Step-up converter for vehicle

Abstract

This step-up converter (102) for a vehicle comprises: a switching element (Q1) that switches between energization and interruption of an inductor (L1); a capacitor (C1) that smooths and outputs power released from the inductor (L1); and an input voltage detection unit (6) that detects an input voltage (VIN) from a battery (101). A control unit (1) inputs, to the switching element (Q1), a control signal (CS) with a predetermined control frequency, and controls the switching element (Q1) by controlling the duty ratio of the control signal (CS). When a decrease in the input voltage (VIN) is detected, the control unit (1) reduces the control frequency of the control signal (CS) so as to be able to set a duty ratio with which an output voltage (VOUT) can be maintained and a discharge period for releasing the energy accumulated in the inductor (L1) to the capacitor (C1) can be ensured.

Description

Vehicle boost converter

[0001] The present disclosure relates to a boost converter for a vehicle.

[0002] A boost converter as a DC / DC converter is used, for example, as a power supply that supplies power to vehicle lighting fixtures. Patent Document 1 listed below discloses a technology for preventing switching noise generated in a vehicle DC / DC converter from affecting the reception of the vehicle radio by setting the switching frequency of the DC / DC converter higher than the upper limit frequency (e.g., 1.71 MHz) of the AM broadcast band.

[0003] Generally, the input voltage of a DC / DC converter for a vehicle is supplied from a lead battery, but this voltage is not always constant. For example, when a large amount of power is consumed, such as when starting the engine, the input voltage of the DC / DC converter may temporarily drop. The ratio of the output voltage to the input voltage of the DC / DC converter, also known as the step-up ratio or step-down ratio, is determined by the on-duty ratio (the ratio of the on-period to the switching cycle, hereinafter simply referred to as the "duty ratio") of the switching elements that make up the DC / DC converter. Therefore, if the input voltage of the DC / DC converter drops, the duty ratio can be increased to maintain the output voltage.

[0004] However, the duty ratio is limited by the performance of the switching element and its control circuit, specifically, the switching time of the switching element (turn-on time, turn-off time) and the change time of the control signal (rise time and fall time), and there is an upper limit to the settable duty ratio. In particular, when the switching frequency is high, the proportion of the switching time of the switching element and the change time of the control signal in the switching period becomes large, so the maximum duty ratio, which is the upper limit of the duty ratio, becomes small.

[0005] Patent Document 2 listed below discloses a technique for increasing the maximum duty ratio in a step-down DC / DC converter (hereinafter referred to as a "step-down converter") by lowering the switching frequency when the input voltage drops.

[0006] Patent No. 7275412 International Publication No. 2024 / 029230

[0007] A boost-side DC / DC converter (hereinafter referred to as a "boost converter") has an additional constraint on the duty ratio. In other words, in a boost converter, in order to make the output voltage higher than the input voltage, the energy stored in the inductor (coil) when the switching element is turned on must be released from the inductor to the output side when the switching element is turned off, and a discharge period for this must be ensured. Therefore, in a boost converter, the duty ratio is set while ensuring that the off period of the switching element is longer than the discharge period of the inductor. Because the DC / DC converter in Patent Document 2 is a step-down converter, the technology in Patent Document 2 does not take into account the discharge period of the inductor.

[0008] The present disclosure has been made to solve the above-mentioned problems, and aims to provide a boost converter for a vehicle that can prevent a drop in output voltage even if the input voltage temporarily drops.

[0009] The vehicular boost converter of the present disclosure includes a charge / discharge unit that stores and releases power input from a power source, a switching unit that switches the charge / discharge unit between energized and cut-off, a one-way flow element connected to the charge / discharge unit and the switching unit, an output unit that is connected to the charge / discharge unit and the switching unit via the one-way flow element and smooths and outputs the power released from the charge / discharge unit, a control unit that controls the switching unit, and an input voltage detection unit that detects the input voltage from the power source, wherein the control unit inputs a control signal of a predetermined control frequency to the switching unit and controls the switching unit by controlling the duty ratio of the control signal, and when a drop in the input voltage is detected, the control unit lowers the control frequency so that a duty ratio can be set that can maintain the output voltage and ensure a discharge period for releasing the energy stored in the charge / discharge unit to the output unit.

[0010] According to the boost converter for a vehicle according to the present disclosure, a drop in output voltage can be prevented even if the input voltage temporarily drops.

[0011] The objects, features, aspects, and advantages of the present disclosure will become more apparent from the following detailed description and the accompanying drawings.

[0012] 1 is a schematic diagram of a vehicle equipped with a boost converter according to embodiment 1. FIG. 2 is a diagram showing the configuration of the boost converter according to embodiment 1. FIG. 3 is a diagram showing an example configuration of a headlight which is a load of the boost converter according to embodiment 1. FIG. 4 is a waveform diagram of a control signal of the boost converter according to embodiment 1. FIG. 5 is a diagram for explaining the operation of the boost converter according to embodiment 1. FIG. 6 is a diagram for explaining a modified example of the operation of the boost converter according to embodiment 1. FIG. 7 is a diagram for explaining the ideal operation of the boost converter according to embodiment 1. FIG. 8 is a diagram for explaining the actual operation of the boost converter according to embodiment 1. FIG. 9 is a diagram for explaining the operation when the value of the input voltage of the boost converter according to embodiment 1 is recovered. FIG. 10 is a configuration diagram showing a buck-boost converter according to embodiment 2.

[0013] 1 is a schematic diagram of a vehicle equipped with a vehicular boost converter (hereinafter simply referred to as a "boost converter") according to embodiment 1. Vehicle 100 includes a battery 101 as a power source, a boost converter 102, and headlights 103 and a radio 104 as loads. Here, the load of boost converter 102 is headlights 103, but the load is not limited to headlights and may be any load.

[0014] Headlight 103 is a vehicle lamp that illuminates the area ahead in the traveling direction of vehicle 100. Boost converter 102 is connected to battery 101 and headlight 103, and receives power from battery 101 to drive headlight 103. In this embodiment, headlight 103 is made up of a plurality of LEDs (Light Emitting Diodes) that are semiconductor light-emitting elements connected in series, and its drive voltage is 30V to 70V.

[0015] The voltage output from the battery 101 is the input voltage V ＩＮThe rated voltage of battery 101 is, for example, 12 V. Vehicle 100 may be a gasoline-powered vehicle or an electrically powered vehicle such as an electric vehicle or a hybrid vehicle. When vehicle 100 is an electrically powered vehicle, battery 101 corresponds to an auxiliary battery. Note that vehicle 100 is not limited to a four-wheeled vehicle, and may be, for example, a two-wheeled vehicle. The arrangement of battery 101 and boost converter 102 is not limited to the example in FIG. 1 , and, for example, battery 101 and boost converter 102 may be arranged in a position close to headlight 103, such as in the engine compartment.

[0016] The radio 104 has a function of receiving an AM broadcast signal BS, which is a broadcast signal with a frequency within the AM broadcast band, and generating the audio of an AM broadcast program. In this embodiment, the AM broadcast band is a frequency band from 0.52 MHz to 1.71 MHz.

[0017] Fig. 2 is a diagram showing the configuration of the boost converter 102. The boost converter 102 shown in Fig. 2 is an asynchronous boost DC / DC converter.

[0018] The boost converter 102 includes a switching element Q1 as a switching unit, an inductor L1 as a charging / discharging unit, a diode D1 as a one-way current element, a capacitor C1 as an output unit or boost unit, a control unit 1, and an input voltage detection unit 6.

[0019] The switching element Q1 and the inductor L1 are connected in series. The inductor L1 is connected between the positive electrode node of the battery 101 and the switching element Q1, and stores and releases power input from the battery 101. The switching element Q1 is connected between the inductor L1 and the negative electrode node of the battery 101, and switches between conducting and cutting off the inductor L1. While FIG. 1 shows an example in which the switching element Q1 is a MOSFET (Metal-Oxide-Semiconductor Field Effect Transistor), the switching element Q1 is not limited to a MOSFET and may be, for example, an IGBT (Insulated Gate Bipolar Transistor).

[0020] Various components may be provided between the positive electrode node of the battery 101 and the inductor L1. Examples of the various components include a harness for supplying power from the battery 101, a protection circuit for protecting the boost converter 102 when the battery 101 is erroneously connected in reverse polarity, and a filter circuit for reducing noise and voltage fluctuations. In addition, a component such as a harness for supplying power from the battery 101 may also be provided between the negative electrode node of the battery 101 and the switching element Q1.

[0021] The diode D1 is connected to the inductor L1 and the switching element Q1. Specifically, the anode of the diode D1 is connected to the connection node between the inductor L1 and the switching element Q1. The cathode of the diode D1 is connected to the capacitor C1 and the headlight 103, which is a load. The capacitor C1 and the headlight 103 are connected between the cathode of the diode D1 and the negative node of the battery 101.

[0022] The capacitor C1 is connected to the inductor L1 and the switching element Q1 via the diode D1, and smoothes and outputs the power discharged from the inductor L1. For example, a harness for supplying power to the headlight 103 or a step-down converter (FIG. 3) described below may be provided between the diode D1 and the headlight 103.

[0023] In this embodiment, in order to suppress noise that affects the reception quality of the radio 104, the control frequency (switching frequency) of the switching element Q1 is set to a frequency higher than the upper limit frequency of the AM broadcast band. The diode D1 also switches at the same high frequency. Because the loss generated in the diode D1 increases with the number of switching operations, thermal breakdown of the diode D1 becomes a problem when the diode D1 is switched at a high frequency. To avoid this problem, the diode D1 is preferably a trench diode with a fast switching speed and low switching loss. Furthermore, from the perspective of reducing the forward loss of the diode D1, the diode D1 is preferably a Schottky diode with a low forward voltage (voltage drop). Therefore, the diode D1 is more preferably a trench Schottky diode. If it is sufficient to simply reduce switching loss, the diode D1 need not be a Schottky diode, as long as it is a trench diode with a fast switching speed.

[0024] Since the loss generated by the switching element Q1 also increases with the number of switching operations, thermal destruction of the switching element Q1 itself becomes a problem when the switching element Q1 is driven at a high control frequency. However, as mentioned above, this problem can be avoided by using a diode with a high switching speed as the diode D1. The switching loss of the switching element Q1 is the product of the current that flows during switching and the time required for switching, or what is known as the current product. If the switching speed of the diode D1 is high, the current that flows during switching of the switching element Q1 can be switched on and off quickly, resulting in a reduction in the loss of the switching element Q1.

[0025] In this embodiment, the drive voltage of the headlight 103, which is the load, is 30 V to 70 V, so the diode D1 is selected to have a reverse voltage resistance of about 40 V to 100 V. The capacitor C1 stores the energy released from the inductor L1 and generates the output voltage V ＯＵＴA capacitor is selected that has the capacity to boost the voltage to the desired level.

[0026] The control unit 1 inputs a control signal CS, which controls the switching of the switching element Q1, to the gate terminal of the switching element Q1. The control signal CS is a pulse modulation signal such as PWM (Pulse Width Modulation). The control frequency of the control signal CS corresponds to the switching frequency of the switching element Q1 and is determined according to the carrier frequency of the PWM control. The control unit 1 controls the duty ratio of the switching element Q1 to adjust the output voltage V ＯＵＴ Control.

[0027] The control unit 1 includes a CPU (Central Processing Unit) 2 and a memory 3 including a ROM (Read Only Memory) 4 and a RAM (Random Access Memory) 5. The CPU 2 executes PWM control in accordance with a program stored in the ROM 4, and drives the switching element Q1 via a drive circuit (not shown). The RAM 5 is a storage medium that temporarily stores the calculation results of the CPU 2, etc.

[0028] The configuration of the control unit 1 is not limited to the above. For example, the control unit 1 may be an analog circuit including an operational amplifier and a comparator, or a digital circuit including an analog-to-digital converter (ADC), a field programmable gate array (FPGA), a central processing unit (CPU), or a microcontroller unit (MCU). Alternatively, the control unit 1 may include both an analog circuit and a digital circuit.

[0029] In addition, the control unit 1 may monitor the current flowing through the inductor L1 or the switching element Q1 (the current between the drain and source of the MOSFET) using a current sense resistor (not shown), and use the monitored current as a comparison triangular wave for pulse modulation (current mode control method).

[0030] The input voltage detection unit 6 detects the input voltage V ＩＮ The value of the detected input voltage V ＩＮ The value of is input to the control unit 1.

[0031] When the control unit 1 turns on the switching element Q1, the input current I ＩＮ flows through the inductor L1 to the switching element Q1. While the switching element Q1 is on, the inductor L1 ＩＮ The amount of energy stored by the inductor L1 varies depending on the duty ratio of the switching element Q1.

[0032] Furthermore, when the control unit 1 turns off the switching element Q1, the input current I ＩＮ While the switching element Q1 is turned off, the inductor L1 ＩＮ In addition, the energy stored during the ON period of the switching element Q1 is supplied to the capacitor C1 and the headlight 103 through the diode D1. As a result, the output voltage V ＯＵＴ is the input voltage V ＩＮ The voltage becomes higher than ＯＵＴ ≧V ＩＮ ).

[0033] In this way, the boost converter 102 converts the input voltage V ＩＮ is boosted, and the boosted voltage is the output voltage V ＯＵＴ In this embodiment, the input voltage V ＩＮ is 12V, and the output voltage V ＯＵＴ is 30V to 70V.

[0034] FIG. 3 is a diagram showing an example configuration of a headlight 103, which is a load connected to the boost converter 102. The headlight 103 includes an LED array 7 consisting of a plurality of LEDs 7-1, 7-2, ..., 7-n connected in series, and a step-down converter 8 that functions as a constant current power supply that supplies a desired current to the LED array 7. The LED array 7 may be composed of only one LED. The step-down converter 8 may be arranged on the same circuit board as the step-up converter 102, or may be arranged inside the headlight 103 together with the LED array 7. In this embodiment, a set of the step-down converter 8 and the LED array 7 is also referred to as a "unit 9."

[0035] The brightness of each of the LEDs 7-1, 7-2, . . . , 7-n is determined by the current I ｄ In recent years, the number of LEDs constituting the LED array 7 has tended to increase as the headlight 103 has become more sophisticated and colorful. For example, if the number n of LEDs constituting the LED array 7 is 8 and the current I ｄ is about 1 A to 1.5 A, the forward voltage of the LED array 7 (i.e., the sum of the forward voltages of the LEDs 7-1, 7-2, ..., 7-n) is typically about 24 V to 27 V. Therefore, in many cases, the voltage applied to the LED array 7 is higher than the rated voltage (e.g., 12 V) of the battery 101. Therefore, a boost converter 102 is required to boost the voltage.

[0036] The step-down converter 8 converts the output voltage V ＯＵＴ The step-down converter 8 steps down the current I that flows through the LED array 7 and supplies it to the LED array 7. For example, if the number of LEDs that make up the LED array 7 is small and the forward voltage of the LED array 7 is lower than the output voltage of the step-up converter 102, it is necessary to reduce the voltage supplied to the LED array 7 accordingly. ｄ is monitored using a current sense resistor (not shown), and the current I ｄ The step-down converter 8 adjusts its own output voltage so that a constant current I ｄIn short, the step-down converter 8 reduces the current I ｄ The brightness of the LED array 7 is adjusted by adjusting

[0037] If the configuration of the headlight 103 differs, the voltage required to pass the required current also differs. For example, consider a case where the headlight 103 has two units 9 connected in parallel, one unit 9 (referred to as the "first unit 9") having an LED array 7 with eight LEDs connected in series, and the other unit 9 (referred to as the "second unit 9") having an LED array 7 with sixteen LEDs connected in series. The voltage required for the LED array 7 of the first unit 9 is 27 V or more, and the voltage required for the LED array 7 of the second unit 9 is 54 V or more. In this case, the boost converter 102 generates a voltage equal to or greater than the output voltage V ＯＵＴ The step-down converter 8 of the first unit 9 maintains the output voltage V ＯＵＴ to the voltage required for the LED array 7 of the first unit 9, and the step-down converter 8 of the second unit 9 outputs the output voltage V ＯＵＴ is stepped down to a voltage required for the LED array 7 of the second unit 9.

[0038] The headlight 103 does not necessarily have to include the buck converter 8. If the buck converter 8 of the headlight 103 is omitted, the boost converter 102 supplies a constant current I ｄ In this case, the boost converter 102 supplies its own output current I ＯＵＴ , i.e., the current I of the LED array 7 ｄ is monitored using a current sense resistor (not shown), and the current I ｄ The output voltage V ＯＵＴ This allows a constant current I to be supplied to the LED array 7 even if the step-down converter 8 is omitted. ｄ is supplied.

[0039] The input voltage V of the boost converter 102 ＩＮ Output voltage V ＯＵＴThe ratio of the ON period to the ON period, or the so-called step-up ratio, is determined by the duty ratio (the ratio of the ON period to the switching period) of the control signal for the switching element Q1. As mentioned above, the duty ratio is restricted by the performance of the switching element Q1 and the control unit 1 that controls it, and there is an upper limit to the value that can be set. In particular, when the control frequency (switching frequency) of the switching element Q1 is high, the maximum duty ratio, which is the upper limit of the duty ratio, becomes small.

[0040] In this embodiment, in order to prevent switching noise from interfering with the AM broadcast band, the control frequency of the switching element Q1 is set higher than the upper limit frequency of the AM broadcast band, which results in an extremely short switching period of the switching element Q1 and a low maximum duty ratio.

[0041] Furthermore, the voltage of the battery 101 is not always constant. For example, when a large amount of power is consumed by the starter motor, such as when starting the engine or when recovering from an idling stop, the voltage input from the battery 101 to the boost converter 102 temporarily drops. At this time, the output voltage V ＯＵＴ In order to maintain this, it is necessary to increase the duty ratio of the switching element Q1 and the boost ratio of the boost converter 102. If the required duty ratio cannot be ensured, the output voltage V ＯＵＴ Specifically, the output voltage V of the boost converter 102 decreases, and the headlight 103 does not operate normally. ＯＵＴ becomes lower than the total value of the forward voltages of the LED array 7 of the headlight 103, and the LED array 7 cannot be turned on. Also, for example, if the load of the boost converter 102 includes an ECU (Electric Control Unit), the output voltage V ＯＵＴ It is also possible that a power-on reset of the ECU is performed when the voltage drops.

[0042] Here, the input voltage V ＩＮ and output voltage V ＯＵＴ The relationship between the duty ratio D and the pulse width W is expressed by the following equation (1).

[0043]

[0044] 4 shows the waveform of the control signal CS, which is the gate voltage of the switching element Q1. As shown in FIG. 4, the switching period of the control signal CS is t ＳＷ , the ON time, which is the length of the High level period of the control signal CS, is t ＯＮ , the off time, which is the length of the low level period of the control signal CS, is t ＯＦＦ When this definition is given, the duty ratio D is expressed by the following equation (2).

[0045]

[0046] From equations (1) and (2), the output voltage V of the boost converter 102 is ＯＵＴ is expressed as the following equation (3).

[0047]

[0048] For example, the switching frequency f ＳＷ When the frequency is 2 MHz, the switching period t ＳＷ The switching period t ＳＷ is 500 nanoseconds (hereinafter referred to as "nsec"). ＯＵＴ Assume that the input voltage of the boost converter 102 is 50 V and the output voltage V ＯＵＴ The duty ratio required to maintain the switching period t at 50 V is 88%. ＳＷ is 500 nsec, so the on time t ＯＮ is 440 nsec, off time t ＯＦＦ must be a very short time of 60 nsec.

[0049] However, the boost converter 102 outputs an output voltage V ＯＵＴ is the input voltage V ＩＮ In order to make the voltage higher than t, the energy stored in the inductor L1 during the ON period of the switching element Q1 needs to be released from the inductor L1 to the capacitor C1 during the OFF period of the switching element Q1, and therefore a discharge period for this needs to be secured. For example, in order to secure this discharge period, ＯＦＦIf it is necessary to secure at least 80 nsec, the upper limit (maximum duty ratio) of the duty ratio D becomes 84%, and the output voltage V ＯＵＴ can only be increased to 37.5V.

[0050] Therefore, in this embodiment, the control unit 1 detects the input voltage V ＩＮ The value of the input voltage V ＩＮ When a drop in output voltage V ＯＵＴ The control frequency of the control signal CS (i.e., the switching frequency f ＳＷ ) to reduce the input voltage V ＩＮ Since the decrease in the switching period t is temporary, when the control unit 1 lowers the control frequency, the control frequency may be lower than the upper limit frequency of the AM broadcast band. For example, when the control unit 1 lowers the switching frequency from 2 MHz to 1.5 MHz, the switching period t ＳＷ is 667 nsec, and the off time t ＯＦＦ Even if only 80 nsec is secured, the duty ratio D can be set to 88%, and the output voltage V ＯＵＴ can be maintained at 50V.

[0051] The operation of the boost converter 102 according to the first embodiment will be described in more detail with reference to Fig. 5. The upper graph in Fig. 5 shows the input voltage V ＩＮ and switching frequency f ＳＷ The graph at the bottom of FIG. 5 shows the relationship between the input voltage V ＩＮ and output voltage V ＯＵＴ Here, when there is no voltage drop in the battery 101, the input voltage V ＩＮ is the normal voltage Vtyp, and the switching frequency f ＳＷ When f1, the output voltage V ＯＵＴ The input voltage V that can maintain the desired voltage ＩＮ The minimum value of Vth is the threshold voltage, and the minimum input voltage V at which the boost converter 102 must operate is ＩＮ is the minimum voltage Vmin.

[0052] As shown in the dotted line graph in Figure 5, the input voltage V ＩＮ Even if the switching frequency f ＳＷ If f1 is maintained, the required duty ratio cannot be secured and the output voltage V ＯＵＴ decreases.

[0053] In contrast, the control unit 1 of the boost converter 102 according to this embodiment controls the input voltage V ＩＮ is higher than the threshold voltage Vth, the switching frequency f ＳＷ is maintained at f1, and the input voltage V ＩＮ When the switching frequency f ＳＷ As a result, the output voltage V ＯＵＴ can be maintained at a desired value.

[0054] In FIG. 5, the input voltage V ＩＮ is higher than the threshold voltage Vth, the control unit 1 controls the switching frequency f ＳＷ 6, the control unit 1 can change the input voltage V ＩＮ As the switching frequency f ＳＷ The control unit 1 may also reduce the input voltage V ＩＮ As the switching frequency f ＳＷ may be decreased continuously (for example, linearly).

[0055] Ideally, as shown in FIG. ＩＮ At the same time as the switching frequency f ＳＷ However, in reality, there is a response delay of the input voltage detection unit 6 due to a low-pass filter for preventing malfunction of the input voltage detection unit 6, and a response delay of the control unit 1, so as shown in FIG. ＩＮ After the control unit 1 detects the switching frequency f ＳＷ The delay time t ＤＥＬＡＹ This delay time t ＤＥＬＡＹ During this period, the desired output voltage V ＯＵＴTherefore, in this embodiment, the capacitor C1 is connected to the delay time t ＤＥＬＡＹ During this period, the output voltage V ＯＵＴ The capacitance of the capacitor C1 is increased to such an extent that the delay time t ＤＥＬＡＹ During this period, the output voltage V ＯＵＴ This can prevent the deterioration of the

[0056] Next, the input voltage V ＩＮ 9, the control unit 1 controls the input voltage V ＩＮ When the switching frequency f ＳＷ is decreased from f1 to f2, and then the input voltage V ＩＮ When the switching frequency f ＳＷ Return from f2 to f1.

[0057] In reality, the input voltage V ＩＮ When the input voltage V ＩＮ After recovery, the control unit 1 switches to the switching frequency f ＳＷ The delay time t ＤＥＬＡＹ This delay time t ＤＥＬＡＹ During this period, the upper limit of the duty ratio D simply increases, and no operational problems occur. However, ＳＷ If the switching frequency f is changed suddenly, the operation of the boost converter 102 may become unstable. ＳＷ The speed at which the control unit 1 increases the switching frequency f ＳＷ In other words, the control unit 1 controls the input voltage V ＩＮ When the switching frequency f ＳＷ It is preferable to quickly reduce the input voltage V ＩＮ When the power supply recovers, the stability of the operation is prioritized, and the switching frequency f ＳＷ It is preferable to increase slowly.

[0058] The boost converter 102 of this embodiment operates in response to an input voltage V ＩＮ When the output voltage V ＯＵＴ This operation maintains the input current I ＩＮ However, this is achieved by increasing the input current I ＩＮ If the increased state of V continues for a long time, the loss in the diode D1 and the switching element Q1 will increase, and there is a concern that they may be thermally destroyed. ＩＮ Alternatively, the control unit 1 may stop the operation when the input voltage V remains equal to or lower than the threshold voltage Vth for a certain period of time (for example, about 1 second). ＩＮ When the state where the threshold voltage Vth or less continues for a certain period of time (for example, about 1 second), the switching frequency f ＳＷ may be restored to its original value (f1). This modification is also useful for reducing the desired output voltage V ＯＵＴ This prioritizes circuit protection over gain.

[0059] Second Embodiment A buck-boost converter has the functions of both a boost converter and a buck converter. The technology according to the present disclosure is also applicable to a boost converter included in the buck-boost converter.

[0060] Fig. 10 is a configuration diagram showing a step-up / step-down converter 102A according to embodiment 2. The step-up / step-down converter 102A shown in Fig. 10 is an asynchronous step-up / step-down DC / DC converter.

[0061] The step-up / step-down converter 102A includes a switching element Q11 as a switching unit, an inductor L11 as a charging / discharging unit, a diode D11 as a one-way current element, a capacitor C11 as an output unit or step-up unit, a control unit 1, and an input voltage detection unit 6.

[0062] The switching element Q11 and the inductor L11 are connected in series, and the inductor L11 is connected to the positive electrode node of the battery 101 via the switching element Q11. The inductor L11 is also connected between the switching element Q11 and the negative electrode node of the battery 101. The switching element Q11 switches between conducting and cutting off the inductor L11, and the inductor L11 stores and releases power input from the battery 101 through the switching element Q11. In Fig. 10, the switching element Q11 is a MOSFET, but the switching element Q11 is not limited to a MOSFET and may be, for example, an IGBT.

[0063] The diode D11 is connected to the inductor L11 and the switching element Q11. Specifically, the cathode of the diode D11 is connected to the connection node between the inductor L11 and the switching element Q11. The anode of the diode D11 is connected to the capacitor C11 and the headlight 103, which is a load. That is, the capacitor C11 and the headlight 103 are connected between the anode of the diode D11 and the negative node of the battery 101. The capacitor C11 is connected to the inductor L11 and the switching element Q11 via the diode D11 and smooths and outputs the power released from the inductor L11. Like the diode D1 described in the first embodiment, the diode D11 is preferably a trench Schottky diode.

[0064] For example, when it is necessary to supply a voltage higher than the voltage of battery 101 to headlight 103, such as when LED array 7 of headlight 103 includes a large number of LEDs, step-up / step-down converter 102A operates in the step-up mode. When step-up / step-down converter 102A operates in the step-up mode, it is effective to apply the technology of embodiment 1.

[0065] The buck-boost converter 102A may be a Cuk converter, a Zeta converter, a SEPIC (Single Ended Primary Inductor Converter), or the like.

[0066] It is possible to freely combine the embodiments, and to modify or omit the embodiments as appropriate.

[0067] The above description is illustrative in all respects, and it is understood that countless variations not illustrated can be envisioned.

[0068] 100 Vehicle, 101 Battery, 102 Boost converter, 102A Buck-boost converter, 103 Headlight, 104 Radio, 1 Control unit, 2 CPU, 3 Memory, 4 ROM, 5 RAM, 6 Input voltage detection unit, 7 LED array, 8 Buck converter, 9 Unit, BS AM broadcast signal, Q1, Q11 Switching elements, L1, L11 Inductors, D1, D11 Diodes, C1, C11 Capacitors.

Claims

1. A boost converter for a vehicle comprising: a charge / discharge unit that stores and releases power input from a power source; a switching unit that switches between energizing and cutoff of the charge / discharge unit; a one-way flow element connected to the charge / discharge unit and the switching unit; an output unit connected to the charge / discharge unit and the switching unit via the one-way flow element and that smooths and outputs the power released from the charge / discharge unit; a control unit that controls the switching unit; and an input voltage detection unit that detects the input voltage from the power source, wherein the control unit inputs a control signal of a predetermined control frequency to the switching unit and controls the switching unit by controlling the duty ratio of the control signal, and when a drop in the input voltage is detected, the control unit lowers the control frequency so that the duty ratio can be set so that the output voltage can be maintained and a discharge period can be secured for releasing the energy stored in the charge / discharge unit to the output unit.

2. The vehicular boost converter according to claim 1, wherein the control unit maintains the control frequency constant until the input voltage drops below a predetermined threshold, and reduces the control frequency when the input voltage drops below the threshold.

3. The vehicle boost converter according to claim 2, wherein the control unit lowers the control frequency continuously or in multiple stages as the input voltage decreases.

4. The boost converter for a vehicle according to claim 1, wherein the control frequency before the input voltage is reduced is a frequency higher than an AM broadcast band.

5. The boost converter for a vehicle according to claim 1, wherein the one-way current element is a trench diode.

6. The boost converter for a vehicle according to claim 1, wherein the one-way current element is a Schottky diode.

7. The boost converter for a vehicle according to claim 1, wherein the output section maintains the output voltage without reducing it during a period from when the input voltage decreases until when the control section reduces the control frequency.

8. The vehicular boost converter according to claim 2, wherein the control unit increases the control frequency when the input voltage becomes higher than the threshold value after lowering the control frequency.

9. The boost converter for a vehicle according to claim 8, wherein the speed at which the control unit increases the control frequency is slower than the speed at which the control unit decreases the control frequency.

10. The boost converter for a vehicle according to claim 1, wherein the control unit stops operating when the input voltage remains low for a certain period of time.

11. The vehicular boost converter according to claim 1, wherein, when the input voltage remains reduced for a certain period of time, the control unit returns the control frequency to the value before the input voltage was reduced.

12. The boost converter for a vehicle according to claim 1, wherein the output section is connected to a semiconductor light emitting element.

13. The vehicular boost converter according to claim 12, wherein the semiconductor light emitting element is a lighting fixture for a vehicle.

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