Motor driving circuit for preventing Miller conduction

Abstract

The invention discloses a motor driving circuit for preventing Miller conduction, and relates to the technical field of motor control. The circuit comprises a half-bridge circuit, a driving chip and a Miller conduction prevention circuit, the Miller conduction prevention circuit is composed of a discharge transistor, a diode and a current-limiting resistor. When dV / dt generated by switching actions of an upper tube and a lower tube causes a voltage peak on a grid electrode of a corresponding tube through a Miller capacitor, the circuit can automatically detect and quickly conduct a discharge transistor, and quickly discharge Miller charges, so that the voltage of the grid electrode is clamped below a safety value, and bridge arm direct connection is effectively prevented. The invention has the advantages of simple structure, low cost, high reliability, low power consumption and no influence on normal switching speed.

Description

Technical Field

[0001] This invention relates to the field of power electronics and motor control technology, specifically to a circuit for driving power switching devices (such as MOSFETs), and particularly to a motor drive circuit that can effectively prevent the bridge arm power transistors from being mis-turned due to the Miller effect. Background Technology

[0002] In a half-bridge motor drive circuit, when the upper power switch is turned on or off, its drain potential changes drastically. This change is coupled to the gate of the lower power switch, which is in the off state, through the Miller capacitance (Cgd), generating a displacement current and forming a voltage spike across the gate resistor. If this spike voltage exceeds the turn-on threshold voltage (Vth) of the power transistor, it will cause the lower transistor to momentarily turn on, i.e., Miller conduction. Miller conduction can cause both the upper and lower transistors in the bridge arm to conduct simultaneously, resulting in problems such as high current, high heat generation, electromagnetic interference, and even device burnout. Traditional methods suppress voltage spikes by reducing the gate drive resistance, but this increases power consumption, affects switching speed, and may cause oscillations. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a motor drive circuit that is simple in structure, highly reliable, and low in cost to prevent Miller conduction. It can effectively eliminate the risk of bridge arm misconduct caused by the Miller effect and improve the reliability and efficiency of the system.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: A motor drive circuit for preventing Miller conduction includes: A half-bridge circuit includes two power switches connected in series: an upper power switch and a lower power switch. The connection point between the upper and lower power switches serves as the output terminal and is connected to the motor windings. The driver chip is used to output drive signals to control the on and off of the upper and lower power switches; The power switch is equipped with a Miller conduction prevention circuit, which includes a discharge transistor, a diode, and a current-limiting resistor. The emitter of the discharge transistor is connected to the gate of the corresponding power switch, and the collector is connected to the source of the corresponding power switch. The cathode of the diode is connected to the emitter of the discharge transistor, and the anode is connected to the base of the discharge transistor; One end of the current-limiting resistor is connected to the output terminal of the driver chip, and the other end is connected to the base of the discharge transistor and the anode of the diode.

[0005] Furthermore, the discharge transistor is a PNP bipolar junction transistor.

[0006] Furthermore, both the upper and lower power switches are N-channel enhancement-mode MOSFETs.

[0007] Furthermore, the anti-Miller conduction circuit is correspondingly disposed on the lower MOSFET power switch; the driver chip is used to drive the lower MOSFET power switch; the upper MOSFET power switch is controlled by another independent driver unit.

[0008] Furthermore, the discharge transistor is configured such that when the gate of the corresponding power switch generates a voltage spike higher than its conduction threshold due to the Miller effect, the discharge transistor instantaneously saturates and conducts, forming a low-impedance discharge path with a resistance of less than 1Ω between the gate and source of the power switch.

[0009] Furthermore, a pull-down resistor is connected between the gate and source of the power switch.

[0010] An electric motor drive system includes a motor drive circuit for preventing Miller conduction as described above, and a motor driven by the motor drive circuit.

[0011] The working principle of this invention is: During normal operation, the high-level drive voltage output by the driver chip directly drives the power switch to saturation conduction through the current-limiting resistor and diode. The discharge transistor is in a non-conducting state.

[0012] When the power switch needs to be turned off, the driver chip outputs a low level. At this time, because the emitter voltage of the transistor is greater than the base voltage, the diode is cut off, and the discharge transistor is in the conducting state, quickly discharging the gate charge of the power switch and providing a low-impedance path.

[0013] When the upper power switch generates dV / dt noise during operation, and this noise is coupled to the gate of the lower power switch through the Miller capacitance, attempting to raise its gate voltage: When the bleeder transistor is in a saturated conduction state, it forms a low-impedance path between the gate and the source, which quickly discharges the charge generated by the Miller current, thereby clamping the gate voltage at a low level (approximately equal to the saturation voltage drop Vec(sat) of the bleeder transistor).

[0014] Because the clamped gate voltage is lower than the power transistor's turn-on threshold Vth, Miller conduction is completely avoided.

[0015] The beneficial effects of this invention are as follows: 1. Highly effective in preventing false conduction; it can quickly and actively discharge Miller charge and clamp the gate voltage below a safe value, fundamentally eliminating the possibility of Miller conduction. 2. It only operates when Miller voltage spikes occur, and introduces almost no additional power consumption during static and normal switching processes, which is superior to the solution of simply reducing the gate resistance; 3. It does not affect the normal switching speed, and can accelerate the shutdown process, improving dynamic performance; 4. The structure is simple, requiring only a few common discrete components, resulting in low cost and easy integration into existing driver designs; 5. It adopts passive and discrete semiconductor devices, resulting in good circuit stability, high reliability, and long lifespan. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the motor drive circuit for preventing Miller conduction as described in this invention.

[0017] Key reference numerals in the diagram: 1-Half-bridge circuit; 2-Driver chip; 3-Anti-Miller conduction circuit; Q1-Upper transistor power switch; Q2-Lower transistor power switch; Q3-Upper transistor discharge transistor; Q4-Lower transistor discharge transistor; D1-Upper transistor diode; D2-Lower transistor diode; R1-Upper transistor current limiting resistor; R2-Lower transistor current limiting resistor; SA-Motor winding. Detailed Implementation

[0018] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.

[0019] like Figure 1 As shown, the present invention provides a motor drive circuit for preventing Miller conduction, which mainly includes a half-bridge circuit 1, a drive chip 2, and a Miller conduction prevention circuit 3.

[0020] Half-bridge circuit 1 consists of two power switches, Q1 and Q2 (both N-channel MOSFETs), connected in series. Specifically, the DC bus voltage VCC is connected to the drain of the upper power switch Q1, and the source of the upper power switch Q1 is connected to the drain of the lower power switch Q2. The source of Q2 is grounded to GND, meaning the DC bus voltage VCC is applied between the drain of Q1 and the source of Q2. The connection point between the source of Q1 and the drain of Q2 serves as the output terminal, connected to the motor winding SA (SB and SC are similar and will not be described further). The gates of Q1 and Q2 are controlled by their respective driver circuits.

[0021] The driver chip is used to drive the half-bridge power switches. Its output pins are connected to the gates of Q1 and Q2 through gate resistors R1 and R2.

[0022] The Miller conduction prevention circuit 3 is the core of this invention. The power switch is equipped with the Miller conduction prevention circuit 3. Each Miller conduction prevention circuit 3 includes a PNP transistor as a discharge transistor (Q3, Q4), a diode (D1, D2) and a current limiting resistor (R1, R2).

[0023] Here, we take the lower-side power switch Q2 as an example: The emitter of the discharge transistor Q4 is connected to the gate of Q2; the collector of Q4 is connected to the source of Q2 (i.e., power ground); the cathode of diode D2 is connected to the emitter of Q4; one end of the current-limiting resistor R2 is connected to the output terminal of the driver chip, and the other end is connected to the base of Q4 and the anode of D2.

[0024] Work process: Q2 is normally turned on: U1 outputs 12V, and the current flows through R2 to turn on D2.

[0025] Q2 is normally turned off: U1 outputs 0V. Since the emitter voltage of Q4 is greater than the base voltage, diode D2 is cut off, and Q4 is in the conducting state, which quickly discharges the gate charge of power switch Q2 and provides a low impedance path.

[0026] Suppressing Miller conduction: When the high-speed switching of the upper power switch Q1 causes a drastic change in its drain voltage, this change couples through the Miller capacitance Cgd1 of Q1 and the Miller capacitance Cgd2 of the lower power switch Q2, generating a positive voltage spike at the gate of Q2 when it is in the off state. This voltage spike causes the discharge transistor Q4 to momentarily saturate and conduct. A very low resistance (typically less than 1Ω) is formed between the E and C terminals of Q4, rapidly discharging the Miller charge on the gate of Q2 to the source, thereby clamping the gate voltage at the saturation voltage drop level of Q4. This voltage is far below the turn-on threshold (3V) of Q2, thus effectively preventing mis-conduction of Q2.

[0027] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A motor drive circuit for preventing Miller conduction, comprising: A half-bridge circuit includes two power switches connected in series: an upper power switch and a lower power switch. The connection point between the upper and lower power switches serves as the output terminal and is connected to the motor windings. The driver chip is used to output drive signals to control the on and off of the upper and lower power switches; The feature is that the power switch is correspondingly configured with an anti-Miller conduction circuit, which includes a discharge transistor, a diode, and a current-limiting resistor; The emitter of the discharge transistor is connected to the gate of the corresponding power switch, and the collector is connected to the source of the corresponding power switch. The cathode of the diode is connected to the emitter of the discharge transistor, and the anode is connected to the base of the discharge transistor; One end of the current-limiting resistor is connected to the output terminal of the driver chip, and the other end is connected to the base of the discharge transistor and the anode of the diode.

2. The motor drive circuit for preventing Miller conduction according to claim 1, characterized in that, The discharge transistor is a PNP bipolar junction transistor.

3. The motor drive circuit for preventing Miller conduction according to claim 1, characterized in that, The upper and lower power switches are N-channel enhancement-mode MOSFETs.

4. The motor drive circuit for preventing Miller conduction according to claim 1, characterized in that, The anti-Miller conduction circuit is correspondingly located on the lower power switch; the driver chip is used to drive the lower power switch; the upper power switch is controlled by another independent driver unit.

5. The motor drive circuit for preventing Miller conduction according to claim 1, characterized in that, The discharge transistor is configured such that when the gate of the corresponding power switch generates a voltage spike higher than its conduction threshold due to the Miller effect, the discharge transistor instantaneously saturates and conducts, forming a low-impedance discharge path with a resistance of less than 1Ω between the gate and source of the power switch.

6. The motor drive circuit for preventing Miller conduction according to claim 1, characterized in that, A pull-down resistor is also connected between the gate and source of the power switch.

7. A motor drive system, characterized in that, It includes the motor drive circuit for preventing Miller conduction as described in claim 1, and the motor driven by the motor drive circuit.

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