Switching control circuit and switching power supply apparatus

Abstract

This switching control circuit is configured to control a switching element of a switching power supply apparatus configured to generate an output voltage from an input voltage. The switching control circuit includes: a ripple injection circuit configured to inject a ripple voltage into a feedback voltage based on the output voltage; a comparator configured to perform duty control of the switching element by comparing a second voltage and a first voltage generated by injecting the ripple voltage into the feedback voltage; and a hysteresis width variable circuit configured to vary the variation width of the second voltage.

Description

Switching control circuit and switching power supply device

[0001] The present disclosure relates to a switching control circuit and a switching power supply device.

[0002] 2. Description of the Related Art Conventionally, switching power supply devices that generate a desired output voltage from an input voltage have been used in a variety of applications.

[0003] Incidentally, examples of related art technologies include Patent Documents 1 and 2.

[0004] JP 2018-133916 A International Publication No. 2018 / 207880

[0005] The magnitude of switching loss and the frequency of switching noise in a switching power supply depend on the drive frequency of the switching power supply. Therefore, depending on the application in which the switching power supply is used, a switching power supply that can change the drive frequency over a wide range may be desirable.

[0006] In the voltage-mode control switching power supply disclosed in Patent Document 1, if one attempts to change the drive frequency while maintaining the same target value of the output voltage without changing the circuit constants, it is necessary to change the amplitude of the slope voltage used to generate the PWM signal. Therefore, it is difficult to change the drive frequency while maintaining the same target value of the output voltage without changing the circuit constants, and it is difficult to change the drive frequency over a wide range.

[0007] The PWM comparator that generates the PWM signal compares the slope voltage with the output of the error amplifier. Even if the amplitude of the slope voltage can be changed, the PWM comparator cannot operate normally unless the variation range of the error amplifier output is reduced.

[0008] In the hysteresis control type switching power supply device disclosed in Patent Document 2, the drive frequency remains almost constant if the target value of the output voltage is maintained at the same value without changing the circuit constants.

[0009] A switching control circuit disclosed in this specification is configured to control a switching element of a switching power supply device configured to generate an output voltage from an input voltage, and includes: a ripple injection circuit configured to inject a ripple voltage into a feedback voltage based on the output voltage, a comparator configured to compare a first voltage generated by injecting the ripple voltage into the feedback voltage with a second voltage to perform duty control of the switching element, and a hysteresis width variable circuit configured to vary the variation width of the second voltage.

[0010] The switching power supply device disclosed in this specification includes the switching control circuit configured as described above and the switching element.

[0011] FIG. 1 is a diagram showing a schematic configuration of a switching power supply device according to an embodiment. FIG. 2 is a timing chart showing the relationship between the change width of a first voltage and a second voltage. FIG. 3 is a diagram showing a first configuration example of a ripple injection circuit. FIG. 4 is a diagram showing a second configuration example of a ripple injection circuit. FIG. 5 is a diagram showing a third configuration example of a ripple injection circuit. FIG. 6 is a diagram showing a fourth configuration example of a ripple injection circuit. FIG. 7 is a diagram showing a fifth configuration example of a ripple injection circuit. FIG. 8 is a diagram showing a first configuration example of a variable hysteresis width circuit. FIG. 9 is a diagram showing a second configuration example of a variable hysteresis width circuit. FIG. 10 is a diagram showing a third configuration example of a variable hysteresis width circuit. FIG. 11 is a diagram showing an example configuration of a voltage source that outputs a time-varying voltage. FIG. 12 is a diagram showing a first separation circuit in which only a voltage source that outputs an output voltage remains in a circuit that generates a first voltage. FIG. 13 is a diagram showing a second separation circuit in which only a voltage source that outputs a comparison result voltage remains in a circuit that generates a first voltage. FIG. 14 is a diagram showing a third separation circuit in which only a voltage source that outputs a reference voltage remains in a circuit that generates a second voltage. Fig. 15 is a diagram showing a fourth separation circuit in which only a voltage source that outputs a square wave voltage remains in the circuit that generates the second voltage. Fig. 16 is a flowchart showing a design procedure for a switching power supply. Fig. 17 is a diagram showing the schematic configuration of a step-up switching power supply.

[0012] [Detailed Description] <Switching Power Supply> Fig. 1 is a diagram showing a schematic configuration of a switching power supply PS1 according to an embodiment. The switching power supply PS1 is a step-down switching power supply of a hysteresis control system. The switching power supply PS1 comprises a voltage generation circuit DW1, a feedback voltage generation circuit 1, and a switching control circuit SC1. The switching control circuit SC1 comprises a ripple injection circuit 2, a comparator 3, a hysteresis width variable circuit 4, and a gate driver 5. The switching power supply PS1 also comprises a DC power supply 6 and a load R Ｏ is connected.

[0013] The voltage generating circuit DW1 includes an input terminal T1, a switching element Tr, a diode Di, an inductor L, and a capacitor C. Ｏ and an output terminal T2. The voltage generating circuit DW1 receives an input voltage V supplied from a DC power supply 6. ｉｎ The switching voltage generated in the inductor L based on the on / off of the switching element Tr is supplied to the capacitor C Ｏ The voltage is smoothed by the capacitor C Ｏ The voltage smoothed by the output voltage V ｏｕｔ The switching element Tr functions as a step-down converter that outputs a current from the output terminal T2 as a voltage Vin. The switching element Tr is a negative-channel metal oxide semiconductor field effect transistor (NMOSFET). The anode of the diode Di is connected to a constant potential (for example, ground potential), and the cathode of the diode Di is connected to the connection node between the source of the switching element Tr and the inductor L.

[0014] The feedback voltage generating circuit 1 includes a voltage dividing resistor R ｕ and R ｄ and an output voltage V ｏｕｔ The feedback voltage generating circuit 1 is removed from the switching power supply device PS1, and the output voltage V ｏｕｔ It may itself be the feedback voltage.

[0015] The ripple injection circuit 2 generates a ripple voltage and injects the ripple voltage into the feedback voltage.

[0016] The comparator 3 receives a first voltage V － and a second voltage V supplied to the non-inverting input terminal. ＋ and the comparison result voltage V ｃｏｍ The first voltage V － is a voltage generated by injecting a ripple voltage into the feedback voltage. That is, the first voltage V － is a voltage in which a ripple voltage is superimposed on the feedback voltage. ＋ is the voltage output from the hysteresis width variable circuit 4. The comparator 3 outputs the first voltage V － is the second voltage V ＋ If the comparison result voltage V ｃｏｍ and outputs the first voltage V － is the second voltage V ＋ If the comparison result voltage V ｃｏｍ The comparator 3 outputs a comparison result voltage V ｃｏｍ is supplied to the gate driver 5, and the duty of the switching element Tr is controlled via the gate driver 5.

[0017] The positive power supply terminal of the comparator 3 is connected to the reference voltage V ｒｅｆ is applied to the resistor 11 and connected to a constant potential (for example, 10 V). ｒｅｆ The potential of the comparator 3 is higher than a constant potential (for example, ground potential). The negative power supply terminal of the comparator 3 is connected to a constant potential (for example, ground potential). The comparator 3 also has an inverting output terminal, and outputs a comparison result voltage V ｃｏｍ The inverted comparison result voltage V ｃｏｍ＿ｉｎｖ Output.

[0018] The hysteresis width variable circuit 4 controls the second voltage V ＋ and generates a second voltage V ＋ The change range ΔV ＋ The hysteresis width variable circuit 4 varies the comparison result voltage V ｃｏｍ is at a low level, the first value V＋１ The second voltage V ＋ When the switching element Tr is on, that is, when the comparison result voltage V ｃｏｍ is at a high level, the second value V ＋２ The second voltage V ＋ The second value V ＋２ is the first value V ＋１ The second value V ＋２ to the first value V ＋１ The value obtained by subtracting this is the second voltage V ＋ The change range ΔV ＋ is.

[0019] The gate driver 5 receives the comparison result voltage V ｃｏｍ and the comparison result voltage V ｃｏｍ The control voltage V Ｇ１ to the gate of the switching element Tr. The gate driver 5 supplies the comparison result voltage V ｃｏｍ is at a high level, the high-level control voltage V Ｇ１ is supplied to the gate of the switching element Tr, and the comparison result voltage V ｃｏｍ is at a low level, the low-level control voltage V Ｇ１ is supplied to the gate of the switching element Tr to control the on / off of the switching element Tr.

[0020] FIG. 2 shows the first voltage V － and the second voltage V ＋ The change range ΔV ＋ 2 is a timing chart showing the relationship between the first voltage V and the voltage V. The horizontal axis of the timing chart shown in FIG. 2 represents time, and the vertical axis of the timing chart shown in FIG. 2 represents a voltage value. － is the first value V ＋１ When the comparison result voltage V ｃｏｍ The first voltage V － is the second value V ＋２ When it becomes larger, the comparison result voltage V ｃｏｍis switched from high level to low level, and the switching element Tr is turned off. Therefore, when the switching power supply device PS1 is in a steady state, the output voltage V ｏｕｔ converges to a constant value.

[0021] The switching power supply device PS1 controls the second voltage V ＋ The change range ΔV ＋ Since is variable, the output voltage V ｏｕｔ The drive frequency can be changed within a wide range (for example, 100 kHz to 1 MHz) while keeping the target value of .gtoreq. the same.

[0022] <Ripple Injection Circuit> Fig. 3 is a diagram showing a first configuration example of the ripple injection circuit 2. The ripple injection circuit 2 shown in Fig. 3 includes an inverter INV and a resistor R ｒ and capacitor C ｒ The inverter INV has an input terminal connected to an inverted comparison result voltage V ｃｏｍ＿ｉｎｖ The output terminal of the inverter INV is connected to a resistor R ｒ is connected to the first end of the resistor R ｒ The second end of the capacitor C ｒ is connected to the first end of the capacitor C ｒ The second terminal of the inverter INV is connected to a constant potential (for example, ground potential). ｃｏｍ＿ｉｎｖ Resistor R ｒ and capacitor C ｒ integrates the voltage output from the inverter INV to generate a ripple voltage. The ripple voltage is the comparison result voltage V ｃｏｍ Sync to.

[0023] The ripple injection circuit 2 shown in FIG. 3 is not directly connected to the voltage generation circuit DW1, so the ripple voltage is ｏｕｔ Furthermore, the ripple injection circuit 2 shown in FIG. ｃｏｍ＿ｉｎｖ Since the inverter INV operates based on the comparison result between the logic threshold voltage and the inverted comparison result voltage V ｃｏｍ＿ｉｎｖThe threshold voltage (logical threshold voltage) of the inverter INV is not limited to a fixed value and may be variable. For example, the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is higher than the threshold voltage (logical threshold voltage), in order to prevent the logic from being switched by noise, the threshold voltage (logical threshold voltage) is set low, and conversely, the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ When is lower than the threshold voltage (logical threshold voltage), the threshold voltage (logical threshold voltage) may be set high in order to prevent logic from being switched due to noise.

[0024] 4 is a diagram showing a second configuration example of the ripple injection circuit 2. The ripple injection circuit 2 shown in FIG. ｒ and capacitor C ｒ and a resistor R ｒ The first terminal of the comparison result voltage V ｃｏｍ is supplied. ｒ The second end of the capacitor C ｒ is connected to the first end of the capacitor C ｒ The second end of the resistor R is connected to a constant potential (e.g., ground potential). ｒ and capacitor C ｒ is the comparison result voltage V ｃｏｍ The ripple voltage is generated by integrating the comparison result voltage V ｃｏｍ Sync to.

[0025] The ripple injection circuit 2 shown in FIG. 4 is not directly connected to the voltage generation circuit DW1, so the ripple voltage is ｏｕｔ This can prevent the effects of shaking from reaching the building.

[0026] 5 is a diagram showing a third configuration example of the ripple injection circuit 2. The ripple injection circuit 2 shown in FIG. ｃｃ and a switch Tr which is an NMOSFET. ｃｃｎ and resistor R ｒ and capacitor C ｒ The negative terminal of the voltage source VS1 is connected to a constant potential (for example, ground potential). The positive terminal of the voltage source VS1 is connected to a resistor Rｃｃ is connected to the first end of the resistor R ｃｃ The second end of the switch Tr ｃｃｎ and resistor R ｒ The switch Tr is connected to the first end of the ｃｃｎ The gate of the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is supplied. ｒ The second end of the capacitor C ｒ The switch Tr is connected to the first end of the ｃｃｎ and the capacitor C ｒ The second end of the voltage source VS1 is connected to a constant potential (for example, ground potential). ｃｃ Switch Tr ｃｃｎ By turning on and off the constant voltage V ｃｃ is chopped and the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ The square wave voltage is generated in synchronization with the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is at a high level, it becomes a low level, and the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is at a low level. ｒ and capacitor C ｒ integrates the square wave voltage to generate a ripple voltage. The ripple voltage is the comparison result voltage V ｃｏｍ Resistor R ｃｃ is the switch Tr ｃｃｎ This prevents the positive and negative terminals of the voltage source VS1 from shorting out when the power supply VS1 is on.

[0027] The ripple injection circuit 2 shown in FIG. 5 is not directly connected to the voltage generation circuit DW1, so the ripple voltage is ｏｕｔ Furthermore, the ripple injection circuit 2 shown in FIG. ｃｏｍ＿ｉｎｖ and a switch Tr that operates based on the comparison result between the ｃｃｎ Therefore, the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ This can improve the resistance to noise that may be included in the switch Tr. ｃｃｎ The threshold voltage of the switch Tr is not limited to a fixed value and may be variable. ｃｃｎWhen the gate-source voltage of the switch Tr is higher than the threshold voltage, noise ｃｃｎ To prevent the switch Tr from switching off, the threshold voltage is set low. ｃｃｎ When the gate-source voltage of the switch Tr is lower than the threshold voltage, noise ｃｃｎ Since it is desired to prevent the transistor from switching on, the threshold voltage may be set high.

[0028] 6 is a diagram showing a fourth configuration example of the ripple injection circuit 2. The ripple injection circuit 2 shown in FIG. 6 differs from the ripple injection circuit 2 shown in FIG. 5 in that the resistor R ｃｃ is a PMOSFET switch Tr ｃｃｐ The switch Tr is replaced by ｃｃｐ The source of the switch Tr is connected to the positive terminal of the voltage source VS1. ｃｃｐ The drain of the switch Tr ｃｃｎ and resistor R ｒ and a switch Tr ｃｃｐ The gate of the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is supplied. ｃｃｐ is the switch Tr ｃｃｎ When the switch Tr is turned on, it prevents the positive and negative terminals of the voltage source VS1 from shorting out. ｃｃｐ The threshold voltage of the switch Tr is not limited to a fixed value and may be variable. ｃｃｐ When the gate-source voltage of the switch Tr is lower than the threshold voltage, noise ｃｃp To prevent the switch Tr from switching off, the threshold voltage is set high. ｃｃｐ When the gate-source voltage of the switch Tr is higher than the threshold voltage, noise ｃｃp Since it is desired to suppress the switching on of the transistor, the threshold voltage may be set low.

[0029] 7 is a diagram showing a fifth configuration example of the ripple injection circuit 2. The ripple injection circuit 2 shown in FIG. ｒ and capacitor C ｒ and a resistor R ｒand capacitor C ｒ is the inductor L and resistor R ｒ The voltage generated at the connection node between the two is integrated to generate a ripple voltage. The ripple voltage is the comparison result voltage V ｃｏｍ Sync to.

[0030] <Variable Hysteresis Width Circuit> Fig. 8 is a diagram showing a first configuration example of the variable hysteresis width circuit 4. The variable hysteresis width circuit 4 includes a voltage source VS2 and a resistor R ｈ and a switch Tr which is an NMOSFET. ｈｎ and capacitor C ｈ , a voltage source VS3, and a resistor R １ and resistor R ２ The voltage source VS2 supplies a time-varying voltage V ｈ , i.e., a voltage V whose value changes over time ｈ In FIG. 8, the symbol of the voltage source VS2 shows a waveform indicating a triangular wave, but the voltage V ｈ is not limited to a triangular wave as long as it changes over time. ｒｅｆ The negative terminal of the voltage source VS2 is connected to a constant potential (for example, ground potential). The positive terminal of the voltage source VS2 is connected to a resistor R ｈ is connected to the first end of the resistor R ｈ The second end of the switch Tr ｈｎ and the drain of the capacitor C ｈ The switch Tr is connected to the first end of the ｈｎ The source of the switch Tr is connected to a fixed potential (for example, ground potential). ｈｎ The gate of the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ is supplied to the capacitor C ｈ The second end of the resistor R １ and the first end of the resistor R ２ is connected to the first end of the resistor R １ The second end of the resistor R is connected to the positive terminal of the voltage source VS3. ２ The second terminal of the voltage source VS1 and the negative terminal of the voltage source VS3 are connected to a constant potential (for example, ground potential).

[0031] Switch Tr ｈｎ By turning on and off the voltage V ｈis chopped and the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ A rectangular wave voltage V synchronized with the ｈｐ That is, the voltage source VS2, the resistor R ｈ , and switch Tr ｈｎ The circuit configured by the voltage source VS2, the resistor R ｈ , and switch Tr ｈｎ The circuit configured by the above generates an inverted comparison result voltage V ｃｏｍ＿ｉｎｖ A rectangular wave voltage V synchronized with the ｈｐ This is a circuit that generates a square wave voltage V ｈｐ is the inverted comparison result voltage V ｃｏｍ＿ｉｎｖ Since it is synchronized with the comparison result voltage V ｃｏｍ The square wave voltage is also synchronized with the comparison result voltage V ｃｏｍ is at a low level, the comparison result voltage V ｃｏｍ is at a high level. ｈ is the switch Tr ｈｎ When the switch Tr is turned on, it prevents the positive and negative terminals of the voltage source VS2 from shorting out. ｈｎ The threshold voltage of the switch Tr is not limited to a fixed value and may be variable. ｈｎ When the gate-source voltage of the switch Tr is higher than the threshold voltage, noise ｈｎ To prevent the switch Tr from switching off, the threshold voltage is set low. ｈｎ When the gate-source voltage of the switch Tr is lower than the threshold voltage, noise ｈｎ Since it is desired to prevent the transistor from switching on, the threshold voltage may be set high.

[0032] Capacitor C ｈ is the square wave voltage V ｈｐ This is a bias cut capacitor that cuts the bias (DC component) of the

[0033] Square wave voltage V ｈｐ is a voltage having hysteresis characteristics. ｈｐto the capacitor C ｈ If the bias (DC component) is cut off, the median value will be 0V, so the second voltage V ＋ Therefore, the reference voltage V ｒｅｆ Resistor R １ and resistor R ２ The voltage divided by is converted into a square wave voltage V ｈｐ to the capacitor C ｈ The voltage superimposed on the voltage with the bias (DC component) cut is the second voltage V ＋ It states that:

[0034] 9 is a diagram showing a second configuration example of the hysteresis width variable circuit 4. The hysteresis width variable circuit 4 shown in FIG. 9 is the same as the hysteresis width variable circuit 4 shown in FIG. 8 except that a resistor R ｆ and capacitor C ｆ The noise reduction filter is added. ｆ and capacitor C ｆ The noise removal filter configured by the resistor R is a low-pass filter that removes high-frequency noise. ｆ The first end of the capacitor C ｈ and a second end of the resistor R １ and a first end of a resistor R ２ and a first end of the resistor R ｆ The second end of the capacitor C ｆ is connected to the first end of the capacitor C ｆ The second end of the resistor is connected to a constant potential (for example, ground potential).

[0035] 10 is a diagram showing a third configuration example of the hysteresis width variable circuit 4. The hysteresis width variable circuit 4 shown in FIG. 10 is the same as the hysteresis width variable circuit 4 shown in FIG. 9 except that the resistor R ｈ is a PMOSFET switch Tr ｈｐ The switch Tr is replaced by ｈｐ The source of the switch Tr is connected to the positive terminal of the voltage source VS2. ｈｐ The drain of the switch Tr ｈｎ and the drain of the capacitor C ｈ and a switch Tr ｈｐ The gate of the inverted comparison result voltage Vｃｏｍ＿ｉｎｖ is supplied. ｈｐ The threshold voltage of the switch Tr is not limited to a fixed value and may be variable. ｈｐ When the gate-source voltage of the switch Tr is lower than the threshold voltage, noise ｈｐ To prevent the switch Tr from switching off, the threshold voltage is set high. ｈｐ When the gate-source voltage of the switch Tr is higher than the threshold voltage, noise ｈｐ Since it is desired to suppress the switching on of the transistor, the threshold voltage may be set low.

[0036] FIG. 11 is a diagram showing an example of the configuration of the voltage source VS2 used in the first to third configuration examples of the hysteresis width variable circuit 4.

[0037] The voltage source VS2 shown in FIG. 11 includes offset applying units 21 and 22, a multiplexer 23, an LPF (low pass filter) 24, and a clamper 25.

[0038] The offset applying unit 21 applies a voltage V ｈ The reference value V ｈ A positive offset value +Δ is added to 0 to obtain the first offset voltage (V ｈ０ +Δ).

[0039] The offset applying unit 22 applies a voltage V ｈ The reference value V ｈ０ A negative offset value −Δ is applied to the second offset applied voltage (V ｈ０ -Δ).

[0040] The multiplexer 53 selects a first offset voltage (V ｈ０ +Δ) and the second offset voltage (V ｈ０ −Δ) is selected and applied to the selected voltage V ｈＳ For example, when the change direction determination signal VG is at a high level, V ｈＳ = (V ｈ０ +Δ), and when the change direction determination signal VG is at a low level, V ｈＳ = (V ｈ０-Δ).

[0041] The change direction determining signal VG is a voltage V ｈ After the change, if the loss in the voltage generating circuit DW1 is reduced, the previous logic level is maintained, but if the loss in the voltage generating circuit DW1 is increased, the logic level is inverted.

[0042] The LPF 24 changes the output voltage V ｏｕｔ To suppress the fluctuation of the selected voltage V ｈＳ By slowing down the voltage V ｈ Therefore, the voltage V ｈ The change direction (slope) of V ｈＳ = (V ｈ０ +Δ), it is "positive" and V ｈＳ = (V ｈ０ When |Δ| is small, the amplitude of the drive frequency is small, and the output voltage V ｏｕｔ Since the fluctuation is small, the LPF 24 is not necessary.

[0043] In addition, the voltage V ｈ After the voltage V changes, if the loss in the voltage generating circuit DW1 is reduced, the change direction determining signal VG is maintained at the previous logic level. ｈ The change direction (gradient) of the voltage V is also maintained at the previous "positive" or "negative" state. On the other hand, if the loss in the voltage generating circuit DW1 increases, the logic level of the change direction determining signal VG is inverted. Therefore, the voltage V ｈ The direction of change (gradient) of the voltage is also inverted from "positive" to "negative" or from "negative" to "positive."

[0044] The clamper 25 includes Schottky barrier diodes 251 and 252. The cathode of the Schottky barrier diode 251 is connected to an upper clamp voltage V ｈ１ The anode of the Schottky barrier diode 252 is connected to the application terminal of the lower clamp voltage V ｈ２The anode of the Schottky barrier diode 251 and the cathode of the Schottky barrier diode 252 are both connected to the application terminal of the voltage V ｈ According to the clamper 25 of this configuration example, the voltage V ｈ is within a predetermined voltage range (V ｈ２ <V ｈ <V ｈ１ ) is clamped to

[0045] <First voltage V － Partial formulation> First voltage V － The formulation of the part can be considered as a superposition of the circuit shown in Figure 12 and the circuit shown in Figure 13. Figure 12 shows the first voltage V － In a circuit that generates an output voltage V ｏｕｔ 13 is a diagram showing a first isolation circuit in which only a voltage source that outputs a first voltage V － In the circuit that generates the comparison result voltage V ｃｏｍ 12 and 13 show the second isolation circuit, with only the voltage source outputting (V) remaining. In FIGS. 12 and 13, the circuit constants of each passive element are shown, and the circuit constants of each passive element are denoted by the same symbols as those of the passive elements. By superimposing the circuit shown in FIG. 12 and the circuit shown in FIG. 13, the following solution is obtained by formulating and solving a circuit equation:

[0046] Here, H(t) is a Heaviside step function, T is the switching period of the switching element TR (the reciprocal of the drive frequency of the switching power supply device PS1), D is the on-duty of the switching element TR, and τ １ and τ ２ is expressed by the following formula:

[0047] Considering the case where the switching element TR is turned on and off and the case where the switching power supply device PS1 is in a steady state, in the steady state, when the switching element TR is turned on, the first voltage V － is a function expressed by the following equation (1), and when the switching element TR is turned off, the first voltage V － is a function expressed by the following equation (2).

[0048] <Second voltage V ＋ Partial formulation> First voltage V ＋ The formulation of the part can be considered as a superposition of the circuit shown in FIG. 14 and the circuit shown in FIG. 15. ＋ In the circuit that generates the reference voltage V ｒｅｆ 15 is a diagram showing a third isolation circuit in which only a voltage source outputting a second voltage V ＋ In the circuit that generates the square wave voltage V ｈｐ 14 and 15 show a fourth isolation circuit in which only a voltage source outputting a voltage Vout is left. In FIGS. 14 and 15, the circuit constants of each passive element are shown, and the circuit constants of each passive element are denoted by the same symbols as those of the passive elements. By superimposing the circuit shown in FIG. 14 and the circuit shown in FIG. 15, the following solution is obtained by formulating and solving a circuit equation:

[0049] where H(t) is a Heaviesite step function, T is the switching period of the switching element TR (the reciprocal of the drive frequency of the switching power supply device PS1), D is the on-duty of the switching element TR, and E is the square wave voltage V ｈｐ is the amplitude of the signal, and τ is expressed by the following equation:

[0050] In the following explanation, Let F be the

[0051] Considering the switching power supply device PS1 in a steady state when the switching element TR is on and off, in the steady state, when the switching element TR is on, the second voltage V ＋ is a function expressed by the following equation (3), and when the switching element TR is turned off, the second voltage V ＋ is a function expressed by the following equation (4).

[0052] Capacitor C ｈ operates normally as a high-pass filter, the median value of F when the switching power supply PS1 is in a steady state should be ((1 / 2)-D)E. The condition is that T<<τ and DT<<τ.

[0053] Divide F into the ON and OFF times of the switching element TR, and when T<<τ and DT<<τ, |x|<<1 and using the approximation of exp(x)≒1+x, F ＯＮ (0) = (1-D) E and F ＯＦＦ (0) = -DE, {F ＯＮ (0) + F ＯＦＦ (0)} / 2 = ((1 / 2) - D)E. Therefore, the median of F is ((1 / 2) - D)E.

[0054] <Method of Designing a Switching Power Supply> In the switching power supply PS1, the first voltage V － The median value of and the second voltage V ＋ The median values ​​of the first voltage V － Median V －Ｃ is expressed by the following equation (5).

[0055] In addition, the first voltage V － The change range ΔV － is expressed by the following equation (6) when the switching element TR is on.

[0056] Furthermore, using the approximations T<<τ and DT<<τ, the following equation holds:

[0057] Therefore, the second voltage V ＋ Median V ＋Ｃ and the second voltage V ＋ The change range ΔV ＋ is expressed by the following formula:

[0058] The switching power supply PS1 is ＋Ｃ =V －Ｃ And ΔV ＋ = ΔV － Therefore, the switching power supply device PS1 can be designed according to the procedure shown in FIG.

[0059] First, the output voltage V ＯＵＴ , switching period T, on-duty D, reference voltage V ｒｅｆThe values ​​of the on-duty D and the output voltage V are determined (step S1). ＯＵＴ and the input voltage V ＩＮ is determined by the value of

[0060] Next, the resistance value R ｒ , resistance value R ｕ , resistance value R ｄ , resistance value R １ is determined (step S2).

[0061] In the ripple injection circuit 2 shown in FIG. ｒ Since current flows through ｒ When is small, resistor R ｒ and resistor R ｃｃ The voltage divider generated by resistor R ｒ and resistor R ｃｃ The amplitude of the voltage generated at the connection node is a constant voltage V ｃｃ Therefore, the capacitance value C ｒ is as small as possible, and the resistance value R ｒ needs to be as large as possible.

[0062] In addition, the resistance value R ｕ , resistance value R ｄ is the resistance value R ｒ If the first voltage V － The change range ΔV － The capacitance value C ｒ , resistance value R ｒ Therefore, the resistance value R ｕ , resistance value R ｄ The first voltage V － The change range ΔV － is the resistance value R ｕ , resistance value R ｄ If it is acceptable to depend on the resistance value R ｕ , resistance value R ｄ does not need to be as large as possible.

[0063] As mentioned above, τ ２ =C ｒ (R ｒ / / R ｕ / / R ｄ ), so Rｒ <<R ｕ , R ｒ <<R ｄ If so, then τ ２ is the capacitance value C ｒ , resistance value R ｒ It depends only on R ｒ <<R ｕ , R ｒ <<R ｄ If so, the first voltage V － The change range ΔV － The capacitance value C ｒ , resistance value R ｒ can be made to depend only on

[0064] Next, the first voltage V － Median V －Ｃ is calculated using the above formula (5), and the first voltage V － The change range ΔV － is calculated using the above formula (6) (step S3).

[0065] Finally, ΔV ＋ =E, the first voltage V calculated in step S3 － The change range ΔV － Using E = ΔV － And V ＋Ｃ =V －Ｃ The resistance value R ２ That is, the resistance value R is determined by the following formula derived from the above formula (7): ２ is determined (step S4).

[0066] The resistance value R ２ must be a positive value, so by the above formula (8), 2V －Ｃ > (1-2D) E and 2V ｒｅｆ >2V －Ｃ -(1-2D)E is a necessary condition. Furthermore, the resistance value R ２ becomes constant regardless of the switching period (resistor R ２ In order to avoid changing the circuit constants, －Ｃ >>(1-2D)E is a necessary condition.

[0067] First voltage V － Median V －ＣIn order for T / τ to be constant regardless of the switching period T, the above equation (5) ２ << 1, DT / τ ２ <<1 is a necessary condition. When D=0.5, the first voltage V － Median V －Ｃ is constant regardless of the switching period T.

[0068] In addition, the second voltage V ＋ Median V ＋Ｃ is the first voltage V － Median V －Ｃ Since the circuit constants are determined to be the same as the first voltage V － Median V －Ｃ If is constant regardless of the switching period T, the second voltage V ＋ Median V ＋Ｃ is constant regardless of the switching period T.

[0069] Furthermore, as described in the above paragraph

[0056] , T<<τ and DT<<τ are also necessary conditions.

[0070] In addition, in this specification, when B is 10 times or more as large as A, it can be considered that A<<B is satisfied.

[0071] In the operation simulation of the switching power supply PS1 designed in this manner, the voltage V ｈ When the input voltage V ｉｎ is 12V (design value), output voltage V ｏｕｔ It was confirmed that the output voltage was 5V (design value).

[0072] <Load fluctuation> In the explanation so far, the load R Ｏ The fluctuation of the load R Ｏ Even if fluctuations occur in the output voltage V ｏｕｔ It is necessary to prevent the load R from fluctuating. Ｏ When a fluctuation occurs, the loss of the voltage generating circuit DW1 changes basically, so that the on-duty D of the switching element TR changes depending on the load R ＯIt changes before and after the fluctuation.

[0073] The change in the on-duty D causes the second voltage V ＋ Median V ＋Ｃ changes, and the output voltage V ｏｕｔ Therefore, the second voltage V ＋ Median V ＋Ｃ is the load R Ｏ However, in this case, it is desirable to prevent fluctuations due to the second voltage V ＋ Median V ＋Ｃ Consider the case where the change in is small.

[0074] As described in the previous paragraph

[0047] , in the steady state, when the switching element TR is turned on, the first voltage V － is a function expressed by the following equation (9), and when the switching element TR is turned off, the first voltage V － is a function expressed by the following equation (10).

[0075] From the above equations (9) and (10), the first voltage V － If the first term is smaller than the other terms, the output voltage V ｏｕｔ Regardless of the first voltage V － changes, that is, the output voltage V ｏｕｔ The control of the load R Ｏ The output voltage V before and after the fluctuation ｏｕｔ Therefore, the change in the load R Ｏ The output voltage V before and after the fluctuation ｏｕｔ The condition for reducing the change of τ １ V ｏｕｔ / C ｒ R ｕ , that is, (R ｒ / / R ｄ )V ｏｕｔ / {(R ｒ / / R ｄ ) + R ｕ} is not too small (e.g., 0.45V ｏｕｔ The above is considered to be the case.

[0076] In the operation simulation of the switching power supply device PS1, when a load fluctuation in the first state is generated, for example, (R ｒ / / R ｄ )V ｏｕｔ / {(R ｒ / / R ｄ ) + R ｕ}=0.046V ｏｕｔ If so, the output voltage V immediately after the load change ｏｕｔ The change range of R ｒ / / R ｄ )V ｏｕｔ / {(R ｒ / / R ｄ ) + R ｕ}=0.48V ｏｕｔ If so, the output voltage V immediately after the load change ｏｕｔ It was confirmed that the change in R ｒ / / R ｄ )V ｏｕｔ / {(R ｒ / / R ｄ ) + R ｕ}=0.046V ｏｕｔ If so, the output voltage V immediately after the load change ｏｕｔ The change range of R ｒ / / R ｄ )V ｏｕｔ / {(R ｒ / / R ｄ ) + R ｕ}=0.48V ｏｕｔ If so, the output voltage V immediately after the load change ｏｕｔ It was confirmed that the change in voltage can be suppressed to 470 mV.

[0077] <Others> In addition to the above embodiments, various modifications can be made to the various technical features disclosed in this specification without departing from the spirit of the technical creation. The above embodiments are illustrative in all respects and should be considered not to be limiting. The technical scope of the present disclosure is defined by the claims, not by the description of the above embodiments, and should be understood to include all modifications that fall within the meaning and scope equivalent to the claims.

[0078] For example, while the switching power supply PS1 according to the embodiment described above was a hysteresis control type step-down switching power supply, the switching control circuit CNT1 of the present disclosure can also be used in a hysteresis control type step-up switching power supply, a hysteresis control type step-up / step-down switching power supply, etc. For example, when the switching control circuit CNT1 is used in a hysteresis control type step-up switching power supply, the configuration is as shown in Fig. 17. The switching power supply PS2 shown in Fig. 17 has a configuration in which the voltage generation circuit DW1 in the switching power supply PS1 is replaced with a voltage generation circuit UP1.

[0079] The voltage generating circuit UP1 includes an input terminal T1, a switching element Tr, a diode Di, an inductor L, a capacitor Co, and an output terminal T2. The voltage generating circuit UP1 first turns on the switching element Tr to generate the input voltage V ｉｎ A current corresponding to the voltage V is passed through the inductor L to store magnetic energy in the inductor L, and then the switching element Tr is turned off to release the magnetic energy in the inductor L, generating a high voltage. The voltage thus boosted is smoothed by the capacitor Co to produce an output voltage V ｏｕｔ The diode Di plays a role in stably supplying the energy generated in the inductor L to the output terminal T2 when the switching element Tr is off.

[0080] Although the switching power supplies PS1 and PS2 use diodes Di as rectifying elements, synchronous rectifying elements may be used as rectifying elements. When a synchronous rectifying element is used as the rectifying element, a driver for driving the synchronous rectifying element may be added to the switching control circuit CNT1 of the present disclosure.

[0081] <Supplementary Note> Supplementary notes are provided for the present disclosure, the specific configuration examples of which have been shown in the above-described embodiments.

[0082] The switching control circuit (SC1) of the present disclosure is a switching control circuit configured to control a switching element (Tr) of a switching power supply device (PS1, PS2) configured to generate an output voltage from an input voltage, and is configured (first configuration) to include: a ripple injection circuit (2) configured to inject a ripple voltage into a feedback voltage based on the output voltage; a comparator (3) configured to compare a first voltage generated by injecting the ripple voltage into the feedback voltage with a second voltage to perform duty control of the switching element; and a hysteresis width variable circuit (4) configured to vary the change width of the second voltage.

[0083] According to the switching control circuit of the first configuration, the drive frequency of the switching power supply device can be changed over a wide range while maintaining the target value of the output voltage at the same value without changing the circuit constants.

[0084] In the switching control circuit of the first configuration, the hysteresis width variable circuit is a circuit (R １ , R ２ , VS3), and a circuit (VS2, R ｈ , Tr ｈｎ , Tr ｈｐ ) and a capacitor (C) configured to cut the bias of the AC voltage. ｈ ) and the second voltage is a voltage in which the DC voltage is superimposed on an AC component of the AC voltage (second configuration).

[0085] In the switching control circuit of the second configuration, the AC voltage may be a square wave voltage synchronized with the output voltage of the comparator (third configuration).

[0086] In the switching control circuit of the third configuration, the AC voltage may be at a high level when the output voltage of the comparator is at a high level, and at a low level when the output voltage of the comparator is at a low level (fourth configuration).

[0087] In the switching control circuit of any of the first to fourth configurations, the hysteresis width variable circuit may be configured (fifth configuration) to include a voltage source (VS2) configured to output a voltage that changes over time.

[0088] In the switching control circuit of any one of the first to fifth configurations, the hysteresis width variable circuit includes a noise removal filter (R ｆ , C ｆ ) (sixth configuration).

[0089] In the switching control circuit of any one of the first to sixth configurations, the ripple voltage may be synchronized with the output voltage of the comparator (seventh configuration).

[0090] In the switching control circuit of the seventh configuration, the ripple injection circuit may be configured to receive the output voltage of the comparator or an inverted voltage thereof (eighth configuration).

[0091] In the switching control circuit of the seventh or eighth configuration, the ripple injection circuit includes an element (INV, Tr) configured to operate based on a comparison result between the output voltage or the inverted voltage of the comparator and a first threshold voltage. ｃｃｎ , Tr ｃｃｐ ) (ninth configuration).

[0092] In the switching control circuit of the ninth configuration, the ripple injection circuit may be configured to generate the ripple voltage based on the output voltage of the comparator or an inverted voltage thereof (tenth configuration).

[0093] In the switching control circuit of the ninth or tenth configuration, the first threshold voltage may be varied (eleventh configuration).

[0094] In the switching control circuit of any of the first to eleventh configurations above, the hysteresis width variable circuit may be configured (twelfth configuration) to include an element configured to operate based on the result of comparing the output voltage or its inverted voltage of the comparator with a second threshold voltage.

[0095] In the switching control circuit of the twelfth configuration, the second threshold voltage may be varied (thirteenth configuration).

[0096] In the switching control circuit of any one of the first to thirteenth configurations, －Ｃ >(1-2D)E (fourteenth configuration).

[0097] In the switching control circuit of any one of the first to fourteenth configurations, ｒｅｆ >2V －Ｃ -(1-2D)E can be satisfied (the 15th configuration).

[0098] In the switching control circuit of any one of the first to fifteenth configurations, －Ｃ >>It is sufficient to use a configuration that satisfies (1-2D)E (16th configuration).

[0099] In the switching control circuit of any one of the first to sixteenth configurations, T / τ ２ <<1<1 (seventeenth configuration).

[0100] In the switching control circuit of any one of the first to seventeenth configurations, DT / τ ２ <<1<1 (the eighteenth configuration).

[0101] In the switching control circuit of any of the first to eighteenth configurations, it is sufficient to adopt a configuration (the nineteenth configuration) that satisfies T<<τ.

[0102] In the switching control circuit of any of the first to nineteenth configurations, it is sufficient to adopt a configuration (twentieth configuration) that satisfies DT<<τ.

[0103] The switching power supply device (PC1, PC2) of the present disclosure has a configuration (21st configuration) including a switching control circuit of any one of the first to 20th configurations and the switching element.

[0104] REFERENCE SIGNS LIST 1 Feedback voltage generating circuit 2 Ripple injection circuit 3 Comparator 4 Hysteresis width variable circuit 5 Gate driver 6 DC power supply 21, 22 Offset applying unit 23 Multiplexer 24 LPF 25 Clamper 241 Resistor 242 Capacitor 251, 252 Schottky barrier diodes C ｆ , C ｈ , C Ｏ , C ｒ Capacitor Di Diode DW1, UP1 Voltage generation circuit INV Inverter L Inductor PS1, PS2 Switching power supply R １ , R ２ , R ｃｃ , R ｄ , R ｆ , R ｈ , R ｒ , R ｕ Resistor R Ｏ Load SC1 Switching control circuit T1 Input terminal T2 Output terminal Tr Switching element Tr ｃｃｎ , Tr ｃｃｐ , Tr ｈｎ , Tr ｈｐ Switch VS1, VS2, VS3 Voltage source

Claims

1. A switching control circuit configured to control a switching element of a switching power supply device configured to generate an output voltage from an input voltage, comprising: a ripple injection circuit configured to inject a ripple voltage into a feedback voltage based on the output voltage; a comparator configured to compare a first voltage generated by injecting the ripple voltage into the feedback voltage with a second voltage to perform duty control of the switching element; and a hysteresis width variable circuit configured to vary the change width of the second voltage.

2. The switching control circuit according to claim 1, wherein the hysteresis width variable circuit comprises: a circuit configured to generate a DC voltage; a circuit configured to generate an AC voltage whose amplitude changes over time; and a bias cut capacitor configured to cut the bias of the AC voltage; and the second voltage is a voltage in which the DC voltage is superimposed on the AC component of the AC voltage.

3. The switching control circuit according to claim 2, wherein the AC voltage is a square wave voltage synchronized with the output voltage of the comparator.

4. The switching control circuit according to claim 3, wherein the AC voltage is at a high level when the output voltage of the comparator is at a high level, and is at a low level when the output voltage of the comparator is at a low level.

5. A switching control circuit according to any one of claims 1 to 4, wherein the hysteresis width variable circuit includes a voltage source configured to output a voltage that changes over time.

6. A switching control circuit according to any one of claims 1 to 5, wherein the hysteresis width variable circuit includes a noise removal filter in an output stage.

7. A switching control circuit according to any one of claims 1 to 6, wherein the ripple voltage is synchronized with the output voltage of the comparator.

8. The switching control circuit of claim 7, wherein the ripple injection circuit is configured to receive the output voltage of the comparator or an inverted voltage thereof.

9. The switching control circuit of claim 7, wherein the ripple injection circuit includes an element configured to operate based on a result of comparing the output voltage or an inverted voltage of the comparator with a first threshold voltage.

10. The switching control circuit of claim 9, wherein the ripple injection circuit is configured to generate the ripple voltage based on an output voltage of the comparator or an inverted voltage thereof.

11. A switching control circuit according to claim 9 or 10, wherein the first threshold voltage is variable.

12. A switching control circuit according to any one of claims 1 to 11, wherein the hysteresis width variable circuit includes an element configured to operate based on a result of comparing the output voltage or its inverted voltage of the comparator with a second threshold voltage.

13. The switching control circuit according to claim 12, wherein the second threshold voltage is variable.

14. A switching power supply device comprising: a switching control circuit according to any one of claims 1 to 13; and the switching element.

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