A protection circuit for a video input signal line against short circuit to power supply

Abstract

This invention discloses a protection circuit for a short circuit in a video input signal line to the power supply. The circuit includes a switching circuit positioned between the video input signal line and a video chip. The switching circuit comprises a voltage divider network, a transistor, and a MOSFET. The video input signal line is connected to the input terminal of the voltage divider network and the drain of the MOSFET. The output terminal of the voltage divider network is connected to the input terminal of the transistor. The output terminal of the transistor is connected to the gate of the MOSFET. The source of the MOSFET is connected to the video chip. This invention protects the stability and safety of the circuit in the event of a short circuit between the video input signal line and the power supply.

Description

Technical Field

[0001] This utility model relates to the automotive field, and in particular to a protection circuit for short circuits in the power supply of a video input signal line. Background Technology

[0002] In modern video surveillance systems, vehicle electronics, and other video devices, video input signal lines often need to be connected to a power supply (such as 12V or 24V). When a short circuit or other electrical fault occurs in the power supply of these devices, the video input signal lines may be subjected to excessive voltage surges, potentially damaging related circuit components. Existing protection measures mostly focus on protecting the power supply itself or the output terminals, but short-circuit protection between the video input signal lines and the power supply is lacking. Therefore, there is an urgent need for an efficient protection method to ensure the normal operation of the equipment and prevent damage to the video input signal lines caused by power supply failures. Existing video input signal circuits use resistors and capacitors, and their basic signal input principle block diagram is shown below. Figure 1 As shown. Under current conditions, the chip's video input pin is directly connected via a current-limiting resistor R1, a 75Ω matching resistor R2, and a DC blocking capacitor C1. When the CVBS_IN video signal is short-circuited to the power supply, resistors R1 and R2 cannot withstand the large current and burn out. Utility Model Content

[0003] The main purpose of this invention is to provide a protection circuit for short circuits between the video input signal line and the power supply. By setting up a switching circuit, the stability and safety of the circuit can be protected when a short circuit occurs between the video input signal line and the power supply.

[0004] The present invention adopts the following technical solution:

[0005] A protection circuit for short circuit of a video input signal line to the power supply includes: a switching circuit disposed between the video input signal line and a video chip; the switching circuit includes a voltage divider network, a transistor, and a MOSFET; the video input signal line is connected to the input terminal of the voltage divider network and the drain of the MOSFET, respectively; the output terminal of the voltage divider network is connected to the input terminal of the transistor; the output terminal of the transistor is connected to the gate of the MOSFET; and the source of the MOSFET is connected to the video chip.

[0006] Preferably, the voltage divider network includes a second resistor and a third resistor; one end of the second resistor is connected to the video input line, and the other end of the second resistor is connected to the transistor and one end of the third resistor; the other end of the transistor is grounded.

[0007] Preferably, the protection circuit for short circuit of the video input signal line to the power supply further includes: a fourth resistor and a fifth resistor; the fourth resistor is disposed between the MOSFET and the video chip; one end of the fifth resistor is connected to the video chip, and the other end is grounded.

[0008] Preferably, the protection circuit for short circuit to the power supply of the video input signal line further includes: a DC blocking capacitor; the DC blocking capacitor is disposed between the MOSFET and the video chip.

[0009] Preferably, the protection circuit for short circuit of the video input signal line to the power supply further includes a first resistor; one end of the first resistor is connected to the output terminal of the transistor, and the other end of the first resistor is connected to a DC power supply.

[0010] Preferably, the transistor is an NPN transistor; the input terminal of the transistor is the base, and the output terminal of the transistor is the collector.

[0011] Preferably, the MOS transistor is an N-channel MOS transistor.

[0012] Compared with the prior art, the beneficial effects of this utility model are as follows:

[0013] This invention, by setting a switching circuit including a voltage divider network, transistors, and MOSFETs in the video input signal line and video chip, can not only realize the transmission of video signals, but also automatically detect whether the signal is short-circuited to the power supply. It can effectively avoid damage to the video input signal line and its related circuit components caused by power supply short circuit, protect the stability and safety of the circuit, and improve the reliability of the equipment.

[0014] The above description is merely an overview of the technical solution of this utility model. In order to better understand the technical means of this utility model so that it can be implemented in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this utility model more obvious and understandable, the following lists specific embodiments of this utility model.

[0015] The above and other objects, advantages and features of this utility model will become more apparent to those skilled in the art from the following detailed description of specific embodiments of this utility model in conjunction with the accompanying drawings. Attached Figure Description

[0016] Figure 1 This is a protection circuit diagram of the prior art in the embodiments of this utility model;

[0017] Figure 2 This is a circuit diagram illustrating the protection circuit for short circuit of the video input signal line to the power supply in an embodiment of this utility model. Detailed Implementation

[0018] To make the technical solution and advantages of this utility model clearer, the following description is provided in conjunction with the accompanying drawings and embodiments.

[0019] The present invention will now be described in further detail. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of protection of the present invention.

[0020] For the sake of brevity and intuitiveness, the present invention will be described below through several representative embodiments. Numerous details in the embodiments are provided only to aid in understanding the present invention. However, it is clear that the implementation of the present invention may not be limited to these details. To avoid unnecessarily obscuring the present invention, some embodiments are not described in detail, but only a framework is given. In the following text, "comprising" means "including but not limited to," and "according to..." means "at least according to..., but not limited to only according to...". Due to Chinese language habits, unless the quantity of a component is specifically indicated below, it means that the component can be one or more, or can be understood as at least one.

[0021] See Figure 2 As shown, a protection circuit for a short circuit to the power supply of a video input signal line includes: a switching circuit disposed between the video input signal line and a video chip; the switching circuit includes a voltage divider network, a transistor Q1, and a MOSFET Q2; the video input signal line is connected to the input terminal of the voltage divider network and the drain D of the MOSFET Q2, respectively; the output terminal of the voltage divider network is connected to the input terminal of the transistor Q1; the output terminal of the transistor Q1 is connected to the gate G of the MOSFET Q2; and the source S of the MOSFET Q2 is connected to the video chip.

[0022] Specifically, the voltage divider network includes a second resistor R2 and a third resistor R3; one end of the second resistor R2 is connected to the video input line, and the other end of the second resistor R2 is connected to the transistor Q1 and one end of the third resistor R3; the other end of the transistor Q1 is grounded.

[0023] The video input signal line short-circuit protection circuit further includes: a fourth resistor R4 and a fifth resistor R5; the fourth resistor R4 is disposed between the MOS transistor Q2 and the video chip; one end of the fifth resistor R5 is connected to the video chip, and the other end is grounded.

[0024] The protection circuit for short circuit of the video input signal line to the power supply further includes: a DC blocking capacitor C1; the DC blocking capacitor C1 is disposed between the MOS transistor Q2 and the video chip.

[0025] The video input signal line short-circuit protection circuit further includes a first resistor R1; one end of the first resistor R1 is connected to the output terminal of the transistor Q1, and the other end of the first resistor R1 is connected to the DC power supply VCC.

[0026] In this embodiment, transistor Q1 is an NPN transistor; the input terminal of transistor Q1 is the base, and the output terminal of transistor Q1 is the collector. MOSFET Q2 is an N-channel MOSFET.

[0027] In this embodiment, the voltage divider network formed by the second resistor R2 and the third resistor R3 can be configured according to the specific application scenario; that is, the resistance values ​​of the second resistor R2 and the third resistor R3 can be set according to the actual situation. Furthermore, considering that automotive systems typically use 12V / 24V systems, and the current that the fourth resistor R4 (e.g., 33Ω) and the fifth resistor R5 (e.g., 75Ω) can withstand, the input voltage CVBS_IN of the video input signal line is generally set to a threshold voltage, such as around 9V.

[0028] When the CVBS_IN voltage is lower than the threshold voltage, the voltage divider network formed by the second resistor R2 and the third resistor R3 makes the voltage of the third resistor R3 less than the 0.6V turn-on voltage of the PN junction of transistor Q1, so transistor Q1 is in the off state. The voltage between the gate and source of the N-channel MOSFET Q2 is greater than the turn-on voltage, so the drain and source of MOSFET Q2 is normally turned on. The CVBS_IN signal is transmitted to the ADC input terminal of the video chip through the source (S) and drain (D) of MOSFET Q2.

[0029] When the CVBS_IN voltage is higher than the threshold voltage, the voltage divider network formed by the second resistor R2 and the third resistor R3 makes the voltage of the third resistor R3 greater than the 0.6V turn-on voltage of the PN junction of transistor Q1, so transistor Q1 is in the on state. The voltage between the gate and source of N-channel MOSFET Q2 is less than the turn-on voltage. The drain and source of MOSFET Q2 cannot be turned on, so the CVBS_IN signal cannot pass through the source and drain of MOSFET Q2 and cannot be transmitted to the ADC input terminal of the video chip.

[0030] The above are merely specific embodiments of this utility model, but the design concept of this utility model is not limited thereto. Any non-substantial modifications made to this utility model using this concept shall be considered as an infringement of the protection scope of this utility model.

Claims

1. A protection circuit for a video input signal line pair against a power supply short circuit, characterized in that include: A switching circuit is installed between the video input signal line and the video chip; The switching circuit includes a voltage divider network, a transistor, and a MOSFET; the video input signal line is connected to the input terminal of the voltage divider network and the drain of the MOSFET, respectively; the output terminal of the voltage divider network is connected to the input terminal of the transistor; the output terminal of the transistor is connected to the gate of the MOSFET; and the source of the MOSFET is connected to the video chip.

2. The protection circuit against short-circuit of a video input signal line pair according to claim 1, characterized in that, The voltage divider network includes a second resistor and a third resistor; one end of the second resistor is connected to the video input line, and the other end of the second resistor is connected to a transistor and one end of the third resistor; the other end of the transistor is grounded.

3. The protection circuit against short-circuit of a video input signal line to a power supply according to claim 1, characterized in that, Also includes: The fourth resistor and the fifth resistor; the fourth resistor is disposed between the MOSFET and the video chip; One end of the fifth resistor is connected to the video chip, and the other end is grounded.

4. The protection circuit against short-circuit of a video input signal line to a power supply according to claim 1, characterized in that, Also includes: DC blocking capacitor; the DC blocking capacitor is disposed between the MOS transistor and the video chip.

5. The protection circuit for video input signal line-to-power supply short circuit according to claim 1, characterized in that, It also includes a first resistor; one end of the first resistor is connected to the output terminal of the transistor, and the other end of the first resistor is connected to a DC power supply.

6. The protection circuit for video input signal line-to-power supply short circuit according to claim 1, characterized in that, The transistor is an NPN transistor; the input terminal of the transistor is the base, and the output terminal of the transistor is the collector.

7. The protection circuit for video input signal line-to-power supply short circuit according to claim 1, characterized in that, The MOS transistor is an N-channel MOS transistor.

Images