A power tool switch-on current detection circuit

Abstract

The application discloses a kind of electric tool switch machine current detection circuit, it is related to current detection technical field, mainly includes: motor control unit is in motor energized state, receives the control signal of main control chip and controls the real-time rotating speed of motor;Voltage detection unit collects the voltage signal of motor under current rotating speed, and utilizes the metal semiconductor field effect of field effect transistor, carries out isometric conduction output to the voltage signal of low voltage state, and carries out voltage reduction processing output to the voltage signal of high voltage state;Main control chip receives the voltage signal after processing of voltage detection unit, and shows the real-time voltage of motor by display.This application realizes the isometric output of low voltage signal, and the limited output of high voltage signal, to avoid the leakage detection, false detection of traditional voltage drop circuit to low voltage signal, greatly improve the security of electric tool use.

Description

Technical Field

[0001] This invention relates to the field of current detection technology, and more specifically to a current detection circuit for power tool switching on / off. Background Technology

[0002] Powered products, especially power tools used in production and construction, pose a significant safety hazard if operated without the user's knowledge of their startup status. Therefore, voltage detection devices are typically used to monitor the power tool's operating voltage and determine its startup status. However, power tools typically operate at high voltages, and direct detection can burn out the detection chip. Therefore, a step-down circuit is usually used to reduce the voltage before detection. However, this step-down circuit, regardless of the actual voltage, scales it down proportionally, which can lead to missed detections when the voltage is relatively low. Furthermore, once the operating voltage reaches a certain value, it indicates the motor is fully operational; once this limit is reached, further precise voltage monitoring is unnecessary. Therefore, a new voltage reduction method is urgently needed to ensure accurate detection of low-voltage signals. Summary of the Invention

[0003] To address the shortcomings of existing voltage signal detection methods based on step-down circuits, particularly in detecting low-voltage signals, this invention proposes a power tool on / off current detection circuit, comprising:

[0004] A motor switch is used to switch the power on and off state of the motor.

[0005] The motor control unit is used to receive control signals from the main control chip to control the real-time speed of the motor when the motor is powered on.

[0006] The voltage detection unit is used to acquire the voltage signal of the motor at the current speed, and uses the metal-semiconductor field effect of the field-effect transistor to output the voltage signal under low voltage conditions in a proportional manner, and to output the voltage signal under high voltage conditions by stepping down the voltage.

[0007] 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 on the display.

[0008] Furthermore, the motor control unit includes a motor driver chip, which has a first pin to a fifth pin, wherein:

[0009] 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 negative terminal of the Zener diode, while the positive terminal of the Zener diode and the other end of the first capacitor are grounded.

[0010] The third pin is connected to the gate of the second field-effect transistor and one end of the eleventh resistor through the seventh resistor. 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 anode of the second diode, the cathode of the motor power supply, and the drain of the third field-effect transistor. The cathode of the second diode is connected to the cathode 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.

[0011] Furthermore, the voltage detection unit includes a fifth field-effect transistor, wherein:

[0012] The drain of the fifth field-effect transistor is connected to the negative terminal of the motor power supply through the eighth resistor; the gate of the fifth field-effect transistor is connected to the start-up voltage output by the main control chip and 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 connected in parallel.

[0013] Furthermore, the resistance value of the eighth resistor is much smaller than that of the thirteenth resistor.

[0014] Furthermore, when the fifth field-effect transistor is not fully turned on, the voltage signal output by the voltage detection unit is proportional to the voltage at the negative terminal of the motor power supply.

[0015] Furthermore, it also includes a power failure protection unit, which is used to transmit the capacitor voltage signal before and after the capacitor is powered off to the main control chip.

[0016] Furthermore, the power failure protection unit specifically includes:

[0017] The fifty-fourth resistor and the sixth diode are connected in parallel. The negative terminal of the sixth diode is connected to the positive terminal of the motor power supply, and the positive terminal of the sixth diode is grounded through the twenty-sixth capacitor and 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 outputs the capacitor voltage signal to the ninth pin of the main control chip. The other end of the fifty-third resistor is grounded.

[0018] Compared with the prior art, the present invention has at least the following beneficial effects:

[0019] The present invention discloses a power tool switching current detection circuit that utilizes the metal-semiconductor effect of a field-effect transistor and Ohm's law to achieve proportional output of low-voltage signals and limited output of high-voltage signals. This avoids the missed detection and false detection of low-voltage signals by traditional voltage drop circuits, and greatly improves the safety of power tool use. Attached Figure Description

[0020] Figure 1 This is a modular schematic diagram of a power tool on / off current detection circuit;

[0021] Figure 2 This is a schematic diagram of the motor control unit circuit;

[0022] Figure 3 This is a schematic diagram of the voltage detection unit circuit;

[0023] Figure 4 A schematic diagram of the main control chip pinout;

[0024] Figure 5 This is a schematic diagram of the power failure protection unit circuit. Detailed Implementation

[0025] The following are specific embodiments of the present invention, which are described in conjunction with the accompanying drawings to further illustrate the technical solutions of the present invention. However, the present invention is not limited to these embodiments.

[0026] Example 1

[0027] In common circuits, it is generally difficult to detect the on / off state of the trigger of an electric product. To ensure the safety of power tools during use and avoid accidental operation while they are running, such as... Figure 1 As shown, this invention proposes a power tool on / off current detection circuit, comprising:

[0028] A motor switch is used to switch the power on and off state of the motor.

[0029] The motor control unit is used to receive control signals 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 acquire the voltage signal of the motor at the current speed, and uses the metal-semiconductor field effect of the field-effect transistor to output the voltage signal under low voltage conditions in a proportional manner, and to output the voltage signal under high voltage conditions by stepping down the voltage.

[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 on the display.

[0032] Among them, such as Figure 2As shown, the motor control unit includes a motor driver chip (U2, CM532), which has pins one through five, wherein:

[0033] The fifth pin is connected to the main control chip (e.g. Figure 4 As shown, the control signal (DSG) of U3 (CM9M132A-R-SOP14) is connected to the fourth pin, which is connected to the working 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 negative terminal of the Zener diode ZD1, and the positive terminal of the Zener diode and the other end of the first capacitor are grounded.

[0034] The third pin is connected to both 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 grounded together. The drain of the second field-effect transistor Q2 is simultaneously connected to the anode of the second diode D2, the negative terminal 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 terminal 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 terminals of the motor M1 are connected to the positive and negative terminals of the motor power supply, respectively, and their conduction states are switched by the first switch K1.

[0035] The existence of the motor control unit enables the motor to adjust its speed according to the control signal from the main control chip, and different operating voltages exist at different speeds. At low speeds, the voltage is relatively low. To proportionally detect the low-voltage signal, this invention designs as follows... Figure 3 The voltage detection unit shown is mainly composed of the fifth field-effect transistor Q5, wherein:

[0036] The drain of the fifth field-effect transistor Q5 is connected to the negative terminal P- of the motor power supply through the eighth resistor R8; the gate of the fifth field-effect transistor Q5 is connected to the start-up voltage output by the main control chip U3 and 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 grounded through the parallel thirteenth resistor R6 and the sixth capacitor C6.

[0037] like Figure 3 As shown, when the first switch K1 is closed and the electric product is energized, the main control chip U3 outputs a 5V start signal PWR. Theoretically, for the fifth field-effect transistor Q5 to conduct, 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, since the conduction capacity of the fifth field-effect transistor Q5 is limited, it is in the constant current region, that is, 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 the constant current region to the variable resistance region, and the current changes with the voltage at P-. Since the resistance values ​​of the eighth resistor R8 and the fifth field-effect transistor Q5 are much smaller than those of the thirteenth resistor R13, they can be almost ignored. Therefore, for low voltage, the voltage signal output by the voltage detection unit is proportional to the voltage at P-.

[0039] This allows for the acquisition of the voltage signal value at point P- at a 1:1 ratio, and the signal changes with the voltage at P-. However, as the voltage at P- increases, acquiring the specific voltage value becomes largely meaningless, as operator error with power tools at this point could easily lead to a safety accident. With the voltage detection unit of this invention, due to the limited current-carrying capacity of the field-effect transistor, the fifth field-effect transistor inevitably reaches the constant current region as the voltage at P- increases, and the output voltage signal reaches its maximum limit.

[0040] Furthermore, to determine whether the power tool is transitioning from a standby state to a start state or from a stop state to a start state, this invention also proposes a power-off protection unit, used to transmit the capacitor voltage signal before and after the capacitor is de-energized to the main control chip, such as... Figure 5 As shown, it specifically includes:

[0041] The fifty-fourth resistor R54 and the sixth diode D6 are connected in parallel. The negative terminal of the sixth diode D6 is connected to the positive terminal P+ of the motor power supply. The positive terminal of the sixth diode D6 is grounded through the twenty-sixth capacitor C26 and 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. The other end of the fifty-third resistor R53 is grounded.

[0042] The principle is that when the motor is in standby mode, although it is not running, the circuit is still energized. Therefore, there is a potential within the 26th capacitor, C26. When the motor switches from standby to running mode, the potential within the circuit changes, and the capacitor voltage changes from a high potential. Conversely, when the motor is off, the circuit is de-energized, and the potential within the 26th capacitor, C26, is immediately dissipated. Therefore, when the motor switches from off to running 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] In summary, the power tool switching current detection circuit of 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 power 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 positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0045] Furthermore, in this invention, descriptions involving terms such as "first," "second," and "a" are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0046] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection or an electrical connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0047] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

Claims

1. A power tool on / off current detection circuit, characterized in that, include: A motor switch is used to switch the power on and off state of the motor. The motor control unit is used to receive control signals 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 acquire the voltage signal of the motor at the current speed, and uses the metal-semiconductor field effect of the field-effect transistor to output the voltage signal under low voltage conditions in a proportional manner, and to output the voltage signal under high voltage conditions by stepping down the voltage. The voltage detection unit contains a fifth field-effect transistor (FET). The drain of the fifth FET is connected to the negative terminal of the motor power supply through an eighth resistor. The gate of the fifth FET is connected to the start-up voltage output by the main control chip and is grounded through a twelfth resistor. The source of the fifth FET outputs a processed voltage signal to the twelfth pin of the main control chip and is grounded through a thirteenth resistor and a sixth capacitor connected in parallel. The resistance value of the eighth resistor is much smaller than that of the thirteenth resistor. 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 on the display.

2. The power tool on / off current detection circuit as described in claim 1, characterized in that, The motor control unit includes a motor driver chip, which has 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 negative terminal of the Zener diode, while the positive terminal of the Zener diode and the other end of the first capacitor are grounded. The third pin is connected to the gate of the second field-effect transistor and one end of the eleventh resistor through the seventh resistor. 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 anode of the second diode, the cathode of the motor power supply, and the drain of the third field-effect transistor. The cathode of the second diode is connected to the cathode 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.

3. The power tool on / off current detection circuit as described in claim 1, characterized in that, When the fifth field-effect transistor is not fully turned on, the voltage signal output by the voltage detection unit is proportional to the voltage at the negative terminal of the motor power supply.

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

5. The power tool on / off current detection circuit as described in claim 4, characterized in that, The power failure protection unit specifically includes: The fifty-fourth resistor and the sixth diode are connected in parallel. The negative terminal of the sixth diode is connected to the positive terminal of the motor power supply, and the positive terminal of the sixth diode is grounded through the twenty-sixth capacitor and 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 outputs the capacitor voltage signal to the ninth pin of the main control chip. The other end of the fifty-third resistor is grounded.

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