Switching Power Supply

Abstract

To provide a COT control switching power supply that can reduce the dependence of input voltage on a ripple current.SOLUTION: In a switching power supply 21, an ON timing generation circuit 6 generates a timing at which a switching element 1 for generating an output voltage VOUT stepped down by switching an input voltage VIN is turned on, and an ON time generation unit 22 generates time to maintain the ON state of the switching element 1. The ON time generation unit 22 comprises: a current source circuit for passing a constant current in proportion to voltage obtained by subtracting an off-set voltage from the input voltage VIN; a capacitor charged with the constant current; a ramp wave signal generation circuit for generating a ramp wave signal in combination with a switching circuit for discharging the capacitor; and a comparator for comparing an output voltage with the ramp wave signal.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a switching power supply device that generates a stepped-down output voltage by switching an input voltage using a switching element. [Background technology]

[0002] In COT (Constant On Time) control, a control method for switching power supplies, the frequency varies depending on the load current and input voltage, but the ripple voltage also varies accordingly, which presents a problem. AOT (Adaptive On Time) control has been proposed as a technology to suppress frequency fluctuations that depend on the input voltage. While AOT control can suppress ripple voltage fluctuations to some extent, in principle, dependence on the input voltage remains. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-108189 Summary of the Invention [Problem to be solved by the invention]

[0004] 9, switching elements 1 and 2, such as N-channel MOSFETs, are connected in series between an input power supply Vin and ground. The common connection point of switching elements 1 and 2 is connected to ground via a series circuit of an inductor 3 and a capacitor 4. The common connection point of inductor 3 and capacitor 4 serves as the output terminal for voltage VOUT.

[0005] The output voltage VOUT is input to a Ton time generation circuit 5 and an ON timing generation circuit 6. As shown in Fig. 10, the Ton time generation circuit 5 is composed of a series circuit of a current source circuit 7 and a capacitor 8 connected between a power supply and ground, and a comparator 10 having an inverting input terminal to which the output voltage VOUT is input and a non-inverting input terminal connected to a common connection point of the current source circuit 7 and the capacitor 8, and also connected to ground via a switch circuit 9. The current source circuit 7 supplies a constant current Gm*VIN proportional to the input voltage VIN.

[0006] 9, the output terminal of a comparator 10, which is a comparison circuit, is connected to a reset terminal R of an RS flip-flop 11. The output terminal Q of the RS flip-flop 11 is connected to an input terminal of a pre-driver 12. The output terminal of an ON timing generation circuit 6 is connected to a set terminal S of the RS flip-flop 11.

[0007] When the RS flip-flop 11 is set and the output terminal Q goes high, the pre-driver 12 turns on the switching element 1 and turns off the switching element 2. At this time, the capacitor 4 is charged via the inductor 3. When the RS flip-flop 11 is reset and the output terminal Q goes low, the pre-driver 12 turns off the switching element 1 and turns on the switching element 2. At this time, the capacitor 4 is discharged via the inductor 3.

[0008] If the signal output from output terminal Q is D, then switch circuit 9 of Ton time generation circuit 5 is turned on by signal DB, which is the inverse of signal D. ON timing generation circuit 6 sets RS flip-flop 11 and sets signal D to high level based on the result of comparing the voltage obtained by dividing output voltage VOUT with a reference voltage. The above constitutes switching power supply device 13.

[0009] As shown in FIG. 11, the ripple current ΔIL is expressed by equation (1). ΔIL=(VIN-VOUT) / L×Ton …(1) Ton is the time during which signal D maintains a high level, and is determined by constant current charging of capacitor 4 under AOT control. Ton=(VOUT×C) / (Gm×VIN) …(2) In other words, it is inversely proportional to the input voltage VIN.

[0010] Substituting equation (2) into equation (1), the ripple current ΔIL is expressed by equation (3). ΔIL= {VOUT×C / (L×Gm)} ×(1-VOUT / VIN) …(3) That is, in equation (3), the term for the input voltage VIN remains, so the dependency is not resolved. An example of calculating the on-time Ton and ripple current ΔIL is shown in Figure 12. The ripple current ΔIL increases as the input voltage VIN increases.

[0011] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a COT control switching power supply device that can reduce the dependency of the input voltage on the ripple current. [Means for solving the problem]

[0012] According to the switching power supply device of claim 1, an on-timing generation unit generates timing to turn on a switching element that generates a stepped-down output voltage by switching on an input voltage, and an on-time generation unit generates time for maintaining the on-state of the switching element. The on-time generation unit includes a current source circuit that supplies a constant current proportional to a voltage obtained by subtracting an offset voltage from the input voltage, a capacitor that is charged by the constant current, a ramp signal generation unit that generates a ramp signal by combining a discharging switching element that discharges the capacitor, and a comparison circuit that compares the output voltage with the ramp signal.

[0013] 9 and 10, the current source circuit that constitutes the on-time generating unit charges the capacitor by supplying a constant current proportional to the voltage obtained by subtracting the offset voltage from the input voltage. This reduces the influence of the input voltage VIN on the ripple current ΔIL in equation (3) by the amount of the offset voltage. This reduces the dependency of the input voltage on the ripple current.

[0014] According to the switching power supply device of claim 2, the offset voltage is set equal to the output voltage, thereby eliminating the dependency of the input voltage on the ripple current.

[0015] According to the switching power supply device of claim 3, the first current mirror circuit constituting the current source circuit operates to subtract a second current obtained by converting an offset voltage using a resistor from a first current obtained by converting an input voltage using a resistor. The second current mirror circuit mirrors and flows a current obtained by subtracting the second current from the first current. With this configuration, a constant current proportional to the voltage obtained by subtracting the offset voltage from the input voltage can be generated to charge the capacitor. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a diagram illustrating a configuration of a switching power supply device according to a first embodiment. [Figure 2] Diagram showing the configuration of the Ton time generation circuit [Figure 3] Circuit diagram showing the detailed configuration of the current source [Figure 4] Waveform diagram of each signal showing the operation sequence [Figure 5] A diagram showing an example of calculation of the relationship between the input voltage VIN, the on-time Ton, and the ripple current ΔIL. [Figure 6] Diagram showing another example of power stage configuration (part 1) [Figure 7] Diagram showing another example of power stage configuration (part 2) [Figure 8] Diagram showing another example of power stage configuration (part 3) [Figure 9] Diagram showing the configuration of a switching power supply device using a conventional AOT control method [Figure 10] Diagram showing the configuration of the Ton time generation circuit [Figure 11] Diagram showing the waveform of ripple current ΔIL [Figure 12] A diagram showing an example of calculation of the relationship between the input voltage VIN, the on-time Ton, and the ripple current ΔIL. DETAILED DESCRIPTION OF THE INVENTION

[0017] An embodiment will now be described. A switching power supply device 21 of this embodiment shown in FIG. 1 is configured by replacing the Ton time generation circuit 5 in the conventional switching power supply device 13 with a Ton time generation circuit 22. As shown in FIG. 2, the Ton time generation circuit 22 replaces the current source circuit 7 with a current source circuit 23, which supplies a constant current Gm*(VIN-VOUT) proportional to the difference between the input voltage VIN and the output voltage VOUT. In other words, in this embodiment, the offset voltage is set equal to the output voltage VOUT. Furthermore, the capacitor 8, the switch circuit 9, and the current source circuit 23 constitute a ramp wave signal generation circuit 30.

[0018] In this embodiment, the Ton time generation circuit 22 offsets the current that charges the capacitor 8 to the negative side. If the offset current is Ioffset and the effect of the offset current Ioffset is added to equation (2), the following is obtained: Ton=(VOUT×C) / {(Gm×VIN)-Ioffset} …(4) So, Ioffset=Gm×VOUT …(5) If we set it to , then equation (4) becomes Ton=(VOUT×C) / {(Gm×VIN)-Gm×VOUT} =(VOUT×C) / {(Gm×(VIN-×VOUT)}…(6) Substituting equation (6) into equation (1), we get ΔIL=(VOUT×C) / (L×Gm) …(7) This eliminates the input voltage VIN term, eliminating the dependency of the ripple current ΔIL. Figure 5 shows an example of calculating the on-time Ton and ripple current ΔIL. It shows that the ripple current ΔIL does not depend on the input voltage VIN.

[0019] 3, in the current source circuit 23, N-channel MOSFETs 24a and 24b form a first current mirror circuit 25. N-channel MOSFETs 26a and 26b form a second current mirror circuit 27. The sources of the FETs 24a and 24b are connected to ground, and the gates are commonly connected to the drain of the FET 24a. The input voltage VIN is supplied to the drain of the FET 24a via a resistor element R1.

[0020] The sources of FETs 26a and 26b are connected to ground, and their gates are commonly connected to the drain of FET 26a. The output voltage VOUT is supplied to the drain of FET 26a via resistor R2. Note that R1=R2. The drain of FET 26b is connected to the drain of FET 24a.

[0021] The P-channel MOSFETs 28a and 28b form a third current mirror circuit 29. The sources of the FETs 28a and 28b are connected to a power supply, and the gates are commonly connected to the drain of the FET 28b. The drain of the FET 28b is connected to the drain of the FET 24b. The drain of the FET 28a is connected to one end of the capacitor 8.

[0022] Next, the operation of the current source circuit 23 will be described. The gate-source tube voltage of the FETs 24 and 26 is Vgs. The current flowing through the resistance element R1 is (VIN-Vgs) / R1, and the current flowing through the resistance element R2 is (VOUT-Vgs) / R1. The second current mirror circuit 27 draws a current (VOUT-Vgs) / R1 from the drain of the FET 24a, so if R1=R2=R, the current flowing through the drain of the FET 24b is (VIN-Vgs) / R-(VOUT-Vgs) / R=(VIN-VOUT) / R The third current mirror circuit 29 turns back the above current and passes it through the capacitor 8, so the charging current of the capacitor 8 becomes Gm×(VIN−VOUT).

[0023] As shown in Figure 4, the on-time Ton is determined by the output voltage VOUT and a ramp wave with a slope of Gm × (VIN - VOUT) / C. The off-time Toff is determined by the timing at which the divided voltage signal FB of the output voltage VOUT is compared with the reference voltage VREF.

[0024] As described above, according to this embodiment, in the switching power supply device 21, the ON timing generation circuit 6 generates the timing to turn on the switching element 1, which generates the stepped-down output voltage VOUT by switching the input voltage VIN, and the ON time generation unit 22 generates the time for maintaining the ON state of the switching element 1. Specifically, the ON time generation unit 22 includes: a current source circuit 23 that supplies a constant current proportional to a voltage obtained by subtracting an offset voltage from the input voltage VIN; a capacitor 8 that is charged by the constant current; a ramp signal generation circuit 30 that generates a ramp signal by combining the capacitor 8 with a switch circuit 9 that is a discharging switching element that discharges the capacitor 8; and a comparator 10 that compares the output voltage with the ramp signal.

[0025] By setting the offset voltage equal to the output voltage VOUT, the ripple current ΔIL is expressed as equation (7), which reduces the influence of the input voltage VIN by the amount of the offset voltage and eliminates the dependency of the input voltage on the ripple current.

[0026] Furthermore, the first current mirror circuit 25 constituting the current source circuit 23 operates to subtract a second current obtained by converting the output voltage VOUT using a resistor element R2 from a first current obtained by converting the input voltage VIN using a resistor element R1. The second current mirror circuit 27 mirrors and supplies a current obtained by subtracting the second current from the first current. This current is supplied to the capacitor 8 via the third current mirror circuit 29. This generates a constant current proportional to the voltage obtained by subtracting the output voltage VOUT from the input voltage VIN, thereby charging the capacitor 8.

[0027] (Other embodiments) 6 to 8 show other configuration examples of power stages that perform switching. FIG. 6 shows a configuration in which the switching element 1 and the inductor 3 are interchanged. FIG. 7 shows a configuration in which a diode 24 is arranged in place of the switching element 2. FIG. 8 shows a configuration in which a diode 24 is arranged in place of the switching element 1 in the configuration shown in FIG. 6.

[0028] The offset voltage does not necessarily have to be set equal to the output voltage, but may be set to a value equal to or less than the output voltage. Although the present disclosure has been described with reference to the embodiments, it is understood that the present disclosure is not limited to the embodiments or structures. The present disclosure also encompasses various modifications and equivalent modifications. In addition, various combinations and forms, including only one element, more than one element, or less than one element, are also within the scope and spirit of the present disclosure. [Explanation of symbols]

[0029] In the drawing, 1 indicates a switching element, 6 indicates an ON timing generation circuit, 8 indicates a capacitor, 9 indicates a switch circuit, 10 indicates a comparator, 21 indicates a switching power supply device, 22 indicates a Ton time generation circuit, 23 indicates a current source circuit, 25 indicates a first current mirror circuit, 27 indicates a second current mirror circuit, and 30 indicates a ramp wave signal generation circuit.

Claims

1. The input voltage is switched by a switching element (1) to generate a stepped-down output voltage, an on-timing generating unit (6) that generates timing for turning on the switching element; an on-time generating unit (22) that generates a time for maintaining the on-state of the switching element; The on-time generating unit includes a current source circuit (23) that supplies a constant current proportional to a voltage obtained by subtracting an offset voltage from the input voltage, a capacitor (8) that is charged by the constant current, and a ramp signal generating unit (30) that generates a ramp signal by combining a discharging switching element (9) that discharges the capacitor; A switching power supply device comprising a comparison circuit (10) that compares the output voltage with the ramp wave signal.

2. 2. The switching power supply device according to claim 1, wherein the offset voltage is used as the output voltage.

3. The current source circuit includes a first current mirror circuit (25) that operates to subtract a second current obtained by converting the offset voltage using a resistor from a first current obtained by converting the input voltage using a resistor; 3. The switching power supply device according to claim 1, further comprising a second current mirror circuit (27) for mirroring and flowing a current obtained by subtracting the second current from the first current.

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