A high-side current detection circuit

Abstract

The present invention relates to a high-side current detection circuit, comprising: a first cascaded current source respectively connected to a vehicle-mounted battery and a vehicle-mounted control unit, the first cascaded current source including a first resistor and at least two sequentially connected PNP transistor pairs, one of the PNP transistor pairs being connected to the first resistor; a second cascaded current source, whose output terminal is connected to a micro-control unit and whose grounding terminal is grounded, the second cascaded current source including a second resistor, a third resistor and at least two sequentially connected NPN transistor pairs, one of the NPN transistor pairs being connected to one of the PNP transistor pairs, and the other being respectively connected to the second resistor and the third resistor. The present invention provides two cascaded current sources, which improves the output impedance, thereby achieving a relatively high current detection accuracy. Moreover, the current of the current source in the present invention is not affected by external factors, resulting in a relatively high power supply rejection ratio, thereby achieving a relatively high stability accuracy.

Description

Technical Field

[0001] The present invention relates to the field of electricity, and more particularly to a high-side current detection circuit. Background Art

[0002] With the increasing number of electronic devices used in automobiles, the demand for monitoring the circuit status of these electronic devices to provide timely protection is also increasing. The current source output impedance of the detection circuits in the prior art is relatively low, resulting in low detection accuracy. Moreover, the current sources of the detection circuits in the prior art are vulnerable to external influences, resulting in low stability accuracy. Summary of the Invention

[0003] To solve the above problems in the prior art, the present invention provides a high-side current detection circuit, which can improve the detection accuracy and stability accuracy of the circuit.

[0004] A high-side current detection circuit provided by the present invention includes:

[0005] A first cascaded current source, which is respectively connected to a vehicle-mounted battery and a vehicle-mounted control unit. The first cascaded current source includes a first resistor and at least two sequentially connected PNP transistor pairs, and one of the PNP transistor pairs is connected to the first resistor; a second cascaded current source, whose output end is connected to a microcontroller unit and whose ground end is grounded. The second cascaded current source includes a second resistor, a third resistor and at least two sequentially connected NPN transistor pairs, one of the NPN transistor pairs is connected to one of the PNP transistor pairs, and the other is respectively connected to the second resistor and the third resistor.

[0006] Further, the number of the PNP transistor pairs is equal to the number of the NPN transistor pairs.

[0007] Preferably, the first cascaded current source includes two PNP transistor pairs, and the second cascaded current source includes two NPN transistor pairs.

[0008] Further, the first cascaded current source includes a first transistor, a second transistor, a third transistor and a fourth transistor, and the second cascaded current source includes a fifth transistor, a sixth transistor, a seventh transistor and an eighth transistor;

[0009] Further, one end of the first resistor is connected to the vehicle-mounted battery, and the other end is connected to the emitter of the first triode. The base of the first triode is connected to the base of the second triode. The collector of the first triode is connected to the emitter of the third triode. The emitter of the second triode is connected to the vehicle-mounted control unit. The collector of the second triode is connected to the emitter of the fourth triode, and the collector of the second triode is also connected to the base of the first triode. The base of the third triode is connected to the base of the fourth triode. The collector of the third triode is the output terminal of the first cascaded current source, which is connected to the collector of the fifth triode. The collector of the fourth triode is connected to the collector of the sixth triode, and the collector of the fourth triode is connected to the base of the third triode;

[0010] The collector of the fifth triode is connected to the base of the sixth triode. The base of the fifth triode is connected to the base of the sixth triode. The emitter of the fifth triode is connected to the collector of the seventh triode. The emitter of the sixth triode is connected to the collector of the eighth triode. The collector of the seventh triode is connected to the base of the eighth triode, and the base of the seventh triode is connected to the base of the eighth triode. The emitter of the seventh triode is the output terminal of the second cascaded current source, which is respectively connected to the micro-control unit and the second resistor. The other end of the second resistor is the grounding terminal of the second cascaded current source, which is connected to the ground. The emitter of the eighth triode is connected to one end of the third resistor, and the other end of the third resistor is the grounding terminal of the second cascaded current source, which is connected to the ground.

[0011] Further, the first triode, the second triode, the third triode, and the fourth triode are all PNP triodes.

[0012] Further, the fifth triode, the sixth triode, the seventh triode, and the eighth triode are all NPN triodes.

[0013] Further, a current detection resistor is connected between the vehicle-mounted battery and the vehicle-mounted control unit.

[0014] Further, the output impedance R of the first cascaded current source 01 is:

[0015]

[0016] In the formula, r 03 represents the output impedance of the third triode, and g m03 represents the transconductance of the third triode, and r 02represents the output impedance of the second triode, r π3 represents the input impedance of the third triode.

[0017] Furthermore, the output impedance R of the second cascaded current source 02 is:

[0018]

[0019] wherein, r 06 represents the output impedance of the sixth triode, g m06 represents the transconductance of the sixth triode, r 08 represents the output impedance of the eighth triode, r π6 represents the input impedance of the sixth triode.

[0020] The present invention provides two cascaded current sources, which improves the output impedance, thereby achieving a higher current detection accuracy. Moreover, the current of the current source in the present invention is not affected by external factors, resulting in a higher power supply rejection ratio, and thus achieving a higher stability accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic structural diagram of a high-side current detection circuit according to the present invention.

[0022] FIG. 2(a) is Figure 1 the relationship curve of the output current and its reference current of the first cascaded current source in Figure 1 ; FIG. 2(b) is

[0023] the relationship curve of the output current and its reference current of the second cascaded current source in DETAILED DESCRIPTION OF THE INVENTION

[0024] The following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings.

[0025] As Figure 1 shown, a high-side current detection circuit provided by the present invention includes a first cascaded current source CM1 and a second cascaded current source CM2 connected to each other. The input end of the first cascaded current source CM1 is connected to the vehicle-mounted battery V, and the output end is connected to the vehicle-mounted control unit B. The output end of the second cascaded current source CM2 is connected to a micro control unit MCU and the ground end is grounded. In addition, a current detection resistor R is also connected between the vehicle-mounted battery V and the vehicle-mounted control unit B.

[0026] The first cascaded current source CM1 includes a first resistor R1, a first triode Q1, a second triode Q2, a third triode Q3, and a fourth triode Q4. The second cascaded current source CM2 includes a second resistor R2, a third resistor R3, a fifth triode Q5, a sixth triode Q6, a seventh triode Q7, and an eighth triode Q8. The first triode Q1, the second triode Q2, the third triode Q3, and the fourth triode Q4 are all PNP triodes, and the fifth triode Q5, the sixth triode Q6, the seventh triode Q7, and the eighth triode Q8 are all NPN triodes.

[0027] Among them, the first triode Q1 and the second triode Q2 form a pair of PNP triodes, the third triode Q3 and the fourth triode Q4 form a pair of PNP triodes, the fifth triode Q5 and the sixth triode Q6 form a pair of NPN triodes, and the seventh triode Q7 and the eighth triode Q8 form a pair of NPN triodes. That is, the first cascaded current source CM1 has two pairs of PNP triodes, and the second cascaded current source CM2 has two pairs of NPN triodes. It should be noted that in other embodiments, the first cascaded current source CM1 may have more than two PNP triodes, and the second cascaded current source CM2 may have more than two NPN triodes with the same number as the number of pairs of PNP triodes. For example, in the first cascaded current source CM1, PNP triodes Q9 and Q10 may be added after the third triode Q3 and the fourth triode Q4, and then in the second cascaded current source CM2, NPN triodes Q11 and Q12 are correspondingly added after the seventh triode Q7 and the eighth triode Q8.

[0028] Specifically, one end of the first resistor R1 is connected to the vehicle-mounted battery V, and the other end is connected to the emitter of the first triode Q1. The base of the first triode Q1 is connected to the base of the second triode Q2, and the collector of the first triode Q1 is connected to the emitter of the third triode Q3. The emitter of the second triode Q2 is connected to the vehicle-mounted control unit B, the collector of the second triode Q2 is connected to the emitter of the fourth triode Q4, and the collector of the second triode Q2 is connected to the base of the first triode Q1. The base of the third triode Q3 is connected to the base of the fourth triode Q4, the collector of the third triode Q3 is the output terminal of the first cascaded current source CM1, and it is connected to the collector of the fifth triode Q5 in the second cascaded current source CM2. The collector of the fourth triode Q4 is connected to the collector of the sixth triode Q6 in the second cascaded current source CM2 and is connected to the base of the third triode Q3.

[0029] In addition to being connected to the collector of the third triode Q3, the collector of the fifth triode Q5 is also connected to the base of the sixth triode Q6, and the base of the fifth triode Q5 is connected to the base of the sixth triode Q6. The emitter of the fifth triode Q5 is connected to the collector of the seventh triode Q7. The emitter of the sixth triode Q6 is connected to the collector of the eighth triode Q8. In addition to being connected to the emitter of the fifth triode Q5, the collector of the seventh triode Q7 is also connected to the base of the eighth triode Q8, and the base of the seventh triode Q7 is connected to the base of the eighth triode Q8. The emitter of the seventh triode Q7 is the output terminal of the second cascaded current source CM2, which is respectively connected to the microcontroller MCU and one end of the second resistor R2. The other end of the second resistor R2 is the ground terminal of the second cascaded current source, which is connected to the ground. The emitter of the eighth triode Q8 is connected to one end of the third resistor R3, and the other end of the third resistor R3 is the ground terminal of the second cascaded current source, which is connected to the ground.

[0030] In the first cascaded current source CM1, the first triode Q1 can be regarded as an impedance connected in series with the emitter of the third triode Q3. After small-signal analysis, the output impedance R of the first cascaded current source CM1 can be obtained. 01 It is:

[0031]

[0032] In the formula, r 03 represents the output impedance of the third triode Q3, g m03 represents the transconductance of the third triode Q3, r 02 represents the output impedance of the second triode Q2, r π3 represents the input impedance of the third triode Q3.

[0033] In the second cascaded current source CM2, the second resistor R2 and the third resistor R3 are of equal size, so that the second cascaded current source CM2 forms a 1:1 current mirror. Similarly, after small-signal analysis, the output impedance R of the second cascaded current source CM2 can be obtained. 02 It is:

[0034]

[0035] In the formula, r 06 represents the output impedance of the sixth triode Q6, g m06 represents the transconductance of the sixth triode Q6, r 08 represents the output impedance of the eighth triode Q8, r π6 represents the input impedance of the sixth triode Q6.

[0036] From the output impedance R of the above-mentioned first cascaded current source CM1 01and the output impedance R of the second cascaded current source CM2 02 As can be seen from the calculation formula, compared with the prior art, the output impedance R 01 and R 02 significantly increase, thus achieving higher current detection accuracy.

[0037] From the current analysis, the output current I at the output terminal of the first cascaded current source CM1 out1 is:

[0038]

[0039] V be1 represents the voltage between the base and emitter of the first triode Q1, V be2 represents the voltage between the base and emitter of the first triode Q1, R1 is the resistance value of the first resistor R1, V T represents the thermal voltage, I ref1 represents the reference current of the first cascaded current source CM1.

[0040] The output current I at the output terminal of the second cascaded current source CM2 out2 is: I out2 = I ref2 , that is, the output current of the second cascaded current source CM2 is equal to its reference current.

[0041] The relationship curve between the output current I out1 at the output terminal of the first cascaded current source CM1 and its reference current I ref1 is shown in Figure 2(a). The relationship curve between the output current I out2 at the output terminal of the second cascaded current source CM2 and its reference current I ref2 is shown in Figure 2(b). As can be seen from the figure, I out1 and I ref1 are roughly in a logarithmic relationship, I out2 and I ref2 are in a linear relationship. When the first cascaded current source CM1 and the second cascaded current source CM2 are connected together, there is I out1 = I ref2 , I out2 = I ref1 , so the simultaneous equations can be solved to obtain I out1 and I out2 . Placing these two relationship curves in the same coordinate system, as shown in Figure 2(c), the circuit will operate at the intersection of the two curves, which makes the current of the current source of the present invention not affected by external factors, especially not affected by the change of the battery voltage, and achieves a very high power supply rejection ratio.

[0042] Figure 3(a) is the simulation waveform diagram of the detection circuit of the present invention when the load current changes from 1A to 24A, and Figure 3(b) is the simulation waveform diagram of the detection circuit of the present invention when the battery voltage changes from 6V to 18V. It can be seen from the figure that when the load current changes between 1A and 24A, the error range of the test current is [4.5%, 0.9%], and the error decreases as the load current increases; when the battery voltage changes between 6V and 18V, it has only a very small impact on the test value, and the stable accuracy is 0.016 / 5 = 0.32%. It can be seen that the detection circuit of the present invention not only has high detection accuracy, but also has high stable accuracy and has good performance.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various changes can be made to the above embodiments of the present invention. That is, all simple, equivalent changes and modifications made according to the claims and the content of the specification of the present invention application fall within the scope of protection of the claims of the present invention patent. The content not described in detail in the present invention is all conventional technical content.

Claims

1. A high-side current detection circuit, characterized in that Comprising: A first cascaded current source, whose input terminal is connected to the vehicle-mounted battery and whose output terminal is connected to the vehicle-mounted control unit. The first cascaded current source includes a first resistor and at least two sequentially connected PNP transistor pairs, and the first one of the at least two sequentially connected PNP transistor pairs is connected to the first resistor; A second cascaded current source, whose output terminal is connected to a micro-control unit and whose ground terminal is grounded. The second cascaded current source includes a second resistor, a third resistor and at least two sequentially connected NPN transistor pairs, and the first one of the at least two sequentially connected NPN transistor pairs is connected to one of the at least two sequentially connected PNP transistor pairs. The last one of the NPN transistor pairs is respectively connected to the second resistor and the third resistor; The first PNP transistor pair of the first cascaded current source includes a first transistor and a second transistor, and the last PNP transistor pair includes a third transistor and a fourth transistor; One end of the first resistor is connected to the vehicle-mounted battery, and the other end is connected to the emitter of the first transistor. The base of the first transistor is connected to the base of the second transistor. The collector of the first transistor is connected to the emitter of the third transistor. The emitter of the second transistor is connected to the vehicle-mounted control unit. The collector of the second transistor is connected to the emitter of the fourth transistor, and the collector of the second transistor is connected to the base of the first transistor. The base of the third transistor is connected to the base of the fourth transistor. The collector of the third transistor is the output terminal of the first cascaded current source, which is connected to the collector of the fifth transistor. The collector of the fourth transistor is connected to the collector of the sixth transistor. The collector of the fourth transistor is connected to the base of the third transistor; The first NPN transistor pair of the second cascaded current source includes a fifth transistor and a sixth transistor, and the last NPN transistor pair includes a seventh transistor and an eighth transistor; The collector of the fifth transistor is connected to the base of the sixth transistor. The base of the fifth transistor is connected to the base of the sixth transistor. The emitter of the fifth transistor is connected to the collector of the seventh transistor. The emitter of the sixth transistor is connected to the collector of the eighth transistor. The collector of the seventh transistor is connected to the base of the eighth transistor, and the base of the seventh transistor is connected to the base of the eighth transistor. The emitter of the seventh transistor is the output terminal of the second cascaded current source, which is respectively connected to the micro-control unit and the second resistor. The other end of the second resistor is the ground terminal of the second cascaded current source, which is connected to the ground. The emitter of the eighth transistor is connected to one end of the third resistor, and the other end of the third resistor is the ground terminal of the second cascaded current source, which is connected to the ground; In the first cascaded current source, the first triode can be regarded as an emitter of the third triode connected in series with an impedance; the output current I at the output end of the first cascaded current source out1 is as follows: Among them, V be1 represents the voltage between the base and the emitter of the first triode, V be2 represents the voltage between the base and the emitter of the second triode, R1 is the resistance value of the first resistor, V T represents the thermal voltage, I ref1 represents the reference current of the first cascaded current source; In the second cascaded current source, the second resistor and the third resistor are of equal size, so that the second cascaded current source forms a 1:1 current mirror; The output current at the output terminal of the second cascaded current source is equal to its reference current; And when the first cascaded current source and the second cascaded current source are connected together, I out1 = I ref2 , I out2 = I ref1 . Therefore, the current of the current source is not affected by the voltage change of the vehicle-mounted battery.

2. The high-side current detection circuit according to claim 1, wherein The number of the PNP transistor pairs is equal to the number of the NPN transistor pairs.

3. The high-side current detection circuit according to claim 1, wherein The first cascaded current source includes two PNP transistor pairs, and the second cascaded current source includes two NPN transistor pairs.

4. The high-side current detection circuit according to claim 1, wherein The first transistor, the second transistor, the third transistor, and the fourth transistor are all PNP transistors.

5. The high-side current detection circuit according to claim 1, wherein The fifth transistor, the sixth transistor, the seventh transistor, and the eighth transistor are all NPN transistors.

6. The high-side current detection circuit according to claim 1, wherein, A current detection resistor is connected between the vehicle-mounted battery and the vehicle-mounted control unit.

7. The high-side current detection circuit according to claim 1, wherein The output impedance R of the first cascaded current source 01 is as follows: where r 03 represents the output impedance of the third triode, and g m03 represents the transconductance of the third triode, r 02 represents the output impedance of the second triode, and r π3 represents the input impedance of the third triode.

8. The high-side current detection circuit according to claim 1, wherein The output impedance R of the second cascaded current source 02 is as follows: where r 06 represents the output impedance of the sixth triode, and g m06 represents the transconductance of the sixth triode, r 08 represents the output impedance of the eighth triode, and r π6 represents the input impedance of the sixth triode.

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