JPH0477233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a cooling fan control device that saves power.

[Conventional technology]

BACKGROUND ART In control devices that house electronic components, etc., cooling fans are generally used because if the internal temperature reaches high temperatures, the electronic components may malfunction and reduce reliability. FIG. 2 is a circuit diagram showing a conventional cooling fan control device of this type, which includes a position detection circuit 1 for detecting the rotational position of the fan motor, and an overcurrent detection circuit 2 for detecting overcurrent and a driver circuit 3. Then, from the input terminals 4a and 4b, a DC (direct current) power source, for example
When DC12V is supplied, the above circuit operates, current flows through the coil 5 of the fan motor which is the load, and the cooling fan rotates. At that time, position detection circuit 1
The overcurrent detection circuit 2 detects the rotational position of the fan motor and switches the direction of the current flowing through the coil 5, and the overcurrent detection circuit 2 detects when an overcurrent flows when the fan motor is started or when the fan motor is mechanically locked. When this occurs, the fan motor is stopped to protect the circuit components. Further, the driver circuit 3 performs an operation of causing current to flow through the coil 5 as described above based on a signal from the position detection circuit 1.

Next, the operation of each circuit described above will be explained in detail. First, the position detection circuit 1 is equipped with an integrated circuit (hereinafter referred to as Hall IC) 6 that uses a Hall element, and when the fan motor rotates, a permanent magnet (not shown) provided in the rotating part of the fan motor is activated by the Hall IC.
Approach IC6. This permanent magnet is configured with N poles and S poles alternately, so the N poles and S poles approach the Hall IC 6 alternately, and the Hall IC 6 outputs a digital signal (logical signal) "1" or "0". ” is output. When the output of Hall IC6 is “1”, inverter transistor TR ₁ turns on and becomes “0”
It turns OFF when . And transistor TR ₁
As the transistors turn on and off, the switching transistors TR ₂ and TR ₃ also turn on alternately. In addition, R ₁ to R ₄
is a current limiting resistor.

When the switching transistors TR ₂ and TR ₃ of the position detection circuit 1 are alternately turned ON and OFF, the driver circuit 3 receives the ON and OFF signals and causes a current to flow through the coil 5. That is, transistor TR ₃ is ON
Then, the base current flows through the resistor _R5 to the transistor _TR4 , and at the same time, the base current of the transistor _TR5 flows, turning on the transistors _TR4 and _TR5.The base current also flows through the resistor _R6 to the transistor _TR6 , turning it on. Become. As a result, transistor TR ₆ - coil 5 is connected to coil 5 of the fan motor.
- Current flows in the direction of arrow A through the path of transistor _TR5 , and the rotor of the fan motor rotates. Due to this rotation, the polarity approaching the Hall IC 6 is reversed,
Transistor TR ₃ turns off and transistor TR ₂
turns on. And transistor TR ₂ is ON
Then, through the resistor _R7 , the transistor _TR7 ,
The base current flows through TR ₈ , and these TR ₇ and TR ₈
It becomes ON. At the same time, transistor TR ₉ also resistor R ₈
Base current flows through it, turning it ON. As a result, coil 5 has transistor TR ₉ - coil 5
- Current flows in the direction of arrow B through the path of transistor _TR8 , and the rotor of the fan motor rotates further. Thereafter, the polarity approaching the Hall IC 6 is switched in the same manner, and currents in the A direction and B direction alternately flow through the coil 5, and the fan motor continues to rotate. In addition,
T ₁₀ , TR ₁₁ are protection transistors to be described later, R ₉ ,
_R10 is the current limiting resistor.

The overcurrent detection circuit 2 also serves as a comparator 7, which compares the detected value of the current flowing through the coil 5 with a reference value to detect an overcurrent. A voltage obtained by dividing the input power supply voltage by resistors _R11 and _R12 is applied to the inverting input terminal (-) of comparator 7 as a reference voltage, and a voltage drop due to resistor _R13 is applied to the non-inverting input terminal (+). voltage is applied as the detection voltage. Then, the comparator 7 compares the reference voltage value with the detected voltage value, and outputs a signal to stop the energization of the coil 5 when the detected voltage value exceeds the reference voltage value. During normal fan motor rotation, the voltage drop across resistor _R15 is small, so comparator 7
The output of the comparator 7 is "0", but when an overcurrent condition occurs and the voltage across the resistor R ₁₃ becomes higher than the reference voltage, the output of the comparator 7 becomes "1", and the protection transistors TR ₁₀ and TR ₁₁ described above is operated to stop energizing the coil 5. That is, when the output of the comparator 7 becomes "1", the transistor
Both TR ₁₀ and TR ₁₁ are turned ON, and the output stage transistors TR ₅ and TR ₆ are both turned OFF because their base voltages are suppressed by the collector voltages of transistors TR ₁₀ and TR ₁₁ , respectively (generally, the collector saturation voltage of a transistor is , lower than the base current drive voltage). Therefore, no current flows through the coil 5, and circuit components and the like are protected.

[Problem that the invention seeks to solve]

The conventional fan motor control device is configured as described above, and detects overcurrent by comparing the detected value of the current flowing through the coil 5 of the fan motor with a predetermined reference value. When used in a cold place, unnecessary cooling may be performed when the temperature is low, resulting in a problem of high power consumption.

The present invention has been made in view of these problems, and an object of the present invention is to provide a cooling fan control device that drives a fan motor in response to temperature changes and saves power.

[Means for solving problems]

A cooling fan is provided with an overcurrent detection circuit that compares a detected value of the current flowing through the fan motor with a reference value, and limits the drive of the fan motor when the detected value exceeds the reference value and an overcurrent is detected. The control device is provided with reference value changing means that substantially lowers the reference value to lower the overcurrent detection level when the temperature decreases.

[Effect]

The overcurrent detection circuit compares the detected value of the current flowing through the fan motor with a reference value to detect an overcurrent, and limits the drive of the fan motor. At this time, cooling is not required at low temperatures, but at this time, the reference value changing means substantially lowers the reference value as the temperature decreases, thereby lowering the overcurrent detection level. Therefore, when the temperature is low, it is determined that there is an overcurrent state, and the drive of the fan motor is restricted.

〔Example〕

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

FIG. 1 is a circuit diagram of a cooling fan control device according to the present invention, in which 1 is a fan motor position detection circuit, 2 is an overcurrent detection circuit, and 3 is a driver circuit for the coil 5. has the same circuit configuration as the conventional one shown in FIG. Thermistor 8 is connected in series to resistor _R12 of overcurrent detection circuit 2.
is connected, and this thermistor 8 and resistor R ₁₂
The voltage value divided by is inputted to one side (- side) of the comparator 7 as a reference voltage value. This thermistor 8 is provided as a reference value changing means for lowering the reference voltage value to lower the overcurrent detection level when the temperature decreases.

In the cooling fan control device configured in this manner, as the temperature rises, the reference voltage value input to the comparator 7 increases, and the overcurrent detection level increases. Therefore, the fan motor rotates normally and the rated rotation is maintained. Next, as the temperature decreases, the resistance value of the thermistor 8 increases, so the reference voltage value decreases, and the overcurrent detection level decreases. Therefore, when a small amount of current begins to flow through the coil 5 at low temperatures, it is determined that an overcurrent has occurred, and the output of the comparator 7 becomes 1, and no current flows through the coil 5 as described above. Therefore, unnecessary cooling at low temperatures is prevented. It is possible to save power, and if the fan motor is stopped when the temperature is low, there is no wind noise, so it is quiet. Furthermore, when used as a ventilation fan, the fan can be automated in a normal room or greenhouse, which is beneficial.

In addition, in the above embodiment, the overcurrent detection level changes depending on the resistance value of the thermistor 8,
Although the rotation of the fan motor can be controlled from high speed rotation to low speed rotation, this thermistor may be used in place of the resistor _R13 . Even with such a configuration, the reference voltage value can be substantially lowered at low temperatures to lower the overcurrent detection level, and the same effect can be achieved.

Moreover, the reference value changing means may be replaced with a thermistor and may be a resistor whose resistance value increases as the temperature rises. That is, even if a POSISTOR is connected in place of the resistor _R12 , the reference voltage value can be lowered at low temperatures. Furthermore, a variable resistor may be used in place of the resistor _R12 , and in this case, the temperature detection level can be set to any level, making it possible to freely set the fan rotation speed in response to temperature changes. Become.

〔Effect of the invention〕

As explained above, according to the present invention, the reference value for comparison with the detected value of the current flowing through the fan motor is substantially lowered at low temperatures, and the overcurrent detection level at low temperatures is lowered. Necessary cooling can be prevented, resulting in the effects of power saving and noise suppression.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional control device. 1...Position detection circuit, 2...Overcurrent detection circuit,
3... Driver circuit, 5... Coil of fan motor, 7... Comparator, 8... Thermistor (reference value changing means).

Claims (1)

[Claims] 1. An overcurrent detection circuit that compares the detected value of the current flowing through the fan motor with a reference value, and limits the drive of the fan motor when the detected value exceeds the reference value and an overcurrent is detected. A cooling fan control device comprising: a reference value changing means for substantially lowering the reference value to lower an overcurrent detection level when the temperature drops. Device. 2. The cooling fan control device according to claim 1, wherein the overcurrent detection circuit stops driving the fan motor when the detected current value exceeds a reference value. 3. The cooling fan control device according to claim 1 or 2, wherein the reference value changing means is a thermistor.