JP3265637B2 - Fan motor drive control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fan motor drive control circuit for heat dissipation of an audio amplifier.

[0002]

2. Description of the Related Art In an audio amplifier, when a heat-dissipating fan is used to enhance the heat-dissipating effect, there is a problem that noise of a fan motor can be heard. In order to make the noise of the fan motor inconspicuous, a fan motor drive control circuit is used which does not drive the fan when there is no signal and the volume is low and drives the fan only when there is a lot of heat when the volume is high. .

Hereinafter, an example of the above-described conventional fan motor drive control circuit will be described with reference to the drawings. FIG. 2 shows an example of a conventional fan motor drive control circuit. In FIG. 2, reference numerals 1 and 2 denote amplification circuits, 3, 4,
Reference numerals 5 and 6 denote respective resistors constituting a bridge circuit, reference numeral 7 denotes a feedback circuit of the entire amplifier, reference numeral 8 denotes a load of the amplifier circuit, reference numeral 9 denotes a signal level detection circuit, reference numeral 10 denotes a motor drive circuit, reference numeral 11 denotes a fan motor,
12 is a non-inverting input terminal of the amplifier circuit 1, and 13 is an amplifier circuit 1
14 is a non-inverting input terminal of the amplifier circuit 2,
Reference numeral 15 denotes an inverting input terminal of the amplifier circuit 2. The resistance values of the resistors 3, 4, 5, and 6 are R3, R4, R5, and R6, and the relationship among them is R3: R5 = R4: R6.

First, an amplifier circuit 1, an amplifier circuit 2, a resistor 3,
The operation of the portion constituted by the resistor 4, the resistor 5, the resistor 6, the feedback circuit 7, and the load 8 will be described. It is assumed that a signal is applied to the input terminal of the amplifier circuit 1 and some current flows through the load 8. At this time, the currents flowing through the resistors 3, 4, 5, and 6 are defined as i3, i4, i5, and i6. When the amplification factor of the amplifier circuit 2 is sufficiently large, the potential of the non-inverting input terminal 14 of the amplifier circuit 2 and the potential of the inverting input terminal 15 are considered to be equal.

[0005]

(Equation 1)

[0006]

[0007]

(Equation 2)

From (Equation 1) and (Equation 2)

[0009]

(Equation 3)

Assuming that no current flows through the inverting input terminal 15,

[0011]

(Equation 4)

Further, as described above, since R3: R5 = R4: R6,

[0013]

(Equation 5)

Substituting (Equation 4) and (Equation 5) into (Equation 3)

[0015]

(Equation 6)

Therefore, from (Equation 1)

[0017]

(Equation 7)

## EQU1 ## From (Equation 4) and (Equation 7), the load 8
It can be understood that all the currents flowing through are supplied from the amplifier circuit 2. As described above, in the amplifier circuit including the amplifier circuit 1, the amplifier circuit 2, the resistor 3, the resistor 4, the resistor 5, the resistor 6, the feedback circuit 7, and the load 8, the non-inverting input terminal 12 of the amplifier circuit 1 An amplification operation is performed on the added input signal, and at this time, it is not necessary to supply a current flowing through the load 8 from the amplification circuit 1, so that the amplification circuit 1 can perform an amplification operation with very little distortion.

A signal level detection circuit 9 is connected to the load 8, and detects a voltage of the load 8 and outputs a motor drive signal when the voltage is equal to or higher than a predetermined voltage.
The motor drive circuit 10 drives the fan motor 11 accordingly. As shown in FIG. 3, this drive circuit drives the fan when the signal exceeds a certain level, drives the fan only when the heat generated in the amplifier circuit is large, and drives the fan when the signal level is low. I try not to.

[0020]

However, since the conventional fan motor drive control circuit as described above detects only the voltage of the output signal irrespective of the impedance of the load 8, the impedance of the load 8 varies. Then, there is a problem that appropriate fan control cannot be performed. For example, if the output signal voltage is the same between when the impedance of the load 8 is 8Ω and when the load 8 is 4Ω,
When the impedance of the load is 4Ω, the load 8
Is twice as large. Since this current is supplied from the amplifier circuit 2, the power consumed by the amplifier circuit 2 is 2 when the load 8 has an impedance of 4Ω compared to when the impedance of the load 8 is 8Ω.
Double. From this fact, it can be said that the lower the impedance of the load 8, the more heat generated by the amplifier circuit 2 increases.
Therefore, it is necessary to drive the fan at a lower output voltage as the impedance of the load 8 is lower.

The present invention has been made in view of the above-mentioned conventional problems, and has as its object to provide a fan drive control circuit that appropriately drives a fan according to heat generated by an amplifier circuit even when a load changes. It is.

[0022]

In order to solve the above problems, a fan drive control circuit according to the present invention comprises two amplifier circuits,
A bridge circuit connected to the outputs of the two amplifier circuits, a signal level detection circuit connected to the bridge circuit, and a fan motor drive circuit connected to the output of the signal level detection circuit. is there.

[0023]

According to the present invention, the above-described configuration detects the voltage generated in the resistor constituting the bridge circuit connected to the output of the amplifier circuit and drives the fan, thereby allowing the amplifier circuit to operate even when the load changes. The fan can be driven appropriately according to the heat generation.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a fan motor drive control circuit according to the present invention will be described below in detail with reference to FIG.

FIG. 1 shows the configuration of a fan motor drive control circuit according to an embodiment of the present invention. In FIG. 1, reference numerals 1 and 2 denote amplification circuits, 3, 4, 5, and 6 denote resistors constituting a bridge circuit, 7 denotes a feedback circuit of the entire amplifier, 8 denotes a load of the amplification circuit, 9 denotes a signal level detection circuit, Is a motor drive circuit, 11 is a fan motor, 12 is a non-inverting input terminal of the amplifier circuit 1, 13 is an inverting input terminal of the amplifier circuit 1, 14
Is a non-inverting input terminal of the amplifier circuit 2, and 15 is an inverting input terminal of the amplifier circuit 2. The resistance values of the resistors 3, 4, 5, and 6 are R3, R4, R5, and R6, and the relationship between them is R3: R5 = R4: R6.
It is.

The operation of the fan motor drive control circuit configured as described above will be described below. First, in the circuit of FIG. 1, when the impedance of the load 8 changes, the current flowing through the load 8 increases as the impedance of the load 8 decreases, even if the level of the output signal is the same. Accordingly, the current supplied by the amplifier circuit 2 increases, and the heat generation also increases. At this time, the current flowing through the load 8 is
From the amplifying circuit 2, each resistor 3, which constitutes a bridge circuit,
It is supplied via 4, 5, and 6. Each resistor has R3 and R4
Alternatively, the current supplied by the amplifier circuit 2 flows at a ratio according to the resistance value of R5 and R6. Therefore, each of the resistors 3, 4, 5, 6
, A voltage proportional to the current supplied by the amplifier circuit 2 is generated. Therefore, if the fan motor drive is controlled by detecting the voltage across either of the resistors 3, 4, 5, or 6, the fan is driven when the output signal level is large, and the output signal level is low. When the resistance of the load 8 is low, the output signal level to start driving the fan is reduced, and when the resistance of the load 8 is high, the output signal level to start driving the fan is increased. Can do things. In the example of FIG. 1, a circuit that performs the above control by detecting the voltage across the resistor 5 which is one of the resistors 3, 4, 5, and 6 by the signal level detection circuit 9 and driving the fan. Has been realized.

As described above, according to the present embodiment, it is possible to easily drive the fan appropriately even if the impedance of the connected load changes without adding a special circuit.

[0028]

As described above, the present invention controls the fan motor by detecting the voltage between both ends of the resistor constituting the bridge circuit connected to the output of the amplifier circuit, thereby reducing the impedance of the connected load. The fan can be driven according to the change, and even if the impedance of the connected load changes, the fan is driven only when the heat generated by the amplifier increases and the heat radiation effect needs to be increased, and the output signal level is reduced. When the noise of the fan motor is conspicuous low, the control of stopping the fan motor can be appropriately performed.

[Brief description of the drawings]

FIG. 1 is a block diagram of a fan motor drive control circuit according to one embodiment of the present invention.

FIG. 2 is a block diagram illustrating an example of a conventional fan motor drive control circuit.

FIG. 3 is a diagram showing a relationship between control of a fan motor and the level of an output signal.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 amplifier circuit 2 amplifier circuit 3 resistor 4 resistor 5 resistor 6 resistor 7 feedback circuit 8 load 9 output signal level detection circuit 10 fan motor drive circuit 11 fan motor 12 non-inverting input terminal of amplifier circuit 13 inverting input terminal of amplifier circuit 1 14 Non-inverting input terminal of amplifier circuit 2 15 Inverting input terminal of amplifier circuit 2

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02P 5/00-5/26 H02P 7/00-7/34 F25D 1/00 H03F 1/00 H03F 1 / 52

Claims (1)

(57) [Claims] 1. A bridge circuit comprising a first amplifier circuit, a second amplifier circuit, a first resistor, a second resistor, a third resistor, and a fourth resistor, and signal level detection. An output terminal of the first amplifier circuit is connected to a connection point between the first resistor and the third resistor, and an inverting input terminal of the second amplifier circuit. An inverting input of the first amplifier circuit is connected to a connection point between the third resistor and the fourth resistor and a load through a feedback circuit, and an output terminal of the second amplifier circuit is connected to the first resistor. A non-inverting input of the second amplifier circuit is connected to a connection point of the second resistance and the fourth resistance, and the first amplifier or the first resistance is connected to a connection point of the second amplification circuit; 2
The input terminal of the signal level detection circuit is connected to both ends of the third resistor or the third resistor or the fourth resistor, and the output terminal of the signal level detection circuit is connected to the input terminal of the fan motor drive circuit. Motor drive control circuit having the above configuration.