JPH05227783A - Power supply circuit for brushless motor - Google Patents

Abstract

PURPOSE:To protect a driving circuit when breakdown even when a motor is locked without requiring any additional member such as a temperature fuse or an overcurrent protective resistor. CONSTITUTION:Hooked characteristics of power supply circuit are set arbitrarily depending on the capacity of driving circuit which corresponds to the capacity of a brushless motor. For example, the power supply circuit has hooked characteristics as shown on the drawing wherein point P represents a stable point under locked state of brushless motor and A1, V1 represent output current and output voltage at the stable point P, respectively. Assuming the winding impedance under locked state of brushless motor is R1, a formula V1=A1XR1 is satisfied. When V1 and A1 are set to satisfy a relationship p1<A1<2>XR2, where P1 is allowable loss of driving circuit and R2 is loss resistance of driving circuit, the driving circuit can be protected against thermal breakdown or overcurrent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power supply circuit for a brushless motor such as a switching regulator.

[0002]

2. Description of the Related Art FIG. 4 shows a motor winding L of a conventional brushless motor and a drive circuit 1 for driving the brushless motor. The drive circuit 1 is an IC, and each motor winding L and each output. The transistors Tr _{1 to} Tr ₆ are connected. The driving circuit 1 by inputting a predetermined pulse signal, the output transistor Tr ₁ to Tr ₆ are turned on and off alternately, so as to rotate control brushless motor excites the motor winding L.

[0003]

By the way, when the brushless motor is restrained or short-circuited, an overcurrent flows through the motor winding L, and the drive circuit 1 is destroyed. Therefore, in order to prevent the destruction of the drive circuit 1, the temperature fuse F and the overcurrent protection resistor R ₀ are externally attached to the drive circuit 1 to protect the drive circuit 1.

However, such a conventional example has a problem that a temperature fuse F and a protection resistor R ₀ are separately required.

The present invention has been made to solve the above-mentioned conventional drawbacks, and an object thereof is to eliminate the need for a separate member such as a temperature fuse or an overcurrent protection resistor, and even when the electric motor is restrained. An object of the present invention is to provide a power supply circuit for a brushless electric motor, which can prevent the drive circuit from being destroyed.

[0006]

Therefore, the power supply circuit of the brushless motor according to the present invention drives and controls the brushless motor and supplies power to the drive circuit 1 composed of semiconductor elements. The point where there is a curve of the suppression characteristic of the output current and the output voltage at the time of overcurrent and the drive circuit 1 even when the brushless motor is restrained
Is characterized by matching with a stable point P that maintains a state in which is not destroyed.

[0007]

According to the power supply circuit of the brushless motor, even if the brushless motor is restricted and the output current becomes an overcurrent, the stable point P when the brushless motor is restricted is the power supply circuit 2.
The output voltage and the output current at the stable point P are suppressed to be low, and the drive circuit 1 can be prevented from being destroyed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the power supply circuit for a brushless motor according to the present invention will be described in detail with reference to the drawings. As the power supply for the drive circuit of the brushless motor,
Generally, a switching regulator is used,
In Table 1, the standard is 1.4A at 30V output.
It shows the output current value with respect to the input voltage at a specific temperature of the switching regulator capable of taking the above current.

[0009]

[Table 1]

That is, as shown in Table 1, the ambient temperature is 2
Input voltage is 100 at 5 ℃, -10 ℃ and 55 ℃
The output currents at V, 85V and 110V are shown. Then, as shown in FIG.
Alternatively, when the output is short-circuited, the power supply circuit has a foldback characteristic that reduces the output current and the output voltage.

Therefore, as shown in FIG. 1, it is possible to arbitrarily set the fold-back characteristic of the power supply circuit according to the capacity of the drive circuit corresponding to the capacity of the brushless motor in this embodiment. It is assumed that the fold-back characteristic of is as shown in FIG. In this case, point P is a stable point when the brushless motor is restrained. The output current at the stable point P is A ₁ ,
The output voltage is V ₁ .

If the winding impedance when the brushless motor is restrained is R ₁ , then V ₁ = A ₁ × R ₁ . When the allowable loss of the drive circuit is P ₁ and the loss resistance of the drive circuit is R ₂ , if V ₁ and A ₁ are set so that P ₁ <A ₁ ² × R ₂ , then the drive circuit is It can protect from thermal breakdown and overcurrent.

Next, a method of setting the fold-back characteristic of the power supply circuit 2 including a switching regulator will be described. FIG. 2 shows Rcc (Ringing Cake C).
The circuit constant that is a typical example of the inverter circuit and determines the fold-back characteristic described above is determined by the capacitor C ₂ , the resistor R ₂ , the diode D ₁ and the volume VR ₁ . The resistor R ₁ is a starting resistor.

First, the circuit operation of FIG. 2 will be briefly described. In this circuit, the ON period of the switching transistor Q ₁ is equal to the magnitude of the base current of the transistor Q ₂ ,
It is suppressed by the charging / discharging time of the capacitor C ₂ .

First, when the power is turned on, the output voltage V ₀
Is close to zero, the phototransistor PT of the photocoupler PC ₁ is off. Therefore capacitor C
₂ is a diode D ₁ , a resistor R ₂ , and a volume VR
It is charged only by the current flowing in ₁ . At this time, the capacitor C ₂ has no electric charge at first and is charged in a short time.
The ON period of the switching transistor Q ₁ can be kept small.

When oscillation in this state continues and the output voltage V ₀ rises, charges are accumulated in the reverse direction in the capacitor C ₂ by the voltage generated in the feedback winding Nc during the off period of the switching transistor Q _2. Requires a longer charging time than when the transistor is empty, and the ON period of the switching transistor Q ₁ becomes longer.

After the output voltage V ₀ rises, the phototransistor PT also changes from the ON state to the active state, and the collector current thereof suppresses the charging time of the capacitor C ₂ , which corresponds to the output voltage V ₀ . The ON period of the switching transistor Q ₁ can be obtained.

Here, when the load becomes large (when restrained), it is necessary to lengthen the ON period of the switching transistor Q _{1 in} order to obtain the energy required for it. However, the ON period of the switching transistor Q ₁ is determined by the time constant of the capacitor C ₂ , the resistor R ₂ , the diode D ₁ , and the equivalent series resistance of the volume VR ₁ , so the ON period cannot be longer than a certain value.

Therefore, when the load exceeds a certain level, the output voltage V ₀ drops. At the same time, the flyback voltage to the feedback winding Nc also drops. Since the discharge time of the capacitor C ₂ , that is, the off period of the switching transistor Q ₁ is determined by the magnitude of the flyback voltage of the feedback winding Nc, the off period of the switching transistor Q ₁ is extended and the off period of the switching transistor Q ₁ is increased. It acts to make it shorter and has a foldback characteristic.

By arbitrarily selecting the resistance value of the volume VR ₁ , the drooping point of the fold-back characteristic of FIG. 1 can be selected and can be matched with the stable point P of the brushless motor during constraint.

[0021]

As described above, according to the present invention, in the power supply circuit of the brushless motor for controlling the drive of the brushless motor and supplying power to the drive circuit composed of the semiconductor element, the output current and the output voltage at the time of overcurrent of the power supply circuit. It is characterized by matching the point where there is a curve of the suppression characteristic with and the stable point that maintains the state that the drive circuit is not destroyed even when the brushless motor is constrained. Even if the output current becomes an overcurrent, the stable point when the brushless motor is restrained matches the curve of the suppression characteristics of the power supply circuit, and the output voltage and output current at that stable point can be suppressed to a low level. The circuit can be prevented from being destroyed, and the effect is that the thermal fuse and the protective resistor which have been used conventionally are unnecessary.

[Brief description of drawings]

FIG. 1 is an operation explanatory diagram of an embodiment of the present invention.

FIG. 2 is a circuit diagram of the above switching regulator.

FIG. 3 is a characteristic diagram showing a relationship between an output current and an output voltage of the above.

FIG. 4 is a circuit diagram of a conventional example.

[Explanation of symbols]

 1 Drive circuit 2 Power supply circuit P Stable point

Claims (1)

[Claims] 1. A power supply circuit of a brushless motor for driving and controlling a brushless motor to supply power to a drive circuit (1) composed of a semiconductor element, wherein an output current and an output voltage at an overcurrent of the power supply circuit (2) A power supply circuit for a brushless motor, characterized in that a point having a curve of a suppression characteristic and a stable point (P) for maintaining a state where the drive circuit (1) is not destroyed even when the brushless motor is restrained are matched.