Disclosure of Invention
The embodiment of the application provides an overcurrent protection circuit and an operational amplifier, which can solve the problem that an output power tube in an operational amplifier module is burnt out due to overcurrent possibly caused by the existing overcurrent protection circuit.
In a first aspect, an embodiment of the present application provides an overcurrent protection circuit, including a sampling module, a comparing module and a clamping module, where the sampling module is electrically connected with the comparing module and the clamping module, the comparing module is electrically connected with the clamping module, and the sampling module and the clamping module are both electrically connected with an operational amplifier module;
When the current flowing through the output power tube in the operational amplifier module is larger than or equal to a preset current, the sampling module is used for outputting sampling voltage to the comparing module and the clamping module according to the current flowing through the output power tube, the comparing module is used for outputting a first level signal to the clamping module when the sampling voltage is smaller than a first voltage, and the clamping module is used for outputting a clamping voltage signal to the operational amplifier module according to the first level signal and the sampling voltage, so that the current flowing through the output power tube is reduced.
In a possible implementation manner of the first aspect, the sampling module includes a first resistor and a first switching tube, a first end of the first resistor is used for being electrically connected with a first power supply, a second end of the first resistor is electrically connected with a source electrode of the first switching tube, the comparing module and the clamping module respectively, and a gate electrode of the first switching tube and a drain electrode of the first switching tube are both used for being electrically connected with the operational amplifier module.
In a possible implementation manner of the first aspect, the comparing module includes a first voltage generating unit and a comparing unit, the first voltage generating unit is electrically connected to the comparing unit and the clamping module, the comparing unit is electrically connected to the sampling module and the clamping module, and the first voltage generating unit is used for being electrically connected to a first power supply;
The first voltage generating unit is used for outputting the first voltage to the comparing unit according to the power supply voltage output by the first power supply, and the comparing unit is used for outputting the first level signal to the clamping module when the sampling voltage is smaller than the first voltage.
In one possible implementation manner of the first aspect, the first voltage generating unit includes a second resistor, a third resistor, a fourth resistor, a fifth resistor, a first current source and a second switching tube, where a first end of the second resistor and a source of the second switching tube are electrically connected to the first power supply, a second end of the second resistor is electrically connected to a first end of the third resistor, a first end of the fourth resistor is electrically connected to a second end of the third resistor and a drain of the second switching tube, a second end of the fourth resistor is electrically connected to a first end of the fifth resistor and the comparing unit, a first end of the first current source is electrically connected to a second end of the fifth resistor, a second end of the first current source is grounded, and a gate of the second switching tube is electrically connected to the comparing unit and the clamping module, respectively.
In a possible implementation manner of the first aspect, the comparing unit includes a comparator, a first input terminal of the comparator is electrically connected to the first voltage generating unit, a second input terminal of the comparator is electrically connected to the sampling module, and output terminals of the comparator are respectively electrically connected to the first voltage generating unit and the clamping module.
In a possible implementation manner of the first aspect, the clamping module includes a second voltage generating unit and a clamping unit, the second voltage generating unit is electrically connected to the clamping unit and the comparing module, the clamping unit is electrically connected to the sampling module and the operational amplifier module, and the second voltage generating unit and the clamping unit are both used for being electrically connected to a first power supply;
the second voltage generating unit is used for outputting a second voltage to the clamping unit according to the first level signal and the power supply voltage output by the first power supply, and the clamping unit is used for outputting the clamping voltage signal to the operational amplifier module when the sampling voltage is smaller than the second voltage so as to reduce the current flowing through the output power tube.
In one possible implementation manner of the first aspect, the second voltage generating unit includes a sixth resistor, a seventh resistor, an eighth resistor, a ninth resistor, a second current source, and a third switch tube, where a first end of the sixth resistor and a source of the third switch tube are electrically connected to the first power supply, a second end of the sixth resistor is electrically connected to a first end of the seventh resistor and a drain of the third switch tube, a first end of the eighth resistor is electrically connected to a second end of the seventh resistor, a second end of the eighth resistor is electrically connected to a first end of the ninth resistor and the clamping unit, a first end of the second current source is electrically connected to a second end of the ninth resistor, a second end of the second current source is grounded, and a gate of the third switch tube is electrically connected to the comparison module.
In one possible implementation manner of the first aspect, the clamping unit includes an amplifier, a fourth switching tube, a fifth switching tube and a third current source, a first input end of the amplifier is electrically connected with the second voltage generating unit, a second input end of the amplifier is electrically connected with the sampling module, an output end of the amplifier is respectively electrically connected with a gate electrode of the fourth switching tube and a gate electrode of the fifth switching tube, a source electrode of the fourth switching tube and a source electrode of the fifth switching tube are both used for being electrically connected with the first power supply, a drain electrode of the fourth switching tube is electrically connected with a first end of the third current source, a drain electrode of the fifth switching tube is used for being electrically connected with the operational amplifier module, and a second end of the third current source is grounded.
In a possible implementation manner of the first aspect, the overcurrent protection circuit further includes a first switch module and a second switch module, where the first switch module is electrically connected to the clamp module, and the second switch module is electrically connected to the comparison module and the clamp module, respectively;
The first switch module and the second switch module are both used for being conducted according to the second level signal output by the clamping module.
In a second aspect, an embodiment of the present application provides an operational amplifier, including an operational amplifier module and any one of the overcurrent protection circuits in the first aspect, where the operational amplifier module is electrically connected to a sampling module and a clamping module in the overcurrent protection circuit respectively.
Compared with the prior art, the embodiment of the application has the beneficial effects that:
The overcurrent protection circuit provided by the embodiment of the application comprises a sampling module, a comparison module and a clamping module, and when the current flowing through the output power tube is greater than or equal to the preset current, the overcurrent protection circuit can represent that the operational amplifier module is in an overcurrent state and simultaneously represents that the operational amplifier module is in an output short circuit or in a heavy-load working state. At this time, the sampling module samples the current flowing through the output power tube, and outputs sampling voltage to the comparison module and the clamping module according to the current. The comparison module receives the sampling voltage and outputs a first level signal to the clamping module when the sampling voltage is smaller than the first voltage. The clamping module outputs a clamping voltage signal to the operational amplifier module according to the first level signal and the sampling voltage, so that the current flowing through the output power tube is reduced. Therefore, in the overcurrent protection circuit provided by the embodiment of the application, when the current flowing through the output power tube is greater than or equal to the preset current, the comparison module can output the first level signal, so that the clamping module starts to work, the current flowing through the output power tube is clamped smaller, the operational amplifier module is prevented from being in an overcurrent state, and the output power tube in the operational amplifier module is prevented from being burnt out due to overcurrent. Therefore, even if the operational amplifier module works under heavy load or full load, the output current can not reach the current value of the burnt power tube, so that the safety and reliability of the operational amplifier are improved.
It will be appreciated that the advantages of the second aspect may be found in the relevant description of the first aspect, and will not be described in detail herein.
Detailed Description
In the following description, for purposes of explanation and not limitation, specific details are set forth such as the particular system architecture, techniques, etc., in order to provide a thorough understanding of the embodiments of the present application. It will be apparent, however, to one skilled in the art that the present application may be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, devices, circuits, and methods are omitted so as not to obscure the description of the present application with unnecessary detail.
It should be understood that the terms "comprises" and/or "comprising," when used in this specification and the appended claims, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It should also be understood that the term "and/or" as used in the present specification and the appended claims refers to any and all possible combinations of one or more of the associated listed items, and includes such combinations.
As used in the present description and the appended claims, the term "if" may be interpreted as "when..once" or "in response to a determination" or "in response to detection" depending on the context. Similarly, the phrase "if a determination" or "if a [ described condition or event ] is detected" may be interpreted in the context of meaning "upon determination" or "in response to determination" or "upon detection of a [ described condition or event ]" or "in response to detection of a [ described condition or event ]".
Furthermore, the terms "first," "second," "third," and the like in the description of the present specification and in the appended claims, are used for distinguishing between descriptions and not necessarily for indicating or implying a relative importance.
Reference in the specification to "one embodiment" or "some embodiments" or the like means that a particular feature, structure, or characteristic described in connection with the embodiment is included in one or more embodiments of the application. Thus, appearances of the phrases "in one embodiment," "in some embodiments," "in other embodiments," and the like in the specification are not necessarily all referring to the same embodiment, but mean "one or more but not all embodiments" unless expressly specified otherwise. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless expressly specified otherwise.
Since the operational amplifier has an output short circuit problem, if no overcurrent protection is provided, the power tube inside the operational amplifier may be burned out, and thus an overcurrent protection circuit needs to be provided. However, in the existing overcurrent protection circuit, once the output current is greater than the current set in the overcurrent protection circuit, the overcurrent protection circuit starts to operate, and because of the trade-off between the set current and the load capacity and the maximum current that can be borne by the output power tube in the operational amplifier module, the set current is usually larger in value for carrying heavy load or full load. However, if the set current setting is too large, it may cause the output power tube in the op-amp module to burn out due to overcurrent.
Based on the problems of the over-current protection circuit, the over-current protection circuit provided by the embodiment of the application comprises a sampling module, a comparison module and a clamping module, and when the current flowing through the output power tube is greater than or equal to the preset current, the over-current protection circuit can represent that the operational amplifier module is in an over-current state and simultaneously represents that the output of the operational amplifier module is short-circuited or in a heavy-load working state. At this time, the sampling module samples the current flowing through the output power tube, and outputs sampling voltage to the comparison module and the clamping module according to the current. The comparison module receives the sampling voltage and outputs a first level signal to the clamping module when the sampling voltage is smaller than the first voltage. The clamping module outputs a clamping voltage signal to the operational amplifier module according to the first level signal and the sampling voltage, so that the current flowing through the output power tube is reduced. Therefore, in the overcurrent protection circuit provided by the embodiment of the application, when the current flowing through the output power tube is greater than or equal to the preset current, the comparison module can output the first level signal, so that the clamping module starts to work, the current flowing through the output power tube is clamped smaller, the operational amplifier module is prevented from being in an overcurrent state, and the output power tube in the operational amplifier module is prevented from being burnt out due to overcurrent. Therefore, even if the operational amplifier module works under heavy load or full load, the output current can not reach the current value of the burnt power tube, so that the safety and reliability of the operational amplifier are improved.
In order to illustrate the technical scheme of the application, the following description is made by specific examples.
Fig. 1 shows a schematic block diagram of an overcurrent protection circuit 10 according to an embodiment of the application. Referring to fig. 1, the overcurrent protection circuit 10 includes a sampling module 101, a comparing module 102 and a clamping module 103, where the sampling module 101 is electrically connected with the comparing module 102 and the clamping module 103, the comparing module 102 is electrically connected with the clamping module 103, the sampling module 101 and the clamping module 103 are electrically connected with the op-amp module 20, and the sampling module 101, the comparing module 102 and the clamping module 103 are electrically connected with the first power supply.
Specifically, when the current flowing through the output power tube (output current Iout) is greater than or equal to the preset current, it may be indicated that the operational amplifier module 20 is in an overcurrent state, and at the same time, the operational amplifier module 20 outputs a short circuit or is in a heavy-load working state. At this time, the sampling module 101 samples the output current Iout, and outputs a sampling voltage VS to the comparing module 102 and the clamping module 103 according to the output current Iout. The comparison module 102 receives the sampling voltage VS and outputs a first level signal (for example, the first level signal is a low level signal) to the clamp module 103 when the sampling voltage VS is less than the first voltage VD. The clamp module 103 outputs a clamp voltage signal to the op-amp module 20 according to the first level signal and the sampling voltage VS, so that the output current Iout decreases. As can be seen, in the overcurrent protection circuit 10 provided in the embodiment of the present application, when the output current Iout is greater than or equal to the preset current, the comparison module 102 may output the first level signal, so that the clamping module 103 starts to work, clamps the output current Iout smaller, thereby avoiding the operational amplifier module 20 from being in an overcurrent state, and ensuring that the output power tube in the operational amplifier module 20 is not burned out due to overcurrent. Therefore, even if the operational amplifier module 20 is under heavy load or full load, the output current Iout does not reach the current value of the burning power tube, thereby improving the safety and reliability of the operational amplifier.
It should be noted that, when the output current Iout is smaller than the preset current, it may be indicated that the operational amplifier module 20 is in a non-overcurrent state, and at the same time, the operational amplifier module 20 is in a normal working state. At this time, the comparison module 102 outputs a high level signal, and the clamp module 103 does not clamp the output current Iout, so that the load of the op-amp module 20 is not affected. Therefore, the overcurrent protection circuit 10 provided by the embodiment of the application can ensure that the output power tube cannot be burnt out while ensuring that the operational amplifier module 20 has stronger load capacity, thereby improving the reliability of the operational amplifier.
It should be noted that the op-amp module 20 includes PM0, PM1, PM2, PM3, PM4, NM0, NM1, NM2, NM3, ibias0, R10, and R20. The grid of PM0 is used for receiving inn, namely a feedback signal FB, the grid of PM1 is used for receiving a reference signal VREF, the source of PM0 and the source of PM1 are electrically connected with the second end of Ibias0, the drain of PM0 is electrically connected with the drain of PM1, the grid and the drain of NM0, the grid and the drain of NM1, the grid and the grid of NM3 of NM2, the second ends of NM0, the source of NM1, the source of NM2, the source of NM3 and the second end of R0 are grounded, the first end of Ibias0, the source of PM2, the source of PM3 and the source of PM4 are electrically connected with a first power supply VCC, the grid of PM2 is electrically connected with the grid of PM3, the drain of PM2 and the drain of NM2, the drain of PM3 is electrically connected with the first end of NM 20 and the sampling module 101 and the clamping module 103, the drain of PM4 is electrically connected with the first end of R20 and the second end of R10 is electrically connected with the second end of R20.
It should be noted that, NM0, NM1, NM2, and NM3 form a current mirror, the mirror ratio between any two may be set to 1:1, and the mirror ratio between PM2 and PM3 form a current mirror, which may be set to 1:1. Therefore, the current ip0 flowing through PM0 is equal to the current in3 flowing through NM3, and the current ip1 flowing through PM1 is equal to the current ip2 flowing through PM2 and the current ip3 flowing through PM 3.
In one embodiment of the present application, as shown in fig. 2, the sampling module 101 includes a first resistor R1 and a first switching tube M1, a first end of the first resistor R1 is used for being electrically connected to a first power supply, a second end of the first resistor R1 is electrically connected to a source electrode of the first switching tube M1, the comparing module 102 and the clamping module 103, and a gate electrode of the first switching tube M1 and a drain electrode of the first switching tube M1 are both used for being electrically connected to the op-amp module 20.
Specifically, the mirror ratio between the output power tube PM4 and the first switching tube M1 in the op-amp module 20 is k:1, i.e. the current flowing through the PM4 is K times the current flowing through the first switching tube M1. Therefore, the output current Iout of the operational amplifier module 20 may be sampled by the first switching transistor M1, and a sampling current is obtained. The sampling current flows through the first resistor R1 to generate a voltage drop, thereby obtaining a sampling voltage VS. Since the obtained sampling voltage VS is the voltage at the second end of the first resistor R1, the sampling voltage VS is VCC-I1×r1, where I1 is the sampling current, and since the sampling current and the output current Iout are in a proportional relationship, the larger the output current Iout, the smaller the sampling voltage VS.
For example, a designer may select the type of the first switching transistor M1 according to the actual situation, that is, a fully-controlled power device such as a metal oxide field effect transistor or an insulated gate bipolar transistor may be used. For example, the first switching transistor M1 may be selected as a PMOS transistor.
In one embodiment of the present application, as shown in fig. 2, the comparison module 102 includes a first voltage generation unit 1021 and a comparison unit 1022, the first voltage generation unit 1021 is electrically connected to the comparison unit 1022 and the clamp module 103, the comparison unit 1022 is electrically connected to the sampling module 101 and the clamp module 103, and the first voltage generation unit 1021 is electrically connected to a first power source.
Specifically, the first voltage generating unit 1021 is configured to output a first voltage VD to the comparing unit 1022 according to a power supply voltage VCC output by the first power supply, and the comparing unit 1022 receives the first voltage VD and the sampling voltage VS and compares the first voltage VD and the sampling voltage VS. When the sampling voltage VS is smaller than the first voltage VD, that is, the output current Iout reaches the preset current, the comparison module 102 outputs a first level signal to make the clamping module 103 work, so as to clamp the output current Iout.
In an embodiment of the present application, as shown in fig. 2, the first voltage generating unit 1021 includes a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a first current source Ibias1 and a second switching tube M2, wherein a first end of the second resistor R2 and a source of the second switching tube M2 are electrically connected to the first power source, a second end of the second resistor R2 is electrically connected to a first end of the third resistor R3, a first end of the fourth resistor R4 is electrically connected to a second end of the third resistor R3 and a drain of the second switching tube M2, respectively, a second end of the fourth resistor R4 is electrically connected to a first end of the fifth resistor R5 and the comparing unit 1022, a first end of the first current source Ibias1 is electrically connected to a second end of the fifth resistor R5, a second end of the first current source Ibias1 is grounded, and a gate of the second switching tube M2 is electrically connected to the comparing unit 1022 and the clamping module 103, respectively.
Specifically, the first current source Ibias1 is configured to provide a stable first current, and the second resistor R2, the third resistor R3, the fourth resistor R4, and the fifth resistor R5 are configured to convert the first current into the first voltage VD. The second switching tube M2 is used as a switching device, and can be turned on according to the first level signal output by the comparing unit 1022, when the second switching tube M2 is in the on state, the second resistor R2 and the third resistor R3 can be short-circuited, so that the first voltage VD transmitted to the comparing unit 1022 is higher, and the comparing unit 1022 is further easier to output the first level signal according to the first voltage VD and the sampling voltage VS, so as to ensure that the clamping module 103 can start working.
For example, the preset current may be set according to the values of the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5 and the first current source Ibias1, that is, k×ibias1 (r2+r3+r4+r5)/R1.
For example, a designer may select the type of the second switching transistor M2 according to the actual situation, that is, a fully-controlled power device such as a metal oxide field effect transistor or an insulated gate bipolar transistor may be used. For example, the second switching transistor M2 may be selected as a PMOS transistor.
In one embodiment of the present application, as shown in fig. 2, the comparing unit 1022 includes a comparator COMP, a first input terminal of the comparator COMP is electrically connected to the first voltage generating unit 1021, a second input terminal of the comparator COMP is electrically connected to the sampling module 101, and output terminals of the comparator COMP are respectively electrically connected to the first voltage generating unit 1021 and the clamping module 103.
Specifically, the negative input terminal of the comparator COMP is used as a first input terminal of the comparator COMP for receiving the first voltage VD, and the positive input terminal of the comparator COMP is used as a second input terminal of the comparator COMP for receiving the sampling voltage VS. The comparator COMP compares the received first voltage VD with the sampling voltage VS, when the sampling voltage VS is greater than the first voltage VD, the output current Iout is represented as not reaching the preset current, the OUT0 output by the comparator COMP is a high-level signal, when the first voltage VD is greater than the sampling voltage VS, the output current Iout is represented as reaching the preset current, the OUT0 output by the comparator COMP is turned to be a low-level signal, so that the clamp module 103 is controlled to start working, and the output current Iout is clamped.
It should be noted that the comparator COMP may be a hysteresis current-limiting comparator COMP, which has hysteresis characteristics, that is, when the output state is switched, the input signal needs to cross the hysteresis value. Since the hysteresis comparator COMP has a hysteresis value, the comparator COMP does not switch states frequently around the threshold value, avoiding oscillation of the output signal OUT 0. Meanwhile, due to hysteresis characteristics, the comparator COMP is more stable under noise interference, and the possibility of false triggering is reduced.
Note that only one element composition as the first voltage generating unit 1021 and the comparing unit 1022 is shown in the present application, and it is not represented that only one element composition can realize the functions of the first voltage generating unit 1021 and the comparing unit 1022. Other elements that can perform this function may be substituted, and are not limited thereto.
In one embodiment of the present application, as shown in fig. 2, the clamping module 103 includes a second voltage generating unit 1031 and a clamping unit 1032, the second voltage generating unit 1031 is electrically connected to the clamping unit 1032 and the comparing module 102, the clamping unit 1032 is electrically connected to the sampling module 101 and the operational amplifier module 20, and the second voltage generating unit 1031 and the clamping unit 1032 are both used for electrically connecting to the first power supply.
Specifically, the second voltage generating unit 1031 is configured to output a second voltage VE to the clamping unit 1032 according to the first level signal and the power supply voltage VCC output by the first power supply, and the clamping unit 1032 receives the second voltage VE and the sampling voltage VS and outputs a clamping voltage signal to the op-amp module 20 when the sampling voltage VS is less than the second voltage VE, so as to pull up the voltage at the PG end, so that the output current Iout flowing through the PM4 is reduced.
In one embodiment of the present application, as shown in fig. 2, the second voltage generating unit 1031 includes a sixth resistor R6, a seventh resistor R7, an eighth resistor R8, a ninth resistor R9, a second current source Ibias2, and a third switching tube M3, wherein a first end of the sixth resistor R6 and a source of the third switching tube M3 are electrically connected to the first power source, a second end of the sixth resistor R6 is electrically connected to a first end of the seventh resistor R7 and a drain of the third switching tube M3, respectively, a first end of the eighth resistor R8 is electrically connected to a second end of the seventh resistor R7, a second end of the eighth resistor R8 is electrically connected to a first end of the ninth resistor R9 and the clamping unit 1032, a first end of the second current source Ibias2 is electrically connected to a second end of the ninth resistor R9, a second end of the second current source Ibias2 is grounded, and a gate of the third switching tube M3 is electrically connected to the comparison module 102.
Specifically, the second current source Ibias2 is configured to provide a stable second current, and the sixth resistor R6, the seventh resistor R7, the eighth resistor R8 and the ninth resistor R9 are configured to convert the second current into the second voltage VE. The third switching tube M3 is used as a switching device, and can be turned on according to the first level signal output by the comparator COMP, when the third switching tube M3 is in the on state, the sixth resistor R6 can be short-circuited, so that the second voltage VE transmitted to the clamping unit 1032 is higher, and the clamping unit 1032 clamps the sampling voltage VS higher, thereby ensuring that the output current Iout is smaller.
It should be noted that, when the third switching tube M3 is turned on, the second voltage VE is vcc_ibias 2 (r7+r8).
It should be noted that the number of the substrates, R2 = R6 and, R3 = R7 and, r4=r8 and, R5 = R9 and, ibias1 = Ibias2. When the OUT0 output by the comparator COMP is at a low level, the second switching tube M2 and the third switching tube M3 are both turned on, and the first voltage VD is greater than the second voltage VE.
For example, a designer may select the type of the third switching transistor M3 according to the actual situation, that is, a fully-controlled power device such as a metal oxide field effect transistor or an insulated gate bipolar transistor may be used. For example, the third switching transistor M3 may be selected as a PMOS transistor.
In one embodiment of the present application, as shown in fig. 2, the clamping unit 1032 includes an amplifier AMP, a fourth switching tube M4, a fifth switching tube M5 and a third current source Ibias3, wherein a first input terminal of the amplifier AMP is electrically connected to the second voltage generating unit 1031, a second input terminal of the amplifier AMP is electrically connected to the sampling module 101, an output terminal of the amplifier AMP is electrically connected to a gate of the fourth switching tube M4 and a gate of the fifth switching tube M5, a source of the fourth switching tube M4 and a source of the fifth switching tube M5 are both electrically connected to the first power supply, a drain of the fourth switching tube M4 is electrically connected to a first terminal of the third current source Ibias3, and a drain of the fifth switching tube M5 is electrically connected to the operational amplifier module 20, and a second terminal of the third current source Ibias3 is grounded.
Specifically, the third current source Ibias3 is configured to provide a stable third current, and the fourth switching tube M4 and the fifth switching tube M5 are both used as switching devices, and are turned on or turned off according to the amplified signal output by the amplifier AMP. The negative input of the amplifier AMP serves as a first input of the amplifier AMP for receiving the second voltage VE and the positive input of the amplifier AMP serves as a second input of the amplifier AMP for receiving the sampling voltage VS. The amplifier AMP compares the received second voltage VE with the sampling voltage VS, and when the sampling voltage VS is greater than the second voltage VE, the amplifier AMP outputs a high-level signal to control the fourth switching tube M4 and the fifth switching tube M5 to be turned off, wherein the output current Iout is not yet up to a preset current. When the second voltage VE is greater than the sampling voltage VS, the output current Iout reaches the preset current, the amplifier AMP outputs a signal turned to a low level, and the fourth switching tube M4 and the fifth switching tube M5 are controlled to be both turned on so as to pull up the voltage at the PG end, so that the current flowing through the PM4 is reduced.
For example, a designer may select the types of the fourth switching transistor M4 and the fifth switching transistor M5 according to actual situations, that is, all the fully-controlled power devices such as a metal oxide field effect transistor or an insulated gate bipolar transistor may be adopted. For example, the fourth switching tube M4 and the fifth switching tube M5 may be selected to be PMOS tubes.
It should be noted that, since the purpose of the clamping unit 1032 is to clamp the sampling voltage VS to be equal to the second voltage VE, that is, vs=ve, when the second voltage VE becomes high, the clamping unit 1032 clamps the sampling voltage VS higher, so that the output current Iout is smaller. Where ve=vcc-Ibias 2 (r7+r8), vs=vcc-IM1*R1,IM1 is the current flowing through the first switching tube M1. Recombination of K.times.IM1=IPM4 =iout. From this, the output current Iout can be finally clamped to k×ibias2 (r7+r8)/R1.
Note that only one element composition as the second voltage generating unit 1031 and the clamp unit 1032 is shown in the present application, and it is not represented that only one element composition can realize the functions of the second voltage generating unit 1031 and the clamp unit 1032. Other elements that can perform this function may be substituted, and are not limited thereto.
It should be noted that the clamping unit 1032 further includes a first inverter inv1 and a second inverter inv2, wherein a first end of the first inverter inv1 is electrically connected to the drain of the fourth switching tube M4 and a first end of the third current source Ibias3, respectively, a second end of the first inverter inv1 is electrically connected to a first end of the second inverter inv2, and a second end of the second inverter inv2 is configured to output a second level signal (e.g., the second level signal is a low level signal). The first inverter inv1 and the second inverter inv2 are used for inverting and filtering, and ensure the accuracy of the second level signal output by the clamping unit 1032.
Note that, if VDS is not considered in both the fourth switching transistor M4 and the fifth switching transistor M5, the current ip4 flowing through the fourth switching transistor M4 may be considered to be equal to the current ip5 flowing through the fifth switching transistor M5. If ip4=ip5 < Ibias3, then OUT1 is flipped low.
As can be seen from fig. 2, ip5+ip3=in3, ip0=in3 > ip1=ip2=ip3, that is, ip5=in3-ip3=ip0-ip1=gm [ VREF-VOUT ] R0/(r0+r1+r2) ]=gm+Δv, where gm is the gain of the op amp module 20, and Δv determines the under-voltage of the output voltage due to too heavy load, so that Ibias3 can take gm+Δv, and an appropriate Δv is selected according to the size of PM4 and the process, when the op amp module 20 has an output short circuit or a load with heavy load, ip4=ip5 > Ibias 3=gm+Δv, and the clamp module 103 works normally.
In one embodiment of the present application, as shown in fig. 2, the overcurrent protection circuit 10 further includes a first switch module 104 and a second switch module 105, the first switch module 104 is electrically connected to the clamp module 103, the second switch module 105 is electrically connected to the comparison module 102 and the clamp module 103, and the first switch module 104 and the second switch module 105 are each configured to be electrically connected to the first power supply.
Specifically, the first switch module 104 and the second switch module 105 both receive the second level signal output by the clamp unit 1032, and are turned on according to the second level signal, so that the comparison module 102 and the clamp module 103 exit the working state, and the normal working state is restored. Specifically, the first switch module 104 includes a sixth switch tube M6, a gate of the sixth switch tube M6 is configured to receive the second level signal, a source of the sixth switch tube M6 is configured to be electrically connected to the first power supply, and a drain of the sixth switch tube M6 is electrically connected to a gate of the fourth switch tube M4 and a gate of the fifth switch tube M5, respectively. When the sixth switching tube M6 is turned on according to the second level signal, the gate voltages of the fourth switching tube M4 and the fifth switching tube M5 may be pulled up to the power voltage VCC, so that the fourth switching tube M4 and the fifth switching tube M5 are turned off, and the clamp module 103 is withdrawn from the working state. The second switch module 105 includes a seventh switch tube M7, a gate of the seventh switch tube M7 is configured to receive the second level signal, a source of the seventh switch tube M7 is configured to be electrically connected to the first power supply, and a drain of the seventh switch tube M7 is electrically connected to the gate of the second switch tube M2 and the gate of the third switch tube M3, respectively. When the seventh switching tube M7 is turned on according to the second level signal, the gate voltages of the second switching tube M2 and the third switching tube M3 can be pulled up to the power voltage VCC, so that the second switching tube M2 and the third switching tube M3 are turned off, and the comparison module 102 is out of the working state.
For example, a designer may select the types of the sixth switching transistor M6 and the seventh switching transistor M7 according to actual situations, that is, all the fully-controlled power devices such as a metal oxide field effect transistor or an insulated gate bipolar transistor may be adopted. For example, the sixth switching tube M6 and the seventh switching tube M7 may be selected to be PMOS tubes.
It should be noted that, according to the analysis of the circuit, the output of the operational amplifier module 20 is short-circuited and then exits the short-circuit in four cases:
(1) The operational amplifier module 20 exits the short circuit, the output is still a heavy load, and at this time, the comparing module 102 and the clamping module 103 in the overcurrent protection circuit 10 are both in a working state, so as to clamp the output current Iout. The waveform diagram in this process can be seen in fig. 3, wherein the peak value of the output current Iout is k×ibias1 (r2+r3+r4+r5)/R1, the clamped value is k×ibias2 (r7+r8+r9)/R1, and the hysteresis value is k×ibias1 (r4+r5)/R1. The dashed lines from left to right in fig. 5 sequentially characterize the short, clamp, and exit short.
(2) The op-amp block 20 exits the short circuit and the output is a slightly heavier load, but the load is less than the current limit at which comparator COMP jumps low and greater than the clamp current ip5 of clamp block 103. At this time, the clamp current ip5=ip4 decreases, resulting in the OUT1 output being low, the clamp block 103 is not operated, and the threshold pull-back of the comparator COMP is maximum. At this time, since the clamp module 103 does not operate, the output current Iout (load current) is also restored to a normal value, and the comparator COMP is pulled back to the maximum comparison value, so that the characterization is not in an overcurrent state, and the whole circuit is in a normal operating state. A schematic of waveforms in this process is shown in fig. 4.
(3) The op amp module 20 exits the short circuit, the output is a light load, but the load is smaller than the clamped current and larger than the low threshold current of the comparator COMP, at this time ip5=ip4 < Ibias3, the comparator COMP threshold is pulled back to the maximum value, and the clamp module 103 itself is not operated, and the whole circuit is in a normal operation state. A schematic of waveforms in this process is shown in fig. 5.
(4) The op-amp module 20 exits the short circuit and the output is a very light load that is less than the low threshold current of the comparator COMP, at which time the clamp module 103 is not operating and the comparator COMP also switches back to maximum and the overall circuit is in normal operation. A schematic of waveforms in this process is shown in fig. 6.
As can be seen from the above, the current limiting protection circuit is disabled once triggered, even if it is out of short circuit or disabled, compared to the existing over-current protection circuit, resulting in a power supply comprising the operational amplifier having no load capability at all. The overcurrent protection circuit 10 provided by the embodiment of the application can ensure that the short circuit is withdrawn after the short circuit, so that the whole circuit is restored to the normal working state, the problem that the circuit does not work once the current limiting protection is triggered and the operation amplifier does not work even if the short circuit is withdrawn is avoided, and the performance of the operation amplifier is improved.
The application also discloses an operational amplifier, which comprises the operational amplifier module 20 and the overcurrent protection circuit 10, wherein the operational amplifier module 20 is respectively and electrically connected with the sampling module 101 and the clamping module 103 in the overcurrent protection circuit 10. The operational amplifier adopts the above-mentioned overcurrent protection circuit 10 to clamp the output current within the safety range when the output current is greater than or equal to the preset current, so as to avoid the operational amplifier module 20 being in an overcurrent state, ensure that the output power tube in the operational amplifier module 20 cannot be burnt out due to overcurrent, and improve the safety and reliability of the operational amplifier.
Since the processing and the functions implemented by the operational amplifier in the present embodiment basically correspond to the embodiments, principles and examples of the above-mentioned overcurrent protection circuit, the description of the present embodiment is not exhaustive, and reference may be made to the related description in the foregoing embodiments, which is not repeated herein.
The foregoing embodiments are merely illustrative of the technical solutions of the present application, and not restrictive, and although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that modifications may still be made to the technical solutions described in the foregoing embodiments or equivalent substitutions of some technical features thereof, and that such modifications or substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present application.