A protection circuit

Abstract

The present invention relates to a protection circuit comprising a power supply terminal, a conduction module connected to the power supply terminal, and an output terminal connected to a load. The circuit is characterized in that: the circuit further comprises a first branch and a second branch connected in parallel between the conduction module and the output terminal; a switch module disposed on the second branch and capable of disconnecting the second branch when the output terminal is short-circuited; and a clamping module connected between the output terminal and the conduction module and capable of clamping the current flowing through the first branch when the output terminal is short-circuited and of clamping the current flowing through the first branch and the second branch when the circuit is overloaded. The protection circuit has a wide current limiting range and is capable of voltage monitoring.

Description

Technical Field

[0001] The present invention relates to the technical field of electronic circuits, and in particular to a protection circuit. Background Art

[0002] When designing a circuit, it is necessary not only to consider functional feasibility, device selectivity, and circuit optimality, but also to adapt to actual conditions. For example, in the metering industry, external auxiliary terminals often need to consider short-circuit conditions during actual application. In MBUS circuits and household water and vapor meter circuits, the proper selection of the circuit current limit point directly affects the circuit reliability. For these situations, it is usually necessary to design protection circuits to prevent overload and short-circuit.

[0003] like Figure 1 The figure shows a circuit diagram with overload and short circuit protection in the prior art. In this circuit, when V-OUT is short-circuited or overloaded, the current flowing through R14 is clamped at (V VD4 -0.7) / R14, which prevents overpower damage to circuit components and provides overload and short-circuit protection. However, this circuit places high power demands on transistor V5 and has a narrow current-limiting range. Furthermore, the circuit can only limit current. If the V-OUT voltage drops due to uncontrollable reasons, the circuit will not operate and cannot monitor the voltage, limiting the application scenarios of this protection circuit. Summary of the Invention

[0004] In view of the above problems, an object of the present invention is to provide a protection circuit which has a large current limiting adjustment range, can prevent electronic devices from being damaged by overpower, and can monitor voltage.

[0005] In order to achieve the above-mentioned object, the technical solution of the present invention is: a protection circuit, comprising a power supply end, a conduction module connected to the power supply end, and an output end connected to a load, characterized in that:

[0006] The circuit also includes a first branch and a second branch connected in parallel between the conduction module and the output end, a switch module arranged on the second branch and capable of disconnecting the second branch when the output end is short-circuited, and a clamping module connected between the output end and the conduction module and capable of clamping the current flowing through the first branch when the output end is short-circuited and clamping the current flowing through the first branch and the second branch when the circuit is overloaded.

[0007] Furthermore, the switch module includes a first transistor, the collector of which is electrically connected to the output end and is turned off to disconnect the second branch when the output end is short-circuited.

[0008] Furthermore, the switch module further includes a second transistor, which is connected between the base of the first transistor and the output end and is turned off when the output end is short-circuited to achieve the shutdown of the first transistor.

[0009] Furthermore, the conduction module includes a third transistor, a first resistor, and a second resistor. The third transistor is an NPN transistor. The collector of the third transistor is connected to the power supply end, the base is connected to the clamping module, and 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. The collector and base of the third transistor are connected through the second resistor.

[0010] Furthermore, the clamping module includes a first voltage stabilizing diode, wherein the anode of the first voltage stabilizing diode is connected to the output end and the cathode is connected to the base of the third transistor.

[0011] Furthermore, the first transistor is a PNP transistor, the second transistor is an NPN transistor, the emitter of the first transistor is connected to the other end of the first resistor, the collector is connected to the output end through the fourth resistor, and the base is connected to the collector of the second transistor through the sixth resistor, and the base and emitter of the first transistor are also connected through the fifth resistor.

[0012] Furthermore, the switch module further includes a seventh resistor, a ninth resistor, a tenth resistor and a second voltage stabilizing diode;

[0013] The anode of the second voltage stabilizing diode is grounded and the cathode is connected to the power supply terminal via a tenth resistor. The emitter of the second transistor is connected to the cathode of the second voltage stabilizing diode and the base is connected to the output terminal via a seventh resistor and to the anode of the second voltage stabilizing diode via a ninth resistor.

[0014] The voltage at the output end of the second transistor is lower than (V VD3 +0.7)*(resistance of the ninth resistor+resistance of the seventh resistor) / resistance of the tenth resistor, the output terminal voltage is monitored.

[0015] Furthermore, the first branch includes a third resistor connected between the first resistor and the output terminal.

[0016] Furthermore, the output end is also connected to the ground through an eighth resistor.

[0017] Compared with the prior art, the advantages of the present invention are:

[0018] By setting up two branches, when the output end is short-circuited, the second branch is turned off and the circuit current flows out only through the first branch. The current is controlled by the clamping module and can be adjusted by the first branch and the voltage-dividing resistor of the conduction module. When the output end is overloaded, the first branch and the second branch are turned on together, and the current-limiting current flowing through is regulated by the first branch, the second branch and the voltage-dividing resistor in the conduction module. This achieves an adjustable range of the current-limiting current, while ensuring that the circuit components are not burned due to excessive current, ensuring circuit safety. When the output end voltage is lower than a certain value, the second transistor can be turned off to turn off the switch module, thereby disconnecting the second branch, ensuring that the circuit enters the protection mode and plays a role in monitoring the voltage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a circuit diagram of a protection circuit in the prior art.

[0020] Figure 2 This is a circuit diagram of a protection circuit according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention.

[0022] like Figure 1 The figure shows a circuit diagram with overload and short-circuit protection in the prior art. As shown in the figure, assuming that the voltage regulation value of the voltage regulator 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, thereby protecting the MBUS circuit components from overpower damage; when the V-OUT terminal is overloaded, the voltage regulator diode VD4 is activated and the current is clamped by VD4 at (5.1-0.7) / R14A, thereby protecting the MBUS circuit components from overpower damage.

[0023] However, this circuit has some shortcomings. For example, when the VCC power supply is 30V and R14 is 200Ω, the current limit point is (5.1-0.7) / 200=22mA. When the V-OUT terminal is short-circuited, the power consumption of transistor V5 is 22mA*(30-5.1+0.7)V=0.556W, which exceeds the power of ordinary transistors and easily causes transistor V5 to be damaged by overpower. At the same time, this circuit can only limit current. When the V-OUT voltage drops due to some uncontrollable reasons, the circuit does not operate and cannot detect the voltage, which limits the application scenario. In addition, the current limiting current of this circuit can only be adjusted by resistor R14, resulting in a narrow adjustment range of the current limiting current of the circuit. In order to solve this problem, this application has made special improvements.

[0024] like Figure 2 The figure shows the 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 conduction module 1 connected to the power supply terminal VCC, and an output terminal V-OUT connected to the load. The circuit also includes a first branch 2 and a second branch 3 connected in parallel between the conduction module 1 and the output terminal V-OUT, a switch module 4 arranged 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 conduction module 1 and clamping the current flowing through the first branch 2 when the output terminal V-OUT is short-circuited and clamping the current flowing through the first branch 2 and the second branch 3 when the circuit is overloaded.

[0025] Specifically, the above-mentioned switching module 4 includes a first transistor V1, the collector of which is electrically connected to the output terminal V-OUT and is turned off when the output terminal V-OUT is short-circuited to disconnect the second branch 3; the above-mentioned switching module 4 also includes a second transistor V3, 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 to realize the shutdown of the first transistor V1.

[0026] The conduction module 1 includes a third transistor V6, a first resistor R1, and a second resistor R17. The third transistor V6 is an NPN transistor. The collector of the third transistor V6 is connected to the power supply terminal V-OUT, the base is connected to the clamping module 5, and the emitter 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. The collector and base of the third transistor V6 are connected via the second resistor R17.

[0027] The clamping module 5 includes a first voltage stabilizing diode VD1, the anode of which is connected to the output terminal V-OUT and the cathode of which is connected to the base of the third transistor V6. Of course, it is conceivable that the first voltage stabilizing diode VD1 can also be replaced by a diode or transistor clamping circuit.

[0028] 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 is connected to the output end V-OUT through the fourth resistor R3, and the base is connected to the collector of the second transistor V3 through the sixth resistor R6. The base and emitter of the first transistor V1 are also connected through the fifth resistor R5.

[0029] In order to enable the output terminal V-OUT voltage signal to control the on-off of the second transistor V3, the switch module further includes a seventh resistor R7, a ninth resistor R12, a tenth resistor R11 and a second Zener diode VD3; specifically, the anode of the second Zener diode VD3 is grounded and the cathode is connected to the power supply terminal VCC through the tenth resistor R11, the emitter of the second transistor V3 is connected to the cathode of the second Zener diode VD3 and the base is connected to the output terminal V-OUT through the seventh resistor R7 and is connected to the anode of the second Zener diode VD3 through the ninth resistor R12; when the output terminal V-OUT voltage is lower than (V VD3 +0.7)*(R12+R17) / R12, the second transistor V3 is turned off, the corresponding first transistor V1 is also turned off, the second branch 3 is disconnected, and the circuit enters the protection mode, thereby realizing the monitoring of the output terminal V-OUT voltage, wherein V VD3 is the voltage stabilization value of the second voltage stabilizing diode VD3.

[0030] In this embodiment, the first branch 2 includes a third resistor R2 connected between the first resistor R1 and the output terminal V-OUT. To ensure safe and stable operation of the circuit, the output terminal V-OUT is further connected to ground via an eighth resistor R8.

[0031] The working principle of the protection circuit of this application is as follows:

[0032] When the output terminal V-OUT is short-circuited, the base voltage of V3 is 0V. V3 is turned off, and V1 is also turned off accordingly. All current flows to the output terminal V-OUT through the path of VCC→R2. Assuming that the clamping voltage of VD1 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. As long as the resistance values ​​of R1 and R2 are selected appropriately, there is no risk of overpower damage to transistor V6, ensuring that the circuit components are not damaged.

[0033] When V-OUT is overloaded, the load current is composed of two parts: VCC→R2 and VCC→V1→R3. At this time, the current is clamped at (5.1-0.7) / (R1+R2)+(5.1-0.7) / (R1+R3)A. In the actual circuit, R3 is smaller than R2, so most of the current path is VCC→V1→R3. The power of transistor V6 is [(5.1-0.7) / (R1+R2)+(5.1-0.7) / (R1+R3)]*(VCC-5 .1-V_OUT)W. As long as the resistance values ​​of R1, R2, and R3 are properly selected, there is no risk of power damage to transistor V6. The power of transistor V1 is approximately equal to (5.1-0.7) / (R1+R3)*5.1W. Taking the S0T-89 package transistor as an example, its power consumption is 0.5W. As long as the total resistance value of R1 and R3 is greater than 48Ω, there is no risk of power damage to transistor V1. At this time, the current limit is (5.1-0.7) / 48=98mA, which far exceeds the design requirement.

[0034] From the above analysis, we can see that the current limiting current of the protection circuit can be adjusted by resistors R1, R2, and R3. The current limiting range is large, the applicability is good, and the power consumption requirement of the transistor is low, which is conducive to cost saving. Moreover, when the output terminal V-OUT voltage is lower than (V VD3 +0.7)*(R12+R7) / R12, the transistor V3 is turned off, thus achieving the function of voltage monitoring.

[0035] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the claims and their equivalents.

Claims

1. A protection circuit comprising a power supply terminal, a conduction module (1) connected to the power supply terminal, and an output terminal connected to a load, characterized in that: The circuit further comprises a first branch (2) and a second branch (3) connected between the conduction module (1) and the output end and connected in parallel with each other, a switch module (4) arranged on the second branch (3) and capable of disconnecting the second branch (3) when the output end is short-circuited, and a clamping module (5) connected between the output end and the conduction module (1) and capable of clamping the current flowing through the first branch (2) when the output end is short-circuited and clamping the current flowing through the first branch (2) and the second branch (3) when the circuit is overloaded; The switch module (4) comprises a first transistor, the collector of which is electrically connected to the output end and is turned off to disconnect the second branch when the output end is short-circuited; The switch module (4) further comprises a second transistor, which is connected between the base of the first transistor and the output end and is turned off when the output end is short-circuited to realize the turning off of the first transistor; The conduction module (1) comprises a third transistor, a first resistor and a second resistor, wherein the third transistor is an NPN transistor, the collector of the third transistor is connected to the power supply end, the base is connected to the clamping module (5), and 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 transistor are connected via the second resistor; The first transistor is a PNP transistor, the second transistor is an NPN transistor, the emitter of the first transistor is connected to the other end of the first resistor, the collector is connected to the output end through the fourth resistor, and the base is connected to the collector of the second transistor through the sixth resistor. The base and emitter of the first transistor are also connected through a fifth resistor.

2. The protection circuit according to claim 1, wherein: The clamping module (5) comprises a first voltage-stabilizing diode, wherein the anode of the first voltage-stabilizing diode is connected to the output end and the cathode is connected to the base of the third transistor.

3. The protection circuit according to claim 1, wherein: The switch module (4) further includes a seventh resistor, a ninth resistor, a tenth resistor and a second voltage-stabilizing diode; The anode of the second voltage stabilizing diode is grounded and the cathode is connected to the power supply terminal via a tenth resistor. The emitter of the second transistor is connected to the cathode of the second voltage stabilizing diode and the base is connected to the output terminal via a seventh resistor and to the anode of the second voltage stabilizing diode via a ninth resistor. The voltage at the output end of the second transistor is lower than (V VD3 +0.7)*(9th resistor value + 7th resistor value) / 10th resistor value is turned off to monitor the output voltage, V VD3 is the voltage regulation value of the second Zener diode.

4. The protection circuit according to claim 1, wherein: The first branch (2) comprises a third resistor connected between the first resistor and the output terminal.

5. The protection circuit according to claim 3, wherein: The first branch (2) comprises a third resistor connected between the first resistor and the output terminal.

6. The protection circuit according to claim 1, wherein: The output end is further connected to the ground via an eighth resistor.

Images