CN111614073A

CN111614073A - Low-cost power supply reverse connection protection circuit

Info

Publication number: CN111614073A
Application number: CN202010471825.7A
Authority: CN
Inventors: 李泉; 刘五阳; 曾为华
Original assignee: Hunan Yipu Automobile Technology Co ltd
Current assignee: Hunan Yipu Automobile Technology Co ltd
Priority date: 2020-05-29
Filing date: 2020-05-29
Publication date: 2020-09-01

Abstract

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

Description

Low-cost power supply reverse connection protection circuit

Technical Field

The invention belongs to the technical field of circuit design of automobile power supplies, and relates to a low-cost reverse connection protection circuit for a power supply.

Background

With the development of the automobile industry, various controllers are applied to automobiles more and more, the self-protection function of the controllers is higher and higher, and the power reverse connection prevention function is one of the self-protection functions of electronic products; the reverse connection of the power supply can cause permanent damage to the controller, so a protection circuit needs to be added into a circuit of the controller, and the purpose that the controller cannot be damaged even if the reverse power supply is connected is achieved.

In the prior art, a diode can be connected in series with the anode of a power supply to realize the operation, however, the diode has voltage drop, which causes unnecessary loss to a circuit and greatly reduces the working voltage range of an electronic product; because the MOS voltage drop is small and can be ignored almost, the industry starts to use the PMOS tube as the anode of the power supply and the NMOS tube as the reverse connection protection circuit of the power supply at the cathode of the power supply.

However, because the diode has voltage drop, the diode is connected in series with the anode of the power supply to realize the voltage drop, which causes unnecessary loss to the circuit and greatly reduces the working voltage range of the electronic product; the price of the PMOS tube with the same power is two times more expensive than that of the NMOS tube, and the PMOS tube is realized by using the positive electrode of a power supply, so that the cost of the whole product is greatly increased; because the cathodes of many electronic products have many end points, the reverse connection protection can not be realized by using one NMOS at the cathode, and meanwhile, the closed-loop control of a software program is not carried out by using an MCU chip and an AD acquisition chip which are expensive.

For example, patent application No. CN201920818479.8 discloses a reverse connection protection circuit for a vehicle-mounted dc power supply based on an NMOS transistor, which uses an NMOS transistor to implement reverse connection protection at the positive electrode, however, as can be seen from fig. 1 and the descriptions in paragraphs 24 to 28 of the specification, it uses an MCU and an AD acquisition chip to acquire the current state, and if the difference between the acquired voltage of the bootstrap booster circuit and the voltage of the vehicle-mounted dc power supply is greater than a certain threshold (the value is determined according to the model of a specific MOS transistor), the bootstrap booster circuit is considered to be normal by a program in the MCU, and the MOS is reliably turned on. Therefore, the power supply reverse connection protection of the circuit needs to depend on the expensive MCU chip, AD conversion device and PWM signal generation module, the cost is still high, and a special software program needs to be sintered into the MCU according to the control mode, so that the process is complex, the reliability is not high enough, and the industrial batch production and application are not convenient.

Therefore, a low-cost power supply reverse connection protection circuit is needed to be designed, so that the defect that the cost of the automobile power supply reverse connection protection circuit in the prior art is high is overcome, and industrial batch production and application are facilitated.

Disclosure of Invention

Technical problem to be solved

Based on the technical scheme, the invention discloses a low-cost power supply reverse connection protection circuit, compared with the prior art, the circuit has the advantages of lower cost and high reliability, can realize automatic reverse connection protection without depending on a software program, and is convenient for industrial mass production and application.

(II) technical scheme

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

the positive electrode of a power supply is connected with the source electrode of Q1 and the anode of D2, the drain electrode of Q1 is connected with the cathode of D2, the anode of D3, one end of R1 and the positive power supply end of a square wave generator, and the grid electrode of Q1 is connected with one end of C3 and the cathode of D6;

the cathode of D3 is connected with one end of C7 and the anode of D4, the cathode of D4 is connected with the anode of D5 and one end of C4, the cathode of D5 is connected with one end of C6 and the anode of D6, and the other end of R1 is connected with the other end of C7, the other end of C6 and the collector of Q2;

the negative electrode of the power supply is connected with the other end of the C3, the other end of the C4, the emitter of the Q2, the ground GND and the negative power supply end of the square wave generator, the output end of the square wave generator is connected with one end of the R3, and the other end of the R3 is connected with the base of the Q2.

Further, the square wave generator is a function generator comprising an integrated chip MAX 038.

Further, the power reverse connection protection circuit further includes: the bidirectional TVS tube D1 and the capacitor C1, one end of D1 and one end of C1 are both connected with the drain electrode of Q1, and the other end of D1 and the other end of C1 are both connected with the negative electrode of a power supply.

Furthermore, the power supply reverse connection protection circuit further comprises a capacitor C2, one end of the capacitor C2 is connected with the base of the Q2, and the other end of the capacitor C2 is connected with the ground terminal GND.

Further, the power supply is a vehicle-mounted direct-current power supply of the automobile controller.

Further, the voltage of the positive electrode of the power supply is 8-20V, and the voltage of the negative electrode of the power supply is 0V.

Further, the C3, C4, C6 and C7 are all 100 nF.

Further, a body of diode is connected between the drain electrode and the source electrode of the Q1 in anti-parallel.

Further, the diode D2 is a unidirectional diode.

Further, the capacitors C1 and C2 are filter capacitors.

(III) advantageous effects

Compared with the prior art, the invention has the following beneficial effects:

(1) compared with a patent CN201920818479.8, the invention newly designs a voltage boost circuit (which is different from a bootstrap boost circuit in the prior art) based on the components of D3-D6, C3-C4 and C6-C7, and through the matching of a square wave generator with a set fixed switching frequency and a triode Q2, the voltage in the C3 can be boosted to double the voltage in a short time so as to complete the conduction of Q1 when the power supply is connected positively; when the power supply is in wrong reverse connection, the square wave generator cannot supply power to the corresponding positive electrode and the corresponding negative electrode, so that the square wave generator does not work, the Q2 is in a cut-off state, in addition, the existence of the C3 ensures that the grid voltage of the Q1 is 0, the NMOS tube is not conducted, and meanwhile, the current cannot flow from the positive electrode to the negative electrode due to the C4 and the D3-D6, so that the current cannot flow from the positive electrode to the negative electrode of the power supply, and the controller cannot be damaged.

(2) The power supply reverse connection protection circuit only uses one NMOS tube, and through the matching of low-cost circuit devices such as a triode, a square wave generator and the like, the reverse connection protection of the direct current power supply can be realized through pure hardware, so that the power supply reverse connection protection circuit is lower in cost and high in reliability, and is suitable for industrial-grade mass production and application.

Drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are illustrative and not to be construed as limiting the invention in any way, and in which:

fig. 1 is a circuit schematic diagram of a low-cost reverse power protection circuit according to the present invention.

Fig. 2 is a schematic diagram of a circuit state when a square-wave generator in the power reverse connection protection circuit outputs a first high level when a power supply is connected positively.

Fig. 3 is a schematic diagram of a circuit state when a square-wave generator in the power reverse connection protection circuit outputs a first low level when a power supply is connected positively.

Fig. 4 is a schematic diagram of a circuit state when the square-wave generator in the power reverse connection protection circuit outputs a second high level when the power is connected positively.

FIG. 5 is a schematic diagram of a power reverse protection circuit according to the present invention when the power is reversely connected.

Detailed Description

The present invention will be described more fully hereinafter with reference to the accompanying drawings and examples, in which the technical problems and advantages of the present invention are solved, wherein the described examples are only intended to facilitate the understanding of the present invention, and are not to be construed as limiting in any way.

As shown in fig. 1, it is a schematic circuit diagram of a low-cost reverse power protection circuit disclosed in the present invention, and the reverse power protection circuit includes: NMOS transistor Q1, triode Q2, square wave generator, diodes D2-D6, capacitors C3, C4, C6 and C7, and resistors R1 and R3. After normal power supply, the square wave generator automatically generates a square wave waveform with a fixed frequency, which may be a square wave generator including an integrated chip MAX038 or other integrated chips, so as to reduce cost.

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

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

In another embodiment, in order to protect the circuit from transient high voltage spikes, the reverse power protection circuit further comprises: a bidirectional TVS tube D1 (the bidirectional TVS tube is combined by two unidirectional TVS in a back-to-back way, the front direction and the back direction of the bidirectional TVS tube have the same avalanche breakdown characteristic and clamping characteristic) and a capacitor C1, wherein one end of D1 and one end of C1 are connected with the drain electrode of Q1, and the other end of D1 and the other end of C1 are connected with the negative electrode of a power supply.

In another embodiment, in order to ensure the operation stability of Q1, the reverse power 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 ground GND.

In another embodiment, the voltage of the positive electrode of the power supply is preferably 8-20V, the voltage of the negative electrode of the power supply is 0V, and the power supply is preferably a vehicle-mounted direct-current power supply of an automobile controller; secondly, the specifications of C3, C4, C6 and C7 are the same, and may all be preferably 100 nF; in addition, an individual diode can be connected between the drain electrode and the source electrode of the Q1 in an anti-parallel mode so as to protect the NMOS tube; the type of the D2 diode is preferably a unidirectional diode (namely, a common diode which is not a TVS (transient voltage suppressor)), when the diode is connected in the forward direction, before the Q1 is not conducted, the voltage supplies power to the square wave generator through the D2, so that the square wave generator works, the booster circuit is driven, the Q1 is driven to be conducted, after the Q1 is conducted, because the internal resistance of the NMOS tube Q1 is far smaller than that of the diode D2, the current passes through the Q1 and does not pass through the D2 any more, and the requirement of large-current power supply.

In order to further clarify the working principle and advantages of the low-cost reverse connection protection circuit of the power supply, the circuit operation state when the power supply is in positive and reverse connection is analyzed as follows:

1) positive power supply connection

When a power supply is connected in the positive direction, the NMOS is in a cut-off state at the beginning, current provides voltage for the square wave generator through the diode D2, the positive electrode and the negative electrode of the square wave generator are powered normally, square wave signals with fixed frequency can be automatically generated, and the triode Q2 is driven;

as shown in fig. 2, when the square wave generator outputs the first high level, Q2 is connected to ground, and the power voltage charges C7, C4, C6, and C3 through D2, D3, D4, D5, and D6.

As shown in fig. 3, when the square wave generator outputs low level for the first time, Q2 is turned off, since the voltage across the capacitors cannot change abruptly, the voltage on the left side of the capacitors C7 and C6 is equal to about 2 times the power supply voltage, and the voltage on the right side is equal to the power supply voltage (the voltage drop across the capacitors is still equal to the power supply voltage, and the voltage on the left side is raised to 2 times the power supply voltage by the voltage on the positive pole of the power supply which passes through R1 but is not grounded), then the current continuously charges C4 and C3 through D4 and D6, and after charging, the voltage of C4 and C3 also rises to about 2 times the power supply voltage.

As shown in fig. 4, when the square wave generator outputs high level for the second time, Q2 is turned on again to ground, and since the voltage across the capacitor cannot change suddenly, the voltage on the left side of the capacitor C6 is the power voltage, and the voltage on the right side is 0V (the voltage drop of C6 is still equal to the power voltage); when the voltage of C6 is equal to the power supply voltage, C4 charges C6 because the voltage drop of C4 is 2 times the power supply voltage > C6, and after charging, C4 ≈ C6 ≈ 1.5 times the power supply voltage; because D6 is in the off state, C3 cannot charge C6, and the voltage drop of C3 still maintains 2 times the power supply voltage;

meanwhile, the voltage on the left side of the 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 < the voltage of C4, but since D4 is in the reverse off state, C4 cannot charge C7, and C4 maintains about 1.5 times the power supply voltage.

When the square wave generator outputs a low level for the second time (not shown in the figure), C4 is charged to 2 times of the power voltage again, when the square wave generator outputs a high level for the third time, the 2 times of the power voltage of C4 is larger than the power voltage of C6, C4 charges C6, and C4 ═ C6 ≈ 1.75 power voltage; after the square wave generator outputs high and low level for several times, the voltage of C4 is slowly raised, at the same time, C6 also charges C3, the voltage of C3 is also slowly and stably raised, and as a result of simulation, the voltage of C3 is finally stabilized at about 2 times of power supply voltage (in an actual circuit, circuit loss is removed, and the voltage of Vout is stabilized at about 2 times of power supply voltage), so as to stably drive the NMOS transistor Q1 to be switched on (switched-on Vgs actually needs more than 4V); after the NMOS transistor Q1 is turned on, its impedance is only a few m Ω, and is much smaller than that of the diode D1, and 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.

2) Reverse power supply access

As shown in fig. 5, when the power is turned on in the reverse direction, the positive power supply electrode becomes the negative power supply electrode, the negative power supply electrode becomes the positive power supply electrode, the power current flows to C1, C2, C3, C4, D1 and the square wave generator, and the current cannot flow to C1, C2, C3 and C4 due to the characteristic that the capacitors are connected with alternating current and direct current; further, since D1 is a bidirectional TVS tube, D1 is in a reverse off state; because the grounded negative power supply end of the square wave generator is wrongly connected to the positive electrode of the power supply and the positive power supply end has no power supply signal, the square wave generator does not work and cannot send square waves to drive the Q2; q2 is off, and current cannot flow through Q2; the voltage of the pin 1 of the Q1 is equal to the voltage of the pin 3 connected with the negative pole of the voltage, namely 0V, and the Q1 is cut off; the current can not flow from the positive pole of the power supply to the negative pole of the power supply, and the controller can not be damaged, so that the purpose of self-protection is achieved.

In summary, the invention forms a voltage boosting part by Q2, D2-D6, C3, C4, C6 and C7, the voltage boosting part is matched with a square wave generator and is used for rapidly boosting the voltage to about 2 times of the power supply voltage and providing the driving voltage required by normal conduction for the NMOS tube; meanwhile, part of components in the voltage boosting part also form a power supply reverse protection part, when a power supply is reversely connected, the positive electrode of the power supply is changed into the negative electrode of the power supply, the negative electrode of the power supply is changed into 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 with the positive electrode and the negative electrode of the power supply for pressurization, a power supply loop cannot be formed, and the square wave generator does not work at this time, so that the boosting circuit cannot be driven; because the booster circuit cannot work, the voltage of pin 1 of the Q1 is equal to the voltage of pin 3 (namely 0V), the Q1 is cut off, and the D2 cannot pass current, so that the current cannot flow from the positive pole of the power supply to the negative pole of the power supply, the controller cannot be damaged, and the purpose of self-protection is finally achieved. In addition, in order to enable the circuit to have the function of restraining the peak voltage, a bidirectional TVS tube D1 and a capacitor C1 which are connected in parallel with each other are arranged between two poles of the circuit, and a filter capacitor C2 which is connected with the ground is arranged between bases of R3 and Q1, so that the operation of the switching tube Q1 is more stable.

In the above embodiments provided in the present invention, it should be understood that the disclosed constant current driving circuit may be implemented in other ways. For example, the above-described apparatus embodiments are merely illustrative, and for example, the division of the units and units is only one logical division, and there may be other divisions when actually implemented, for example, a plurality of units or components may be combined or may be integrated into another system, or some features may be omitted, or not executed. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection through some interfaces, devices or units, and may be in an electrical, mechanical or other form. The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment. In addition, functional units in the embodiments of the present invention may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit.

Finally, the description is as follows: the above examples are only intended to illustrate the technical solution of the present invention, but not to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.

Claims

1. A low cost reverse power protection circuit, said reverse power protection circuit comprising: an NMOS transistor Q1, an NPN triode Q2, a square wave generator, diodes D2-D6, capacitors C3, C4, C6 and C7, and resistors R1 and R3;

2. The reverse power supply protection circuit according to claim 1, wherein the square wave generator is a function generator comprising an integrated chip MAX 038.

3. The reverse power protection circuit according to claim 1 or 2, further comprising: the bidirectional TVS tube D1 and the capacitor C1, one end of D1 and one end of C1 are both connected with the drain electrode of Q1, and the other end of D1 and the other end of C1 are both connected with the negative electrode of a power supply.

4. The reverse power protection circuit of claim 1, further comprising a capacitor C2, wherein one end of C2 is connected to the base of Q2, and the other end of C2 is connected to ground GND.

5. The reverse power protection circuit of claim 1, wherein the power source is a vehicle-mounted dc power source of an automotive controller.

6. The reverse power supply connection protection circuit according to claim 1, wherein the voltage of the positive electrode of the power supply is 8-20V, and the voltage of the negative electrode of the power supply is 0V.

7. The reverse power protection circuit of claim 1, wherein the C3, C4, C6 and C7 are all 100 nF.

8. The reverse power protection circuit of claim 1, wherein a diode is externally connected in reverse parallel between the drain and the source of the Q1.

9. The reverse power protection circuit of claim 1, wherein the diode D2 is a unidirectional diode.

10. The reverse power protection circuit of claim 4, wherein the capacitors C1 and C2 are filter capacitors.