Low-energy-consumption current detection circuit applied to speed-adjustable electric tool

Abstract

The utility model relates to a low-energy-consumption current detection circuit applied to a speed-adjustable electric tool, which comprises a load power supply loop, a first MOS (Metal Oxide Semiconductor) tube connected in series in the load power supply loop and used for controlling the power of a load, and a second MOS tube, the first MOS tube is connected in series between the negative electrode end of the load and the negative electrode of a power supply, and the second MOS tube is connected in series between the negative electrode end of the load and the negative electrode of the power supply. The second MOS tube is connected between the negative electrode end of the load and the detection pin of the MCU, the control electrodes of the first MOS tube and the second MOS tube are connected in parallel to the output pin of the MCU, and the MCU controls the first MOS tube and the second MOS tube to be connected or disconnected at the same time. According to the utility model, the technical problems that the traditional method for carrying out circuit current detection and overcurrent protection by using a sampling resistor is high in cost and low in efficiency, and does not conform to the miniaturization development trend of handheld electric tools can be solved.

Description

Technical Field

[0001] This utility model belongs to the field of current detection technology, specifically relating to a low-energy current detection circuit for adjustable-speed power tools. Background Technology

[0002] For circuit safety, almost all high-power products have overcurrent protection. The current common practice is as follows: Figure 1 As shown, a current sampling resistor is connected in series in the current loop. The MCU detects the voltage drop across the sampling resistor to determine the magnitude of the current in the loop. When the voltage across the current sampling resistor reaches the set value, the MCU controls the main control MOSFET in the loop to turn off, thereby achieving overcurrent protection.

[0003] Using a sampling resistor to implement overcurrent protection has the following drawbacks:

[0004] 1. High cost. High-power, high-precision sampling resistors are generally more expensive.

[0005] 2. Large size. High-power sampling resistors inevitably occupy a certain amount of space, which goes against the current trend of increasingly compact handheld power tools and cannot be applied in this field.

[0006] 3. Low efficiency. A large current flowing through the sampling resistor will inevitably result in power loss, affecting the overall efficiency of the device. Utility Model Content

[0007] The technical problem to be solved by this utility model is to provide a low-energy current detection circuit for adjustable speed power tools, which solves the technical problems of high cost, low efficiency and non-compliance with the trend of miniaturization of handheld power tools by using sampling resistors for circuit current detection and overcurrent protection.

[0008] To solve the above-mentioned technical problems, the technical solution adopted by this utility model is: a low-energy current detection circuit for adjustable speed power tools, including a load power supply circuit and a first MOSFET connected in series in the load power supply circuit for controlling the load power, and a second MOSFET. The first MOSFET is connected in series between the negative terminal of the load and the negative terminal of the power supply, and the second MOSFET is connected between the negative terminal of the load and the detection pin of the MCU. The control terminals of the first MOSFET and the second MOSFET are connected in parallel on the output pin of the MCU. The MCU controls the first MOSFET and the second MOSFET to be turned on or off simultaneously.

[0009] As a preferred option, both the first MOSFET and the second MOSFET are N-type MOSFETs.

[0010] As a preferred embodiment, the drains of the first MOSFET and the second MOSFET are connected in parallel to the negative terminal of the load, the source of the first MOSFET is grounded, the source of the second MOSFET is connected to the detection pin of the MCU, and the gates of the first MOSFET and the second MOSFET are connected in parallel to the output pin of the MCU.

[0011] As a preferred embodiment, a current-limiting resistor is connected in series between the drain of the second MOSFET and the negative terminal of the load.

[0012] As a preferred embodiment, a capacitor is connected in parallel between the second MOSFET and the detection pin of the MCU, with the other end of the capacitor grounded.

[0013] The beneficial effects of this utility model are as follows: This utility model detects the current in the power supply circuit by detecting the voltage drop generated by the impedance of the first MOSFET, thereby avoiding the need to use an additional sampling resistor for current detection. Since the first MOSFET is already present as the main control switch of the power tool, its impedance is utilized, eliminating the energy consumption of the sampling resistor. This solves the technical problems of high cost, low efficiency, and non-compliance with the miniaturization trend of handheld power tools that exist in the traditional method of using sampling resistors for circuit current detection and overcurrent protection. Attached Figure Description

[0014] The specific embodiments of this utility model will be further described in detail below with reference to the accompanying drawings, wherein:

[0015] Figure 1 It is a standard overcurrent detection circuit diagram;

[0016] Figure 2 This is a circuit diagram of the low-energy-consumption current detection circuit described in this utility model. Detailed Implementation

[0017] The specific implementation scheme of this utility model will now be described in detail with reference to the accompanying drawings.

[0018] like Figure 2The low-energy-consumption current detection circuit for adjustable-speed power tools shown includes a load power supply circuit and a first MOSFET Q1 connected in series in the load power supply circuit for controlling the load power. The load power supply circuit is formed by a power supply and a load M connected in series. It also includes a second MOSFET Q2. The first MOSFET Q1 is connected in series between the negative terminal of the load M and the negative terminal B- of the power supply. The second MOSFET Q2 is connected between the negative terminal of the load M and the detection pin 2 of the MCU. The control terminals of the first MOSFET Q1 and the second MOSFET Q2 are connected in parallel to the output pin 1 of the MCU. The MCU simultaneously controls the first MOSFET Q1 and the second MOSFET Q2 to turn on or off. Thus, when the first MOSFET Q1 is on, the load power supply circuit is on, the load M is powered, and the current flowing through the first MOSFET Q1 generates a voltage drop. This voltage signal is transmitted to the detection pin 2 of the MCU through the second MOSFET Q2. The MCU detects the voltage received at the detection pin 2 and determines whether there is an overcurrent in the load power supply circuit. If there is an overcurrent, the first MOSFET Q1 is turned off, achieving overcurrent protection.

[0019] In this embodiment, both the first MOSFET Q1 and the second MOSFET Q2 are N-type MOSFETs, so that the first MOSFET Q1 and the second MOSFET Q2 are turned on by the MCU outputting a high level.

[0020] The drains of the first MOSFET Q1 and the second MOSFET Q2 are connected in parallel to the negative terminal of the load M. The source of the first MOSFET Q1 is connected to the negative terminal of the power supply B-, which is equivalent to grounding. The source of the second MOSFET Q2 is connected to the detection pin 2 of the MCU. The gates of the first MOSFET Q1 and the second MOSFET Q2 are connected in parallel to the output pin 1 of the MCU to achieve synchronous control and ensure the timeliness and accuracy of current detection.

[0021] In this embodiment, a current-limiting resistor R2 is preferably connected in series between the drain of the second MOS transistor Q2 and the negative terminal of the load M to improve the safety of the MCU.

[0022] In this embodiment, a capacitor C1 is connected in parallel between the second MOSFET Q2 and the MCU's detection pin 2, with the other end of capacitor C1 grounded. Capacitor C1 can smooth out current spikes, protecting the MCU's operational safety. Simultaneously, it discharges when the second MOSFET Q2 is turned off, maintaining the high-level state of the MCU's detection pin 2, ensuring continuous detection by the MCU and preventing repeated voltage fluctuations on the MCU's detection pin 2.

[0023] The calculation of the impedance R(ds-on) of the first MOSFET Q1 is existing technology. It can be achieved by connecting a constant current source, such as 50A, to the positive terminal B+ and the negative terminal B- of the power supply, turning on both MOSFETs Q1 and Q2. The 50A current creates a voltage drop across the impedance R(ds-on), which is transmitted through the current-limiting resistor R2 and the first MOSFET Q2 to the detection pin 1 of the MCU (e.g., 0.12V). Using the formula R=U / I, the impedance R(ds-on) is calculated as 0.12V / 50A = 2.4mΩ. By accurately calculating the value of the impedance R(ds-on) of the first MOSFET Q1 and storing this value inside the MCU as a standard parameter for current sampling, subsequent current calculations can be performed using this parameter, achieving the same effect as traditional current detection schemes.

[0024] The above embodiments are merely illustrative of the principles and effects of the present invention, as well as some examples of its application, and are not intended to limit the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention.

Claims

1. A low-energy-consumption current detection circuit for adjustable-speed power tools, comprising a load power supply circuit and a first MOSFET connected in series in the load power supply circuit for controlling the load power, characterized in that, It also includes a second MOSFET. The first MOSFET is connected in series between the negative terminal of the load and the negative terminal of the power supply. The second MOSFET is connected between the negative terminal of the load and the detection pin of the MCU. The control terminals of the first MOSFET and the second MOSFET are connected in parallel to the output pin of the MCU. The MCU controls the first MOSFET and the second MOSFET to be turned on or off simultaneously.

2. The low-energy-consumption current detection circuit according to claim 1, characterized in that, Both the first and second MOSFETs are N-type MOSFETs.

3. The low-energy-consumption current detection circuit according to claim 2, characterized in that, The drains of the first and second MOSFETs are connected in parallel to the negative terminal of the load. The source of the first MOSFET is grounded, the source of the second MOSFET is connected to the detection pin of the MCU, and the gates of the first and second MOSFETs are connected in parallel to the output pin of the MCU.

4. The low-energy-consumption current detection circuit according to claim 3, characterized in that, A current-limiting resistor is connected in series between the drain of the second MOSFET and the negative terminal of the load.

5. The low-energy-consumption current detection circuit according to any one of claims 1 to 4, characterized in that, A capacitor is connected in parallel between the second MOSFET and the MCU's detection pin, with the other end of the capacitor grounded.

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