JPH09240422A - Step-up power supply device for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a step-up power supply device for vehicle which can protect a switching element securely, in an abnormal switching condition, by a simple and a low cost of structure. SOLUTION: In either one case of the reduction of the resistance value of a loading circuit; a trouble of the loading circuit; the capacity reduction of a smoothing circuit; and an abnormal condition of the output voltage V UP; a duty controller 1 stops the switching of an FET. In the built-in resistor of a variable means 2, or in a memory allowable to be read from the variable means 2, a data to prescribe the switching operation area of the FET is set. The variable means 2 calculates the limit value of the duty in the switching of the FET depending on the above data, and the value of the input voltage VB, and carries out the switching of the FET not to exceeding the limit value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a step-up power supply device for a vehicle, which protects components constituting the step-up power supply device for a vehicle during abnormal operation.

[0002]

2. Description of the Related Art FIG. 4 is a circuit diagram showing an example of a step-up power supply device for a vehicle. In this figure, when the ignition switch IGSW is turned on, the input current IB flows through the coil L,
The current energy is stored. Duty controller 1
When a FET (field effect transistor) switches at a predetermined duty, a current ISW flows when the FET is in the ON state, and a current ID when the FET is in the OFF state.
Flows. When the current ID flows, the current energy stored in the coil L is charged in the smoothing capacitor C as voltage energy. By repeating the above, the input voltage VB of the battery is boosted and becomes the output voltage VUP of the capacitor, which is applied to the load circuit.

In this figure, the load circuit is composed of a switch SW and a resistor R, and for example, an ignition circuit of an air bag system of an automobile can be considered.

Normally, the ignition circuit of an air bag system of a vehicle is mechanically activated when an ignition transistor which is turned on by the input of a collision signal from a collision determination block for detecting a collision of the vehicle and acceleration of a predetermined value or more is applied. A mechanical safing sensor that is turned on and a squib resistor that generates heat when a large current flows are connected in series to the boost power supply circuit. That is, when the ignition transistor and the mechanical safing sensor are both turned on due to the collision of the automobile, a large current flows through the squib resistor to expand the airbag.

By the way, in the step-up power supply device for a vehicle shown in FIG. 4, when an abnormality occurs in the duty control unit 1, the FE
There was a possibility that abnormal switching of T occurred and the FET failed. Therefore, in order to prevent the above-mentioned breakdown of the FET, various limitation and protection circuits are provided in the conventional vehicular boost power supply device. Usually, this limit and protection circuit is a low voltage detection circuit, a duty limit circuit,
It has a current limiting circuit and a thermal shutdown circuit.

The above-mentioned low voltage detection circuit has a function of stopping the switching of the FET when the input voltage VB of the control means becomes equal to or lower than a preset fixed value (input voltage threshold V0). . Further, the duty limiting circuit limits the duty of the switching of the FET so as not to exceed the duty threshold D0 when the duty becomes equal to or more than a preset fixed value (duty threshold D0). It is a function.

The current limiting circuit has a function of limiting the switching of the FET when the input current or output current of the control means exceeds a preset fixed value (current threshold value). Finally, the thermal shutdown circuit has a function of stopping switching of the FET when the temperature of the FET becomes equal to or higher than a preset value (temperature threshold value).

[0008]

By the way, in the above-mentioned conventional step-up power supply device, FET switching is performed by the MPU.
It is performed by digital control. In this case, in order to realize the current limiting circuit and the thermal shutdown circuit described above, a dedicated MPU peripheral circuit (for example, a dedicated IC) must be separately provided, which makes the configuration of the entire device complicated and expensive. There was a problem of becoming.

Therefore, in order to make the structure of the limiting and protecting circuit simple and inexpensive, it is conceivable to limit and protect only by the above-mentioned low voltage detecting circuit and duty limiting circuit. In this case, however, the following problems will occur. there were.

FIG. 5 is a graph showing an example of the switching operation area of the FET of the booster power supply circuit when the limitation and protection by the low voltage detecting circuit and the duty limiting circuit are applied. In this figure, V0 is the input voltage threshold and D0 is the duty threshold. As shown in this figure, M that controls the switching of the FET
The PU stops switching of the FET when the input voltage VB of the step-up power supply device becomes equal to or lower than the input voltage threshold V0.

On the other hand, when the input voltage VB of the step-up power supply device is equal to or higher than the input voltage threshold value V0, the MPU switches the FET. In that state, if an abnormality of the duty control unit 1 occurs, abnormal switching of the FET may occur and the duty of the FET may increase. As a result, when the duty becomes equal to or higher than the duty threshold D0, the MPU limits the duty to the duty threshold D0.

However, in the case of limiting and protecting only by the low voltage detecting circuit and the duty limiting circuit described above, if the abnormal switching occurs when the input voltage VB is near the target voltage (area A in FIG. 5), the FE
The peak current flowing in T rises sharply, which causes
The loss in the FET increased, and the FET could be damaged.

Therefore, in the conventional limitation and protection, in order to prevent the failure of the FET due to the above-mentioned loss, the above-mentioned current limiting circuit and thermal shutdown circuit must be provided even though the configuration becomes complicated and expensive. It was

Furthermore, when the limitation and protection by only the low voltage detection circuit and the duty limitation circuit described above are applied to the power source of the ignition circuit of the airbag system described above, the switch of the load circuit is turned on, which is seen from the capacitor. When the resistance R of the load circuit drops, the load circuit fails (corresponds to the GND short of the mechanical safing sensor and the squib resistor), the capacity of the smoothing capacitor C shown in FIG. 4 is lost, and the boost output of the boost power supply circuit is abnormal. Also, increase of output current → current cannot be supplied → output voltage drop → FET
There was a problem that the duty increase of → the FET failed.

The present invention has been made in view of such a background, and has a simple and inexpensive structure, but can reliably protect a switching element such as an FET when abnormal switching occurs, and a booster power supply for a vehicle. The purpose is to provide a device.

[0016]

According to the first aspect of the present invention,
A battery that supplies power, an ignition switch,
The charging of the coil from the battery and the charging of the capacitor with the current energy stored in the coil are switched by the diode and the switching element, and the control means for controlling the duty based on the voltage of the capacitor is connected to the capacitor as a load. A boosting power supply device for a vehicle, the switching duty being restricted with respect to the control means, and the limiting value is provided with a varying means that changes based on the voltage of the battery. To do.

According to a second aspect of the present invention, in the vehicle booster power source device according to the first aspect, the variable means causes the control means to stop the switching when the capacity of the capacitor decreases. It is characterized by

According to a third aspect of the present invention, in the vehicle booster power source device according to the first or second aspect, the variable means is provided to the control means when an abnormality occurs in the output voltage of the capacitor. Then, the switching is stopped.

According to a fourth aspect of the present invention, in the vehicle booster power source device according to any one of the first to third aspects, the variable means is used when the resistance value of the load circuit is lowered, or When a short circuit occurs in the load circuit, the control means is caused to stop the switching.

According to a fifth aspect of the present invention, in the boosting power source device for a vehicle according to any one of the first to fourth aspects, the variable means includes a calculation formula storage means for storing a calculation formula for the limit value. The calculating means for calculating the limit value by substituting the current input voltage of the battery into the calculating expression stored in the calculating expression storage means.

According to a sixth aspect of the present invention, in the boosting power source device for a vehicle according to any of the first to fourth aspects, the variable means stores a limit value corresponding to each input voltage value of the battery. And a reading means for reading the limit value corresponding to the current input voltage of the battery from the limit value storage means.

[0022]

DETAILED DESCRIPTION OF THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a vehicle booster power source device according to an embodiment of the present invention. In this figure, the control circuit and the load circuit other than the variable means 2 are the same as the circuit shown in FIG. 4, and therefore their explanations are omitted.

The duty control unit 1 is an MPU having a built-in A / D converter. Further, the duty control unit 1 always takes in the potential of the output voltage VUP of the capacitor while the ignition switch IGSW is ON, and A / D-converts the fetched potential by using the A / D converter. And
The duty control unit 1 determines the switching duty Dn of the switching element (FET) based on the conventional processing, and switches the FET with the duty Dn.

In addition, data defining a switching operation area of the FET is set in a built-in register of the variable means 2 or a memory (not shown) which can be read from the variable means 2. FIG. 2 shows the FET according to this embodiment.
3 is a graph showing an example of the switching operation area of FIG. In this figure, the amount of change in duty when the input voltage VB is between V2 and V3, that is, the slope of the graph is determined based on the allowable loss of the FET. In the present embodiment, the built-in register or memory is provided with V shown in FIG.
It is assumed that the values of 1, V2, V3 and D1 are preset as set values. In this embodiment, as a specific example, V1 is 5 [V], V2 is 7.5 [V], V3 is 15 [V], and D1 is 70%.

Next, referring to FIG. 3, the operation of the variable means 2 and the duty control section 1 having the above construction will be described.
FIG. 3 is a flowchart showing an operation example of the variable unit 2 and the duty control unit 1 according to this embodiment. The processing of the variable means 2 and the duty control unit 1 proceeds to step SA1 in order to perform the interrupt processing shown in this figure each time an interrupt is received at intervals of 1 [ms].

In step SA1, it is determined whether any of the following determination conditions 1 to 3 has occurred. Reduction of resistance value due to switch ON of load circuit (for example, load short state at ignition) Load circuit failure (for example, mechanical safing sensor and squib resistor GND short) Smoothing capacitor C capacity reduction Smoothing Output abnormality of capacitor C

If the result of this determination is "YES", then the operation proceeds to step SA2. In step SA2, after the duty control is stopped, the interrupt processing shown in FIG. 3 is ended.

On the other hand, the determination result of step SA1 is "N
In the case of “O”, the process proceeds to step SA3 and
The duty is calculated based on the voltage of the smoothing capacitor C.

At step SA4, V1, V2, V3 and D1 (see FIG. 2) are read from the built-in register of the variable means 2 or the memory readable by the variable means 2.
After calculating the limit value L based on the following equation (6), the interrupt processing shown in FIG. 3 is terminated. L = ((V3-VB) / (V3-V2)) * D1 (6) In this formula, V2, V3 and D1 are set values (see FIG. 2), and VB is the battery Input voltage. This is the end of the description of the operation of the booster power supply device having the above configuration.

Next, the correspondence between the claimed invention and this embodiment will be described. Control means: Duty control section 1 Variable means: Variable means 2

Although the embodiments of the present invention have been described in detail with reference to the drawings, the specific configuration is not limited to the embodiments, and changes in design and the like may be made without departing from the gist of the present invention. Even if there is, it is included in the present invention. For example, in the above-described embodiment, the formula (6) is used as the calculation formula for obtaining the duty limit value L, but the formula for the limit value L is not limited to this. . Further, a calculation formula is not used when obtaining the duty limit value L, and instead, a table is prepared in which the limit value L obtained by the experiment is stored in association with each input voltage VB, and the current input from the table is prepared. A method of reading the duty limit value L corresponding to the voltage VB is also conceivable.

[0032]

As described above, according to the present invention, it is possible to prevent damage to the switching element with a simple and inexpensive structure even during abnormal switching due to disturbance or the like.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration example of a vehicle booster power source device according to an embodiment of the present invention.

FIG. 2 is a graph showing an example of a switching operation region of the FET in the same embodiment.

FIG. 3 is a flowchart showing an operation example of a duty control unit and a variable unit according to the same embodiment.

FIG. 4 is a block diagram showing an example of a conventional vehicle booster power supply device.

FIG. 5 is a graph showing an example of FET switching operation regions in a conventional vehicle booster power supply device.

[Explanation of symbols]

1 ... Duty controller, 2 ... Variable means, L ... Coil, D ... Diode, C ... Smoothing capacitor,
FET: Field effect transistor, R: Load

Front page continuation (72) Inventor Tsutomu Fukui 1-4-1 Chuo, Wako-shi, Saitama, Ltd. Honda R & D Co., Ltd. Electronic Technology Research Institute Kakuda Office

Claims (6)

[Claims] 1. A battery for supplying power, an ignition switch, charging of a coil from the battery and charging of a capacitor of current energy stored in the coil are switched by a diode and a switching element, and the voltage of the capacitor is changed. In a booster power supply device for a vehicle, which comprises a control means for controlling the duty based on the above, and a load circuit connected as the load of the capacitor, the switching duty is limited to the control means, and the limit value is the battery. A boosting power supply device for a vehicle, comprising: a variable unit that changes according to the voltage. 2. The vehicle booster power supply device according to claim 1, wherein the variable means causes the control means to stop the switching when the capacity of the capacitor decreases. Booster power supply. 3. The booster power supply device for a vehicle according to claim 1, wherein the variable means stops the switching with respect to the control means when an abnormality occurs in the output voltage of the capacitor. A booster power supply device for a vehicle, which is characterized in that: 4. The step-up power supply device for a vehicle according to claim 1, wherein the variable means causes a short circuit in the load circuit when the resistance value of the load circuit decreases. In this case, the boosting power supply device for vehicles is characterized in that the switching is stopped by the control means. 5. The booster power source device for a vehicle according to claim 1, wherein the variable unit stores a formula for storing the limit value, and the formula storage unit. A boosting power supply device for a vehicle, comprising: a calculation unit that substitutes a current input voltage of the battery into a calculation formula stored in the calculation formula to calculate a limit value. 6. The booster power supply device for a vehicle according to claim 1, wherein the variable unit includes a limit value storage unit that stores a limit value corresponding to each input voltage value of the battery. A boosting power supply device for a vehicle, comprising: a reading unit that reads a limit value corresponding to a current input voltage of the battery from the limit value storage unit.