Device and method for preventing inductive load driving circuit from being damaged by back electromotive force

Abstract

The present invention discloses a device and method for preventing an inductive load driving circuit from being damaged by back electromotive force. The device includes a logic control module and an H-bridge driving module. Under the control of the logic control module, the H-bridge driving module can have three states: state one: all four switch modules are turned off; state two: the first switch module and the second switch module are turned on and the third switch module and the fourth switch module are turned off; or the first switch module and the second switch module are turned off and the third switch module and the fourth switch module are turned on; state three: the second switch module and the fourth switch module are turned on and the first switch module and the third switch module are turned off. The method includes: when it is necessary to make the H-bridge driving unit change from state two to state one, the H-bridge driving unit is first changed from state two to state three, and then from state three to state one. The present invention can effectively solve the damage of back electromotive force to the chip.

Description

Technical Field

[0001] The present invention relates to electronic circuits, and in particular to a device and method for preventing an inductive load driving circuit from being damaged by back electromotive force. Background Art

[0002] Common inductive loads include relays. The driving part of the relay is a coil with large inductance, and the action is often a short-time pulse. In this way, energy is stored in the inductance of the coil after the relay is actuated. When the relay is completed and the power supply is removed, the energy stored in the coil has no proper release path, and current will be fed back to the chip in the form of reverse voltage. Because the impedance is very high, the reverse electromotive force generated will be very high, which will often exceed the design carrying capacity of the chip and damage the chip.

[0003] Due to the existence of the back electromotive force of the relay, it is necessary to establish a path for energy release. Since the traditional relay is driven in a single phase, a reverse diode can be connected in parallel at the control end. When the reverse electromotive force is generated, the energy will be released through the diode, such as Figure 1 As shown in D1.

[0004] Since magnetic latching relays do not have a holding current, they have a great advantage over traditional relays in terms of energy consumption. However, the opening and closing of magnetic latching relays are achieved by current pulses in different directions given by the control circuit, so its driving circuit is no longer a simple power on and off. Existing magnetic latching relays usually use H-bridge circuits for drive control because they require a bidirectional drive coil, such as Figure 2 The logical correspondence between the two inputs INA and INB and the two outputs OUTA and OUTB of the existing H-bridge circuit is usually as follows: Figure 3 As shown. Among them, Figure 3 The state of high impedance of the middle output corresponds to that all four switches in the H-bridge circuit are in the closed state, and the magnetic latching relay is turned off; Figure 3 The state when the two output ports OUTA and OUTB output "10" and "01" corresponds to the state where the two switches on the same side of the H-bridge circuit are turned on and the two switches on the other side are turned off. At this time, the magnetic latching relay is turned on. However, since the control terminal level alternates between positive and negative, that is, OUTA and OUTB output "01" and "10" alternately, the existing magnetic latching relay drive circuit cannot use a parallel diode to prevent damage by back electromotive force. Summary of the invention

[0005] Purpose of the invention: In order to effectively solve the problem of damage to chips caused by back electromotive force, the present invention provides a device and method for preventing an inductive load driving circuit from being damaged by back electromotive force.

[0006] Technical solution: On the one hand, the present invention discloses a device for preventing an inductive load driving circuit from being damaged by back electromotive force. The device comprises a logic control module and an H-bridge driving module; the H-bridge driving unit comprises four switch modules; the first end of the first switch module and the first end of the third switch module are both connected to a power supply; the second end of the first switch module, the first end of the load and the first end of the second switch module are connected to a first node; the second end of the third switch module, the second end of the load and the first end of the fourth switch module are connected to a second node; the second end of the second switch module and the second end of the fourth switch module are both grounded; the first node and the second node are respectively connected to two input ports of the inductive load; the logic control module comprises two input ports and four output ports; the four output ports are respectively connected to the control ends of the four switch modules; the H-bridge driving module can have three states under the control of the logic control module: state one: all four switch modules are turned off; state two: the first switch module and the second switch module are turned on and the third switch module and the fourth switch module are turned off; or the first switch module and the second switch module are turned off and the third switch module and the fourth switch module are turned on; state three: the second switch module and the fourth switch module are turned on and the first switch module and the third switch module are turned off.

[0007] Furthermore, each of the four switch modules includes a MOS tube and a diode; the source and drain of each MOS tube are electrically connected to the positive and negative electrodes of the corresponding diode respectively, and the gate of each MOS tube is led out as the control terminal of the corresponding switch module.

[0008] Furthermore, the logic control module includes a selector circuit.

[0009] Further, the second end of the second switch module and the second end of the fourth switch module are both grounded via a current limiting resistor connected in series.

[0010] Furthermore, the inductive load includes a magnetic latching relay.

[0011] Further, the four switch modules in the H-bridge driving unit are all turned on in response to a low level; and: when the first input port and the second input port of the logic control module both receive a low level, the second output port and the fourth output port in the logic control module output a low level, and the first output port and the third output port output a high level; when the first input port of the logic control module receives a low level and the second input port receives a high level, the first output port and the second output port in the logic control module output a high level, and the third output port and the fourth output port output a low level; when the first input port of the logic control module receives a high level and the second input port receives a low level, the first output port and the second output port in the logic control module output a low level, and the third output port and the fourth output port output a high level; when the first input port and the second input port of the logic control module both receive a high level, the four output ports of the logic control module all output a high level.

[0012] Furthermore, the above-mentioned device also includes a first signal stabilization module and a second signal stabilization module; the first external input signal is connected to the first input port of the logic control unit via the first signal stabilization module; the second external input signal is connected to the second input port of the logic control module via the second signal stabilization module; the first and second signal stabilization units each include a diode, a resistor and an inverter; in each signal stabilization module, the cathode of the diode, one end of the resistor and one end of the inverter are all connected to the corresponding external input signal, the anode of the diode and the other end of the resistor are both grounded, and the other end of the inverter is connected to the corresponding input port of the logic control module.

[0013] On the other hand, the present invention discloses a method for preventing an inductive load driving circuit from being damaged by back electromotive force by using the above-mentioned device. The method includes: when it is necessary to make the H-bridge driving unit change from state two to state one, the levels of the first input port and the second input port of the logic control module are controlled, so that the H-bridge driving unit first changes from state two to state three, and then changes from state three to state one. Specifically, it includes: changing the input levels of the first input port and the second input port of the logic control module from a "high level-low level" or "low level-high level" combination to a "low level-low level" combination, and then changing from a "low level-low level" combination to a "high level-high level" combination.

[0014] Furthermore, the method also includes that when the H-bridge driving unit needs to be switched from state 2 to state 1, the time for the H-bridge driving unit to be in state 3 is 10 to 100 us.

[0015] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0016] (1) Through improved driving mode and appropriate input control, the flyback electromotive force can be discharged during the driving of the relay, so as to protect the control chip and the main circuit and ensure that the equipment operates normally according to the expected logic;

[0017] (2) Improve the chip's ultimate driving capability, improve system reliability, and reduce protection circuit costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the connection method of a common relay drive circuit and a protection diode;

[0019] Figure 2 This is a schematic diagram of the back electromotive force discharge principle of an existing magnetic latching relay;

[0020] Figure 3 It is a logic diagram of the existing magnetic latching relay back electromotive force discharge protection drive input;

[0021] Figure 4 A schematic diagram of a back electromotive force discharge protection drive input logic of a magnetic latching relay in one embodiment of the present invention;

[0022] Figure 5 A schematic diagram of input signal timing in one embodiment of the present invention;

[0023] Figure 6 FIG. 1 is a schematic diagram of a circuit structure of an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The present invention is described in detail below with reference to the accompanying drawings.

[0025] like Figure 6 The device for preventing the inductive load driving chip from being damaged by back electromotive force in this embodiment includes a logic control module and an H-bridge driving module.

[0026] The H-bridge driving unit includes four switch modules. The first end of the first switch module S1 and the first end of the third switch module S3 are both connected to the power supply; the second end of the first switch module S1, the first end of the load and the first end of the second switch module S2 are connected to the first node OA; the second end of the third switch module S3, the second end of the load and the first end of the fourth switch module S4 are connected to the second node OB; the second end of the second switch module S2 and the second end of the fourth switch module S4 are preferably both grounded via a current limiting resistor R; the first node OA and the second node OB are respectively connected to the two input ports of the load. In other embodiments, the current limiting resistor R can also be omitted depending on the specific situation.

[0027] The load is usually an inductive load, such as a magnetic latching relay. Each of the four switch modules S1 to S4 includes a MOS tube and a diode. The source and drain of each MOS tube are electrically connected to the positive and negative electrodes of the corresponding diode, respectively, and the gate of each MOS tube is led out as the control terminal of the corresponding switch module.

[0028] The logic control module includes two input ports 1A and 1B and four output ports D1 to D4. The four output ports D1 to D4 correspond to and are connected to the control terminals of the four switch modules S1 to S4 one by one.

[0029] like Figure 6 , when the first input port 1A and the second input port 1B of the logic control module both receive a high level (corresponding to logic "1"), the four output ports D1~D4 all output a high level. Correspondingly, the four switch modules S1~S4 of the H-bridge drive unit are all in the off state. At this time, the H-bridge drive unit corresponds to state 1, the first node OA and the second node OB both output a low level, and the magnetic latching relay is closed. At this time, the H-bridge drive unit corresponds to state 1.

[0030] When the first input port 1A of the logic control module receives a high level and the second input port 1B receives a low level (corresponding to logic "0"), the first output port D1 and the second output port D2 both output a low level, and the third output port D3 and the fourth output port D4 both output a high level. Correspondingly, the first switch module S1 and the second switch module S2 of the H-bridge drive unit are turned on, the third switch module S3 and the fourth switch module S4 are turned off, the first node OA outputs a high level, the second node OB outputs a low level, and the magnetic latching relay obtains a forward input voltage. When the first input port 1A of the logic control module receives a low level and the second input port 1B receives a high level, the first output port D1 and the second output port D2 both output a high level, and the third output port D3 and the fourth output port D4 both output a low level. Correspondingly, the first switch module S1 and the second switch module S2 of the H-bridge drive unit are turned off, the third switch module S3 and the fourth switch module S4 are turned on, the first node OA outputs a low level, the second node OB outputs a high level, and the magnetic latching relay obtains a reverse input voltage. In both cases, the H-bridge drive unit corresponds to state two.

[0031] When the first input port 1A and the second input port 1B of the logic control module both receive a low level, the first output port D1 and the third output port D3 output a high level, and the second output port D2 and the fourth output port D4 output a low level. Accordingly, the first switch module S1 and the third switch module S3 of the H-bridge drive unit are turned off, the second switch module S2 and the fourth switch module S4 are turned off, the first node OA outputs a high level, the second node OB outputs a high level, and the magnetic latching relay discharges the back electromotive force through the loop formed by the second switch module and the fourth switch module. At this time, the H-bridge drive unit corresponds to state three.

[0032] The above logic control module can be implemented by a selector circuit. Since the specific circuit device structure and connection relationship in the selector circuit can be implemented by existing design software according to the design requirements of the input and output of the selector circuit, and there are many ways to implement it, no specific limitation is made here, and it is only necessary that the input and output of the selector meet the previously described logical correspondence. Designing a selector circuit according to the existing input and output logical correspondence is a prior art.

[0033] As mentioned before, the back electromotive force occurs when the relay action is completed and the power supply is removed, that is, when the logic level of the two input ports of the logic control unit changes from "10" or "01" to "11" (corresponding to the H-bridge drive unit changing from state 2 to state 1). At this time, the energy in the inductive load coil has no appropriate release path, and current will be fed back to the H-bridge drive unit in the form of reverse voltage.

[0034] In order to prevent the above phenomenon from occurring, when the H-bridge driving unit needs to be changed from state two to state one, the levels of the first input port 1A and the second input port 1B of the logic control module can be controlled so that the H-bridge driving unit first changes from state two to state three, and then changes from state three to state two. Figure 5 The figure shows a state of the input signals of the two input ports of the logic control module during the switching process, wherein the signal input to the first input port 1A changes from high level "1" to low level "0" at the moment before the signal input to the second input port 1B suddenly changes from "0" to "1", and then from "1" to "0", which makes the H-bridge drive unit change from state 2 to state 3 first, and then from state 3 to state 1. Since the second switch unit S2 and the fourth switch unit S4 of the H-bridge drive unit are both in the on state in state 3, and the first switch unit S1 and the third switch unit S3 are both in the off state, the current fed back from the inductive load coil to the H-bridge drive unit can be released in the loop formed by the second switch unit S2 and the fourth switch unit S4 without damaging the devices in the switch unit, thereby achieving the purpose of preventing the inductive load drive circuit from being damaged by the back electromotive force.

[0035] Usually the relay contact action time is about 20ms. In order to ensure the reliable action of the inductive load, the enable signal provided to the logic control unit will generally maintain a pulse of at least 30ms. The discharge period (i.e., the input signal of the first input port 1A and the second input port 1B of the logic control module is "00") only takes 10 to 100us.

[0036] In order to ensure the stability of the signals input to the two input ports of the logic control module, the above-mentioned device also includes a first signal stabilization unit and a second signal stabilization module. Among them, the first external input signal INA is connected to the first input port 1A of the logic control unit via the first signal stabilization unit; the second external input signal INB is connected to the second input port 1B of the logic control unit via the second signal stabilization unit. The first and second signal stabilization units each include a diode, a resistor and an inverter. In each signal stabilization unit, the cathode of the diode, one end of the resistor and one end of the inverter are all connected to the corresponding external input signal, the anode of the diode and the other end of the resistor are grounded, and the other end of the inverter is connected to the corresponding input port of the logic control unit. Due to the presence of the inverter in each signal stabilization unit, the correspondence between the two external input signals INA and INB and the two output signals OUTA and OUTB at the two output ends of the entire device (the two output ends of the entire device are respectively drawn from the first node OA and the second node OB) is as follows: Figure 4 As shown. Figure 3 Compared with the prior art in the present embodiment, when INA and INB are at a high level, OUTA and OUTB are both at a low level, while in the prior art they are in a high impedance state.

[0037] It should be noted that Figure 6 The corresponding relationship between the logic levels of the input port and the output port in the logic control module is only exemplary and can be adjusted in other embodiments as long as the H-bridge driving circuit has the above three states.

Claims

1. A device for preventing an inductive load driving circuit from being damaged by back electromotive force, characterized in that: It comprises a logic control module and an H-bridge driving module; the H-bridge driving module comprises four switch modules; the first end of the first switch module and the first end of the third switch module are both connected to a power supply; the second end of the first switch module, the first end of the load and the first end of the second switch module are connected to a first node; the second end of the third switch module, the second end of the load and the first end of the fourth switch module are connected to a second node; the second end of the second switch module and the second end of the fourth switch module are both grounded; the first node and the second node are respectively connected to two input ports of the inductive load; The logic control module includes two input ports (1A, 1B) and four output ports (D1, D2, D3, D4); the four output ports correspond to the four switch modules one by one and are respectively connected to the control ends of the four switch modules; The H-bridge driving module can have three states under the control of the logic control module: State 1: All four switch modules are turned off; State 2: the first switch module and the second switch module are turned on and the third switch module and the fourth switch module are turned off; or the first switch module and the second switch module are turned off and the third switch module and the fourth switch module are turned on; State three: the second switch module and the fourth switch module are turned on and the first switch module and the third switch module are turned off; The method of converting the H-bridge driving module from state 2 to state 1 is: controlling the input levels of the two input ports (1A, 1B) so that the H-bridge driving module first changes from state 2 to state 3, and then changes from state 3 to state 1; Each of the four switch modules includes a MOS tube and a diode; the source and drain of each MOS tube are electrically connected to the positive electrode and the negative electrode of the corresponding diode respectively, and the gate of each MOS tube is led out as the control terminal of the corresponding switch module; The MOS tubes in the four switch modules in the H-bridge driving module are all turned on in response to the low level; and: When the first input port (1A) and the second input port (1B) of the logic control module both receive a low level, the second output port (D2) and the fourth output port (D4) in the logic control module output a low level, and the first output port (D1) and the third output port (D3) output a high level; When the first input port (1A) of the logic control module receives a low level and the second input port (1B) receives a high level, the first output port (D1) and the second output port (D2) in the logic control module output a high level, and the third output port (D3) and the fourth output port (D4) output a low level; When the first input port (1A) of the logic control module receives a high level and the second input port (1B) receives a low level, the first output port (D1) and the second output port (D2) in the logic control module output a low level, and the third output port (D3) and the fourth output port (D4) output a high level; When the first input port (1A) and the second input port (1B) of the logic control module both receive a high level, the four output ports (D1, D2, D3, D4) of the logic control module all output a high level.

2. The device for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 1, characterized in that: The logic control module includes a selector circuit.

3. The device for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 1, characterized in that: The second end of the second switch module and the second end of the fourth switch module are both grounded via a current limiting resistor connected in series.

4. The device for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 1, characterized in that: The inductive load includes a magnetic latching relay.

5. The device for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 1, characterized in that: It also includes a first signal stabilization module and a second signal stabilization module; the first external input signal is connected to the first input port of the logic control module via the first signal stabilization module; the second external input signal is connected to the second input port of the logic control module via the second signal stabilization module; the first and second signal stabilization units each include a diode, a resistor and an inverter; in each signal stabilization module, the cathode of the diode, one end of the resistor and one end of the inverter are all connected to the corresponding external input signal, the anode of the diode and the other end of the resistor are both grounded, and the other end of the inverter is connected to the corresponding input port of the logic control module.

6. A method for preventing an inductive load driving circuit from being damaged by back electromotive force using the device according to any one of claims 1 to 5, characterized in that: When it is necessary to make the H-bridge driving module change from state two to state one, the input levels of the first input port (1A) and the second input port (1B) of the logic control module are controlled so that the H-bridge driving module first changes from state two to state three, and then changes from state three to state one.

7. The method for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 6, characterized in that: When the H-bridge driving module needs to be switched from the state 2 to the state 1, the time for the H-bridge driving module to be in the state 3 is 10 to 100 us.

8. The method for preventing an inductive load driving circuit from being damaged by back electromotive force according to claim 6, characterized in that: Controlling the input levels of the first input port (1A) and the second input port (1B) of the logic control module so that the H-bridge driving module first changes from state two to state three, and then changes from state three to state one, specifically includes: The input levels of the first input port (1A) and the second input port (1B) of the logic control module are changed from a "high level-low level" or "low level-high level" combination to a "low level-low level" combination, and then from a "low level-low level" combination to a "high level-high level" combination.

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