On / off current detection circuit for electric tool

Abstract

An on / off current detection circuit for an electric tool, the circuit comprising: an electric motor regulation unit, which receives, when an electric motor is in a power-on state, a regulation signal of a main control chip to regulate the real-time rotational speed of the electric motor; a voltage detection unit, which collects voltage signals of the electric motor at the current rotational speed, performs proportional conduction output of voltage signals in a low-voltage state by using a metal-semiconductor field effect of a field effect transistor, and performs step-down processing output of voltage signals in a high-voltage state; and the main control chip, which receives the voltage signals that are processed by the voltage detection unit, and displays the real-time voltage of the electric motor by means of a display. The present current detection circuit implements proportional output of low-voltage signals and limited output of high-voltage signals, so that missed detection and false detection of low-voltage signals in conventional voltage drop circuits are avoided, thereby greatly improving the use safety of electric tools.

Description

A current detection circuit for power tool switch Technical Field

[0001] The present invention relates to the technical field of current detection, and in particular to a current detection circuit for turning on and off an electric tool. Background Art

[0002] Electric products, especially those used in production and construction, can easily cause irreversible production safety accidents if users operate them without knowing whether they are in the active state. Therefore, voltage detection devices are often used to detect the current operating voltage of the power tool, thereby enabling detection of the power tool's active state. However, the operating voltage of power tools is very high, and direct detection would burn through the detection chip. Therefore, a step-down circuit is typically used to reduce the voltage before voltage detection. However, using a step-down circuit for detection always scales the operating voltage by a certain percentage regardless of the voltage level. This can easily lead to missed detection of the operating voltage when the operating voltage is relatively low. Furthermore, once the operating voltage of a power tool reaches a certain value, it indicates that the motor is fully operational. Once the operating voltage reaches a certain limit, accurate detection of the operating voltage is no longer necessary. Therefore, a new voltage reduction method is urgently needed to ensure accurate detection of low-voltage signals. Technical issues

[0003] In order to solve the deficiency of low voltage signal detection when detecting voltage signals based on a conventional step-down circuit, the present invention proposes a power tool power on / off current detection circuit. Solution

[0004] The present invention provides a power tool power on / off current detection circuit, comprising:

[0005] Motor switch, used to switch the power on and off state of the motor;

[0006] The motor control unit is used to receive the control signal from the main control chip to control the real-time speed of the motor when the motor is powered on;

[0007] The voltage detection unit is used to collect the voltage signal of the motor at the current speed, and use the metal semiconductor field effect of the field effect tube to perform proportional conduction output on the voltage signal in the low voltage state and step down the voltage signal in the high voltage state;

[0008] The main control chip is used to receive the voltage signal processed by the voltage detection unit and display the real-time voltage of the motor through the display.

[0009] Furthermore, the motor control unit includes a motor driver chip having a first pin to a fifth pin, wherein:

[0010] The fifth pin is connected to the control signal of the main control chip; the fourth pin is connected to the operating voltage; the second pin is grounded; the first pin is connected to the power supply voltage and is simultaneously connected to one end of the first capacitor and the cathode of the voltage-stabilizing diode, and the anode of the voltage-stabilizing diode and the other end of the first capacitor are grounded;

[0011] The third pin is connected to the gate of the second field effect transistor and one end of the eleventh resistor at the same time through the seventh resistor, and the source of the second field effect transistor and the other end of the eleventh resistor are grounded together; the drain of the second field effect transistor is connected to the positive electrode of the second diode, the negative electrode of the motor power supply and the drain of the third field effect transistor at the same time; the negative electrode of the second diode is connected to the positive electrode of the motor power supply; the gate of the third field effect transistor is connected to the source of the second field effect transistor, and the source of the third field effect transistor is grounded.

[0012] Furthermore, the voltage detection unit includes a fifth field effect transistor, wherein:

[0013] The drain of the fifth field effect transistor is connected to the negative pole of the motor power supply through the eighth resistor; the gate of the fifth field effect transistor is connected to the starting voltage output by the main control chip and is grounded through the twelfth resistor; the source of the fifth field effect transistor outputs the processed voltage signal to the twelfth pin of the main control chip and is grounded through the thirteenth resistor and the sixth capacitor in parallel.

[0014] Furthermore, the resistance of the eighth resistor is much smaller than the resistance of the thirteenth resistor.

[0015] Furthermore, when the fifth field effect transistor is in a partially turned-on state, the voltage signal output by the voltage detection unit is in proportional relationship with the voltage at the negative electrode of the motor power supply.

[0016] Furthermore, it also includes a power-off protection unit for transmitting capacitor voltage signals before and after the capacitor is powered off to the main control chip.

[0017] Furthermore, the power-off protection unit specifically includes:

[0018] The fifty-fourth resistor and the sixth diode are connected in parallel, the cathode of the sixth diode is connected to the positive electrode of the motor power supply, the anode of the sixth diode is grounded through the twenty-sixth capacitor, and is connected to the emitter of the seventeenth transistor; the base of the seventeenth transistor is connected to the collector of the eighteenth transistor through the fifty-first resistor, the collector of the seventeenth transistor is connected to one end of the fifty-third resistor through the fifty-second resistor, and the capacitor voltage signal is output to the ninth pin of the main control chip, and the other end of the fifty-third resistor is grounded. Beneficial effects

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] The power tool power on / off current detection circuit described in the present invention utilizes the metal semiconductor effect of field-effect transistors and Ohm's law to achieve proportional output of low-voltage signals and limited output of high-voltage signals, thereby avoiding missed detection and false detection of low-voltage signals by traditional voltage drop circuits and greatly improving the safety of power tool use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG1 is a modular schematic diagram of a power tool power on / off current detection circuit;

[0022] Figure 2 is a schematic diagram of the motor control unit circuit;

[0023] FIG3 is a schematic diagram of a voltage detection unit circuit;

[0024] Figure 4 is a schematic diagram of the main control chip pins;

[0025] FIG5 is a schematic diagram of a power-off protection unit circuit. Modes for Carrying Out the Invention

[0026] The following are specific embodiments of the present invention and the accompanying drawings to further describe the technical solutions of the present invention, but the present invention is not limited to these embodiments. Example 1

[0027] In common circuits, it is generally difficult to detect the on / off state of a power tool trigger. To ensure the safety of power tools during use and avoid misoperation during the start-up state, the present invention proposes a power tool on / off current detection circuit, as shown in FIG1 , comprising:

[0028] Motor switch, used to switch the power on and off state of the motor;

[0029] The motor control unit is used to receive the control signal from the main control chip to control the real-time speed of the motor when the motor is powered on;

[0030] The voltage detection unit is used to collect the voltage signal of the motor at the current speed, and use the metal semiconductor field effect of the field effect tube to perform proportional conduction output on the voltage signal in the low voltage state and step down the voltage signal in the high voltage state;

[0031] The main control chip is used to receive the voltage signal processed by the voltage detection unit and display the real-time voltage of the motor through the display.

[0032] As shown in FIG2 , the motor control unit includes a motor driver chip (U2, CM532), which includes pins 1 to 5, where:

[0033] The fifth pin is connected to the control signal (DSG) of the main control chip (as shown in Figure 4, U3, CM9M132A-R-SOP14); the fourth pin is connected to the operating voltage (VDD); the second pin is grounded; the first pin is connected to the power supply voltage (VCC) and is simultaneously connected to one end of the first capacitor C1 and the cathode of the Zener diode ZD1. The anode of the Zener diode and the other end of the first capacitor are grounded.

[0034] The third pin is connected to the gate of the second field-effect transistor Q2 and one end of the eleventh resistor R11 via the seventh resistor R7. The source of the second field-effect transistor Q2 and the other end of the eleventh resistor R11 are both grounded. The drain of the second field-effect transistor Q2 is simultaneously connected to the anode of the second diode D2, the negative electrode P- of the motor power supply, and the drain of the third field-effect transistor Q3. The cathode of the second diode D2 is connected to the positive electrode P+ of the motor power supply. The gate of the third field-effect transistor Q3 is connected to the source of the second field-effect transistor Q2, and the source of the third field-effect transistor Q3 is grounded. The positive and negative electrodes of the motor M1 are respectively connected to the positive and negative electrodes of the motor power supply, and the conduction state is switched by the first switch K1.

[0035] It is precisely because of the presence of the motor control unit that the motor can adjust its speed according to the control signal of the main control chip. At different speeds, there are different operating voltages. At low speeds, its voltage is relatively small. In order to detect low-voltage electrical signals in proportion, the present invention designs a voltage detection unit as shown in Figure 3. Its main body is composed of the fifth field-effect transistor Q5, in which:

[0036] The drain of the fifth field effect transistor Q5 is connected to the negative electrode P- of the motor power supply through the eighth resistor R8; the gate of the fifth field effect transistor Q5 is connected to the starting voltage output by the main control chip U3 and is grounded through the twelfth resistor R12; the source of the fifth field effect transistor Q5 outputs the processed voltage signal to the twelfth pin of the main control chip U3 and is grounded through the thirteenth resistor R6 and the sixth capacitor C6 connected in parallel.

[0037] As shown in Figure 3, when the first switch K1 is closed and the electric product is powered on, the main control chip U3 outputs a 5V startup signal PWR. Theoretically, to turn on the fifth field-effect transistor Q5, the condition Vgs>Vgs(th) must be met. Therefore, when P- is at a high voltage, the fifth field-effect transistor Q5 is fully turned on. At this time, due to the limited conduction capacity of the fifth field-effect transistor Q5, it is in the constant current region, which means that the voltage signal output by the voltage detection unit is a fixed value.

[0038] When P- is at a low voltage, the fifth field-effect transistor Q5 changes from a constant current region to a variable resistance region, and the current changes with the change of the voltage at P-. Since the resistance values ​​of the eighth resistor R8 and the fifth field-effect transistor Q5 are smaller than the resistance value of the thirteenth resistor R13 and are almost negligible, for low voltage, the voltage signal output by the voltage detection unit is output proportionally to the voltage at P-.

[0039] In this way, the voltage signal value at P- can be collected at a 1:1 ratio, and the value changes as the voltage at P- changes. However, as the voltage at P- increases, collecting the specific voltage value is no longer meaningful, because if the operator mistakenly operates the power tool at this time, it is very likely to cause a production safety accident. With the voltage detection unit of the present invention, due to the limited flow of the field-effect transistor, as the voltage at P- increases, the fifth field-effect transistor will inevitably enter the constant current region, and the output voltage signal will also reach the maximum limit.

[0040] Furthermore, in order to determine whether the current power tool enters the start state from the standby state or the shutdown state, the present invention also proposes a power-off protection unit for transmitting the capacitor voltage signal before and after the capacitor is powered off to the main control chip, as shown in FIG5 , which specifically includes:

[0041] The fifty-fourth resistor R54 and the sixth diode D6 are connected in parallel, the cathode of the sixth diode D6 is connected to the positive electrode P+ of the motor power supply, the anode of the sixth diode D6 is grounded through the twenty-sixth capacitor C26, and is connected to the emitter of the seventeenth transistor Q17; the base of the seventeenth transistor Q17 is connected to the collector of the eighteenth transistor Q18 through the fifty-first resistor R51, the collector of the seventeenth transistor Q17 is connected to one end of the fifty-third resistor R53 through the fifty-second resistor R52, and outputs the capacitor voltage signal (ON / OFF_AD) to the ninth pin of the main control chip U3, and the other end of the fifty-third resistor R53 is grounded.

[0042] The principle is that when the motor is in standby mode, although the motor is not in operation, the entire circuit is energized. Therefore, there is a potential in the twenty-sixth capacitor C26. When the motor switches from standby mode to operation mode, the potential in the circuit changes, and the capacitor voltage changes from a high potential. When the motor is in shutdown mode, the potential in the twenty-sixth capacitor C26 is immediately depleted because the circuit is powered off. Therefore, when the motor switches from shutdown mode to operation mode, the capacitor voltage changes from a zero potential. Based on these characteristics, the current trend of the motor's operating state can be accurately determined.

[0043] To sum up, the electric tool power on / off current detection circuit described in the present invention utilizes the metal semiconductor effect of the field effect transistor and Ohm's law to achieve proportional output of low voltage signals and limited output of high voltage signals, thereby avoiding the missed detection and false detection of low voltage signals by traditional voltage drop circuits, and greatly improving the safety of electric tool use.

[0044] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative position relationship, movement status, etc. between the various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0045] In addition, in the present invention, descriptions such as "first," "second," and "one" are for descriptive purposes only and should not be understood to indicate or imply their relative importance or implicitly specify the number of the technical features indicated. Therefore, a feature specified as "first" or "second" may explicitly or implicitly include at least one of such features. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0046] In the present invention, unless otherwise specified or limited, the terms "connection" and "fixation" should be understood in a broad sense. For example, "fixation" can mean fixed connection, detachable connection, or integration; mechanical connection or electrical connection; direct connection or indirect connection through an intermediate medium; internal communication between two elements or interaction between two elements, unless otherwise specified. Those skilled in the art will be able to understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0047] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

Claims

1. A power tool power on / off current detection circuit, characterized in that: include: A motor switch, used to switch the power on and off state of the motor; The motor control unit is used to receive the control signal from the main control chip to control the real-time speed of the motor when the motor is powered on; The voltage detection unit is used to collect the voltage signal of the motor at the current speed, and use the metal semiconductor field effect of the field effect tube to perform proportional conduction output on the voltage signal in the low voltage state and step down the voltage signal in the high voltage state; The main control chip is used to receive the voltage signal processed by the voltage detection unit and display the real-time voltage of the motor through the display.

2. The electric tool power on / off current detection circuit according to claim 1, characterized in that: The motor control unit includes a motor drive chip, which includes a first pin to a fifth pin, wherein: The fifth pin is connected to the control signal of the main control chip; the fourth pin is connected to the working voltage; the second pin is grounded; the first pin is connected to the power supply voltage and is simultaneously connected to one end of the first capacitor and the cathode of the voltage-stabilizing diode, and the anode of the voltage-stabilizing diode and the other end of the first capacitor are grounded; The third pin is connected to the gate of the second field effect tube and one end of the eleventh resistor through the seventh resistor, and the source of the second field effect tube and the other end of the eleventh resistor are grounded together; the drain of the second field effect tube is connected to the positive electrode of the second diode, the negative electrode of the motor power supply and the drain of the third field effect tube at the same time; the negative electrode of the second diode is connected to the positive electrode of the motor power supply; the gate of the third field effect tube is connected to the source of the second field effect tube, and the source of the third field effect tube is grounded.

3. The electric tool power on / off current detection circuit according to claim 1, characterized in that: The voltage detection unit comprises a fifth field effect transistor, wherein: The drain of the fifth field effect transistor is connected to the negative pole of the motor power supply through the eighth resistor; the gate of the fifth field effect transistor is connected to the starting voltage output by the main control chip and is grounded through the twelfth resistor; the source of the fifth field effect transistor outputs the processed voltage signal to the twelfth pin of the main control chip and is grounded through the thirteenth resistor and the sixth capacitor in parallel.

4. The electric tool power on / off current detection circuit as claimed in claim 3, characterized in that: The resistance of the eighth resistor is much smaller than the resistance of the thirteenth resistor.

5. The electric tool power on / off current detection circuit as claimed in claim 4, characterized in that: When the fifth field effect transistor is in an incompletely turned-on state, the voltage signal output by the voltage detection unit is in equal proportion to the voltage at the negative electrode of the motor power supply.

6. The electric tool power on / off current detection circuit as claimed in claim 1, characterized in that: It also includes a power-off protection unit, which is used to transmit the capacitor voltage signal before and after the capacitor is powered off to the main control chip.

7. The electric tool power on / off current detection circuit as claimed in claim 6, characterized in that: The power-off protection unit specifically includes: The fifty-fourth resistor and the sixth diode are connected in parallel, the cathode of the sixth diode is connected to the positive electrode of the motor power supply, the anode of the sixth diode is grounded through the twenty-sixth capacitor, and is connected to the emitter of the seventeenth transistor; the base of the seventeenth transistor is connected to the collector of the eighteenth transistor through the fifty-first resistor, the collector of the seventeenth transistor is connected to one end of the fifty-third resistor through the fifty-second resistor, and the capacitor voltage signal is output to the ninth pin of the main control chip, and the other end of the fifty-third resistor is grounded.

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