CN112968635A

CN112968635A - Switch tube protection circuit in inductive load follow current process

Info

Publication number: CN112968635A
Application number: CN201911199132.0A
Authority: CN
Inventors: 张长洪; 张海冰
Original assignee: SG Micro Beijing Co Ltd
Current assignee: SG Micro Beijing Co Ltd
Priority date: 2019-11-29
Filing date: 2019-11-29
Publication date: 2021-06-15

Abstract

A switch tube protection circuit in inductive load follow current process comprises an inductive load and an inductive load driving circuit, wherein the inductive load driving circuit comprises a switch tube and a negative current sampling unit arranged between the switch tube and the inductive load, the negative current sampling unit feeds back to a switch tube control unit when detecting that a negative current exists between the switch tube and the inductive load, the switch tube control unit starts the switch tube to enable the negative current to follow current through a low-impedance switch tube of the switch tube, the current cannot flow in a corresponding body diode, and therefore parasitic triodes of the switch tube cannot conduct electric leakage, and parasitic triodes of the switch tube are prevented from being burnt; eliminating the leakage phenomenon of parasitic triode caused by negative pressure; and when the negative current sampling unit detects that the negative current is 0A, the switch tube control unit closes the switch tube. The current feedback efficiency is improved; and since no body diode is needed to participate in the follow current, the electromagnetic interference phenomenon can be greatly improved.

Description

Switch tube protection circuit in inductive load follow current process

Technical Field

The invention relates to a switch tube protection technology, in particular to a switch tube protection circuit in an inductive load follow current process.

Background

The system of the direct current brush motor has low cost, simple control, very high starting torque and wide application, and can be driven by direct current or alternating current. When the motor needs to rotate in two directions, an H-bridge circuit composed of 4 power elements is generally adopted as a driving circuit. In the H bridge, the switch tube on one opposite side is turned on to generate forward current to make the motor rotate forward, and if the switch tube on the other opposite side is turned on, the switch tube on the other opposite side is turned on to generate reverse current to make the motor rotate reversely. When the high side and the low side on the same side of the H bridge are both OFF, the output is in a high impedance state. When the high side of one side is ON and the low side is OFF, the output is active high. When the high side of one side is OFF and the low side is ON, the output is active low. The H-bridge does not absolutely allow the high side and the low side of the same side to be opened simultaneously, which is called shoot through, and may cause the switch tube to be burned out.

As shown in fig. 1, which is an equivalent diagram of an H-bridge driving dc brush motor, if the MOS switches on one side, such as the second high-side MOS switch M2 and the third low-side MOS switch M3, are turned on, and the MOS switches on the other side, such as the first high-side MOS switch M1 and the fourth low-side MOS switch M4, are turned off, the motor operating current I is set_loadFrom point B to point a, the motor rotates. At this time, if the H-bridge is turned into a high-impedance state, that is, all the switching tubes are turned off, due to the existence of the motor winding coil inductance L, the motor current Iload freewheels through the first body diode D1 and the fourth body diode D4, that is, current energy is fed back to VDD, and the first body diode D1 and the fourth body diode D4 are forward-conducted, so that the parasitic triodes of the first high-side MOS switching tube M1 and the fourth low-side MOS switching tube M4 are conducted, as shown in fig. 2 and fig. 3, the parasitic triodes of the first high-side MOS switching tube M1 and the fourth low-side MOS switching tube M4 are conducted schematically. In particular, the (drain voltage) VEC of the parasitic PNP triode on the high side is VDD + VD1 if the motor current I is present at that time_loadIf the power loss exceeds a certain level, the generated thermal effect will be concentrated and the switching tube will be burned out instantly. Due to the fact thatThe motor current Iload freewheels, a parasitic triode of the fourth low-side MOS switch tube M4 is turned on (as shown in fig. 3), the potential of the B end of the output stage at this time is negative pressure, and negative pressure appears at the drain end of the N-type device at the low side, so that the B end of the output stage and the N-type devices around the B end of the output stage together form a parasitic NPN triode (as shown in fig. 4), the collector of the parasitic NPN triode is a surrounding N-type device (N +) of the B end of the output stage, the base of the parasitic NPN triode is a GND end, and the emitter of the parasitic NPN triode is a B, which is also turned on, causing the N-type device around the B end of the output stage to leak electricity to the B; in the whole chip, the area of an output stage is the largest, if the negative voltage is not processed, the negative voltage has great influence on surrounding devices, particularly, in order to pursue low power consumption, the branch current of an H bridge is smaller and smaller (nA stage), the branch is slightly leaked, and the chip cannot normally work. Moreover, the fast switching of the two states of the body diode, i.e., reverse cut-off and forward conduction, can cause serious electromagnetic interference (EMI) problems.

Disclosure of Invention

In order to solve the above problems, the present invention provides a protection circuit for a switching tube during inductive load freewheeling, which can avoid the burning of the switching tube due to freewheeling, eliminate the leakage of an N-type device caused by negative voltage, improve the current feedback efficiency, and improve the electromagnetic interference phenomenon.

The invention is realized by the following technical scheme:

a switch tube protection circuit in inductive load follow current process comprises an inductive load and an inductive load driving circuit, wherein the inductive load driving circuit comprises an MOS switch tube and a negative current sampling unit arranged between the MOS switch tube and the inductive load, the negative current sampling unit feeds back to a switch tube control unit when detecting that a negative current exists between the MOS switch tube and the inductive load, the switch tube control unit enables the MOS switch tube to be opened, and the inductive load continuously flows through the switch tube and feeds back to a power supply voltage end so as to avoid burning of the MOS switch tube; when the negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the MOS switch tube to be closed.

Preferably, the inductive load driving circuit is an H-bridge driving circuit, the H-bridge driving circuit includes a first intermediate node formed by a first high-side MOS switch tube and a third low-side MOS switch tube, and a second intermediate node formed by the second high-side MOS switch tube and the fourth low-side MOS switch tube, one end of the inductive load is connected with a first middle node, the other end of the inductive load is connected with a second middle node, a first negative current sampling unit is arranged between the first middle node and the first high-side MOS switch tube, the first negative current sampling unit feeds back to the switch tube control unit when detecting that a negative current exists between the first high-side MOS switch tube and the inductive load, the switch tube control unit enables the first high-side MOS switch tube to be opened, and the inductive load follow current is fed back to a power supply voltage end through the first high-side MOS switch tube so as to avoid the first high-side MOS switch tube from being burnt; when the first negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the first high-side MOS switch tube to be closed.

Preferably, a second negative current sampling unit is arranged between the second middle node and the second high-side MOS switch tube, the second negative current sampling unit feeds back a switch tube control unit when detecting that a negative current exists between the second high-side MOS switch tube and the inductive load, the switch tube control unit turns on the second high-side MOS switch tube, and the inductive load continuously flows through the second high-side MOS switch tube and is fed back to a power supply voltage end, so as to avoid burning of the second high-side MOS switch tube; when the second negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the second high-side MOS switch tube to be closed.

Preferably, a third negative current sampling unit is arranged between the first middle node and the third low-side MOS switch tube, the third negative current sampling unit feeds back a negative current between the third low-side MOS switch tube and the inductive load to the switch tube control unit when detecting that the negative current exists between the third low-side MOS switch tube and the inductive load, the switch tube control unit turns on the third low-side MOS switch tube, and the inductive load continuously flows through the third low-side MOS switch tube and is fed back to a power supply voltage end, so that the third low-side MOS switch tube is prevented from being burnt; and when the third negative current sampling unit detects that the negative current is 0A, the switch tube control unit closes the third low-side MOS switch tube.

Preferably, a fourth negative current sampling unit is arranged between the second middle node and the fourth low-side MOS switch tube, the fourth negative current sampling unit feeds back a negative current between the fourth low-side MOS switch tube and the inductive load to the switch tube control unit when detecting that the negative current exists between the fourth low-side MOS switch tube and the inductive load, the switch tube control unit turns on the fourth low-side MOS switch tube, and the inductive load continuously flows through the fourth low-side MOS switch tube and is fed back to a power supply voltage end, so that the fourth low-side MOS switch tube is prevented from being burnt; when the fourth negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the fourth low-side MOS switch tube to be closed.

Preferably, the inductive load comprises a dc brushed motor.

The working current when the switching tube normally works is set as positive current, and the current opposite to the working current is set as negative current.

Compared with the prior art, the invention has the advantages that:

1. according to the switch tube protection circuit in the inductive load follow current process, the negative current sampling unit is arranged between the MOS switch tube and the inductive load to detect the negative current between the MOS switch tube and the inductive load, when the negative current exists, the negative current is fed back to the switch tube control unit, the switch tube control unit starts the MOS switch tube, so that the negative current follows current through the low-impedance switch tube of the switch tube, the current cannot flow in the corresponding body diode, and the parasitic triode of the MOS switch tube cannot conduct electric leakage, so that the MOS switch tube is prevented from being burnt; when the negative current sampling unit detects that the negative current is 0 ampere (A), the MOS switch tube is closed by the switch tube control unit. The switching tube protection circuit in the inductive load follow current process solves the problem that an MOS switching tube device is easy to burn; the phenomenon that the negative voltage causes the electric leakage of a parasitic triode so that the circuit of the electric leakage part has false operation is eliminated; the current feedback efficiency is improved; and since no body diode is needed to participate in the follow current, the electromagnetic interference phenomenon can be greatly improved.

2. According to the switch tube protection circuit in the inductive load follow current process, when an H-bridge drive direct current brush motor runs, MOS switch tubes, especially high-side MOS switch tubes M1 and M2, can be well protected, and the parasitic PNP type triode of the high-side MOS switch tubes is prevented from generating large power loss to burn the MOS switch tubes; eliminating the electric leakage phenomenon of the parasitic triode formed by the peripheral N-type devices at the B end of the output stage and the B end of the output stage caused by negative pressure; the current feedback efficiency in the H-bridge driving process is improved; and since no body diode is needed to participate in the follow current, the electromagnetic interference phenomenon can be greatly improved.

Drawings

FIG. 1 is a schematic circuit diagram of an H-bridge drive DC brushed motor;

fig. 2 is a schematic diagram of the conduction of a parasitic transistor M1 of the first high-side MOS switch of the H-bridge driving dc brushed motor circuit;

fig. 3 is a schematic diagram of the conduction of a parasitic transistor M4 of a fourth low-side MOS switch of the H-bridge driving dc brushed motor circuit;

FIG. 4 is a schematic diagram of the conduction of a parasitic NPN transistor formed by the output stage B terminal and the surrounding N-type devices;

fig. 5 is a schematic diagram of a protection circuit for a switching tube during inductive load freewheeling according to the present invention.

The various reference numbers in the figures are listed below: VDD-supply voltage or supply voltage terminal; GND-ground; i is_load-an operating current; m1-first high side MOS switch tube; m2-second high side MOS switch tube; m3-third low side MOS switch tube; m4-fourth low side MOS switch tube; isen 1-first negative current sampling unit; isen 2-second negative current sampling unit; isen 3-third negative current sampling unit; isen 4-fourth negative current sampling unit; d1 — first body diode; d2 — second body diode; d3 — third body diode; d4 — fourth body diode; L-DC brushAn equivalent inductance of the motor; r-equivalent resistance of the direct current brush motor; a-a first intermediate node; b-a second intermediate node; and a surrounding N-type device at the B end of the N + -output stage.

Detailed Description

In order to facilitate an understanding of the invention, the invention is described in more detail below with reference to the accompanying drawings and specific examples.

A switching tube protection circuit in inductive load follow current process is shown in fig. 5, taking a circuit diagram of an H-bridge driven direct current brush motor as an example, an inductive load driving circuit is an H-bridge driving circuit, and the inductive load is a direct current brush motor. The H-bridge driving circuit comprises a first middle node A formed by a first high-side MOS switch tube M1 and a third low-side MOS switch tube M3, and a second middle node B formed by a second high-side MOS switch tube M3 and a fourth low-side MOS switch tube M4, wherein one end of the inductive load is connected with the first middle node A, and the other end of the inductive load is connected with the second middle node B. In this embodiment, the normal forward working current generally flows from VDD to the high-side (H-side) MOS switch tube, then flows to the inductive load, then flows to the Low-side (Low-side) MOS switch tube, and finally flows to GND, i.e., the current flows from the high potential to the Low potential. The negative current, defined relative to the direction of the positive current, is from GND to the inductive load through the Low-side (Low-side) MOS switch tube and then from the high-side (H-side) MOS switch tube to VDD. Preferably, the first high side MOS switch transistor M1 and the second high side MOS switch transistor M2 are PMOS transistors, and the third high side MOS switch transistor M3 and the fourth high side MOS switch transistor M4 are NMOS transistors. Preferably, the first high-side MOS switch transistor M1 and the second high-side MOS switch transistor M2 may further include NMOS transistors.

A first negative current sampling unit Isen1 is arranged between the first intermediate node a and the first high-side MOS switch tube M1, when the first negative current sampling unit Isen1 detects that a negative current exists between the first high-side MOS switch tube M1 and the inductive load, the negative current is fed back to a switch tube control unit, the switch tube control unit enables the first high-side MOS switch tube M1 to be turned on, and the inductive load follow current is fed back to a power supply voltage end through the first high-side MOS switch tube M1, so that the first high-side MOS switch tube M1 is prevented from being burnt; when the first negative current sampling unit Isen1 detects that the negative current is 0A, the switching tube control unit turns off the first high-side MOS switching tube M1. A second negative current sampling unit Isen2 is arranged between the second intermediate node B and the second high-side MOS switch tube M2, when the second negative current sampling unit Isen2 detects that a negative current exists between the second high-side MOS switch tube M2 and the inductive load, the negative current is fed back to a switch tube control unit, the switch tube control unit enables the second high-side MOS switch tube M2 to be turned on, and the inductive load continuously flows through the second high-side MOS switch tube M2 and is fed back to a power supply voltage end, so that the second high-side MOS switch tube M2 is prevented from being burnt; when the second negative current sampling unit Isen2 detects that the negative current is 0A, the switching tube control unit turns off the second high-side MOS switching tube M2. A third negative current sampling unit Isen3 is arranged between the first intermediate node a and the third low-side MOS switch tube M3, when the third negative current sampling unit Isen3 detects that a negative current exists between the third low-side MOS switch tube M3 and the inductive load, the negative current is fed back to a switch tube control unit, the switch tube control unit enables the third low-side MOS switch tube M3 to be turned on, and the inductive load follow current is fed back to a power supply voltage end through the third low-side MOS switch tube M3, so that the third low-side MOS switch tube M3 is prevented from being burnt; when the third negative current sampling unit Isen3 detects that the negative current is 0A, the switching tube control unit turns off the third low-side MOS switching tube M3. A fourth negative current sampling unit Isen4 is arranged between the second intermediate node B and the fourth low-side MOS switch tube M4, the fourth negative current sampling unit Isen4 feeds back to the switch tube control unit when detecting that a negative current exists between the fourth low-side MOS switch tube M4 and the inductive load, the switch tube control unit enables the fourth low-side MOS switch tube M4 to be turned on, and the inductive load follow current is fed back to a power supply voltage end through the fourth low-side MOS switch tube M4, so that the fourth low-side MOS switch tube M4 is prevented from being burnt; when the fourth negative current sampling unit Isen4 detects that the negative current is 0A, the switching tube control unit turns off the fourth low-side MOS switching tube M4.

When the circuit works, if the second high-side MOS switch tube M2 and the third low-side MOS switch tube M3 are turned on, the first high-side MOS switch tube M1 and the fourth low-side MOS switch tube M4 are turned off, and the motor current I is_loadFrom point B to point a, the motor rotates. At this time, if the H-bridge is put into a high-impedance state, the MOS switch transistors M1, M2, M3, and M4 are turned off, and the motor current I is generated due to the presence of the motor winding coil inductance L_loadAt the moment, current can not flow continuously through the body diodes D1 and D4, but continuously flows to vdd through a low-impedance switching tube passage to feed back current energy, so that the body diodes do not flow current any more, further, parasitic triodes of the switching tube can not conduct electric leakage, the parasitic PNP type triodes of the switching tube are prevented from generating large power loss to burn the switching tube, and the problem that the switching tube is easy to burn is solved; the current feedback efficiency is improved; and since no body diode is needed to participate in the follow current, the electromagnetic interference phenomenon can be greatly improved.

It should be noted that the above-described embodiments may enable those skilled in the art to more fully understand the present invention, but do not limit the present invention in any way. Therefore, although the present invention has been described in detail with reference to the drawings and examples, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention.

Claims

1. A switch tube protection circuit in inductive load follow current process is characterized by comprising an inductive load and an inductive load driving circuit, wherein the inductive load driving circuit comprises an MOS switch tube and a negative current sampling unit arranged between the MOS switch tube and the inductive load, the negative current sampling unit feeds back to a switch tube control unit when detecting that a negative current exists between the MOS switch tube and the inductive load, the switch tube control unit enables the MOS switch tube to be opened, and the inductive load continuously flows through the switch tube and feeds back to a power supply voltage end so as to avoid burning of the MOS switch tube; when the negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the MOS switch tube to be closed.

2. The protection circuit of claim 1, wherein the inductive load driving circuit is an H-bridge driving circuit, the H-bridge driving circuit includes a first middle node formed by a first high-side MOS switch tube and a third low-side MOS switch tube, and a second middle node formed by a second high-side MOS switch tube and a fourth low-side MOS switch tube, one end of the inductive load is connected to the first middle node, the other end of the inductive load is connected to the second middle node, a first negative current sampling unit is disposed between the first middle node and the first high-side MOS switch tube, the first negative current sampling unit feeds back a negative current detected by the first high-side MOS switch tube and the inductive load to a switch tube control unit, and the switch tube control unit turns on the first high-side MOS switch tube, the inductive load current is fed back to a power supply voltage end through the first high-side MOS switch tube so as to avoid the first high-side MOS switch tube from being burnt; when the first negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the first high-side MOS switch tube to be closed.

3. The switch tube protection circuit in inductive load freewheeling process of claim 2, wherein a second negative current sampling unit is disposed between the second middle node and the second high-side MOS switch tube, the second negative current sampling unit feeds back to the switch tube control unit when detecting that a negative current exists between the second high-side MOS switch tube and the inductive load, the switch tube control unit turns on the second high-side MOS switch tube, and the inductive load continuously flows through the second high-side MOS switch tube and feeds back to a power supply voltage end to avoid burning of the second high-side MOS switch tube; when the second negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the second high-side MOS switch tube to be closed.

4. The protection circuit of claim 2 or 3, wherein a third negative current sampling unit is disposed between the first middle node and the third low-side MOS switch tube, the third negative current sampling unit feeds back to the switch tube control unit when detecting that a negative current exists between the third low-side MOS switch tube and the inductive load, the switch tube control unit turns on the third low-side MOS switch tube, and the inductive load continues to flow back to the power supply voltage end through the third low-side MOS switch tube, so as to avoid a phenomenon that a negative voltage is generated by the low-side follow current to cause current leakage and a circuit of a leakage part has a false operation; and when the third negative current sampling unit detects that the negative current is 0A, the switch tube control unit closes the third low-side MOS switch tube.

5. The protection circuit of claim 2 or 3, wherein a fourth negative current sampling unit is disposed between the second intermediate node and the fourth low-side MOS switch tube, the fourth negative current sampling unit feeds back to the switch tube control unit when detecting that a negative current exists between the fourth low-side MOS switch tube and the inductive load, the switch tube control unit turns on the fourth low-side MOS switch tube, and the inductive load follow current is fed back to the power voltage end through the fourth low-side MOS switch tube, so as to avoid a phenomenon that a negative voltage is generated by the low-side follow current to cause current leakage and a circuit of a leakage part has a false operation; when the fourth negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the fourth low-side MOS switch tube to be closed.

6. The protection circuit of claim 4, wherein a fourth negative current sampling unit is disposed between the second middle node and the fourth low-side MOS switch tube, the fourth negative current sampling unit feeds back to the switch tube control unit when detecting that a negative current exists between the fourth low-side MOS switch tube and the inductive load, the switch tube control unit turns on the fourth low-side MOS switch tube, and the inductive load follow current is fed back to the power supply voltage end through the fourth low-side MOS switch tube, so as to avoid negative voltage generated by the low-side follow current, which results in current leakage, and false operation of the circuit of the current leakage part; when the fourth negative current sampling unit detects that the negative current is 0A, the switch tube control unit enables the fourth low-side MOS switch tube to be closed.

7. The protection circuit of claim 1, wherein said inductive load comprises a dc brush motor.