JP3282532B2 - Load drive - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a load driving device, and more particularly, to a load driving device for switching power supplied from a power supply by a MOS type FET to a load means or not.

[0002]

2. Description of the Related Art In a load driving circuit for driving a load such as a lamp or a motor using a power MOS FET as a switching element, the ON resistance of the MOS FET, a heat sink,
Under various conditions based on characteristics such as ambient temperature, operating voltage, and operating current, an increase in the temperature of the MOS FET itself may lead to destruction of the MOS FET and a decrease in output.

As described above, in a load drive circuit using a power MOS type FET (particularly, a pulse width modulation control circuit: P
Since a large loss occurs when a large current flows in the WM control circuit, thermal design is important.

Further, in a MOS FET, the temperature of the MOS FET itself rises due to a change due to an external factor such as a change in ambient temperature or a load, and the on-resistance increases. The increase in the on-resistance causes an increase in loss, a decrease in output, and an increase in element temperature, resulting in heating of the MOSFET.

[0005] For this reason, a heating protection device for protecting a power MOS-type FET from heating has been proposed (Japanese Utility Model Application Laid-open No. Hei.
No. 171599). This heating protection device detects the temperature of the cooling fins of the power MOS type FET, determines that the temperature is higher than the set temperature when the detected temperature is lower than the set temperature, and changes the frequency of the motor drive inverter to take heating protection measures. ing.

[0006]

However, in the conventional technique for detecting the temperature of the cooling fin of the power MOS FET as in the prior art, there is a difference from the actual temperature of the power MOS FET and the temperature of the cooling fin is determined based on the temperature of the cooling fin. Because of the time lag due to the transition to the heating protection measure after the temperature of the power MOSFET actually rises, M
The OS type FET may be destroyed or the output may be reduced.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a load driving device capable of suppressing a rise in temperature when a load is driven by using a MOS FET in consideration of the above fact.

[0008]

In order to achieve the above object, a load driving apparatus according to the present invention comprises: a MOS type FET for switching power supplied from a power supply to a load means or not; Monitoring means for monitoring the fluctuation of the power supplied from the power supply, adjusting means for adjusting the driving frequency of the MOS-type FET for switching the supply or non-supply of the power to the load means, and based on the monitoring result of the monitoring means. Control means for adjusting the drive frequency of the adjusting means.

[0009] In the load driving device of the present invention, the control means, when adjusting the driving frequency, select the predetermined driving frequency not to lower the performance of the load means.

[0010] In the load driving apparatus, the load means,
Ru can adopt the lighting device for a vehicle.

[0011] In the load driving device, the lighting device,
Ru can adopt the daytime running lights.

[0012] In the load driving apparatus, the load means,
Ru can adopt a fan means for the vehicle.

In the present invention, the power supplied from the power supply is switched to supply or not supply to the load means by the MOS FET. The load means is operated by the supplied electric power. The fluctuation of the power supplied from the power supply is monitored by monitoring means. Power fluctuations include voltage fluctuations and current fluctuations. The control means adjusts the driving frequency of the adjusting means for adjusting the driving frequency of the MOS FET based on the monitoring result of the monitoring means. For example, when the fluctuation in power due to the monitoring result exceeds a predetermined value at which a temperature rise of the MOS FET is expected, the drive frequency is changed. In the case of voltage fluctuation of the power supply, when the voltage rises, the drive frequency is lowered. That is, an increase in voltage causes an increase in the temperature of the MOS FET, and a load can be driven without inducing heating by lowering the drive frequency.

When the load means is driven by a drive frequency, a frequency range for obtaining proper performance is generally determined by the drive frequency. There <br/>, as in the present invention, if pre-SL control means adjusts the selected driving frequency driving frequency is predetermined, without degrading the performance of the load means, it is possible to load drive .

[0015] The load means may be applied lighting system of the car dual. As is well known, some lighting devices can be switched to obtain a predetermined brightness with minimum power. Therefore, if the power supplied from the power supply is switched by the MOS FET using the lighting device for the vehicle as the load means, the MOS FE
A predetermined brightness can be obtained with minimum power without inducing heating of T. The lighting device can be used daytime running light to maintain the constant lighting state at a constant brightness during the day.

Further, the load means may be applied fan means car dual. That is, the load means is M
It is sufficient that the power supplied from the power supply is switched and driven by the OS type FET, and the fan means can also be switched to obtain a predetermined wind power with the minimum power. By switching the power supplied from the power supply,
A predetermined wind power can be obtained with minimum power without inducing heating of the MOS FET.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In the present embodiment, the present invention is applied to a lamp driving device for a vehicle.

As shown in FIG. 1, the lamp driving apparatus according to the present embodiment includes a lamp 14, one end of which is connected to a battery power supply 12 mounted on a vehicle.
The other end of the lamp 14 is connected to the drain of the power MOSFET 16. First of power MOS type FET16
The gate is connected to the microcomputer 20 via the driver 22. The second gate and source of the power MOS FET 16 are grounded.

The microcomputer 20 has a function of driving the lamp without inducing heating of the power MOS type FET, and is constituted by a microcomputer including a CPU 28, a RAM 30, a ROM 32, and an input / output port (I / O) 24. Are connected by a bus 26 so that commands and data can be exchanged. The microcomputer 20 includes a waveform generator 34 for generating a driving waveform based on a frequency for driving the lamp 14, and is connected to the input / output port 24. This waveform generator 34
The first of the power MOS type FET 16 via the driver 22
Connected to the gate. The driver 22 converts a signal output from the waveform generator 34 into a drive signal for the first gate of the power MOS FET 16. In addition,
The ROM 32 stores a later-described processing routine executed by the microcomputer 20.

The input / output port 24 is connected between the battery power supply 12 and the lamp 14 via the A / D converter 18. The A / D converter 18 converts the power supply voltage of the battery power supply 12 into a digital signal and outputs the digital signal to the microcomputer 20.

With the above configuration, the power MOS FET 16 is switched via the driver 22 with the driving waveform at a predetermined frequency generated by the microcomputer 20, and the lamp 14 is turned on / off by frequency driving, that is, P
WM control is performed. Thus, the lamp 14 is turned on at a predetermined frequency. The predetermined frequency generated by the microcomputer 20, that is, the default frequency Fo is the lamp 1
4 is predetermined in accordance with the initial value of the power supply voltage of the battery power supply 12 and stored in the ROM 32 so as not to lower the lighting performance (brightness and degree of flickering).

Here, the cause of the temperature rise of the power MOS type FET 16 will be described with respect to the power MO during the PWM control.
This will be described together with the characteristics of the S-type FET 16.

First, the temperature of the power MOSFET 16 is determined by the degree of loss in the power MOSFET 16. That is, the temperature of the power MOS type FET 16 (hereinafter referred to as FET temperature) and the power MOS type FE
There is a proportional relationship with the loss of T16 (hereinafter referred to as FET loss), and the FET loss can be expressed by the following equation (1).

FET temperature∝FET loss = (ON loss) + (switching loss) = R _DS (ON) · _ID ² +1/6 _ID · V _DS (ton + toff) · f − (1) where R _DS (ON): ON resistance between drain and source of FET 16 _ID : Drain current of FET 16 V _DS : Drain-source voltage of FET 16 ton: Turn-on time toff: Turn-off time f: PWM frequency (drive frequency)

[0025] As will be appreciated from the above (1), when the power supply voltage rises, the drain current I _D and the drain of the power MOS type FET 16 - for numeric source voltage V _DS increases, FET losses increase Thus, the FET temperature rises. Further, as the PWM frequency f increases, the switching loss increases, and the FET temperature rises (see FIG. 3).

The above-mentioned switching loss represents the power consumed in the switching process of one cycle, and the switching loss _{PSW (ON)} at the time of turn-on can be obtained by the following equation (2). That is, the switching loss _{PSW (ON)} at the time of turn-on can be obtained by integrating the instantaneous values of the current waveform and the voltage waveform at the time of turn-on with the repetition time (cycle) as T. In the present embodiment, as shown in FIG. 2, the current waveform at the time of turn-on has a characteristic of constantly increasing from 0 to the current Ion during the turn-on time ton, and the voltage waveform is the voltage V _DS during the turn-on time ton. It is assumed that the switching loss _{PSW (ON)} at the time of turn-on is obtained on the assumption that the waveform has a characteristic that decreases constantly from 0 to 0.

[0027]

(Equation 1)

Here, v = (− V _DS / ton) · t + V _DS ｝ i = (Ion / ton) · t

The switching loss P at the time of turn-off
_{SW (OFF)} can be obtained by reversing the voltage and current in equation (2).

[0030] Therefore, the switching loss P _SW is by turn-on and turn-off, expressed in the following equation (3).

[0031] _{P SW = P SW (ON)} + P SW (OFF) = 1/6 · Ion · V DS · (ton + toff) · f ··· (3)

Next, the operation of the present embodiment will be described. First, in the microcomputer 20, when the power is turned on, the flowchart of FIG. 4 is executed. The battery power supply 12
Of the power MOS type F
A drive frequency fo is set in advance so that the temperature of the ET 16 does not increase and the performance of the lamp 14 does not decrease.
6 is switched and the lamp 14 is under PWM control.

In step 102, the power supply voltage V of the battery power supply 12 is read. That is, the battery power supply 12
The analog value of the power supply voltage V is converted into a digital value by the A / D converter 18 and input to the microcomputer 20. In the next step 104, it is determined whether or not the power supply voltage V matches the reference power supply voltage Vo.
It is determined whether or not the power supply voltage has changed. It should be noted that the reference power supply voltage Vo has a predetermined voltage δ, σ
(Δ ≠ σ) may be set and the range may be used for the determination.
That is, the power supply voltage range (the range from Vo to Vo + δ, the range from Vo−σ, or the range of Vo ± δ) may be replaced with the reference power supply voltage Vo.

When the input power supply voltage V of the battery power supply 12 matches the reference power supply voltage Vo or is within the power supply voltage range, it is predicted that the temperature of the power MOS FET 16 will not rise. There is no need to adjust the drive frequency. Therefore, step 1
When the determination is negative in 04, the process proceeds to step 108, where the power MOS type FET 16 is driven at a preset drive frequency fo. That is, in the microcomputer 20, the driving frequency f
The digital value of o is output to the waveform generator 34. The waveform generator 34 generates the driving frequency fo of the input digital value as an analog waveform, and outputs the analog driving waveform to the power MOS FET 16 via the driver 22. Thus, the power MOS FET 16 is turned on and off at the drive frequency fo, and the lamp 14 is turned on by PWM control.

On the other hand, when the power supply voltage V of the battery power supply 12 fluctuates, as described above, the power MOS
Since the temperature of the type FET 16 may increase, the power M
It is necessary to adjust the drive frequency of the OS type FET 16.
Therefore, an affirmative determination is made in step 104 and step 1
Proceeding to step 06, the drive frequency is adjusted to perform thermal protection.

For example, the power supply voltage V of the battery power supply 12
Is increased from the reference power supply voltage Vo (Vu <Vo <
Vu), if the drive frequency is constant, the FET loss increases, as described using (2) above,
The FET temperature rises. Therefore, in this case, step 10
6, fu (fo>) in which the driving frequency is reduced from fo
fu). This is because, as shown in the above equation (1) and FIG. 3, the FET temperature rises due to the increase in the drive frequency f.
This is because a rise in temperature can be suppressed.

The present inventor experimented on the relationship among the driving frequency, the power supply voltage, and the temperature, and obtained the following results. Power supply voltage of battery power supply 12 is 12V and 100W PW
If the power supply voltage rises by 0.1 V during the M control, the temperature rise can be suppressed by reducing it by 1 Hz.
In the case of a power supply voltage of 16 V and 100 Hz, the frequency may be set to 60 Hz.

As described above, in the present embodiment, the power M
Since the OS type FET 16 is predicted to increase in temperature due to the increase in the power supply voltage of the battery power supply 12, the power supply voltage of the battery power supply 12 is constantly monitored. When the power supply voltage of the battery power supply 12 increases, the temperature of the power MOS FET 16 does not increase. The driving frequency is reduced as described above. As described above, the number of times the power MOS type FET 16 is switched on and off is reduced, so that the power MOS type FET 16
Reduces the temperature, and enables continuous driving without heating.

In the above embodiment, the power MOS type FE
Power MOS type FET so as not to cause temperature rise of T16
Since the PWM control using 16 is facilitated, the device can be easily configured with the value at the time of the initial design before the PWM control is performed without increasing the size of the cooling fins (radiator plates). For this reason, it is possible to reduce the size of the PWM control device, which has conventionally required a heat generation countermeasure and a need to enlarge the cooling fins in order to perform the PWM control.

In the present embodiment, the fluctuation of the battery power supply voltage can be monitored to prevent the temperature of the power MOS FET 16 from rising, so that direct temperature detection becomes unnecessary, and an expensive temperature sensor and temperature detection circuit are newly provided. There is no need to add, and it is a low cost and simple configuration.
The continuous driving can be stably performed without heating the S-type FET 16.

Further, in this embodiment, since the fluctuation of the battery power supply voltage can be monitored so that the temperature of the power MOS FET 16 does not rise, the operation shifts to the heating protection measures after the temperature of the power MOS FET actually rises. There is no time lag caused by this. That is, the power MO
Since the heating protection can be performed before exceeding the allowable heating point of the S-type FET, the durability of the power MOS-type FET can be improved and the performance can be maximized.

The lamp driving device for a vehicle according to the present embodiment is provided with a day time running light (Day Time Run Light).
ng Light). A daytime running light is a lighting device that maintains a constant lighting state at a constant brightness during the day.To reduce battery power consumption,
Lighting is performed at a brightness lower than the brightness at night. According to the present embodiment, even when the lamp is turned on by the PWM control, the fluctuation of the battery power supply voltage can be monitored and the temperature of the power MOS FET 16 can be prevented from rising. Without reducing the power consumption of the battery,
The lighting of the daytime running light can be controlled.

In this embodiment, the PWM of the lamp is
Although the case where the present invention is applied to control has been described, the present invention
It is not limited to the driving of the lamp, but the MOS type FE
The present invention can be applied to a device driven by PWM control of T, for example, a fan device. Also, from normal drive to MOS type FET
A further effect can be expected in a device that performs the PWM control described above and shifts to energy-saving driving.

[0044]

As described above, according to the present invention, the fluctuation of the electric power supplied from the power supply is monitored by the monitoring means.
The control means is based on the monitoring result of the monitoring means and the MOS type FE
Since the drive frequency of T is adjusted, there is an effect that the load can be driven without inducing the temperature rise of the MOS FET.

According to the present invention, the control means selects a predetermined drive frequency and adjusts the drive frequency.
There is an effect that the load can be driven without deteriorating the performance of the load means.

In the load driving device of the present invention, when a lighting device for a vehicle is used as the load means, the power supplied from the power supply is switched by the MOS-type FET. can be improved, it is possible to obtain a predetermined brightness by suppressing the power consumption of a vehicle, there is a further effect that.

Daytime running as the lighting device
When the light is used , the daytime running light is driven by switching the power supplied from the power supply by the MOS-type FET. Therefore, even if the lighting is always maintained, the power consumption for the vehicle is suppressed and the predetermined brightness is obtained. Has the further effect of being able to obtain

In the load driving device according to the present invention,
When the vehicle fan means is used, the power supplied from the power supply can be switched by the MOS FET, so that a predetermined wind power can be obtained with the minimum power without inducing the heating of the MOS FET. There is a further effect that it can be done.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a vehicle lamp driving device according to an embodiment.

FIG. 2 is a diagram showing a current waveform and a voltage waveform at the time of turn-on for explaining switching loss of a power MOS type FET.

FIG. 3 is a diagram showing a relationship between a driving frequency of a power MOS type FET and a temperature.

FIG. 4 is a flowchart illustrating a flow of a power supply voltage monitoring process executed by the vehicle lamp driving device according to the present embodiment.

[Explanation of symbols]

 12 Battery Power 14 Lamp 16 Power MOS FET 18 A / D Converter 20 Microcomputer 34 Waveform Generator

Claims (4)

(57) [Claims] A MOS type FE for switching power supplied from a power supply to a load means or not to supply the load means.
T; monitoring means for monitoring a change in power supplied from the power supply; adjusting means for adjusting a drive frequency of the MOS-type FET for switching between supply and non-supply of power to the load means; and the monitoring means. based on the monitoring result, when adjusting the driving frequency of the adjusting means decreases the performance of the load means
And a control means for selecting a predetermined driving frequency . 2. The lighting device according to claim 1, wherein said load means is a lighting device for a vehicle.
The load drive device according to claim 1, wherein: 3. The lighting device according to claim 1, wherein the lighting device is a daytime running device.
The load drive according to claim 2, wherein the load drive is a light.
Motion device. 4. The load means is a fan means for a vehicle.
The load driving device according to claim 1, wherein: