JP2007288979A - Dc power supply apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a DC power supply apparatus adapted to shorten the time required for a soft start while suppressing rush currents, in a DC power supply apparatus to which resistance loads are connected. <P>SOLUTION: A step-up/step-down chopper circuit 13 outputs after boosting or bucking an input voltage given from a battery 51 in response to control by a control circuit 15. An output capacitor Cout smoothes an output voltage of the step-up/step-down chopper circuit 13. A correspondence relationship between input voltage and duty of drive signal of transistor Q1 is registered in a soft start management table 16. When an operation of DC power supply apparatus 1 is started, a transistor Q2 is held in off state, while the transistor Q1 is driven by the drive signal having a duty corresponding to the input voltage. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a DC power supply device that supplies power to a resistive load.

  As one form of the DC power supply device, as shown in FIG. 6, the step-up / step-down chopper circuit unit 110, the control unit 120 that controls the step-up / step-down chopper circuit unit 110, and the output capacitor that smoothes the output of the step-up / step-down chopper circuit unit 110 A configuration with Cout is known. Here, a configuration is shown in which the battery voltage is stepped up or stepped down and supplied to the load. Note that the in-vehicle DC power supply device normally generates a predetermined voltage using a battery voltage.

  By the way, when starting a load, it is generally required to operate the load as soon as possible. For example, a heater as a heating device is desired to warm the room as soon as possible. In order to satisfy this requirement, it is necessary to supply a sufficient current from the start of the load.

  On the other hand, when a resistive load such as a heater is connected to the DC power supply device, the electric charge accumulated in the output capacitor Cout flows through the load even after the operation of the DC power supply device is stopped. That is, when the resistive load is connected, the output capacitor Cout is almost empty at the start of the operation of the DC power supply device. Therefore, at the start of power supply to the load, first, a large current (inrush current) flows to charge the output capacitor Cout. And this inrush current has a possibility of destroying a semiconductor element, a coil, etc. which constitute a direct-current power supply device.

Patent Document 1 describes a technique for solving this problem. The DC / DC converter described in Patent Document 1 includes a booster circuit and a step-down circuit, and performs a soft start by the step-down circuit for a certain period of time at startup. In this soft start process, the duty of the switching element of the step-down circuit is gradually increased from zero. Then, normal operation is performed after the input voltage and the output voltage of the DC / DC converter become substantially equal. Therefore, the inrush current is suppressed by this configuration.
Japanese Patent Laying-Open No. 2005-354860 (FIGS. 1 and 2, paragraph 0021 of the specification, etc.)

  As described above, in the DC / DC converter described in Patent Document 1, inrush current can be suppressed. However, since this DC / DC converter is configured to gradually increase the duty of the switching element from zero during the soft start period, the time required for the output voltage to rise to a desired value becomes long. For this reason, for example, when electric power is supplied to a heater as a heating device, generation of warm air is delayed.

  An object of the present invention is to reduce the time required for soft start while suppressing inrush current in a DC power supply device to which a resistive load is connected.

  The DC power supply device of the present invention includes a detecting means for detecting an input voltage, a coil, a first switching element connected to the coil and used for a step-down operation, and a boosting operation connected to the coil. A step-up / step-down chopper circuit including a second switching element used in the control circuit, PWM control means for controlling the first and second switching elements, an output capacitor for smoothing the output of the step-up / step-down chopper circuit, and an input Storage means for storing a correspondence relationship between a voltage and a duty value of a drive signal for driving the first switching element. When the control means starts supplying power to the load, the control means obtains a duty value corresponding to the input voltage detected by the detection means from the storage means, and turns the second switching element off. The first switching element is driven by the drive signal having the duty value while holding the signal.

  In the DC power supply, the inrush current generated at the start of power supply to the load depends on the input voltage. Therefore, if the duty value is appropriately set according to the input voltage, the current flowing through the step-up / step-down chopper circuit at the start of power supply to the load is suppressed. In addition, if an appropriate value other than zero is set as the duty value, the output voltage can be rapidly increased.

  The duty value is, for example, based on the load connected to the DC power supply device and the capacity of the output capacitor, and the maximum value of the current flowing through the step-up / down chopper circuit is less than the allowable value of the coil and the first switching element. And is set in advance so as to approximate. If the duty value is determined in this manner, the time for charging the output capacitor can be shortened while protecting the coil and the first switching element from the inrush current.

  The storage means may store soft start period information defining the duty value and the soft start period in association with the input voltage. In this case, the control means drives the first switching element with a drive signal having the duty value for a period determined by the soft start period information. According to this configuration, the soft start period can be shortened to the minimum necessary according to the input voltage.

  The soft start method of the present invention includes a detection means for detecting an input voltage, a coil, a first switching element connected to the coil and used for a step-down operation, and a step-up operation connected to the coil. Used in a DC power supply device having a step-up / step-down chopper circuit having a second switching element used for the output and an output capacitor for smoothing the output of the step-up / step-down chopper circuit, and starting power supply to a load In addition, the second switching element is held in an OFF state, and the first switching element is driven with a drive signal having a duty value corresponding to the input voltage detected by the detection means.

  ADVANTAGE OF THE INVENTION According to this invention, in the DC power supply device to which a resistive load is connected, the time required for soft start can be shortened while suppressing inrush current.

  FIG. 1 is a diagram illustrating a configuration of a DC power supply device according to an embodiment of the present invention. In addition, the battery 51 is connected to the input terminal of the DC power supply device 1 of the embodiment, and the load 52 is connected to the output terminal. The load 52 is a resistive load, for example, a heater used as a heating device.

  The input voltage detection circuit (detection means) 11 detects the input voltage of the DC power supply device 1. The input voltage of the DC power supply device 1 is substantially the same as the output voltage of the battery 51. The shunt resistor 12 detects the input current of the DC power supply device 1. The step-up / step-down chopper circuit 13 includes a coil L, a transistor (first switching element) Q1, a transistor (second switching element) Q2, and diodes D1 and D2, and increases or decreases the input voltage according to an instruction from the control circuit 15. And output. The operation of the step-up / down chopper circuit 12 will be described later. The output capacitor Cout smoothes the output of the step-up / step-down chopper circuit 13. The output voltage detection circuit 14 detects the output voltage of the DC power supply device 1. The control circuit 15 generates a drive signal for controlling the step-up / step-down chopper circuit 13 based on detected parameters (that is, input voltage, input current, output voltage). The drive signal is composed of a set of drive signals for driving the transistors Q1 and Q2. The control circuit 15 also includes a soft start management table (storage means) 16. As will be described in detail later, the soft start management table 16 stores information for controlling soft start executed when the operation of the DC power supply device 1 is started.

In the DC power supply device 1 configured as described above, during the step-down operation (that is, the operation of generating the output voltage Vout lower than the input voltage Vin), the transistor Q1 is chopper-controlled while the transistor Q2 is kept off. At this time, the switching cycle of the chopper control is “T”, the time for controlling the transistor Q1 to be turned on in each switching cycle is “Ton”, and the time for controlling the transistor Q1 to be turned off in each switching cycle is “Toff”. The duty D of the PWM control drive signal is expressed by the following equation.
D = Ton / T = Ton / (Ton + Toff)
In this case, the output voltage is expressed by the following equation.
Vout = Vin × D = Vin × Ton / (Ton + Toff)
Here, assuming that “Ton” is not zero, “0 <D <1” is satisfied, so that the step-down operation is realized.

On the other hand, during the boosting operation (that is, the operation for generating the output voltage Vout higher than the input voltage Vin), the transistor Q2 is chopper-controlled while the transistor Q1 is kept on. At this time, if the time for controlling the transistor Q2 to be turned on and the time for controlling the transistor Q2 to be turned off in each switching cycle are “Ton” and “Toff”, respectively, the output voltage is expressed by the following equation.
Vout = Vin × (Ton + Toff) / Ton
Here, assuming that “Ton” is not zero, “1 <(Ton + Toff) / Ton”, so that the boosting operation is realized.

  Incidentally, the load 52 connected to the DC power supply device 1 is a resistive load. For this reason, even after the operation of the DC power supply 1 is stopped, the electric charge accumulated in the output capacitor Cout flows through the load 52. That is, when the operation of the DC power supply 1 is started, the output capacitor Cout is almost empty. Therefore, if a predetermined voltage is to be output at the start of power supply to the load 52, in the DC power supply device 1, a large current (inrush current) for charging the output capacitor Cout first flows. Therefore, the DC power supply device 1 according to the embodiment provides a soft start function in order to protect the semiconductor element, the coil, and the like from the inrush current.

  FIG. 2 is an example of the soft start management table 16. In the soft start management table 16, “duty” and “soft start period” are registered in association with “input voltage”. “Input voltage” is a voltage detected by the input voltage detection circuit 11. “Duty” is the duty of the drive signal that drives the transistor Q1 during the step-down operation in the soft start period. As the duty, a value as large as possible is selected with respect to the input voltage as long as the maximum value of the current flowing through the step-up / step-down chopper circuit 13 does not exceed the allowable values of the coil L and the transistor Q1. Note that the maximum value of the current flowing through the step-up / step-down chopper circuit 13 during the step-down operation is substantially determined by the input voltage, the resistance value of the load 52, the capacitance of the output capacitor Cout, and the duty of the transistor Q1. Here, the resistance value of the load 52 and the capacity of the output capacitor Cout are predetermined. Therefore, by specifying the duty of the transistor Q1 with respect to the input voltage, the current flowing through the step-up / down chopper circuit 13 during the step-down operation can be limited to a predetermined value (here, the allowable value of the coil L and the transistor Q1) or less. it can. The “soft start period” represents a time for performing the step-down operation at the above-described “duty” when the operation of the DC power supply device 1 is started. For example, a time required for charging the output capacitor Cout is set. The soft start management table 16 is created in advance by simulation or measurement with an actual machine.

  FIG. 3 is a flowchart showing processing at the start of the operation of the DC power supply device 1. In step S1, the input voltage detection circuit 11 is used to detect the input voltage. In step S2, the soft start management table 16 is searched using the detected input voltage as a key, and the corresponding “duty” is acquired. At this time, a “soft start period” corresponding to the detected input voltage is also extracted. In step S3, the transistor Q2 is kept off.

  In steps S4 to S5, a PWM signal having the “duty” extracted in step S2 is generated as a drive signal for driving the transistor Q1. This PWM signal is continuously output until the “soft start period” elapses from when the DC power supply device 1 starts operating. When the “soft start period” elapses, the DC power supply device 1 shifts to the normal mode. In this embodiment, the normal mode means an operation mode in which a step-up operation or a step-down operation is performed by feedback control that holds the output voltage at a predetermined value.

FIG. 4 is a diagram for explaining the soft start operation of the DC power supply device 1. Here, the boosting operation is performed as the normal mode.
During the soft start period, the transistor Q2 is held in the off state. Further, the duty of the drive signal of the transistor Q1 is set to a value acquired from the soft start management table 16 using the input voltage as a key. Here, the “duty” is set in a range where the maximum value of the current flowing through the step-up / step-down chopper circuit 13 does not exceed the allowable values of the coil L and the transistor Q1. Therefore, these elements can be protected from inrush current. As the “duty”, a value as large as possible within the above range is selected. Therefore, the soft start period can be shortened while protecting the element. In particular, in the DC power supply device 1 of the embodiment, since the transistor Q1 is driven with a predetermined duty that is not zero immediately after the start of the operation, the soft start period can be shortened as compared with the configuration described in Patent Document 1. In the soft start described in Patent Document 1, since the duty of the signal for driving the switching element is gradually increased from zero, the time until the output capacitor is charged as compared with the embodiment of the present invention is increased. As a result, it is necessary to lengthen the soft start period.

  If the soft start period can be shortened, the time from when the load 52 receives the driving instruction until the normal operation starts is also shortened. Therefore, for example, if the load 52 is a heater, warm air is generated within a short time after the switch is turned on.

  In the embodiment shown in FIG. 4, the operation is performed in the step-down mode immediately after the soft start period ends and the mode is changed to the normal mode. However, the boost mode may be operated immediately after the soft start period ends.

  FIG. 5 is a diagram illustrating a simulation result of the soft start operation according to the embodiment. Here, “duty = 9.8%” and “soft start time = 40 ms” are given. According to this simulation, in the soft start period, the input current (corresponding to the current flowing through the step-up / step-down chopper circuit 13) is kept small, while the output voltage rises steeply. Therefore, it is possible to quickly bring the output voltage close to the target voltage while protecting each element constituting the step-up / step-down chopper circuit 13.

  In the above-described embodiment, the duty of the drive signal of the transistor Q1 in the soft start period is constant. However, the duty may be increased gradually or stepwise from a predetermined positive value other than zero.

  Moreover, although the load 52 connected to the DC power supply device 1 has been described as a resistive load, the DC power supply device 1 supplies power to other loads (for example, a capacitive load or an inductive load). It is also possible.

It is a figure which shows the structure of the DC power supply device of embodiment of this invention. It is an Example of a soft start management table. It is a flowchart which shows the process at the time of the operation | movement start of a DC power supply device. It is a figure explaining the soft start operation | movement of a DC power supply device. It is a figure which shows the simulation result of the soft start operation | movement of embodiment. It is a figure which shows the structure of a general DC power supply device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 DC power supply device 11 Input voltage detection circuit 13 Buck-boost chopper circuit 15 Control circuit 16 Soft start management table

Claims (4)

Detection means for detecting the input voltage;
A step-up / step-down chopper circuit comprising a coil, a first switching element connected to the coil and used for a step-down operation, and a second switching element connected to the coil and used for a step-up operation;
Control means for PWM controlling the first and second switching elements;
An output capacitor for smoothing the output of the step-up / down chopper circuit;
Storage means for storing a correspondence relationship between an input voltage and a duty value of a drive signal for driving the first switching element;
The control unit acquires a duty value corresponding to the input voltage detected by the detection unit from the storage unit when starting to supply power to the load, and holds the second switching element in an OFF state. And the first switching element is driven by a drive signal having the duty value. The duty value is based on a load connected to the DC power supply device and a capacity of the output capacitor, and a maximum value of a current flowing through the step-up / down chopper circuit is less than an allowable value of the coil and the first switching element. The DC power supply device according to claim 1, wherein the DC power supply device is preset so as to approximate. The storage means stores soft start period information defining the duty value and soft start period in association with an input voltage,
The DC power supply device according to claim 1, wherein the control means drives the first switching element with a drive signal having the duty value for a period determined by the soft start period information. Detection means for detecting an input voltage, a coil, a first switching element connected to the coil and used for a step-down operation, and a second switching connected to the coil and used for a step-up operation In a soft start method for a DC power supply device comprising a step-up / step-down chopper circuit comprising an element and an output capacitor for smoothing the output of the step-up / step-down chopper circuit,
When the power supply to the load is started, the second switching element is held in the OFF state, and the first switching is performed with a drive signal having a duty value corresponding to the input voltage detected by the detecting means. A soft start method characterized by driving an element.