JPS6031436Y2 - AC motor control circuit - Google Patents

Description

[Detailed description of the invention] This invention relates to a control circuit for an AC motor, in which a feedback circuit using a field effect transistor is connected to a transistor for driving and controlling the motor, thereby increasing the variation range of the circuit gain and ensuring reliable control. It is an object of the present invention to provide a control circuit that is capable of stably controlling power supply voltage fluctuations and the like.

FIG. 1 shows a circuit diagram of an example of a conventional AC motor control circuit.

In the figure, the current from the AC power supply 1 is applied to the controlled motor 2.
The current flows through the windings 2a and 2b, the guiode bridge rectifier circuit 3, the control and driving transistor Tr1, and the resistor R.

At this time, the alternating current flows as indicated by the arrows ■ and @, and the amount of current is controlled by the transistor Tr1 whose conduction state is controlled by the control signal for the motor 2 coming from the terminal 4, thereby controlling the motor 2. be done.

Here, the gain of this circuit is the ladder R and the transistor Tr.
In the above circuit, if the resistance value of resistor R is set to a large value, the power wasted in resistor R when transistor Tr□ becomes fully conductive is determined by the impedance of the circuit connected to the collector of transistor 1. becomes large and motor 2
There is a drawback that a sufficient range of change in the operating current, that is, an operating range corresponding to fluctuations in the current, cannot be achieved.

The present invention eliminates the above-mentioned drawbacks, and each embodiment thereof will be described with reference to FIGS. 2 and 3.

FIG. 2 shows a circuit diagram of a first embodiment of the AC motor control circuit according to the present invention, in which the same components as in FIG. 1 are given the same numbers and symbols.

In the figure, a motor operating current detection resistor R4 and a resistor R3 are connected between the emitter of the transistor Tr1 and the ground.
and a smoothing circuit including a capacitor C are connected in parallel, and the connection point between the resistor R3 and the capacitor C is connected to the gate of a field effect transistor (FET) 5.
The drain of FET5 is connected to the base of transistor Tr1 and resistor R1, and the source thereof is connected to current limiting resistor R2.

In the figure, when the conduction state of the transistor Tr is controlled by the control signal from the terminal 4 to keep the speed of the motor 2 constant, the voltage across the resistor R4 is smoothed by the resistor R3 and the capacitor C. The FET 5 is made conductive (operated) according to its size, and a voltage corresponding to the voltage between the terminals of the resistor R4 is fed back to the base of the transistor Tr1.

Here, when the voltage VrN of the control signal from the terminal 4 is relatively large, the voltage between the terminals of the resistor R1 becomes large, and thereby the gate voltage of the FET 5 becomes large and the FET 5 becomes completely conductive.

At this time, the base of the transistor Tr has a voltage of 2 - V
When a voltage R1+R2 of IN is applied and the impedance of the circuit connected to the collector of the transistor Tr is Z, the gain of the circuit is R2 R1R1+R2.

On the other hand, when the voltage VIN is relatively small, the voltage between the terminals of the resistor R1 becomes small, and as a result, the gate voltage of the FET 5 becomes small and the FET 5 becomes non-conductive.

At this time, a voltage VIN is applied to the base of the transistor Tr□, and the gain of the circuit becomes
It can range from +R2 to ash, and has a sufficient operating range compared to conventional ones.

Note that if the series impedance between the impedance of FET5 and the resistance value of resistor R2 is X, the gain seen from the input side will be an order of magnitude, and the overall gain will be X gray x orders of magnitude.

On the other hand, since the emitter potential of the transistor Tr□ is detected by the resistor R4 and fed back to its base, when the control voltage VIN is constant, for example, the base potential of the transistor Tr1 is kept constant due to fluctuations in the AC power supply 1. and can be controlled more stably than conventional methods.

By using FET 5 in the feedback circuit section, this circuit operates stably even if the voltage generated across resistor B is small.
The control range is wide and the loss of the AC power source is small.

FIG. 3 shows a circuit diagram of a second embodiment of the circuit of the present invention, in which the same components as in FIG. 2 are given the same numbers and symbols.

This device uses transistors Tr and Tr2 as control and drive transistors, and FET5
Adjust the source potential of 1os with variable resistor VR as appropriate.
It can be adjusted to eliminate variations in s (saturated drain current when the gate-source voltage is zero).

The other configurations and effects are the same as those of the first embodiment shown in FIG. 2, so their explanation will be omitted.

As described above, the AC motor control circuit according to the present invention connects a current detection resistor between the emitter and ground of a transistor for driving and controlling the motor, and smoothes the voltage of the resistor to the base and emitter of the transistor. A feedback circuit was constructed by connecting the drain and gate of the FET via a resistor and a capacitor, and a resistor was connected between the drain of the FET and the control signal input terminal and between its source and ground. , the FET can be made conductive (operated) according to the voltage across the current detection resistor, and a voltage corresponding to the voltage across the current detection resistor can be fed back to the transistor, and the circuit gain and FET when the FET is fully conductive are as follows. The range of change in circuit gain when the circuit becomes non-conducting can be made sufficiently larger than in conventional circuits, which were determined only by the emitter resistance of the drive control transistor and the impedance of its collector. The operating range is sufficiently large compared to the conventional one, and since the emitter potential of the drive control transistor is detected by a current detection resistor and fed back to its base, it is not affected by fluctuations in the AC power supply or the temperature of the transistor. Characteristics can be controlled more stably than conventional ones, and FE
By appropriately selecting the resistance values of the resistors connected to the drain and source of T, the operating voltage can be set freely.Furthermore, since FET is used, the voltage generated in the current detection resistor is stable even if it is small. It has features such as low loss due to resistance and wide control range.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of an example of a conventional circuit, and FIGS. 2 and 3 are circuit diagrams of first and second embodiments of the circuit of the present invention, respectively. 1... AC power supply, 2... AC motor,
3...Shiioode bridge rectifier circuit, 4...
...Control signal input terminal, 5...Field effect transistor, Trl, Tr2...Transistor,
RHR29R39R4? Rta* Rtb・・・・・・
・Resistance, C...Capacitor.

Claims (1)

[Scope of utility model registration request] A current full-wave rectified by a bridge rectifier circuit is supplied to the collector, and a control signal for the controlled motor is supplied to the base to control the conduction state of the transistor, which controls the alternating current flowing through the windings of the motor. In an AC motor control circuit, a current detection resistor is connected between the emitter and ground of the above transistor, and the drain and gate of a field effect transistor are connected to its base and emitter via a resistor and a capacitor that smooth the voltage of the resistor. A control circuit for an AC motor, comprising a feedback circuit, and resistors connected between the drain of the field effect transistor and the input terminal of the control signal, and between the source and ground.