A low-cost power supply reverse connection protection circuit

Abstract

The invention discloses a low-cost power reverse connection protection circuit, in which the positive electrode of the power supply in the circuit is connected to the source of Q1 and the anode of D2, the drain of Q1 is connected to the cathode of D2, the anode of D3, one end of R1 and the positive power supply end of a square wave generator, the gate of Q1 is connected to one end of C3 and the cathode of D6; the cathode of D3 is connected to one end of C7 and the anode of D4, the cathode of D4 is connected to the anode of D5 and one end of C4, the cathode of D5 is connected to one end of C6 and the anode of D6, the other end of R1 is connected to the other end of C7, the other end of C6 and the collector of Q2; the negative electrode of the power supply is connected to the other end of C3, the other end of C4, the emitter of Q2, the ground terminal GND and the negative power supply end of the square wave generator. The circuit of the invention has low cost and high reliability, does not rely on MCU and its software program to realize automatic reverse connection protection, and is convenient for industrial mass production and application.

Description

Technical Field

[0001] The invention belongs to the technical field of circuit design of automobile power supplies and relates to a low-cost power reverse connection protection circuit. Background Art

[0002] With the development of the automobile industry, various controllers are used more and more widely in automobiles, and the self-protection function of the controller is getting higher and higher. Anti-reverse power connection is one of the self-protection functions of electronic products. Reverse power connection will cause permanent damage to the controller. Therefore, it is necessary to add a protection circuit to the controller circuit to achieve the purpose of not being damaged even if the power is reversed.

[0003] In the prior art, this can generally be achieved by connecting a diode in series at the positive electrode of the power supply. However, due to the voltage drop of the diode, unnecessary losses will be caused to the circuit, and the operating voltage range of the electronic product will be greatly reduced. Since the MOS voltage drop is small, so small that it can be almost ignored, the industry has begun to use PMOS tubes at the positive electrode of the power supply and NMOS tubes at the negative electrode of the power supply to prevent reverse power protection circuits.

[0004] However, due to the voltage drop of the diode, connecting a diode in series at the positive electrode of the power supply to achieve this will cause unnecessary losses to the circuit and greatly reduce the operating voltage range of the electronic product; since the price of PMOS tubes of the same power is two or three times more expensive than NMOS tubes, using PMOS at the positive electrode of the power supply to achieve this will greatly increase the cost of the entire product; since the negative electrode of many electronic products has many terminals, it is impossible to use an NMOS at the negative electrode to achieve reverse connection protection, and at the same time, the more expensive MCU chip and AD acquisition chip are not used for closed-loop control of the software program.

[0005] For example, the patent application number CN201920818479.8 discloses a vehicle-mounted DC power supply anti-reverse connection protection circuit based on an NMOS tube, which uses an NMOS tube to achieve reverse connection protection at the positive pole. However, according to the invention, Figure 1 As can be seen from the descriptions in paragraphs 24-28 of the specification, the MCU and AD acquisition chip are used to collect the current state. If the difference between the voltage of the bootstrap boost circuit and the on-board DC power supply voltage is greater than a certain threshold (this value is determined according to the specific MOS tube model), the program in the MCU considers that the bootstrap boost circuit is normal and the MOS is reliably turned on. Therefore, the power reverse connection protection of this circuit needs to rely on the more expensive MCU chip, AD conversion device and PWM signal generation module, and the cost is still high. It is also necessary to sinter a special software program into the MCU according to the above control method, which makes the process complicated and the reliability is not high enough, which is not convenient for industrial mass production and application.

[0006] Based on this, it is urgent to design a low-cost power reverse connection protection circuit to overcome the high cost defect of the automotive power reverse connection protection circuit in the prior art and facilitate mass production and application in industry. Summary of the invention

[0007] 1. Technical issues to be resolved

[0008] Based on this, the present invention discloses a low-cost power reverse connection protection circuit. Compared with the prior art, the circuit of the present invention has lower cost and higher reliability, and can realize automatic reverse connection protection without relying on software programs, which is convenient for mass production and application in industry.

[0009] (II) Technical solution

[0010] The present invention discloses a low-cost power reverse connection protection circuit, which includes: an NMOS tube Q1, an NPN transistor Q2, a square wave generator, diodes D2-D6, capacitors C3, C4, C6 and C7, and resistors R1 and R3;

[0011] The positive electrode of the power supply is connected to the source of Q1 and the anode of D2, the drain of Q1 is connected to the cathode of D2, the anode of D3, one end of R1 and the positive power supply end of the square wave generator, and the gate of Q1 is connected to one end of C3 and the cathode of D6;

[0012] The cathode of D3 is connected to one end of C7 and the anode of D4, the cathode of D4 is connected to the anode of D5 and one end of C4, the cathode of D5 is connected to one end of C6 and the anode of D6, and the other end of R1 is connected to the other end of C7, the other end of C6 and the collector of Q2;

[0013] The negative pole of the power supply is connected to the other end of C3, the other end of C4, the emitter of Q2, the ground terminal GND and the negative power supply terminal of the square wave generator. The output end of the square wave generator is connected to one end of R3, and the other end of R3 is connected to the base of Q2.

[0014] Furthermore, the square wave generator is a function generator including an integrated chip MAX038.

[0015] Furthermore, the power reverse connection protection circuit also includes: a bidirectional TVS tube D1 and a capacitor C1, one end of D1 and one end of C1 are connected to the drain of Q1, and the other end of D1 and the other end of C1 are connected to the negative electrode of the power supply.

[0016] Furthermore, the power reverse connection protection circuit also includes a capacitor C2, one end of C2 is connected to the base of Q2, and the other end of C2 is connected to the ground terminal GND.

[0017] Furthermore, the power supply is an on-board DC power supply of an automobile controller.

[0018] Furthermore, the positive voltage of the power supply is 8-20V, and the negative voltage of the power supply is 0V.

[0019] Furthermore, C3, C4, C6 and C7 are all 100nF.

[0020] Furthermore, a body diode is anti-parallel connected between the drain and source of Q1.

[0021] Furthermore, the diode D2 is a unidirectional diode.

[0022] Furthermore, the capacitors C1 and C2 are filter capacitors.

[0023] (III) Beneficial effects

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] (1) Compared with patent CN201920818479.8, the present invention newly designs a voltage boost circuit based on D3~D6, C3~C4, C6~C7 (which is different from the bootstrap boost circuit in the prior art). Through the cooperation of the square wave generator with a fixed switching frequency and the transistor Q2, the voltage in C3 can be increased to twice the voltage in a short time to complete the conduction of Q1 when the power supply is positively connected; when the power supply is incorrectly reversed, the square wave generator cannot realize the corresponding positive and negative pole power supply, so it does not work, so that Q2 is in the cut-off state. In addition, the existence of C3 ensures that the gate voltage of Q1 is 0, so that the NMOS tube is not turned on. At the same time, C4 and D3~D6 also prevent the current from flowing from the positive pole to the negative pole, thereby ensuring from multiple angles that the current cannot flow from the positive pole of the power supply to the negative pole of the power supply, and cannot cause damage to the controller.

[0026] (2) The power reverse connection protection circuit of the present invention uses only one NMOS tube. By cooperating with low-cost circuit devices such as triodes and square wave generators, the reverse connection protection of the DC power supply can be realized by pure hardware, which has lower cost and high reliability and is suitable for industrial-grade mass production and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The features and advantages of the present invention will be more clearly understood by referring to the accompanying drawings, which are schematic and should not be construed as limiting the present invention in any way. In the accompanying drawings:

[0028] Figure 1 The circuit diagram of the low-cost power reverse connection protection circuit in the present invention is shown in FIG.

[0029] Figure 2The schematic diagram of the circuit state when the square wave generator in the power reverse connection protection circuit of the present invention outputs a high level for the first time when the power supply is positively connected.

[0030] Figure 3 The schematic diagram of the circuit state when the square wave generator in the power reverse connection protection circuit of the present invention outputs the first low level when the power supply is positively connected.

[0031] Figure 4 The schematic diagram of the circuit state when the square wave generator in the power reverse connection protection circuit of the present invention outputs a high level for the second time when the power supply is positively connected.

[0032] Figure 5 The diagram is a circuit state diagram of the power reverse connection protection circuit of the present invention when the power is reversely connected. DETAILED DESCRIPTION

[0033] The present invention will be clearly and completely described below in conjunction with the accompanying drawings and embodiments. The technical problems solved by the technical solution of the present invention and the beneficial effects are also described. It should be pointed out that the described embodiments are only intended to facilitate the understanding of the present invention and do not have any limiting effect on it.

[0034] like Figure 1 As shown, it is a circuit schematic diagram of a low-cost power reverse connection protection circuit disclosed in the present invention, and the power reverse connection protection circuit includes: NMOS tube Q1, transistor Q2, square wave generator, diodes D2-D6, capacitors C3, C4, C6 and C7, resistors R1 and R3. Among them, after normal power supply, the square wave generator will automatically generate a square wave waveform with a fixed frequency, which can be a square wave generator including an integrated chip MAX038 or other integrated chips to reduce costs.

[0035] Specifically, the connection relationship of each circuit element is as follows:

[0036] The positive electrode of the power supply is connected to the source of Q1 (i.e., pin 3) and the anode of D2, the drain of Q1 (i.e., pin 2) is connected to the cathode of D2, the anode of D3, one end of R1 and the positive power supply end of the square wave generator, the gate of Q1 (i.e., pin 1) is connected to one end of C3 and the cathode of D6; the cathode of D3 is connected to one end of C7 and the anode of D4, the cathode of D4 is connected to the anode of D5 and one end of C4, the cathode of D5 is connected to one end of C6 and the anode of D6, the other end of R1 is connected to the other end of C7, the other end of C6 and the collector of Q2, the negative electrode of the power supply is connected to the other end of C3, the other end of C4, the emitter of Q2, the ground terminal GND and the negative power supply end of the square wave generator, the output end of the square wave generator is connected to one end of R3, and the other end of R3 is connected to the base of Q2.

[0037] In another embodiment, in order to prevent the circuit from being impacted by transient high-voltage spike pulses, the power reverse connection protection circuit also includes: a bidirectional TVS tube D1 (the bidirectional TVS tube is composed of two unidirectional TVS "back-to-back" combinations, and both the positive and reverse directions have the same avalanche breakdown characteristics and clamping characteristics) and a capacitor C1, one end of D1 and one end of C1 are connected to the drain of Q1, and the other end of D1 and the other end of C1 are connected to the negative electrode of the power supply.

[0038] In another embodiment, in order to ensure the working stability of Q1, the power reverse connection protection circuit further includes a capacitor C2, one end of C2 is connected to the base of Q2, and the other end of C2 is connected to the ground terminal GND.

[0039] In another embodiment, the positive voltage of the power supply is preferably 8-20V, the negative voltage of the power supply is 0V, and the power supply is preferably an on-board DC power supply of an automobile controller; secondly, the specifications of C3, C4, C6 and C7 are the same, and they can all be preferably 100nF; in addition, a body diode can be connected in anti-parallel between the drain and source of Q1 to protect the NMOS tube; the type of the D2 diode is preferably a unidirectional diode (that is, an ordinary diode, not a TVS tube). When connected in the forward direction, before Q1 is turned on, the voltage is supplied to the square wave generator through D2 to make it work, drive the boost circuit, and drive Q1 to turn on. After Q1 is turned on, since the internal resistance of the NMOS tube Q1 is much smaller than the diode D2, the current passes through Q1 and no longer passes through D2, thereby meeting the demand for large current power supply.

[0040] In order to further clarify the working principle and advantages of the low-cost power reverse connection protection circuit of the present invention, the circuit operation state when the power supply is connected forward and reverse is analyzed as follows:

[0041] 1) Power supply forward connection

[0042] When the power supply is connected in the forward direction, NMOS is in the cut-off state at first, and the current passes through diode D2 to provide voltage for the square wave generator. The positive and negative poles of the square wave generator are powered normally, and a square wave signal with a fixed frequency is automatically generated to drive transistor Q2.

[0043] like Figure 2 As shown, when the square wave generator outputs a high level for the first time, Q2 is turned on and grounded, and the power supply voltage charges C7, C4, C6, and C3 through D2, D3, D4, D5, and D6.

[0044] like Figure 3As shown, when the square wave generator outputs a low level for the first time, Q2 is cut off. Since the voltage across the capacitor cannot change suddenly, the voltage on the left side of capacitors C7 and C6 is equal to about twice the power supply voltage, and the voltage on the right side is equal to the power supply voltage (the voltage drop across the capacitor is still equal to the power supply voltage, and the left side is raised to twice the power supply voltage by the voltage of the positive pole of the power supply that passes through R1 but is not grounded). Then, the current continues to charge C4 and C3 through D4 and D6. After charging, the voltage of C4 and C3 also rises to about twice the power supply voltage.

[0045] like Figure 4 As shown, when the square wave generator outputs a high level for the second time, Q2 is turned on and grounded again. Since the voltage across the capacitor cannot change suddenly, at this time, the voltage on the left side of capacitor C6 is the power supply voltage, and the voltage on the right side is 0V (the voltage drop of C6 is still equal to the power supply voltage); when the voltage of C6 is equal to the power supply voltage, since the voltage drop of C4 is 2 times the power supply voltage> the voltage drop of C6, C4 will charge C6, and after charging, C4=C6≈1.5 times the power supply voltage; since D6 is in the cut-off state, C3 cannot charge C6, and the voltage drop of C3 still remains 2 times the power supply voltage;

[0046] At the same time, the voltage on the left side of capacitor C7 is the power supply voltage, and the voltage on the right side is 0V (the voltage drop of C7 is still equal to the power supply voltage); at this time, the voltage of C7 is less than the voltage of C4, but because D4 is in the reverse cut-off state, C4 cannot charge C7, and C4 maintains about 1.5 times the power supply voltage.

[0047] When the square wave generator outputs a low level for the second time (not shown in the figure), C4 is charged to twice the power supply voltage again. When the square wave generator outputs a high level for the third time, twice the power supply voltage of C4> the power supply voltage of C6, C4 charges C6, and C4=C6≈1.75 power supply voltage; after the square wave generator outputs high and low levels several times, the voltage of C4 slowly rises. At the same time, C6 also charges C3, and the voltage of C3 also slowly and steadily rises. According to the simulation results, the voltage of C3 is finally stabilized at about twice the power supply voltage (in the actual circuit, excluding the circuit loss, the voltage of Vout is stabilized at about twice the power supply voltage), which is used to stably drive the NMOS tube Q1 to turn on (the Vgs for conduction actually needs to be above 4V); after the NMOS tube Q1 is turned on, its impedance is only a few mΩ, which is much smaller than the impedance of the diode D1. The current will provide voltage and current to the square wave generator and other loads through Q1, so as to achieve the purpose of reducing the loss of the power supply voltage.

[0048] 2) Reverse power supply

[0049] like Figure 5As shown, when the power supply is connected in reverse, the positive pole of the power supply becomes the negative pole of the power supply, and the negative pole of the power supply becomes the positive pole of the power supply, and the power supply current flows to C1, C2, C3, C4, D1 and the square wave generator. Due to the characteristics of capacitors passing AC and blocking DC, the current cannot flow through C1, C2, C3, and C4; in addition, since D1 is a bidirectional TVS tube, D1 is in a reverse cut-off state; since the grounded negative power supply terminal of the square wave generator is mistakenly connected to the positive pole of the power supply, and there is no power signal at the positive power supply terminal, the square wave generator does not work and cannot send out a square wave to drive Q2; Q2 is cut off, and the current cannot flow through Q2; the voltage of Q1's pin 1 is equal to the voltage of pin 3 connected to the negative pole of the voltage = 0V, and Q1 is cut off; the current cannot flow from the positive pole of the power supply to the negative pole of the power supply, and cannot cause damage to the controller, thereby achieving the purpose of self-protection.

[0050] In summary, the present invention forms a voltage boosting unit through Q2, D2-D6, C3, C4, C6, and C7. The voltage boosting unit cooperates with the square wave generator to quickly increase the voltage to about 2 times the power supply voltage, and provides the driving voltage required for the normal conduction of the NMOS tube; at the same time, some components in the voltage boosting unit also constitute a power reverse protection unit. When the power supply is reversely connected, the positive electrode of the power supply becomes the negative electrode of the power supply, and the negative electrode of the power supply becomes the positive electrode of the power supply. The power supply voltage is isolated by C3, C4, and Q2, and because the square wave generator is not correctly connected to the positive and negative electrodes of the power supply for voltage application, a power supply loop cannot be formed. At this time, the square wave generator does not work, and the boosting circuit cannot be driven; because the boosting circuit cannot work, the voltage of pin 1 of Q1 is equal to the voltage of pin 3 (that is, 0V), Q1 is cut off, and D2 cannot pass current, so that the current cannot flow from the positive electrode of the power supply to the negative electrode of the power supply, and the controller cannot be damaged, thereby ultimately achieving the purpose of self-protection. In addition, in order to enable the circuit to suppress spike voltage, a bidirectional TVS tube D1 and a capacitor C1 connected in parallel can be set between the two poles of the circuit, and a grounded filter capacitor C2 can be set between R3 and the base of Q1, so that the operation of the switch tube Q1 is more stable.

[0051] In the above embodiments provided by the present invention, it should be understood that the disclosed constant current drive circuit can be implemented in other ways. For example, the device embodiments described above are only schematic, for example, the division of the parts and units is only a logical function division, and there may be other division methods in actual implementation, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point, the coupling or direct coupling or communication connection between each other shown or discussed can be through some interfaces, indirect coupling or communication connection of devices or units, which can be electrical, mechanical or other forms. The unit described as a separate component may or may not be physically separated, and the component displayed as a unit may or may not be a physical unit, that is, it may be located in one place, or it may be distributed on multiple network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the present embodiment. In addition, each functional unit in each embodiment of the present invention can be integrated in a processing unit, or each unit can exist physically alone, or two or more units can be integrated in one unit.

[0052] Finally, it is noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-cost power reverse connection protection circuit, characterized in that: The power reverse connection protection circuit includes: an NMOS transistor Q1, an NPN transistor Q2, a square wave generator, diodes D2 to D6, capacitors C3, C4, C6 and C7, and resistors R1 and R3; The positive electrode of the power supply is connected to the source of Q1 and the anode of D2, the drain of Q1 is connected to the cathode of D2, the anode of D3, one end of R1 and the positive power supply end of the square wave generator, and the gate of Q1 is connected to one end of C3 and the cathode of D6; The cathode of D3 is connected to one end of C7 and the anode of D4, the cathode of D4 is connected to the anode of D5 and one end of C4, the cathode of D5 is connected to one end of C6 and the anode of D6, and the other end of R1 is connected to the other end of C7, the other end of C6 and the collector of Q2; The negative pole of the power supply is connected to the other end of C3, the other end of C4, the emitter of Q2, the ground terminal GND and the negative power supply terminal of the square wave generator. The output end of the square wave generator is connected to one end of R3, and the other end of R3 is connected to the base of Q2.

2. The power reverse connection protection circuit according to claim 1, characterized in that: The square wave generator is a function generator including an integrated chip MAX038.

3. The power reverse connection protection circuit according to claim 1 or 2, characterized in that: The power reverse connection protection circuit also includes: a bidirectional TVS tube D1 and a capacitor C1, one end of D1 and one end of C1 are connected to the drain of Q1, and the other end of D1 and the other end of C1 are connected to the negative electrode of the power supply.

4. The power reverse connection protection circuit according to claim 3, characterized in that: The power reverse connection protection circuit further includes a capacitor C2, one end of C2 is connected to the base of Q2, and the other end of C2 is connected to the ground terminal GND.

5. The power reverse connection protection circuit according to claim 1, characterized in that: The power supply is the on-board DC power supply of the car controller.

6. The power reverse connection protection circuit according to claim 1, characterized in that: The positive voltage of the power supply is 8~20V, and the negative voltage of the power supply is 0V.

7. The power reverse connection protection circuit according to claim 1, characterized in that: The values ​​of C3, C4, C6 and C7 are all 100nF.

8. The power reverse connection protection circuit according to claim 1, characterized in that: A diode is externally connected in anti-parallel between the drain and source of Q1.

9. The power reverse connection protection circuit according to claim 1, characterized in that: The diode D2 is a unidirectional diode.

10. The power reverse connection protection circuit according to claim 4, characterized in that: The capacitors C1 and C2 are filter capacitors.

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