JP2000050685A - Speed control circuit of motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a speed control circuit of a motor where change of speed is small, when power source frequency is switched. SOLUTION: The capacitance of a second capacitor C21 and resistance of a second resistor R21 are so reduced that the phase of a voltage VR21 applied to the second resistor R21 leads almost 90 deg. to the phase of a power source. On the basis of a voltage applied to the second resistor R21, a first transistor TR21 makes a first capacitor C22 short-circuit corresponding to 90 deg. of the power source phase and delays application of a power source voltage to the first capacitor C22. Since charging of the first capacitor C22 is started, after the delay of about 90 deg. irrespective of the power source frequency, the time until the voltage of the first capacitor C22 turns on a trigger diode D23 on is not changed greatly by power source frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor speed control circuit, and more particularly to a motor speed control circuit that can be suitably used for controlling the speed of a motor such as a power tool.

[0002]

2. Description of the Related Art An example of a phase control circuit used for controlling the speed of a motor of a power tool will be described with reference to FIG. The trigger circuit consists of a variable resistor R11 and a capacitor C
When the charging voltage of the capacitor C11 reaches a voltage for turning on the trigger diode D11, the triac Q11 turns on and applies a voltage to the motor M. Then, by adjusting the value of the variable resistor R11, the charging time of the capacitor C11 is changed, and the ON time of the triac Q11, that is, the speed of the motor M is adjusted.

[0003]

However, in the trigger circuit described above, when the power supply frequency changes, for example, when the power supply frequency is switched from 50 Hz to 60 Hz, the speed of the motor greatly changes. The reason will be described with reference to FIG. FIG. 8A shows the power supply voltage AC and 60 Hz.
And the charging voltage VC2 of the capacitor C11 at 50 Hz. FIG.
(B) shows the voltage applied to the motor when the frequency is 60 Hz. That is, when the charging voltage VC1 at 60 Hz exceeds the trigger voltage Vg of the trigger diode shown by the one-dot chain line in FIG. 8A (timing t1).
A voltage is applied to the motor as shown by hatching in (B). On the other hand, FIG. 8C shows the voltage applied to the motor when the frequency is 50 Hz. That is, when the charging voltage VC2 at the time of 50 Hz exceeds the trigger voltage Vg of the trigger diode shown by the dotted line in FIG.
In 2), a voltage is applied to the motor as shown by hatching in FIG. R1 when the triac conducts
Since 1 and C11 are short-circuited, no voltage is applied to C11. As can be seen from FIGS. 8B and 8C, the trigger circuit described above has a power supply frequency of 50 Hz to 60 Hz.
When the mode is switched to, the energization time to the motor changes greatly, and the speed of the motor changes greatly.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to provide a speed control circuit for a motor which has a small speed change even when the power supply frequency is switched. is there.

[0005]

According to a first aspect of the present invention, there is provided a trigger diode for connecting a first resistor and a first capacitor in series and providing a triac gate signal therebetween. A motor speed control circuit for connecting the power supply voltage to the first resistor and the first capacitor to apply the charging voltage of the first capacitor to the trigger diode, and controlling the phase of the conduction time of the triac. A short circuit that short-circuits the first capacitor, delays the application of a power supply voltage to the first capacitor, and a second capacitor and a second resistor that are connected in series;
A phase control circuit for applying a voltage applied to a second resistor to the short circuit, and controlling a phase of the short circuit operation of the short circuit, wherein a phase of the voltage applied to the second resistor is a phase of a power supply. And a phase control circuit that reduces the capacitance of the second capacitor and the resistance of the second resistor so as to advance by approximately 90 ° regardless of the power supply frequency.

According to a second aspect of the present invention, in the motor speed control circuit according to the first aspect, the short circuit includes a first diode and a first transistor for short-circuiting the first capacitor in a positive half-wave of the power supply voltage. A circuit in which a second diode and a second transistor are connected in series to short-circuit the first capacitor at a negative half-wave of the power supply voltage, and a voltage of a second resistor of the phase control circuit. Is applied to the bases of the first and second transistors.

According to the first aspect of the present invention, the second phase control circuit includes:
The capacitance of the second capacitor and the resistance of the second resistor are reduced so that the phase of the voltage applied to the resistor advances by approximately 90 ° with respect to the phase of the power supply regardless of the power supply frequency. Based on the voltage applied to the second resistor of the phase control circuit, the short circuit short-circuits the first capacitor by an amount corresponding to the power supply phase of 0 ° to 90 ° and inhibits charging of the first capacitor. For this reason, the charging of the first capacitor is started with a delay of approximately 90 ° irrespective of the power supply frequency, so that the phase at which the trigger diode is turned on by the voltage of the first capacitor does not greatly change with the power supply frequency. That is, even when the power supply frequency is switched, the voltage difference applied to the motor is reduced, and the change in the motor rotation speed is reduced.

According to a second aspect of the present invention, the second phase control circuit
A resistor voltage is applied to the bases of the first and second transistors. Here, when the power supply voltage decreases, the voltage to the second resistor also decreases, the timing for turning off the first and second transistors is accelerated, and the charging of the first capacitor is performed earlier than the 90 ° delay of the power supply phase. Be started. For this reason, the time during which the triac is on becomes longer, so that even if the power supply voltage decreases, the applied voltage to the motor becomes equal and the speed of the motor can be kept constant.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A motor speed control circuit according to one embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 shows a circuit configuration of a motor speed control circuit according to the first embodiment. The speed control circuit 10 includes a trigger circuit 20 and a zero cross detection circuit 30 forming a short circuit.
And a phase control circuit 40.

[0010] The trigger circuit 20 comprises a first resistor R22 and a first capacitor C22 connected in series. A trigger diode D23 is connected between the first resistor R22 and the first capacitor C22. The trigger diode D23
Of the motor armature A and the field winding L1,
It is connected to the gate of a triac Q22 that controls the phase of the current supply to L2. Here, when the power supply voltage is applied to the first resistor R22 and the first capacitor C22, and the charging voltage of the first capacitor C22 reaches a voltage for turning on the trigger diode D23, the triac Q22 turns on and the motor armature A And a voltage is applied to the windings L1 and L2.

The zero-cross detection circuit 30 detects the first capacitor C22 of the trigger circuit 20 at the positive half-wave of the power supply voltage.
Diode D21 and first transistor T for short-circuiting
and a circuit in which a second diode Tr22 and a second transistor Tr22 are connected in series to short-circuit the first capacitor C22 in the negative half-wave of the power supply voltage. The voltage of the second resistor R21 of 40 is applied to the bases of the first and second transistors Tr21 and Tr22, and the first and second transistors Tr21 and Tr22 are applied.
Is turned on, the first capacitor C22 is short-circuited and the first capacitor C22 is short-circuited.
The charging of the capacitor C22 is prohibited. That is, while the voltage of the second resistor R21 of the phase control circuit 40 exceeds the cutoff voltage of the first and second transistors Tr21 and Tr22, the first and second transistors Tr21 and Tr22 are connected to the first capacitor. C22 is short-circuited.

Here, in the phase control circuit 40, the voltage VR21 applied to the second resistor R21 advances by the following Δ with respect to the power supply voltage. ψ = tan ⁻¹ (1 / 2πf C21R21) Here, in the present embodiment, the capacitance of the second capacitor C21 and the resistance of the second resistor R21 are reduced so that the voltage applied to the transistor of the short circuit does not exceed the absolute rating. By doing so, regardless of the power supply frequency f, ie, 50H
At both z and 60 Hz, the value of (1 / 2πf C21R21) is set close to infinity, and the phase advance ψ is set to be constant at approximately 90 °. And 90 ° as described later
, The first capacitor C22 is short-circuited by the amount corresponding to the constant phase lead で, and charging of the first capacitor C22 is prohibited. For this reason, the charging of the first capacitor C22 is started with a delay of about 90 ° regardless of the power supply frequency, and the phase at which the trigger diode D23 is turned on by the voltage of the first capacitor C22 greatly changes depending on the power supply frequency. Disappears. That is, even when the power supply frequency is switched, the voltage difference applied to the motor is reduced, and the change in the motor rotation speed is reduced.

The operation of this circuit will be described in more detail with reference to the waveform diagram of FIG. FIG. 2A shows the phase AC of the power supply voltage and the phase of the voltage VR21 of the second resistor R21. As described above, the phase of the voltage VR21 of the second resistor R21 leads the phase AC of the power supply voltage by 90 °. For this reason,
Zero crossing occurs at time t3 (approximately 90 ° of the power supply phase). Here, during the period from time 0 to time t3, the second
When the first transistor Tr21 is turned on by the voltage VR21 of the resistor R21, the first capacitor C22 is short-circuited, and the charging of the first capacitor C22 is not started.

FIG. 2B shows the charging voltage of the first capacitor C22 after the first transistor Tr21 is turned off (time t3). Here, the curve VC1 indicates the charging voltage of the capacitor C11 at 60 Hz, and the curve VC2 indicates the charging voltage of the capacitor C11 at 50 Hz. 60Hz
When the power supply voltage is applied, the trigger voltage Vg of the trigger diode indicated by the one-dot chain line in FIG.
When the charging voltage VC1 at 0 Hz is exceeded (timing t
In 5), a voltage is applied to the motor as shown by hatching in FIG. On the other hand, similarly, when the power supply voltage of 50 Hz is applied, when the charging voltage VC2 at the time of 50 Hz exceeds the trigger voltage Vg of the trigger diode shown by the dotted line in FIG. 2B (timing t4). , FIG. 2
A voltage is applied to the motor as shown by the shaded line in (C).

In the negative half cycle, similarly, the voltage V21 of the second resistor R21 causes the second transistor T
By turning on r22, the first capacitor C22 is short-circuited,
The charging of the first capacitor C22 is delayed until 90 ° has elapsed from the start of the negative half cycle.

Here, since the first capacitor C22 starts charging from 90 ° where the power supply voltage is maximum irrespective of the power supply frequency, charging proceeds rapidly. For this reason, as shown in FIG.
At which the phase difference between the charging voltage VC1 at 50 Hz and the charging voltage VC2 of the capacitor C22 at 50 Hz remains at a small value, and the time at which the trigger diode Q21 turns on at 50 Hz and the time at which the trigger diode D23 turns on at 60 Hz. The difference from t5 becomes smaller. Specifically, it is less than half as compared with the conventional trigger circuit described above with reference to FIG.
Therefore, even when the power supply frequency is switched between 50 Hz and 60 Hz, the voltage difference applied to the motor is reduced, and the change in the motor rotation speed is reduced.

The result of simulation of the phase difference will be further described with reference to FIGS.
FIGS. 4A and 4B show the phase of the power supply voltage and the first phase.
4 shows a phase of a voltage applied to a second resistor R21 of the motor speed control circuit according to the embodiment. Here, FIG.
In (A), the phase of the power supply voltage at 60 Hz is indicated by □, and
The voltage waveform of the second resistor R21 at Hz is indicated by ●. Also,
In FIG. 4B, the phase of the power supply voltage at 50 Hz is indicated by □, and the voltage waveform of the second capacitor C21 at 50 Hz is indicated by ●. As can be seen from FIGS. 4A and 4B, the second
The voltage waveform of the resistor R21 has a similar curve regardless of the power supply frequency.

On the other hand, the voltage applied to the motor when the power supply voltage was 60 Hz was measured and found to be 65 V. Also, 50
As a result of actually measuring the voltage applied to the motor when the power supply voltage was Hz, it was 67.2 V. That is, even in the actual measurement result, 60
It was found that there was only a 2.2 V difference between Hz and 50 Hz.

Here, for comparison, the result of simulating the circuit of the prior art described above with reference to FIG. 7 will be described with reference to FIGS. 5A and 5B. FIG.
In (A), the phase of the power supply voltage at 60 Hz is indicated by □, and
The voltage waveform of the capacitor C11 at Hz is indicated by ●. In FIG. 5B, the phase of the power supply voltage at 50 Hz is indicated by □, and the voltage waveform of the capacitor C11 at 50 Hz is indicated by ●. As can be seen from a comparison between FIGS. 5A and 5B, the voltage waveform of the capacitor C11 greatly changes depending on the power supply frequency.

Here, the result of actually measuring the voltage applied to the motor by the circuit of the prior art will be described. In this prior art circuit, the voltage applied to the motor is set to be 65 V at 60 Hz. When a power supply voltage of 50 Hz was applied to this circuit, the voltage applied to the motor became 72.5 V. 12.5V at 60Hz and 50Hz from the result of actual measurement
It can be seen that the difference between
It was found that the motor speed greatly changed when switching to 0 Hz.

In the above description with reference to FIG.
It has been described for convenience that the first transistor Tr21 is turned off at the timing t3 when the voltage VR21 of the second resistor R21 crosses zero, but to be precise, the transistor has a cutoff voltage and turns off when the voltage falls below the cutoff voltage.
This operation will be described with reference to FIG. In FIG. 3A, the time from time 0 to time t shown in FIG.
The waveforms of the voltage VR21 up to 3 are shown in an enlarged manner. As described above, since the second resistor R21 is selected to have a relatively small resistance value, the voltage VR21 of the second resistor R21 (first and second transistors Tr21, Tr21,
The base voltage of Tr22) becomes smaller and falls below the cutoff voltage TOFF of the first and second transistors Tr21 and Tr22 indicated by the dotted line in the figure at a relatively early timing (time t6). Thereby, the first and second transistors Tr21, T21
r22 is turned off at an early timing, the trigger circuit 20 is turned on early, and the voltage applied to the motor is set to be increased, so that the rotation speed of the motor is increased.

In FIG. 3A, for comparison, the voltage when the value of the second resistor R21 is increased to the level of the prior art is indicated by a broken line VR21 '. The voltage VR21 'when the resistance value is increased falls below the cutoff voltage TOFF of the first and second transistors Tr21 and Tr22 indicated by broken lines at a relatively late timing (time t7). Since the two transistors Tr21 and Tr22 are turned off slowly, the voltage applied to the motor decreases, and the rotation speed of the motor decreases.

In the motor speed control circuit according to the first embodiment, an operation for maintaining the constant speed of the motor is performed even when the power supply voltage decreases. This will be described with reference to the graph of FIG. In the figure, when the power supply voltage decreases (for example, step-down from 100 V to 90 V), the one-dot chain line VR2 in the figure
As indicated by 1 ″, the voltage of the second resistor R21 decreases, and the cut-off voltage TOFF of the first and second transistors Tr21 and Tr22 indicated by the broken line in the figure becomes earlier (at time t).
8), the first and second transistors Tr21, Tr2
2 is turned off, and the trigger circuit 20 is turned on quickly so as to prevent the voltage applied to the motor from dropping.

That is, when the voltage of the power supply decreases, the first,
The timing of turning off the second transistors Tr21 and Tr22 is accelerated, and the charging of the first capacitor C22 is started earlier than the 90 ° delay of the power supply. For this reason, TRIAC Q22
Is long, so that the motor speed can be kept constant even if the power supply voltage decreases.

Further, in this embodiment, the first and second transistors Tr21 and Tr22 are connected so that the voltage between the collector and the emitter is applied to the triac via the trigger diode D23. Therefore, the withstand voltage between the collector and the emitter of the first and second transistors Tr21 and Tr22 is required only for the trigger voltage of the trigger diode D23. That is, the first and second transistors Tr2
1, there is an advantage that Tr22 having a low withstand voltage can be used.

Next, a circuit configuration of a motor speed control circuit according to a second embodiment of the present invention will be described with reference to FIG. The operation of the motor speed control circuit according to the second embodiment is the same as the operation of the motor speed control circuit of the first embodiment described above. However, in the second embodiment, the circuit operation is stabilized by connecting the resistor R3 in parallel with the second capacitor C2 and the resistor R4 in series. Further, a variable resistor VR1 and a resistor R2 are added to the second resistor VR2, so that the variation of the element,
In particular, the configuration is such that the difference in the characteristics of the trigger diode Q2 can be easily adjusted for each unit.

In the first and second embodiments described above, specific elements have been described. However, it is needless to say that these elements can be replaced by elements capable of performing similar operations. For example, instead of a triac, 2
A set of thyristors can be used, and FETs can be used as transistors.

[0028]

As described above, according to the first aspect of the present invention, the application of the power supply voltage to the first capacitor is delayed by an amount corresponding to the power supply phase of 90 °. For this reason, the charging of the first capacitor is started with a delay of about 90 ° regardless of the power supply frequency, and the phase until the voltage of the first capacitor turns on the trigger diode does not greatly change depending on the power supply frequency. That is, even when the power supply frequency is switched, the amount of change in the motor speed can be reduced.

According to the second aspect of the present invention, when the power supply voltage decreases, the timing at which the first and second transistors are turned off is accelerated, and the charging of the first capacitor is started earlier than the 90 ° delay of the power supply. Therefore, even if the time during which the triac is on becomes longer and the power supply voltage drops, the motor speed can be kept constant.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a motor speed control circuit according to a first embodiment of the present invention.

FIGS. 2A, 2B, and 2C are waveform diagrams of a motor speed control circuit according to the first embodiment.

FIGS. 3A and 3B are waveform diagrams of a motor speed control circuit according to the first embodiment.

FIG. 4A is a graph simulating a phase of a voltage applied to a capacitor at a power supply voltage of 60 Hz in the motor speed control circuit according to the first embodiment, and FIG. 3 is a graph simulating a phase of a voltage applied to a capacitor at a power supply voltage of FIG.

FIG. 5A is a graph simulating the phase of a voltage applied to a capacitor at a power supply voltage of 60 Hz in a conventional motor speed control circuit, and FIG. 4 is a graph simulating a phase of a voltage applied to a capacitor at a power supply voltage.

FIG. 6 is a circuit diagram of a motor speed control circuit according to a second embodiment of the present invention.

FIG. 7 is a circuit diagram of a motor speed control circuit according to the related art.

8 (A), 8 (B) and 8 (C) are waveform diagrams of a motor speed control circuit according to the related art.

[Explanation of symbols]

 Reference Signs List 20 gate circuit 30 zero-cross detection circuit (short circuit) 40 phase control circuit R22 first resistor R21 second resistor C22 first capacitor C21 second capacitor Tr21 first transistor Tr22 second transistor Q21 trigger diode Q22 triac

Claims (2)

[Claims] 1. A first resistor and a first capacitor are connected in series, a trigger diode for providing a triac gate signal is connected between the first resistor and the first capacitor, and a power supply voltage is applied to the first resistor and the first capacitor. A speed control circuit for a motor for applying a charging voltage of the first capacitor to the trigger diode and controlling a phase of a conduction time of the triac, wherein the first capacitor is short-circuited, and a power supply voltage is applied to the first capacitor. A short circuit that delays the application, a second capacitor and a second resistor connected in series, and a voltage applied to the second resistor is applied to the short circuit to control the phase of the short operation of the short circuit Phase control circuit,
A phase control circuit that reduces the capacitance of the second capacitor and the resistance of the second resistor so that the phase of the voltage applied to the second resistor advances by approximately 90 ° with respect to the phase of the power supply regardless of the power supply frequency; A speed control circuit for a motor, comprising: 2. The power supply system according to claim 1, wherein the short-circuit circuit includes a circuit in which a first diode and a first transistor for short-circuiting the first capacitor are connected in series at a positive half-wave of the power supply voltage. A circuit in which a second diode for short-circuiting the first capacitor and a second transistor are connected in series, and a voltage of a second resistor of the phase control circuit is applied to bases of the first and second transistors. 2. The motor speed control circuit according to claim 1, wherein: