Electric tool MCU step-down power supply circuit with wide voltage range

Abstract

The embodiment of the utility model discloses an electric tool MCU step-down power supply circuit with a wide voltage range, which comprises a battery pack, an LDO step-down circuit, a resistor R1, a resistor R2, a resistor R3, a voltage-regulator tube ZD1, a triode Q1 and a triode Q2, the base electrode of the triode Q2 is connected with the emitter electrode of the triode Q1 through the resistor R3, the emitter electrode of the triode Q2 is connected with the LDO step-down circuit, and the voltage-regulator tube ZD1 is connected with the LDO step-down circuit. The collector electrode of the triode Q2 is connected with the collector electrode of the triode Q1 and connected with the positive electrode of the battery pack through a resistor R1, the base electrode and the collector electrode of the triode Q1 are connected through a resistor R2, and the positive electrode and the negative electrode of the voltage-regulator tube ZD1 are grounded and the base electrode of the triode Q1 respectively. According to the utility model, the LDO can work on the 36-80V battery pack control panel, and stable and reliable working voltage with low noise, small ripple and small quiescent current is provided for the MCU on the premise of low cost.

Description

Technical Field

[0001] This utility model relates to the field of power tools, and in particular to a step-down power supply circuit for a power tool MCU with a wide voltage range. Background Technology

[0002] Power tools are common household or outdoor products. Currently, the power supply for power tools is basically a lithium battery pack + control board. The control board controls the lithium battery pack to provide different working modes for the power tool. The control circuit uses an MCU to control the lithium battery pack's power output capability to the power tool. The normal operating voltage of the MCU is provided by a step-down circuit that reduces the high voltage of the lithium battery pack to 3.0V-5.0V to provide the MCU with the normal operating voltage.

[0003] There are currently two types of step-down circuits used: one is a DC-DC step-down circuit, and the other is an LDO (low dropout regulator). Since the DC-DC step-down circuit operates in a switching state, it achieves step-down through PWM control technology and the characteristics of inductors and capacitors. Because the DC-DC step-down circuit operates in a switching state, it inevitably generates noise and has large ripple. The presence of inductors in the circuit makes the overall cost relatively high. The DC-DC step-down circuit also has disadvantages such as large quiescent current when it is working.

[0004] Therefore, the step-down circuit used on the lithium battery pack control board of power tools basically adopts the LDO (Low Dropout) regulator. Currently used LDO step-down technology solutions for MCU power supply in battery pack control boards include... Figure 1 As shown, the battery voltage basically flows through diode D1, current-limiting resistor R4, and filter capacitors C1 and C2 to the input of the LDO (Low Dropout Regulator). The output voltage then flows through filter capacitors C3 and C4 to the MCU power supply pin. Diode D1 provides unidirectional conduction to prevent reverse voltage flow to the battery pack when the battery voltage is low. R4 limits the current, preventing excessive current from flowing through the LDO when the battery pack and control board are connected during production, thus protecting the LDO. Filter capacitors C1, C2, C3, and C4 smooth the input and output voltages, filter out high-frequency interference, and provide a stable and reliable operating voltage to the MCU. The LDO converts the high input voltage into a stable low voltage through its internal circuitry before supplying it to the load.

[0005] Most LDOs on the market have an input voltage rating between 5V and 42V. Due to the limitations of the LDO input voltage rating, they cannot be directly used in 36V-84V battery pack control boards to provide a suitable operating voltage for the MCU. Figure 2This is an improved circuit that adds a ZD1 Zener diode. The ZD1 Zener diode is connected in reverse series between D1 and R4. After the Zener diode is connected, its voltage regulation function steps down the high voltage input from the battery pack before it is connected to the LDO input. Since the Zener diode is connected in series, its voltage rating is selected based on the battery pack voltage. If the battery pack's highest voltage is 84V, the selected Zener diode should be at least 84V-36V=48V. After passing through the Zener diode, the voltage reaching the LDO input will not exceed its rated voltage. Assuming the MCU's maximum operating current is 0.03A, the Zener diode's power dissipation is 0.03A*48V=1.44W. A typical Zener diode's maximum power dissipation is 0.5W-1W. Clearly, this power dissipation exceeds the Zener diode's capacity, potentially damaging it. Assuming the battery pack's highest voltage is 84V (20 cells in series of 3.7V lithium batteries), when the voltage of a single lithium battery cell drops below 2.4V, the total voltage of the battery pack falls below 48V. At this point, the Zener diode (ZVDC) will not operate, and the LDO (Low Voltage Regulator) will also malfunction. Therefore... Figure 2 That solution is not a good design solution either.

[0006] In summary, for power tool lithium battery pack control boards operating in the 36V-84V range, if the requirement is that the lithium battery pack control board can provide a suitable and stable operating voltage for the MCU within a wide input voltage range of 36V-84V, and has low quiescent current, low noise, low ripple, and low cost, there is currently no good design solution. Utility Model Content

[0007] The technical problem to be solved by this utility model embodiment is to provide a power tool MCU step-down power supply circuit with a wide voltage range, so as to provide a suitable and stable operating voltage for the MCU in a wide input voltage range of 36V-84V.

[0008] To address the aforementioned technical problems, this utility model provides a wide-voltage-range step-down power supply circuit for an MCU in power tools. The circuit includes a battery pack and an LDO step-down circuit connected to the MCU. It also includes resistors R1, R2, and R3, a Zener diode ZD1, a transistor Q1, and a transistor Q2. The base of transistor Q2 is connected to the emitter of transistor Q1 via resistor R3. The emitter of transistor Q2 is connected to the LDO step-down circuit. The collector of transistor Q2 is connected to the collector of transistor Q1 and to the positive terminal of the battery pack via resistor R1. The base and collector of transistor Q1 are connected via resistor R2. The positive and negative terminals of Zener diode ZD1 are grounded and the base of transistor Q1, respectively.

[0009] Furthermore, the LDO step-down circuit includes a diode D1, an LDO low-dropout linear regulator, and a resistor R4. The anode of diode D1 is connected to the emitter of transistor Q2, and the cathode of diode D1 is connected to the input terminal of the LDO low-dropout linear regulator through resistor R4. The output terminal of the LDO low-dropout linear regulator is connected to the MCU.

[0010] Furthermore, the LDO step-down circuit also includes two low-frequency filter capacitors and two high-frequency filter capacitors. Both the input and output terminals of the LDO low-dropout linear regulator are connected to a low-frequency filter capacitor and a high-frequency filter capacitor.

[0011] Furthermore, both transistors Q1 and Q2 are NPN transistors.

[0012] Furthermore, the battery pack's output voltage range is 36V-84V.

[0013] The beneficial effects of this utility model are as follows: This utility model can be applied to 36V-84V lithium battery packs + control boards, providing a stable and reliable operating voltage for MCU power supply; the circuit of this utility model is simple, highly reliable, and low in cost; since there is no switching conversion, unlike DC-DC step-down circuits, the ripple is small, and the impact on MCU detection of battery operating voltage is minimal; the static current of this utility model is small, which allows for longer battery standby time and energy saving; this utility model has a wide range of applicable input voltages, and can better adapt to battery packs with different numbers of series. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of the first existing technology.

[0015] Figure 2 This is a schematic diagram of the principle of the second existing technology.

[0016] Figure 3 This is a schematic diagram of the principle of the wide voltage range power supply circuit for the MCU of an electric tool according to an embodiment of the present invention. Detailed Implementation

[0017] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of this application can be combined with each other. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0018] In this embodiment of the invention, directional indicators (such as up, down, left, right, front, back, etc.) are only used to explain the relative positional relationship and movement of the components in a specific posture (as shown in the attached figure). If the specific posture changes, the directional indicators will also change accordingly.

[0019] Furthermore, in this utility model, descriptions involving "first," "second," etc., 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. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features.

[0020] like Figure 1 As shown, the battery pack voltage passes through diode D1, current-limiting resistor R4, and filter capacitors C1 and C2 to the input of the LDO (Low Dropout Regulator). The output voltage then passes through filter capacitors C3 and C4 to the MCU power supply pin. Diode D1 provides unidirectional conduction to prevent reverse voltage flow to the battery pack when the battery voltage is low. R4 limits current to prevent excessive current flowing through the LDO when the battery pack and control board are connected during production. Filter capacitors C1, C2, C3, and C4 smooth the input and output voltages, filter out high and low frequency interference, and provide a stable and reliable operating voltage to the MCU. The LDO converts the high input voltage into a stable low voltage through its internal circuitry before supplying it to the load. Because the LDO's input voltage rating is typically between 5V and 42V, it cannot be directly used on a 36V-84V battery pack control board to provide a suitable operating voltage to the MCU.

[0021] Figure 2 It's an improved circuit that adds a ZD1 Zener diode. Its working principle is the same as... Figure 1 It's the same, except that a Zener diode ZD1 is added and connected in reverse series between D1 and R4. After the Zener diode is connected to the circuit, due to its voltage regulation function, the high voltage input from the battery pack can be stepped down before being connected to the LDO input. However, because the Zener diode is connected in series in the circuit, the loss is too large during operation, so it cannot be used for a wider range of input operating voltages.

[0022] Please refer to Figure 3 The wide voltage range power tool MCU step-down power supply circuit of this utility model embodiment includes a battery pack, an LDO step-down circuit, resistors R1, R2, and R3, a Zener diode ZD1, a transistor Q1, and a transistor Q2.

[0023] This utility model is... Figure 1 Based on this, add R1, R2, R3, ZD1, Q1, Q2. For example... Figure 3As shown, R1 is used for current limiting and voltage reduction, while R2 acts as a current-limiting resistor for the Zener diode ZD1. Its value can be relatively large, reaching the megohm level, to reduce the overall quiescent current of the circuit. The Zener diode ZD1, along with Q1, R3, and Q2, adjust the input voltage to a suitable output voltage, the output voltage value of which is determined by the Zener diode's voltage regulation value. In the circuit, ZD1 is set to 18V. R1 and Q2 are connected in series between D1 and the positive terminal of the battery pack. When the battery pack voltage is between 36V and 84V, since ZD1 is set to 18V, the emitter voltage of Q2 is approximately 17.15V. After passing through diode D1, current-limiting resistor R4, and filter capacitors C1 and C2, the voltage is connected to the input terminal of the LDO low dropout regulator. The output terminal passes through filter capacitors C3 and C4 and then reaches the MCU power supply pin. The filter capacitors C1, C2, C3, and C4 filter out high-frequency interference, providing the MCU with a suitable, stable, and reliable operating voltage of 3.0V / 3.3V / 5.0V.

[0024] R1 is rated at 560Ω-1KΩ, packaged in a 2512. R2 is rated at 2MΩ-5.1MΩ, packaged in a 0805 or 1206. R61 is rated at 2KΩ-5.1KΩ, packaged in a 0805 or 1206. ZD1 is rated between 15V and 22V, with a power rating of 0.5W. Q1 uses an MMBT5551 SOT23 packaged transistor. Q2 uses a CZT5551 SOT-223 packaged high-power transistor.

[0025] In this invention, the base of transistor Q2 is connected to the emitter of transistor Q1 via resistor R3. The emitter of transistor Q2 is connected to an LDO step-down circuit. The collector of transistor Q2 is connected to the collector of transistor Q1 and to the positive terminal of the battery pack via resistor R1. The base and collector of transistor Q1 are connected via resistor R2. The positive and negative terminals of Zener diode ZD1 are grounded and the base of transistor Q1, respectively.

[0026] In one implementation, the LDO step-down circuit includes a diode D1, an LDO low-dropout linear regulator, and a resistor R4. The anode of the diode D1 is connected to the emitter of the transistor Q2, and the cathode of the diode D1 is connected to the input terminal of the LDO low-dropout linear regulator through the resistor R4. The output terminal of the LDO low-dropout linear regulator is connected to the MCU.

[0027] In one implementation, the LDO step-down circuit also includes two low-frequency filter capacitors and two high-frequency filter capacitors. The input and output terminals of the LDO low-dropout linear regulator are each connected to a low-frequency filter capacitor and a high-frequency filter capacitor.

[0028] As one implementation method, such as Figure 3BAT1...BAT form a 36V-84V lithium battery pack. R1 is a current-limiting and voltage-reducing resistor, R2 is a current-limiting resistor, R3 is a current-limiting resistor, R4 is a current-limiting resistor, ZD1 is a Zener diode, Q1 is an NPN transistor, Q2 is an NPN transistor, D1 is a unidirectional isolation diode, C1 is a low-frequency filter capacitor, C2 is a high-frequency filter capacitor, U2 is an LDO low-dropout linear regulator, C3 is a low-frequency filter capacitor, and C4 is a high-frequency filter capacitor.

[0029] Comparison of this utility model Figure 1 and Figure 2 Only R1, R2, R3, ZD1, Q1, and Q2 are added. Therefore, the cost is low, the ripple is small, the interference is small, and the quiescent current is small. Compared with the DC-DC buck circuit, the DC-DC circuit operates in a switching state and at a high frequency, which inevitably generates high-frequency interference, resulting in disadvantages such as large ripple and large quiescent current. Figure 3 The schematic diagram shows that R1 limits current and reduces voltage, while R2 acts as a current-limiting resistor for the Zener diode ZD1. Its value can be relatively large, reaching the megohm level, to reduce the overall quiescent current of the circuit. The Zener diode ZD1, along with Q1, R3, and Q2, adjusts the input voltage to a suitable output voltage, the value of which is determined by the Zener diode's voltage regulation value. In the circuit, ZD1 is rated at 18V. R1 and Q2 are connected in series between D1 and the positive terminal of the battery pack. When the battery pack voltage range is 36V-84V, since ZD1 is rated at 18V, the emitter voltage of Q2 is approximately 17.15V. After passing through diode D1, current-limiting resistor R4, and filter capacitors C1 and C2, the voltage is connected to the input of the LDO low-dropout regulator. The output voltage reaches the MCU power supply pin after passing through filter capacitors C3 and C4. The filter capacitors C1, C2, C3, and C4 filter out high-frequency interference, providing a stable and reliable operating voltage of 3.0V / 3.3V / 5.0V for the MCU. This design is well-suited for lithium battery control boards with a wide voltage range of 36V-84V.

[0030] MCUs typically operate at 3.0V-5.0V, while common power tool battery packs operate at 14.4V, 18V, 36V, 60V, and 84V. Therefore, the MCU power supply on the control board must be stepped down to provide a stable and suitable operating voltage. Step-down circuits typically use LDO linear regulators or DC-DC buck converters to convert the high input voltage to 3.0V-5.0V to provide a stable and suitable operating voltage for the MCU. DC-DC converters are generally not used for power tool battery packs because they have many components, high cost, large ripple, high noise, and high quiescent current. LDO linear regulators are usually used to step down the voltage to provide a suitable operating voltage for the MCU. LDOs are relatively inexpensive, have low noise, and low quiescent current. Since the maximum operating voltage of LDOs is generally 36-42V, they cannot be directly used on 36V-80V battery pack control boards.

[0031] This invention enables the LDO to operate on a 36-80V battery pack control board, providing the MCU with a stable, reliable, low-noise, low-ripple, and low-quiescent-current operating voltage at low cost.

[0032] Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wide voltage range power tool MCU step-down power supply circuit, comprising a battery pack and an LDO step-down circuit connected to the MCU, characterized in that, It also includes resistors R1, R2, and R3, a Zener diode ZD1, a transistor Q1, and a transistor Q2. The base of transistor Q2 is connected to the emitter of transistor Q1 through resistor R3. The emitter of transistor Q2 is connected to the LDO step-down circuit. The collector of transistor Q2 is connected to the collector of transistor Q1 and to the positive terminal of the battery pack through resistor R1. The base and collector of transistor Q1 are connected through resistor R2. The positive and negative terminals of Zener diode ZD1 are grounded and the base of transistor Q1, respectively.

2. The wide voltage range power tool MCU step-down power supply circuit as described in claim 1, characterized in that, The LDO step-down circuit includes a diode D1, an LDO low-dropout linear regulator, and a resistor R4. The anode of diode D1 is connected to the emitter of transistor Q2, and the cathode of diode D1 is connected to the input terminal of the LDO low-dropout linear regulator through resistor R4. The output terminal of the LDO low-dropout linear regulator is connected to the MCU.

3. The wide voltage range power tool MCU step-down power supply circuit as described in claim 2, characterized in that, The LDO step-down circuit also includes two low-frequency filter capacitors and two high-frequency filter capacitors. The input and output terminals of the LDO low dropout linear regulator are each connected to a low-frequency filter capacitor and a high-frequency filter capacitor.

4. The wide voltage range power tool MCU step-down power supply circuit as described in claim 1, characterized in that, Transistors Q1 and Q2 are both NPN type transistors.

5. The wide voltage range power tool MCU step-down power supply circuit as described in claim 1, characterized in that, The battery pack's output voltage range is 36V-84V.

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