DC / DC converter control circuit and control method therefor, and DC / DC converter

Abstract

To provide a DC / DC converter control circuit and control method, as well as a DC / DC converter, that can suppress the occurrence of unintended behavior that may occur when transitioning to pass-through mode, compared to conventional technology. [Solution] The control circuit of a DC / DC converter, which includes a controller that controls the switching elements so that the input voltage becomes a predetermined output voltage by switching the switching elements, includes a comparator. The comparator compares the output voltage with a target voltage which is a voltage offset by a predetermined first voltage from the input voltage or the input voltage itself, and outputs a comparison result signal when the output voltage is less than or equal to the target voltage. The controller switches the switching elements, and after stopping the switching, turns on the switching elements based on the comparison result signal to output the input voltage as the output voltage.

Description

Technical Field

[0001] The present disclosure relates to a control circuit of a DC / DC converter, a control method thereof, and a DC / DC converter.

Background Art

[0002] A synchronous rectification type DC / DC converter outputs a predetermined voltage based on an input voltage by switching two switches on and off complementarily to each other. As a control method for such a DC / DC converter, there is a method called a pass-through mode. When the output current from the DC / DC converter to a load connected to the DC / DC converter is small, the voltage drop is small, so there is no need to boost the input voltage in the DC / DC converter. The pass-through mode is a method of, for example, turning on one of the switches and outputting the input voltage as the output voltage in such a case. For example, Patent Document 1 discloses a technique of reducing the resistance between an input terminal and an output terminal by turning on a switch on a bypass path between the input terminal and the output terminal.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The transition to the pass-through mode is generally performed based on the polarity of a predetermined signal input to a controller for determining whether to perform switching of a switch. However, when the transition to the pass-through mode is determined based only on the polarity of the signal, unintended behaviors such as a reverse flow of current from the load to the input power supply may occur.

[0005] The purpose of this disclosure is to provide a control circuit for a DC / DC converter, a control method for the same, and a DC / DC converter, which can suppress the occurrence of unintended behavior that may occur when transitioning to pass-through mode, compared to the prior art. [Means for solving the problem]

[0006] A control circuit for a DC / DC converter according to one aspect of the present disclosure includes a controller that controls the switching elements so that the input voltage becomes a predetermined output voltage by switching the switching elements, and includes a comparator that compares the output voltage with a target voltage which is a voltage offset by a predetermined first voltage from the input voltage or the input voltage, and outputs a comparison result signal when the output voltage becomes less than or equal to the target voltage, and the controller switches the switching elements, stops the switching, and then turns on the switching elements based on the comparison result signal to output the input voltage as the output voltage. [Effects of the Invention]

[0007] According to this disclosure, it is possible to provide a control circuit for a DC / DC converter and a control method thereof, as well as a DC / DC converter, that can suppress the occurrence of unintended behavior that may occur when transitioning to pass-through mode, compared to the prior art. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 shows a schematic diagram of a DC / DC converter according to Embodiment 1. [Figure 2] Figure 2 is a timing chart showing the operation of the DC / DC converter and control circuit according to Embodiment 1. [Figure 3] Figure 3 is a flowchart showing the control process of the gate controller according to Embodiment 1. [Figure 4] Figure 4 shows a schematic diagram of the DC / DC converter according to Embodiment 2. [Figure 5]Figure 5 is a timing chart showing the operation of the DC / DC converter and control circuit according to Embodiment 2. [Figure 6] Figure 6 is a flowchart showing the control process of the gate controller according to Embodiment 2. [Figure 7] Figure 7 shows a schematic diagram of a DC / DC converter according to a modified example of Embodiment 2. [Figure 8] Figure 8 shows a schematic diagram of a modified DC / DC converter. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure will be described below with reference to the drawings. However, the configurations described below are merely examples of this disclosure, and this disclosure is not limited to the embodiments described below. The technology in this disclosure is not limited thereto, and various modifications, substitutions, additions, and omissions are possible in other embodiments as long as they do not depart from the technical idea of ​​this disclosure, depending on the design, etc.

[0010] While this disclosure is adequately described in relation to preferred embodiments with reference to the accompanying drawings, various modifications and alterations will be obvious to those skilled in the art. Such modifications and alterations should be understood to be included within the scope of this disclosure as defined by the attached claims.

[0011] (Inventor's insights) One control method for synchronous rectification DC / DC converters is called pass-through mode, in which the high-side switch of the two switches is kept in the ON state and output as both the input and output voltages. Conventional DC / DC converter control circuits generally determine whether or not to switch to pass-through mode based on the polarity of the enable signal input to the control circuit. Therefore, if the polarity of the enable signal is undefined, for example, if an input power source such as a battery is connected to the DC / DC converter, it may unintentionally switch to pass-through mode, and an inrush current from the input power source may flow to the load.

[0012] Furthermore, when a DC / DC converter boosts the input voltage and outputs it as an output voltage, the output voltage is higher than the input voltage. If the system switches to pass-through mode in this state, a reverse current flow occurs from the load to the input power supply. If the input power supply is a primary battery, this reverse current can cause power supply failure or reduce the lifespan of the power supply. In addition, the reverse current can generate ringing noise between the capacitors and inductors in the circuit, which can cause malfunctions in the load components.

[0013] The control circuit and control method of a DC / DC converter according to this disclosure, as well as the DC / DC converter itself, are configured to control the transition to pass-through mode based on the polarity of a predetermined signal and other factors. Therefore, the control circuit and control method of a DC / DC converter according to this disclosure, as well as the DC / DC converter itself, can suppress the occurrence of inrush current due to unintended transition to pass-through mode when an input power supply is connected. Furthermore, the control circuit and control method of a DC / DC converter according to this disclosure, as well as the DC / DC converter itself, are configured to compare the output voltage with the input voltage and control the transition to pass-through mode based on the result. Therefore, the occurrence of reverse current flow from the load to the input power supply when transitioning to pass-through mode can be suppressed. In addition, since the occurrence of ringing is suppressed, the occurrence of malfunction of load components can be suppressed. Therefore, the control circuit and control method of a DC / DC converter according to this disclosure, as well as the DC / DC converter itself, can suppress the occurrence of unintended behavior that may occur when transitioning to pass-through mode.

[0014] (Embodiment 1) Referring to Figure 1, the DC / DC converter 1 and its control circuit 10 according to Embodiment 1 of the present disclosure will be described. Figure 1 shows a schematic diagram of the DC / DC converter 1 according to Embodiment 1 of the present disclosure. In Embodiment 1, the DC / DC converter 1, which is a power conversion device, is a synchronous rectification type DC / DC converter.

[0015] As shown in FIG. 1, the DC / DC converter 1 includes a control circuit 10 and a reference voltage source 11 connected to the control circuit 10. The control circuit 10 includes a comparator 12, a comparator 13, and a gate controller 14. Further, the DC / DC converter 1 further includes an inductor 15, a P-channel MOSFET Q1 controlled by the gate controller 14, an N-channel MOSFET Q2, and feedback voltage dividing resistors R1 and R2. The feedback voltage dividing resistors R1 and R2 constitute a feedback voltage output circuit. The feedback voltage output circuit functions as an output voltage detection circuit. The MOSFETs Q1 and Q2 are each an example of a switching element.

[0016] An input voltage Vin is applied to the input terminal T1 of the DC / DC converter 1, and an output voltage Vout is output from the output terminal T2. The output terminal T2 is connected to an output capacitor 16 that smoothes the output voltage Vout and a load 2. One end of each of the output capacitor 16 and the load 2 is connected to the output terminal T2, and the other end of each is connected to the ground GND. Further, the DC / DC converter 1 is configured such that an enable signal EN having a predetermined level is input to the enable terminal T3. The enable signal EN can be output, for example, from a controller or a CPU included in the load 2.

[0017] The control circuit 10 controls the DC / DC converter 1 so as to convert the input voltage Vin into the output voltage Vout by switching the MOSFETs Q1 and Q2 based on the input voltage Vin, the output voltage Vout, and the enable signal EN.

[0018] The reference voltage source 11 outputs a predetermined reference voltage Vref to the comparator 12.

[0019] Comparator 12 compares the feedback voltage Vfb applied from the feedback voltage output circuit based on the output voltage Vout input to the non-inverting input terminal with the reference voltage Vref. Then, comparator 12 outputs a comparison signal S1 having a predetermined level to gate controller 14 according to the comparison result. In Embodiment 1, comparator 12 outputs a comparison signal S1 at a high (H) level when Vfb ≧ Vref, and outputs a comparison signal S1 at a low (L) level when Vfb < Vref. For example, the reference voltage Vref is set so that the feedback voltage Vfb matches the reference voltage Vref when the output voltage Vout is a predetermined set voltage Vset.

[0020] Comparator 13 compares the output voltage Vout input to the non-inverting input terminal with the input voltage Vin input to the inverting input terminal, and outputs a comparison signal S2 having a predetermined level to gate controller 14 according to the comparison result. In Embodiment 1, comparator 13 outputs a comparison signal S2 at the H level when Vout ≦ Vin, and outputs a comparison signal S2 at the L level when Vout > Vin. In this specification, the H level and the L level for the comparison signal S2 are examples of the levels for the comparison result signal.

[0021] The gate controller 14 is configured to accept comparison signals S1 and S2 and an enable signal EN as inputs. The gate controller 14 controls MOSFETs Q1 and Q2 so that the input voltage Vin becomes a predetermined output voltage by switching the MOSFETs Q1 and Q2. The gate controller 14 controls the on / off state of MOSFETs Q1 and Q2 based on predetermined conditions relating to a plurality of signals S1 to S2 and EN. The gate controller 14 switches between a switching operation period in which MOSFETs Q1 and Q2 are switched and a switching stop period in which switching is stopped, based on the polarity of the enable signal EN. By controlling MOSFETs Q1 and Q2 to be turned on and off complementaryly to each other, the gate controller 14 can convert the input voltage Vin to a predetermined voltage and output it as an output voltage Vout. The gate controller 14 may include a controller that determines the on / off state of MOSFETs Q1 and Q2 based on a plurality of signals S1 to S2 and EN, and a driver circuit that controls the gate signal applied to the gates of MOSFETs Q1 and Q2 based on the signal from the controller.

[0022] In Embodiment 1, the inductor 15 is connected between the input terminal T1 and the output terminal T2. The inductor 15 is connected in series with the MOSFET Q1 to the input terminal T1 and the output terminal T2. One end of the inductor 15 is connected to the input terminal T1, and the other end is connected to the source of the MOSFET Q1.

[0023] The source of MOSFET Q1 is connected to inductor 15. The drain of MOSFET Q1 is connected to output terminal T2. The gate of MOSFET Q1 is connected to gate controller 14. The source of MOSFET Q2 is connected to ground GND. The drain of MOSFET Q2 is connected to the connection point between inductor 15 and MOSFET Q1. The gate of MOSFET Q2 is connected to gate controller 14. The gate controller 14 controls the on / off state of each MOSFET Q1 and Q2 by controlling the voltage applied to the gates of MOSFETs Q1 and Q2.

[0024] The feedback voltage output circuit, in which feedback voltage divider resistors R1 and R2 are connected in series, is connected between the connection point between the drain of MOSFET Q1 and the output terminal T2, and the ground GND. The feedback voltage Vfb, divided by the feedback voltage divider resistors R1 and R2 based on the output voltage Vout, is applied to the comparator 12 from the connection point between feedback voltage divider resistor R1 and feedback voltage divider resistor R2.

[0025] The following describes the general operation of the DC / DC converter 1 according to Embodiment 1. Figure 2 is a timing chart showing the operation of the DC / DC converter 1 and control circuit 10 according to Embodiment 1.

[0026] In the timing chart shown in Figure 2, the period from time t1 to time t3 is the switching operation period. The period from time t3 to time t11 is the switching stop period. The period from time t4 to time t11 is the pass-through mode period. During the switching operation period, the gate controller 14 switches MOSFETs Q1 and Q2 complementaryly. As a result, the DC / DC converter 1 boosts the input voltage Vin to a predetermined voltage and outputs it as the output voltage Vout. During the pass-through mode period, the gate controller 14 turns on MOSFET Q1 and turns off MOSFET Q2. As a result, the DC / DC converter 1 outputs a voltage substantially equivalent to the input voltage Vin as the output voltage Vout.

[0027] At time t0 in Figure 2, the power supply is connected to input terminal T1. The power supply is, for example, a battery that applies a DC voltage Vin. At time t1, when the enable signal EN input to enable terminal T3 changes from L level to H level, the gate controller 14 performs switching operations on MOSFETs Q1 and Q2. As a result, the output voltage Vout is boosted to a predetermined set voltage Vset. At time t2, the comparator 12 compares the feedback voltage Vfb with a reference voltage Vref corresponding to the set voltage Vset, and when Vfb ≥ Vref, switches the comparison signal S1 from L level to H level.

[0028] At time t3, when the enable signal EN changes from a high level to a low level, the gate controller 14 stops the switching operation of MOSFETs Q1 and Q2. After the switching operation stops, the output voltage Vout gradually decreases, for example, due to power consumption by load 2. Therefore, the comparator 12 switches the comparison signal S1 from a high level to a low level.

[0029] At time t4, when Vout ≤ Vin, comparator 13 changes the comparison signal S2 from L level to H level. In other words, comparator 13 outputs the comparison result signal when Vout ≤ Vin. When gate controller 14 detects that the comparison signal S2 has reached H level, it turns on MOSFET Q1.

[0030] When operating as described above, the gate controller 14 detects at time t2 that the enable signal EN is at a high level and Vout ≥ Vset. The gate controller 14 also detects at time t3 that the enable signal EN is at a low level. Then, at time t4, the gate controller 14 detects that the enable signal EN is at a low level and Vout ≤ Vin. In this case, the gate controller 14 turns on MOSFET Q1 and keeps MOSFET Q2 off. As a result, the gate controller 14 switches the DC / DC converter 1 to pass-through mode. In this way, the control circuit 10 according to Embodiment 1 switches MOSFETs Q1 and Q2, and after stopping the switching, turns on MOSFET Q1 based on the comparison result signal to output the input voltage Vin as the output voltage Vout.

[0031] When the gate controller 14 detects that the enable signal EN has changed to a high level at time t11, it switches MOSFETs Q1 and Q2. In other words, the gate controller 14 stops the pass-through mode and performs switching operations. Since the output voltage Vout > input voltage Vin, the comparator 13 changes the comparison signal S2 from a high level to a low level. At time t12, when the comparator 12 detects that Vout ≥ Vset, i.e., Vfb ≥ Vref, it changes the comparison signal S1 from a low level to a high level. The processing at time t12 corresponds to the processing at time t2. The processing at time t11 substantially corresponds to the processing at time t1. In this way, the control circuit 10 can repeat the above processing.

[0032] Figure 3 is a flowchart of the control process of the gate controller 14. When power is connected to terminal T1, the gate controller 14 determines whether or not the enable signal EN=H (STEP 1). If it determines that the enable signal EN=H is not (STEP 1: NO), the gate controller 14 executes STEP 1 again. If it determines that the enable signal EN=H (STEP 1: YES), the gate controller 14 starts the switching operation of MOSFETs Q1 and Q2 (STEP 2).

[0033] The gate controller 14 determines whether the comparison signal S1 is high (STEP 3). If it determines that the comparison signal S1 is not high (STEP 3: NO), the gate controller 14 executes STEP 3 again. If it determines that the comparison signal S1 is high (STEP 3: YES), the gate controller 14 determines whether the enable signal EN is low (STEP 4).

[0034] If the gate controller 14 determines that the enable signal EN is not L (STEP4: NO), it executes STEP4 again. If the gate controller 14 determines that the enable signal EN is L (STEP4: YES), it turns off MOSFETs Q1 and Q2 and terminates the switching operation (STEP5).

[0035] Next, the gate controller 14 determines whether the comparison signal S2 is high (STEP 6). If it determines that the comparison signal S2 is not high (STEP 6: NO), the gate controller 14 executes STEP 6 again. If it determines that the comparison signal S2 is high (STEP 6: YES), the gate controller 14 turns on MOSFET Q1 (STEP 7). As a result, the gate controller 14 executes pass-through mode. After that, the gate controller 14 executes STEP 1 again, and if it determines that the enable signal EN is high, it exits pass-through mode and starts switching operation.

[0036] As described above, the gate controller 14 does not determine whether or not to switch to pass-through mode based solely on the polarity of the enable signal EN. Therefore, even if the polarity of the enable signal EN is undefined when the power supply is connected, the pass-through mode will not be executed. Consequently, the DC / DC converter 1 according to this disclosure does not switch to pass-through mode at an unintended timing, and the occurrence of inrush current to the load 2 when the power supply is connected to the input terminal T1 can be suppressed. Consequently, the DC / DC converter 1 and its control circuit 10 according to this disclosure can suppress damage to or malfunction of the load 2.

[0037] Furthermore, the gate controller 14 according to Embodiment 1 executes a pass-through mode when Vout is substantially equal to Vin. Therefore, when MOSFET Q1 is turned on, no current flows back from the output terminal T2 to the input terminal T1, or the amount of current that flows back is reduced. Consequently, the DC / DC converter 1 and its control circuit 10 according to this disclosure can suppress damage to the power supply.

[0038] Furthermore, since MOSFET Q1 is turned on when the difference between the potential of input terminal T1 and the potential of output terminal T2 is substantially 0V, the generation of noise in the inductor 15 during the transition to pass-through mode is reduced. Therefore, the DC / DC converter 1 and its control circuit 10 according to this disclosure can suppress damage to or malfunction of the load 2. Thus, the DC / DC converter 1 and its control circuit 10 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0039] The control circuit 10 and DC / DC converter 1 according to Embodiment 1 of this disclosure can achieve the following effects.

[0040] The control circuit 10 of the DC / DC converter 1, which includes a controller 14 that controls the switching element Q1 so that the input voltage Vin becomes a predetermined output voltage by switching the switching element Q1, includes a comparator 13. The comparator 13 compares the output voltage Vout with a target voltage which is either a voltage offset by a predetermined first voltage from the input voltage Vin or the input voltage Vin itself, and outputs a comparison result signal when the output voltage Vout becomes less than or equal to the target voltage. The controller 14 switches the switching element Q1, and after stopping the switching, turns on the switching element Q1 based on the comparison result signal to output the input voltage Vin as the output voltage Vout.

[0041] With this configuration, the control circuit 10 switches the switching element Q1, and after stopping the switching, decides whether or not to execute pass-through mode based on the comparison result signal. Therefore, the control circuit 10 does not execute pass-through mode when the power supply is connected to the input terminal T1 of the DC / DC converter 1, thereby suppressing the generation of inrush current to the load 2 when the power supply is connected. Thus, the control circuit 10 of the DC / DC converter 1 according to this disclosure can suppress the occurrence of damage or malfunction of the load 2. Furthermore, the control circuit 10 executes pass-through mode when the output voltage Vout ≤ target voltage. Therefore, when the switching element Q1 is turned on, current does not flow back from the output terminal T2 to the input terminal T1, or the current that flows back is reduced. In addition, the generation of noise in, for example, the inductor 15 when transitioning to pass-through mode is reduced. Thus, the control circuit 10 of the DC / DC converter 1 according to this disclosure can suppress damage to the power supply. Furthermore, the control circuit 10 can suppress the occurrence of damage or malfunction of the load 2. Thus, the control circuit 10 of the DC / DC converter 1 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0042] Furthermore, the controller 14 stops switching the switching element Q1 when it receives a predetermined signal. With this configuration, the control circuit 10 is configured to stop switching the switching element Q1 when it receives, for example, an L-level enable signal EN. As the output voltage Vout gradually decreases, the control circuit 10 can execute a pass-through mode so that current does not flow back from the output terminal T2 to the input terminal T1, or so that the current that flows back is reduced.

[0043] Furthermore, the switching element is a P-channel MOSFET. With this configuration, the control circuit 10 can execute pass-through mode by turning on the P-channel MOSFET based on the comparison result signal. Therefore, the control circuit 10 of the DC / DC converter 1 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0044] The DC / DC converter 1 comprises a control circuit 10 and a switching element Q1. With this configuration, the DC / DC converter 1 switches the switching element Q1, and after stopping the switching, it operates to decide whether or not to execute pass-through mode based on the comparison result signal. Therefore, the DC / DC converter 1 according to this disclosure can suppress transitions to pass-through mode at unintended timings. Accordingly, the DC / DC converter 1 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0045] A control method for the control circuit 10 of a DC / DC converter 1, which includes a controller 14 that controls the switching element Q1 so that the input voltage Vin becomes a predetermined output voltage by switching the switching element Q1, includes the comparator 13 comparing the output voltage Vout with a target voltage which is either a voltage offset by a predetermined first voltage from the input voltage Vin or the input voltage Vin, and outputting a comparison result signal when the output voltage Vout becomes less than or equal to the target voltage, and the controller 14 switching the switching element Q1, stopping the switching, and then turning on the switching element Q1 based on the comparison result signal to output the input voltage Vin as the output voltage Vout.

[0046] According to this method, the DC / DC converter 1 can be operated to switch the switching element Q1, and after stopping the switching, to decide whether or not to execute pass-through mode based on the comparison result signal. Compared to the prior art, the control method of the control circuit 10 of the DC / DC converter 1 according to this disclosure allows for transitioning to pass-through mode while suppressing the occurrence of unintended behavior.

[0047] (Embodiment 2) Referring to Figure 4, an overview of the DC / DC converter 1 and its control circuit 10 according to Embodiment 2 of this disclosure will be described. Embodiment 2 mainly describes the differences from Embodiment 1. In Embodiment 2, components that are the same as or equivalent to those in Embodiment 1 are denoted by the same reference numerals. Also, in Embodiment 2, descriptions that overlap with those in Embodiment 1 may be omitted. The DC / DC converter 1 according to Embodiment 2 differs from that in Embodiment 1 in that MOSFET Q1 is an N-channel MOSFET. Figure 4 shows a schematic diagram of the DC / DC converter 1 according to Embodiment 2.

[0048] The DC / DC converter 1 according to Embodiment 2 includes an N-channel MOSFET Q1 instead of the P-channel MOSFET Q1 in Embodiment 1. Furthermore, the DC / DC converter 1 includes a bootstrap circuit 20 as a boost circuit. The gate controller 14 includes a controller 141 and a gate driver circuit 142.

[0049] The controller 141 receives signals S1~S2 and EN input to the gate controller 14, and outputs control signals to the gate driver circuit to control the on / off state of MOSFETs Q1 and Q2 based on signals S1~S2 and EN. The controller 141 is composed of, for example, a predetermined control logic circuit. The gate driver circuit 142 determines the voltage to be applied to the gates of MOSFETs Q1 and Q2 based on the control signals from the controller 141, and switches the on / off state of MOSFETs Q1 and Q2 by applying the voltage.

[0050] The bootstrap circuit 20 boosts the input voltage Vin to a predetermined voltage and inputs it to the gate driver 142, which outputs the boosted voltage. The bootstrap circuit 20 comprises a diode 201 and a capacitor 202 in series. The anode of the diode 201 is connected between the input terminal T1 and the inductor 15. The cathode of the diode 201 is connected to one end of the capacitor 202. The other end of the capacitor 202 is connected between the inductor 15 and the source of the MOSFET Q1. The connection point between the cathode of the diode 201 and the capacitor 202 is connected to the gate driver circuit 142.

[0051] When the switching operation begins, MOSFET Q2 is turned on, and capacitor 202 is charged. As a result, the potential difference across capacitor 202 becomes equivalent to the input voltage Vin. Subsequently, when the gate driver circuit 142 turns off MOSFET Q2, the source of MOSFET Q1 is at the same potential as the other end of capacitor 202, so the gate driver circuit 142 can apply a potential to the gate based on the potential of one end of capacitor 202. A voltage corresponding to the voltage across capacitor 202 is applied between the source and gate of MOSFET Q1, so MOSFET Q1 is turned on. In this way, the bootstrap circuit 20 can boost the input voltage to a predetermined voltage and input it to the gate driver circuit 142. The gate driver circuit 142 can control the operation of MOSFET Q1 using the voltage boosted by the bootstrap circuit 20.

[0052] If an N-channel MOSFET is used for MOSFET Q1, a higher potential than the source of MOSFET Q1 must be applied to the gate of MOSFET Q1 in order to turn it on. The DC / DC converter 1 according to Embodiment 2 includes a bootstrap circuit 20, so the gate driver circuit 142 can turn on MOSFET Q1 by applying a boosted input voltage Vin between the source and gate of MOSFET Q1.

[0053] The following describes the general operation of the DC / DC converter 1 according to Embodiment 2. Figure 5 is a timing chart showing the operation of the DC / DC converter 1 and control circuit 10 according to Embodiment 2. The timing chart shown in Figure 5 further includes the voltage Vboot compared to the timing chart shown in Figure 2. The voltage Vboot represents the voltage across the capacitor 202.

[0054] In the timing chart shown in Figure 5, the operation from time t0 to time t4 is the same as the operation from time t0 to time t4 shown in Figure 2. Also, in the timing chart shown in Figure 5, the operation from time t11 to time t12 is the same as the operation from time t11 to time t12 shown in Figure 2. When MOSFET Q2 is turned on at time t1, the input voltage Vin is applied across capacitor 202. Therefore, capacitor 202 is charged and the voltage Vboot rises from 0 to Vin. As described above, the gate driver circuit 142 turns on MOSFET Q1 using the voltage Vboot. At time t4, the gate controller 14 turns on MOSFET Q1 and starts pass-through mode.

[0055] When the switching operation ends at time t3, MOSFET Q2 remains in the off state, and therefore the Vboot voltage is not charged. Consequently, after time t3, the Vboot voltage gradually decreases, for example, due to natural discharge. As the voltage Vboot decreases, the on-resistance of MOSFET Q1 increases. To suppress the decrease in pass-through mode efficiency due to the increase in on-resistance, at time t5, after a predetermined time period T1 has elapsed from time t3, the gate controller 14 turns off MOSFET Q1 and turns on MOSFET Q2. Then, at time t6, after a predetermined time period T2 has elapsed from time t5, the gate controller 14 turns off MOSFET Q2 and turns on MOSFET Q1.

[0056] Thus, during the execution of pass-through mode, the gate controller 14 operates to turn on MOSFET Q2 for a certain period of time after a predetermined time has elapsed to charge capacitor 202. As a result, the voltage Vboot is maintained above a predetermined voltage, which suppresses the increase in the on-resistance of MOSFET Q1 and reduces power consumption in the DC / DC converter 1. Therefore, with the DC / DC converter 1 according to this disclosure, energy efficiency can be improved even if an N-channel MOSFET is used for the high-side switch.

[0057] Figure 6 is a flowchart showing the control process of the gate controller 14 according to Embodiment 2. Steps 1 to 7 in Figure 6 are the same as steps 1 to 7 in Figure 3.

[0058] After turning on MOSFET Q1, the gate controller 14 determines whether a predetermined time T1 has elapsed (STEP 8). If it determines that the predetermined time T1 has not elapsed (STEP 8: NO), the gate controller 14 determines whether the enable signal EN = H (STEP 9). If it determines that the enable signal EN = H (STEP 9: NO), the gate controller 14 executes STEP 8 again. If it determines that the enable signal EN = H (STEP 9: YES), the gate controller 14 executes STEP 2 again.

[0059] When the gate controller 14 determines that a predetermined time T1 has elapsed (STEP 8: YES), it turns off MOSFET Q1 and turns on MOSFET Q2 (STEP 10). This charges capacitor 202. Then, after a predetermined time T2 has elapsed, the gate controller 14 turns off MOSFET Q2 and turns on MOSFET Q1. After that, the gate controller 14 executes STEP 8 again.

[0060] As described above, the gate controller 14 can turn on the N-channel MOSFET based on the input voltage Vin, even if the high-side switch is an N-channel MOSFET, and execute pass-through mode. Therefore, the DC / DC converter 1 and its control circuit 10 according to Embodiment 2 can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0061] In the above-described embodiment 2, the DC / DC converter 1 includes a bootstrap circuit 20 as a boost circuit, but the boost circuit is not limited to the bootstrap circuit 20. For example, the DC / DC converter 1 may also include a charge pump circuit as a boost circuit.

[0062] Figure 7 shows a schematic diagram of a DC / DC converter 1 according to a modified example of Embodiment 2. The DC / DC converter 1 shown in Figure 7 includes a charge pump circuit 30 instead of the bootstrap circuit 20 in the DC / DC converter 1 according to Embodiment 2.

[0063] One end of the charge pump circuit 30 is connected between the input terminal T1 and the inductor 15. The other end of the charge pump circuit 30 is connected to the gate driver circuit 142. The charge pump circuit 30 includes diodes 301 and 302 and capacitors 303 and 304. Based on the clock signal CL1 and the inverted clock signal / CL1, the charge pump circuit 30 can boost the input voltage Vin and apply the boosted voltage Vchg to the gate driver circuit 142.

[0064] The voltage applied to the gate of MOSFET Q1 by the gate driver circuit 142 is maintained for a long time by the charge pump circuit 30. Therefore, unlike DC / DC converter 1 which has a bootstrap circuit 20 as a boost circuit, it is not necessary to periodically turn on MOSFET Q2 to charge capacitor 202. Accordingly, the modified DC / DC converter 1 can realize a pass-through mode using an N-channel MOSFET with simpler control than DC / DC converter 1 which uses a bootstrap circuit 20.

[0065] The control circuit 10 and DC / DC converter 1 according to Embodiment 2 of this disclosure can achieve the following effects.

[0066] The control circuit 10 of the DC / DC converter 1, which includes a controller 14 that controls the switching element Q1 so that the input voltage Vin becomes a predetermined output voltage by switching the switching element Q1, includes a comparator 13. The comparator 13 compares the output voltage Vout with a target voltage which is either a voltage offset by a predetermined first voltage from the input voltage Vin or the input voltage Vin itself, and outputs a comparison result signal when the output voltage Vout becomes less than or equal to the target voltage. The controller 14 switches the switching element Q1, and after stopping the switching, turns on the switching element Q1 based on the comparison result signal to output the input voltage Vin as the output voltage Vout. The control circuit 10 further includes boost circuits 20, 30 that boost the input voltage Vin to a predetermined second voltage and input the boosted voltage to the controller 14 which outputs the boosted voltage. The switching element Q1 is an N-channel MOSFET. The controller 14 controls the switching of the switching element Q1 using the boosted voltage.

[0067] With this configuration, even if the switching element Q1 is an N-channel MOSFET, the control circuit 10 can turn on the N-channel MOSFET using the voltage obtained by boosting the input voltage Vin by the boost circuits 20 and 30. Therefore, the control circuit 10 can execute pass-through mode by turning on the N-channel MOSFET based on the comparison result signal. Accordingly, the control circuit 10 of the DC / DC converter 1 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0068] Furthermore, the boost circuits 20 and 30 are either a bootstrap circuit 20 or a charge pump circuit 30. With this configuration, the control circuit 10 can boost the input voltage Vin using the bootstrap circuit 20 or the charge pump circuit 30. Therefore, even if the switching element Q1 is an N-channel MOSFET, the control circuit 10 of the DC / DC converter 1 according to this disclosure can transition to pass-through mode while suppressing the occurrence of unintended behavior compared to the prior art.

[0069] (modified version) In the embodiment described above, the comparator 13 uses the input voltage Vin as a reference value, but the reference value is not limited to the input voltage Vin. The comparator 13 may compare the output voltage Vout with a target voltage substantially equal to the input voltage Vin, or with a target voltage offset by a predetermined first voltage from the input voltage Vin. Figure 8 shows a schematic diagram of a modified DC / DC converter 1. The DC / DC converter 1 shown in Figure 8 further includes an offset voltage generator 17. In the modified DC / DC converter 1, a voltage obtained by adding a predetermined first voltage to the input voltage Vin is applied to the inverting input terminal of the comparator 13. With this configuration, the comparator 13 can be configured to compare the output voltage Vout with a target voltage offset by a predetermined first voltage from the input voltage Vin. Thus, the target voltage used as a reference value in the comparator 13 may be the input voltage Vin, or it may be a voltage having a predetermined variation range with respect to the input voltage Vin.

[0070] In the embodiment described above, the inductor 15 is provided inside the DC / DC converter 1, but the placement of the inductor 15 is not limited to this position. The inductor 15 may be located outside the DC / DC converter 1. For example, the inductor 15 may be configured to be connected to the outside of the input terminal T1 with respect to the DC / DC converter 1.

[0071] In the embodiment described above, the gate controller 14 performs a switching operation when the enable signal EN is at a high level, and performs a pass-through mode when the enable signal EN is at a low level and the comparison signal S2 is at a high level. However, the control by the gate controller 14 is not limited to the above polarity. The gate controller 14 may be configured to perform each operation based on a different polarity than described above, such as performing a switching operation when the enable signal EN is at a low level.

[0072] In the embodiment described above, the gate controller 14 executes a pass-through mode based on a predetermined signal after detecting that the comparison signal S1 is at a high level. However, the operation of the gate controller 14 is not limited to this process. For example, the gate controller 14 may be configured to execute a pass-through mode based on a predetermined signal without detecting that the comparison signal S1 is at a high level, after switching the MOSFETs Q1 and Q2 and stopping the switching.

[0073] (Summary of characteristics) As is clear from the above description, this disclosure includes the following embodiments. In the following, reference numerals are enclosed in parentheses solely to indicate their correspondence with the embodiments.

[0074] (Aspect 1) The control circuit (10) of the DC / DC converter (1) according to the present disclosure is a control circuit of a DC / DC converter comprising a controller (14) that controls a switching element (Q1) so that the input voltage becomes a predetermined output voltage by switching the switching element, The system includes a comparator (13) that compares the output voltage with a target voltage which is either the input voltage or a voltage offset by a predetermined first voltage from the input voltage, and outputs a comparison result signal when the output voltage becomes less than or equal to the target voltage. The controller switches the switching element, and after stopping the switching, turns on the switching element based on the comparison result signal to output the input voltage as the output voltage.

[0075] (Aspect 2) In the control circuit (10) of Aspect 1, the controller (14) may stop the switching of the switching element (Q1) when it receives a predetermined signal.

[0076] (Aspect 3) In the control circuit (10) of Aspect 1 or Aspect 2, the switching element (Q1) may be a P-channel MOSFET.

[0077] (Aspect 4) The control circuit (10) of aspect 1 or aspect 2 further comprises a boost circuit (20, 30) that boosts the input voltage to a predetermined second voltage and inputs it to the controller which outputs the boosted voltage, The switching element (Q1) is an N-channel MOSFET, The controller (14) may use the boosted voltage to control the switching of the switching element.

[0078] (Aspect 5) In the control circuit (10) of aspect 4, the boost circuits (20, 30) may be bootstrap circuits (20) or charge pump circuits (30).

[0079] (Aspect 6) The DC / DC converter (1) relating to this disclosure comprises the control circuit (10) described in any of aspects 1 to 5, The switching element (Q1) and, It is equipped with.

[0080] (Aspect 7) A control method for a control circuit (10) of a DC / DC converter (1) according to the present disclosure, comprising a controller (14) that controls a switching element (Q1) by switching the switching element so that the input voltage becomes a predetermined output voltage, The comparator (13) compares the output voltage with a target voltage which is either the input voltage offset by a predetermined first voltage or the input voltage itself, and outputs a comparison result signal when the output voltage becomes less than or equal to the target voltage. The controller (14) switches the switching element, and after stopping the switching, turns on the switching element based on the comparison result signal to output the input voltage as the output voltage. Includes.

[0081] In this specification, terms such as “First,” “Second,” etc., are used for illustrative purposes only and should not be understood as expressing or implying relative importance or ranking of technical features. Features designated as “First” or “Second” express or imply that they include one or more such features.

[0082] The control circuits and DC / DC converters described in this disclosure are realized through the cooperation of hardware resources, such as a processor and memory, and software (computer programs). [Industrial applicability]

[0083] According to this disclosure, a control circuit for a DC / DC converter and a control method thereof, as well as a DC / DC converter, can be provided that can suppress the occurrence of unintended behavior that may occur when transitioning to pass-through mode, compared to the prior art. Therefore, it can be suitably used in this type of industrial field. [Explanation of symbols]

[0084] 1 DC / DC converter 2 loads 10 Control circuits 11. Reference voltage source 12 Comparator 13 Comparator 14 Gate Controller 15 Inductors 20 Bootstrap Circuits 30 Charge pump circuit Q1, Q2 MOSFET

Claims

1. A control circuit for a DC / DC converter, comprising a controller that controls the switching elements so that the input voltage becomes a predetermined output voltage by switching the switching elements, The comparator includes a comparison device that compares the output voltage with a target voltage which is either the input voltage offset by a predetermined first voltage from the input voltage, and outputs a comparison result signal when the output voltage becomes less than or equal to the target voltage. The controller switches the switching element, and after stopping the switching, turns on the switching element based on the comparison result signal to output the input voltage as the output voltage. Control circuit for a DC / DC converter.

2. The control circuit according to claim 1, wherein the controller stops the switching of the switching element when it receives a predetermined signal.

3. The control circuit according to claim 1, wherein the switching element is a P-channel MOSFET.

4. The system further comprises a boost circuit that boosts the input voltage to a predetermined second voltage and inputs it to the controller that outputs the boosted voltage. The switching element is an N-channel MOSFET. The controller controls the switching of the switching element using the boosted voltage. The control circuit according to claim 1.

5. The boost circuit is a bootstrap circuit or a charge pump circuit. The control circuit according to claim 4.

6. A control circuit according to any one of claims 1 to 5, The aforementioned switching cable, A DC / DC converter equipped with the following features.

7. A control method for the control circuit of a DC / DC converter, which includes a controller that controls the switching elements so that the input voltage becomes a predetermined output voltage by switching the switching elements, The comparator compares the output voltage with a target voltage which is either the input voltage offset by a predetermined first voltage or the input voltage itself, and outputs a comparison result signal when the output voltage becomes less than or equal to the target voltage. The controller switches the switching element, and after stopping the switching, turns on the switching element based on the comparison result signal to output the input voltage as the output voltage. A control method for the control circuit of a DC / DC converter, including [the specified element].

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