that output voltage Vout of a switching power supply circuit 20 gradually increases. The comparator 70 compares feedback voltage Vfb obtained by resistance-dividing output voltage Vout with reference voltage Vref. The counter 50 counts logic change of the comparator 70 and outputs a count value to the slow start reference voltage circuit 60. The slow start reference voltage circuit 60 supplies voltage which increases according to an increase of the count value of the counter 50 to the comparator 70 and an error amplifier 42 as slow start reference voltage Vref.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a switching regulator. [Background technology]

[0002] In a switching regulator, which converts an input DC voltage into a set DC voltage and outputs it as an output voltage, a slow start circuit (also called a soft start circuit) is used to gradually increase the output voltage in order to suppress output voltage overshoot and prevent a large inrush current from flowing (see, for example, Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-288054 A [Patent Document 2] JP 2017-060383 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the switching regulator described above, when a PWM (Pulse Width Modulation) method is used as a switching control method, a high-frequency clock signal is used for switching control. In addition, in the slow-start circuit, a circuit configuration may be used in which the number of input clock signals is counted by a counter and a reference voltage corresponding to the count value is output to generate a reference voltage for slow start that gradually increases. However, the frequency of the high-frequency clock signal used for switching control is too high for the clock signal used in the slow-start circuit. Therefore, it is necessary to divide the frequency of the high-frequency clock signal by a frequency divider circuit to generate a low-frequency clock signal, which is then used to generate a reference voltage for slow start in the slow-start circuit.

[0005] However, the frequency divider circuit is large in circuit scale and occupies a large area when configured as a semiconductor device. Therefore, if a slow start circuit can be configured without the need for a frequency divider circuit for dividing the frequency of a high-frequency clock signal, it is possible to reduce the circuit scale and the area occupied by the semiconductor device.

[0006] An object of the present invention is to provide a switching regulator equipped with a slow-start circuit capable of generating a reference voltage that gradually increases without requiring a frequency divider circuit for dividing a high-frequency clock signal. [Means for solving the problem]

[0007] In order to solve the above problems, the switching regulator of the present invention comprises: a switching power supply circuit that converts an input DC voltage into a preset DC voltage by switching control and outputs the converted DC voltage as an output voltage; a control circuit that controls an operation of the switching power supply circuit based on an input clock signal; a slow-start circuit for operating the control circuit so as to increase an output voltage of the switching power supply circuit, the slow-start circuit having a comparator for comparing a feedback voltage obtained by resistively dividing the output voltage of the switching power supply circuit with a reference voltage, a counter for counting a logic change of the comparator, and a slow-start reference voltage generating circuit for supplying a voltage which increases in accordance with an increase in the count value of the counter to the comparator and the control circuit as the reference voltage for slow start; It is equipped with:

[0008] In the switching regulator of the present invention, the control circuit comprises: a driver circuit for controlling on / off of a switching transistor in the switching power supply circuit; an error amplifier that amplifies and outputs a voltage difference between a feedback voltage obtained by resistively dividing an output voltage of the switching power supply circuit and a reference voltage; The power supply may further include a clock control unit that controls operation of the driver circuit based on the input clock signal so that the output voltage of the switching power supply circuit corresponds to the output voltage of the error amplifier. Effect of the Invention

[0009] According to the present invention, it is possible to provide a switching regulator equipped with a slow-start circuit capable of generating a reference voltage that gradually increases without requiring a frequency divider circuit for dividing a high-frequency clock signal. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram showing a circuit configuration of a switching regulator 100 as a comparative example. [Diagram 2] 2 is a diagram showing operational waveforms in the switching regulator 100 of the comparative example shown in FIG. 1. [Diagram 3] 1 is a diagram showing a circuit configuration of a switching regulator 10 according to an embodiment of the present invention. [Figure 4] 4 is a diagram showing operational waveforms in the switching regulator 10 of the embodiment of the present invention shown in FIG. 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Next, an embodiment of the present invention will be described in detail with reference to the drawings.

[0012] First, before describing the switching regulator of this embodiment, a circuit configuration of a general PWM switching regulator will be described as a comparative example.

[0013] FIG. 1 is a diagram showing a circuit configuration of a switching regulator 100 as the comparative example.

[0014] As shown in FIG. 1, the switching regulator 100, which is the comparative example, includes a switching power supply circuit 20, resistive elements 31 and 32, change-over switches 33 and 34, a reference voltage circuit 41, an error amplifier 42, a clock control unit 43, a driver circuit 44, a counter 50, a slow-start reference voltage circuit 60, and a frequency divider circuit 80.

[0015] The switching power supply circuit 20 converts an input DC voltage into a preset DC voltage by switching control, and outputs it as an output voltage Vout.

[0016] The switching power supply circuit 20 is composed of an inductor 21, a switching transistor 22, a diode 23, and a capacitance element 24. A series circuit of the inductor 21 and the switching transistor 22 is connected between an input voltage and ground, and the anode of the diode 23 is connected to the connection point of the inductor 21 and the switching transistor 22. The cathode of the diode 23 is connected to an output terminal to which a load is connected, and is also grounded via the capacitance element 24. With this circuit configuration, the switching power supply circuit 20 functions as a DC / DC converter that supplies an output voltage Vout to the load.

[0017] The driver circuit 44 controls the on / off of the switching transistor 22 in the switching power supply circuit 20 .

[0018] The error amplifier 42 amplifies and outputs the voltage difference between a feedback voltage Vfb obtained by resistively dividing the output voltage Vout of the switching power supply circuit 20 using resistor elements 31 and 32 and a reference voltage Vref supplied by the reference voltage circuit 41 or the slow-start reference voltage circuit 60.

[0019] The clock control unit 43 controls the operation of the driver circuit 44 based on the input high-frequency clock signal 101 so that the output voltage Vout of the switching power supply circuit 20 becomes a voltage according to the output voltage of the error amplifier 42 .

[0020] The resistive elements 31, 32, the reference voltage circuit 41, the error amplifier 42, the clock control unit 43, and the driver circuit 44 constitute a control circuit that controls the operation of the switching power supply circuit 20 based on the input high-frequency clock signal 101.

[0021] The frequency divider circuit 80, the counter 50, and the slow-start reference voltage generating circuit 60 constitute a slow-start circuit.

[0022] The frequency divider circuit 80 divides the frequency of the high-frequency clock signal 101 and outputs it as a low-frequency clock signal 102. Here, for example, when the high-frequency clock signal 101 is 1 MHz, the frequency divider circuit 80 divides the frequency of the high-frequency clock signal 101 by a division ratio of 100 and outputs a low-frequency clock signal 102 of 10 kHz to the counter 50.

[0023] The counter 50 counts the clock signal of the low frequency clock signal 102 from the frequency divider circuit 80 .

[0024] The slow-start reference voltage circuit 60 supplies a voltage that increases in accordance with an increase in the count value of the counter 50 to the error amplifier 42 as a reference voltage Vref for slow start.

[0025] Here, the changeover switch 33 is controlled so that during normal operation, it is in the on state and the reference voltage generated in the reference voltage circuit 41 is supplied to the error amplifier 42 as the reference voltage Vref.

[0026] Furthermore, the changeover switch 34 is controlled to be in an on state at the time of startup so that the reference voltage for slow start generated in the slow start reference voltage circuit 60 is supplied to the error amplifier 42 as the reference voltage Vref.

[0027] That is, during a slow start period at the time of startup immediately after a voltage is supplied to the switching regulator 100, the changeover switch 34 is in the ON state and the changeover switch 33 is in the OFF state. Then, during normal operation after the output voltage Vout reaches a set voltage, the changeover switch 34 is in the OFF state and the changeover switch 33 is in the ON state.

[0028] During normal operation, the change-over switch 34 is in the OFF state and the change-over switch 33 is in the ON state, so that the error amplifier 42 amplifies and outputs the voltage difference between the feedback voltage Vfb, which is obtained by resistively dividing the output voltage Vout using the resistive elements 31 and 32, and the reference voltage Vref supplied by the reference voltage circuit 41.

[0029] During the slow-start period at startup, the change-over switch 34 is turned on and the change-over switch 33 is turned off, so that the error amplifier 42 amplifies and outputs the voltage difference between the feedback voltage Vfb, which is obtained by resistively dividing the output voltage Vout using resistor elements 31 and 32, and the slow-start reference voltage Vref supplied by the slow-start reference voltage circuit 60.

[0030] With the above-described circuit configuration, in the switching regulator 100 of the comparative example, the number of clocks of the low-frequency clock signal 102 generated in the frequency divider circuit 80 is counted by the counter 50, and the count value of the counter 50 gradually increases. Therefore, the slow-start reference voltage circuit 60 generates a gradually increasing reference voltage for slow start and supplies it to the error amplifier 42 as the reference voltage Vref.

[0031] As a result, the output voltage Vout of the switching power supply circuit 20 also increases gradually, achieving a slow start function.

[0032] Next, FIG. 2 shows operating waveforms in the switching regulator 100 of the comparative example shown in FIG.

[0033] 2, it can be seen that the count value of the counter 50 increases sequentially from n, n+1, n+2, n+3, ... every time a clock of the low-frequency clock signal 102 is input. And, every time the count value of the counter 50 increases, the reference voltage Vref for slow start generated by the slow-start reference voltage circuit 60 gradually increases in stages. And, every time the reference voltage Vref increases by one stage, the control circuit consisting of the error amplifier 42, the clock control unit 43, and the driver circuit 44 operates so that the output voltage Vout output from the switching power supply circuit 20 increases. Therefore, it can be seen that the feedback voltage Vfb also gradually increases.

[0034] In this way, even in the switching regulator 100 shown as a comparative example, a slow start function is realized in which the output voltage Vout generated in the switching power supply circuit 20 gradually increases. However, this switching regulator 100 requires a frequency divider circuit 80 for dividing the frequency of the high-frequency clock signal 101 to generate a low-frequency clock signal 102 and supplying it to the counter 50. This is because the frequency of the high-frequency clock signal 101 is too high, and if it is directly input to the counter 50, the output voltage Vout will increase suddenly, making it impossible to realize the slow start function.

[0035] [One embodiment of the present invention] Next, a circuit configuration of a switching regulator 10 according to an embodiment of the present invention is shown in FIG.

[0036] The switching regulator 10 of this embodiment is used to generate drive power by PWM in a driver IC such as a source driver that controls the drive of a display device such as an in-vehicle liquid crystal display panel with a built-in power supply.

[0037] A switching regulator 10 according to an embodiment of the present invention has a configuration in which the frequency divider circuit 80 is removed and a comparator 70 is added to the switching regulator 100 of the comparative example shown in Fig. 1. In the circuit configuration shown in Fig. 3, components similar to those in the circuit configuration shown in Fig. 1 are denoted by the same reference numerals, and description of their operation will be omitted.

[0038] The slow start circuit in one embodiment of the present invention is composed of a comparator 70, a counter 50, and a slow start reference voltage circuit 60, and realizes a slow start function for operating a control circuit that controls the operation of the switching power supply circuit 20 so that the output voltage Vout of the switching power supply circuit 20 gradually increases.

[0039] The comparator 70 compares a feedback voltage Vfb obtained by dividing the output voltage Vout of the switching power supply circuit 20 by resistor elements 31 and 32 with a reference voltage Vref.

[0040] The counter 50 in this embodiment counts the logic changes of the comparator 70 and outputs the count value to the slow-start reference voltage circuit 60 .

[0041] Further, the slow-start reference voltage circuit 60 in this embodiment supplies a voltage that increases in accordance with an increase in the count value of the counter 50 as a slow-start reference voltage Vref to the comparator 70 and the error amplifier 42 that constitutes the control circuit.

[0042] Next, operating waveforms in the switching regulator 10 according to the embodiment of the present invention shown in FIG. 3 are shown in FIG.

[0043] First, when the feedback voltage Vfb exceeds the reference voltage Vref (time T1), the output voltage Vcomp of the comparator 70 changes from a low level (hereinafter abbreviated as an L level) to a high level (hereinafter abbreviated as an H level) (time T2).

[0044] Then, since the counter 50 counts and amplifies the count value at the logic change of the comparator 70, specifically, at the rising edge, the count value of the counter 50 automatically counts up from n to n+1 (time T3).

[0045] Then, as a result of the count value of the counter 50 being counted up, the slow-start reference voltage circuit 60 increases the level of the slow-start reference voltage Vref by one step (time T4).

[0046] Then, the reference voltage Vref becomes higher than the feedback voltage Vfb, and the control circuit consisting of the error amplifier 42, the clock control unit 43, and the driver 44 controls the switching power supply circuit 20 so that Vout becomes higher. As a result, the output voltage Vout gradually increases, and the feedback voltage Vfb obtained by resistively dividing the output voltage Vout also gradually increases (time T5).

[0047] Since the reference voltage Vref is now higher than the feedback voltage Vfb, the output voltage Vcomp of the comparator 70 changes from the H level to the L level.

[0048] Then, as the feedback voltage Vfb gradually increases, the feedback voltage Vfb exceeds the reference voltage Vref (time T6), and the above operation is repeated until the output voltage Vout reaches a preset voltage.

[0049] In addition, the slow-start reference voltage circuit 60 reduces the voltage setting of the reference voltage Vref that increases each time the count value of the counter 50 increases, and the number of steps in the slow-start period increases, thereby lengthening the rise time until the output voltage Vout reaches the set voltage, making it possible to make the rise of the output voltage Vout more gradual. In other words, it is possible to control the rise time of the output voltage Vout by adjusting the step of the voltage change of the slow-start reference voltage circuit 60.

[0050] As described above, according to the switching regulator 10 of this embodiment, by configuring the counter 50 to count the logical changes of the comparator 70, there is no need for the frequency divider circuit 80 for dividing the frequency of the high-frequency clock signal 10 as in the comparative example of FIG. 1.

[0051] In other words, according to the switching regulator 10 of the present embodiment, it is possible to realize a switching regulator 10 equipped with a slow start circuit capable of generating a gradually increasing reference voltage Vref, without requiring a frequency divider circuit 80 having a relatively large circuit scale. [Explanation of symbols]

[0052] 10. Switching Regulators 20 Switching power supply circuit 21 Inductor 22 Switching transistor 23 Diode 24 Capacitive element 31, 32 Resistance element 33, 34 Changeover switch 41 Reference voltage circuit 42 Error Amplifier 43 Clock control section 44 Driver circuit 50 Counter 60 Slow start reference voltage circuit 70 Comparator 80 divider circuit 100 Switching Regulator 101 High Frequency Clock Signal 102 Low Frequency Clock Signal

Claims

1. a switching power supply circuit that converts an input DC voltage into a preset DC voltage by switching control and outputs the converted DC voltage as an output voltage; a control circuit that controls an operation of the switching power supply circuit based on an input clock signal; a slow-start circuit for operating the control circuit so that an output voltage of the switching power supply circuit gradually increases, the slow-start circuit having a comparator for comparing a feedback voltage obtained by resistively dividing the output voltage of the switching power supply circuit with a reference voltage, a counter for counting a logic change of the comparator, and a slow-start reference voltage generating circuit for supplying a voltage which increases in accordance with an increase in the count value of the counter to the comparator and the control circuit as the reference voltage for slow start; A switching regulator equipped with

2. The control circuit, a driver circuit for controlling on / off of a switching transistor in the switching power supply circuit; an error amplifier that amplifies and outputs a voltage difference between a feedback voltage obtained by resistively dividing an output voltage of the switching power supply circuit and a reference voltage; a clock control unit that controls the operation of the driver circuit based on the input clock signal so that the output voltage of the switching power supply circuit becomes a voltage corresponding to the output voltage of the error amplifier; 2. The switching regulator according to claim 1, comprising:

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