Over-current detection circuit

Abstract

An over-current detection circuit comprises a power supply input end, a power supply output end, resistors R1 to R4, a current limiting circuit, PNP triodes Q1 and Q2, and NPN triodes Q3 and Q4. The power input end is connected with the first ends of the resistor R1 and the resistor R2, and the power output end is connected with the second end of the resistor R2 and the emitting electrode of the PNP triode Q2. The PNP triodes Q1 and Q2 share the base electrode, the emitter electrode of the Q1 is connected with the second end of the R1, the base electrode of the Q2 is in short circuit with the emitter electrode, the first end of the current limiting circuit is respectively connected with the base electrodes of the PNP triodes Q1 and Q2, and the second end of the current limiting circuit is grounded. The NPN triode Q3 and the NPN triode Q4 share the same base electrode, the collector electrode of the Q3 is connected with the collector electrode of the Q1 and is in short circuit with the base electrode of the Q3, and the emitter electrode of the Q3 is connected with the first end of the R3; the collector of the Q4 is connected with the collector of the Q2, and the emitter of the Q4 is connected with the first end of the R4; and the second ends of the resistors R3 and R4 are grounded. According to the utility model, low-cost over-current detection is realized.

Description

Technical Field

[0001] The utility model relates to an overcurrent detection circuit. Background Art

[0002] Many manufacturers have the following requirements for vehicle interior lights: the power consumption of the device (including the vehicle interior light and its rear-end device) shall not exceed 2.5W when short-circuited. For example, if the input voltage is 13.5V and a device at the rear end of the vehicle interior light is short-circuited, the transient increase in current shall not exceed 185mA. If this current is exceeded, the circuit needs to be protected. By monitoring the input current of the vehicle interior light, the circuit short-circuit fault can be identified.

[0003] Existing technical solutions usually use operational amplifier chips and sampling resistors to monitor current, which is relatively costly. Summary of the invention

[0004] The technical problem to be solved by the utility model is to provide an overcurrent detection circuit which can realize overcurrent detection at a relatively low cost.

[0005] The utility model embodiment provides an overcurrent detection circuit, including a power input end, a power output end, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a current limiting circuit, a PNP transistor Q1, a PNP transistor Q2, an NPN transistor Q3 and an NPN transistor Q4; the PNP transistor Q1 and the PNP transistor Q2 are of the same model, the NPN transistor Q3 and the NPN transistor Q4 are of the same model, the emitter-collector voltage of the PNP transistor Q1 is equal to the collector-emitter voltage of the NPN transistor Q4, the emitter-base voltage of the PNP transistor Q2 is equal to the base-emitter voltage of the NPN transistor Q3, and the resistance value of the resistor R3 is equal to that of the resistor R4; the power input end is respectively connected to the first end of the resistor R1 and the first end of the resistor R2, and the power output end is respectively connected to the second end of the resistor R2 and the PNP transistor Q4. The emitter of Q2; the PNP transistor Q1 and the PNP transistor Q2 share a base, the emitter of the PNP transistor Q1 is connected to the second end of the resistor R1, the base of the PNP transistor Q2 is short-circuited with the emitter of the PNP transistor Q2, the first end of the current limiting circuit is connected to the base of the PNP transistor Q1 and the base of the PNP transistor Q2 respectively, and the second end of the current limiting circuit is grounded; the NPN transistor Q3 and the NPN transistor Q4 share a base, the collector of the NPN transistor Q3 is connected to the collector of the PNP transistor Q1 and is short-circuited with the base of the NPN transistor Q3, and the emitter of the NPN transistor Q3 is connected to the first end of the resistor R3; the collector of the NPN transistor Q4 is connected to the collector of the PNP transistor Q2, and the emitter of the NPN transistor Q4 is connected to the first end of the resistor R4; the second end of the resistor R3 and the second end of the resistor R4 are both grounded.

[0006] The utility model has at least the following advantages and features:

[0007] 1. In the overcurrent detection circuit of the embodiment of the utility model, the voltage change of the resistor R3 is proportional to the current change of the power input terminal. By detecting the voltage of the resistor R3, the input current can be monitored to achieve overcurrent detection;

[0008] 2. The embodiment of the utility model adopts multiple transistors and multiple resistors to form an overcurrent detection circuit, and the implementation cost is low. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 A circuit schematic diagram of an overcurrent detection circuit according to an embodiment of the utility model is shown. DETAILED DESCRIPTION

[0010] The utility model is described in detail below with reference to the accompanying drawings and specific embodiments.

[0011] See also Figure 1 The overcurrent detection circuit according to an embodiment of the utility model includes a power input terminal Vin, a power output terminal Vout, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a current limiting circuit 1, a PNP transistor Q1, a PNP transistor Q2, an NPN transistor Q3 and an NPN transistor Q4.

[0012] The PNP transistor Q1 and the PNP transistor Q2 are of the same model (the same model means the same operating parameters for both), the NPN transistor Q3 and the NPN transistor Q4 are of the same model, the emitter-collector voltage of the PNP transistor Q1 is equal to the collector-emitter voltage of the NPN transistor Q4, the emitter-base voltage of the PNP transistor Q2 is equal to the base-emitter voltage of the NPN transistor Q3, and the resistance values ​​of the resistor R3 and the resistor R4 are equal. The aforementioned emitter-collector voltage, collector-emitter voltage, emitter-base voltage and base-emitter voltage refer to the nominal voltages of the transistors, and the aforementioned resistance values ​​of the resistors refer to the nominal resistance values ​​of the resistors.

[0013] The power input terminal Vin is connected to the first end of the resistor R1 and the first end of the resistor R2, respectively, and the power output terminal Vout is connected to the second end of the resistor R2 and the emitter of the PNP transistor Q2, respectively. The power output terminal Vout is used to connect the power input terminal of the device to be protected. In a specific embodiment, the power output terminal Vout is connected to the power input terminal of the vehicle interior lamp. In this embodiment, the resistor R2 is a milliohm resistor.

[0014] The PNP transistor Q1 and the PNP transistor Q2 share a base, the emitter of the PNP transistor Q1 is connected to the second end of the resistor R1, the base of the PNP transistor Q2 is short-circuited with the emitter of the PNP transistor Q2, the first end of the current limiting circuit 1 is respectively connected to the base of the PNP transistor Q1 and the base of the PNP transistor Q2, and the second end of the current limiting circuit 1 is grounded. In this embodiment, the current limiting circuit 1 is composed of a resistor R5, the first end of the resistor R5 constitutes the first end of the current limiting circuit 1, and the second end of the resistor R5 constitutes the second end of the current limiting circuit 1.

[0015] The NPN transistor Q3 and the NPN transistor Q4 share a base, the collector of the NPN transistor Q3 is connected to the collector of the PNP transistor Q1 and is short-circuited with the base of the NPN transistor Q3, and the emitter of the NPN transistor Q3 is connected to the first end of the resistor R3; the collector of the NPN transistor Q4 is connected to the collector of the PNP transistor Q2, and the emitter of the NPN transistor Q4 is connected to the first end of the resistor R4.

[0016] A second end of the resistor R3 and a second end of the resistor R4 are both grounded.

[0017] The input voltage of this embodiment supplies power to the back end through resistor R2. When there is power input, the current flows into the ground GND through resistor R1, the emitter and base of PNP transistor Q1 and resistor R5, and PNP transistor Q1 is turned on. At the same time, the current flows into the ground GND through resistor R2, the emitter and base of PNP transistor Q2 and resistor R5, and PNP transistor Q2 is also turned on. After PNP transistor Q1 is turned on, the current flows into the ground GND through the base and emitter of NPN transistor Q3 and resistor R3, and NPN transistor Q3 is also turned on. At the same time, the base voltage of NPN transistor Q4 exceeds the turn-on voltage threshold, so that NPN transistor Q4 is turned on.

[0018] Combination Figure 1 As shown, Figure 1 In the figure, the voltage at point g is Vg = Vgd + Vca + Va; the voltage at point h is Vh = Vhf + Veb + Vb. Where Va and Vb are the voltage at point a and point b respectively, Vgd is the voltage difference between point g and point d (i.e., the emitter-collector voltage of the PNP transistor Q1), Vca is the voltage difference between point c and point a (i.e., the base-emitter voltage of the NPN transistor Q3), Vhf is the voltage difference between point h and point f (i.e., the emitter-base voltage of the NPN transistor Q2), and Veb is the voltage difference between point e and point b (i.e., the collector-emitter voltage of the NPN transistor Q4).

[0019] Since the PNP transistor Q1 and the PNP transistor Q2 are of the same model (the amplification factor and the conduction voltage drop of the PNP transistor Q1 and the PNP transistor Q2 are the same), the NPN transistor Q3 and the NPN transistor Q4 are of the same model (the amplification factor and the conduction voltage drop of the NPN transistor Q3 and the NPN transistor Q4 are the same), the emitter-collector voltage of the PNP transistor Q1 is equal to the collector-emitter voltage of the NPN transistor Q4, the emitter-base voltage of the PNP transistor Q2 is equal to the base-emitter voltage of the NPN transistor Q3, and the resistance values ​​of the resistor R3 and the resistor R4 are equal, so Va=Vb, Vca=Vhf, Vgd=Veb. It can be seen that the voltage at point h is equal to the voltage at point g, that is, Vh=Vg; therefore, the fluctuation of the voltage at point h means that the voltage at point g also changes in the same way. The ratio of the voltage fluctuation on the resistor R1 to the voltage fluctuation on the resistor R3 is equal to the ratio of the resistance values ​​of the two.

[0020] Assuming that the input current increases by 1A, the voltage at point h will decrease by 1A×R2. Similarly, the voltage at point g will also decrease by 1A×R2. Then the voltage at point a will decrease by 1A×R2×(R3 / R1). That is, the voltage change of resistor R3 is proportional to the current change at the power input. Therefore, by detecting the voltage of resistor R3, the input current can be monitored to achieve overcurrent detection.

[0021] Furthermore, the common point of the emitter of the NPN transistor Q3 and the first end of the resistor R3 is connected to the controller. In some specific embodiments, the controller is an MCU, and the common point of the emitter of the NPN transistor Q3 and the first end of the resistor R3 is connected to the ADC (analog-to-digital converter) of the MCU, and the change of the input terminal current is monitored by the ADC of the MCU. When a short circuit occurs at the back end, the MCU will monitor the sudden change of the voltage signal, thereby notifying the system to disconnect the power supply to avoid damage to the subsequent devices.

[0022] This embodiment converts the current change at the power input terminal into a voltage, and feeds back the current change through the voltage change, thereby realizing low-cost monitoring of the input current.

[0023] The above description is a further explanation of the utility model in combination with the specific implementation methods and the accompanying drawings. However, the utility model can obviously be implemented in a variety of other methods different from the description, and those skilled in the art can generalize and deduce according to actual usage without violating the content of the present invention. Therefore, the content of the above specific embodiments should not limit the protection scope determined by the utility model.

Claims

1. An overcurrent detection circuit, characterized in that: It includes a power input terminal, a power output terminal, a resistor R1, a resistor R2, a resistor R3, a resistor R4, a current limiting circuit, a PNP transistor Q1, a PNP transistor Q2, an NPN transistor Q3 and an NPN transistor Q4; the PNP transistor Q1 and the PNP transistor Q2 are of the same model, the NPN transistor Q3 and the NPN transistor Q4 are of the same model, the emitter-collector voltage of the PNP transistor Q1 is equal to the collector-emitter voltage of the NPN transistor Q4, the emitter-base voltage of the PNP transistor Q2 is equal to the base-emitter voltage of the NPN transistor Q3, and the resistance value of the resistor R3 is equal to that of the resistor R4; The power input end is respectively connected to the first end of the resistor R1 and the first end of the resistor R2, and the power output end is respectively connected to the second end of the resistor R2 and the emitter of the PNP transistor Q2; The PNP transistor Q1 and the PNP transistor Q2 share a base, the emitter of the PNP transistor Q1 is connected to the second end of the resistor R1, the base of the PNP transistor Q2 is short-circuited with the emitter of the PNP transistor Q2, the first end of the current limiting circuit is respectively connected to the base of the PNP transistor Q1 and the base of the PNP transistor Q2, and the second end of the current limiting circuit is grounded; The NPN transistor Q3 and the NPN transistor Q4 share a base, the collector of the NPN transistor Q3 is connected to the collector of the PNP transistor Q1 and is short-circuited with the base of the NPN transistor Q3, the emitter of the NPN transistor Q3 is connected to the first end of the resistor R3; the collector of the NPN transistor Q4 is connected to the collector of the PNP transistor Q2, and the emitter of the NPN transistor Q4 is connected to the first end of the resistor R4; A second end of the resistor R3 and a second end of the resistor R4 are both grounded.

2. The overcurrent detection circuit according to claim 1, characterized in that: The current limiting circuit includes a resistor R5, a first end of the resistor R5 constitutes a first end of the current limiting circuit, and a second end of the resistor R5 constitutes a second end of the current limiting circuit.

3. The overcurrent detection circuit according to claim 1, characterized in that: The resistor R2 is a milliohm resistor.

4. The overcurrent detection circuit according to claim 1, characterized in that: A common point between the emitter of the NPN transistor Q3 and the first end of the resistor R3 is connected to the controller.

5. The overcurrent detection circuit according to claim 4, characterized in that: The controller is MCU.

6. The overcurrent detection circuit according to claim 1, characterized in that: The power output end of the overcurrent detection circuit is connected to the power input end of the vehicle interior lamp.

Images