Protection circuit applied to NTC sampling circuit

Abstract

The utility model relates to the field of LED (Light Emitting Diode) control device circuits, and provides a protection circuit applied to an NTC (Negative Temperature Coefficient) sampling circuit, which comprises a sampling voltage division circuit, a signal following circuit, a clamping protection circuit and a signal filtering circuit, the output end of the signal follower circuit is connected with the input end of the signal filter circuit through the clamping protection circuit, the clamping protection circuit is used for protecting a post-stage circuit when the protection circuit is connected with high voltage, and the output end of the signal follower circuit is connected with the input end of the signal filter circuit and is used for improving the signal-to-noise ratio of a temperature acquisition signal. The output end of the signal filter circuit is connected with the input end of the MCU chip; the NTC signal sampling protection circuit is applied to an LED control device and can protect NTC signal sampling of an LED lamp.

Description

Technical Field

[0001] The utility model relates to the field of LED control device circuits, and more specifically, to a protection circuit applied to an NTC sampling circuit. Background Art

[0002] In an LED control device, it is usually necessary to accurately detect the temperature change of an LED lamp. Due to its high sensitivity and high precision, the NTC circuit has been well applied to temperature measurements that attach importance to durability, reliability, and stability. In low-cost temperature measurement solutions, a general NTC acquisition circuit, as Figure 1 shown, will connect a resistor in series between the NTC thermistor and the positive power supply. By collecting the voltage change across the NTC thermistor and sending it to the ADC pin of the MCU for calculation, the temperature change of the LED lamp is determined.

[0003] However, the above NTC acquisition circuit does not protect the input of the NTC circuit to the MCU. In actual use, factors such as the wire length, wiring method, and incorrect wiring installation of the NTC circuit cause the thermistor RT1 to be affected by external interference, resulting in high-frequency noise, spike voltage, or the situation of misconnecting high-voltage signals, which will affect the accuracy of the collected data and even damage the subsequent MCU, leading to product failure. Summary of the Utility Model

[0004] The problem solved by the utility model is how to provide a circuit for protecting the NTC signal sampling of a lamp in an LED control device.

[0005] To solve the above problems, the utility model provides a protection circuit applied to an NTC sampling circuit, including: a sampling voltage division circuit, a signal follower circuit, a clamping protection circuit, and a signal filtering circuit. The input end of the sampling voltage division circuit is connected to the signal end of the NTC sampling resistor, and the output end is connected to the input end of the signal follower circuit through the clamping protection circuit. The clamping protection circuit is used to protect the subsequent circuit when a high voltage is connected to the protection circuit. The output end of the signal follower circuit is connected to the input end of the signal filtering circuit to improve the signal-to-noise ratio of the temperature acquisition signal. The output end of the signal filtering circuit is connected to the input end of the MCU chip.

[0006] Further, the clamping protection circuit includes a first diode, a second diode, a first resistor, and a second resistor. The cathode of the first diode is connected to the 3.3V power supply, and the anode is connected to the positive input end of the signal follower circuit. The cathode of the second diode is connected to the anode of the first diode, and the anode is grounded. The first end of the first resistor is connected to the cathode of the first diode, and the second end is connected to the anode of the first diode. The first end of the second resistor is connected to the cathode of the second diode, and the second end is grounded.

[0007] Further, the clamping protection circuit further includes a first capacitor. The first end of the first capacitor is connected to the 3.3V power supply, and the second end is connected to the anode of the second diode.

[0008] Further, the sampling voltage dividing circuit includes a third resistor and the second resistor. The first end of the third resistor is connected to the first end of the second resistor, the second end is connected to the positive signal end of the NTC sampling resistor, and the negative signal end of the NTC sampling resistor is connected to the second end of the second resistor.

[0009] Further, the signal follower circuit includes a first operational amplifier and a fourth resistor. The positive input terminal of the first operational amplifier is connected to the output terminal of the clamping protection circuit, the output terminal is connected to the input terminal of the signal filtering circuit, and the fourth resistor is disposed between the negative input terminal and the output terminal of the first operational amplifier.

[0010] Further, the signal filtering circuit includes a second capacitor and a fifth resistor. The first end of the fifth resistor is connected to the output terminal of the signal follower circuit, the second end is connected to the input terminal of the MCU chip, the first end of the second capacitor is connected to the second end of the fifth resistor, and the second end is grounded.

[0011] Further, it further includes a third capacitor, which is connected to the power supply terminal of the MCU chip for power filtering of the MCU chip.

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

[0013] Under the condition of ensuring accurate temperature acquisition, a follower circuit is formed by using an operational amplifier, and a clamping protection circuit is formed by using the clamping function of a diode, effectively solving the problems of input signal disturbance of the NTC circuit and device damage caused by misconnection of high-voltage signal lines, and ensuring the stability and accuracy of temperature acquisition. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is the circuit schematic diagram of the existing NTC circuit of the embodiment of the present utility model;

[0015] Figure 2 is the overall principle structure schematic diagram of the embodiment of the present utility model;

[0016] Figure 3 is the circuit principle schematic diagram of the embodiment of the present utility model. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] In order to make the above objects, features, and advantages of the present utility model more obvious and understandable, the following detailed description of the specific embodiments of the present utility model is given with reference to the accompanying drawings.

[0018] In the description of the present utility model, it should be noted that unless otherwise clearly specified and defined, the terms "set", "installed", "connected", and "coupled" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific situations.

[0019] In the description of this specification, the descriptions referring to terms such as "embodiment", "one embodiment", and "one implementation manner" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or implementation manner are included in at least one embodiment or implementation manner of the present utility model. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or implementation manner. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or implementation manners.

[0020] As Figure 2 shown, the present utility model provides a protection circuit applied to an NTC sampling circuit, including: a sampling voltage dividing circuit, a signal following circuit, a clamping protection circuit, and a signal filtering circuit. The input end of the sampling voltage dividing circuit is connected to the signal end of the NTC sampling resistor, and the output end is connected to the input end of the signal following circuit through the clamping protection circuit. The clamping protection circuit is used to protect the subsequent circuit when a high voltage is connected to the protection circuit. The output end of the signal following circuit is connected to the input end of the signal filtering circuit to improve the signal-to-noise ratio of the temperature acquisition signal. The output end of the signal filtering circuit is connected to the input end of the MCU chip.

[0021] As Figure 1 shown, in the existing NTC circuit, an NTC sampling resistor RT1, a capacitor C1, and a resistor R1 are adopted. The resistor R1 is connected in series with the NTC sampling resistor RT1 and arranged between the power supply and the ground. The capacitor C1 is connected in parallel with the NTC sampling resistor RT1. The first end of the NTC sampling resistor RT1, that is, the positive signal, is sent to the ADC pin of the MCU, and the second end, that is, the negative signal end, is grounded. In this way, when RT1 is interfered by the outside world, generating high-frequency noise and spike voltage, or when the power supply of the NTC circuit is accidentally connected to a high voltage (the high voltage means a voltage higher than the normal working voltage), it will cause inaccurate sampling, and even damage the subsequent MCU chip by the high voltage. Therefore, a protection circuit is needed to process the temperature sampling signal and protect the subsequent MCU chip. Among them, the MCU chip can adopt any type of single-chip microcomputer chip with an ADC receiving port.

[0022] As Figure 3As shown, in this embodiment, a protection circuit applied to the NTC sampling circuit is composed of a first operational amplifier UN3, a first diode DN1, a second diode DN2, a first resistor RN1, a second resistor RN7, a third resistor RN8, a fourth resistor RN10, a fifth resistor RN9, a first capacitor CN5, and a second capacitor CN2.

[0023] Figure 3 In it, NTC+ and NTC-, that is, the positive and negative signals of the NTC sampling resistor RT1, are respectively connected to the first end and the second end of the NTC sampling resistor RT1. After the third resistor RN8 is connected in series with the NTC sampling resistor RT1 and then connected in parallel with the second resistor RN7, they together form a lower voltage division circuit for NTC sampling. The resistance value of the NTC sampling resistor changes with temperature, and the voltage at pin 1 of the first operational amplifier UN3 changes. Through the follower function of the operational amplifier, the voltage at pin 4 of the operational amplifier changes synchronously. Through the RC filtering composed of RN9 and CN2, it is sent to the UN1 MCU for data acquisition and processing, and the current ambient temperature value is calculated.

[0024] After the signals of NTC+ and NTC- pass through the voltage follower of the operational amplifier, the NTC temperature acquisition circuit has a lower input impedance and a higher output impedance, so that the signal output by the operational amplifier has less loss during transmission, improving the signal fidelity and enabling the MCU to more accurately collect the NTC data. The voltage follower circuit composed of the first operational amplifier UN3 has good noise performance, can reduce the noise interference of the signal during transmission, enables the circuit to adapt to different signal sources and environments, and improves the signal-to-noise ratio of the signal.

[0025] When the signals of NTC+ and NTC- are misconnected to high-voltage signals, when NTC+ is connected to the negative pole of the high voltage and NTC- is connected to the positive pole of the high voltage, that is, NTC- forms a forward high voltage. The input signal forms a loop through the second diode DN2 and the third resistor RN8 (the input impedance of pin 1 of the operational amplifier is high), thereby protecting the subsequent stage UN1. When NTC+ is connected to the positive pole of the high voltage and NTC- is connected to the negative pole of the high voltage, that is, NTC+ forms a forward high voltage. The input signal forms a loop through the third resistor RN8, the first resistor DN1, and the power supply C3.3V. The positive pole of DN1 is clamped at about 3.7V, and the high-voltage signal is dissipated on the third resistor RN8, thereby protecting the subsequent stage UN1 and preventing the product from being damaged.

[0026] Although the present disclosure is disclosed as above, the protection scope of the present disclosure is not limited thereto. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present disclosure, and these changes and modifications will all fall within the protection scope of the present invention.

Claims

1. A protection circuit applied to an NTC sampling circuit, characterized in that Comprising: A sampling voltage-dividing circuit, a signal follower circuit, a clamping protection circuit, and a signal filtering circuit. The input end of the sampling voltage-dividing circuit is connected to the signal end of the NTC sampling resistor, and the output end is connected to the input end of the signal follower circuit through the clamping protection circuit. The clamping protection circuit is used to protect the subsequent circuit when a high voltage is applied to the protection circuit. The output end of the signal follower circuit is connected to the input end of the signal filtering circuit to improve the signal-to-noise ratio of the temperature acquisition signal. The output end of the signal filtering circuit is connected to the input end of the MCU chip.

2. The protection circuit applied to the NTC sampling circuit according to claim 1, characterized in that, The clamping protection circuit includes a first diode, a second diode, a first resistor, and a second resistor. The cathode of the first diode is connected to the 3.3V power supply, and the anode is connected to the positive input end of the signal follower circuit. The cathode of the second diode is connected to the anode of the first diode, and the anode is grounded. The first end of the first resistor is connected to the cathode of the first diode, and the second end is connected to the anode of the first diode. The first end of the second resistor is connected to the cathode of the second diode, and the second end is grounded.

3. The protection circuit applied to the NTC sampling circuit according to claim 2, characterized in that The clamping protection circuit further includes a first capacitor. The first end of the first capacitor is connected to the 3.3V power supply, and the second end is connected to the anode of the second diode.

4. The protection circuit applied to the NTC sampling circuit according to claim 2, characterized in that, The sampling voltage-dividing circuit includes a third resistor and the second resistor. The first end of the third resistor is connected to the first end of the second resistor, and the second end is connected to the positive signal end of the NTC sampling resistor. The negative signal end of the NTC sampling resistor is connected to the second end of the second resistor.

5. The protection circuit applied to the NTC sampling circuit according to claim 4, characterized in that, The signal follower circuit includes a first operational amplifier and a fourth resistor. The positive input end of the first operational amplifier is connected to the output end of the clamping protection circuit, and the output end is connected to the input end of the signal filtering circuit. The fourth resistor is disposed between the negative input end and the output end of the first operational amplifier.

6. The protection circuit applied to the NTC sampling circuit according to claim 5, characterized in that, The signal filtering circuit includes a second capacitor and a fifth resistor. The first end of the fifth resistor is connected to the output end of the signal follower circuit, and the second end is connected to the input end of the MCU chip. The first end of the second capacitor is connected to the second end of the fifth resistor, and the second end is grounded.

7. The protection circuit applied to the NTC sampling circuit according to claim 1, characterized in that, It further includes a third capacitor, which is connected to the power supply end of the MCU chip for power supply filtering of the MCU chip.

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