Control circuit and switching power supply

Abstract

The control circuit (100) of the present application includes: a soft start control section (130) that sets a soft start period when a startup voltage Vcc of a switching power supply (1) exceeds a prescribed startup threshold voltage or when a COMP voltage again exceeds a standby voltage after the COMP voltage has become lower than the prescribed standby voltage; an error voltage dischargeable period setting section (140) that sets an error voltage dischargeable period during which the COMP voltage can be discharged, in accordance with the soft start period; and an error voltage discharge section (170) that discharges the COMP voltage during a discharge period from when a feedback voltage FB exceeds a prescribed error voltage discharge threshold value until either when the COMP voltage falls below the error voltage discharge threshold value or when the COMP voltage decreases to an oscillation stop voltage, whichever comes first. The control circuit (100) of the present application can suppress overshoot and stabilize the output voltage more than in the past.

Description

[0001] Cross-references

[0002] This application claims priority based on Japanese Patent Application No. 2024-061210, filed in Japan on April 5, 2024, all contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates to control circuits and switching power supplies. Background Technology

[0004] In the past, in PFC circuits, the output voltage control delayed its response to avoid responding to the commercial power supply voltage. However, overshoot of the output voltage may occur during startup and when the load changes drastically. Therefore, control circuits that clamp the output voltage to prevent overvoltage when the output voltage exceeds a specified threshold voltage are known (see Patent Document 1).

[0005] Previous control circuits 900, etc. Figure 12 As shown, it includes: a startup voltage monitoring unit 910, an output current control unit 950, a gate control unit 960, a drive unit 962, a zero current detection unit 990, a conduction width calculation unit 992, an error amplifier 972, and an overvoltage detection unit 980.

[0006] In the conventional control circuit 900, the overvoltage detection unit 980 monitors the feedback voltage FB corresponding to the output voltage Vo, and detects overvoltages exceeding a predetermined overvoltage threshold voltage (refer to...). Figure 13 When the OVP voltage is reached, a signal to stop the switching element from turning on and off is output to the gate control unit 960 to clamp the output voltage Vo (see reference). Figure 13 ).

[0007] [Preliminary Technical Documents]

[0008] [Patent Document 1] Japanese Patent Application Publication No. 2004-297915

[0009] However, in the conventional control circuit 900, control cannot be performed until the feedback voltage FB reaches the overvoltage threshold voltage (OVP voltage). Therefore, a control circuit that can suppress overshoot and stabilize the output voltage is needed compared to the conventional one.

[0010] Therefore, the present invention has been made in view of the above circumstances, and its object is to provide a control circuit that can suppress overshoot and stabilize the output voltage compared to conventional circuits. Furthermore, another object of the present invention is to provide a switching power supply equipped with such a control circuit. Summary of the Invention

[0011] The control circuit of the present invention is characterized by the following: the control circuit for controlling the switching element of a switching power supply having a switching element includes: a soft-start control unit that sets a soft-start period for changing an overcurrent threshold that limits the maximum value of the current flowing through the switching element when the startup voltage of the switching power supply exceeds a predetermined startup threshold voltage, or when the error voltage generated based on the difference between the feedback voltage corresponding to the output voltage of the switching power supply and the reference voltage of the error amplifier exceeds the predetermined standby voltage again after it has fallen below the predetermined standby voltage; an error voltage discharge period setting unit that sets an error voltage discharge period for discharging the error voltage based on the soft-start period; and an error voltage discharge unit that, during the error voltage discharge period, discharges the error voltage during any earlier of the following: when the feedback voltage exceeds the predetermined error voltage discharge threshold, until the feedback voltage falls below the error voltage discharge threshold, or when the error voltage drops to the oscillation stop voltage.

[0012] Furthermore, the control circuit of the present invention is characterized in that: the control circuit for controlling the switching element of a switching power supply having a switching element includes: a startup voltage monitoring unit, an error voltage monitoring unit, a soft-start control unit, an error voltage discharge period setting unit, an output current control unit, a gate control unit, a drive unit, and an error voltage discharge unit, wherein the startup voltage monitoring unit detects the startup voltage, and when the startup voltage exceeds a predetermined startup threshold voltage, sends a startup signal to the gate control unit and the soft-start control unit; the error voltage monitoring unit monitors a feedback voltage based on the output voltage of the switching power supply and... The error voltage generated by the difference between the reference voltage of the error amplifier, when lower than a predetermined standby voltage, outputs a standby signal to the gate control unit. When the error voltage exceeds the standby voltage again after falling below it, a restart signal is output to the soft-start control unit and the gate control unit. The soft-start control unit sets a soft-start period based on the start signal or the restart signal. During this soft-start period, it changes an overcurrent threshold used to limit the maximum current flowing through the switching element, and outputs a soft-start signal to the output current control unit and the error voltage discharge period setting unit. The differential voltage discharge period setting unit sets an error voltage discharge period that enables the error voltage to discharge based on the soft-start signal, and outputs this error voltage discharge period information to the error voltage discharge unit. The output current control unit monitors the current flowing through the switching element, and during the soft-start period, sets an overcurrent threshold that limits the maximum value of the current flowing through the switching element based on the soft-start signal. When the maximum value of the current reaches the overcurrent threshold, the unit outputs a stop signal to the gate control unit. The gate control unit then starts to supply power to the drive based on the start signal or the restart signal. The driving unit outputs a control signal to turn the switching element on and off, and stops outputting the control signal when the stop signal or the standby signal is input. The driving unit turns the switching element on and off based on the control signal output from the gate control unit. The error voltage discharge unit discharges the error voltage based on the error voltage discharge period information, and discharges the error voltage during the period from the earliest of the following: when the feedback voltage exceeds the reference voltage of the error amplifier and then falls below the reference voltage of the error amplifier, or when the error voltage drops to the oscillation stop voltage.

[0013] The switching power supply of the present invention is characterized by comprising: a switching element; and a control circuit of the present invention for controlling the switching element.

[0014] Invention Effects

[0015] According to the control circuit and switching power supply of the present invention, since it includes an error voltage discharge section that discharges the error voltage during the error voltage discharge period, defining a period from when the feedback voltage exceeds a predetermined error voltage discharge threshold to when the feedback voltage falls below the error voltage discharge threshold or when the error voltage drops to the oscillation stop voltage, it is possible to suppress the output voltage starting from a stage before the feedback voltage reaches the overvoltage threshold voltage (a relatively early stage of timing when the error voltage discharge threshold is exceeded), thereby preventing the output voltage from significantly exceeding the rated output voltage (refer to...). Figure 3 As a result, overshoot can be suppressed more effectively than before, resulting in a more stable output voltage. Attached Figure Description

[0016] Figure 1 This is a circuit diagram of the switching power supply 1 according to embodiment 1.

[0017] Figure 2 This is a block diagram of the control circuit 100 in Embodiment 1.

[0018] Figure 3 This is a timing diagram of the heavy-load switching power supply 1 during startup in Embodiment 1. Additionally, in Figure 3 and Figure 4 In the diagram, the dashed line representing the main switch current ID indicates the overcurrent threshold.

[0019] Figure 4 This is a timing diagram of the switching power supply 1 during startup under light load conditions in Implementation 1.

[0020] Figure 5 This is a timing diagram of the switching power supply 1 restarting according to implementation method 1.

[0021] Figure 6 This is a timing diagram showing the relationship between the COMP discharge period and the COMP voltage and output voltage Vo. Figure 6 (a) is a timing diagram of COMP voltage and output voltage Vo when the discharge current is large and the COMP discharge period is short. Figure 6 (b) is a timing diagram of COMP voltage and output voltage Vo when the discharge current is appropriate and the COMP discharge period is appropriate. Figure 6 (c) is a timing diagram of COMP voltage and output voltage Vo under the condition of small discharge current and long COMP discharge period.

[0022] Figure 7 This is a timing diagram of the switching power supply during startup according to Embodiment 2 of the present invention.

[0023] Figure 8 This is a timing diagram of the switching power supply when it restarts according to Embodiment 2 of the present invention.

[0024] Figure 9 This is a timing diagram of the switching power supply during startup in Implementation Method 3.

[0025] Figure 10 This is a schematic diagram illustrating the main switch current ID during soft start.

[0026] Figure 11 This is a diagram used to illustrate the overcurrent threshold during the soft start of the modified example.

[0027] Figure 12 This is a block diagram used to illustrate the conventional control circuit 900.

[0028] Figure 13 It is a timing diagram of a traditional switching power supply during startup. Detailed Implementation

[0029] The control circuit and switching power supply of the present invention will now be described with reference to the embodiments shown in the accompanying drawings. The embodiments described below do not limit the invention as claimed in the appended claims. Furthermore, not all elements and combinations thereof described in the embodiments are essential to the solutions of the present invention.

[0030] [Implementation Method 1]

[0031] 1. Implementation method 1 relates to the structure of the switching power supply 1

[0032] like Figure 1 As shown, the switching power supply 1 according to Embodiment 1 includes a rectifier circuit 10, a converter 20, and an output capacitor C3. The converter 20 performs a current critical operation.

[0033] The rectifier circuit 10 includes, for example, a bridge diode BD that performs full-wave rectification of the AC power from a commercial power supply and turns it into a pulsating current, and a smoothing capacitor C2.

[0034] The converter 20 includes an inductor 21, a switching element 22, a diode D1, and a control circuit 100. The inductor 21, the switching element 22, and the diode D1 constitute a boost chopper circuit. Furthermore, the circuit constituting the converter 20 is not limited to a boost chopper circuit; appropriate circuits can be used.

[0035] In embodiment 1, the switching element 22 is a metal-oxide-semiconductor field-effect transistor (MOSFET), but an IGBT or other suitable switching element may also be used. The inductor 21 and diode D1 may also be suitable inductors and diodes.

[0036] The control circuit 100 has seven terminals: Vcc, OUT, GND, ZC, OCL, COMP, and FB.

[0037] The Vcc terminal is connected to the external power supply Vcc, receiving the voltage from the external power supply Vcc. The OUT terminal is connected to the gate of the switching element 22, outputting a signal to the gate to control the on / off state of the switching element 22. The GND terminal is connected to the reference potential.

[0038] The ZC terminal is connected to the midpoint of resistors R1 and R2, which are connected in series from the drain electrode of switching element 22. The input voltage is obtained by dividing the drain voltage of switching element 22 through resistors R1 and R2. Alternatively, an auxiliary winding can be provided on inductor 21, and the ZC terminal can be connected to this auxiliary winding.

[0039] The OCL terminal is connected to resistor R4 and capacitor C7, and is connected via resistor R4 to the source electrode of switching element 22 and the midpoint of resistor R3. The OCL terminal monitors whether overcurrent flows to switching element 22 by monitoring the voltage determined by resistor R3.

[0040] The FB terminal is connected to capacitor C5 and resistors R5 and R6. The voltage obtained by dividing the output voltage using resistors R5 and R6 is input to the FB terminal. The COMP terminal (error voltage terminal) is the output terminal of the error amplifier 172, described later, and is connected to capacitor C6.

[0041] 2. Structure of the control circuit 100 involved in Implementation Method 1

[0042] Next, the internal structure of the control circuit 100 will be described.

[0043] Control circuit 100 Figure 2 As shown, it includes: a startup voltage monitoring unit 110, a COMP voltage monitoring unit 120 (error voltage monitoring unit), a soft-start control unit 130, an error voltage discharge period setting unit 140, an output current control unit 150, a gate control unit 160, a drive unit 162, a COMP discharge unit 170, an error amplifier 172, a discharge switch 174, a discharge current source 176, an overvoltage detection unit 180, a zero current detection unit 190, and a conduction width calculation unit 192.

[0044] The startup voltage monitoring unit 110 detects the startup voltage VCC (voltage from external power supply VCC) of the switching power supply 1, and sends a startup signal (refer to) when the startup voltage VCC exceeds the specified startup threshold voltage VCC(start). Figure 3 The VCC (start) is sent to the gate control unit 160 and the soft start control unit 130.

[0045] The COMP voltage monitoring unit 120 monitors the error voltage (COMP voltage) generated based on the difference between the feedback voltage FB and the reference voltage FB_ref of the error amplifier 172. Furthermore, when the switching power supply performs normal switching operations after startup, if the COMP voltage is lower than the specified standby voltage Vcomp(stb) (see reference...) Figure 5 When the COMP voltage drops below the standby voltage Vcomp(stb) and then exceeds the standby voltage Vcomp(stb) again, a restart signal is output to the soft-start control unit 130 and the gate control unit 160 (see reference). Figure 5 VCC(start)).

[0046] The soft-start control unit 130 sets an overcurrent threshold for changing the maximum value of the current flowing through the switching element during a soft-start period when the startup voltage VCC of the switching power supply 1 exceeds the specified startup threshold voltage VCC(start), or when the error voltage (hereinafter referred to as COMP voltage) generated based on the difference between the feedback voltage FB corresponding to the output voltage Vo of the switching power supply 1 and the reference voltage FB_ref of the error amplifier 172 exceeds the specified standby voltage VCOMP(stb) again after it has fallen below the standby voltage VCOMP(stb).

[0047] In other words, the soft-start control unit 130 sets the soft-start period based on the start signal from the start voltage monitoring unit 110 or the restart signal from the COMP voltage monitoring unit 120, limiting the maximum current value of the output current ID of the switching element 22, and outputs the soft-start signal to the output current control unit 150 and the error voltage discharge period setting unit 140.

[0048] Specifically, at the start of the soft start period, the soft start timer (not shown) within the soft start control unit 130 is activated simultaneously (see reference). Figure 3 The SS timer outputs a soft-start signal to the output current control unit 150 and the error voltage discharge period setting unit 140. Then, at predetermined intervals, a soft-start signal is output to the output current control unit 150, and the output current I is increased in stages by the output current control unit 150. D (Refer to Figure 3 Main switch current I D Then, at the end of the soft-start period, a soft-start signal is output to the output current control unit 150 to release the output current I. D The maximum current value (overcurrent threshold) is limited, and a signal is output to the error voltage discharge period setting unit 140 to notify the soft-start period to end (see reference). Figure 3 (SS timer).

[0049] Additionally, in Embodiment 1, the soft-start period is an overcurrent threshold (refer to) that limits the maximum amount of current flowing through the switching element 22. Figure 3 Main switch current I D The period from when the dashed line becomes the normal value (until it becomes a state of repeating the same waveform).

[0050] The error voltage dischargeable period setting unit 140 sets the error voltage dischargeable period that allows the COMP voltage to discharge based on the soft-start signal from the soft-start control unit 130, and outputs it to the COMP discharge unit 170 as error voltage dischargeable period information. In Embodiment 1, the soft-start period and a predetermined period thereafter are set as the error voltage dischargeable period (see reference). Figure 3 COMP discharge can be detected during the period.

[0051] Furthermore, the "subsequent specified period" refers to the period from the end of the soft-start period to the voltage stabilization period, that is, the period until the voltage fluctuation, which is longer than the AC cycle, stops, specifically about 10 cycles for a commercial power supply. Additionally, in PFC circuits, due to the delayed response to avoid responding to the commercial AC cycle, long-cycle voltage fluctuations occur; however, the period before these long-cycle voltage fluctuations cease is considered the "subsequent specified period." In other words, the "subsequent specified period" includes the aforementioned "time to start the power supply during the voltage stabilization period after the soft-start period," and is a period set with a specified margin, calculated backwards from the timing of power supply startup.

[0052] The output current control unit 150 monitors the amount of current flowing through the switching element 22, and controls the output current (main switch current I) accordingly. D When the maximum value of ) becomes the specified overcurrent threshold, a stop signal is output to the gate control unit 160 to turn off the switching element 22 (refer to Figure 3 The main switch current (ID). During soft start, the output current control unit 150 adjusts to increase in stages at predetermined intervals based on the soft start signal. In addition, under normal conditions (after soft start), a predetermined overcurrent threshold is set.

[0053] The gate control unit 160 outputs a control signal to the drive unit 162 to turn on / off the switching element 22 based on a start signal from the start-up voltage monitoring unit 110 or a restart signal from the COMP voltage monitoring unit 120. The gate control unit 160 turns the switching element on / off at a time when a zero-current detection signal is input from the zero-current detection unit 190, and outputs a control signal to adjust the on-time (on-width) of the switching element based on the on-width information from the on-width calculation unit 192. Furthermore, upon receiving a stop signal from the output current control unit 150 or the overvoltage detection unit 180, or a standby signal from the COMP voltage monitoring unit 120, the output of the control signal is stopped, and the switching operation of the switching element 22 is stopped.

[0054] The drive unit 162 turns on the cut-off switching element 22 based on the control signal output from the gate control unit 160.

[0055] The COMP discharge unit 170 discharges the error voltage (COMP voltage) within the error voltage discharge period set by the error voltage discharge period setting unit 140, from the time when the feedback voltage FB exceeds the predetermined error voltage discharge threshold to the time when the feedback voltage FB falls below the error voltage discharge threshold, or when the error voltage (COMP voltage) drops to the oscillation stop voltage.

[0056] Specifically, the COMP discharge unit 170 receives error voltage discharge period information input from the error voltage discharge period setting unit 140 and determines whether it is an error voltage discharge period. If it is an error voltage discharge period, the feedback voltage FB is compared with a predetermined error voltage discharge threshold. When the feedback voltage FB exceeds the predetermined error voltage discharge threshold, the discharge period begins, and a signal to turn on the discharge switch 174 is output to the discharge switch 174.

[0057] Additionally, during the discharge period, the signal to the discharge switch 174 is output to the discharge switch 174 at either the early time when the feedback voltage FB is lower than the error voltage discharge threshold or when the error voltage (COMP voltage) drops to the oscillation stop voltage.

[0058] In the first embodiment, the error voltage discharge threshold is the reference voltage FB_ref of the error amplifier 172. Furthermore, the discharge current of the COMP voltage during discharge is greater than the normal discharge current of the COMP voltage, but smaller than the discharge current of the error voltage when the feedback voltage FB exceeds the overvoltage threshold voltage.

[0059] When the feedback voltage FB exceeds the error voltage discharge threshold, the COMP discharge unit 170 increases the discharge current by slowing down the rise rate of the output voltage and without causing undershoot. Furthermore, the discharge current of the COMP voltage (error voltage) during the discharge period is greater than the discharge current of the COMP voltage under normal conditions.

[0060] In addition, in this specification, "discharging the COMP voltage (error voltage)" refers to discharging the charge that has been charged to the capacitor C6 connected to the COMP terminal, and "discharging current of the COMP voltage (error voltage)" refers to the current flowing from the capacitor C6 through the COMP terminal to the discharge current source in order to discharge the charge that has been charged to the capacitor C6 connected to the COMP terminal.

[0061] Error amplifier 172 generates the COMP voltage based on the difference between the feedback voltage FB and the reference voltage FB_ref. The input terminal of error amplifier 172 is connected to the FB terminal, and the output terminal is connected to the COMP terminal.

[0062] The drain electrode of the discharge switch 174 is connected to the COMP terminal, the source electrode is connected to the discharge current source 176, and the gate electrode is connected to the COMP discharge section 170. The discharge switch 174 performs switching action based on the signal from the COMP discharge section 170.

[0063] The discharge current source 176 is connected to the source side of the discharge switch 174.

[0064] The overvoltage detection unit 180 monitors the feedback voltage FB and, when it exceeds the specified overvoltage threshold voltage (OVP voltage), outputs a signal to the gate control unit 160 to stop the on / off operation of the switching element 22. Since the overvoltage threshold voltage (OVP voltage) detected by the overvoltage detection unit 180 is greater than FB_ref, and the COMP voltage is discharged through the COMP discharge unit 170 during soft-start, the overvoltage detection unit 180 typically does not detect overvoltages.

[0065] The zero-current detection unit 190 detects the timing when the current flowing through the inductor 21 becomes zero based on the voltage after the drain voltage of the switching element 22 input from the ZC terminal is divided by resistors R1 and R2, and outputs the zero-current detection signal to the gate control unit 160.

[0066] The conduction width calculation unit 192 determines the conduction width of the control signal of the switching element 22 based on the COMP voltage, and outputs it to the gate control unit 160 as conduction width information.

[0067] 3. Operation of the control circuit 100 and switching power supply 1 in Implementation Method 1

[0068] (1) At startup

[0069] Next, regarding the operation of the control circuit 100 and the switching power supply 1 during startup involved in Embodiment 1, according to... Figure 3 and Figure 4 The timing diagram is used for illustration.

[0070] (1―1) Under heavy load

[0071] Figure 3 This is a timing diagram of the switching power supply 1 during startup under heavy load in Implementation Method 1. First, when the external power supply Vcc is turned on, the startup voltage Vcc begins to rise. Then, when the startup voltage VCC exceeds the specified startup threshold voltage VCC(start), the switching power supply 1 starts, and the switching element 22 begins its on / off operation (refer to the main switch current ID).

[0072] At this time, a start signal (VCC(start)) is output to the soft-start control unit 130, and the soft-start timer of the soft-start control unit 130 starts measuring, thus beginning the soft-start period (see...). Figure 3 (SS timer in the middle). Then, the soft start control unit 130 outputs a soft start signal to the error voltage dischargeable period setting unit 140, and sets and starts the error voltage dischargeable period (refer to COMP discharge detectable period) during the soft start period and the specified period thereafter.

[0073] In addition, as the switching power supply 1 starts up, the output voltage Vo, feedback voltage FB, and COMP voltage begin to rise.

[0074] During soft start, if a predetermined time has elapsed from the soft start control unit 130, a soft start signal is output to the output current control unit 150. Each time the output current control unit 150 receives a soft start signal, the overcurrent threshold is progressively increased (see reference). Figure 3 Main switch current I D ).

[0075] When the feedback voltage FB rises and exceeds the reference voltage FB_ref, which serves as the error voltage discharge threshold, the error voltage dischargeable period setting unit 140 outputs COMP voltage dischargeable information to the COMP discharge unit 170, and the COMP discharge unit 170 outputs the SS_COMP discharge signal (refer to...). Figure 3 After the SS_COMP is discharged, the discharge switch 174 is turned on. This causes the COMP voltage to discharge.

[0076] When the COMP voltage discharges, the COMP voltage decreases. Consequently, the conduction width of the conduction width calculation unit 192 shortens, the output voltage Vo of the switching power supply 1 decreases, and the feedback voltage FB also decreases.

[0077] Soon after, the soft-start period ends, and the overcurrent threshold voltage becomes its normal value. However, during the error voltage discharge period, if the feedback voltage FB exceeds the reference voltage FB_ref, COMP discharge is maintained.

[0078] When the feedback voltage FB drops to the reference voltage FB_ref during the error voltage discharge period, a signal is output from the COMP discharge unit 170 to turn off the discharge switch (SS_COMP discharge off), and the discharge period ends. Then, the feedback voltage FB operates to maintain the reference voltage FB_ref. Then, after a predetermined period after the soft-start period ends, the error voltage discharge period ends.

[0079] In this way, the switching power supply 1 can suppress the output voltage Vo from a relatively early stage during startup. Therefore, by stopping oscillation through COMP discharge, the main switching current ID can be prevented from increasing during output undershoot and re-oscillation.

[0080] (1-2) Light load

[0081] Figure 4 This is a timing diagram of the switching power supply 1 during startup in Embodiment 1 under light load. Even under light load, the operation is essentially the same as under heavy load, but the timing of stopping the discharge differs from that under heavy load. That is, as... Figure 4 As shown in the waveforms of the FB and COMP voltages, under light load, even if the oscillation stops, it takes time for the feedback voltage FB to drop to the reference voltage (FB_ref). Therefore, the discharge stops at the moment when the COMP voltage is the oscillation stop voltage (the voltage at which discharge stops when oscillation stops). In this way, it is possible to prevent the time before the next oscillation from being too long due to over-discharging the COMP voltage.

[0082] (2) Restart

[0083] Next, we will refer to Figure 5 Describes the situation during a reboot. Even during a reboot, the soft-start period and the error voltage discharge period are defined.

[0084] That is, the error voltage (COMP voltage) generated based on the difference between the feedback voltage FB and the reference voltage FB_ref of the error amplifier 172 is monitored. When it is lower than the predetermined standby voltage VCOMP(stb), a standby signal is output to the gate control unit 160. When the COMP voltage drops below the standby voltage Vcomp(stb) and then exceeds the standby voltage Vcomp(stb) again, a restart signal is output to the soft-start control unit 130 and the gate control unit 160 (see reference). Figure 5 VCC (start)). In this way, the switching action of power supply 1 is restarted (refer to...). Figure 5 Main switching power supply I DSimultaneously, during the soft-start period and the error voltage discharge period (refer to...) Figure 5 The SS timer and COMP discharge can be detected during the period.

[0085] The subsequent actions are the same as those at startup. Figure 5 This is the timing diagram corresponding to heavy load conditions. Although the diagram for light load conditions is also omitted, it corresponds to... Figure 4 The timing diagram.

[0086] In this way, the output voltage Vo is controlled not only during startup but also during restart, by setting the soft-start period and the error voltage discharge period.

[0087] 3. Effects of the control circuit 100 and switching power supply 1 involved in Implementation Method 1

[0088] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since a COMP discharge unit 170 is provided that discharges the COMP voltage during any early period during the error voltage discharge period, from when the feedback voltage FB exceeds a predetermined error voltage discharge threshold (FB_ref) to when the feedback voltage FB falls below the error voltage discharge threshold (FB_ref), or when the COMP voltage drops to the oscillation stop voltage, the output voltage Vo can be suppressed from a relatively early stage, such as when the timing exceeds the error voltage discharge threshold (FB_ref), thereby preventing the output voltage Vo from significantly exceeding the rated output voltage (ref). Figure 3 As a result, overshoot can be suppressed more effectively than before, resulting in a more stable output voltage.

[0089] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the error voltage discharge period setting unit 140 sets the two periods, including at least the soft start period and the subsequent specified period, as the error voltage discharge period, overshoot can be suppressed more reliably even when the timing of overshoot varies depending on the input voltage and load conditions.

[0090] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the error voltage discharge threshold is the reference voltage FB_ref of the error amplifier 172, the output voltage Vo can be reliably suppressed from an earlier stage, thereby preventing the output voltage Vo from significantly exceeding the rated output voltage. As a result, overshoot can be suppressed more reliably than before, and the output voltage can be stabilized.

[0091] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the discharge current of the COMP voltage during discharge is larger than the discharge current of the COMP voltage under normal conditions, but smaller than the discharge current of the COMP voltage when the feedback voltage FB exceeds the overvoltage threshold voltage, it is possible to prevent the COMP voltage from reaching the overvoltage threshold voltage (OVP voltage), thereby enabling the feedback voltage FB to approach the reference voltage FB_ref. Specifically, this discharge current is approximately twice the discharge current before the maximum discharge current (OVP) of the error amplifier is applied, and approximately 1 / 10 of the discharge current when OVP is activated.

[0092] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the discharge switch 174 is turned on and connected to the discharge current source based on the signal from the COMP discharge unit 170, the discharge current flows toward the discharge current source to discharge the COMP voltage. Therefore, the COMP voltage can be discharged in the early stage after the feedback voltage FB exceeds the reference voltage FB_ref.

[0093] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the error amplifier 172 is a transconductance amplifier, the control circuit can be configured with a relatively low cost and simple structure.

[0094] In Embodiment 1, the control circuit 100 and the COMP discharge section 170 of the switching power supply 1 control the discharge switch 174 when the feedback voltage FB corresponding to the output voltage Vo exceeds the reference voltage FB_ref of the error amplifier 172. This slows down the rise rate of the output voltage Vo and prevents undershoot discharge current. By employing this structure, it is possible to prevent phenomena such as... Figure 6 As shown in (a), drastically reducing the output voltage Vo can actually cause undershoot, or as... Figure 6 As shown in (c), the rate of rise of the output voltage Vo does not change significantly, leading to insufficient suppression of the output voltage Vo, and sometimes even exceeding the OVP voltage. Therefore, as Figure 6 As shown in (b), no undershoot is generated, and the output voltage Vo can be appropriately suppressed.

[0095] According to the control circuit 100 and switching power supply 1 of embodiment 1, since the overcurrent threshold voltage is smaller than that during the soft start period and increases at predetermined intervals, the sharp rise of the output voltage Vo can be suppressed, thereby achieving soft start.

[0096] According to the control circuit 100 and switching power supply 1 of Embodiment 1, since the monitoring feedback voltage FB is included and a signal to stop the switching element 22 from turning on and off is output to the overvoltage detection unit 180 of the gate control unit 160 when the overvoltage threshold voltage (OVP voltage) is exceeded, the switching operation can be stopped when the output voltage Vo rises unexpectedly, thereby preventing damage to the switching power supply.

[0097] [Implementation Method 2]

[0098] The control circuit in Embodiment 2 has a structure that is substantially the same as that of the control circuit 100 in Embodiment 1, but the error voltage discharge period differs from that of the control circuit 100 in Embodiment 1. In Embodiment 2, the error voltage discharge period setting unit sets the soft-start period itself as the error voltage discharge period, instead of "the soft-start period and the specified period thereafter" (see [reference]). Figure 7 and Figure 8 ).

[0099] In this way, although the control circuit according to Embodiment 2 differs from the control circuit 100 according to Embodiment 1 in that the error voltage discharge period is similar to that of the control circuit 100 according to Embodiment 1, it has a COMP discharge unit 170 that discharges the COMP voltage during the error voltage discharge period, from when the feedback voltage FB exceeds the predetermined error voltage discharge threshold (FB_ref) to when the feedback voltage FB falls below the error voltage discharge threshold (FB_ref), or when the COMP voltage drops to the oscillation stop voltage, at any earlier time. Therefore, it is possible to suppress the output voltage Vo from a relatively early stage, such as the timing when the error voltage discharge threshold (FB_ref) is exceeded, thereby preventing the output voltage Vo from significantly exceeding the rated output voltage (see reference). Figure 7 as well as Figure 8 As a result, overshoot can be suppressed more effectively than before, resulting in a more stable output voltage.

[0100] Furthermore, according to the control circuit of Embodiment 2, since the soft-start period setting unit sets the soft-start period itself to the period during which the error voltage can be discharged, the output voltage Vo can be reliably suppressed during the soft-start period when the possibility of overshoot during startup and restart is high. In addition, if only the soft-start period is set to the period during which the error voltage can be discharged, the structure of the error voltage possible period setting unit can be included in the soft-start control unit, and a simpler structure can be achieved.

[0101] Furthermore, since the control circuit according to Embodiment 2 has the same structure as the control circuit 100 according to Embodiment 1 at points other than the period during which the error voltage can be discharged, it has the same effects as the control circuit 100 according to Embodiment 1.

[0102] [Implementation Method 3]

[0103] The control circuit in Embodiment 3 has a configuration that is basically the same as that in Embodiment 2, but the error voltage discharge threshold differs from that in Embodiment 2. Specifically, in Embodiment 3, the error voltage discharge threshold is a predetermined voltage value that is greater than the reference voltage FB_ref of the error amplifier 172 and less than the overvoltage threshold voltage OVP (see reference). Figure 9 ).

[0104] In addition, although the illustration is omitted, the error voltage discharge threshold is a specified voltage value that is larger than the error amplifier 172 reference voltage FB_ref and smaller than the overvoltage threshold voltage OVP, not only during startup but also during restart.

[0105] As such, although the control circuit of Embodiment 3 differs from the control circuit of Embodiment 2 in that the error voltage discharge threshold is the same as that of Embodiment 2, it is similar in that it includes a COMP discharge unit 170 that discharges the COMP voltage during the error voltage discharge period. This discharge period is defined as any early time, from when the feedback voltage FB exceeds the predetermined error voltage discharge threshold (FB_ref) to when the feedback voltage FB falls below the error voltage discharge threshold (FB_ref), or when the COMP voltage drops to the oscillation stop voltage. Therefore, it is possible to suppress the output voltage Vo from a relatively early stage, such as when the timing exceeds the error voltage discharge threshold (FB_ref), thereby preventing the output voltage Vo from significantly exceeding the rated output voltage (see reference). Figure 9 As a result, overshoot can be suppressed more effectively than before, resulting in a more stable output voltage.

[0106] Furthermore, according to the control circuit of Embodiment 3, since the error voltage discharge threshold is a specified voltage value that is larger than the reference voltage FB_ref of the error amplifier 172 and smaller than the overvoltage threshold voltage OVP, not only can the reference voltage of the error amplifier be controlled more tightly, but the output voltage can also be controlled more tightly.

[0107] Furthermore, since the control circuit according to embodiment 3 has the same configuration as the control circuit according to embodiment 2 in aspects other than the error voltage discharge threshold, it has the same effect as the control circuit according to embodiment 2.

[0108] The present invention has been described above based on the embodiments described above, but the present invention is not limited to the embodiments described above. It can be implemented in various ways without departing from the concept, for example, the following modifications can be made.

[0109] (1) The above embodiments (including variations) are as described above. The same applies below. The positions, connections, numbers, etc., described in the description are illustrative and may be modified without impairing the effects of the present invention.

[0110] (2) In Embodiment 1 above, the soft-start period and the specified period thereafter are defined as the error voltage discharge period. In Embodiment 2, the soft-start period is defined as the error voltage discharge period. However, the present invention is not limited to this. The period including the specified period before the soft-start period may also be defined as the error voltage discharge period, or the period including the specified period before and after the soft-start period may also be defined as the error voltage discharge period.

[0111] (3) In the above embodiments, although the soft-start period is set to the overcurrent threshold that limits the maximum current flowing through the switching element (see reference 10 ... Figure 3 Main switch current I D The period until the dashed line becomes the normal value (see reference). Figure 10 (a)), but the invention is not limited thereto. The soft-start period may also be set as the period from when the overcurrent threshold limiting the maximum current flowing through the switching element becomes its normal value until a predetermined time has elapsed (see reference). Figure 10 (b)).

[0112] (4) In the above embodiments, although the overcurrent threshold voltage is increased periodically at predetermined intervals during soft start, the present invention is not limited thereto. The overcurrent threshold voltage may also be smaller than at steady state and continuously increased over time (see reference). Figure 11 This also allows for soft booting.

[0113] (5) In the above embodiments, the error amplifier is set as a transconductance amplifier, but the present invention is not limited to this. Amplifiers other than transconductance amplifiers may also be used.

[0114] (6) In the above embodiments, although the control circuit includes a startup voltage monitoring unit, an error voltage monitoring unit, a soft-start control unit, an error voltage discharge period setting unit, an output current control unit, a gate control unit, and a drive unit, the present invention is not limited thereto. Even if one or more of these elements are absent, the present invention can be applied as long as an error voltage discharge unit is provided, and the COMP voltage generated based on the difference between the feedback voltage and the error amplifier is discharged during the period from when the feedback voltage FB corresponding to the output voltage Vo exceeds the reference voltage of the error amplifier to when it decreases.

[0115] (7) In the above embodiments, although the maximum value of the output current (main switch current ID) is limited during soft start, the present invention is not limited thereto. The conduction width of the switching element can also be reduced and expanded over time.

[0116] Symbol Explanation

[0117] 1…Switching power supply; 22…Switching element; 100…Control circuit; 110…Start-up voltage monitoring unit; 120…Error voltage monitoring unit (COMP voltage monitoring unit); 130…Soft-start control unit; 140…Error voltage discharge period setting unit; 150…Output current control unit; 160…Gate control unit; 162…Drive unit; 170…COMP discharge unit (error voltage discharge unit); 172…Error amplifier; 174…Discharge switch; 176…Discharge current source; 180…Overvoltage detection unit; FB…Feedback voltage; FB_ref…Reference voltage.

Claims

1. A control circuit, characterized in that: The control circuit for controlling the switching element of a switching power supply having a switching element includes: The soft-start control unit sets a soft-start period for changing the overcurrent threshold that limits the maximum amount of current flowing through the switching element when the startup voltage of the switching power supply exceeds a predetermined startup threshold voltage, or when the error voltage generated based on the difference between the feedback voltage corresponding to the output voltage of the switching power supply and the reference voltage of the error amplifier exceeds the predetermined standby voltage again after it has fallen below the standby voltage. The error voltage discharge period setting unit sets an error voltage discharge period that allows the error voltage to discharge based on the soft-start period; and The error voltage discharge unit discharges the error voltage during the error voltage discharge period, from the time when the feedback voltage exceeds a predetermined error voltage discharge threshold until the time when the feedback voltage falls below the error voltage discharge threshold or the time when the error voltage drops to the oscillation stop voltage.

2. The control circuit according to claim 1, characterized in that: The error voltage discharge period setting unit sets the soft-start period to the error voltage discharge period.

3. The control circuit according to claim 1, characterized in that: The error voltage discharge period setting unit sets the period that includes at least the soft-start period and a subsequent predetermined period as the error voltage discharge period.

4. The control circuit according to any one of claims 1 to 3, characterized in that: The error voltage discharge threshold is the reference voltage of the error amplifier.

5. The control circuit according to any one of claims 1 to 3, characterized in that, Further includes: The overvoltage detection unit monitors the feedback voltage and outputs a signal to stop the switching element's on / off operation when the overvoltage exceeds a predetermined overvoltage threshold voltage. The error voltage discharge threshold is a specified voltage value that is greater than the reference voltage of the error amplifier and less than the overvoltage threshold voltage.

6. The control circuit according to claim 5, characterized in that: The discharge current of the error voltage during the discharge period is larger than the discharge current of the error voltage under normal conditions and smaller than the discharge current of the error voltage when the feedback voltage exceeds the overvoltage threshold voltage.

7. The control circuit according to any one of claims 1 to 3, characterized in that, Further includes: The error amplifier generates the error voltage; The error voltage terminal is connected to a capacitor that maintains the error voltage; A discharge switch is connected to the error voltage terminal and is turned on and off based on a signal from the error voltage discharge section. as well as A discharge current source is connected to the discharge switch. The error voltage discharge section discharges the capacitor by turning on the discharge switch and connecting the error voltage terminal and the discharge current source, so that the discharge current flows from the capacitor to the discharge current source.

8. The control circuit according to claim 7, characterized in that: The error amplifier is a transconductance amplifier.

9. The control circuit according to any one of claims 1 to 3, characterized in that: When the feedback voltage exceeds the error voltage discharge threshold, the error voltage discharge unit increases the discharge current by slowing down the rise rate of the output voltage and without causing undershoot.

10. The control circuit according to any one of claims 1 to 3, characterized in that, Further includes: The output current control unit monitors the amount of current flowing through the switching element, and if the amount of current reaches the overcurrent threshold during the soft-start period, stops the switching operation of the switching element. During the soft start, the overcurrent threshold increases over time.

11. The control circuit according to any one of claims 1 to 3, characterized in that, Further includes: The output current control unit monitors the current flowing through the switching element, and if the current reaches the overcurrent threshold during the soft-start period, stops the switching operation of the switching element. During the soft start, the overcurrent threshold increases periodically at predetermined intervals.

12. A control circuit, characterized in that: The control circuit for controlling the switching element of a switching power supply having a switching element includes: The system includes a startup voltage monitoring unit, an error voltage monitoring unit, a soft-start control unit, an error voltage discharge period setting unit, an output current control unit, a gate control unit, a drive unit, and an error voltage discharge unit. The startup voltage monitoring unit detects the startup voltage and, when the startup voltage exceeds a predetermined startup threshold voltage, sends a startup signal to the gate control unit and the soft-start control unit. The error voltage monitoring unit monitors the error voltage generated based on the difference between the feedback voltage corresponding to the output voltage of the switching power supply and the reference voltage of the error amplifier. When the error voltage is lower than a predetermined standby voltage, a standby signal is output to the gate control unit. When the error voltage exceeds the standby voltage again after falling below the standby voltage, a restart signal is output to the soft-start control unit and the gate control unit. The soft-start control unit sets a soft-start period based on the start signal or the restart signal. During this soft-start period, it changes an overcurrent threshold used to limit the maximum current flowing through the switching element, and outputs a soft-start signal to the output current control unit and the error voltage discharge period setting unit. The error voltage discharge period setting unit sets the error voltage discharge period that enables the error voltage to discharge based on the soft-start signal, and outputs it as error voltage discharge period information to the error voltage discharge unit. The output current control unit monitors the amount of current flowing through the switching element, and during the soft-start period, sets an overcurrent threshold based on the soft-start signal to limit the maximum value of the current flowing through the switching element. If the maximum value of the current reaches the overcurrent threshold, the unit outputs a stop signal to the gate control unit. The gate control unit starts outputting a control signal to the drive unit to turn the switching element on or off based on the start signal or the restart signal, and stops outputting the control signal when the stop signal or the standby signal is input. The driving unit controls the switching element to turn on and off based on the control signal output from the gate control unit. The error voltage discharge unit discharges the error voltage during the period specified in the error voltage discharge information, specifically during the period from the earliest of the following: when the feedback voltage exceeds the reference voltage of the error amplifier but then falls below the reference voltage of the error amplifier, or when the error voltage drops to the oscillation stop voltage.

13. The control circuit according to claim 12, characterized in that, Further includes: The overvoltage detection unit monitors the feedback voltage and, when the overvoltage threshold voltage is exceeded, outputs a signal to the gate control unit to stop the switching element's on / off operation. The discharge current of the error voltage during the discharge period is larger than the discharge current of the error voltage under normal conditions, but smaller than the discharge current of the error voltage when the feedback voltage exceeds the overvoltage threshold voltage.

14. A switching power supply, characterized in that, include: Switching elements; as well as The control circuit according to claim 1 or 12 for controlling the switching element.

Images