TWI828419B - Current sensing and overcurrent protection circuit for brushless DC motors - Google Patents

Abstract

The invention provides a current detection and overcurrent protection circuit for a DC brushless motor. The brushless DC motor includes a three-phase full-bridge inverter circuit, and the current detection and over-current protection circuit includes: a current sampling unit configured to collect a sampling voltage corresponding to the current of the three-phase full-bridge inverter circuit. , and set the bias voltage according to the power of the three-phase full-bridge inverter circuit, apply the bias voltage to the sampling voltage to generate a bias sampling voltage, and amplify the bias sampling voltage to generating an amplified sampling voltage; and an overcurrent protection unit configured to compare the amplified sampling voltage with a predetermined threshold to determine whether the current of the three-phase full-bridge inverter circuit is overcurrent.

Description

Current sensing and overcurrent protection circuit for brushless DC motors

The present invention relates to the field of circuits, and in particular, to a current detection and overcurrent protection circuit for a brushless DC motor.

Brushless DC motors are becoming more and more widely used due to their high efficiency and large starting torque. Generally, the brushless DC motor includes a brushless DC motor (BLDC) whose back electromotive force is a square wave and a permanent magnet synchronous motor (PMSM) whose back electromotive force is a sinusoidal wave.

In order to monitor the working status of the brushless DC motor, its current needs to be detected and overcurrent protection implemented. Usually, peripheral circuits are set up to detect current and provide overcurrent protection. However, this peripheral circuit is usually complex, prone to interference from other signals, and cannot be flexibly applied to different brushless DC motors, resulting in poor detection and overcurrent protection effects.

Therefore, a method that can accurately and flexibly perform current detection and overcurrent protection on brushless DC motors is needed.

According to an exemplary embodiment of the present invention, a current detection and overcurrent protection circuit for a brushless DC motor is provided. The brushless DC motor includes a three-phase full-bridge inverter circuit. The current detection and overcurrent protection circuit It includes: a current sampling unit configured to collect a sampling voltage corresponding to the current of the three-phase full-bridge inverter circuit, and set a bias voltage according to the power of the three-phase full-bridge inverter circuit, and set the bias a voltage is applied to the sampling voltage to generate a bias sampling voltage, and the bias sampling voltage is amplified to generate an amplified sampling voltage; and an overcurrent protection unit configured to compare the amplified sampling voltage with a predetermined threshold Compare to determine whether the current of the three-phase full-bridge inverter circuit is overcurrent.

Current detection for brushless DC motor according to exemplary embodiments of the present invention And the overcurrent protection circuit can set different bias voltages according to different brushless DC motors, and can use the amplified sampling voltage for overcurrent protection, so that the current of the brushless DC motor can be detected more accurately and flexibly, improving With improved anti-interference performance, it can more accurately protect different brushless DC motors from overcurrent.

100: Three-phase full-bridge inverter circuit

201,203,204:Detection circuit

202: Protection circuit

300: Overcurrent protection circuit

310,PGA1,PGA2: current sampling unit

311: Sampling connection unit

312: Bias voltage unit

312-1: Input bias voltage unit

312-2: Output bias voltage unit

313: Amplification unit

320: Overcurrent protection unit

321: Comparison unit

322: Time filter unit

330:Average current unit

331: Second selection unit

331-1, 331-2, 331-3: Sub-selection unit

332: Filter unit

333:Output unit

340: First selection unit

ADC: Analog to Digital Converter

C1,CR: capacitor

CMP: Comparator

GND: base ground

OP0, OP1, OP2: Amplifier

PCB: printed circuit board

PGA: operational amplifier

PGA_AVG_ADC: Average amplified sampling voltage

PGA0: Current sampling unit

PGA0_ADC, PGA1_ADC, PGA2_ADC: amplify the sampling voltage

PGA0_N,PGA0_O,PGA0_P,PGA1_N,PGA1_O,PGA1_P,PGA2_N,PGA2_O,P GA2_P: pin

PWM_FLT: Output comparison signal

PWM_FLT Interrupt: signal

R1,R2,R3,R4,R5,R6,R7,R8,R9,R10,R11,R12,R13,R14,R15,Rfilter: resistors

RC: low pass filter

Rcs0, Rcs1, Rcs2: current sensing resistors

SW, SW1: switch

Vcs, Vcs1, V _OP0 , V _OP1 : voltage

VDD: input bias voltage

Voffset: output offset voltage

The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the drawings, in which: Figure 1 shows a circuit diagram of a current detection and overcurrent protection circuit of a brushless DC motor according to an exemplary embodiment. .

FIG. 2 shows a schematic diagram of voltage signals of the current detection and overcurrent protection circuit of the brushless DC motor of FIG. 1 according to an exemplary embodiment.

3 shows a circuit diagram of a current detection and overcurrent protection circuit of a brushless DC motor according to another exemplary embodiment.

FIG. 4 shows a schematic diagram of voltage signals of the current detection and overcurrent protection circuit of the brushless DC motor of FIG. 3 according to an exemplary embodiment.

5 shows a block diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to an exemplary embodiment of the present invention.

FIG. 6 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to an exemplary embodiment of the present invention.

7 shows a circuit diagram of an average current unit in a current detection and overcurrent protection circuit for a brushless DC motor according to an exemplary embodiment of the present invention.

8 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to another exemplary embodiment of the present invention.

FIG. 9 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to another exemplary embodiment of the present invention.

Features and exemplary embodiments of various aspects of the invention are described in detail below. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the present invention may be practiced without some of these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples of the invention. The present invention is in no way limited to any specific configurations and algorithms set forth below, but covers any modifications, substitutions and improvements of elements, components and algorithms without departing from the spirit of the invention. In the drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the present invention.

FIG. 1 shows a circuit diagram of a current detection and overcurrent protection circuit of a brushless DC motor according to an exemplary embodiment.

As shown in Figure 1, the brushless DC motor usually includes a three-phase full-bridge inverter circuit 100. Usually, the current detection and over-current protection of the brushless DC motor is to detect and detect the current of the three-phase full-bridge inverter circuit 100. Overcurrent protection.

For example, the current of the busbar of the three-phase full-bridge inverter circuit 100 of the brushless DC motor can be detected and overcurrent protected. The current detection and overcurrent protection circuit generally includes a detection circuit 201 and a protection circuit 202. The detection circuit 201 is connected to both ends of the current detection resistor Rcs0 on the bus of the three-phase full-bridge inverter circuit 100 to detect the current of the bus by detecting the voltage Vcs across the current detection resistor Rcs0. In other words, the current information of the three-phase full-bridge inverter circuit 100 can be obtained by detecting the voltage Vcs. In addition, position information of the rotor of a brushless DC motor (for example, a permanent magnet synchronous motor (PMSM)) can also be obtained by detecting the voltage Vcs.

In order to limit the power consumption of the current detection resistor Rcs0, the current detection resistor Rcs0 with a smaller resistance value is usually selected, for example, a resistor in the milliohm or ten milliohm level. Therefore, the voltage Vcs across the current sensing resistor Rcs0 will also be relatively small, usually 0 to several hundred millivolts (mV). In order to easily identify changes in the voltage Vcs, the voltage Vcs usually needs to be amplified. Therefore, the detection circuit 201 generally includes an amplifier OP0 (operational amplifier) and resistors R2 and R4, so that the amplifier OP0 has an amplification gain Gain=(1+R4/R2). Should be reasonable Solution, R2 and R4 in the above equation represent the resistance values of resistors R2 and R4 respectively.

In addition, the signal output by the amplifier OP0 usually needs to be input to an ADC (Analog-to-digital Converter, analog-to-digital converter) for conversion and subsequent processing. The resolution range of the ADC usually starts from a few hundred millivolts, so it needs to change from 0V. The voltage Vcs is biased so that it is within the resolution range of the ADC. Therefore, it is usually necessary to set the bias resistors R3 and R1 and the input bias voltage VDD so that the output bias voltage applied to the voltage Vcs from the node between the resistors R1 and R3 is Voffset=VDD×R1/(R1+ R3). Therefore, the voltage output from amplifier OP0 is V _OP0 =Gain×(Vcs+VDD×R1/(R1+R3)). It should be understood that R1 and R3 in the above equation represent the resistance values of resistors R1 and R3 respectively.

FIG. 2 shows a schematic diagram of voltage signals of the current detection and overcurrent protection circuit of the brushless DC motor of FIG. 1 according to an exemplary embodiment.

FIG. 2 shows the detected voltage Vcs across the current detection resistor Rcs0, the voltage Vcs+Voffset input to the amplifier OP0, and the voltage V _OP0 output from the amplifier OP0. The dashed line in Figure 2 represents a voltage of 0V. As can be seen from Figure 2, after the output bias voltage Voffset is applied, the voltage Vcs+Voffset input to the amplifier OP0 has a voltage value greater than 0V, that is, its amplified minimum voltage value can be located at the minimum resolution of the subsequent ADC. voltage value or above.

In addition, it can be seen from FIG. 2 that the detected voltage signal (and the resulting voltages Vcs+Voffset, V _OP0 ) has a function affected by the switch SW (for example, a semiconductor power device (for example, MOSFET) of the three-phase full-bridge inverter circuit 100 or IGBT)) (the fluctuation part on the left side of the voltage signal in Figure 2).

Referring back to FIG. 1 , the three-phase full-bridge inverter circuit 100 may sometimes experience abnormal operating conditions, resulting in transient overcurrent, for example, when a bridge arm is short-circuited or a motor phase line is short-circuited. However, the maximum normal operating time of the switch SW (eg, power transistor) of the three-phase full-bridge inverter circuit 100 when an overcurrent flows is usually only about 10 milliseconds (ms). Therefore, it is necessary to Overcurrent is detected within the time range and overcurrent protection is performed. For this purpose, a protection circuit 202 as shown in Figure 1 is usually provided.

The protection circuit 202 filters the voltage Vcs across the current sensing resistor Rcs0 through the resistor R5 and the capacitor C1 to reduce the switching noise as shown in FIG. 2, and compares the voltage Vcs with the voltage through the resistor through the comparator CMP. R6 and R7 are compared with the overcurrent threshold (VDD×R7(R6+R7)/Rcs) set by the input bias voltage VDD to output the comparison signal PWM_FLT. When the voltage Vcs is greater than the overcurrent threshold, the comparator CMP flips over for overcurrent protection.

However, the input end of the comparator CMP usually has an offset voltage, and the sampled voltage Vcs is usually relatively small. Therefore, the offset voltage will bring a larger error to the smaller voltage Vcs, resulting in lower accuracy of overcurrent protection.

In addition, after the detection circuit 201 and the protection circuit 202 as shown in FIG. 1 are formed on the PCB (Printed Circuit Board), usually the above input bias voltage, output bias voltage, amplification factor, filter bandwidth, threshold current, etc. Neither of them can be adjusted any more, resulting in that the above detection circuit 201 and protection circuit 202 are only suitable for brushless DC motors of a specific power, and cannot be expanded to other power segments and cannot be flexibly applied to different brushless DC motors. If it needs to be applied to brushless DC motors with other powers, the above resistors and capacitors need to be reconfigured on the PCB, resulting in inflexible application of the detection circuit and protection circuit.

3 shows a circuit diagram of a current detection and overcurrent protection circuit of a brushless DC motor according to another exemplary embodiment.

FIG. 3 shows a situation where it is necessary to simultaneously detect the bus current and the bridge arm current of the three-phase full-bridge inverter circuit 100 and perform overcurrent protection on the three-phase full-bridge inverter circuit 100 .

As shown in Figure 3, on the basis of the circuit shown in Figure 1, current detection resistors Rcs1 and Rcs2 are also provided on the two bridge arms of the three-phase full-bridge inverter circuit 100. detection circuits 203 and 204 on the current detection resistors Rcs1 and Rcs2. The two detection circuits 203 and 204 are the same as the detection circuit 201 shown in FIG. 1 and will not be described again here.

Different from the current on the bus, the current on the bridge arm has both positive and negative current directions (as shown by the arrows in Figure 3), so both ends of the current sensing resistors Rcs1 and Rcs2 The voltage has both positive and negative voltages relative to the reference ground GND. Therefore, (e.g. in a 5V or 3.3V single voltage operating system) the voltage inputs to amplifiers OP1 and OP2 need to be biased to a positive voltage, for example this can be done by choosing bias resistors R8, R10 with appropriate resistance values , R12 and R14 to achieve.

FIG. 4 shows a schematic diagram of voltage signals of the current detection and overcurrent protection circuit of the brushless DC motor of FIG. 3 according to an exemplary embodiment.

FIG. 4 shows an example of the voltage signal of one bridge arm. It should be understood that the voltage signal of the other bridge arm is the same as shown in FIG. 4 .

As shown in FIG. 4 , the detected voltage Vcs1 across the current detection resistor Rcs1 has a voltage value greater than 0V and a voltage value less than 0V. Both the voltage Vcs1+Voffset input to the amplifier OP1 after the bias and the voltage V _OP1 output from the amplifier OP1 are above 0V. The dashed line in Figure 4 represents a voltage of 0V.

For example, to ensure that the voltage output from the amplifier OP1 has a voltage value greater than 0V and the minimum voltage value is above the minimum resolution voltage value of the subsequent ADC, the output offset voltage Voffset can be set to VDD/2.

However, the circuit shown in Figure 3 still has the above-mentioned shortcomings of the circuit shown in Figure 1. In addition, the circuit shown in Figure 3 is relatively complex and requires 15 resistors on the PCB (the resistors R1- R15) and a capacitor, and requires 11 connection terminals connected to the three-phase full-bridge inverter circuit 100, which requires a large wiring space on the PCB.

In order to at least partially overcome the above drawbacks, embodiments of the present invention provide the following current detection and overcurrent protection circuit for a brushless DC motor.

FIG. 5 shows a block diagram of a current detection and overcurrent protection circuit 300 for a brushless DC motor according to an exemplary embodiment of the present invention.

As shown in FIG. 5 , the brushless DC motor may be any type of brushless DC motor including the three-phase full-bridge inverter circuit 100 as shown in FIG. 1 or 3 above. For example, a DC brushless motor whose back electromotive force is a square wave. Brush motor (BLDC) or permanent magnet synchronous motor (PMSM) with sinusoidal back electromotive force.

In one embodiment, the current detection and overcurrent protection circuit 300 according to the embodiment of the present invention may be a Field Oriented Control (FOC) integrated in a control chip of a DC brushless motor (eg, CUP, PMSM). chips or other control chips). Furthermore, the current detection and overcurrent protection circuit 300 according to the exemplary embodiment of the present invention may also be formed as a separate module.

The current detection and overcurrent protection circuit 300 includes: a current sampling unit 310 and an overcurrent protection unit 320.

The current sampling unit 310 is configured to collect a sampling voltage corresponding to the current of the three-phase full-bridge inverter circuit 100, set a bias voltage according to the power of the three-phase full-bridge inverter circuit 100, and apply the bias voltage to the sampling voltage to Generate a bias sampling voltage, and amplify the bias sampling voltage to generate an amplified sampling voltage.

In one embodiment, the current of the above-mentioned three-phase full-bridge inverter circuit 100 can be the current on the bus of the three-phase full-bridge inverter circuit 100. For example, on the bus of the three-phase full-bridge inverter circuit, it is only necessary to detect In the case of current. In addition, it should be understood that the above-mentioned current may also be the current on the bridge arm of the three-phase full-bridge inverter current, as described below.

The overcurrent protection unit 320 is configured to compare the amplified sampling voltage with a predetermined threshold to determine whether the current of the three-phase full-bridge inverter circuit 100 is overcurrent.

By setting the bias voltage according to the power of the three-phase full-bridge inverter circuit, the current detection and overcurrent protection circuit for the brushless DC motor according to the embodiment of the present invention can be flexibly applied to different three-phase Full-bridge inverter circuit to accurately perform current detection and over-current protection on different brushless DC motors.

Referring to FIGS. 5 and 6 , FIG. 6 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to an exemplary embodiment of the present invention.

In one embodiment, the current sampling unit 310 may be regarded as a programmable amplification operational amplifier (PGA, for example, PGA0 shown in FIG. 6 ), and may include: a sampling connection unit 311 , a bias voltage unit 312 and amplification unit 313.

The sampling connection unit 311 may be configured to be connected to a three-phase full-bridge inverter circuit 100 across the current sampling resistor (for example, the current sense resistor Rcs0 on the bus) to collect the sampling voltage (for example, Vcs).

The sampling connection unit 311 may be a pin at both ends of the current detection resistor connected to the three-phase full-bridge inverter circuit 100 on the control chip in which the current detection and overcurrent protection circuit 300 is integrated, for example, as shown in FIG. 6 Pins PGA0_P and PGA0_N are shown.

The bias voltage unit 312 may be configured to set the bias voltage according to the power of the three-phase full-bridge inverter circuit 100 and the resistance value of the current sampling resistor, and apply the bias voltage to the sampling voltage to generate the bias sampling voltage.

In one embodiment, the bias voltage unit 312 may include an input bias voltage unit 312-1 and an output bias voltage unit 312-2.

The input bias voltage unit 312-1 may be configured to generate an input bias voltage (eg, VDD) according to the power of the three-phase full-bridge inverter circuit and the resistance value of the current sampling resistor.

For example, the switch in the input bias voltage unit 312-1 as shown in FIG. 6 can be controlled to be turned on or off to control the turn on or off of the corresponding power source (eg, current source or voltage source). Generate input bias voltages corresponding to the resistance values of the power and current sampling resistors of the full-bridge inverter circuit.

The output bias voltage unit 312-2 may be configured to generate an offset sampling voltage (Voffset) according to the input bias voltage and the sampling voltage.

For example, the variable resistor in the output bias voltage unit 312-2 schematically shown in FIG. 6 may correspond to a plurality of switches in an actual integrated circuit, and the turning on or off of the plurality of switches may be controlled. to set the corresponding resistor value to generate the corresponding bias sampling voltage.

By setting the input bias voltage and bias sampling voltage as above, the current detection and overcurrent protection circuit according to the embodiment of the present invention can be flexibly applied to three-phase full-bridge inverter circuits with different powers, as well as the same three-phase Detection and overcurrent protection of busbar and arm currents in full-bridge inverter circuits (for example, the situations shown in Figures 1 and 3).

The amplification unit 313 may be configured to amplify the bias sampling voltage according to the power of the three-phase full-bridge inverter circuit 100 and the resistance value of the current sampling resistor to generate an amplified sampling voltage (eg, V _OP0 ).

For example, the variable resistor in the amplification unit 313 schematically shown in FIG. 6 may correspond to multiple switches in an actual integrated circuit, and the multiple switches may be controlled to be turned on or off to set the corresponding resistance. value, thereby generating a corresponding amplification factor, and then generating a corresponding amplified sampling voltage through the amplifier OP0 in the amplifying unit 313 .

By adjusting the amplification factor of the amplification unit 313 as described above, the current detection and overcurrent protection circuit according to the embodiment of the present invention can be further flexibly applied to a three-phase full bridge with current sampling resistors of different powers and different resistance values. The inverter circuit further improves the accuracy of current sampling and subsequent overcurrent protection.

In one embodiment, the overcurrent protection unit 320 may include: a comparison unit 321 and a time filtering unit 322.

The comparison unit 321 may be configured to set a predetermined threshold according to the power of the three-phase full-bridge inverter circuit 100 and compare the amplified sampling voltage with the predetermined threshold to generate a comparison signal.

For example, the threshold voltage input to the comparator CMP in the comparison unit 321 shown in FIG. 6 may be set according to the detected power of the three-phase full-bridge inverter circuit 100 .

By setting different threshold voltages according to the power of different three-phase full-bridge inverter circuits, the current detection and over-current protection circuits according to embodiments of the present invention can be further flexibly applied to three-phase full-bridge inverters with different powers. Change the circuit.

In addition, the comparison unit 321 shown in FIG. 6 receives the amplified sampling voltage from the current sampling unit 310. Therefore, there is no need to set a pin for the comparison unit 321 in the control chip in which the current detection and overcurrent protection circuit is integrated. pins, saving chip pin resources.

The time filtering unit 322 may be configured to set the filtering time according to the switching performance and overcurrent performance of the power transistor in the three-phase full-bridge inverter circuit 100 (for example, SW shown in FIG. 1, FIG. 3, and FIG. 5), And the comparison signal is filtered within the filtering time, so as to determine whether the current of the three-phase full-bridge inverter circuit 100 is overcurrent through the filtered comparison signal.

In one embodiment, the switching performance can be the switching time of the power transistor (for example, usually 1us-2us), and the overcurrent performance can be the maximum normal working time of the power transistor when overcurrent flows (for example, 10us in the above example).

For example, the filtering time can be set to be greater than 2us and less than 10us to eliminate the influence of switching noise in the voltage signal (for example, the fluctuation part on the left side of the voltage signal in Figures 2 and 4). It should be understood that the time filtering unit 322 can set different filtering times according to the switching performance and overcurrent capability of the power transistors used in different three-phase full-bridge inverter circuits.

Therefore, errors caused by the influence of switching noise on the signal output by the over-current protection unit (for example, PWM_FLT Interrupt) can be flexibly and accurately avoided, so that over-current protection can be performed more accurately.

In addition, since the input signal of the comparator CMP input to the comparison unit 321 is an amplified voltage signal (for example, V _OP0 ), and the amplified voltage signal is usually tens or even several times the voltage across the detected current detection resistor, Hundred times, so the relative impact of the offset voltage at the input end of the comparator on the input signal will be greatly reduced, thereby further improving the accuracy of over-current protection.

Furthermore, in one embodiment, in order to output the detected current of the three-phase full-bridge inverter circuit, the current detection and overcurrent protection circuit 300 according to the embodiment of the present invention may further include: an average current unit 330. The average current unit 330 may be configured to perform low-pass filtering on the amplified sampling voltage to generate an average amplified sampling voltage corresponding to the average current of the three-phase full-bridge inverter circuit 100 .

FIG. 7 shows a circuit diagram of the average current unit 330 in the current detection and overcurrent protection circuit 300 for a brushless DC motor according to an exemplary embodiment of the present invention.

As shown in Figure 7, one end of the average current unit 330 may be connected to the node PGA between the current sampling unit 310 and the overcurrent protection unit 320 in the current detection and overcurrent protection circuit 300 shown in Figure 6, and the other end One end can be set to the pin PGA0_O in the control chip in which the current detection and overcurrent protection circuit 300 is integrated.

The average current unit 330 may include a resistor Rfilter, and the resistor and the capacitor CR at the pin PGA0_O may form an RC low-pass filter, thereby performing low-pass filtering on the amplified sampling voltage at the node PGA to generate a three-phase full-bridge inverse The average amplified sampling voltage PGA_AVG_ADC corresponding to the average current of the variable circuit. In this case, the bandwidth of the low-pass filter can be set by adjusting the capacitance value of the capacitor CR at the pin PGA0_O to adapt to the currents of different three-phase full-bridge inverter circuits and to adapt to different brushless DC motors. .

8 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to another exemplary embodiment of the present invention.

In order to conveniently and flexibly sample the current on the bus and the current on the bridge arm of the three-phase full-bridge inverter circuit 100, in one embodiment, the current detection and overcurrent protection circuit 300 according to the embodiment of the present invention may include Three current sampling units 310 (PGA0, PGA1 and PGA2 in Figure 8). Each current sampling unit 310 may be configured to be connected to both ends of a bus current sampling resistor (eg, the current sensing resistor Rcs0 in FIG. 5 ) on the bus of the three-phase full-bridge inverter circuit 100, or to a three-phase full-bridge inverter circuit 100. Two ends of the bridge arm current sampling resistor (for example, the current sensing resistor Rcs1 or Rcs2 in Figure 5) on one of the three bridge arms of the phase full-bridge inverter circuit.

For example, in one embodiment, one of the three current sampling units 310 may be connected to both ends of the bus current sampling resistor (for example, PGA0 in Figure 8 is connected to the Figure 8 through pin PGA0_P and pin PGA0_N). 5), the other two current sampling units 310 of the three current sampling units may be connected to the bridge arm current sampling on the two bridge arms of the three-phase full-bridge inverter circuit 100 respectively. Both ends of the resistor (PGA1 in Figure 8 are connected to both ends of the current sensing resistor Rcs1 in Figure 5 through pins PGA1_P and PGA1_N, PGA2 in Figure 8 is connected to the current sense resistor Rcs1 in Figure 5 through pins PGA2_P and PGA2_N across the sense resistor Rcs2).

In this case, in order to perform overcurrent protection on the three-phase full-bridge inverter circuit 100 through the above-mentioned overcurrent protection unit 320, in one embodiment, the overcurrent protection circuit 300 according to the embodiment of the present invention may also include: First selection unit 340.

The first selection unit 340 may be configured to input the amplified sampling voltage generated by the current sampling unit (for example, PGA0 in FIG. 8 ) connected to both ends of the bus current sampling resistor among the three current sampling units to the overcurrent protection unit 320 , for overcurrent protection.

In this case, in one embodiment, the above-mentioned average current unit 330 may include: a second selection unit 331, a filtering unit 332, and an output unit 333.

The second selection unit 331 may include three sub-selection units 331-1, 331-2 and 331-3 respectively corresponding to the three current sampling units.

Each sub-selection unit may be configured to output the amplified sampling voltage generated by the corresponding current sampling unit (eg, PGA0_ADC, PGA1_ADC, and PGA2_ADC shown in FIG. 8) to the output unit 333 (eg, the pins shown in FIG. 8). pins PGA0_O, PGA1_O and PGA2_O) for output, or allow the amplified sampling voltage generated by the corresponding current sampling unit to pass through the filtering unit (for example, a low-pass filter formed by the resistor Rfilter and the capacitor at the corresponding pin) for low pass Filtered to generate the average amplified sample voltage PGA_AVG_ADC for output through the output unit.

For example, as shown in Figure 8, when the amplified sampling voltage generated by the corresponding current sampling unit needs to be directly output to the output unit for output, the switch SW1 can be turned off so that the amplified sampling voltage is not low-pass filtered. When it is necessary to low-pass filter the amplified sampling voltage generated by the corresponding current sampling unit to generate an average amplified sampling voltage, the switch SW1 can be turned on to form a low-pass filter composed of the resistor Rfilter and the capacitor at the pin. To perform low-pass filtering on the amplified sampling voltage.

In one embodiment, among the three sub-selection units, the sub-selection unit corresponding to the current sampling unit connected to the bus current sampling resistor (for example, sub-selection unit 331-1 in FIG. 8) makes the corresponding current sampling unit ( For example, the amplified sampling voltage generated by PGA0 in Figure 8 (e.g., PGA0_ADC in Figure 8) is low-pass filtered by the filter unit to generate an average amplified output by the output unit (e.g., pin PGA0_O in Figure 8) Sample voltage.

In addition, in some cases, to save current sensing and overcurrent protection circuitry The number of pins integrated in the control chip may not be provided for the output of the average current unit, but only the pins used for the current sampling unit 310, as shown in FIG. 9 .

FIG. 9 shows a schematic circuit diagram of a current detection and overcurrent protection circuit for a brushless DC motor according to another exemplary embodiment of the present invention.

As shown in FIG. 9 , the current detection and overcurrent protection circuit for the brushless DC motor may only have pins PGA0_P, PGA0_N, PGA1_P, PGA1_N, PGA2_P, and PGA2_N corresponding to the three current sampling units 310 . The actual current detection and overcurrent protection circuit may still have an average current unit (not shown in Figure 9) integrated inside the control chip for corresponding monitoring and processing of the detected voltage inside the control chip.

According to the current detection and overcurrent protection circuit for a brushless DC motor according to an exemplary embodiment of the present invention, different bias voltages can be set according to different brushless DC motors, and an amplified sampling voltage can be used for overcurrent protection, so that the current of the brushless DC motor can be detected more accurately and flexibly, the anti-interference performance is improved, and the overcurrent protection of different brushless DC motors can be more accurately performed.

The present invention may be implemented in other specific forms without departing from its spirit and essential characteristics. For example, algorithms described in specific embodiments may be modified without departing from the basic spirit of the invention. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being defined by the appended claims rather than the foregoing description, and the meanings and equivalents falling within the claims. All changes within the scope are therefore included in the scope of the invention.

100: Three-phase full-bridge inverter circuit

300: Overcurrent protection circuit

310: Current sampling unit

311: Sampling connection unit

312: Bias voltage unit

313: Amplification unit

320: Overcurrent protection unit

Rcs0, Rcs1, Rcs2: current sensing resistors

SW: switch

Vcs1: voltage

Claims (11)

A current detection and overcurrent protection circuit for a brushless DC motor. The brushless DC motor includes a three-phase full-bridge inverter circuit. The current detection and overcurrent protection circuit includes: three current sampling units configured In order to collect the sampling voltage corresponding to the current of the three-phase full-bridge inverter circuit and set the bias voltage according to the power of the three-phase full-bridge inverter circuit, the bias voltage is applied to the sampling voltage to Generate a bias sampling voltage and amplify the bias sampling voltage to generate an amplified sampling voltage, and one of the three current sampling units is connected to both ends of the bus current sampling resistor, The other two current sampling units among the three current sampling units are respectively connected to both ends of the bridge arm current sampling resistors on the two bridge arms of the three-phase full-bridge inverter circuit; and the overcurrent protection unit, Configured to compare the amplified sampling voltage with a predetermined threshold to determine whether the current of the three-phase full-bridge inverter circuit is overcurrent. The current detection and overcurrent protection circuit of claim 1, wherein the current sampling unit includes: a sampling connection unit configured to be connected to both ends of the current sampling resistor of the three-phase full-bridge inverter circuit. , to collect the sampling voltage; a bias voltage unit configured to set the bias voltage according to the power of the three-phase full-bridge inverter circuit and the resistance value of the current sampling resistor, and set the bias voltage a setting voltage is applied to the sampling voltage to generate a bias sampling voltage; and an amplification unit configured to sample the bias according to the power of the three-phase full-bridge inverter circuit and the resistance value of the current sampling resistor. The voltage is amplified to generate the amplified sampling voltage. The current detection and overcurrent protection circuit of claim 2, wherein the bias voltage unit includes: an input bias voltage unit configured to operate according to the power of the three-phase full-bridge inverter circuit and The resistance value of the current sampling resistor generates an input bias voltage; and the output bias voltage unit is configured to generate the bias sampling voltage according to the input bias voltage and the sampling voltage. The current detection and overcurrent protection circuit of claim 1, wherein the overcurrent protection unit includes: a comparison unit configured to set the predetermined threshold according to the power of the three-phase full-bridge inverter circuit, and Comparing the amplified sampling voltage with the predetermined threshold to generate a comparison signal; and a time filtering unit configured to set filtering according to the switching performance and overcurrent performance of the power transistor in the three-phase full-bridge inverter circuit time, and filter the comparison signal within the filtering time to determine whether the current of the three-phase full-bridge inverter circuit is overcurrent through the filtered comparison signal. The current detection and overcurrent protection circuit as claimed in claim 4, wherein the switching performance is the switching time of the power transistor, and the overcurrent performance is when an overcurrent flows through the power transistor. maximum normal working hours. The current detection and overcurrent protection circuit according to any one of claims 1 to 5, wherein the current is the current on the bus of the three-phase full-bridge inverter circuit. The current detection and overcurrent protection circuit of claim 2, wherein the current detection and overcurrent protection circuit further includes: an average current unit configured to perform low-pass filtering on the amplified sampling voltage to generate a The average current of the three-phase full-bridge inverter circuit corresponds to the average amplified sampling voltage. The current detection and overcurrent protection circuit of claim 1, wherein the current protection circuit further includes: a first selection unit configured to connect one of the three current sampling units to the bus current sampling resistor. The amplified sampling voltage generated by the current sampling unit at both ends of the device is input to the overcurrent protection unit. The current detection and overcurrent protection circuit as described in claim 8, wherein the The average current unit includes: a second selection unit, a filter unit and an output unit, wherein the second selection unit includes three sub-selection units respectively corresponding to the three current sampling units, wherein each sub-selection unit is configured to The amplified sampling voltage generated by the corresponding current sampling unit is output to the output unit for output, or the amplified sampling voltage generated by the corresponding current sampling unit is low-pass filtered by the filtering unit to generate output through the output unit. of the average amplified sampling voltage. The current detection and overcurrent protection circuit of claim 9, wherein among the three sub-selection units, the sub-selection unit corresponding to the current sampling unit connected to the bus current sampling resistor causes the corresponding current sampling unit to The generated amplified sampling voltage is low-pass filtered by the filter unit to generate the average amplified sampling voltage output by the output unit. The current detection and overcurrent protection circuit as described in any one of claims 1-5 and 7-10, wherein the current detection and overcurrent protection circuit is integrated in the control chip of the brushless DC motor. integrated circuits.

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