Constant current protection circuit of water level sensor for diesel filter
By introducing a diode into the diesel filter water level sensor circuit to form a constant current protection circuit, the problem of transistor damage caused by short circuit in the signal output line of the water level sensor is solved, ensuring the normal operation of the sensor.
Patent Information
- Application Number
- CN202422567034.0
- Authority / Receiving Office
- CN · China
- Patent Type
- Utility models(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-23
- Publication Date
- 2025-11-04
- Estimated Expiration
- 2034-10-23
AI Technical Summary
In existing diesel filter water level sensors, when the signal output line is short-circuited, the NPN transistor Q1 is easily burned out by the large current, leading to sensor damage.
Introducing diodes D2 and D3 into the water level sensor circuit forms a constant current protection circuit. By clamping the base voltage of the NPN transistor Q1 through the series diodes, it is ensured that the voltage across the sampling resistor is constant and the current flowing through the sampling resistor is constant, thus preventing damage to the transistor.
Short-circuit protection for the water level sensor is implemented to prevent damage to the NPN transistor Q1 due to high current, ensuring the normal operation of the sensor.
Smart Images
Figure CN223514602U_ABST
Abstract
Description
Technical Field
[0001] This utility model relates to the field of diesel filter water level sensor technology, specifically a constant current protection circuit for diesel filter water level sensor. Background Technology
[0002] Diesel fuel contains a certain amount of water, which will slowly settle in the diesel fuel filter after filtration. Over time, this can easily clog the filter. Currently, a water level sensor is installed at the bottom of the filter to detect the water level inside the diesel fuel filter. When the water level reaches a certain level, the water level sensor is triggered and outputs an alarm signal. The car ECU or the water level sensor sends a drive signal to illuminate the water level indicator light, thereby reminding the driver to drain the water.
[0003] Currently, the water level detection circuit of the water level sensor includes an operational amplifier U and an NPN transistor Q1. The inverting input of the operational amplifier U is connected to the positive terminal VCC of the power supply, and the non-inverting input is connected to the detection electrode 1 of the water level sensor. The detection electrode 2 of the water level sensor is connected to the power supply ground GND. The output of the operational amplifier U is connected to the base of the NPN transistor Q1, and the collector of the NPN transistor Q1 is the output terminal Vout of the water level sensor. A load is connected between the positive terminal VCC and the output terminal Vout. When the operational amplifier U outputs a high level, the NPN transistor Q1 conducts, and the collector of the NPN transistor Q1, i.e., the output terminal Vout of the water level sensor, outputs a low level. When a short circuit occurs in the load connected to the output terminal Vout of the water level sensor, since the NPN transistor Q1 does not employ any protection mechanism, a large current will flow directly through the NPN transistor Q1, causing the NPN transistor Q1 to burn out, resulting in damage to the water level sensor and rendering it unusable. Utility Model Content
[0004] The technical problem to be solved by this utility model is to provide a constant current protection circuit for a diesel filter water level sensor, so that the maximum current in the conduction circuit of NPN transistor Q1 is always a constant value, which will not cause damage to NPN transistor Q1, thereby playing a short circuit protection role and avoiding the problem of water level sensor being damaged due to short circuit between signal output line and power supply.
[0005] The technical solution of this utility model is as follows:
[0006] A constant current protection circuit for a diesel filter using a water level sensor is disclosed. The water level detection circuit of the water level sensor includes an operational amplifier U and an NPN transistor Q1. The constant current protection circuit is connected to the NPN transistor Q1. The inverting input terminal of the operational amplifier U is connected to the positive terminal VCC of the power supply, the non-inverting input terminal of the operational amplifier U is connected to the detection electrode 1 of the water level sensor, the detection electrode 2 of the water level sensor is connected to the power supply ground GND, the output terminal of the operational amplifier U is connected to the base of the NPN transistor Q1, the collector of the NPN transistor Q1 is the output terminal Vout of the water level sensor, and a load is connected between the positive terminal VCC and the output terminal Vout. The constant current protection circuit includes a diode and a sampling resistor. The anode of the diode is connected to the base of the NPN transistor Q1, the cathode of the diode is connected to the power supply ground GND, and the sampling resistor is connected between the emitter of the NPN transistor Q1 and the power supply ground GND.
[0007] The constant current protection circuit includes diodes D2 and D3. The anode of diode D2 is connected to the base of NPN transistor Q1, the cathode of diode D2 is connected to the anode of diode D3, and the cathode of diode D3 is connected to power ground GND.
[0008] The load is a pull-up resistor or an indicator light.
[0009] The inverting input terminal of the operational amplifier U is connected to the positive terminal VCC of the power supply through a voltage divider resistor R3, and the inverting input terminal of the operational amplifier U is connected to the power ground GND through a voltage divider resistor R4.
[0010] Both diodes D2 and D3 are SOD323 surface mount diodes.
[0011] Advantages of this utility model:
[0012] The structure of this invention is simple. The small package of the SOD323 surface mount diode occupies little circuit board area. The base voltage of the NPN transistor Q1 is clamped by two series-connected diodes, which limits the voltage across the sampling resistor to a constant voltage. Since the resistance of the sampling resistor is constant, the current flowing through the sampling resistor is constant. The constant current flowing through the sampling resistor will not cause damage to the NPN transistor Q1, thus protecting the water level sensor from damage. Attached Figure Description
[0013] Figure 1 This is the circuit diagram of this utility model. Detailed Implementation
[0014] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the protection scope of the present utility model.
[0015] See Figure 1 The water level detection circuit of the water level sensor includes an operational amplifier U and an NPN transistor Q1. The inverting input of the operational amplifier U is connected to the positive terminal VCC of the power supply through a voltage divider resistor R3. The inverting input of the operational amplifier U is connected to the power ground GND through a voltage divider resistor R4. One end of the resistor R2 is connected to the power supply VCC. One end of the capacitor C1 and the non-inverting input of the operational amplifier U1 are both connected to the other end of the resistor R2. The other end of the capacitor C1 is grounded. The power-on self-test circuit composed of the resistor R2 and the capacitor C1 realizes the power-on self-test. The non-inverting input of the operational amplifier U is connected to the detection electrode 1 of the water level sensor. The detection electrode 2 of the water level sensor is connected to the power ground GND. The output of the operational amplifier U is connected to the base of the NPN transistor Q1. The collector of the NPN transistor Q1 is the output terminal Vout of the water level sensor. A load is connected between the positive terminal VCC of the power supply and the output terminal Vout. The load is a pull-up resistor or an indicator light.
[0016] A constant current protection circuit for a diesel filter using a water level sensor includes diodes D2 and D3 and a sampling resistor R7. The anode of diode D2 is connected to the base of NPN transistor Q1, the cathode of diode D2 is connected to the anode of diode D3, the cathode of diode D3 is connected to power ground GND, and the sampling resistor R7 is connected between the emitter of NPN transistor Q1 and power ground GND. Both diodes D2 and D3 are SOD323 surface mount diodes.
[0017] When diodes D2 and D3 are connected in series, the voltage drop is approximately 0.7V. Therefore, the base voltage (point B) of NPN transistor Q1 is clamped at 1.4V by diodes D2 and D3. The voltage drop between the base (point B) and collector (point E) of NPN transistor Q1 when it is conducting is approximately 0.7V. Thus, the voltage across sampling resistor R7 is 1.4V minus 0.7V, which is a constant value of approximately 0.7V. According to the Pythagorean theorem, the current flowing through a resistor is equal to the voltage across the resistor divided by the resistance value. Since the resistance of sampling resistor R7 is constant and the voltage across sampling resistor R7 is constant, the current flowing through sampling resistor R7 is also constant. Regardless of whether the load connected to the output terminal Vout of the water level sensor is short-circuited or not connected to a load, the current through sampling resistor R7 remains constant. This constant current will not cause damage to NPN transistor Q1, thus avoiding damage to the water level sensor.
[0018] Although embodiments of the present 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 these embodiments without departing from the principles and spirit of the present invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A constant current protection circuit for a diesel filter using a water level sensor, wherein the water level detection circuit of the water level sensor includes an operational amplifier U and an NPN transistor Q1, the constant current protection circuit being connected to the NPN transistor Q1; the inverting input terminal of the operational amplifier U is connected to the positive terminal VCC of the power supply, the non-inverting input terminal of the operational amplifier U is connected to the detection electrode 1 of the water level sensor, the detection electrode 2 of the water level sensor is connected to the power supply ground GND, the output terminal of the operational amplifier U is connected to the base of the NPN transistor Q1, the collector of the NPN transistor Q1 is the output terminal Vout of the water level sensor, and a load is connected between the positive terminal VCC and the output terminal Vout; characterized in that: The constant current protection circuit includes a diode and a sampling resistor. The positive terminal of the diode is connected to the base of the NPN transistor Q1, and the negative terminal of the diode is connected to the power supply ground GND. The sampling resistor is connected between the emitter of the NPN transistor Q1 and the power supply ground GND.
2. The constant current protection circuit for a diesel filter using a water level sensor according to claim 1, characterized in that: The constant current protection circuit includes diodes D2 and D3. The anode of diode D2 is connected to the base of NPN transistor Q1, the cathode of diode D2 is connected to the anode of diode D3, and the cathode of diode D3 is connected to power ground GND.
3. The constant current protection circuit for a diesel filter using a water level sensor according to claim 1, characterized in that: The load is a pull-up resistor or an indicator light.
4. The constant current protection circuit for a diesel filter using a water level sensor according to claim 1, characterized in that: The inverting input terminal of the operational amplifier U is connected to the positive terminal VCC of the power supply through a voltage divider resistor R3, and the inverting input terminal of the operational amplifier U is connected to the power ground GND through a voltage divider resistor R4.
5. The constant current protection circuit for a diesel filter using a water level sensor according to claim 1, characterized in that: Both diodes D2 and D3 are SOD323 surface mount diodes.