A high-current series linear filtering circuit

Abstract

The present invention discloses a large power supply series linear filter circuit, which includes a passive filter circuit, a diode clamp circuit, a follower circuit module and an auxiliary power supply module. The passive filter circuit is composed of a resistor and a capacitor; the diode clamp circuit is composed of two general diodes; the follower circuit module is composed of an input amplifier part, a current mirror, a MOSFET drive part and a MOSFET power tube, and multiple follower modules can be used in parallel. The input positive pole of the linear filter circuit is connected to the output positive pole of the power supply to be filtered, and the negative pole of the linear filter circuit is connected to the output negative pole of the power supply to be filtered. The output positive pole and the negative pole of the linear filter circuit constitute a load output port. The output voltage of the filter circuit of the present invention follows the input voltage, maintains a constant voltage difference, and is easy to modify and control; the filter circuit of the present invention uses a low-voltage, high-current MOSFET as the main power device, and has the ability to connect modules in parallel, which is suitable for output filtering of large-current switching power supplies.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics applications, in particular to a series linear filter circuit for a high-current direct current power supply. Background Art

[0002] In high-power DC applications, switching power supplies are often used to generate the target voltage. Due to the pulsating topology of these switching power supplies, voltage ripple is unavoidable. To reduce DC power ripple, common solutions include increasing the inductance and capacitance of the circuit, adding LC filters, and so on. These solutions not only increase system size but also reduce the power supply's response speed. Increasing the switching frequency or pulsation frequency can reduce ripple to some extent, but in practice, this can lead to increased switching losses and more complex control.

[0003] Besides adding an LC passive filter, existing methods for reducing power supply ripple include series low-dropout linear regulators (LDOs) and parallel active filters. Series LDO solutions cannot ensure that the LDO output voltage follows the output voltage of the switching power supply. Modifying the switching power supply's feedback loop to maintain a constant value between the switching power supply output voltage and the LDO output voltage is necessary to achieve ideal efficiency. Parallel active filters require specialized high-current power amplifiers and coupling circuits. They inject a reversed ripple current into the switching power supply's output to reduce ripple voltage. Their complex structure and control methods, coupled with amplifier power limitations, make them difficult to apply to high-current applications.

[0004] Therefore, there is an urgent need for a high-current series linear filter circuit that can suppress the ripple of the switching power supply without excessively changing the structure and loop of the switching power supply itself. Summary of the Invention

[0005] In order to solve the problems in the above applications, the present invention proposes a series linear filter circuit for a large current DC power supply:

[0006] The purpose of the present invention can be achieved through the following technical solutions:

[0007] A high-current series linear filter circuit, comprising a passive filter circuit, a diode clamp circuit, a follower circuit module and an auxiliary power supply module;

[0008] A linear filter circuit has a positive input, a positive output, and a negative output. Its main structure is connected in series with the positive output of a switching power supply. The positive input of the linear filter circuit is connected to the positive output of the switching power supply, while the negative output is connected to the negative output of the switching power supply. Together, the positive and negative outputs of the linear filter circuit form the output port. As a series voltage regulator, the linear filter circuit suppresses the output ripple of the switching power supply. Furthermore, within a range below the switching frequency, the output voltage of the linear filter circuit closely tracks the output voltage of the switching power supply, and the voltage difference between its positive input and output electrodes fluctuates within a small range.

[0009] The passive filtering circuit is composed of a resistor and a capacitor, the resistor and the capacitor are connected in series, the other end of the resistor is connected to the positive input of the linear filtering circuit, and the other end of the capacitor is connected to the negative input of the linear filtering circuit;

[0010] The diode clamping circuit is composed of two universal diodes, which are connected in anti-phase parallel. The diode clamping circuit is connected in parallel with the resistor of the passive filter circuit. The auxiliary power supply module is a universal isolated power supply module.

[0011] The control port of the follower circuit module is connected to the negative terminal of the passive filter circuit. The input port of the follower circuit module is the positive input terminal of the linear filter circuit, and the output port of the follower circuit module is the positive output terminal of the linear filter circuit. The follower circuit module can be replaced with multiple follower circuit modules with current sharing capabilities connected in parallel to form a follower module with higher current output capability.

[0012] Furthermore, the follower circuit module consists of NPN and PNP transistors, a resistor, and an N-channel MOSFET, and is powered by an auxiliary power supply module. The follower circuit module uses a low-voltage N-channel MOSFET as its primary power device. Compared to NPN transistors, low-voltage N-channel MOSFETs can carry higher currents in the linear region, enabling normal operation in high-current applications. The module's current-sharing control capability allows multiple modules to be connected in parallel to form a linear filter circuit, further expanding its high-current application range. The follower circuit module has a voltage signal input port, a current input port, and a current output port. In addition to the MOSFET as the primary power device, the follower circuit module is internally subdivided into an input amplifier section, a current mirror, and a MOSFET driver section. The MOSFET in the follower circuit module is controlled by the driver circuit and other components to operate in the linear region, maintaining the average voltage difference between its input voltage signal port and its current output port within the range of 1.4V-2V.

[0013] The follower module uses N-channel MOSFET as the main power device, and the follower circuit module consists of NPN transistors Q1, Q2, Q5, PNP transistors Q3, Q4, resistors R1, R2, R3, R e 、R g 、R g′ and N-channel MOSFET power tube Q6; among them, Q1 and R3 form an emitter follower circuit, Q2, R e Composed of common base amplifier circuit, Q1, R3, Q2, R e The cascaded circuit forms the input amplifier; Q3, Q4, R1, and R2 form a current mirror, and the input end of the current mirror is connected to the collector of Q2; R g ,Q5,R g′ Composed of MOSFET drive part, R g The output terminal of the current mirror is connected to the base of Q5, R g′ Connect the emitter of Q5 to form an emitter follower. The output of the emitter follower is connected to the gate of Q6; the output voltage V generated by the auxiliary power supply bias The negative pole is connected to the source of Q6, the negative poles of each module are connected to the source of Q6, and the positive poles are connected to V bias Positive electrode; the base of Q1 is the control port, the drain of Q6 is the input port, and the source of Q6 is the output port.

[0014] Furthermore, the follower circuit module can be replaced with multiple follower circuit modules with current sharing capability connected in parallel to form a follower module with a larger current output capability. A small resistor is connected in series to the output port of each module, and the other end of the small resistor serves as the output port, and R g The fixed value resistor is changed to a negative temperature coefficient resistor (NTC); when the modules are connected in parallel, the base of Q2 of each module is connected, the input ports of each module are connected, and the output ports of each module are connected through a small value resistor.

[0015] After connecting a small resistor in series with the output port of the follower circuit module, the resistor controlling the gain of the MOSFET driver within the follower circuit module is replaced with a negative temperature coefficient (NTC) resistor. This small series resistor generates a voltage drop, which, through the module's input amplifier, uses negative feedback to regulate the current in each module, balancing the load current across them. The NTC resistor, placed close to the MOSFET, reduces the circuit's gain as the MOSFET temperature rises, thereby compensating for the MOSFET's negative temperature characteristic.

[0016] Beneficial effects of the present invention:

[0017] 1. This invention uses a hardware circuit to implement series active filtering. The filter output automatically follows the output voltage of the switching power supply, eliminating the need for an additional control loop. The voltage drop of the filter's power components remains constant, and the power consumed depends only on the output current, not the output voltage, facilitating component selection and heat dissipation design.

[0018] 2. This invention uses a low-voltage N-channel MOSFET as the primary power device, allowing the device's withstand voltage to be lower than the output voltage. This design fully utilizes the device's high current and high power dissipation characteristics, achieving high output current at a low cost.

[0019] 3. The present invention proposes a follower circuit module that can be connected in parallel and a parallel connection method thereof, which greatly improves the carrying current of the linear filter current by connecting the modules in parallel. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, those skilled in the art can derive other drawings based on these drawings without inventive effort.

[0021] Figure 1 This is a principle block diagram of a high current series linear filter circuit in this application

[0022] Figure 2 The circuit topology of the follower module of this application;

[0023] Figure 3 Mark the circuit topology and operating current of the follower module;

[0024] Figure 4 This is a schematic diagram of the parallel connection of the follower modules of this application;

[0025] Figure 5 This is the working waveform when the test prototype outputs 3A;

[0026] Figure 6 This is the working waveform when the test prototype outputs 10A. Specific implementation methods

[0027] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] In a specific embodiment, Figure 1 As shown, a series linear filter circuit consists of a passive filter circuit, a diode clamp circuit, a follower circuit module, and an auxiliary power supply module. The passive filter circuit consists of a resistor R and a capacitor C; the diode clamp circuit consists of two universal diodes connected in antiparallel and in parallel with the passive filter circuit's resistor R; and the auxiliary power supply module is a universal isolated power supply module.

[0029] The follower module circuit structure is as follows Figure 2 As shown. The follower circuit module is composed of NPN, PNP transistors, resistors and N-channel MOSFETs, and is powered by an auxiliary power supply module. The follower circuit module has a voltage signal input port, a current input port and a current output port. In addition to MOSFET as the main power device, the follower circuit module can be subdivided into an input amplifier part, a current mirror, and a MOSFET drive part. The MOSFET in the follower circuit module is controlled by the drive circuit and operates in the linear region, and maintains the average value of the voltage difference between its input voltage signal port and the current output port within the range of 1.4V-2V.

[0030] The passive filter circuit, composed of resistors and capacitors, forms a low-pass filter with a cutoff frequency significantly lower than the switching frequency of the switching power supply being filtered. The resistor in the passive filter circuit is connected to the positive input of the linear filter circuit, while the capacitor is connected to the negative input of the linear filter circuit. Ignoring the current flowing into the follower module, the voltage across the capacitor in steady-state operation is equal to the average value of the linear filter circuit's input voltage.

[0031] The diode clamp circuit consists of two universal diodes connected in anti-parallel, in parallel with the passive filter circuit's resistor. Its function is to ensure that when the input voltage fluctuates rapidly and significantly, if the instantaneous fluctuation exceeds the diode's forward voltage, the clamp circuit causes the passive filter circuit's capacitor voltage to quickly follow the input voltage change. This diode clamp circuit enables the linear filter circuit to respond more quickly to large changes in output voltage while maintaining the voltage drop across the follower module within a predetermined range, preventing overvoltage conditions on the MOSFET.

[0032] The detailed working principle of the follower circuit module is as follows:

[0033] Q1, Q2, R e It forms the input amplifier part, where Q1 acts as an emitter follower to follow the input voltage of the control port; Q2, R e As a common base amplifier circuit, R e At the same time as a voltage drop occurs on the collector, a sink current equivalent to the emitter current is generated at the collector. Q3, R1, Q2, and R2 form a current mirror that copies the sink current generated by Q2 as a source current; Rg ,Q5,R g′ The MOSFET driver section is composed of the current mirror, and the source current generated by the current mirror is in R g A voltage drop occurs on the pin, and Q5 acts as an emitter follower, with the pull-down resistor R g′ It forms a MOSFET drive circuit and drives the capacitive load of the MOSFET gate with a large push-pull current capability. bias An isolated power supply module is used as auxiliary power supply.

[0034] like Figure 3 As shown in the figure, the important parameters in the circuit are marked. be The voltage drop is 0.7V, so we can get:

[0035]

[0036]

[0037]

[0038] For general MOSFETs:

[0039]

[0040] If the follower module is considered as a new MOSFET, V i -V s Considered as V gs ', its working status can be deduced:

[0041]

[0042]

[0043]

[0044] Ignore transistor V be The new MOSFET brings a 0.7V voltage drop. because The source follower Module equivalent MOSFET when When V th The MOSFET's native 3V is reduced to about 1.6V, and the MOSFET's native V th Due to the changes in these parameters, the voltage drop of the module is significantly reduced when it works as a source follower.

[0045] The follower circuit module can be replaced with multiple follower circuit modules with current balancing capability connected in parallel to form a follower module with a larger current output capability. Based on the above follower circuit module based on low-voltage MOSFET, it is modified to have current balancing and temperature compensation functions, and can be used in parallel. An example of two parallel circuits is as follows Figure 4 As shown. A small resistor is connected in series to the output port of the original follower circuit module, and the resistor R g Replace with a negative temperature coefficient resistor (NTC). The small value resistor in series generates a certain voltage drop. Through the input amplifier part of the module, negative feedback regulates the current of each module, which can largely compensate for the discreteness of MOSFET parameters and balance the load current of each module. The NTC is placed close to the MOSFET. When the MOSFET temperature rises, the gain of the gate drive part is reduced, which reduces the V gs , thereby compensating for the negative temperature characteristics of MOSFET.

[0046] When multiple follower modules are connected in parallel, in order to prevent overshoot oscillation between modules, a passive RC filter circuit can be added to the input port of each module to reduce the available bandwidth of the follower. At the same time, the input port of each follower module can be isolated to reduce crosstalk and achieve the purpose of suppressing oscillation.

[0047] In order to verify the performance of the filter circuit structure and its parallel connection method, a prototype was built for testing. The prototype uses two follower modules in parallel to form a linear filter circuit, and uses a 50kHz Buck circuit as the filtered object. The prototype uses a 60V input, a 15V output, and a maximum output current of 10A. When the prototype output current is 3A and 10A, the ripple waveform of the output after the linear filter circuit and the original output of the Buck circuit is as follows Figure 5 、 Figure 6 As shown in the figure, the measured data shows that the original output ripple of the Buck is about 400mV under light load and full load conditions. pp , 120mV RMS After the linear filter circuit, the peak value of the ripple is about 1 / 5 of the original Buck output, and the effective value is less than 1 / 10 of the original Buck output. When fully loaded, the voltage drop on the follower module is about 1.5V DC The prototype operates stably in the entire load range without oscillation.

[0048] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0049] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A high current series linear filter circuit, characterized in that: The circuit includes a passive filter circuit, a diode clamp circuit, a follower circuit module and an auxiliary power supply module; The linear filter circuit has an input positive electrode, an output positive electrode, and a negative electrode; the main structure of the linear filter circuit is connected in series to the output positive electrode of the switching power supply, the input positive electrode of the linear filter circuit is connected to the output positive electrode of the switching power supply, the negative electrode of the linear filter circuit is connected to the output negative electrode of the switching power supply, and the output positive electrode and the negative electrode of the linear filter circuit together form an output port; The passive filtering circuit is composed of a resistor and a capacitor, the resistor and the capacitor are connected in series, the other end of the resistor is connected to the positive input of the linear filtering circuit, and the other end of the capacitor is connected to the negative input of the linear filtering circuit; The diode clamp circuit is composed of two general diodes, the two diodes are connected in parallel in anti-phase, and the diode clamp circuit is connected in parallel with the resistor of the passive filter circuit; The control port of the follower circuit module is connected to the negative electrode of the passive filter circuit, the input port of the follower circuit module is connected to the positive input electrode of the linear filter circuit, and the output port of the follower circuit module is connected to the positive output electrode of the linear filter circuit; The follower circuit module is based on a low-voltage N-channel MOSFET. The follower circuit module consists of NPN transistors Q1, Q2, Q5, PNP transistors Q3, Q4, resistors R1, R2, R3, R e 、R g 、R g′ and N-channel MOSFET power tube Q6; among them, Q1 and R3 form an emitter follower circuit, Q2, R e Composed of common base amplifier circuit, Q1, R3, Q2, R e The cascaded circuit forms the input amplifier; Q3, Q4, R1, and R2 form a current mirror, and the input end of the current mirror is connected to the collector of Q2; R g ,Q5,R g′ Composed of MOSFET drive part, R g The output terminal of the current mirror is connected to the base of Q5, R g′ Connect the emitter of Q5 to form an emitter follower, and the output of the emitter follower is connected to the gate of Q6; the output voltage V generated by the auxiliary power supply bias The negative pole is connected to the source of Q6, the negative poles of each module are connected to the source of Q6, and the positive poles are connected to V bias Positive electrode; the base of Q1 is the control port, the drain of Q6 is the input port, and the source of Q6 is the output port; MOSFET is the abbreviation of metal-oxide semiconductor field effect transistor.

2. A high current series linear filter circuit according to claim 1, characterized in that: The auxiliary power supply module is a universal isolated power supply module.

3. A high current series linear filter circuit according to claim 1, characterized in that: The follower circuit module is powered by an auxiliary power supply module.

4. A high current series linear filter circuit according to claim 1, characterized in that: The linear filter circuit serves as a series voltage stabilization circuit and has a suppressive effect on the output ripple of the switching power supply.

5. A high current series linear filter circuit according to claim 1, characterized in that: In a range lower than the switching frequency, the output voltage of the linear filter circuit closely follows the output voltage of the switching power supply, and the input-output voltage difference of the linear filter circuit is maintained at 1.4V-2V.

6. A high current series linear filter circuit according to claim 1, characterized in that: The MOSFET in the follower circuit module is controlled by the driving circuit to operate in the linear region.

7. The high current series linear filter circuit according to claim 1, characterized in that: The follower circuit module can be replaced with multiple follower circuit modules with current sharing capability connected in parallel to form a follower module with a larger current output capability. The output port of each module is connected in series with a small resistor, and the other end of the small resistor serves as the output port, and R g The fixed value resistor is changed to a negative temperature coefficient resistor; when the follower circuit modules are connected in parallel, the base of Q2 of each module is connected, the input ports of each module are connected, and the output ports of each module are connected through a small value resistor.

8. A high current series linear filter circuit according to claim 7, characterized in that: The small value resistors connected in series generate a certain voltage drop, which is passed through the input amplifier part in the module and negatively feedbacked to adjust the current of each module so that the load current of each module is balanced.

9. The high current series linear filter circuit according to claim 7, characterized in that: The negative temperature coefficient resistor is placed closely to the MOSFET, and reduces the gain of the circuit when the temperature of the MOSFET rises, thereby compensating for the negative temperature characteristic of the MOSFET.

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