MLCC capacitor test power supply output bidirectional current limiting circuit

Abstract

This invention discloses a bidirectional current-limiting circuit for the output of a power supply for MLCC capacitor testing. The circuit includes a power supply module, a DAC output module circuit, a first filter capacitor, a second filter capacitor, an operational amplifier comparator output drive circuit, a first isolation diode, a second isolation diode, a first current-limiting resistor, a second current-limiting resistor, a third current-limiting resistor, a fourth current-limiting resistor, a fast shutdown circuit, a clamping protection diode circuit, a current-limiting switch circuit, and a current-limiting sampling circuit. The power supply module includes positive and negative power supply modules. In this invention, the test power supply output simultaneously possesses forward charging current-limiting and reverse charging current-limiting functions. Furthermore, the current-limiting parameter value for the tested load can be freely adjusted and set, making it suitable for various types of MLCC capacitors. The technical solution provided by this invention also features a fast shutdown current-limiting switch capability, which improves the safety and reliability of the test power supply output, reduces costs, and facilitates widespread use.

Description

Technical Field

[0001] This invention relates to electronic application technology and the field of capacitance testing, and in particular to a bidirectional current limiting circuit for the output power supply of an MLCC capacitor test power supply. Background Technology

[0002] MLCC (Multi-layer Ceramic Capacitors) is an abbreviation for multilayer ceramic chip capacitors. They are made by stacking ceramic dielectric films with printed electrodes (internal electrodes) in a staggered manner, then sintering them at high temperature in a single process to form a ceramic chip. Metal layers (external electrodes) are then sealed to both ends of the chip, creating a monolithic structure, hence the name monolith capacitor.

[0003] MLCC capacitors have a wide range of applications, primarily in the consumer electronics sector. The end-market for MLCC capacitors mainly covers mobile phones, audio-visual equipment, computers, automobiles, and other industrial and medical fields. With the increasing demand and production of MLCC capacitors, concerns arise regarding defective products, reliability, performance, and voltage withstand capability. Manufacturers must use an MLCC capacitor test power supply to charge and reverse-charge MLCC capacitors before testing to ensure they meet performance requirements before shipment. To ensure the safety of MLCC capacitor testing, current limiting is essential during charging to prevent damage from excessive current. A short circuit in the tested MLCC capacitor could cause a sharp increase in the output current of the test power supply. Without proper protection, this could burn out electronic components or even cause a fire.

[0004] Currently, most MLCC capacitor test power supplies on the market have a single output current limiting direction. They require additional test stations, have complex processes, numerous components, and are expensive, in order to meet the bidirectional current limiting protection function for both forward and directional charging of MLCC capacitors, making them difficult to widely apply.

[0005] Therefore, a solution is needed to address the problems in the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide a bidirectional current limiting circuit, a solution, and a technical solution for the output of an MLCC capacitor test power supply, which can be widely applied to various MLCC capacitor test power supplies, improve the safety and reliability of the test power supply output, reduce costs, and facilitate widespread use.

[0007] This invention provides a bidirectional current limiting circuit for MLCC capacitor test power supply output, comprising: a power supply module, a DAC output module circuit, a first filter capacitor, a second filter capacitor, an operational amplifier comparator output drive circuit, a first isolation diode, a second isolation diode, a first current limiting resistor, a second current limiting resistor, a third current limiting resistor, a fourth current limiting resistor, a fast turn-off circuit, a clamping protection diode circuit, a current limiting switch circuit, and a current limiting sampling circuit. The power supply module includes positive and negative power supply modules.

[0008] The DAC output module is connected to the operational amplifier comparator output drive circuit.

[0009] The operational amplifier comparator output drive circuit is connected to the DAC output module, the isolation diode and fast turn-off circuit, and the current limiting sampling circuit.

[0010] The isolation diode is connected to the operational amplifier comparator output drive circuit and the fast turn-off circuit.

[0011] The fast shutdown circuit is connected to the operational amplifier comparator output drive circuit, the isolation diode, and the current limiting switch circuit.

[0012] The clamping protection diode circuit is located between the fast shutdown circuit and the current limiting switch circuit.

[0013] The current limiting switch circuit is connected to the positive and negative power supply modules and the current limiting sampling circuit.

[0014] The current-limiting sampling circuit, the current-limiting switch circuit, and the operational amplifier comparator output drive circuit are connected.

[0015] Furthermore, the power supply module includes: a current-limiting DC power supply, positive and negative power supply module input terminals, positive and negative power supply module output terminals, an operational amplifier power supply, and a DC power supply. The characteristics of each type of power supply are as follows:

[0016] The current-limiting protection power supply has a potential reference to the ground plane;

[0017] The positive and negative power supply output terminals are referenced to the ground plane.

[0018] The current-limiting protection power supply and the positive and negative power supply output terminals are isolated from each other.

[0019] Furthermore, the DAC output module circuit is used to output a settable voltage to adjust the current value of the MLCC capacitor under test for charging current limiting. The methods for outputting the settable voltage include: using a control unit to control the DAC function, using PWM to simulate the output function of the DAC chip, and using a dedicated DAC chip for output. The control unit includes a microcontroller, a PLC, and an FPGA. One end of the first filter capacitor and one end of the second filter capacitor are both connected to the DAC output module circuit, and the other ends of the first filter capacitor and the second filter capacitor are both connected to the DC power supply.

[0020] Furthermore, the operational amplifier comparator output drive circuit includes a first operational amplifier and a second operational amplifier. The first operational amplifier has pins including a first pin, a second pin, a third pin, a fourth pin, and an eighth pin. The second operational amplifier has pins including a fifth pin, a sixth pin, and a seventh pin.

[0021] The first pin is connected to the anode of the first isolation diode, the second pin is connected to the third current-limiting resistor, the third pin is connected to the common connection terminal of the first filter capacitor and the DAC output module circuit, the fourth pin is connected to the negative terminal of the operational amplifier power supply, and the eighth pin is connected to the positive terminal of the operational amplifier power supply. The first operational amplifier is used to drive the current-limiting switch circuit during forward charging.

[0022] The fifth pin is connected to the common connection terminal of the second filter capacitor and the DAC output module circuit, the sixth pin is connected to the fourth current limiting resistor, the seventh pin is connected to the anode of the second isolation diode, and the second operational amplifier is used to drive the current limiting switch circuit during reverse charging.

[0023] Furthermore, the anode of the first isolation diode is connected to the first pin of the first operational amplifier, and the cathode of the first isolation diode is connected to the first current-limiting resistor; the anode of the second isolation diode is connected to the first pin of the second operational amplifier, and the cathode of the first isolation diode is connected to the second current-limiting resistor.

[0024] Furthermore, the clamping protection diode circuit includes a first clamping protection diode circuit and a second clamping protection diode circuit. The first clamping protection diode circuit includes a first protection diode and a second protection diode. The anode of the first protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the first fast turn-off circuit and the first current-limiting resistor. The cathode of the first protection diode is connected to a DC power supply. The anode of the second protection diode is connected to the current-limiting protection power supply, and the cathode of the second protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the first fast turn-off circuit and the first current-limiting resistor.

[0025] The second clamping protection diode circuit includes a third protection diode and a fourth protection diode. The anode of the third protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor. The cathode of the third protection diode is connected to a DC power supply. The anode of the fourth protection diode is connected to the current-limiting protection power supply, and the cathode of the fourth protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor.

[0026] Furthermore, the current limiting switch circuit includes a first current limiting switch circuit and a second current limiting switch circuit. The first current limiting switch circuit includes: a first current limiting switch circuit MOSFET, the gate of the first current limiting switch circuit MOSFET being connected to a common connection terminal where the source of the three-terminal semiconductor of the first fast turn-off circuit is connected to the first current limiting resistor; the source of the first current limiting switch circuit MOSFET is connected to a common connection terminal where the first sampling resistor and the third current limiting resistor are connected; and the drain of the first current limiting switch circuit MOSFET is connected to the output terminal of the positive and negative power supply module.

[0027] The second current-limiting switch circuit MOSFET has its gate connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor; the source of the second current-limiting switch circuit MOSFET is connected to the common connection terminal of the second sampling resistor and the fourth current-limiting resistor; and the drain of the second current-limiting switch circuit MOSFET is connected to the load under test.

[0028] Furthermore, the current limiting sampling circuit includes a first current limiting sampling circuit and a second current limiting sampling circuit. The first current limiting sampling circuit includes a third current limiting resistor and a first sampling resistor. One end of the third current limiting resistor is connected to the common connection terminal of the source of the MOS transistor in the first current limiting switch circuit and the first sampling resistor. The other end of the third current limiting resistor is connected to the current limiting protection power supply. The first sampling resistor is connected to the current limiting protection power supply.

[0029] The second current-limiting sampling circuit includes a fourth current-limiting resistor and a second sampling resistor. One end of the fourth current-limiting resistor is connected to the common connection terminal of the MOS source of the second current-limiting switch circuit and the second sampling resistor, and the other end of the fourth current-limiting resistor is connected to the sixth pin of the second operational amplifier. The second sampling resistor is connected to the common connection terminal of the current-limiting protection power supply and the first sampling resistor.

[0030] The first current-limiting sampling circuit is used to sample the forward charging current, and the second current-limiting sampling circuit is used to sample the reverse charging current.

[0031] The beneficial effects of this invention are as follows: The technical solution provided by this invention provides a test power supply output that simultaneously possesses forward charging current limiting and reverse charging current limiting functions. Furthermore, the current limiting parameter value for the tested load MLCC capacitor can be freely adjusted and set, making it suitable for various types of MLCC capacitors. The technical solution provided by this invention also has the ability to quickly turn off the current limiting switch, which can improve the safety and reliability of the test power supply output, reduce costs, and facilitate widespread use. Attached Figure Description

[0032] Figure 1 This is a block diagram of a bidirectional current limiting circuit for the output of a test power supply for MLCC capacitors according to the present invention.

[0033] Figure 2 This is one feasible circuit diagram of the bidirectional current limiting circuit for the MLCC capacitor test power supply output of the present invention;

[0034] Figure 3 This is another feasible circuit diagram of the bidirectional current limiting circuit for the MLCC capacitor test power supply output of the present invention;

[0035] Figure 4 This is a flowchart of the method steps for testing using the present invention. Detailed Implementation

[0036] The following is in conjunction with the appendix Figures 1 to 4 The description and embodiments further illustrate the present invention.

[0037] The present application will be further described below with reference to the accompanying drawings and specific embodiments. The described embodiments should not be considered as limitations on the present application, and all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of the present application.

[0038] In the following description, references are made to “some embodiments,” which describe a subset of all possible embodiments. However, it is understood that “some embodiments” may be the same subset or different subsets of all possible embodiments and may be combined with each other without conflict.

[0039] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0040] This invention provides a bidirectional current-limiting circuit for the output power supply of an MLCC capacitor test power supply, comprising a DAC output module circuit, a first operational amplifier comparator output drive circuit, a second operational amplifier comparator output drive circuit, a first isolation diode, a second isolation diode, a first fast turn-off circuit, a second fast turn-off circuit, a first clamping protection diode circuit, a second clamping protection diode circuit, a first current-limiting switch circuit, a second current-limiting switch circuit, a first current-limiting sampling circuit, a positive and negative power supply module, and the MLCC capacitor under test. The DAC output module circuit includes a control unit with DAC function or a PWM analog DAC function outputting a settable voltage, or a dedicated DAC chip outputting a settable voltage, used to adjust the charging current-limiting value of the MLCC capacitor under test, making it suitable for various types of MLCC capacitors.

[0041] It should be noted that the control unit in this embodiment of the invention includes a microcontroller, a PLC, an FPGA, etc.

[0042] The first operational amplifier comparator output drive circuit is used to drive the output of the forward charging current limiting switch circuit; the second operational amplifier comparator output drive circuit is used to drive the output of the reverse charging current limiting switch circuit.

[0043] The first and second fast shutdown circuits are used to quickly limit the current and shut down the current limiting switch when the charging current of the MLCC capacitor under test is too large or when the MLCC capacitor under test is short-circuited, so as to protect the MLCC capacitor under test and the MLCC capacitor test power supply, etc.

[0044] The first isolation diode is used to prevent the current from passing through the IC when the charge on the gate-source capacitor of the first current-limiting switch MOS is discharged, and the second isolation diode is used to prevent the current from passing through the IC when the charge on the gate-source capacitor of the second current-limiting switch MOS is discharged, thereby improving the reliability of the entire circuit.

[0045] The first clamping protection diode circuit and the second clamping protection diode circuit are used to protect the driving voltage of the drive switching circuit within the specified range and prevent excessive voltage from burning out the electronic components of the switching circuit.

[0046] The first current-limiting switch circuit is an N-channel enhancement-mode MOSFET, used to turn on and off the forward current-limiting charging current output; the second current-limiting switch circuit is an N-channel enhancement-mode MOSFET, used to turn on and off the reverse current-limiting charging current output.

[0047] The first current-limiting sampling circuit is used to sample the forward charging current; the second current-limiting sampling circuit is used to sample the reverse charging current.

[0048] The positive and negative power supply module is responsible for providing high-precision positive and negative charging voltage and current to the MLCC capacitor under test;

[0049] The bidirectional current limiting circuits of the MLCC capacitor test power supply output are the MLCC capacitor test power supply output forward charging current limiting circuit and the MLCC capacitor test power supply output reverse charging current limiting circuit.

[0050] Figure 1 A block diagram of a bidirectional current limiting circuit for the output of a test power supply for an MLCC capacitor, as described in this embodiment of the invention.

[0051] Detailed instructions for instance connection:

[0052] The DAC output of the DAC output module circuit is connected to VCC1; one end of the first filter capacitor C3 is connected to VCC1, and the other end is connected to the DC power supply GND; one end of the second filter capacitor C7 is connected to VCC1, and the other end is connected to the DC power supply GND.

[0053] The operational amplifier IC1 has its pin 3 connected to VCC1, pin 2 connected to VCC4, pin 1 (output) connected to VCC2, pin 5 connected to VCC1, pin 6 connected to VCC8, pin 7 (output) connected to VCC6, pin 8 connected to the DC power supply VCC, and pin 4 connected to the DC power supply GND.

[0054] The anode (positive terminal) of the first isolation diode D2 is connected to VCC2, the cathode (negative terminal) of D2 is connected to one end of the current-limiting resistor R1, and the other end of the current-limiting resistor R1 is connected to VCC3; the anode (positive terminal) of the second isolation diode D5 is connected to VCC6, the cathode (negative terminal) of D5 is connected to one end of the current-limiting resistor R8, and the other end of the current-limiting resistor R8 is connected to VCC7.

[0055] The first fast turn-off circuit consists of resistor R2, P-channel enhancement-mode MOSFET Q2 and R3. One end of resistor R2 is connected to VCC2, and the other end of resistor R2 is connected to the gate G of P-channel enhancement-mode MOSFET Q2. The source S of P-channel enhancement-mode MOSFET Q2 is connected to VCC3, and the drain D of P-channel enhancement-mode MOSFET Q2 is connected to resistor R3. The other end of resistor R3 is connected to DC power supply GND.

[0056] The second fast turn-off circuit consists of resistor R9, P-channel enhancement-mode MOSFET Q7 and R10. One end of resistor R9 is connected to VCC6, and the other end of resistor R9 is connected to the gate G of P-channel enhancement-mode MOSFET Q4. The source S of P-channel enhancement-mode MOSFET Q4 is connected to VCC7, and the drain D of P-channel enhancement-mode MOSFET Q4 is connected to resistor R10. The other end of resistor R10 is connected to the DC power supply GND.

[0057] The first clamping protection diode circuit consists of D1 and D3. The anode (positive terminal) of protection diode D1 is connected to VCC3, and the cathode (negative terminal) of protection diode D1 is connected to the DC power supply +VCC. The anode (positive terminal) of protection diode D3 is connected to the DC power supply GND, and the cathode (negative terminal) of protection diode D3 is connected to VCC3.

[0058] The second clamping protection diode circuit consists of D4 and D6. The anode (positive terminal) of protection diode D4 is connected to VCC3, and the cathode (negative terminal) of protection diode D4 is connected to the DC power supply +VCC. The anode (positive terminal) of protection diode D6 is connected to the DC power supply GND, and the cathode (negative terminal) of protection diode D6 is connected to VCC3.

[0059] The first current limiting switch circuit is an N-channel enhancement-mode MOSFET Q1, which is a forward charging current limiting switch for MLCC capacitors. The gate G of the N-channel enhancement-mode MOSFET Q1 is connected to VCC3, the source S of the N-channel enhancement-mode MOSFET Q1 is connected to VCC5, and the drain D of the N-channel enhancement-mode MOSFET Q1 is connected to VCC_A, which is output by the positive and negative power supply module.

[0060] The second current limiting switch circuit is an N-channel enhancement-mode MOSFET Q3, which is a forward charging current limiting switch for MLCC capacitors. The gate G of the N-channel enhancement-mode MOSFET Q3 is connected to VCC7, the source S of the N-channel enhancement-mode MOSFET Q3 is connected to VCC9, and the drain D of the N-channel enhancement-mode MOSFET Q3 is connected to VCC_B.

[0061] In the schematic diagram, C1, C2, and C4, connected by dashed lines, are the parasitic capacitances of the forward charging current limiting switch N-channel enhancement-mode MOSFET Q1; C5, C6, and C8, connected by dashed lines in the schematic diagram, are the parasitic capacitances of the reverse charging current limiting switch N-channel enhancement-mode MOSFET Q3.

[0062] The first sampling circuit is an MLCC capacitor forward charging current sampling resistor R5. One end of the current sampling resistor R5 is connected to VCC5, and the other end is connected to the DC power supply GND.

[0063] The second sampling circuit is the MLCC capacitor reverse charging current sampling resistor R6. One end of the current sampling resistor R6 is connected to VCC9, and the other end is connected to the DC power supply GND.

[0064] One end of the MLCC capacitor C9 under test is connected to V_OUT, and the other end is connected to COM output by the positive and negative power supply module.

[0065] The third current-limiting resistor R4 is connected to VCC4 at one end and to VCC5 at the other end; the fourth current-limiting resistor R7 is connected to VCC8 at one end and to VCC9 at the other end.

[0066] The GND is the DC power reference ground plane of the current limiting protection module; the COM is the DC power reference ground plane output by the positive and negative power modules; the GND and COM ground planes are isolated from each other.

[0067] In this embodiment of the invention, the working principle of the bidirectional current limiting circuit for the MLCC capacitor test power supply output is as follows:

[0068] The DAC output module circuit sets the current limiting parameter value for the tested MLCC capacitor to VCC1. Since operational amplifier IC1 acts as a comparator drive output, it is characterized by high impedance, comparability, and strong driving capability. Due to the high impedance characteristic of the operational amplifier, there is no current at its negative input terminal, and no current flows through the third current-limiting resistor R4 and the fourth current-limiting resistor R7. Therefore, the following is obtained:

[0069] VCC4 = VCC5 (1)

[0070] VCC8 = VCC9 (2)

[0071] The working principle of the forward charging current limiting circuit for MLCC capacitor test power supply output is as follows:

[0072] The positive and negative power supply module outputs a positive voltage and a charging current of i. 正 The voltage difference across its sampling resistor R5 is

[0073] VCC5 = R5 × i 正 (3)

[0074] The voltage difference across the sampling resistor R6 is VCC9 = -R6 × i 正 (4), the negative sign indicates the direction of the current, and the current flows from VCC_A to VCC_B;

[0075] From formulas (1) and (3) above, we can derive VCC4 = R5 × i 正 ;

[0076] When VCC1 > VCC4, the output voltage VCC2 of the first pin of operational amplifier IC1 is VCC2 = +VCC, that is, it has a strong driving ability. After passing through the first isolation diode D2, the voltage is VCC3 = +VCC - 0.7V. The voltage between the gate G and the source S of the N-channel enhancement-mode MOS transistor Q1, which is the forward charging current limiting switch of the MLCC capacitor, is much greater than the turn-on voltage of MOS transistor Q1, and MOS transistor Q1 conducts. At this time, the current i 正 will flow through MOS transistor Q1; at the same time, the P-channel enhancement-mode MOS transistor Q2 of the fast turn-off circuit is cut off;

[0077] When the forward charging current i 正 is too large, causing VCC1 < VCC4, the output voltage VCC2 of the first pin of operational amplifier IC1 is VCC2 = -VCC, isolation diode D2 is cut off, and the current when the charge on the capacitance between the gate and source of the isolation current limiting switch MOS does not pass through IC during discharge; the P-channel enhancement-mode MOS transistor Q2 of the fast turn-off circuit conducts to provide a path with as low an impedance as possible for the capacitance between the gate and source of MOS transistor Q1 to quickly discharge the charge during the turn-off moment of the current limiting switch MOS transistor Q1, so as to discharge the charge in the shortest time and ensure that the switching transistor can be quickly turned off, thereby protecting the measured load MLCC capacitor and the MLCC capacitor test power supply.

[0078] From the above formulas (2) and (4), we get VCC8 = -R6 × i 正 ;

[0079] When VCC1 >> VCC8, the output voltage VCC6 of the seventh pin of operational amplifier IC1 is VCC6 = +VCC, that is, it has a strong driving ability. After passing through isolation diode D5, the voltage is VCC7 = +VCC - 0.7V. The parasitic diode of the N-channel enhancement-mode MOS transistor Q3, which is the reverse charging current limiting switch of the MLCC capacitor, will conduct first. The voltage between the gate G and the source S is much greater than the turn-on voltage of MOS transistor Q3, and MOS transistor Q2 conducts to short-circuit the parasitic diode. At this time, the current i 正 will flow through MOS transistor Q3; at the same time, the P-channel enhancement-mode MOS transistor Q of the fast turn-off circuit is cut off 4, and finally charge the measured load MLCC capacitor safely and reliably in the forward direction.

[0080] The working principle of the reverse charging current limiting circuit of the MLCC capacitor test power supply is as follows:

[0081] The reverse voltage charging current output by the positive and negative power supply module is i 反 , and the voltage difference across the sampling resistor R5 is:

[0082] VCC5 = -R5 × i 反 (5)

[0083] The voltage difference across the sampling resistor R6 is:

[0084] VCC9 = R6 × i 反 Equation (6), the negative sign indicates the current direction, and the current direction is from VCC_B to VCC_A;

[0085] From the above formulas (2) and (6), we get VCC8 = R6 × i 反 ;

[0086] When VCC1 > VCC8, the output voltage VCC6 of the 7th pin of the operational amplifier IC1 is VCC6 = +VCC, that is, it has a strong driving ability. After passing through the isolation diode D5, the voltage is VCC7 = +VCC - 0.7V. The voltage between the gate G and the source S of the N-channel enhancement-mode MOS transistor Q3, which is the forward charging current limiting switch of the MLCC capacitor, is much greater than the turn-on voltage of the MOS transistor Q3, and the MOS transistor Q3 conducts. At this time, the current i 反 will flow through the MOS transistor Q3; at the same time, the P-channel enhancement-mode MOS transistor Q4 of the fast turn-off circuit is cut off;

[0087] When the reverse charging current i 反 is too large, causing VCC1 < VCC8, the output voltage VCC6 of the 7th pin of the operational amplifier IC1 is VCC6 = -VCC, the isolation diode D5 is cut off, and the current when the charge on the capacitance between the gate and source of the isolation current limiting switch MOS does not pass through the IC; the P-channel enhancement-mode MOS transistor Q4 of the fast turn-off circuit conducts to provide a path with as low an impedance as possible for the capacitance between the gate and source of the MOS transistor Q3 to quickly discharge the charge when the MOS transistor QIII is turned off instantaneously, so as to discharge the charge in the shortest time and ensure that the switching transistor can be quickly turned off, thereby protecting the measured load MLCC capacitor and the MLCC capacitor test power supply.

[0088] From the above formulas (1) and (5), we get VCC4 = -R5 × i 反 ;

[0089] When VCC1 >> VCC4, the output voltage VCC2 of the 1st pin of the operational amplifier IC1 is VCC2 = +VCC, that is, it has a strong driving ability. After passing through the isolation diode D2, the voltage is VCC3 = +VCC - 0.7V. The parasitic diode of the N-channel enhancement-mode MOS transistor Q1, which is the positive charging current limiting switch of the MLCC capacitor, will conduct first. The voltage between the gate G and the source S is much greater than the turn-on voltage of the MOS transistor Q1, and the MOS transistor Q1 conducts to short-circuit the parasitic diode. At this time, the current i 反 will flow through the MOS transistor Q1; at the same time, the P-channel enhancement-mode MOS transistor Q2 of the fast turn-off circuit is finally cut off, and finally a safe and reliable reverse charge is given to the measured load MLCC capacitor.

[0090] In the embodiment of the present invention, Figure 3A schematic diagram of a bidirectional current limiting circuit for MLCC capacitor test power supply output and an embodiment of the present invention. Figure 2 The schematic diagrams are similar, the difference being that the P-channel enhancement-mode MOSFET Q2 in the first fast turn-off circuit is replaced with a PNP transistor, and the P-channel enhancement-mode MOSFET Q4 in the second fast turn-off circuit is replaced with a PNP transistor; both have the same fast turn-off current-limiting switching capability.

[0091] Figure 4 The specific steps of the automatic current limiting protection circuit in this embodiment of the invention are as follows:

[0092] S1. Set the current limiting value according to the parameters of the capacitor of the MLCC being tested;

[0093] S2. Sample and acquire the charging current value of the MLCC under test;

[0094] S3. Compare and determine whether the current exceeds the range;

[0095] S4. If the current exceeds the set value, the circuit will automatically and quickly shut off the current limiting switch output to ensure safety and reliability.

[0096] In step S1, the current limiting value of the circuit is adjusted by controlling the output of the DAC (digital-to-analog converter).

[0097] In this embodiment of the invention, steps S2 and S3 are automatically performed by the current limiting sampling circuit in the circuit to measure and compare the current, which can be completed without manual operation, as described in the specific implementation.

[0098] In step S4, if the current exceeds the set value, the current limiting switch is controlled by the fast shutdown circuit in the circuit, and the principle is the same as described in the specific implementation.

Claims

1. A bidirectional current limiting circuit for MLCC capacitor test power supply output, characterized in that, include: The power supply module includes a power supply module, a DAC output module circuit, a first filter capacitor, a second filter capacitor, an operational amplifier comparator output drive circuit, a first isolation diode, a second isolation diode, a first current limiting resistor, a second current limiting resistor, a third current limiting resistor, a fourth current limiting resistor, a fast shutdown circuit, a clamping protection diode circuit, a current limiting switch circuit, and a current limiting sampling circuit. The power supply module includes positive and negative power supply modules. The DAC output module is connected to the operational amplifier comparator output drive circuit. The operational amplifier comparator output drive circuit is connected to the DAC output module, the isolation diode and fast turn-off circuit, and the current limiting sampling circuit. Both the first isolation diode and the second isolation diode are connected to the operational amplifier comparator output drive circuit and the fast turn-off circuit; The fast shutdown circuit is connected to the operational amplifier comparator output drive circuit, the isolation diode, and the current limiting switch circuit. The clamping protection diode circuit is located between the fast shutdown circuit and the current limiting switch circuit. The current limiting switch circuit is connected to the positive and negative power supply modules and the current limiting sampling circuit. The current-limiting sampling circuit, the current-limiting switch circuit, and the operational amplifier comparator output drive circuit are connected; The operational amplifier comparator output drive circuit includes a first operational amplifier and a second operational amplifier. The first operational amplifier has pins including a first pin, a second pin, a third pin, a fourth pin, and an eighth pin. The second operational amplifier has pins including a fifth pin, a sixth pin, and a seventh pin. The first pin is connected to the anode of the first isolation diode, the second pin is connected to the third current-limiting resistor, the third pin is connected to the common connection terminal of the first filter capacitor and the DAC output module circuit, the fourth pin is connected to the negative terminal of the operational amplifier power supply, and the eighth pin is connected to the positive terminal of the operational amplifier power supply. The first operational amplifier is used to drive the current-limiting switch circuit during forward charging. The fifth pin is connected to the common connection terminal of the second filter capacitor and the DAC output module circuit, the sixth pin is connected to the fourth current limiting resistor, the seventh pin is connected to the anode of the second isolation diode, and the second operational amplifier is used to drive the current limiting switch circuit during reverse charging.

2. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 1, characterized in that, The power supply module includes: a current-limiting protection power supply, positive and negative power supply module input terminals, positive and negative power supply module output terminals, an operational amplifier power supply, and a DC power supply, wherein: The current-limiting protection power supply has a potential reference to the ground plane; The positive and negative power supply output terminals are referenced to the ground plane. The current-limiting protection power supply and the positive and negative power supply output terminals are isolated from each other.

3. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 1, characterized in that, The DAC output module circuit is used to control the DAC function through the control unit, to simulate the DAC chip function through PWM, or to output a settable voltage through a dedicated DAC chip. The settable voltage is used to adjust the current value of the MLCC capacitor under test for charging current limiting.

4. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 2, characterized in that, The anode of the first isolation diode is connected to the first pin of the first operational amplifier, and the cathode of the first isolation diode is connected to the first current-limiting resistor; the anode of the second isolation diode is connected to the seventh pin of the second operational amplifier, and the cathode of the first isolation diode is connected to the second current-limiting resistor.

5. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 4, characterized in that, The fast shutdown circuit includes a first fast shutdown circuit and a second fast shutdown circuit. The first fast shutdown circuit includes a first resistor, a second resistor, and a three-terminal semiconductor of the first fast shutdown circuit. One end of the first resistor is connected to the common connection terminal of the first pin of the first operational amplifier and the anode of the first isolation diode; the other end of the first resistor is connected to the gate of the three-terminal semiconductor of the first fast shutdown circuit; the source of the three-terminal semiconductor of the first fast shutdown circuit is connected to the first current-limiting resistor; the drain of the three-terminal semiconductor of the first fast shutdown circuit is connected to the second resistor; and the other end of the second resistor is connected to the current-limiting protection power supply. The second fast shutdown circuit includes: a third resistor, a fourth resistor, and a three-terminal semiconductor for the second fast shutdown circuit. One end of the third resistor is connected to the common connection terminal of the seventh pin of the second operational amplifier and the anode of the second isolation diode; the other end of the third resistor is connected to the gate of the three-terminal semiconductor for the second fast shutdown circuit; the source of the three-terminal semiconductor for the second fast shutdown circuit is connected to the second current-limiting resistor; the drain of the three-terminal semiconductor for the second fast shutdown circuit is connected to the fourth resistor; and the other end of the fourth resistor is connected to the current-limiting protection power supply.

6. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 5, characterized in that, The clamping protection diode circuit includes a first clamping protection diode circuit and a second clamping protection diode circuit. The first clamping protection diode circuit includes a first protection diode and a second protection diode. The anode of the first protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the first fast turn-off circuit and the first current limiting resistor. The cathode of the first protection diode is connected to the DC power supply. The anode of the second protection diode is connected to the current-limiting protection power supply, and the cathode of the second protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the first fast shutdown circuit and the first current-limiting resistor. The second clamping protection diode circuit includes a third protection diode and a fourth protection diode. The anode of the third protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor. The cathode of the third protection diode is connected to a DC power supply. The anode of the fourth protection diode is connected to the current-limiting protection power supply, and the cathode of the fourth protection diode is connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor.

7. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 6, characterized in that, The current limiting switch circuit includes a first current limiting switch circuit and a second current limiting switch circuit. The first current limiting switch circuit includes a first current limiting switch circuit MOSFET. The gate of the first current limiting switch circuit MOSFET is connected to the common connection terminal of the source of the three-terminal semiconductor of the first fast turn-off circuit and the first current limiting resistor. The source of the first current limiting switch circuit MOSFET is connected to the common connection terminal of the first sampling resistor and the first current limiting sampling resistor. The drain of the first current limiting switch circuit MOSFET is connected to the output terminal of the positive and negative power supply module. The second current-limiting switch circuit MOSFET has its gate connected to the common connection terminal of the source of the three-terminal semiconductor of the second fast turn-off circuit and the second current-limiting resistor; the source of the second current-limiting switch circuit MOSFET is connected to the common connection terminal of the second sampling resistor and the second current-limiting sampling resistor; and the drain of the second current-limiting switch circuit MOSFET is connected to the load under test.

8. The bidirectional current limiting circuit for MLCC capacitor test power supply output according to claim 7, characterized in that, The current limiting sampling circuit includes a first current limiting sampling circuit and a second current limiting sampling circuit. The first current limiting sampling circuit includes a third current limiting resistor and a first sampling resistor. One end of the third current limiting resistor is connected to the common connection terminal of the source of the MOS transistor of the first current limiting switch circuit and the first sampling resistor. The other end of the third current limiting resistor is connected to the second pin of the first operational amplifier. The first sampling resistor is connected to the current limiting protection power supply. The second current-limiting sampling circuit includes a fourth current-limiting resistor and a second sampling resistor. One end of the fourth current-limiting resistor is connected to the common connection terminal of the MOS source of the second current-limiting switch circuit and the second sampling resistor, and the other end of the fourth current-limiting resistor is connected to the sixth pin of the second operational amplifier. The second sampling resistor is connected to the common connection terminal of the current-limiting protection power supply and the first sampling resistor. The first current-limiting sampling circuit is used to sample the forward charging current, and the second current-limiting sampling circuit is used to sample the reverse charging current.

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