Switching power supply device

Abstract

To provide a switching power supply device which can be configured by suppressing tolerance dose of a switch as much as possible and is configured to appropriately perform a protection operation when an abnormality is detected.SOLUTION: A first drive unit 11 comprises a high voltage level shift unit 21 which operates by using a bootstrap power supply Vbst to perform level shift of control voltage by a control unit 10, and drives a first switch SW1 through the high voltage level shift unit 21. A second drive unit 12 inputs the control voltage by the control unit 10 and drives a second switch SW2 without using the high voltage level shift unit 21. The control unit 10 causes an unnecessary second switch SW2 of the level shift unit 21 to operate as a switch for energization off on a primary side of a transformer 14 when the first switch SW1 is controlled by using the first drive unit 11 and the second switch SW2 is controlled by using the second drive unit 12.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a switching power supply device. [Background technology]

[0002] Conventionally, switching power supply devices have been used in various electronic control devices (see, for example, Patent Document 1). According to the technology described in Patent Document 1, a main switching element that switches a DC voltage applied to the primary side of a transformer is provided, the secondary side output voltage of the transformer is detected, and the switching pulse width of the main switching element is controlled according to the detected voltage. According to the technology described in Patent Document 1, a ripple voltage generated in a smoothing capacitor is detected, and when a detection unit connected to the primary side of the transformer detects a short-circuit current, the "switch element" (SW1 in Patent Document 1) is opened to cut off the main switching element (Q1 in Patent Document 1).

[0003] Although the cited document 1 does not disclose detailed applications of the drive circuit, if the input voltage is high, a boost power supply (e.g., a power supply using a bootstrap circuit) is required to drive the "switch element" in the cited document 1. The control device can adjust the output voltage by adjusting the control voltage applied to the switch element. However, depending on the value of the control voltage, the voltage may drop, causing the "switch element" to turn off or become unstable. In such a case, if there is no abnormality detection for the "switch element," the abnormality cannot be detected and normal operation cannot be achieved when the device falls into an abnormal state.

[0004] In addition, the drive circuit that drives the switch element causes the boost power supply to be turned on and off (rising / falling) every time. A high-voltage level shift unit is also required to transmit the drive command. The control voltage is applied to the switch element through the high-voltage level shift unit, but the delay time of the level shift unit is large, and it takes a long time to shut off the switch element.

[0005] If the delay in the high-voltage level shift section has a large effect, abnormality determination and protective action will be delayed, and the secondary output voltage of the transformer may become an overvoltage immediately after shutoff, causing the component to malfunction. In addition, the high-voltage level shift section may have a risk of causing the control current value to exceed the set value due to the delay, increasing the ripple of the output voltage. There is also a risk of the transformer becoming magnetic flux saturated. In this case, a switch element with a larger than necessary tolerance must be used to prevent abnormalities from occurring. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-228538 A Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present disclosure is to provide a switching power supply device that can be configured while minimizing the tolerance of the switch, suppresses ripple in the output voltage during normal operation, and is capable of performing appropriate protective operation when an abnormality is detected. [Means for solving the problem]

[0008] The switching power supply device of claim 1 includes a first switch, a second switch, a detection unit, a control unit, a first drive unit, and a second drive unit. The first switch and the second switch correspond to the switch elements described in the Background of the Invention section. The first switch is connected to the high voltage side on the primary side of the transformer. The second switch is connected to the low voltage side in series with the first switch. The detection unit detects the current flowing on the primary side of the transformer.

[0009] The control unit determines the on / off timing of the first switch and the second switch. The first drive unit is provided with a level shift unit that operates using a boost power supply and level-shifts a control voltage by the control unit, and drives the first switch through the level shift unit. The second drive unit receives the control voltage by the control unit and drives the second switch without using the level shift unit. When the control unit controls the first switch using the first drive unit based on a detection value by the detection unit and controls the second switch using the second drive unit, the control unit operates the unnecessary second switch of the level shift unit as a switch for turning off current on the primary side of the transformer.

[0010] According to the invention of claim 1, the control unit controls the first switch connected to the high voltage side using a bootstrap power supply and a level shift unit, and controls the second switch without using a level shift unit. Therefore, the control unit can quickly turn off the current to the primary side of the transformer by operating the second switch, which is not required for the level shift unit, as a switch for turning off the current to the primary side of the transformer.

[0011] During normal operation, the current on the primary side of the transformer can be reduced the moment it reaches the control threshold, and the current does not exceed the control threshold. This makes it possible to minimize ripple in the output voltage. The second switch can be configured while minimizing the withstand capability of the second switch. Furthermore, since the second switch is operated as a switch for turning off current to the primary side of the transformer, even when an abnormality is detected, the control unit can turn off the second switch using the second drive unit, quickly turning off current to the primary side of the transformer, and appropriate protective operation can be performed when an abnormality is detected. [Brief description of the drawings]

[0012] [Figure 1] Electrical configuration diagram of a switching power supply device according to a first embodiment [Diagram 2] 1 is a flowchart illustrating an operation according to a first embodiment. [Diagram 3] A time chart showing the operation of Comparative Example 1 [Figure 4]A time chart showing the operation of the second comparative example [Diagram 5] 5 is a time chart showing an operation of the first embodiment; [Figure 6] 11 is a flowchart illustrating an operation according to a second embodiment. [Figure 7] 11 is a flowchart illustrating an operation according to a third embodiment. [Figure 8] 13 is a time chart showing an operation according to the third embodiment; [Figure 9] Electrical configuration diagram of a switching power supply device according to a fourth embodiment [Figure 10] 11 is a flowchart illustrating an operation according to a fourth embodiment. [Figure 11] 13 is a time chart showing an operation of the fourth embodiment; [Figure 12] Electrical configuration diagram of a switching power supply device according to a fifth embodiment [Figure 13] 13 is a flowchart illustrating an operation according to the fifth embodiment. [Figure 14] Electrical configuration diagram of a switching power supply device according to a sixth embodiment. [Figure 15] 13 is a time chart showing an operation of the sixth embodiment; [Figure 16] 13 is a time chart showing an operation of the seventh embodiment; DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, several embodiments of a switching power supply will be described with reference to the drawings. In the embodiments, the same or similar components are denoted by the same or similar reference numerals, and the description thereof may be omitted.

[0014] (First embodiment) The first embodiment will be described with reference to Fig. 1 to Fig. 5. As illustrated in Fig. 1, the switching power supply device 1 mainly includes a control unit 10, a first driving unit 11, a second driving unit 12, a detection unit 13, a transformer 14, an input side smoothing circuit 15, an output side smoothing circuit 16, and a feedback unit 17. The switching power supply device 1 is configured as an isolated flyback type. The transformer 14 includes a primary winding consisting of a main winding and an auxiliary winding, and a secondary winding.

[0015] An input DC voltage Vin is applied to one end of the main winding of the primary winding of the transformer 14. A first switch SW1 is connected in series to the high voltage side of the other end of the main winding, and a second switch SW2 is connected in series to the low voltage side. The first switch SW1 is, for example, an N-channel MOSFET. The second switch SW2 is also, for example, an N-channel MOSFET. The first switch SW1 and the second switch SW2 may be configured with IGBTs. IGBT stands for Insulated Gate Bipolar Transistor.

[0016] The other end of the main winding is connected in series to the drain-source (current-carrying terminals) of the first switch SW1, the drain-source (current-carrying terminals) of the second switch SW2, and through a current detection resistor Rs to ground.

[0017] On the other hand, an input-side smoothing circuit 15 is connected to the auxiliary winding on the primary side of the transformer 14. The input-side smoothing circuit 15 is configured by combining a diode D2 and an input smoothing capacitor C2 as shown in the figure, and rectifies and smoothes the voltage generated in the auxiliary winding on the primary side of the transformer 14 and outputs the output DC voltage to a feedback unit 17.

[0018] An output-side smoothing circuit 16 is connected to the secondary winding of the transformer 14. The output-side smoothing circuit 16 is configured by combining a diode D3 and an output smoothing capacitor C3 as shown in the figure, and rectifies and smoothes the voltage generated on the secondary side of the transformer 14 and outputs it to a load 18 as an output voltage Vout.

[0019] The first driving unit 11 is provided to drive the first switch SW1. The second driving unit 12 is provided to drive the second switch SW2. The first driving unit 11 includes a high-voltage level shift unit 21, a first gate driving unit 22, a first on / off determination unit 24, and a high-voltage level shift unit 23. The second driving unit 12 includes a second gate driving unit 31 and a second on / off determination unit 32.

[0020] A voltage V1 and a bootstrap power supply Vbst are individually applied to the high-voltage level shift unit 21. The bootstrap power supply circuit uses a diode D1, a capacitor C1, and the voltage V1 to generate the bootstrap power supply Vbst as a control power supply.

[0021] The gate of the first switch SW1, which serves as a control terminal, is connected to the first drive unit 11. The control unit 10 outputs, as an ON command, a pulse of a control voltage modulated by, for example, PFM modulation corresponding to a target voltage of the output voltage Vout to the high-withstand voltage level shift unit 21. The high-withstand voltage level shift unit 21 level-shifts the input control voltage pulse to the high-voltage side and outputs it to the first gate drive unit 22.

[0022] The first gate driver 22 is provided with a bootstrap power supply Vbst by a bootstrap power supply circuit. The first gate driver 22 drives the gate of the first switch SW1 using this bootstrap power supply Vbst. The first on / off judger 24 is connected to the gate of the first switch SW1. The first on / off judger 24 detects the gate voltage of the first switch SW1. The first on / off judger 24 judges the on / off state of the first switch SW1 by comparing the gate voltage with a predetermined threshold voltage, and outputs this judgment result to the high-withstand voltage level shifter 21. The high-withstand voltage level shifter 21 level-shifts the judgment signal of the first on / off judger 24 to the low voltage side and outputs it to the controller 10. This allows the controller 10 to control the on / off of the first switch SW1 while detecting the on / off state of the first switch SW1.

[0023] The gate of the second switch SW2 as a control terminal is connected to the second drive unit 12. When controlling the second switch SW2 to be on, the control unit 10 applies an on-control voltage to the gate of the second switch SW2 via the second gate drive unit 31. When controlling the second switch SW2 to be off, the control unit 10 applies a zero control voltage to the gate of the second switch SW2 via the second gate drive unit 31. This allows the control unit 10 to control the on-off of the second switch SW2.

[0024] A second on / off determination unit 32 is connected to the gate of the second switch SW2. The second on / off determination unit 32 detects the gate voltage of the second switch SW2, and compares the gate voltage with a predetermined threshold voltage to determine the on / off state of the second switch SW2 and output the determination result to the control unit 10. This allows the control unit 10 to control the on / off of the second switch SW2 while detecting the on / off state of the second switch SW2.

[0025] The detection unit 13 includes a current detection resistor Rs, a first comparator 33 that compares a detection voltage VRs applied to the current detection resistor Rs with a predetermined short-circuit threshold, and a second comparator 34 that compares the voltage applied to the current detection resistor Rs with a predetermined control threshold. The first comparator 33 and the second comparator 34 are used as a comparison unit. The short-circuit threshold is predetermined to be higher than the control threshold.

[0026] The control threshold indicates a voltage corresponding to a control current threshold (see FIG. 3) of the current I1 on the primary side of the transformer 14, which is predetermined for outputting an OFF command from the detection unit 13. The control threshold is proportional to the control current threshold. When the primary side of the transformer 14 is short-circuited, the current I1 on the primary side of the transformer 14 increases and a short-circuit current flows. The short-circuit threshold indicates a voltage corresponding to a short-circuit current threshold which is predetermined for detecting this short-circuit current. The short-circuit threshold is proportional to the short-circuit current threshold.

[0027] When a short-circuit current flows through the current detection resistor Rs, the first comparator 33 detects the short-circuit current and outputs a short-circuit detection signal to the control unit 10. When a control current value for ON flows through the current detection resistor Rs, the second comparator 34 detects the control current value and outputs an OFF command signal to the control unit 10. The control unit 10 controls the first switch SW1 and / or the second switch SW2 to OFF based on the short-circuit detection signal of the first comparator 33 and the OFF command signal of the second comparator 34. For example, when the control unit 10 receives an OFF command signal from the second comparator 34, it controls the second switch SW2 to OFF. The detailed timing of the ON / OFF control of the second switch SW2 will be described later.

[0028] On the other hand, the input side smoothing circuit 15 rectifies and smoothes the voltage generated in the auxiliary winding on the primary side, and outputs the rectified voltage to the feedback unit 17. The feedback unit 17 outputs an ON command to the control unit 10 based on the output voltage of the input side smoothing circuit 15. Upon receiving the ON command, the control unit 10 controls the first switch SW1 to ON in response to the ON command. The timing of the ON / OFF control of the first switch SW1 will be described later.

[0029] The control unit 10 controls the on / off of the first switch SW1 using the first drive unit 11, and also controls the on / off of the second switch SW2 using the second drive unit 12, thereby generating an AC voltage in the primary winding of the transformer 14. The transformer 14 converts the AC voltage generated in the primary winding of the transformer 14 and generates it in the secondary winding. An output-side smoothing circuit 16 is connected to the secondary winding. The output-side smoothing circuit 16 rectifies and smoothes the AC voltage, and supplies an output voltage Vout to a load 18. This allows the switching power supply device 1 to supply a DC output voltage Vout to the load 18.

[0030] Next, a basic operation for outputting the DC output voltage Vout and a process for monitoring the first switch SW1 will be described with reference to the flowchart in Fig. 2. In the following description, a case will be described in which only the first switch SW1 is monitored for a short-circuit abnormality.

[0031] In the initial standby state, as shown in S101 of Fig. 2, the control unit 10 controls the first switch SW1 to be OFF and the second switch SW2 to be ON to enter the standby state. Since the first switch SW1 is OFF, the current I1 does not flow to the primary side of the transformer 14. At this time, the control unit 10 waits while charging the bootstrap power supply circuit. Initially, the control unit 10 generates a PFM modulated ON command pulse in S103, and controls the first switch SW1 to be ON by the first drive unit 11 in response to the ON command.

[0032] As shown in S104, the first switch SW1 and the second switch SW2 are both turned on. As a result, the current I1 starts to flow through the primary side of the transformer 14. The current I1 also starts to flow through the current detection resistor Rs. In S105, the second comparator 34 detects the detection voltage VRs of the current detection resistor Rs and determines whether it exceeds the control threshold. When the detection voltage VRs reaches the control threshold, the comparator 34 outputs an OFF command to the control unit 10. Upon receiving the OFF command, the control unit 10 stops the current I1 by controlling the second switch SW2 to be turned off by the second drive unit 12 in S106. In this case, the second switch SW2 does not require a high-voltage level shift, so the current I1 can be turned off without delay.

[0033] Thereafter, the control unit 10 determines in S107 whether the second switch SW2 has been turned off. At this time, whether the second switch SW2 has been turned off may be determined by detecting whether the gate voltage of the second switch SW2 has dropped below a predetermined threshold voltage using the second on / off determination unit 32. Alternatively, for example, the detection unit 13 may detect that the voltage across the current detection resistor Rs has reached zero to determine whether the second switch SW2 has been turned off.

[0034] When the control unit 10 confirms that the second switch SW2 is in the OFF state, it controls the first switch SW1 to be OFF in S108, thereby making it possible to sequentially control the second switch SW2 and the first switch SW1 to be OFF.

[0035] Thereafter, the control unit 10 checks whether the state of the first switch SW1 has become OFF in S109. At this time, whether the state of the first switch SW1 has become OFF may be determined by detecting whether the gate voltage has dropped below a predetermined threshold voltage by the first ON / OFF determination unit 24. Note that, for example, the control unit 10 may start a built-in timer from the timing when the drive unit starts the OFF drive control, and may determine that the first switch SW1 has become OFF when a predetermined time has elapsed on the timer.

[0036] When the control unit 10 confirms that the first switch SW1 is in the OFF state, it controls the second switch SW2 to be ON in S101. This allows the second switch SW2 to be ON after confirming that the first switch SW1 is OFF. As a result, the first switch SW1 is in the OFF state and the second switch SW2 is in the ON state. The second switch SW2 is turned ON from the OFF state, and charging of the bootstrap power supply Vbst is started (see timing t3 shown in FIG. 5, which will be described later). As shown in S102 of FIG. 2, the control unit 10 repeats the determination processes of S102 and S103 unless the detection voltage VRs of the current detection resistor Rs falls below a predetermined short-circuit threshold that is determined in advance in response to the short-circuit current threshold of the current I1 and an ON command is received from the feedback unit 17 in S103.

[0037] In the standby state of S101 to S103, the control unit 10 waits with the first switch SW1 controlled to be off and the second switch SW2 controlled to be on, and during this time, the control unit 10 can continue to supply the voltage V1 as a boost power supply and the bootstrap power supply Vbst from the capacitor C2 to the first drive unit 11.

[0038] While the control unit 10 is repeating the determination process in the standby state of S101 to S103, the feedback unit 17 monitors the voltage V1 of the capacitor C2 of the transformer 14 and determines the on-timing. Then, the feedback unit 17 outputs an on command for the current I1 on the primary side of the transformer 14 to the control unit 10 at the determined on-timing.

[0039] When the feedback unit 17 detects that the voltage V1 on the primary side of the transformer 14 has dropped below a predetermined charging start voltage, it outputs an ON command to the control unit 10. The voltage V1 is consumed as power by the high-voltage level shift unit 21, the high-voltage level shift unit 23, the first gate driver 22, and the second gate driver 31 operating.

[0040] The above-mentioned predetermined charging start voltage is set with a margin in mind for the threshold voltage at which the voltage V1 is consumed and becomes unusable. Therefore, when the high-voltage level shift unit 21, the high-voltage level shift unit 23, the first gate driver 22, and the second gate driver 31 operate and consume power, and the voltage V1 falls to the predetermined threshold voltage, the feedback unit 17 outputs an on command for the current I1 on the primary side of the transformer 14 to the control unit 10.

[0041] Here, the feedback unit 17 monitors the voltage V1 on the primary side of the transformer 14 to determine the on-timing, but the part that the feedback unit 17 monitors may be changed as appropriate. For example, the feedback unit 17 may monitor the output voltage Vout on the secondary side of the transformer 14 to determine the on-timing. The output voltage Vout gradually decreases as the load 18 consumes power. For this reason, the feedback unit 17 may determine the timing of the on command for the current I1 on the primary side of the transformer 14 on the condition that the output voltage Vout has decreased to the charging start threshold. In this case, the output voltage Vout may be input to the feedback unit 17 via an insulating element. That is, the feedback unit 17 may determine the timing of the on command based on either or both of the voltage V1 on the primary side of the transformer 14 or the output voltage Vout on the output side.

[0042] When the control unit 10 receives an ON command from the feedback unit 17, in S104, the control unit 10 causes the first drive unit 11 to turn on the first switch SW1. This allows both the first switch SW1 and the second switch SW2 to be controlled to be ON. Furthermore, when the control unit 10 detects in S105 that the detected current by the detection unit 13 has reached the control current threshold, i.e., that the detected voltage VRs has reached the control threshold, the control unit 10 turns off the second switch SW2.

[0043] Thereafter, when the control unit 10 confirms in S107 that the second switch SW2 is off using the second on / off determination unit 32, it turns off the first switch SW1 in S108. Also, when it confirms in S109 that the first switch SW1 is off, it turns on the second switch SW2. Then, it returns to the standby state of S101. Usually, the processes of S101 to S109 can be repeated through such state transitions. Therefore, the control unit 10 controls the on / off of the first switch SW1 and the second switch SW2 based on the on command received from the feedback unit 17, the off command received from the detection unit 13, and the short circuit detection signal.

[0044] <Detection of short circuit abnormality in the first switch SW1> While the control unit 10 is repeating the determination processes of S102 and S103, if the detection unit 13 detects via the first comparator 33 that the detection voltage VRs of the current detection resistor Rs has become equal to or greater than the short circuit threshold, the control unit 10 outputs a short circuit detection signal to the control unit 10.

[0045] When the control unit 10 receives the short circuit detection signal, it determines that a short circuit abnormality has occurred because the detection voltage VRs exceeds the short circuit threshold even though the first switch SW1 is in an OFF command. In this case, the control unit 10 controls both the first switch SW1 and the second switch SW2 to the OFF state in S110. In this case, for example, a predetermined fail-safe process is performed.

[0046] <Explanation of Comparative Example 1> Timing charts in the case where the technology of the comparative example is applied are shown in Figures 3 and 4. Figure 3 shows a timing chart in the case where an electrical configuration similar to that of the switching power supply circuit shown in Figure 1 is used, but the first switch SW1 is used for protection purposes and the second switch SW2 is used for on / off control.

[0047] When the first switch SW1 is used for protection purposes, the control unit 10 keeps the first switch SW1 on during normal operation. Then, the control unit 10 controls the second switch SW2 to be on / off as shown at timings ta2, ta4, and ta6 in FIG. 3, thereby generating an AC voltage on the primary side of the transformer 14.

[0048] In the circuit configuration described above, since the off period of the second switch SW2 is long, power is not supplied to the bootstrap power supply Vbst and the bootstrap power supply Vbst continues to be consumed, causing the voltage to drop.

[0049] Therefore, as shown at timings ta1, ta3, and ta5, the first switch SW1 turns off and cannot maintain the on state in a period in which the bootstrap power supply Vbst falls below a predetermined threshold voltage Vt. When the first switch SW1 turns off at these timings ta1, ta3, and ta5, the second switch SW2 is also off. This causes the supply of the bootstrap power supply Vbst to the high-voltage level shift unit 21 and the gate driver to become unstable.

[0050] , 3, if the controller 10 turns on both the first switch SW1 and the second switch SW2 at the timings ta2, ta4, and ta6 shown in Fig. 3, power is charged to the bootstrap power supply Vbst, causing the bootstrap power supply Vbst to rise. However, as described above, the first switch SW1 periodically repeats on-off operation every time the bootstrap power supply Vbst falls below the predetermined threshold voltage Vt, resulting in an unstable operating state.

[0051] 3, if the first switch SW1 subsequently experiences a short-circuit failure at timing t20 in Fig. 3, the control unit 10 controls the first switch SW1 to be turned off at the following timing t11. The first switch SW1 requires the high-voltage level shift unit 21 to convert the command voltage and issue an off command.

[0052] For this reason, an extra delay time Tdls occurs in the level shift operation of the high-voltage level shift unit 21, and as shown by the delay time Tdls from timing t11 to t11a, the off control time of the first switch SW1 is also delayed. This makes it difficult to instantly stop the operation at the timing when the short circuit threshold for the overcurrent is reached. As shown after timing t11 to t11a in FIG. 3, the output voltage Vout of the switching power supply device 1 generates an overvoltage that significantly deviates from the target voltage, which is not preferable.

[0053] <Explanation of Comparative Example 2> FIG. 4 shows a timing chart for a case in which a circuit having the same electrical configuration as the switching power supply device 1 shown in FIG. 1 is used, but the first switch SW1 is used for on / off control and the second switch SW2 is used for protection.

[0054] When the second switch SW2 is used for protection purposes, the control unit 10 keeps the second switch SW2 on at all times during normal operation. The control unit 10 then controls the first switch SW1 on and off to generate an AC voltage on the primary side of the transformer 14.

[0055] When the control unit 10 performs on / off control via the first switch SW1, the high-voltage level shift unit 21 converts the voltage of the on / off command to perform on / off control. This causes an extra delay time Tdls based on the operation of the high-voltage level shift unit 21, and the output voltage Vout fluctuates significantly even after the original target control threshold is reached. See the fluctuating voltage ΔV2 in FIG. 4. This makes it difficult to precisely control the output voltage Vout. A large voltage ripple is generated in the output voltage Vout, making it difficult to control the output voltage Vout to the target voltage.

[0056] <Explanation of the Technical Significance of the Present Embodiment> In contrast, an example of a timing chart when the configuration of this embodiment is adopted is shown in Fig. 5. As shown in Fig. 5, the first switch SW1 generates a delay time Tdls in the action of the high-voltage level shift unit 21. Therefore, the first switch SW1 actually turns on / off with a delay from the on / off command. On the other hand, the second switch SW2 does not require the high-voltage level shift unit 21, so it turns on / off with as little delay as possible from the on / off command.

[0057] In the standby state of S101, the second switch SW2 is turned on while the first switch SW1 is kept off, and if the detection voltage VRs of the detection unit 13 is below the short circuit threshold, the second switch SW2 is turned off. This makes it possible to immediately turn off the second switch SW2 without causing a delay time Tdls due to the level shift action by the high-voltage level shift unit 21. This makes it possible to suppress voltage ripple as much as possible, and the output voltage Vout of the switching power supply device 1 can be controlled to a predetermined range centered on the target voltage, and no overvoltage occurs in the output voltage Vout.

[0058] <Effects of this embodiment> The control unit 10 controls the first switch SW1 connected to the high voltage side using the voltage V1 and the high voltage level shift unit 21, and controls the second switch SW2 without using the high voltage level shift unit 21. Therefore, the control unit 10 operates the unnecessary second switch SW2 of the high voltage level shift unit 21 as a switch for turning off the current supply to the primary side of the transformer 14, thereby enabling the primary side of the transformer 14 to be turned off quickly.

[0059] During normal operation, the detection voltage VRs can be reduced the moment it reaches the control threshold, and the current I1 does not exceed the control current threshold. In addition, the bootstrap power supply Vbst does not rise / fall as shown in Comparative Example 1, and the first switch SW1 does not turn on / off at unintended times. Moreover, the ripple of the output voltage Vout can be suppressed as much as possible, and the second switch SW2 can be configured while suppressing its tolerance as much as possible. The output voltage Vout can be controlled at the desired target current value, and the standby state can be quickly returned to.

[0060] In addition, since the second switch SW2 is operated as a switch for turning off current to the primary side of the transformer 14, even when an abnormality is detected, the control unit 10 can quickly turn off current to the primary side of the transformer 14 by turning off the second switch SW2 using the second drive unit 12, thereby enabling appropriate protective operation to be performed when an abnormality is detected.

[0061] Second embodiment The second embodiment will be described with reference to FIG. 6. In the first embodiment, the control unit 10 turns off the second switch SW2 and the first switch SW1 in stages. However, when turning off the first switch SW1, the control unit 10 may turn off the first switch SW1 after the second switch SW2 has been turned off and the first predetermined time Td1 has elapsed. In addition, the second switch SW2 may be turned on when the first predetermined time Td1 has elapsed after the second predetermined time Td2 has elapsed and the first switch SW1 has elapsed after the first switch SW1 has been turned off. Here, the first predetermined time Td1 and the second predetermined time Td2 may be the same time or different times.

[0062] For example, as shown in FIG. 6, the control unit 10 turns on both the first switch SW1 and the second switch SW2 in S104, and then determines in S105 whether the detection voltage VRs exceeds the control threshold. If the detection voltage VRs exceeds the control threshold, the control unit 10 turns off the second switch SW2 in S106 while keeping the first switch SW1 on.

[0063] The control unit 10 starts a timer from the timing when the second switch SW2 is commanded to be turned off, and when it is determined in S107a that the first predetermined time Td1 has elapsed, it commands the first switch SW1 to be turned off. The control unit 10 also restarts the timer from the timing when the first switch SW1 is commanded to be turned off, and when it is determined in S109a that the second predetermined time Td2 has elapsed, the control unit 10 returns the process to S101 and controls the second switch SW2 to be turned on. This allows the transition to the standby state of S101. This provides the same effects as the first embodiment.

[0064] Third embodiment A third embodiment will be described with reference to Fig. 7 and Fig. 8. In the first embodiment, the second switch SW2 and the first switch SW1 are turned off stepwise at different timings, but the processes of S106 and S107 in Fig. 2 may be omitted and the first switch SW1 and the second switch SW2 may be turned off simultaneously.

[0065] As shown in FIG. 7, the control unit 10 turns on both the first switch SW1 and the second switch SW2 in S104, and then determines in S105 whether or not the control threshold has been exceeded. If the control threshold has been exceeded, the control unit 10 may simultaneously turn off the first switch SW1 and the second switch SW2 in S108.

[0066] As shown in Fig. 8, the control unit 10 controls the first switch SW1 to be on at timing t1. After that, when the detection unit 13 detects that the detection voltage VRs has reached the control threshold, the control unit 10 controls both the first switch SW1 and the second switch SW2 to be off at the same time at S108 in Fig. 7 and timing t2b in Fig. 8. When the control unit 10 confirms that the first switch SW1 is in the off state, it controls the second switch SW2 to be on. After confirming that the first switch SW1 is in the off state, the control unit 10 may immediately control the second switch SW2 to be on.

[0067] Alternatively, after confirming that the first switch SW1 is OFF, the control unit 10 may start a timer to determine whether or not a third predetermined time Td3 has elapsed, and turn on the second switch SW2 after the third predetermined time Td3 has elapsed. The control unit 10 turns on the second switch SW2 again at timing t3 after the third predetermined time Td3 has elapsed. This allows the second switch SW2 to be turned on in S101 after the third predetermined time Td3 has elapsed after the first switch SW1 is confirmed to be OFF.

[0068] This allows the transition to the standby state of S101. This provides the same effects as those of the first embodiment. The first to third predetermined times Td1 to Td3 may all be the same time, any two of them may be the same time and the other one may be a different time, or all of them may be different times.

[0069] (Fourth embodiment) The fourth embodiment will be described with reference to Figures 9 to 11. In the switching power supply device 1 of the above-described embodiment, the second drive unit 12 is provided with the second on / off determination unit 32 that detects the gate voltage of the second switch SW2, but the method of detecting the state of the second switch SW2 is not limited to this method.

[0070] 9, a third comparator 35 for current off detection may be provided in a detection unit 213. The detection unit 213 includes a first comparator 33, a second comparator 34, and a third comparator 35. A second drive unit 212 replacing the second drive unit 12 includes a second gate drive unit 31, but does not include the second on / off determination unit 32 described in the first embodiment.

[0071] The second switch SW2 is provided for turning off the current flow on the primary side of the transformer 14. When the control unit 10 drives the gate of the second switch SW2 off by the second gate drive unit 31, the current I1 on the primary side of the transformer 14 is turned off. As a result, the current I1 flowing through the current detection resistor Rs is cut off. When the detection voltage VRs of the current detection resistor Rs falls below a predetermined short-circuit threshold in S102a of Fig. 10 and the detection voltage VRs becomes zero V in S102b, the third comparator 35 of the detection unit 213 outputs an off detection signal of the second switch SW2 to the control unit 10.

[0072] When the control unit 10 receives an off detection signal of the second switch SW2 from the third comparator 35, it determines that the second switch SW2 is off. This makes it possible to confirm that the second switch SW2 is off without providing the second on / off determination unit 32. After that, the control unit 10 controls the first switch SW1 to be off in S108. That is, before determining that the second switch SW2 is short-circuited in S102a→S110, the control unit 10 controls the first switch SW1 to be off when the detection voltage VRs of the current detection resistor Rs becomes zero in S102b. This makes it possible to accurately determine whether or not a short-circuit abnormality has occurred. The subsequent processing contents are the same as those in the above-described embodiment, and therefore will not be described.

[0073] The operation will be described when the second switch SW2 is short-circuited at timing t20 in Fig. 11 while the first switch SW1 is in the OFF state and the second switch SW2 is in the ON state in standby mode. The control unit 10 generates an ON command for the first switch SW1 at timing t21 after timing t20. The first switch SW1 is controlled to be ON at timing t21d delayed from timing t21 due to the influence of the delay time Tdls of the first drive unit 11.

[0074] When the detection voltage VRs reaches the control threshold in S105, the control unit 10 controls the second switch SW2 to be turned off at timing t22. Because the first switch SW1 is controlled to be turned on and the second switch SW2 is short-circuited, the current I1 continues to flow and the detection voltage VRs continues to rise. When the detection voltage VRs reaches the short-circuit threshold in S102a, the control unit 10 determines that the second switch SW2 is short-circuited.

[0075] As a result, the control unit 10 can determine a short circuit abnormality of the first switch SW1 in S102 and can determine a short circuit abnormality of the second switch SW2 in S102a, and can distinguish the abnormalities of the first switch SW1 and the second switch SW2 individually. When the control unit 10 determines a short circuit abnormality, it controls the second switch SW2 to be turned off at timing t11 in FIG. 11. This can protect the circuit. At this time, elements having the same tolerance characteristics can be used for both the first switch SW1 and the second switch SW2. The circuit configuration of this embodiment also achieves the same effects as the previous embodiment.

[0076] Fifth embodiment The fifth embodiment will be described with reference to Figs. 12 and 13. Fig. 12 is an electrical configuration diagram of a switching power supply device 501 shown in place of Fig. 1 of the first embodiment, and Fig. 13 is a flowchart shown in place of Fig. 7 of the third embodiment. Differences from the other embodiments will be described. In addition to the configuration of the switching power supply device 1, the switching power supply device 501 is provided with a first drive unit 211 instead of the first drive unit 11, and a second drive unit 212 instead of the second drive unit 12.

[0077] 12, the first driving section 211 includes a high-voltage level shift section 21, a first gate driving section 22, a capacitor C1, and a diode D1, but does not include the first on / off determination section 24 and the high-voltage level shift section 23 of the first driving section 11 described in the first embodiment. In addition, the second driving section 212 includes a second gate driving section 31, but does not include the second on / off determination section 32 described in the first embodiment.

[0078] 13, the control unit 10 turns off both the first switch SW1 and the second switch SW2 in S108, and then determines whether a predetermined time has elapsed using a timer in S109a. If the predetermined time has elapsed, the control unit 10 turns on the first switch SW1 and continues. By repeating the process in this manner, it becomes possible to configure the device without providing the first on / off determination unit 24 and the second on / off determination unit 32, thereby reducing the circuit area and the circuit scale.

[0079] Sixth embodiment The sixth embodiment will be described with reference to Figs. 14 and 15. Fig. 14 is an electrical configuration diagram of a switching power supply device 601 shown in place of Fig. 1 of the first embodiment and Fig. 12 of the fifth embodiment, and Fig. 15 is a flow chart shown in place of Fig. 3 of the first embodiment. Differences from the other embodiments will be described. In addition to the configuration of the switching power supply device 1, the switching power supply device 601 includes a first drive unit 211 instead of the first drive unit 11, and a second drive unit 212 instead of the second drive unit 12. The switching power supply device 601 includes a detection unit 613 instead of the detection unit 13.

[0080] As shown in Fig. 14, the first driving section 211 does not include a first on / off determination section 24. The second driving section 212 does not include a second on / off determination section 32. Therefore, as in the fifth embodiment, the circuit area can be reduced and the circuit scale can be made smaller. The detection section 613 includes a second comparator 34, but does not include the first comparator 33 and the third comparator 35 described in the above embodiments. Therefore, compared to these embodiments, the circuit area can be reduced and the circuit scale can be made smaller.

[0081] The switching power supply device 601 differs from the switching power supply devices 1 and 501 of the above-described embodiments in that the second comparator 34 of the detection unit 613 is shared between control and short-circuiting. The control unit 10 sets the control threshold to the same control threshold as in the above-described embodiments, and repeats on / off control of the first switch SW1 and the second switch SW2 as shown in FIG.

[0082] 15, during normal operation, in a standby state in which the first switch SW1 is in an OFF state and the second switch SW2 is in an ON state, the control unit 10 controls the first switch SW1 to turn on at timing t1, thereby increasing the current I1 on the primary side of the transformer 14. After that, when the detection voltage VRs reaches a control threshold corresponding to the control current threshold of the current I1, the detection unit 613 outputs a detection signal indicating that the control threshold has been reached to the control unit 10.

[0083] When the control unit 10 receives the detection signal, it controls the second switch SW2 to be OFF at timing t2. After a predetermined time has elapsed by a timer, the control unit 10 controls the first switch SW1 to be OFF at timing t2a. After that, when the control unit 10 confirms that the first switch SW1 is OFF at timing t3, it controls the second switch SW2 to be ON and returns to the standby state.

[0084] Therefore, in a standby state in which the first switch SW1 is in an OFF state and the second switch SW2 is in an ON state, the current I1 on the primary side of the transformer 14 does not basically increase. In the standby state, if the first switch SW1 is short-circuited due to some influence, the current I1 on the primary side of the transformer 14 starts to increase, as shown at timing t10 ​​in Fig. 15. When the detection voltage VRs reaches the control threshold, the control unit 10 inputs a detection signal indicating that the control threshold has been reached, and controls the second switch SW2 to be turned off.

[0085] Since the first switch SW1 is short-circuited, the control unit 10 controls the second switch SW2 to turn off, thereby stopping the current I1. This makes it possible to suppress an increase in the output voltage Vout when protection is stopped. This makes it possible to implement protection control equivalent to that achieved by setting the short-circuit threshold to the same value as the control threshold, as explained in the previous embodiment. Since the short-circuit threshold during short-circuit protection can be set to the same value as the control threshold during normal operation, it is possible to suppress a significant increase in the output voltage Vout, even compared to the previous embodiment.

[0086] This embodiment also provides the same effects as the previous embodiment. Moreover, the control threshold value and the short-circuit threshold value are set to be the same, so that the circuit can be shared.

[0087] Seventh embodiment The seventh embodiment will be described with reference to Fig. 16. Descriptions of the same parts as in the sixth embodiment will be omitted, and only parts different from the sixth embodiment will be described. The control unit 10 controls the first switch SW1 to turn on at timing t1 in Fig. 16 from a standby state in which the second switch SW2 is on and the first switch SW1 is off. The first switch SW1 turns on at timing t1d after the delay time Tdls has elapsed. After that, when the detection voltage VRs reaches the control threshold, the control unit 10 controls the second switch SW2 to turn off at timing t2 while keeping the first switch SW1 on.

[0088] The control unit 10 measures the time from timing t2 when the second switch SW2 is turned off, and after a predetermined time has elapsed, determines whether the detection voltage VRs has reached the control threshold. If the detection voltage VRs has not reached the control threshold, the control unit 10 turns off the first switch SW1 at timing t30. After that, the control unit 10 turns on the second switch SW2 at timing t3 to return to the standby state. The control unit 10 repeats this series of control operations.

[0089] Then, for example, assume that the second switch SW2 is short-circuited at timing t20 when both the first switch SW1 and the second switch SW2 are in the OFF state. If the control unit 10 controls the second switch SW2 to turn on after timing t20, causing the first switch SW1 to turn off and the second switch SW2 to turn on, the short-circuit abnormality of the second switch SW2 cannot be detected because the current I1 does not flow.

[0090] However, when the control unit 10 subsequently controls the first switch SW1 to ON, the current I1 begins to flow. Then, the control unit 10 controls the second switch SW2 to OFF at timing t32 when the detection voltage VRs reaches the control threshold. However, because the second switch SW2 is short-circuited, the current I1 on the primary side of the transformer 14 continues to flow. Therefore, the current I1 continues to rise even after the detection voltage of the current detection resistor Rs reaches the control threshold.

[0091] Even at timing t32, a predetermined time after the second switch SW2 is turned off, the second comparator 34 continues to output a detection signal indicating that the detection voltage VRs is higher than the control threshold to the control unit 10. Therefore, the control unit 10 can determine that the second switch SW2 is short-circuited. Then, the control unit 10 controls the first switch SW1 to turn off at timing t32 to stop the current I1. After that, the first switch SW1 is turned off after the delay time Tdls has elapsed from timing t32, thereby stopping the current I1.

[0092] According to this embodiment, in a state where the first switch SW1 is ON and the second switch SW2 is ON, the control unit 10 turns off the second switch SW2 and then determines that the second switch SW2 is short-circuited if a predetermined control threshold is exceeded after a certain period of time has elapsed. This provides the same effects as the above-described embodiment. Also, by setting the short-circuit threshold and the control threshold to the same value, the circuit can be shared.

[0093] (Other embodiments) The present disclosure is not limited to the above-described embodiment, and for example, the following modifications or extensions are possible.

[0094] Although the first switch SW1 is shown as being configured by a MOSFET, the present invention is not limited to this, and any type of commonly known switch, such as an IGBT, can be used as the first switch SW1.

[0095] In addition, when the voltage to be handled is a low voltage input, particularly the voltage of an auxiliary battery (such as a 12V battery), a P-channel MOSFET may be applied, or an N-channel MOSFET may be applied. When the voltage to be handled is a high voltage such as the driving battery of an electric vehicle (for example, about 600V or 800V), it is preferable to use an N-channel MOSFET. Even when the voltage to be handled is low, it is more preferable to use an N-channel MOSFET because the withstand voltage can be lowered and the on-resistance is also lower.

[0096] If the first switch SW1 is an N-channel MOSFET, a boost power supply using a bootstrap circuit is required. If the first switch SW1 is a P-channel MOSFET, a high-voltage power supply is required at the upper reference of the switch. For this reason, the above-mentioned problem occurs whether an N-channel or P-channel MOSFET is used, and it is possible to obtain the same effect by configuring as in the above-mentioned embodiment.

[0097] For example, when a binary control signal is used as exemplified above, the first switch SW1 may be configured to close when an L-level signal is received and to open when an H-level signal is received. Therefore, any commonly known switch may be used as the first switch SW1.

[0098] The techniques described in the present disclosure may be implemented by a special purpose computer provided by configuring a processor and memory programmed to perform one or more functions embodied in a computer program. Alternatively, the techniques described in the present disclosure may be implemented by a special purpose computer provided by configuring a processor with one or more dedicated hardware logic circuits. Alternatively, the techniques described in the present disclosure may be implemented by one or more special purpose computers configured by a combination of a processor and memory programmed to perform one or more functions and a processor configured with one or more hardware logic circuits. Also, the computer program may be stored in a computer-readable non-transitory tangible recording medium as instructions executed by the computer.

[0099] Although the present disclosure has been described based on the above-mentioned embodiment, it is understood that the present disclosure is not limited to the embodiment or the structure described in the embodiment. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one element, or less than one element, are also within the scope and concept of the present disclosure. [Explanation of symbols]

[0100] In the drawings, 1, 201, 501, and 601 indicate switching power supplies, SW1 indicates a first switch, SW2 indicates a second switch, 10 indicates a control unit, 11 and 211 indicate a first drive unit, 12 and 212 indicate a second drive unit, 13 and 613 indicate a detection unit, 14 indicates a transformer, 21 indicates a level shift unit, and Vbst indicates a bootstrap power supply.

Claims

1. A switching power supply device (1; 201; 501; 601), A first switch (SW1) connected to a high-voltage side on the primary side of the transformer; a second switch (SW2) connected in series to the first switch and to a low-voltage side of the first switch; A detection unit (13; 613) for detecting a current flowing through a primary side of the transformer; a control unit (10) that determines on / off timings of the first switch and the second switch and outputs a control voltage; A first driving unit (11; 211) including a level shift unit (21) that operates using a bootstrap power supply (Vbst) and level-shifts the control voltage by the control unit, and drives the first switch through the level shift unit; A second drive unit (12; 212) that receives a control voltage from the control unit and drives the second switch without using the level shift unit, The control unit controls the first switch to be turned on and off using the first drive unit based on the detection value of the detection unit, and controls the second switch to be turned on and off using the second drive unit. This switching power supply device operates the second switch, which does not require the level shift unit, as a switch for turning off current to the primary side of the transformer.

2. 2. The switching power supply device according to claim 1, wherein the control section waits in a state in which the first switch is controlled to be OFF and the second switch is controlled to be ON, and during this period supplies electric charge to the bootstrap power supply.

3. The control unit is The first switch is turned on by the first drive unit in response to the on command; When the detection unit detects that the detection value has reached a control threshold value, the second switch is turned off. When it is confirmed that the second switch is off, the first switch is controlled to be off; 3. The switching power supply device according to claim 1, wherein the second switch is controlled to be on when it is confirmed that the first switch is off.

4. The control unit is The first switch is turned on by the first drive unit in response to an on command; When the detection unit detects that the detection value has reached a control threshold value, the first switch and the second switch are simultaneously turned off; 3. The switching power supply device according to claim 1, wherein the second switch is controlled to be on when it is confirmed that the first switch is off.

5. The control unit is controlling the first switch to be on by using the first drive unit in response to an on command; when a first predetermined time has elapsed since the detection value by the detection unit reaches a control threshold and the second switch is turned off, the first switch is turned off; 3. The switching power supply device according to claim 1, wherein the second switch is turned on when a second predetermined time has elapsed after the first switch is turned off.

6. The control unit is In response to an ON command, a first drive unit controls the first switch to be ON; When a value detected by the detector reaches a control threshold, the detector turns off the first switch and the second switch; 3. The switching power supply device according to claim 1, wherein the second switch is turned on when a third predetermined time has elapsed after the first switch is turned off.

7. The control unit is 3. The switching power supply device according to claim 1, wherein, during a standby state in which the first switch is controlled to be off and the second switch is controlled to be on, if a detection value detected by the detection unit does not decrease and reaches a predetermined short-circuit threshold value exceeding zero, it is determined that a short-circuit abnormality has occurred in the first switch.

8. 3. The switching power supply device according to claim 1, wherein the control unit determines that a short circuit abnormality has occurred in the second switch when a detection value detected by the detection unit does not decrease and reaches a predetermined short circuit threshold value exceeding zero after the first switch is in an on state and the second switch has been controlled to be off.

9. The detection unit is 3. The switching power supply device according to claim 1, further comprising a comparison unit (34) for comparing a control threshold for outputting an OFF command for the second switch with a short-circuit threshold for detecting a short circuit on the primary side of the transformer by making the control threshold and the short-circuit threshold the same.

10. 10. The switching power supply device according to claim 9, wherein, in a state in which the first switch is controlled to be on and the second switch is controlled to be on, the control unit determines that a short-circuit abnormality has occurred in the second switch if a predetermined threshold value is exceeded after a predetermined fixed time has elapsed after the control unit controls the second switch to be off.

11. 9. The switching power supply device according to claim 8, wherein the control unit controls to turn off the first switch when the detection value by the detection unit becomes zero before it is determined that the second switch is short-circuited.

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