CN219574231U - Overcurrent detection circuit - Google Patents

Abstract

The utility model provides an overcurrent detection circuit. The overcurrent detection circuit comprises a first transistor, a second transistor, a first resistor, a second resistor, a first current reference circuit for providing a first reference current and a second current reference circuit for providing a second reference current. Wherein the first resistor and the second resistor are connected in series between the emitter of the first transistor and the emitter of the second transistor. The base electrode of the first transistor is connected with the base electrode of the second transistor. Wherein the collector of the first transistor is connected to the first current reference circuit and the collector of the second transistor is connected to the second current reference circuit.

Description

Overcurrent detection circuit

Technical Field

The present utility model relates generally to emergency protection circuits and, more particularly, to an over-current detection circuit that may be used in an automotive audio amplifier.

Background

In an automotive audio amplifier, an over-current protection function is generally required, so that when an over-current condition occurs, an amplifier circuit can be isolated from a battery, thereby protecting the amplifier circuit, and other devices connected to the same battery conductor can work normally.

A common over-current protection design is to provide a switch between the power supply or battery and the amplifier circuit and monitor the load current of the amplifier circuit by means of an over-current detection circuit. When the load current of the amplifier circuit exceeds a threshold value, the switch is opened by the switch driving circuit to isolate the amplifier circuit from the power supply or the battery. Existing over-current detection circuits typically employ over-current detection integrated circuits, such as dedicated over-current detection chips (e.g., INA302, etc.). However, the cost of such an overcurrent detection chip is high.

Accordingly, there is a need for an improved technique to address the cost issue.

Disclosure of Invention

The present utility model is directed to an overcurrent detection circuit with a simple structure and low cost, so as to overcome the above-mentioned problems in the prior art.

According to an aspect of the present utility model, there is provided an overcurrent detection circuit. The overcurrent detection circuit comprises a first transistor, a second transistor, a first resistor, a second resistor, a first current reference circuit for providing a first reference current and a second current reference circuit for providing a second reference current. Wherein the first resistor and the second resistor are connected in series between the emitter of the first transistor and the emitter of the second transistor. The base electrode of the first transistor is connected with the base electrode of the second transistor. Wherein the collector of the first transistor is connected to the first current reference circuit and the collector of the second transistor is connected to the second current reference circuit.

The second transistor is turned off when a value of a current flowing through the first resistor is equal to a value of the first reference current.

According to one or more embodiments, the over-current detection circuit further includes a capacitor, one end of the capacitor is connected to the collector of the second transistor, the other end of the capacitor is grounded, and the second reference current is a current for discharging the capacitor.

According to one or more embodiments, wherein the first current reference circuit comprises a third transistor and the second current reference circuit comprises a fourth transistor and a fifth transistor; the bases of the third transistor, the fourth transistor and the fifth transistor are connected together, the emitters of the third transistor, the fourth transistor and the fifth transistor are grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

The second current reference circuit further comprises a third resistor connected between the collector of the fifth transistor and a supply voltage.

The one or more embodiments, wherein the first reference current and the second reference current are equal in value.

The one or more embodiments, wherein the first current reference circuit includes a third transistor and a sixth transistor, and the second current reference circuit includes a fourth transistor and a fifth transistor; the bases of the third transistor and the sixth transistor are connected with each other, the bases of the fourth transistor and the fifth transistor are connected with each other, the emitters of the third transistor, the fourth transistor, the fifth transistor and the sixth transistor are all grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

The second current reference circuit further comprises a third resistor connected between the collector of the fifth transistor and a supply voltage, and the first current reference circuit further comprises a fourth resistor connected between the collector of the sixth transistor and the supply voltage.

The one or more embodiments further include a fifth resistor connected between the collector of the fourth transistor and the collector of the sixth transistor.

The one or more embodiments, wherein the first reference current and the second reference current are not equal in value.

Drawings

The utility model may be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates an exemplary system to which an over-current detection circuit according to the present utility model is applied;

FIG. 2 schematically illustrates an overcurrent detection circuit schematic of one or more embodiments in accordance with an aspect of the utility model;

FIG. 3 illustrates an over-current detection circuit schematic diagram in accordance with one or more embodiments of another aspect of the utility model;

FIG. 4 illustrates an over-current detection circuit schematic diagram of one or more embodiments in accordance with another aspect of the utility model, showing one example circuit for implementing the first and second current reference circuits of FIG. 3;

fig. 5 illustrates an over-current detection circuit schematic diagram of one or more embodiments in accordance with another aspect of the utility model, showing another example circuit for implementing the first and second current reference circuits of fig. 3.

Detailed Description

Embodiments of the present utility model are described in detail below, examples of which are illustrated in the accompanying drawings, wherein like or similar reference numerals refer to like or similar elements or elements having like or similar functions throughout. The embodiments described below by referring to the drawings are illustrative only and are not to be construed as limiting the utility model.

It should be understood that the following description of the embodiments is given for the purpose of illustration only and is not limiting. The division of examples among functional blocks, modules or units shown in the drawings should not be construed as indicating that these functional blocks, modules or units must be implemented as physically separate units. The functional blocks, modules or units shown or described may be implemented as separate units, circuits, chips, functional blocks, modules or circuit elements. One or more of the functional blocks or units may also be implemented in a common circuit, chip, circuit element, or unit.

Unless defined otherwise, technical or scientific terms used herein should be given the ordinary meaning as understood by one of ordinary skill in the art to which this utility model belongs. The use of a singular term (e.g., without limitation, "a") is not intended to limit the number of items. The use of relational terms, such as, but not limited to, "top," "bottom," "left," "right," "upper," "lower," "downward," "upward," "side," "first," "second," "third," and the like are used for descriptive purposes and are not intended to limit the scope of the utility model unless otherwise indicated for clarity in specific reference to the figures. The terms "including" and "such as" are intended to be illustrative, but not limiting, and the word "may" means "may, but need not, be" unless otherwise specified. Although any other language is used in the present utility model, the embodiments shown in the drawings are examples given for the purpose of illustration and explanation, and are not the only embodiments of the subject matter herein.

Fig. 1 schematically illustrates an exemplary system, such as a vehicle audio amplifier system, to which the over-current detection circuit according to the present utility model is applied. The system includes a vehicle battery 102, a switch 104, an amplifier circuit 106, an over-current detection circuit 108, and a switch control circuit 110. The overcurrent detection circuit 108 monitors the current flowing to the amplifier circuit 106 (for example, detects the current through the current detection resistor, as shown by a black rectangular block in the figure), and generates an abnormality warning signal when an abnormality is found (for example, when a load overcurrent or a short circuit occurs), so as to open the switch 104 through the switch control circuit 110, thereby isolating the amplifier circuit 106 from the vehicle battery 102. Wherein the switch 104 may be implemented, for example, by a MOSFET tube.

Fig. 2 schematically illustrates an overcurrent detection circuit schematic of one or more embodiments in accordance with an aspect of the utility model. A current mirror circuit is shown in fig. 2, including transistors 202, 204, 206, 208. The circuit of fig. 2 further includes resistors 210, 212, 214, 216, a load resistor 218 (e.g., which may be understood as a load on the audio amplifier side), a battery voltage 220, a reference voltage 222, a voltage comparator circuit 224, an inductance 226, and a switch 228, which are specifically connected as shown in fig. 2. For ease of understanding, fig. 2 also shows four nodes A, B, C, D. In the circuit shown in fig. 2, node D outputs a voltage proportional to the load current flowing through resistor 212. When the voltage at node D is high enough to exceed the reference voltage 222, the voltage comparator circuit 224 outputs a valid signal E indicating that an over-current has occurred.

The overcurrent detection circuit shown in fig. 2 can realize detection of an overcurrent condition at a lower cost. However, this circuit has a circuit failure problem when the load 218 on the amplifier side is shorted. Specifically, when a short circuit occurs, the right side of resistor 212 (e.g., node B) becomes the ground voltage. Thus, transistors 204 and 208 will lose power, at which point node D outputs the ground voltage, rather than the intended high voltage. Since node D outputs the ground voltage, comparator circuit 224 will not output valid signal E. That is, the circuit shown in fig. 2 fails when a short circuit occurs. In addition, the circuit shown in fig. 2 requires a voltage comparator to output an active signal for controlling the switch by first converting the current into a voltage and then comparing the voltage using the voltage comparator.

Based on the foregoing, it can be appreciated that the overcurrent detection circuit shown in fig. 2 still has room for improvement.

In order to further simplify the circuit, save the cost, and realize the detection and protection functions under both overcurrent and short-circuit conditions, the utility model provides an overcurrent detection circuit in another aspect. The operation principle of the overcurrent detection circuit of the other aspect is as follows: when the overcurrent or short circuit does not occur in a normal working state, the overcurrent detection circuit outputs high voltage; and the current detection circuit outputs a low voltage when either an overcurrent or a short circuit occurs. The overcurrent detection circuit of the other aspect can have the detection and protection functions of overcurrent and short circuit at the same time. Furthermore, the overcurrent detection circuit of this other aspect uses only low-cost transistors and passive elements, and the circuit performs comparison in the current domain, so that no additional voltage comparator is required. Thus, the overcurrent detection circuit of this other aspect can further simplify the circuit and save costs.

Fig. 3 shows an overcurrent detection circuit schematic according to one or more embodiments of another aspect of the utility model. As shown in fig. 3, the overcurrent detection circuit includes a first transistor 302, a second transistor 304, a first resistor 306, and a second resistor 308. Wherein the first resistor 306 is a shunt resistor for shunt and the second resistor 308 is a current reducing resistor for converting current into voltage. In some examples, the first transistor 302 and the second transistor 304 may be, for example, two BJT PNP transistors. The base of the first transistor 302 and the base of the second transistor 304 are connected to each other. The first resistor 306 and the second resistor 308 are connected in series between the emitter of the first transistor 302 and the emitter of the second transistor 304. The left side of node a in the figure is the side of the battery output. For example, point a may be connected to the output of the battery via a switching circuit. The load in the figure generally represents the load of the subsequent circuit, and may represent the load of the subsequent audio amplifier circuit, for example. The voltage output at point G in the diagram may be used as a control signal to control the switch control circuit to drive the switch on and off.

The over-current detection circuit may also include a first current reference circuit 310 and a second current reference circuit 312. Wherein the first current reference circuit 310 is connected between the collector of the first transistor 302 and ground. The second current reference circuit 312 is connected between the collector of the second transistor 304 and ground. The first current reference circuit 310 may provide a first reference current I1. The first reference current I1 may be used as a threshold current for current comparison. The second current reference circuit 312 may provide a second reference current I2. The second reference current is the reference current for discharging the capacitor 314. The values of the first reference current I1 and the second reference current I2 may be the same or different.

The working principle of the overcurrent detection circuit is further described below with reference to fig. 3. From the connection of the resistors to the transistors in fig. 3, it can be appreciated that during normal operation, where no over-current or short circuit condition occurs, the current IR through the first resistor 306 is the resistance of the second resistor 308 divided by the resistance of the first resistor 306 multiplied by the load current IL. This is because the Vbe (voltage between base and collector) of the first transistor 302 and the second transistor 304 is equal, so the voltage across the first resistor 306 is equal to the voltage across the second resistor 308. The current IR will be compared with a first reference current I1 provided by the first current reference circuit 310. Thus, it can be appreciated that in the design of the overcurrent detection circuit, the current IR flowing through the first resistor 306 varies with the variation of the load current IL. Therefore, the overcurrent detection circuit can realize timely detection on whether the load has overcurrent or not by monitoring the current IR. And, depending on whether the current IR flowing through the first resistor 306 reaches the first reference current I1, the collector of the second transistor 304 outputs a different voltage (such as a voltage at a node G in the figure), which can be used as an output signal of the overcurrent detection circuit to control a switch between the battery and the audio amplifier circuit, so that the audio amplifier can be timely isolated and protected. As will be described in further detail below.

For example, when the value of the load current IL is lower than the overcurrent threshold, the value of the current IR is smaller than the value of the current I1, and the first transistor 302 will obtain the difference current Ib from the second transistor 304 (for example, ib=i1-IR). Thus, the second transistor 302 is saturated and the output voltage at the node G is a high voltage. When the load current IL exceeds the overcurrent threshold, the current IR increases to I1 and the differential current Ib will become 0. At this time, the second transistor 304 is turned off, and the voltage output at the node G is pulled toward the ground voltage by the second reference current I2.

The term "overcurrent threshold" is a value that characterizes the load current that turns off the second transistor 304 in the overcurrent detection circuit. For ease of understanding, the overcurrent threshold current may be expressed as the following equation:

overcurrent threshold= (first resistance value/second resistance value) ×first reference current value.

Wherein the over-current threshold is tunable by changing the value of the first resistor, the second resistor or the first reference current.

Based on the above, when no overcurrent condition occurs, the output voltage of the overcurrent detection circuit of the present utility model (the output voltage at the G point) is a high voltage; and when an overcurrent condition occurs, the output voltage of the overcurrent detection circuit of the utility model (the output voltage at the G point) is a low voltage (i.e., ground potential).

The operation of the overcurrent detection circuit of the present utility model when a load short circuit occurs will be discussed. In the overcurrent detection circuit shown in fig. 3, when the load is shorted to the ground, since the second transistor 304 loses power, the voltage output at the node G is a low voltage (i.e., the ground potential).

Based on the above, it can be understood that the voltage output at the node G is a low voltage in both the case of overcurrent and short circuit, and is a high voltage in a normal operation state in which neither of these cases occurs. Therefore, the overcurrent detection circuit can detect the overcurrent and short circuit simultaneously, and timely isolate the subsequent circuit from the battery, thereby playing a role in circuit protection. In addition, the comparison in the overcurrent detection circuit is directly performed in the current domain, so that a voltage comparator is not needed, and the cost is further saved.

In some embodiments, the over-current detection circuit may further include a capacitor 314, where one end of the capacitor 314 is connected to the collector of the second transistor 304, and the other end is grounded. In some examples, the capacitance 314 is a timed capacitance. During normal operation of the system, the second transistor 304 is saturated and the capacitor 314 is charged to the battery voltage Vbatt. When an overcurrent condition occurs, the second transistor 304 turns off and the capacitor 314 slowly discharges through the second reference circuit 312. In other words, the second reference current I2 of the second reference circuit 312 is a reference current for discharging the capacitor 314. At this time, the voltage of the node G linearly drops. By means of the capacitor 314, a delay window can be created. Thus, when an overcurrent or short circuit condition occurs, the output voltage of node G does not immediately trigger the control circuit (e.g., the "switch control circuit" of FIG. 1) due to the presence of capacitor 314. Instead, it will wait until the voltage at node G drops from the battery voltage Vbatt to a preset voltage value (e.g., 2.5V) to trigger the control circuit. For example, the time t_delay of the delay (i.e., the discharge time of the capacitor) can be calculated as:

t_delay=capacitance value (Vbatt-2.5)/I2

It can be appreciated that the smaller the second reference current I2, the longer the discharge time of the capacitor 314; the greater the second reference current I2, the shorter the discharge time of the capacitor 314.

Based on the above, the design of the delay is advantageous in circuitry comprising an audio amplifier. In practical use, an audio amplifier sometimes experiences a transient over-current, but the duration of the over-current is very short, so that it is actually undesirable that this transient over-current will result in over-current protection. The capacitor 314 is configured to avoid such an undesirable false triggering condition of the over-current protection.

Fig. 4 illustrates an over-current detection circuit schematic diagram of one or more embodiments in accordance with another aspect of the utility model, showing one example circuit for implementing the first and second current reference circuits of fig. 3.

As shown in fig. 4, the connection relationship between the first transistor 402, the second transistor 404, the first resistor 406, the second resistor 408, and the capacitor 414 is identical to the connection relationship and the operation principle between the first transistor 302, the second transistor 304, the first resistor 306, the second resistor 308, and the capacitor 314 in fig. 3, and will not be described herein.

Fig. 4 further illustrates an exemplary implementation of the first and second current reference circuits of fig. 3. In some examples, the first current reference circuit may include a third transistor 410, and the second current reference circuit may include a fourth transistor 412, a fifth transistor 416, and a third resistor 418. The third transistor 410, the fourth transistor 412 and the fifth transistor 416 form a current mirror circuit, and the bases of these transistors are connected together, and the emitters of these transistors are all grounded. The collector of the third transistor 410 is connected to the collector of the first transistor 402 and the collector of the fourth transistor 412 is connected to the collector of the second transistor 404. The third resistor 418 is connected between the collector of the fifth transistor 416 and the power supply voltage VCC. Although the third transistor 410, the fourth transistor 412, the fifth transistor 416, and the third resistor 418 are described as being divided into a first current reference circuit and a second current reference circuit for clarity of description, it is understood that these components commonly implement the first current reference circuit and the second current reference circuit through connection to each other.

In the overcurrent detection circuit shown in fig. 4, since the bases of the third transistor 410, the fourth transistor 412, and the fifth transistor 416 are connected together and their emitters are all grounded, the current values of the first reference current I1 and the second reference current I2 are equal. That is, the current values of I1 and I2 are both equal to (VCC-Vbe)/the third resistance value, where Vbe refers to the voltage between the collector and base of the fifth transistor 416. Further, although not shown in the drawings, in some examples, emitter decay resistors (e.g., small resistance of 100R) may be provided between the third transistor 410, the fourth transistor 412, and the fifth transistor 416, respectively, and the ground terminal, to further improve the current matching accuracy.

The operation principle of the overcurrent detection circuit shown in fig. 4 is the same as that of fig. 3, that is, the voltage output at the node G is a low voltage in both the overcurrent and short-circuit cases, and the voltage output at the node G is a high voltage in the normal operation state in which neither of the cases occurs. The detailed operation principle of the circuit is not described here in detail.

Fig. 5 illustrates an over-current detection circuit schematic diagram of one or more embodiments in accordance with another aspect of the utility model, showing another example circuit for implementing the first and second current reference circuits of fig. 3.

As shown in fig. 5, the connection relationship between the first transistor 502, the second transistor 504, the first resistor 506, the second resistor 508 and the capacitor 514 is identical to the connection relationship and the operation principle between the first transistor 302, the second transistor 304, the first resistor 306, the second resistor 308 and the capacitor 314 in fig. 3, and will not be described herein.

Fig. 5 further illustrates another exemplary implementation of the first and second current reference circuits of fig. 3. In some examples, the first current reference circuit may include a third transistor 510, a sixth transistor 518, and a fourth resistor 522. The second current reference circuit may include a fourth transistor 512, a fifth transistor 516, and a third resistor 520. The emitters of the third transistor 510, the fourth transistor 512, the fifth transistor 516 and the sixth transistor 518 are all grounded. The bases of the third transistor 510 and the sixth transistor 518 are connected to each other. The bases of the fourth transistor 512 and the fifth transistor 516 are connected to each other. The collector of the third transistor 510 is connected to the collector of the first transistor 502. The collector of the fourth transistor 512 is connected to the collector of the second transistor 504. The third resistor 520 is connected between the collector of the fifth transistor 516 and the power supply voltage VCC. The fourth resistor 522 is connected between the collector of the fifth transistor 518 and the power supply voltage VCC.

In the overcurrent detection circuit shown in fig. 5, the current values of the first reference current I1 and the second reference current I2 are not equal. Thus, the first transistor 502 and the second transistor 504 are biased by different currents. In addition, the overcurrent detection circuit further includes a hysteresis resistor, namely a fifth resistor 524, for adding hysteresis to the circuit. A fifth resistor 524 is connected between the collector of the sixth transistor 518 and the collector of the fourth transistor 512.

Also, although not shown in the drawings, in some examples, emitter decay resistors (e.g., small resistance of 100R) may be provided between the third transistor 510, the fourth transistor 512, the fifth transistor 516, and the sixth transistor 518, respectively, and the ground, to further improve the current matching accuracy.

The operation principle of the overcurrent detection circuit shown in fig. 5 is the same as that of fig. 3, that is, the voltage output at the node G is a low voltage in both the overcurrent and short-circuit cases, and the voltage output at the node G is a high voltage in the normal operation state in which neither of the cases occurs. The detailed operation principle of the circuit is not described here in detail.

Based on the above, the improved overcurrent detection circuit provided by the utility model adopts a simple structure, and can detect both the load overcurrent condition and the short circuit condition, thereby saving the cost and improving the detection capability, further protecting the amplifier circuit more accurately and further improving the safety of the whole circuit system.

The schematic circuit diagrams and configuration diagrams herein are merely exemplary circuit implementation diagrams presented for better understanding and implementing the teachings of the present utility model by those skilled in the art, and are not meant to be a specific limitation on the technical solutions of the present utility model. Those skilled in the art will appreciate that components may be added or subtracted or component parameter values may be changed depending on the specific application conditions of the circuit.

Item 1. An overcurrent detection circuit, including first transistor, second transistor, first resistance and second resistance, its characterized in that, overcurrent detection circuit still includes:

a first current reference circuit for providing a first reference current, and

a second current reference circuit for providing a second reference current;

wherein the first resistor and the second resistor are connected in series between an emitter of the first transistor and an emitter of the second transistor;

wherein the base electrode of the first transistor is connected with the base electrode of the second transistor;

the collector of the first transistor is connected with the first current reference circuit, and the collector of the second transistor is connected with the second current reference circuit.

Item 2. The over-current detection circuit of item 1, wherein the second transistor is turned off when a value of a current flowing through the first resistor is equal to a value of the first reference current.

The overcurrent detection circuit according to any one of the preceding claims, further comprising a capacitor, one end of the capacitor being connected to the collector of the second transistor, the other end of the capacitor being grounded, the second reference current being a current for discharging the capacitor.

The overcurrent detection circuit according to any one of the preceding claims, wherein the first current reference circuit includes a third transistor, and the second current reference circuit includes a fourth transistor and a fifth transistor; the bases of the third transistor, the fourth transistor and the fifth transistor are connected together, the emitters of the third transistor, the fourth transistor and the fifth transistor are grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

The overcurrent detection circuit according to any one of the preceding claims, wherein the second current reference circuit further includes a third resistor connected between the collector of the fifth transistor and a power supply voltage.

The overcurrent detection circuit according to any one of the preceding items, wherein the first reference current and the second reference current are equal in value.

The overcurrent detection circuit according to any one of the preceding claims, wherein the first current reference circuit includes a third transistor and a sixth transistor, and the second current reference circuit includes a fourth transistor and a fifth transistor; the bases of the third transistor and the sixth transistor are connected with each other, the bases of the fourth transistor and the fifth transistor are connected with each other, the emitters of the third transistor, the fourth transistor, the fifth transistor and the sixth transistor are all grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

The overcurrent detection circuit according to any one of the preceding claims, wherein the second current reference circuit further comprises a third resistor connected between the collector of the fifth transistor and a supply voltage, and the first current reference circuit further comprises a fourth resistor connected between the collector of the sixth transistor and a supply voltage.

The overcurrent detection circuit according to any one of the preceding claims, further comprising a fifth resistor connected between a collector of the fourth transistor and a collector of the sixth transistor.

The overcurrent detection circuit according to any one of the preceding claims, wherein the values of the first reference current and the second reference current are not equal.

The description of the embodiments has been presented for purposes of illustration and description. Suitable modifications and adaptations to the embodiments may be performed in view of the above description or may be acquired by practicing the methods. The described methods and associated actions may also be performed in a variety of orders, in parallel, and/or simultaneously other than that described in the present disclosure. The described system is exemplary in nature and may include other elements and/or omit elements. The subject matter of the utility models includes all novel and non-obvious combinations and subcombinations of the various systems and configurations disclosed, as well as other features, functions and/or properties.

As used in this disclosure, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural said elements or steps, unless such exclusion is indicated. Furthermore, references to "one embodiment" or "an example" of the present utility model are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. The utility model has been described above with reference to specific embodiments. However, one of ordinary skill in the art appreciates that various modifications and changes can be made thereto without departing from the broader spirit and scope of the utility model as set forth in the claims below.

Claims (10)

1. An overcurrent detection circuit comprising a first transistor, a second transistor, a first resistor and a second resistor, wherein the overcurrent detection circuit further comprises:

a first current reference circuit for providing a first reference current, and

a second current reference circuit for providing a second reference current;

wherein the first resistor and the second resistor are connected in series between an emitter of the first transistor and an emitter of the second transistor;

wherein the base electrode of the first transistor is connected with the base electrode of the second transistor;

the collector of the first transistor is connected with the first current reference circuit, and the collector of the second transistor is connected with the second current reference circuit.

2. The overcurrent detection circuit of claim 1, wherein the second transistor is turned off when a value of a current flowing through the first resistor is equal to a value of the first reference current.

3. The overcurrent detection circuit of claim 1, further comprising a capacitor having one end connected to a collector of the second transistor and the other end grounded, the second reference current being a current for discharging the capacitor.

4. The overcurrent detection circuit of claim 1, wherein the first current reference circuit comprises a third transistor, and the second current reference circuit comprises a fourth transistor and a fifth transistor; the bases of the third transistor, the fourth transistor and the fifth transistor are connected together, the emitters of the third transistor, the fourth transistor and the fifth transistor are grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

5. The overcurrent detection circuit of claim 4, wherein the second current reference circuit further comprises a third resistor connected between a collector of the fifth transistor and a supply voltage.

6. The overcurrent detection circuit of claim 5, wherein the first reference current is equal to the second reference current in value.

7. The overcurrent detection circuit of claim 1, wherein the first current reference circuit comprises a third transistor and a sixth transistor, and the second current reference circuit comprises a fourth transistor and a fifth transistor; the bases of the third transistor and the sixth transistor are connected with each other, the bases of the fourth transistor and the fifth transistor are connected with each other, the emitters of the third transistor, the fourth transistor, the fifth transistor and the sixth transistor are all grounded, the collector of the third transistor is connected with the collector of the first transistor, and the collector of the fourth transistor is connected with the collector of the second transistor.

8. The overcurrent detection circuit of claim 7, wherein the second current reference circuit further comprises a third resistor connected between the collector of the fifth transistor and a supply voltage, and the first current reference circuit further comprises a fourth resistor connected between the collector of the sixth transistor and the supply voltage.

9. The overcurrent detection circuit of claim 8, further comprising a fifth resistor connected between a collector of the fourth transistor and a collector of the sixth transistor.

10. The overcurrent detection circuit of claim 9, wherein the first reference current and the second reference current are not equal in value.