A current sampling comparator circuit

Abstract

The present invention provides a current sampling comparator circuit, including: a current ratio sensor and a current comparator. A large current of a power switch tube of several hundred milliamperes to several amperes is directly compared with a threshold current of the microampere level, thereby ultimately achieving the purpose of judging the magnitude of the power switch tube current and controlling it. The sampling efficiency, the quality and accuracy of the sampling signal, and the cost are taken into account, and the beneficial effects of high sampling efficiency, high sampling quality and low cost are obtained at the same time.

Description

Technical Field

[0001] The invention belongs to the technical field of current sampling of switching power supplies, and in particular relates to a current sampling comparator circuit. Background Art

[0002] Since the dual-loop control of the voltage loop and the current loop has special advantages in the loop stability of the switching power supply and the suppression of the input ripple, the control of the switching power supply has transitioned from the original single-loop control of the voltage loop to the now popular dual-loop control. Since the size of the switch current needs to be detected, judged, and controlled in each cycle, how to efficiently and accurately detect the current size passing through the power switch has become a topic that people continue to study.

[0003] like Figure 1 The figure shows a commonly used sampling method of sensing current by connecting a resistor in series under the power tube. The current through the power switch tube generates a voltage drop on the sampling resistor. This voltage can be compared with the threshold voltage by a comparator to determine the current size. Adjusting the threshold voltage can control the size of the turn-on current. The biggest advantage of this sampling method is that it is simple and direct. It is more suitable for applications with small currents. Therefore, it is most widely used in the field of small and medium-power ACDCs, because the input voltage of ACDC itself is high, and the corresponding excitation current is small. However, in the application of high-power ACDCs and medium-power DCDCs with low input voltages, due to the large excitation current, the sampling resistor heats up, which not only leads to low efficiency of the switching power supply, but also easy to damage. The sampling resistor has a large area, and multiple resistors need to be connected in parallel to pass large currents. In applications with large currents, the following three methods are often used for current sampling:

[0004] The first method is to use a current transformer. Figure 2 As shown in the figure, a current transformer is connected in series below the power switch instead of a sampling resistor. The current flows in from the main transformer and flows out from the secondary side. The current flowing out is attenuated N times, and the attenuation factor is the ratio of the turns ratio of the main transformer to the secondary side of the transformer. It is easy to sample the current after proportional attenuation using a resistor. The advantage of this method is that the sampling efficiency is high because the internal resistance of the transformer coil is small. The disadvantage is that such a transformer requires a magnetic core, which is not small in size, is not easy to manufacture, and has a high cost. Moreover, according to actual experience, failure due to open circuit often occurs in applications.

[0005] The second method is to differentially amplify the sampling resistor voltage. For example, TI has a chip called INA180, which can amplify the sampling resistor voltage by dozens of times, and then compare it with the threshold voltage that controls the current. In this way, the sampling resistor can be reduced exponentially. The reason why the sampling voltage needs to be differentially amplified first and then compared with the threshold voltage, rather than reducing the comparison threshold by multiples and still comparing the voltage on the sampling resistor directly with the threshold voltage, is because the latter greatly reduces the signal-to-noise ratio of the sampling. For example, Figure 3 The original minimum threshold voltage is 200mV and the maximum is 1V. If the threshold voltage is reduced to 1 / 50, although the sampling resistor can also be reduced by 1 / 50 accordingly, the minimum comparison threshold voltage becomes 4mV and the maximum becomes 20mV, which is a very small comparison voltage. The switching noise generated on the sampling resistor or the interference signal on the path from the resistor to the inside of the chip is likely to exceed this voltage and trigger the shutdown of the power switch tube by mistake. The sampling voltage is first amplified by a differential amplifier. Since the two input ports are directly connected to the two ends of the resistor and are very close, the interference signal is considered to be a common-mode signal and is suppressed. The resistors that generate the amplification factor are inside the chip and matched, which also prevents the error amplifier itself from generating additional noise. Therefore, pre-amplification can significantly suppress noise and improve the signal-to-noise ratio. The advantage of this sampling method is to reduce the sampling resistor to a certain extent, reduce the loss and the area occupied by the resistor. The disadvantage is that the pre-amplification factor is limited, otherwise there is still a problem of poor signal-to-noise ratio. At the same time, the offset voltage of the differential amplifier has a direct impact on the accuracy of current sampling. The offset voltage is at the same order of magnitude as the voltage before amplification.

[0006] The third method uses the parasitic resistance of the power MOS tube source itself or its own internal resistance as the sampling resistor to sense the current. This method does not cause unnecessary losses due to the additional series resistance for current sampling, so it is often called lossless current sampling. Figure 4 As shown in the figure, it is a principle block diagram of the current sampling part of a common chip integrated with LDNMOS. The sampling resistor RSENSE under the power tube is the parasitic resistance of the metal wiring of the power tube source, which is inherent. The internal resistance of the metal wiring is very small, so it is necessary to pre-amplify the sampling for comparison, which has the same signal-to-noise ratio and other problems as the second sampling method. At the same time, due to the poor resistance accuracy of the metal wiring and the large positive temperature coefficient, the accuracy of this current sampling is poor, generally outside ±20%.

[0007] It is easy to conclude from comparing the above current sampling methods that each method has its own advantages and disadvantages, but they all have the same feature, which is that they all convert current into voltage, and then compare it with the threshold voltage that limits the current size through a comparator. Such a comparator requires a large area and power consumption to achieve high speed and high precision. Summary of the invention

[0008] In order to solve the above technical problem, the present invention provides a current sampling comparator circuit.

[0009] In order to have a basic understanding of some aspects of the disclosed embodiments, a brief summary is given below. This summary is not intended to be a general review, nor is it intended to identify key / important components or to delineate the scope of protection of these embodiments. Its only purpose is to present some concepts in a simple form as a preface to the detailed description that follows.

[0010] The present invention adopts the following technical solution:

[0011] In some optional embodiments, a current sampling comparator circuit is provided, comprising: a current ratio sensor for sampling a current to be sensed; the current ratio sensor comprises: a power MOS tube, a detection MOS tube, an operational amplifier and a follower current mirror tube;

[0012] The current to be sensed generates a conduction voltage on the conduction internal resistance of the power MOS tube, and the conduction voltage is copied to the conduction resistance of the detection MOS tube through the operational amplifier to generate a following current. The following current mirror tube mirrors the following current to generate a following current mirror current source proportional to the current to be sensed.

[0013] In some optional embodiments, the current ratio sensor includes: a power current input port, a control port, a voltage input positive port, a voltage input negative port and a sampling mirror current source output port; the voltage input positive port and the voltage input negative port are respectively connected to the positive pole and the negative pole of the power supply, and the power current input port and the control port are respectively connected to the current to be detected and the control signal provided outside the current ratio sensor.

[0014] In some optional embodiments, the current sampling comparator circuit further includes: a current comparator for comparing the follower current mirror current source output by the current ratio sensor with the current threshold and outputting a judgment result; the sampling mirror current source output port of the current ratio sensor is connected to the current input port of the current comparator.

[0015] In some optional embodiments, the current comparator includes: a current input port, a threshold current input port, an input voltage positive port, an input voltage negative port, and a comparison result output port for outputting a judgment result; the threshold current input port is connected to the threshold current signal outside the current comparator, and the input voltage positive port and the input voltage negative port are respectively connected to the positive pole and the negative pole of the power supply.

[0016] In some optional embodiments, the follower current mirror tube includes: a transistor PM1 and a transistor PM2; the drain of the power MOS tube is connected to the reverse input port of the operational amplifier; the gate of the power MOS tube is connected to the gate of the detection MOS tube and the enable port of the operational amplifier; the positive input port of the operational amplifier is connected to the drain of the transistor PM1 and the drain of the detection MOS tube; the output port of the operational amplifier is connected to the gate of the transistor PM1 and the gate of the transistor PM2; the positive voltage port of the operational amplifier is connected to the source of the transistor PM1 and the source of the transistor PM2; the negative voltage port of the operational amplifier is connected to the source of the power MOS tube and the source of the detection MOS tube; the drain of the transistor PM2 serves as the sampling mirror current source output port of the current proportional sensor.

[0017] In some optional embodiments, the current comparator includes: a current drain and a Schmitt; the input port of the current drain is connected to the input port of the Schmitt and serves as the current input port of the current comparator; the output port of the current drain is connected to the negative port of the Schmitt voltage input; the positive port of the Schmitt voltage input is connected to the positive pole of the power supply; the output port of the Schmitt serves as the comparison result output port of the current comparator.

[0018] In some optional embodiments, the current comparator includes: a current drain, a MOS tube NM8 and a load resistor R1; the input port of the current drain is connected to the gate of the MOS tube NM8 and serves as the current input port of the current comparator; the output port of the current drain is connected to the source of the MOS tube NM8; the drain of the MOS tube NM8 is connected to the second port of the load resistor R1 and serves as the comparison result output port of the current comparator; the first port of the load resistor R1 is connected to the positive pole of the power supply.

[0019] In some optional embodiments, the follower current mirror tube includes: transistor NM6 and transistor NM7; the gate of the power MOS tube is connected to the gate of the detection MOS tube and the enable port of the operational amplifier; the drain of the power MOS tube is connected to the reverse input terminal of the operational amplifier; the negative voltage port of the operational amplifier is connected to the source of the transistor NM6 and the source of the transistor NM7; the drain of the power MOS tube is connected to the drain of the detection MOS tube and the positive voltage port of the operational amplifier; the gate of the transistor NM7 is connected to the gate of the transistor NM6 and the output port of the operational amplifier; the drain of the transistor NM6 is connected to the positive input terminal of the operational amplifier; the drain of the transistor NM7 serves as the sampling mirror current source output port of the current proportional sensor.

[0020] In some optional embodiments, the current comparator includes: a MOS transistor PM3, a MOS transistor PM4, a MOS transistor NM9 and a load resistor R2; the drain of the MOS transistor PM4 is connected to the gate of the MOS transistor NM9 and serves as a current input port of the current comparator; the drain of the MOS transistor NM9 is connected to the second port of the load resistor R2 and serves as a comparison result output port of the current comparator; the gate of the MOS transistor PM3 is respectively connected to the drain of the MOS transistor PM3 and the gate of the MOS transistor PM4; the source of the MOS transistor PM3 is connected to the source of the MOS transistor PM4 and the first port of the load resistor R2.

[0021] The beneficial effects brought about by the present invention are: sampling of power current at the ampere level is achieved, and comparison is made with the bias current leakage current at the microampere level, taking into account sampling efficiency, quality and accuracy of the sampling signal, and cost, while obtaining the beneficial effects of high sampling efficiency, high sampling quality and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a circuit schematic diagram of current sampling by directly sensing current through series resistance in the prior art;

[0023] Figure 2 This is a circuit schematic diagram of current sampling through a series transformer in the prior art;

[0024] Figure 3 This is a circuit schematic diagram of the prior art for sampling the resistor voltage by differential amplification to obtain current;

[0025] Figure 4 This is a circuit schematic diagram of current sampling using parasitic metal resistance of a MOS tube structure in the prior art;

[0026] Figure 5 This is a principle block diagram of the present invention;

[0027] Figure 6 It is an implementation circuit diagram of the low voltage end current sampling comparator circuit of the present invention;

[0028] Figure 7 It is a circuit diagram of the transistor level implementation of the low voltage terminal current sampling comparator circuit of the present invention;

[0029] Figure 8 It is a circuit diagram for implementing the two-stage amplification comparison of the low voltage end current sampling comparator circuit of the present invention;

[0030] Fig. 9 It is an implementation circuit diagram of the high voltage end NMOS tube power current sampling comparator circuit of the present invention;

[0031] Fig.10It is an implementation circuit diagram of the high voltage end PMOS tube power current sampling comparator circuit of the present invention. DETAILED DESCRIPTION

[0032] The following description and accompanying drawings fully demonstrate specific embodiments of the present invention so that those skilled in the art can practice them. Other embodiments may include structural, logical, electrical, process and other changes. The embodiments represent possible variations only. Unless clearly required, separate components and functions are optional, and the order of operation may vary. The parts and features of some embodiments may be included in or replace the parts and features of other embodiments.

[0033] Embodiment 1:

[0034] like Figures 5 to 8 As shown, a current sampling comparator circuit is provided, including: a current ratio sensor 201 and a current comparator 202. A large current of a power switch tube of several hundred milliamperes to several amperes is directly compared with a threshold current of microamperes, thereby ultimately achieving the purpose of determining the magnitude of the power switch tube current and controlling it.

[0035] The current ratio sensor 201 is used to sample the current to be sensed; the current comparator 202 is used to compare the follower current mirror current source output by the current ratio sensor 201 with the current threshold and output a determination result.

[0036] The current proportional sensor 201 includes: a power MOS tube NM0, a detection MOS tube NM1, an operational amplifier OPA and a follower current mirror tube, and the follower current mirror tube includes: a transistor PM1 and a transistor PM2. The current to be sensed generates a conduction voltage on the conduction internal resistance of the power MOS tube NM0, and the conduction voltage is copied to the conduction resistance of the detection MOS tube NM1 through the operational amplifier OPA to generate a follower current. The follower current mirror tube mirrors the follower current to generate a follower current mirror current source proportional to the current to be sensed.

[0037] The current ratio sensor 201 includes: a power current input port 101, a control port 102, a voltage input positive port 105, a voltage input negative port 103, and a sampling mirror current source output port 104. The voltage input positive port 105 and the voltage input negative port 103 are respectively connected to the positive electrode and the negative electrode of the power supply, and the power current input port 101 and the control port 102 are respectively connected to the current to be detected and the control signal provided outside the current ratio sensor.

[0038] The current comparator 202 includes: a current input port 106, a threshold current input port 107, an input voltage positive port 110, an input voltage negative port 108, and a comparison result output port 109 for outputting a judgment result. The threshold current input port 107 is connected to a threshold current signal outside the current comparator, and the input voltage positive port 110 and the input voltage negative port 108 are connected to the positive electrode and the negative electrode of the power supply, respectively. The sampling mirror current source output port 104 is connected to the current input port 106.

[0039] When the Drive_H input of the control port 102 of the current ratio sensor 201 is at a valid level, the current ratio sensor 201 receives the input current, the current flows in from the power current input port 101, and flows out from the voltage input negative port 103. At the same time, under the action of the signal of the control port 102, the current ratio sensor 201 starts to work and outputs a sensed current that decays in proportion to the input power current; the current comparator 202 directly compares the sensed current output from the current ratio sensor 201 with the threshold current and outputs a judgment result.

[0040] The follower current mirror transistor includes: transistor PM1 and transistor PM2. Transistor PM1 is used for follower current injection, and can be a P-type channel MOS transistor. In a transistor or BCD semiconductor process, a PNP transistor can be used; transistor PM2 is used for mirror sampling current, and can be a P-type channel MOS transistor. In a transistor or BCD semiconductor process, a PNP transistor can be used.

[0041] The drain of the power MOS tube NM0 is connected to the inverting input port VN of the operational amplifier OPA and serves as a power current input port 101 .

[0042] The gate of the power MOS tube NMO is connected to the gate of the detection MOS tube NM1 and the enable port EN of the operational amplifier OPA, and serves as the control port 102 .

[0043] The positive input port VP of the operational amplifier OPA is connected to the drain of the transistor PM1 and the drain of the detection MOS tube NM1.

[0044] An output port VO of the operational amplifier OPA is connected to a gate of the transistor PM1 and a gate of the transistor PM2.

[0045] The voltage positive port of the operational amplifier OPA is connected to the source of the transistor PM1 and the source of the transistor PM2 and is input as a voltage to the positive port 105 .

[0046] The voltage negative port of the operational amplifier OPA is connected to the source of the power MOS tube NM0 and the source of the detection MOS tube NM1 and is used as a voltage input to the negative port 103 .

[0047] The drain of transistor PM2 serves as a sampling mirror current source output port 104 of the current proportional sensor.

[0048] The current comparator 202 includes: a current drain and a Schmitt. The bias current port of the current drain is used as a threshold current input port 107; the input port of the current drain is connected to the input port of the Schmitt SMT and is used as a current input port 106 of the current comparator; the output port of the current drain is connected to the negative voltage input port of the Schmitt SMT to form an input voltage negative port 108; the positive voltage input port of the Schmitt SMT is connected to the positive input voltage port 110; the output port of the Schmitt SMT is used as a comparison result output port 109 of the current comparator.

[0049] The working principle is that when the control port 102 of the current proportional sensor 201 is at a high level, the power MOS tube NM0 is turned on, and the power current I in The conduction voltage drop is formed by the power MOS tube NM0, and the operational amplifier OPA also starts to detect. It forms a voltage follower with the transistor PM1. According to the principle of operational amplification, the operational amplifier OPA will control the gate voltage of the transistor PM1 and generate a certain follower current. This current will also flow into the detection MOS tube NM1, and finally make the drain voltages of NM0 and NM1 equal. NM0 and NM1 are N-channel transistors of the same type but different sizes, and have the same driving voltage. Assuming that the size of NM0 is n times that of NM1, and the on-resistance of NM0 is r0, it is easy to know that the on-resistance of NM1 is n*r0. From the equal drain voltages of NM0 and NM1, we can get:

[0050] I i* r0=I PM1 *n*T0;

[0051] Then the follower current through transistor PM1 is one nth of the power current Iin.

[0052] In order to ensure the matching accuracy of NM0 and NM1, that is, when the size of NM0 is n times that of NM1, the on-resistance of NM1 is also approximately n times that of NM0. The size of NM1 cannot be designed to be too small, otherwise the matching accuracy will deteriorate due to the boundary effect of device parameters caused by the small size, so the multiple n cannot be too large. Then the current passing through PM1 is also not small. For example, the current passing through the power MOS tube NM0 is 2A, n=5000, and the current passing through the transistor PM1 is 400uA. On the one hand, this current value is still too large to be directly used as the input of the current comparator. On the other hand, the current passing through the transistor PM1 can only flow into the detection MOS tube NM1 so that its drain voltage is equal to that of the power MOS tube NM0, and cannot be used as the output current of the current ratio sensor. Therefore, it is necessary to use the transistor PM2 of the same type as the transistor PM1 to mirror the follower current passing through the transistor PM1, and attenuate the current ratio again by m times, and use it as the output current of the current ratio sensor. Assuming that m=8, the total attenuation multiple is mn=400000 times. Such two-fold proportional attenuation can greatly improve the accuracy of current sensing. At the same time, since the output current is reduced to 50uA, it can be used as the input current of the current comparator.

[0053] Before explaining the current comparator, we first explain the two professional terms current source and current drain in integrated circuits. For example, the current generated by transistor PM2 flows into the positive port of the power input and flows out of the drain of transistor PM2. This current can be used as an input source signal for other circuits, so it is often called a current source. Figure 6 The specific implementation circuit of the medium current leakage is as follows Figure 7 In the MOS tube NM3, current flows into the drain of the MOS tube NM3, flows out from the source and directly to the input voltage negative port 108, so it only absorbs current, like a current funnel, and is often called a current drain.

[0054] The transistor PM2 is used as the input current source, and the current drain formed by the MOS tube NM3 is used as the load end for current comparison. Since the small signal impedance of the transistor PM2 and the MOS tube NM3 is large, the single-stage amplifier formed by them can achieve a gain of dozens or even hundreds of times. Then, when the current output by the transistor PM2 is greater than the current that the current drain can absorb, the drain voltage gradually increases with the increase of the current difference, and finally reaches the maximum voltage of the power supply. As the single-stage amplifier has a certain amplification factor, but because it is not large enough, the drain voltage does not rise fast enough, so for applications with low precision requirements, the drain voltage waveform is shaped into a logic level using Schmidt, which can be used as the result of the current size judgment. Figure 7 This is a Schmitt structure commonly used in integrated circuits. The current of transistor PM2 exceeds the current value allowed by the current drain by a certain amplitude, and the Schmitt output is low, indicating that the power current is too large.

[0055] The current comparator 202 may also adopt a two-stage amplification, such as Figure 8 The current comparator 202 includes: a current drain, a MOS transistor NM8 and a load resistor R1; the input port of the current drain is connected to the gate of the MOS transistor NM8 and serves as the current input port 106 of the current comparator; the output port of the current drain is connected to the source of the MOS transistor NM8; the drain of the MOS transistor NM8 is connected to one end of the load resistor R1 and serves as the comparison result output port 109 of the current comparator; the other end of the load resistor R1 serves as the input voltage positive port 110.

[0056] The input current and MOS tube NM3 form the first stage transimpedance amplifier, and its amplified output voltage is the drain voltage of NM3. The second stage voltage amplifier is composed of MOS tube NM8 and load resistor R1. It is a common source amplifier. If npn transistor is used to replace MOS tube NM8, it is a common emitter amplifier. In the integrated circuit, current source is often used as load to replace load resistor R1.

[0057] This current sampling comparator is used in the switching power supply. As long as the output voltage of the voltage-stabilizing error amplifier is used to control the threshold current Ith, the current can be controlled through the power MOS tube switch, and the duty cycle can be continuously adjusted to stabilize the output voltage of the switching power supply at the set value.

[0058] Embodiment 2:

[0059] like Figures 9 to 10 As shown, a current sampling comparator circuit is provided, including: a current ratio sensor 301 and a current comparator 302. The current ratio sensor 301 is used to sample the current to be sensed; the current comparator 302 is used to compare the follower current mirror current source output by the current ratio sensor 301 with the current threshold and output a judgment result.

[0060] The current proportional sensor 301 includes: a power MOS tube NM4, a detection MOS tube NM5, an operational amplifier OPA and a follower current mirror tube, and the follower current mirror tube includes: a transistor NM6 and a transistor NM7. The current to be sensed generates a conduction voltage on the conduction internal resistance of the power MOS tube NM4, and the conduction voltage is copied to the conduction resistance of the detection MOS tube NM5 through the operational amplifier OPA to generate a follower current. The follower current mirror tube mirrors the follower current to generate a follower current mirror current source proportional to the current to be sensed.

[0061] Example 1 is an implementation method of the present invention for current sampling at the low voltage end. The low voltage end here refers to the power tube and the sampling circuit being at the negative input port of the power supply, for example Figure 6The source of the medium power MOS tube NM0 is connected to the power ground, and the drain voltage of the power MOS tube NM0 is also very small when it is turned on, so that the common mode input voltage of the sampled current is low voltage relative to the positive input port voltage of the power supply. In practice, the present invention can also be applied to high-end current sampling, such as the commonly used buck topology non-isolated switching power supply, asymmetric half-bridge, and flyback active clamping, which all have high gate drive MOS tubes, so the high end of the voltage is required for current sampling.

[0062] like Fig. 9 The schematic diagram of the present embodiment 2 is shown, which is the current high-end current sampling circuit of the present invention. Its port number and port function are the same as those in the embodiment 1, and will not be repeated here. Port 101 is the power current input port 101. The difference from the embodiment 1 is that the current flows out, which is equivalent to the negative current flowing out. Because the power MOS tube NM4 is at the high voltage end, the drain is connected to the positive port of the power input, and the source is also close to the voltage of the positive port of the power input when it is turned on; the control port 102 is the driving signal of the power MOS tube NM4 and the detection MOS tube NM5, and is also the enable signal of the operational amplifier.

[0063] When the Drive_H input of the control port 102 of the current ratio sensor 301 is at a valid level, the current ratio sensor 301 receives the input current, the current flows in from the power current input port 101, and flows out from the voltage input negative port 103. At the same time, under the action of the signal of the control port 102, the current ratio sensor 301 starts to work and outputs a sensed current that decays in proportion to the input power current; the current comparator 302 directly compares the sensed current output from the current ratio sensor 301 with the threshold current and outputs a judgment result.

[0064] The gate of the power MOS tube NM4 is connected to the gate of the detection MOS tube NM5 and the enable port EN of the operational amplifier OPA, and serves as the control port 102 .

[0065] The drain of the power MOS tube NM4 is connected to the reverse input terminal VN of the operational amplifier OPA and serves as a power current input port 101.

[0066] The voltage negative port of the operational amplifier OPA is connected to the source of the transistor NM6 and the source of the transistor NM7 and is input as a voltage to the negative port 103 .

[0067] The drain of the power MOS tube NM4 is connected to the drain of the detection MOS tube NM5 and the voltage positive port of the operational amplifier OPA, and is used as the voltage input positive port 105 .

[0068] The gate of the transistor NM7 is connected to the gate of the transistor NM6 and the output port of the operational amplifier OPA.

[0069] The drain of the transistor NM6 is connected to the source of the transistor NM7 and the positive input terminal VP of the operational amplifier OPA.

[0070] The drain of transistor NM7 serves as the sampling mirror current source output port 104 of the current ratio sensor.

[0071] The current comparator 302 includes: a MOS transistor PM3, a MOS transistor PM4, a MOS transistor NM9 and a load resistor R2. The drain of the MOS transistor PM4 is connected to the gate of the MOS transistor NM9 and serves as a current input port 106 of the current comparator; the drain of the MOS transistor NM9 is connected to the second port of the load resistor R2 and serves as a comparison result output port 109 of the current comparator; the gate of the MOS transistor PM3 is connected to the drain of the MOS transistor PM3 and serves as a threshold current input port 107; the source of the MOS transistor PM3 is connected to the source of the MOS transistor PM4 and the first port of the load resistor R2 and serves as an input voltage positive port 110; the source of the MOS transistor NM9 serves as an input voltage negative port 108.

[0072] The voltage high-end current sampling comparator of Example 2 is the same as the voltage low-end current sampling comparator of Example 1 in principle, and has the same port, but due to the different current directions, the device names are different according to the commonly used professional terms. For example, in order to make the conduction voltage drop of the power MOS tube and the detection MOS tube equal, the operational amplifier controls the transistor NM6 to extract the follower current, which is equivalent to the previous negative injection. Then the transistor NM7 proportionally mirrors the current of the transistor NM6, forming a current drain from the drain of the transistor NM7 to the power ground. The current of the current drain is used as the input signal of the current comparator. The load end of the operational amplifier corresponds to the current source, which is formed by the control current of the MOS tube PM4 mirroring the MOS tube PM3. When the current to be sampled flowing through the power MOS tube NM4 is too large, the current allowed to pass by the transistor NM7 is greater than the current provided by the MOS tube PM4, then the gate voltage of the common source amplifier MOS tube NM9 is reduced, and the comparison result output port 109 becomes a low level, so that the low level indicates that the current of the power MOS tube NM4 is too large.

[0073] The present invention is applied to the high-end voltage current sampling circuit, which can be used for current sampling of P-channel power MOS tubes, such as Fig. 9 shown. Fig.10As shown, in the circuit structure, the power MOS tube is changed from N-channel MOS tube NM4 to P-channel MOS tube PM5, the detection MOS tube is changed from N-channel MOS tube NM5 to P-channel MOS tube PM6, and the negative input port VN of the operational amplifier has a circle to indicate that the operational amplifier performs current sampling when the low level input is effective. Because the turn-on threshold voltage of the P-channel MOS tube is a negative value, the effective level of the control drive signal Drive_L is a low level, that is, when it is a low voltage, the power MOS tube and the detection MOS tube are turned on, and the operational amplifier performs current sampling. The circuits and functions of other parts are the same, and the specific working principle will not be repeated.

[0074] In combination with Example 1 and Example 2, the detection MOS tube of the present invention is an insulated gate transistor of the same type but different sizes on the same chip as the power MOS tube. When the power MOS tube is turned on, the detection MOS tube is also turned on, and they are turned on under the same gate-source drive voltage. When the power MOS tube is turned on, the current to be sensed generates a turn-on voltage on the on-state internal resistance of the power MOS tube, and the turn-on voltage is copied to the on-state resistance of the detection MOS tube through an operational amplifier to generate a follower current.

[0075] The following current means that in order to make the on-voltage of the detection MOS tube equal to the on-voltage of the power MOS tube, the operational amplifier must inject or extract a certain current to flow through the on-resistance of the detection MOS tube, so that the voltage drop of the two MOS tubes when turned on is equal. The injected or extracted current is the following current. Since the two MOS tubes are N-channel transistors of the same type on the same chip and are turned on at the same driving voltage, they have the same resistivity, so the following current flowing through the detection MOS tube is proportional to the current to be sensed flowing through the power MOS tube, and the proportionality coefficient is their size proportionality coefficient.

[0076] The current comparator uses the current mirror current source output by the current ratio sensor as the input stage, and a controllable current drain or current source as the load to form the first stage transimpedance amplifier. The output voltage of the transimpedance amplifier is then amplified or Schmidt shaped by the second stage of the common source or common emitter amplifier to accurately compare the current size of the mirror current source and the current drain.

[0077] Controllable current leakage means that the current size of the current leakage can be controlled and changes with the change of the control signal, but the current size of the current leakage is constant when the control signal is stable.

[0078] Compared with traditional sampling technology, the present invention has the following advantages:

[0079] Firstly, the voltage generated by the current to be sampled on the internal resistance of the power MOS tube is used as the sampling signal source. Since no additional resistance is added by a series resistor or a transformer, it has the advantage of high efficiency of lossless sampling. Secondly, compared with the method of sampling voltage by differential amplifier resistor, the internal resistance of the power MOS tube is much larger than the resistance value of the sampling resistor connected in series, so the conduction voltage drop of the power MOS tube is relatively large, so the signal-to-noise ratio is relatively high. In addition, the sampling of the present invention is realized inside the internal chip, and the common mode noise is removed by differential sampling. Thirdly, through the voltage following effect of the operational amplifier, a small current proportional to the current of the power MOS tube is generated on the same device as the power MOS tube, that is, the function similar to the magnetic coupling method of the current transformer is realized by voltage operation, so that the magnitude of the current is independent of the magnitude and temperature coefficient of the internal resistance of the power MOS tube, and the accuracy of current sampling is effectively improved. Finally, the sampled current is directly compared with the current threshold through the current comparator, which has low power consumption, high speed, simple circuit and small area.

[0080] Therefore, the present invention can realize the sampling of power current at the ampere level and compare it with the current of the bias current leakage at the microampere level. When the current of the current mirror current source is greater than the current of the controllable current leakage, the first transimpedance amplifier outputs a higher voltage, which is then amplified by the second-stage amplifier and outputs a logic level indicating that the sampled mirror current is greater than the controllable current leakage current. Under the action of this logic level, the power MOS tube is turned off to control the current size passing through the power MOS tube. In this way, as long as the signal voltage reflecting the output voltage of the switching power supply is error-amplified with the reference voltage and then the current size of the controllable current leakage is changed, the current size of the MOS tube, or the proportion of the switching power supply, can be adjusted, and finally the output voltage of the switching power supply is stabilized at the set value.

[0081] Therefore, in view of the fact that the existing current sampling technologies have obvious shortcomings while maintaining their respective advantages, the present invention proposes a new sampling method that takes advantage of the strengths and overcomes the weaknesses, takes into account the sampling efficiency, the quality and accuracy of the sampling signal, and the cost, and simultaneously obtains the beneficial effects of high sampling efficiency, high sampling quality and low cost.

[0082] Those skilled in the art will also appreciate that the various illustrative logic blocks, modules, circuits, and algorithmic steps described in conjunction with the embodiments herein can all be implemented as electronic hardware, computer software, or a combination thereof. In order to clearly illustrate the interchangeability between hardware and software, various illustrative components, blocks, modules, circuits, and steps are generally described above around their functions. Whether such functions are implemented as hardware or software depends on specific applications and the design constraints imposed on the entire system. A skilled person can implement the described functions in an alternative manner for each specific application, but such implementation decisions should not be interpreted as departing from the scope of protection of the present disclosure.

Claims

1. A current sampling comparator circuit, characterized in that: include: A current proportional sensor for sampling the current to be sensed; The current ratio sensor includes: a power MOS tube, a detection MOS tube, an operational amplifier and a follower current mirror tube; The current to be sensed generates a conduction voltage on the conduction internal resistance of the power MOS tube, and the conduction voltage is copied to the conduction resistance of the detection MOS tube through the operational amplifier to generate a follower current, and the follower current mirror tube mirrors the follower current to generate a follower current mirror current source proportional to the current to be sensed; It also includes a current comparator, which includes: a current input port, a threshold current input port, an input voltage positive port, an input voltage negative port, a comparison result output port for outputting a judgment result, a current drain and a Schmidt; the threshold current input port is connected to a threshold current signal outside the current comparator, the input voltage positive port and the input voltage negative port are respectively connected to the positive pole and the negative pole of the power supply, and the current input port input follows the current mirror current source; the input port of the current drain is connected to the input port of the Schmidt and serves as the current input port of the current comparator; the output port of the current drain is connected to the negative port of the Schmidt voltage input; the positive port of the Schmidt voltage input is connected to the positive pole of the power supply; the output port of the Schmidt serves as the comparison result output port of the current comparator.

2. A current sampling comparator circuit according to claim 1, characterized in that: The current ratio sensor comprises: a power current input port, a control port, a voltage input positive port, a voltage input negative port and a sampling mirror current source output port; the voltage input positive port and the voltage input negative port are respectively connected to the positive pole and the negative pole of the power supply, the power current input port and the control port are respectively connected to the current to be detected and the control signal provided outside the current ratio sensor; the sampling mirror current source output port is connected to the current input port of the current comparator.

3. A current sampling comparator circuit according to claim 2, characterized in that: The current comparator is used for comparing the follow-up current mirror current source output by the current ratio sensor with the current threshold and outputting a judgment result.

4. The current sampling comparator circuit according to claim 1, characterized in that: The follower current mirror tube includes: a transistor PM1 and a transistor PM2; the drain of the power MOS tube is connected to the reverse input port of the operational amplifier; the gate of the power MOS tube is connected to the gate of the detection MOS tube and the enable port of the operational amplifier; the positive input port of the operational amplifier is connected to the drain of the transistor PM1 and the drain of the detection MOS tube; the output port of the operational amplifier is connected to the gate of the transistor PM1 and the gate of the transistor PM2; the positive voltage port of the operational amplifier is connected to the source of the transistor PM1 and the source of the transistor PM2; the negative voltage port of the operational amplifier is connected to the source of the power MOS tube and the source of the detection MOS tube; the drain of the transistor PM2 serves as the sampling mirror current source output port of the current proportional sensor.

5. The current sampling comparator circuit according to claim 1, characterized in that: The current comparator is replaced by: including a current drain, a MOS tube NM8 and a load resistor R1; the input port of the current drain is connected to the gate of the MOS tube NM8 and serves as the current input port of the current comparator; the output port of the current drain is connected to the source of the MOS tube NM8; the drain of the MOS tube NM8 is connected to the second port of the load resistor R1 and serves as the comparison result output port of the current comparator; the first port of the load resistor R1 is connected to the positive electrode of the power supply.

6. The current sampling comparator circuit according to claim 1, characterized in that: The follower current mirror tube includes: a transistor NM6 and a transistor NM7; the gate of the power MOS tube is connected to the gate of the detection MOS tube and the enable port of the operational amplifier; the drain of the power MOS tube is connected to the reverse input terminal of the operational amplifier; the negative voltage port of the operational amplifier is connected to the source of the transistor NM6 and the source of the transistor NM7; the drain of the power MOS tube is connected to the drain of the detection MOS tube and the positive voltage port of the operational amplifier; the gate of the transistor NM7 is connected to the gate of the transistor NM6 and the output port of the operational amplifier; the drain of the transistor NM6 is connected to the positive input terminal of the operational amplifier; the drain of the transistor NM7 serves as the sampling mirror current source output port of the current proportional sensor.

7. The current sampling comparator circuit according to claim 1, characterized in that: The current comparator is replaced by: including a MOS transistor PM3, a MOS transistor PM4, a MOS transistor NM9 and a load resistor R2; the drain of the MOS transistor PM4 is connected to the gate of the MOS transistor NM9 and serves as a current input port of the current comparator; the drain of the MOS transistor NM9 is connected to the second port of the load resistor R2 and serves as a comparison result output port of the current comparator; the gate of the MOS transistor PM3 is respectively connected to the drain of the MOS transistor PM3 and the gate of the MOS transistor PM4; the source of the MOS transistor PM3 is connected to the source of the MOS transistor PM4 and the first port of the load resistor R2.

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