JP2001339984A - Starting method for dc brushless motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent increase in cost and eliminate unnecessary power consumption by having to select a semiconductor having a large permissible loss to cope with inrush current of a DC brushless motor for a fan used in a refrigerator. SOLUTION: The time to start up a power source circuit A is made more than three times the time constant of a DC brushless motor circuit by having a time constant circuit which consists of a capacitor Cd and a resistor Rd in the dead time control input DT of the power source IC1 of the power source circuit A which is connected to the DC brushless motor M. The increase in cost is prevented by regulating inrush current when the DC brushless motor is started, and unnecessary power consumption is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for starting a DC brushless motor used for a fan in a refrigerator or a freezer, for example.

[0002]

2. Description of the Related Art A DC brushless motor has high reliability because it has no mechanical contact with a brush and is simple in structure. Further, since the motor efficiency is high and the power consumption is small and the heat generation is small, it is used, for example, as a fan motor for cooling the inside of a refrigerator such as a refrigerator.

[0003] By the way, such a DC for the fan in the refrigerator is used.
In the brushless motor, in order to take advantage of the features of the brushless motor, as shown in FIG. 7, an A using a power supply IC1 that can convert AC to DC with high efficiency (can reduce heat generation) is used.
A voltage is directly applied to the DC brushless motor M by the C-DC power supply circuit.

[0004] However, the coil resistance of the DC brushless motor M is usually 20 m in order to reduce loss during rotation.
Ω to about 50 mΩ, and the current i is as shown in FIG.
As shown in the following, i = E / Re- ^{R / Lt,} where E: power supply voltage R: coil resistance L: coil inductance, and a startup current 5 to 6 times the steady state current flows at startup. I have.

Therefore, it is necessary to select an output element of the power supply circuit having a large allowable loss in consideration of the peak current value.

[0006]

However, selecting a semiconductor having a large allowable loss according to the peak current as described above increases the cost.

[0007] Further, the flow of a large current means that unnecessary power consumption is generated, which is a major problem that must be solved also from the aspect of heat generation (increase in the temperature of the refrigerator) of the DC brushless motor. .

It is an object of the present invention to prevent an increase in cost and to prevent unnecessary power consumption.

[0009]

In order to solve the above-mentioned problems, according to the present invention, a DC power supply circuit connected to a DC brushless motor for an in-compartment fan of a refrigerator has a rise in output voltage when the power supply circuit is started. A regulating means for setting the time is provided, and the rise time of the output voltage by the regulating means is set to be three times or more of the time constant of the motor circuit, and the method of starting the DC brushless motor is adopted.

By employing such a method, the rise time of the DC power supply circuit (the time required for 10% to 90% of the final voltage value in the step response) can be made three times or more the time constant of the motor circuit. By setting, the rise of the applied voltage is suppressed.

By doing so, the applied voltage applied to the stopped motor at the time of power-on can be set low.
The current flowing at startup can be reduced.

Further, when the applied voltage gradually increases and the motor starts rotating with the increase, the impedance of the motor circuit also increases with the rotation of the motor, so that a large current does not flow through the motor.

At this time, if the rise time of the output voltage of the DC power supply circuit is set to be three times or less the time constant of the motor circuit,
Since the rate of rise of the voltage is higher than the rise of the coil impedance of the motor, a large amount of current flows.

[0014]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows a power supply circuit A for an in-compartment fan for a refrigerator (freezing) using a DC brushless motor M according to the present invention.

As shown in FIG. 1, the power supply circuit A includes a power supply IC 1, a rectifier circuit 2, a switching transistor 3, a flywheel diode 4, an inductance L, a capacitor C and a power supply IC 1 having an output voltage regulating means H at the time of startup. The input voltage is supplied to the motor M via the LC circuit during the conduction period of the switching transistor 3, and when the switching transistor 3 enters the non-conduction period, the energy stored in L is supplied to the diode 4. Through the motor M.

The power supply IC 1 is a switching regulator IC for PWM. As shown in FIG. 2, the power supply IC 1 includes a comparator 10, a reference voltage 11, an oscillation circuit 12, a flip-flop 13, and output transistors Q1 and Q2. As shown in FIG. 3, the "sawtooth wave" output of the circuit 12 is compared with a detection voltage by the comparator 10 to change the duty ratio of the output pulse.

Further, the power supply IC is provided with a dead time comparator 14, which compares the oscillation output with the input from the dead time control input DT as shown in FIG. By regulating the outputs of the transistors Q1 and Q2 in the subsequent stage, the dead time (invalid time) of the output can be increased or decreased.

The dead time control input DT is provided with the restricting means H shown in FIG. As shown in FIG. 4, the regulating means H is a time constant circuit in which one end of a capacitor Cd and one end of a resistor Rd are connected in series, and a connection point between the capacitor Cd and the resistor Rd of the time constant circuit is controlled by the dead time control. While being connected to the input DT, the other end of the capacitor Cd is connected to the reference voltage output of the power supply IC1, and the other end of the resistor Rd is grounded.

As a result, when the voltage at the connection point between the capacitor Cd and the resistor Rd of the time constant circuit is higher than the "sawtooth wave" output of the oscillation circuit 12, as shown in FIG. Q1 and Q2 are regulated and turned off. Conversely, the capacitor Cd and the resistor Rd
When the voltage at the point of connection with the circuit becomes lower than the "sawtooth" output of the oscillation circuit 12, the gate of the NOR circuit releases the regulation of the output transistors Q1 and Q2. Therefore, the output transistors Q1 and Q2 output an oscillation output.

At this time, the capacitor Cd and the resistor R
The time constant of d is set to be three times or more the time constant of the motor M circuit.

This embodiment is configured as described above, and its operation will be described below.

That is, in the power supply IC1, the capacitor Cd is not charged when the power is turned on.
The capacitor Cd is pulled to the reference voltage Vref, and the dead time control input DT receives the reference voltage Vref.

At this time, the oscillation circuit 12 has started oscillating, and the dead time comparator 14 detects the voltage Vr
ef and the output of the oscillation circuit 12 are compared,
The output transistors Q1 and Q2 are regulated and turned off. Therefore, no voltage is applied to the motor M.

Thereafter, when charging of the capacitor Cd is started, the voltage at the connection point with the resistor Rd decreases, and when the decreased voltage falls below the "sawtooth wave" output of the oscillation circuit 12, the dead time increases. The regulation by the comparator 14 is released, and the output transistors Q1 and Q2 output the oscillation circuit 12 output.

Therefore, as shown in FIG. 5, since the applied voltage gradually increases, a large current does not flow even if the impedance of the motor M during stop is low. Also,
When the current increases with an increase in the applied voltage, the motor M starts to rotate accordingly, so that the impedance of the motor M increases and no overcurrent flows.

As described above, the rise of the applied voltage is regulated by the time constant of the capacitor Cd and the resistor Rd of the regulating means H. As shown in FIG. 5, the applied voltage to the stopped motor M when the power is turned on can be reduced. Inrush current at startup can be reduced.

At this time, by setting the rise time of the applied voltage to be three times or more the time constant of the motor circuit, a large current does not flow before the brushless motor M starts rotating.

Next, in order to confirm the effectiveness of the present invention,
Start-up when the rise time of the AC-DC power supply of the present application is set to three times the motor time constant and when the voltage of the AC-DC power supply is applied without regulation to an actual DC brushless motor (12V specification). Took properties.

The results are shown in FIGS. 6 (a) and 6 (b).

FIG. 6A shows a case where the rise time of the applied voltage is set to be three times or more the time constant of the motor circuit.
FIG. 6B shows a conventional case in which the rise time is not regulated.

As is clear from the characteristics, the rise time of the applied voltage is set to be at least three times the time constant of the motor circuit.
In the case of (a), it takes about 3 seconds to reach the steady voltage, and it can be seen that a high voltage is not applied until the brushless motor M rotates to increase the impedance.

On the other hand, in FIG. 6B, it can be seen that a very large inrush current flows as soon as the voltage is applied.

From these facts, according to the present invention, the motor can start rotating following the rise of the voltage, so that unnecessary heat generation does not occur (the motor cannot follow three times or less).

On the other hand, in the case of FIG. 6B, the inrush current flows at the same time as the start-up, and the steady voltage is reached in about 0.6 seconds. Seems to occur.

As described above, according to the present invention, the inrush current can be suppressed and unnecessary power consumption due to the inrush current can be prevented, so that heat generation at the time of startup can be reduced and safety can be improved. Further, it is not necessary to use a switching transistor having a large allowable loss, and the cost can be reduced.

[0037]

According to the present invention, the power supply circuit and the motor drive circuit can be made safe and inexpensive by having the above configuration.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment.

FIG. 2 is a block diagram of a power supply IC.

FIG. 3 is a diagram illustrating the operation of a power supply IC.

FIG. 4 is a block diagram of a power supply IC.

FIG. 5 is an operation explanatory view of the embodiment.

6A is a diagram showing a starting characteristic of the embodiment, and FIG. 6B is a diagram showing a conventional starting characteristic.

FIG. 7 is a conventional circuit block diagram.

FIG. 8 is a diagram illustrating the operation of a conventional example.

[Explanation of symbols]

 1 power supply IC Cd capacitor Rd resistance H regulating means M DC brushless motor

Claims (1)

[Claims] 1. A DC power supply circuit connected to a DC brushless motor for a fan in a refrigerator of a refrigerator, a regulating means for setting a rise time of an output voltage when the power supply circuit is started,
A method of starting a DC brushless motor, wherein a rise time of an output voltage by the regulating means is set to be three times or more a time constant of the motor circuit, and the DC brushless motor is started.