A freewheeling protection circuit for a DC motor

Abstract

The present invention discloses a freewheeling protection circuit for a DC motor. This invention is used to protect the H-bridge drive power supply VM so that its potential is not raised by the current released from the inductor during fast freewheeling of the motor, thereby avoiding the need to connect a large-area bypass capacitor to the drive power supply VM when the H-bridge is usually used as the drive circuit. The inventive circuit includes an H-bridge drive circuit, an operational amplifier (OP), a shoot-through protection circuit, an operational amplifier reference generation circuit, a digital logic control circuit, and a motor (DCM). The H-bridge drive circuit drives the motor to operate and generates corresponding voltages OUT1 and OUT2 at both ends of the motor; the positive terminal of the operational amplifier samples the voltage of OUT1 or OUT2, the negative terminal samples the reference voltage VREF, and the output of the operational amplifier controls the gate terminal of the low-side power transistor through the processing of the digital logic control circuit, thereby controlling the output voltage of the H-bridge to form a negative feedback loop.

Description

Technical Field

[0001] The present invention relates to the field of integrated circuits, and particularly to a freewheeling protection circuit for a DC motor. Background Art

[0002] Motors can be seen everywhere in our daily life, from large airplanes and cars to cameras and toys that can be seen everywhere. In the consumer electronics market, since most products are powered by batteries, DC motors occupy a significant share in the consumer electronics market. In today's consumer electronics market that pursues miniaturization, it is the general trend to reduce the area of the chip motherboard.

[0003] Traditional DC motor chips using H-bridge drive circuits need to externally connect a large-area bypass capacitor, which greatly increases the motherboard area, obviously not meeting the requirements of today's market.

[0004] The reason for externally connecting a large-area bypass capacitor is that the current released by the motor during freewheeling charges the power supply through the body diode of the power transistor, resulting in an increase in the power supply voltage, and the increase in the power supply voltage may cause irreversible damage to the inside of the chip.

[0005] Therefore, on the premise of being able to control the current decay rate, discharging the current to the ground is a way to eliminate the externally connected capacitor. Summary of the Invention

[0006] The present invention provides a freewheeling protection circuit for a DC motor, which solves the drawback that traditional DC motor chips need to externally connect large-area capacitors, enabling the motherboard area to be greatly reduced and better meeting the requirements of the consumer electronics market.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A freewheeling protection circuit for a DC motor includes an H-bridge drive circuit, an operational amplifier, an anti-shoot-through protection circuit, an operational amplifier reference generation circuit, a digital logic control circuit, and a motor;

[0009] The internal drive circuit of the H-bridge drive circuit is driven by the gate voltages of four NMOS power transistors, and the motor to be driven is connected between the outputs OUT1 and OUT2; the positive input terminal of the operational amplifier samples the OUT1 / OUT2 signal, the negative input terminal samples the reference voltage VREF generated by the operational amplifier reference generation circuit, and the output is connected to the input of the digital logic control circuit. After processing, it is connected to the gate of the NMOS power transistor at the lower end of the corresponding output; the input terminal of the anti-shoot-through protection circuit is the gate signal of the NMOS power transistor, and the output is connected to the enable terminal of the operational amplifier; the input terminal of the operational amplifier reference generation circuit is VM, and the output terminal is the reference voltage required for the negative terminal of the operational amplifier; the digital logic control circuit is connected to the output of the operational amplifier, and after processing, it is connected to the gate of the power transistor at the lower end of the corresponding output; the motor is respectively connected to OUT1 and OUT2, and the motor is arranged between the outputs OUT1 and OUT2.

[0010] Further, when the H-bridge drive circuit is working normally, the diagonal power transistors are turned on to drive the motor to work normally. When the motor needs to enter fast freewheeling, all the power transistors need to be turned off. According to the direction of the fast-decaying current, OUT1 or OUT2 will be pushed to VM plus the voltage value of the conduction voltage drop of the high-side power transistor body diode by the current released by the inductor, thus forming a charging circuit. The current released by the inductor charges the power supply through the body diode of the upper NMOS power transistor and raises the power supply potential. When the H-bridge is in fast freewheeling, the output voltage on one side will be pulled up to a value higher than the power supply voltage by a diode conduction voltage drop. Therefore, only the output voltage needs to be sampled, and after logical processing through the operational amplifier, it is connected to the gate of the NMOS power transistor at the lower end of the corresponding output. The pull-down generated by the output voltage through this NMOS power transistor cancels the pull-up generated by the motor on the output voltage, forming a negative feedback loop to stabilize the output voltage until the freewheeling current on the motor is released.

[0011] In addition to the core feedback loop of this protection circuit, this circuit also has an operational amplifier reference generation circuit, an anti-shoot-through protection circuit, and a digital logic control circuit. The operational amplifier reference generation circuit is responsible for converting VM into a more practical voltage VREF. In fact, directly connecting VM to the negative terminal of the operational amplifier can also complete the function of discharging the motor freewheeling current to the ground, but in this way, the performance of the feedback loop cannot be adjusted. For example, when a faster decay rate is required, VM is too low, and when the heat generation of the NMOS power transistor is to be reduced, VM is too high; thus, it can be seen that in order to meet a wider range of application scenarios, it is necessary to perform a certain conversion on the power supply voltage VM to obtain the reference voltage VREF.

[0012] Further, for the operational amplifier, the positive input terminal samples the OUT signal, and the negative terminal samples VREF. The decay rate of the freewheeling current is proportional to the value of VREF. The upper limit of the VREF value depends on the voltage that turns on the body diode of the upper NMOS power transistor. When VREF is greater than this voltage, the inductor current charges the motor power supply. When the output of the operational amplifier reaches the gate terminal of the power transistor at the lower end corresponding to the output after being processed by the digital logic control circuit, the output is pulled down to form a feedback loop until the freewheeling current on the motor decays to zero.

[0013] Further, to prevent the power transistor from being broken down by the large current of the power supply, the power transistors on the same side of the anti-shoot-through protection circuit and the H-bridge drive circuit cannot be turned on simultaneously. By detecting the gate signal of the high-side NMOS power transistor, when the signal turns off the high-side power transistor, the enable terminal of the operational amplifier is made effective to avoid the feedback loop starting to work when the high-side NMOS power transistor has not been turned off yet.

[0014] Further, the operational amplifier reference voltage generation circuit converts VM into a VREF with adjustable voltage value, which can effectively control the decay rate of the motor freewheeling current, the chip power consumption, and the heat generation of the low-side freewheeling power transistor.

[0015] Further, the low-side power transistor of the digital logic control circuit also receives LS_GATE1 and LS_GATE2 generated by the internal drive circuit of the chip. Through corresponding logic control, when the motor is working normally, the gate of the low-side power transistor only receives the signal from the internal drive circuit, and when the circuit is in fast freewheeling, it only receives the output signal of the operational amplifier.

[0016] The beneficial effects of the present invention are as follows:

[0017] 1. The freewheeling protection circuit for a DC motor of the present invention solves the drawback that traditional DC motor chips need to externally connect large-area capacitors, greatly reducing the main board area and better meeting the requirements of the consumer electronics market.

[0018] 2. The freewheeling protection circuit for a DC motor of the present invention forms a negative feedback loop by using the pull-down of the output voltage generated by the NMOS power transistor to offset the pull-up of the output voltage generated by the motor, making the output voltage stable until the freewheeling current on the motor is released completely.

[0019] 3. The freewheeling protection circuit for a DC motor of the present invention, the digital logic control circuit ensures that the gate voltage signal generated by the digital logic control circuit for the low-side power transistor during normal operation of the motor does not conflict with the gate voltage signal generated by the operational amplifier for the power transistor during fast decay.

[0020] 4. The freewheeling protection circuit of a DC motor according to the present invention has a stable output voltage under the action of feedback until the freewheeling current of the motor is released; the anti-short-circuit protection circuit prevents the NMOS power transistors on the same side of the H-bridge from being turned on simultaneously. The present invention solves the drawback that the traditional H-bridge drive circuit for a DC motor requires a large-area bypass capacitor externally connected to the power supply. Its structure is simple, and the decay rate of the current can be controlled by controlling the magnitude of VREF, which can greatly reduce the area of the chip main board. Brief Description of the Drawings

[0021] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required in the embodiments. It should be understood that the proportional relationships of the various components in the drawings of this specification do not represent the proportional relationships in actual material selection and design. They are merely schematic diagrams of the structure or position, where:

[0022] Figure 1 is a simplified schematic diagram of the operational amplifier reference generation circuit of the present invention;

[0023] Figure 2 is a simplified diagram of the operational amplifier reference generation circuit of the present invention;

[0024] Figure 3 is the working flow chart of the feedback loop of the present invention;

[0025] Figure 4 is the freewheeling protection circuit diagram of the present invention. Detailed Embodiments

[0026] In order to make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further details the present invention in conjunction with the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention, that is, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0027] The following combines Figures 1 to 4 , and details the present invention.

[0028] Embodiment 1

[0029] A freewheeling protection circuit for a DC motor includes an H-bridge drive circuit, an operational amplifier, an anti-short-circuit protection circuit, an operational amplifier reference generation circuit, a digital logic control circuit, and a motor;

[0030] The H-bridge drive circuit drives the internal drive circuit through the gate voltages of four NMOS power transistors, and a driven motor is connected between the outputs OUT1 and OUT2; the positive input terminal of the operational amplifier samples the OUT1 / OUT2 signal, the negative input terminal samples the reference voltage VREF generated by the level shift circuit and the attenuation speed control circuit, and the output is connected to the input of the digital logic control circuit. After processing, it is connected to the gate of the NMOS power transistor at the lower end of the corresponding output; the input terminal of the anti-short-circuit protection circuit is the gate signal of the NMOS power transistor, and the output is connected to the enable terminal of the operational amplifier; the input terminal of the operational amplifier reference generation circuit is VM, and the output terminal is the reference voltage required by the negative terminal of the operational amplifier; the digital logic control circuit is connected to the output of the operational amplifier, and after processing, it is connected to the gate of the power transistor at the lower end of the corresponding output; the motor is respectively connected to OUT1 and OUT2, and the motor is arranged between the outputs OUT1 and OUT2.

[0031] The working principle / working process of the present invention is as follows: As Figure 1 shown, one way of the reference generation circuit is to use a boost-buck circuit to complete. Since there is no load demand for this reference, the boost circuit can be implemented using a cross-coupled charge pump, and the buck circuit can be directly implemented using a simple resistor voltage divider network. Finally, only need to select these two signals according to actual needs to obtain the reference voltage VREF required by the negative terminal of the operational amplifier.

[0032] As Figure 2 shown, another way of the operational amplifier reference generation circuit is to construct an asymmetric operational amplifier, that is, artificially introduce an offset voltage. The polarity of the offset voltage is not marked in the figure, that is, VREF = VM + Vos can be greater than VM or less than VM, and the polarity and magnitude of Vos can be flexibly adjusted according to actual needs.

[0033] Since the power supply range of the DC motor is relatively large, the specific operational amplifier circuit is not shown in this article. Because as the output voltage changes, the structure of the operational amplifier will change greatly. If it is a low-voltage power supply, a common two-stage operational amplifier can complete the process from sampling to output. If it is a high-voltage power supply, it is necessary to increase the common-mode input range of the operational amplifier, and various protection circuits for the comparator are also required. The specific process of the feedback loop is shown in Figure 3 .

[0034] Embodiment 2

[0035] As Figure 3As shown in the figure, this embodiment is optimized on the basis of Embodiment 1. To prevent the power tube from being broken down by the large current of the power supply, the power tubes on the same side of the anti-shoot-through protection circuit and the H-bridge drive circuit cannot be turned on simultaneously. By detecting the gate signal of the high-side NMOS power tube, when the signal turns off the high-side power tube, the enable terminal of the operational amplifier is made effective, avoiding the feedback loop from starting to work when the high-side NMOS power tube has not been turned off yet. The anti-shoot-through protection circuit can control the enable of the operational amplifier, ensuring that there is no situation where the power tubes on the same side are turned on during freewheeling, thus avoiding the device from being broken down by the large current. Usually, the anti-shoot-through protection circuit needs to consider complex factors such as process deviation and temperature. However, it is not necessary to do so when detecting whether the high-side power tube is turned off during the freewheeling stage. Because when the H-bridge enters the freewheeling state, the gate voltage of the high-side power tube will drop rapidly. Therefore, it is only necessary to compare the gate signal of the high-side power tube with its corresponding output signal through a comparator. And due to the margin of the threshold voltage, the input offset voltage and input reference noise of the comparator have no impact on the output.

[0036] The design of the anti-shoot-through protection circuit is the same as that of the operational amplifier, which is greatly affected by the power supply voltage range, but has almost no requirements for the input offset voltage and input reference noise of the comparator.

[0037] The low-side power tube of the digital logic control circuit also receives LS_GATE1 and LS_GATE2 generated by the internal drive circuit of the chip. Through the corresponding logic control, when the motor is working normally, the gate of the low-side power tube only receives the signal of the internal drive circuit, and when the circuit is in fast freewheeling, it only receives the output signal of the operational amplifier. The digital logic control circuit ensures that the gate voltage signal generated by the low-side power tube during the normal operation of the motor will not conflict with the gate voltage signal generated by the operational amplifier when the power tube is in fast decay.

[0038] The design of the digital logic control circuit is not universal because different chips have different internal logic controls. Therefore, the specific circuit is not given in this article. The actual design idea should be able to transmit the signal of the internal drive circuit and the output signal of the operational amplifier to the gate terminal of the low-side NMOS power tube with almost no loss.

[0039] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A flyback protection circuit for a DC motor, characterized in that including an H-bridge drive circuit, an operational amplifier, a shoot-through protection circuit, an operational amplifier reference generation circuit, a digital logic control circuit, and a motor; the H-bridge drive circuit is internally driven by the gate voltages of four NMOS power transistors, and drives the motor connected between the drive output OUT1 terminal and the output OUT2 terminal; the positive input terminal of the operational amplifier samples the signal of the output OUT1 terminal / the output OUT2 terminal, the negative input terminal of the operational amplifier samples the reference voltage VREF generated by the operational amplifier reference generation circuit, and the output terminal of the operational amplifier is connected to the input terminal of the digital logic control circuit. After being processed by the digital logic control circuit, it is connected to the gate of the corresponding output lower-bridge-arm NMOS power transistor; the input terminal of the shoot-through protection circuit inputs the gate signal of the upper-bridge-arm NMOS power transistor, and the output terminal of the shoot-through protection circuit is connected to the enable terminal of the operational amplifier; the input terminal of the operational amplifier reference generation circuit is the drive power supply VM, and the output terminal of the operational amplifier reference generation circuit is the reference voltage VREF required by the negative input terminal of the operational amplifier; the digital logic control circuit is connected to the output terminal of the operational amplifier, and after processing the output signal of the operational amplifier, it is connected to the gate of the corresponding output lower-bridge-arm NMOS power transistor; the motor is respectively connected to the output OUT1 terminal and the output OUT2 terminal, and the motor is arranged between the output OUT1 terminal and the output OUT2 terminal.

2. The freewheeling protection circuit of a DC motor according to claim 1, characterized in that, When the H-bridge drive circuit is working normally, the diagonal NMOS power transistors are turned on to drive the motor to work normally. When it is necessary to make the motor enter fast freewheeling, all the NMOS power transistors need to be turned off. According to the flow direction of the fast-decaying current, the signal of the output OUT1 terminal or the output OUT2 terminal will be pushed by the current released by the inductor to the voltage value of the drive power supply VM plus the conduction voltage drop of the body diode of the upper-bridge-arm NMOS power transistor, thus forming a charging circuit. The current released by the inductor charges the drive power supply VM through the body diode of the upper-bridge-arm NMOS power transistor and raises the power supply potential.

3. The freewheeling protection circuit of a DC motor according to claim 1, characterized in that For the operational amplifier, the positive input terminal samples the signal of the output OUT1 terminal / the output OUT2 terminal, and the negative input terminal samples the reference voltage VREF. The decay rate of the freewheeling current is proportional to the value of the reference voltage VREF. The upper limit of the value of the reference voltage VREF depends on the voltage that makes the body diode of the upper-bridge-arm NMOS power transistor conduct. When the reference voltage VREF is greater than the voltage that makes the body diode of the upper-bridge-arm NMOS power transistor conduct, the inductor current charges the drive power supply VM of the motor. When the output terminal of the operational amplifier reaches the gate of the corresponding output lower-bridge-arm NMOS power transistor after being processed by the digital logic control circuit, the output OUT1 terminal / the output OUT2 terminal is pulled down, forming a feedback loop until the freewheeling current on the motor decays to zero.

4. The freewheeling protection circuit of a DC motor according to claim 3, characterized in that The NMOS power transistors on the same side of the anti-direct connection protection circuit and the H-bridge drive circuit cannot be turned on simultaneously, avoiding the NMOS power transistors from being broken down by the large current of the drive power supply VM. By detecting the gate signal of the upper-bridge-arm NMOS power transistor, when the gate signal of the upper-bridge-arm NMOS power transistor turns off the upper-bridge-arm NMOS power transistor, the enable terminal of the operational amplifier is made effective, avoiding the feedback loop from starting to work when the upper-bridge-arm NMOS power transistor has not been turned off yet.

5. The freewheeling protection circuit of a DC motor according to claim 1, wherein The operational amplifier reference voltage generation circuit converts the drive power supply VM into a reference voltage VREF with an adjustable voltage value, which can effectively control the decay rate of the motor freewheeling current, the chip power consumption, and the heat generation of the lower-bridge-arm freewheeling NMOS power transistor.

6. The freewheeling protection circuit of a DC motor according to claim 1, wherein The lower-bridge-arm NMOS power transistor of the digital logic control circuit also receives the gate signals LS_GATE1 and LS_GATE2 of the lower-bridge-arm NMOS transistor generated by the internal drive circuit of the chip. Through corresponding logic control, when the motor is working normally, the gate of the lower-bridge-arm NMOS power transistor only receives the gate signals LS_GATE1 and LS_GATE2 generated by the internal drive circuit. When the motor enters fast freewheeling, the gate of the lower-bridge-arm NMOS power transistor only receives the output signal of the operational amplifier.

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