JP2731131B2 - Constant current 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 constant current control circuit for controlling a power supply circuit for charging a rechargeable storage battery with an output current obtained by once rectifying an AC power supply and supplying the power to a charge / AC power tool.

[0002]

2. Description of the Related Art In addition to a power tool, a shaver, a small vacuum cleaner, and the like are known as electric equipment that can be operated directly from an AC power supply for both charging and AC, that is, home use or by a rechargeable storage battery. However, especially with power tools, the point at which the load varies greatly
Different from other devices. That is, the motor load of the power tool frequently changes from a no-load state to a locked state, and the power tool itself is often used continuously or repeatedly for a long time.

[0003]

With such conventional tools, it has been difficult to maintain good constant current characteristics with respect to changes in the load condition.

[0004] The present invention has been made in view of the above,
An object of the present invention is to provide a constant current control circuit having good constant current characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention provides a power supply circuit and a negative circuit.
Disposed between the load, a current detection resistor for detecting the supply current supplied to the load from the power supply circuit, an operational amplifier for amplifying a voltage generated in the current detecting resistor, according to the output voltage level of the operational amplifier A constant current control circuit having a control circuit for holding the supply current at a predetermined level, wherein the load is a motor of a power tool, and a constant voltage element is provided between the operational amplifier and the control circuit ( Claim 1).

According to this configuration, a voltage corresponding to the supply current to the load composed of the motor of the power tool is generated in the current detection resistor, and the generated voltage is amplified by the operational amplifier, and is controlled by the control circuit in accordance with the output voltage level of the operational amplifier. The supply current is maintained at a predetermined level. Here, since the constant voltage element is provided between the operational amplifier and the control circuit, the output voltage of the operational amplifier is transmitted to the control circuit only when the output voltage level of the operational amplifier exceeds a predetermined voltage determined by the constant voltage element. . Therefore, the amplification factor of the operational amplifier can be increased, whereby the supply current can be accurately maintained at a predetermined level regardless of the load state, and good constant current characteristics can be obtained.

A power supply circuit is provided between the power supply circuit and the load.
The power supply circuit detects the supply current supplied to the load.
And the voltage generated at this current detection resistor
The operational amplifier to amplify and the output voltage level of this operational amplifier
Control circuit to maintain the supply current at a predetermined level according to the
In the constant current control circuit and a road, the load electric
A secondary battery for supplying power to the motor of the tool, the
A constant voltage element is interposed between the operational amplifier and the control circuit (claim 2).

With this configuration, electric power is supplied to the motor of the power tool.
Supply current to the load consisting of a secondary battery
A corresponding voltage is generated in the current detection resistor, and this generated voltage is turned off.
Amplified by operational amplifier and controlled by operational circuit
The supply current reaches a predetermined level according to the output voltage level of
Will be retained. Here, a constant voltage is applied between the operational amplifier and the control circuit.
The output voltage level of the operational amplifier is
Only when the voltage exceeds the specified voltage determined by the constant voltage element.
The output voltage of the operational amplifier is transmitted to the control circuit. Therefore,
The amplification factor of the operational amplifier can be increased, the charging current can be accurately maintained at a predetermined level regardless of the state of the secondary battery, and good constant current characteristics can be obtained.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a charging and charging system to which the present invention is applied.
One embodiment of the overall configuration of the alternating-current power tool will be described with reference to the block diagram of FIG. In the figure, 1 is an AC power supply,
2 is a noise filter circuit, 3 is a rectifier circuit, 4 is a switching circuit, 5 is a transformer, 6 is a rectifier circuit, and 7 is a battery to be charged.

Reference numeral 8 denotes a voltage detection circuit for detecting whether the voltage of the battery 7 is higher or lower than a set value, 9 denotes a sensor for detecting the temperature of the battery 7, and 10 denotes a battery detected by the sensor 9. 7, a temperature detection circuit for detecting whether the temperature is higher or lower than a set value; 11, an RS flip-flop in which outputs of the voltage detection circuit 8 and the temperature detection circuit 10 are reset and input to a set terminal, respectively; 12 is a constant current circuit to which the signal from the output current detecting resistor R12 and the output of the flip-flop 11 are inputted, 13 is a constant voltage circuit to which the output voltage of the rectifier circuit 6 is inputted, and 14 is the constant current circuit A PWM control circuit 15 to which an output of the constant voltage circuit 12 and the output of the constant voltage circuit 13 is input and which outputs a signal for feedback control to the switching circuit 4. Motor as the load connected to Te,
Reference numeral 16 denotes a constant temperature control circuit that measures the temperature of the heat-generating component on the load side and sends out an output according to the temperature measurement result.

FIG. 2 shows a more specific circuit diagram of the power tool shown in FIG. In the figure, first, the configuration and operation of each circuit will be described. The PWM control circuit 14 controls the output current or voltage of the rectifier circuit 6 based on the output signal from the constant current circuit 12 and the output signal from the constant voltage circuit 13. The on-off duty of the switching circuit 4 is feedback-controlled so as to be constant.

Next, the constant current circuit 12 will be described. The output current is detected by a resistor R12, the voltage of which is determined by an operational amplifier OP1, a thermistor (hereinafter, referred to as a positive resistor) Rth2 having a positive characteristic described later, resistors R19, R20, R21 and The signal is input to the amplifier circuit composed of the capacitor C6.

This amplifying circuit has a function of [1+ (R19
+ Rth2) / R2021] times, and [1+ (R19 +
Rth2) / R20] times. Here, R2021 is the combined resistance value of the parallel resistors R20 and R21.

The output terminal of the operational amplifier OP1 is
The anode of the Zener diode Dz5 is connected to the light emitting diode of the photocoupler PC1 via the resistor R7 and the forward diode D5.

A current flows through the photocoupler PC1 by the output of the operational amplifier OP1, and the pulse duty of the switching circuit 4 is determined by the PWM control IC in the PWM control circuit 14. That is, when the output current increases,
The output voltage of the amplifier circuit increases based on the above equation, and the current to the photocoupler PC1 increases, so that the pulse duty decreases. As a result, negative feedback control is performed so that the output current decreases and settles to a constant value.

The switching of the amplification factor, that is, the switching of the output current, is performed by switching the resistance circuit of the amplifier circuit by the switch SW2. That is, during charging, the resistors R20 and R20
And 21 are connected in parallel to increase the amplification factor and control the output current with good response. On the other hand, only the resistor R20 is connected to suppress the amplification factor so that the response is not excessively sensitive to a load change during the AC driving, and the response is somewhat lowered compared to the charging.

The switch SW2 is interlocked with the main switch SW1. When charging, that is, when the main switch SW1 is off, the switch SW2 is connected to the side a. On the other hand, when AC driving is performed, that is, when the main switch SW1 is on, the switch SW2 is connected. SW2 is connected to the b side.

The constant voltage circuit 13 comprises a plurality of diodes D10 to D13 as shown in the figure, and the constant voltage is determined by VF (forward voltage) × N (the number of diodes). When the output voltage becomes equal to or higher than VF × N, a current flows to the photocoupler PC1 through the diode, and the PWM control circuit 14 operates to reduce the pulse duty. Therefore, the output voltage is reduced and negative feedback is performed so as to settle to a constant value. Controlled. That is, the fluctuation of the output voltage has an effect on the load side, and if no (light) load operation or the like is performed during the AC driving, the output voltage increases, an overvoltage exceeding the rating is applied to the battery 7, and the overcharge occurs. Will be done. The constant voltage circuit 13 is provided to prevent these.

As described above, the constant voltage circuit 13 is required at the time of AC driving in order to cope with the fluctuation of the output voltage due to the load fluctuation. However, when the same operation is performed at the time of charging, the battery is charged. As the voltage increases, the output voltage decreases and the current is limited, so that the battery is not completely charged. For this reason, the set voltage at the time of charging is set slightly higher than the set voltage at the time of AC drive within a range that does not affect the charge control, so that insufficient charging does not occur. The setting voltage is switched by the switch SW
2 and is connected to the b side during AC driving, and the diodes D8 and D9 are short-circuited so that the set voltage during AC driving is lower than that during charging.

The primary power supply 17 and the secondary power supply 18 are provided because the circuits are connected by the transformer 5. The primary power supply 17 is used as a power supply for the PWM control circuit 14 and is used as a secondary power supply 18. Is a constant current circuit 12, a constant voltage circuit 1
3. It functions as a power supply for the voltage detection circuit 8, the temperature detection circuit 10, and a constant temperature control circuit 16 described later.

The voltage detecting circuit 8 and the temperature detecting circuit 1
0, the output signal of the voltage detection circuit 8 is connected to the reset terminal of the flip-flop 11 and the temperature detection circuit 1
The output signal of 0 is input to the set terminal of the flip-flop 11. Now, assuming that the battery 7 is not sufficiently charged, the voltage of the battery 7 is equal to or lower than the set voltage, and the voltage detection circuit 8 inputs HIGH to the reset terminal, so that the output of the flip-flop 11 becomes LOW. Control so that the output current becomes the rated current.

When the battery 7 is charged with the rated current, the voltage of the battery 7 increases, and the voltage detection circuit 8 sets the reset terminal to LOW. Then, the charging is continued and 100
%, The battery temperature rises above the set temperature and the temperature detection circuit 10 inputs HIGH to the set terminal, so that the output of the flip-flop 11 becomes HIGH and the output current becomes the terminal current. Control.

Next, when the battery 7 is consumed, the battery 7
, The voltage detection circuit 8 outputs the HI signal to the reset terminal.
Since GH is input, the output of the flip-flop 11 is L
Become OW. On the other hand, at this time, even if the temperature of the battery 7 is relatively high and the set terminal maintains the HIGH state, the output current is rated because the flip-flop 11 outputs LOW as described above. Control to maintain the current.

Next, the constant temperature control circuit 16 will be described. Rth2 is a posistor and is connected in series with the amplification resistor R19 of the operational amplifier OP1 in the constant current circuit 12.
The posistor Rth2 has such a characteristic that the relationship between temperature and resistance value is as shown in FIG. 3, and a heat-generating component having a large temperature rise on the load side, for example, a diode D6 of the rectifier circuit 6,
D7 or the choke coil L3 is disposed in contact therewith. Therefore, when the temperature of the heat-generating component rises and becomes equal to or higher than a certain temperature, the resistance value of the posistor Rth2 increases exponentially, and the value of the second term in the above-described amplification factor sharply increases. Therefore, the amplification factor of the operational amplifier OP1 increases, and the output voltage of the operational amplifier OP1 increases, so that the PWM control circuit 14 reduces the on-off duty of the switching circuit 4 to reduce the output current.
Then, due to the decrease in the output current, the temperature rise of the heat-generating components is suppressed, and the components are balanced at a desired temperature. The above-mentioned equilibrium temperature is set within a design-permissible range based on the temperature characteristics of the posistor Rth2, the amount of feedback control, and the like.

In the above configuration, the constant current circuit 1
When the Zener diode Dz5 is not connected between the operational amplifier OP1 and the photocoupler PC1, the feedback current that is the output of the operational amplifier OP1 is determined by (V0 -2VF) / R17. Here, 2VF is a forward voltage of the diode D5 and the light emitting diode of the photocoupler PC1.

Therefore, if the temperature characteristic of the posistor Rth2, that is, the amplification factor, is increased, the output voltage V0 of the operational amplifier OP1 will change until the output current of the rectifier circuit 6 exceeds the rating and changes to a current level requiring control. Beyond 2 VF, a very sensitive control circuit is formed in which feedback control works. For this reason, it was necessary to form a circuit in which the amplification factor was suppressed to some extent, but this would result in a very poor constant current characteristic.

However, in this embodiment, the feedback current becomes (V0−Vz−2VF) / R17 by connecting the zener diode Dz5 between the operational amplifier OP1 and the photocoupler PC1, so that the output V0 of the operational amplifier OP1 is V0. If not> Vz + 2VF, no feedback current flows. However,
Vz is the Zener voltage of the Zener diode Dz5.

With the Zener diode Dz5, it is possible to provide a control circuit with a high amplification factor and good constant current characteristics.

FIG. 4 shows a power supply output characteristic obtained by this embodiment. In the figure, a dotted line d1 shows an ideal constant current characteristic, and a solid line d2 shows a constant current characteristic when a Zener diode Dz5 is used. , A chain line d3 shows the constant current characteristics when the Zener diode Dz5 is not provided. As shown in FIG. 4, according to the present embodiment, a good constant current characteristic close to the ideal characteristic is obtained as compared with the case where the Zener diode Dz5 is not provided.

[0030]

As described in the foregoing, according to the invention of claim 1 is disposed between the power supply circuit load, a current detection resistor for detecting the supply current supplied to the load from the power supply circuit A constant current control circuit comprising: an operational amplifier for amplifying a voltage generated in the current detection resistor; and a control circuit for maintaining the supply current at a predetermined level according to the output voltage level of the operational amplifier. In this motor, since a constant voltage element is interposed between the operational amplifier and the control circuit, the amplification factor of the operational amplifier can be increased, and the supply current is accurately maintained at a predetermined level regardless of the load state. As a result, good constant current characteristics can be obtained with a simple configuration.

Further, according to the invention of claim 2, according to claim 1,
Similarly to the described invention, the amplification factor of the operational amplifier can be increased, the charging current can be accurately maintained at a predetermined level regardless of the state of the secondary battery, and a good constant current can be obtained with a simple configuration. Properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a block diagram showing the overall configuration of an embodiment of a power tool for both charging and AC to which the present invention is applied.

FIG. 2 is a more specific circuit diagram of the power tool shown in FIG.

FIG. 3 is a characteristic curve diagram showing a relationship between temperature and resistance value of a posistor Rth2.

FIG. 4 shows a power supply output characteristic obtained by the present embodiment.

[Explanation of symbols]

 4 Switching circuit 7 Battery 12 Constant current circuit 14 PWM control circuit 16 Constant temperature control circuit Rth2 Posistar Dz5 Zener diode OP1 Operational amplifier PC1 Photocoupler

Claims (2)

(57) [Claims] 1. A disposed between the power supply circuit and the load, a current detecting resistor for detecting a supply current supplied to the load from the electric <br/> supply circuit, a voltage generated in the current detecting resistor In a constant current control circuit comprising an operational amplifier for amplifying and a control circuit for holding the supply current at a predetermined level according to an output voltage level of the operational amplifier, the load is a motor of a power tool, and the operational amplifier and the control circuit A constant current control circuit comprising a constant voltage element interposed therebetween. A power supply circuit disposed between the power supply circuit and the load;
Power supply circuit to detect the supply current supplied to the load.
Amplifies the current detection resistor and the voltage generated at this current detection resistor
Op amp and the output voltage level of this op amp
A control circuit for keeping the supply current at a predetermined level
Wherein the load is a power tool.
A secondary battery for supplying power to the motor, the operating
Constant current control circuit you characterized in that a constant voltage element is interposed between the amplifier and the control circuit.