CN111162513A

CN111162513A - Protective circuit

Info

Publication number: CN111162513A
Application number: CN202010127590.XA
Authority: CN
Inventors: 高金强; 彭照辉; 俞志根; 郭园; 蒋宗财
Original assignee: Ningbo Sanxing Electric Co Ltd
Current assignee: Ningbo Sanxing Electric Co Ltd
Priority date: 2020-02-28
Filing date: 2020-02-28
Publication date: 2020-05-15

Abstract

The invention relates to a protection circuit, which comprises a power supply end, a conduction module connected with the power supply end and an output end connected with a load, and is characterized in that: the circuit further comprises a first branch circuit and a second branch circuit which are connected between the conduction module and the output end and are connected in parallel, a switch module which is arranged on the second branch circuit and can enable the second branch circuit to be disconnected when the output end is in short circuit, and a clamping module which is connected between the output end and the conduction module and clamps the current flowing through the first branch circuit when the output end is in short circuit and clamps the current flowing through the first branch circuit and the second branch circuit when the circuit is overloaded. The protection circuit has a large current-limiting current range and can monitor voltage.

Description

Protective circuit

Technical Field

The invention relates to the technical field of electronic circuits, in particular to a protection circuit.

Background

In the circuit design, not only functional realizability, device optimization and circuit optimality need to be considered, but also the circuit design needs to adapt to actual conditions, for example, in the meter industry, the short circuit condition in practical application needs to be considered in the external auxiliary terminal; for example, the reliability of the circuit is directly affected by selecting a current limiting point of the circuit such as an MBUS circuit and a household steam meter circuit, and for these situations, a protection circuit design for preventing overload and short circuit is usually required.

FIG. 1 shows a prior art circuit diagram with overload and short-circuit protection, in which the current flowing through R14 is clamped at (V) by the action of a voltage regulator diode VD4 when V-OUT is short-circuited or overloaded_VD4-0.7)/R14, thereby preventing the circuit device from over-power damage, and playing the role of overload and short-circuit protection. However, the circuit has a high requirement on the power of the triode V5, the range of the current limiting point of the circuit is narrow, and meanwhile, the circuit can only limit the current for the current, and when the V-OUT voltage is reduced due to some uncontrollable reason, the circuit does not operate, the voltage cannot be monitored, so that the application scene of the protection circuit is limited.

Disclosure of Invention

In view of the above problems, it is an object of the present invention to provide a protection circuit that has a large adjustment range of the current limiting current, can prevent the over-power damage of the electronic device, and can monitor the voltage.

In order to achieve the purpose, the technical scheme of the invention is as follows: the utility model provides a protection circuit, includes the power end, the output that switches on the module and link to each other with the load that links to each other with the power end links to each other, its characterized in that:

the circuit further comprises a first branch circuit and a second branch circuit which are connected between the conduction module and the output end and are connected in parallel, a switch module which is arranged on the second branch circuit and can enable the second branch circuit to be disconnected when the output end is in short circuit, and a clamping module which is connected between the output end and the conduction module and clamps the current flowing through the first branch circuit when the output end is in short circuit and clamps the current flowing through the first branch circuit and the second branch circuit when the circuit is overloaded.

Further, the switch module comprises a first triode, and a base electrode of the first triode is electrically connected with the output end and is turned off to disconnect the second branch circuit when the output end is short-circuited.

Furthermore, the switch module further comprises a second triode, and the second triode is connected between the base electrode of the first triode and the output end and is turned off when the output end is in short circuit, so that the first triode is turned off.

Furthermore, the conduction module comprises a third triode, a first resistor and a second resistor, the third triode is an NPN type triode, a collector of the third triode is connected with a power supply end, a base of the third triode is connected with the clamping module, an emitter of the third triode is connected with one end of the first resistor, the other end of the first resistor is connected with the first branch circuit and the second branch circuit, and the collector of the third triode is connected with the base of the third triode through the second resistor.

Further, the clamping module comprises a first voltage stabilizing diode, wherein the anode of the first voltage stabilizing diode is connected with the output end, and the cathode of the first voltage stabilizing diode is connected with the base electrode of the third triode.

Furthermore, the first triode is a PNP triode, the second triode is an NPN triode, an emitting electrode of the first triode is connected with the other end of the first resistor, a collector electrode of the first triode is connected with an output end through a fourth resistor, a base electrode of the first triode is connected with a collector electrode of the second triode through a sixth resistor, and the base electrode and the collector electrode of the first triode are further connected through a fifth resistor.

Further, the switch module further includes a seventh resistor, a ninth resistor, a tenth resistor, and a second zener diode;

the positive electrode of the second voltage-stabilizing diode is grounded, the negative electrode of the second voltage-stabilizing diode is connected with the power supply end through a tenth resistor, the emitting electrode of the second triode is connected with the negative electrode of the second voltage-stabilizing diode, the base electrode of the second triode is connected with the output end through a seventh resistor and is connected with the positive electrode of the second voltage-stabilizing diode through a ninth resistor;

the second triode has an output terminal voltage lower than (V)_VD3And +0.7) and (the ninth resistance value + the seventh resistance value)/the tenth resistance value, the circuit is turned off to monitor the voltage of the output end.

Further, the first branch circuit comprises a third resistor connected between the first resistor and the output terminal.

Further, the output end is also connected with the ground through an eighth resistor.

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

by arranging two branches, the second branch is switched off when the output end is short-circuited, so that the circuit current only flows out through the first branch, the current is controlled by the clamping module and can be adjusted by the cooperation of the first branch and the divider resistor of the conduction module, the first branch and the second branch are switched on together when the output end is overloaded, and the flowing current-limiting current is adjusted and controlled by the cooperation of the first branch, the second branch and the divider resistor in the conduction module, so that the adjustable range of the current-limiting current is realized, the circuit device is prevented from being burnt due to overlarge current, and the circuit safety is ensured; when the voltage of the output end is lower than a certain value, the second triode can be turned off to turn off the switch module, so that the second branch circuit is disconnected, the circuit is ensured to enter a protection mode, and the voltage monitoring function is achieved.

Drawings

Fig. 1 is a circuit diagram of a protection circuit in the prior art.

Fig. 2 is a circuit diagram of a protection circuit according to an embodiment of the present application.

Detailed Description

Reference will now be made in detail to embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to the same or similar elements or elements having the same or similar function throughout. The embodiments described below with reference to the accompanying drawings are illustrative only for the purpose of explaining the present invention, and are not to be construed as limiting the present invention.

As shown in fig. 1, which is a circuit diagram with overload and short-circuit protection in the prior art, assuming that the regulated voltage of the zener diode VD4 is 5.1V, when the output terminal V-OUT is short-circuited, the current flowing through R14 is clamped at (5.1-0.7)/R14A, so as to protect the MBUS circuit device from over-power damage; when the V-OUT terminal is overloaded, the voltage stabilizing diode VD4 acts, and the current is clamped at (5.1-0.7)/R14A by VD4, thereby protecting MBUS circuit devices from over-power damage.

However, the circuit has some disadvantages, for example, when the VCC power supply is 30V and R14 is 200 Ω, the current limiting point is (5.1-0.7)/200 ═ 22mA, when the V-OUT terminal is short-circuited, the power consumption of the transistor V5 is 22mA × (30-5.1+0.7) V ═ 0.556W, and the power of the transistor V5 is already over-powered and damaged; meanwhile, the circuit can only limit the current according to the current, when the V-OUT voltage is reduced due to some uncontrollable reason, the circuit does not act, the voltage cannot be detected, and the application scene is limited; in addition, the current limiting current of the circuit can be adjusted only through the resistor R14, so that the adjustment range of the current limiting current of the circuit is narrow. In order to solve the problem, the application is specially improved.

As shown in fig. 2, which is a circuit diagram of the protection circuit of the present application, as shown in the figure, the protection circuit includes a power supply terminal VCC, a conducting module 1 connected to the power supply terminal VCC, and an output terminal V-OUT connected to a load, the circuit further includes a first branch 2 and a second branch 3 connected between the conducting module 1 and the output terminal V-OUT and connected in parallel, a switch module 4 disposed on the second branch 3 and capable of disconnecting the second branch 3 when the output terminal V-OUT is short-circuited, and a clamping module 5 connected between the output terminal V-OUT and the conducting module 1 and clamping a current flowing through the first branch 2 when the output terminal V-OUT is short-circuited and clamping a current flowing through the first branch 2 and the second branch 3 when the circuit is overloaded.

Specifically, the switch module 4 includes a first transistor V1, a base of the first transistor V1 is electrically connected to the output terminal V-OUT and is turned off to disconnect the second branch 3 when the output terminal V-OUT is short-circuited; the switch module 4 further includes a second transistor V3, and the second transistor V3 is connected between the base of the first transistor V1 and the output terminal V-OUT and is turned off when the output terminal V-OUT is short-circuited, so as to turn off the first transistor V1.

The conducting module 1 includes a third transistor V6, a first resistor R1 and a second resistor R17, the third transistor V6 is an NPN transistor, a collector of the third transistor V6 is connected to the power supply terminal V-OUT, a base of the third transistor V6 is connected to the clamping module 5, an emitter of the third transistor V6 is connected to one end of the first resistor R1, the other end of the first resistor R1 is connected to the first branch 2 and the second branch 3, and a collector and a base of the third transistor V6 are connected through the second resistor R17.

The clamping module 5 comprises a first voltage-stabilizing diode VD1, wherein the anode of the first voltage-stabilizing diode VD1 is connected to the output terminal V-OUT and the cathode is connected to the base of the third transistor V6. Of course, it is conceivable that the first zener diode VD1 could be replaced by a diode or a triode clamp circuit.

In this embodiment, the first transistor V1 is a PNP transistor, the second transistor V3 is an NPN transistor, the emitter of the first transistor V1 is connected to the other end of the first resistor R1, the collector of the first transistor V1 is connected to the output terminal V-OUT through the fourth resistor R3, the base of the first transistor V1 is connected to the collector of the second transistor V3 through the sixth resistor R6, and the base and the collector of the first transistor V1 are further connected through the fifth resistor R5.

In order to enable the output end V-OUT voltage signal to control the on-off of the second triode V3, the switch module further comprises a seventh resistor R7, a ninth resistor R12, a tenth resistor R11 and a second voltage stabilizing diode VD 3; specifically, the anode of the second zener diode VD3 is grounded while the cathode is connected to the power supply terminal VCC through a tenth resistor R11, the emitter of the second triode V3 is connected to the cathode of the second zener diode VD3 while the base is connected to the output terminal V-OUT through a seventh resistor R7 and to the anode of the second zener diode VD3 through a ninth resistor R12; when the V-OUT voltage at the output end is lower than (V)_VD3+0.7) ((R12 + R17)/R12, the second triode V3 is turned off, the corresponding first triode V1 is also turned off, the second branch 3 is turned off, and the circuit is in a protection mode, so that the output end V-OUT voltage is monitored, wherein V-OUT voltage is monitored_VD3The regulated voltage value of the second voltage regulation diode VD 3.

In the present embodiment, the first branch 2 includes a third resistor R2 connected between the first resistor R1 and the output terminal V-OUT. For safe and stable operation of the circuit, the output terminal V-OUT is also connected to ground through an eighth resistor R8.

The working principle of the protection circuit of the application is as follows:

when the output end V-OUT is short-circuited, the voltage of the base of V3 is 0V, and V3 is closed, then V1 is correspondingly closed, and all current flows to the output end V-OUT through the path VCC → R2, and assuming that the VD1 clamping voltage is 5.1V, the current is clamped at (5.1-0.7)/(R1+ R2) a, and the power of V6 is (5.1-0.7)/(R1+ R2) (VCC-5.1) W, so long as the resistances of R1 and R2 are properly selected, the triode V6 has no risk of over-power damage, and ensures that the circuit device is not damaged.

When V-OUT is overloaded, the load current consists of VCC → R2 and VCC → V1 → R3, and the current is clamped at (5.1-0.7)/(R1+ R2) + (5.1-0.7)/(R1+ R3) A, and R3 is smaller than R2 in the actual circuit, most of the current path is VCC → V1 → R3, the power of the triode V6 is [ (5.1-0.7)/(R1+ R2) + (5.1-0.7)/(R1+ R3) ] (VCC-5.1-V _ OUT) W, and as long as the resistances of R1, R2 and R3 are properly selected, the triode V6 cannot have the risk of power damage; the power of the triode V1 is approximately equal to (5.1-0.7)/(R1+ R3) × 5.1W, taking S0T-89 as an example to package the triode, the power consumption is 0.5W, as long as the total resistance of R1 and R3 is greater than 48 Ω, the triode V1 has no risk of power damage, and the current-limiting current (5.1-0.7)/48 ═ 98mA at this time, which is far beyond the design requirement.

From the above analysis, the current-limiting current of the protection circuit can be adjusted through the resistors R1, R2 and R3, the current-limiting range is large, the applicability is good, the power consumption requirement on the triode is low, the cost is saved, and when the voltage of the output end V-OUT is lower than (V-OUT)_VD3+0.7) ((R12 + R7)/R12, transistor V3 turns off, thereby achieving the voltage monitoring function.

While embodiments of the invention have been shown and described, it will be understood by those skilled in the art that: various changes, modifications, substitutions and alterations can be made to the embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A protection circuit comprising a power supply terminal, a conduction module (1) connected with the power supply terminal and an output terminal connected with a load, characterized in that:

The circuit further comprises a first branch (2) and a second branch (3) connected in parallel between the conduction module (1) and the output end, arranged on the second branch (3) and connected to the second branch (3). A switch module (4) that can disconnect the second branch (3) when the output terminal is short-circuited, and a switch module (4) that is connected between the output terminal and the conduction module (1) and that flows through the first branch circuit (2) when the output terminal is short-circuited A clamping module (5) that clamps the current flowing through the first branch (2) and the second branch (3) when the circuit is overloaded.

2. The protection circuit according to claim 1, wherein:

The switch module (4) includes a first triode, the base of the first triode is electrically connected to the output end, and is turned off to disconnect the second branch when the output end is short-circuited.

3. The protection circuit according to claim 2, wherein:

The switch module (4) also includes a second triode, the second triode is connected between the base of the first triode and the output end and is turned off when the output end is short-circuited to realize the first triode tube off.

4. The protection circuit according to claim 3, wherein:

The conduction module (1) includes a third triode, a first resistor and a second resistor, the third triode is an NPN triode, the collector of the third triode is connected to the power supply terminal and the base It is connected to the clamping module (5), the emitter is connected to one end of the first resistor, the other end of the first resistor is connected to the first branch and the second branch, and the collector and base of the third triode are connected through the second resistor .

5. The protection circuit according to claim 4, wherein:

The clamping module (5) includes a first Zener diode, the positive pole of the first Zener diode is connected to the output terminal and the negative pole is connected to the base of the third triode.

6. The protection circuit according to claim 4, wherein:

The first triode is a PNP type triode, the second triode is an NPN type triode, the emitter of the first triode is connected to the other end of the first resistor, and the collector is connected to the output end through the fourth resistor and the base electrode is connected to the collector electrode of the second triode through a sixth resistor, and the base electrode and the collector electrode of the first triode are also connected through a fifth resistor.

7. The protection circuit according to claim 6, wherein:

The switch module (4) further comprises a seventh resistor, a ninth resistor, a tenth resistor and a second Zener diode;

The anode of the second Zener diode is grounded and the cathode is connected to the power supply terminal through the tenth resistor, the emitter of the second transistor is connected to the cathode of the second Zener diode, and the base is connected to the output terminal through the seventh resistor and passed through. The ninth resistor is connected to the anode of the second Zener diode;

The second transistor is turned off when the output terminal voltage is lower than (V _VD3 +0.7)*(the ninth resistance value+the seventh resistance value)/the tenth resistance value to monitor the output terminal voltage.

8. The protection circuit according to claim 4, wherein:

The first branch (2) includes a third resistor connected between the first resistor and the output terminal.

9. The protection circuit according to claim 7, wherein:

10. The protection circuit according to claim 1, wherein:

The output terminal is also connected to the ground through an eighth resistor.