阅读说明：本技术 一种全环路自振荡式d类功放电路 (Full-loop self-oscillation type D-class power amplifier circuit ) 是由 张太武 于 2019-11-12 设计创作，主要内容包括：本发明提供一种全环路自振荡式D类功放电路,属于有源音箱电路领域。本发明包括互相独立的低音功放电路和高音功放电路,所述低音功放电路和高音功放电路均设有信号调制模块、触发器整形模块、驱动模块、开关放大模块和低通滤波器,其中,所述信号调制模块的输出端与所述触发器整形模块输入端相连,所述触发器整形模块输出端与驱动模块的输入端相连,所述驱动模块的输出端与开关放大模块的输入端相连,所述开关放大模块输出端与低通滤波器的输入端相连,所述低通滤波器的输出端设有正反馈引脚和同时作为输出引脚的负反馈引脚,所述正反馈引脚和负反馈引脚分别接信号调制模块的输入端,组成全环路反馈电路。本发明极大地降低了失真度。(The invention provides a full-loop self-oscillation type D-class power amplifier circuit, and belongs to the field of active loudspeaker box circuits. The low-pitch power amplifier circuit and the high-pitch power amplifier circuit are independent of each other, the low-pitch power amplifier circuit and the high-pitch power amplifier circuit are respectively provided with a signal modulation module, a trigger shaping module, a driving module, a switch amplification module and a low-pass filter, wherein the output end of the signal modulation module is connected with the input end of the trigger shaping module, the output end of the trigger shaping module is connected with the input end of the driving module, the output end of the driving module is connected with the input end of the switch amplification module, the output end of the switch amplification module is connected with the input end of the low-pass filter, the output end of the low-pass filter is provided with a positive feedback pin and a negative feedback pin which are used as output pins at the same time, and the positive feedback pin and the negative feedback pin are respectively connected with. The invention greatly reduces the distortion degree.)

1. The utility model provides a full loop self oscillation formula D class power amplifier circuit which characterized in that: comprises a bass power amplifier circuit and a treble power amplifier circuit which are mutually independent and are respectively used for driving a treble loudspeaker and a woofer, wherein, the bass power amplifier circuit and the treble power amplifier circuit are respectively provided with a signal modulation module, a trigger shaping module, a driving module, a switch amplifying module and a low-pass filter, wherein the output end of the signal modulation module is connected with the input end of the trigger shaping module, the output end of the trigger shaping module is connected with the input end of the driving module, the output end of the driving module is connected with the input end of the switch amplifying module, the output end of the switch amplification module is connected with the input end of the low-pass filter, the output end of the low-pass filter is provided with a positive feedback pin and a negative feedback pin which is used as an output pin at the same time, and the positive feedback pin and the negative feedback pin are respectively connected with the input end of the signal modulation module to form a full-loop feedback circuit.

2. The full-loop self-oscillating class-D power amplifier circuit according to claim 1, wherein: the high pitch power amplifier circuit adopts a half-bridge output stage topological structure, and the low pitch power amplifier circuit adopts a full-bridge output stage topological structure.

3. The full-loop self-oscillating class-D power amplifier circuit according to claim 2, wherein: the drive module comprises a normal phase drive unit and an inverse phase drive unit, the switch amplification module comprises two switch amplification units which are respectively connected with the output ends of the normal phase drive unit and the inverse phase drive unit, and the output end of the switch amplification unit is connected with the input end of the low-pass filter.

4. The full-loop self-oscillating class-D power amplifier circuit according to claim 3, wherein: the low-pass filter of the bass power amplifier circuit is a common-mode inductor low-pass filter and comprises a common-mode inductor L1, wherein a first-path switch amplification unit is connected with an input pin 4 of a common-mode inductor L1, a second-path switch amplification unit is connected with an input pin 1 of a common-mode inductor L1, the common-mode inductor low-pass filter further comprises a grounding capacitor C7 and a grounding capacitor C22, an output pin 3 of a common-mode inductor L7 is connected with one end of the grounding capacitor C7 and outputs bass audio OUTW +, an output pin 2 of the common-mode inductor L7 is connected with one end of the grounding capacitor C22 and outputs bass audio OUTW-.

5. The full-loop self-oscillating class-D power amplifier circuit according to claim 4, wherein: a differential filter is further arranged between the output end of the common-mode inductor low-pass filter and an output pin, the differential filter comprises resistors R73, R75 and a capacitor C18, wherein one end of each resistor R73 and R75 is connected with the output pin 3 of the common-mode inductor L7 after being connected in parallel, the other end of each resistor R3583 is connected with one end of a capacitor C18, the other end of the capacitor C18 is connected with the output pin 2 of the common-mode inductor L7, a first positive feedback pin is connected with one end of the capacitor C18 through a capacitor C142 and a capacitor C12 which are connected in parallel, and a second positive feedback pin is connected with the other end of the capacitor C18 through a capacitor C143 and a capacitor C21 which are connected.

6. The full-loop self-oscillating class-D power amplifier circuit according to claim 5, wherein: the signal modulation module of the bass power amplifier circuit comprises a high-speed comparator IC5 and a peripheral resistance-capacitance device thereof, wherein,

the inverting input end of the high-speed comparator IC5 is respectively connected with one end of a resistor R8 and one end of a capacitor C5, the other end of the capacitor C5 is connected with a first positive feedback pin FB1, the other end of a resistor R8 is respectively connected with one end of a resistor R5, one end of a resistor R7 and a grounded capacitor C8, the other end of a resistor R5 is connected with an output pin OUTW +, the other end of the resistor R7 is connected with an audio signal INW-through a capacitor C3,

the non-inverting input end of the high-speed comparator IC5 is respectively connected with one end of a resistor R17 and one end of a capacitor C16, the other end of the capacitor C16 is connected with a second positive feedback pin FB2, the other end of a resistor R17 is respectively connected with one end of a resistor R19, one end of a resistor R16 and a grounded capacitor C9, the other end of a resistor R19 is connected with an output pin OUTW-, the other end of the resistor R16 is connected with an audio signal INW + through a capacitor C13,

pins 5 and 6 of the high-speed comparator IC5 are suspended, pins 1 and 4 are connected to-15A power supply and are grounded through a capacitor C19, and pin 8 is connected to +15A power supply and is grounded through a capacitor C4; pin 7 of the high speed comparator IC5 is the output pin,

the signal modulation module of the high-pitch power amplifier circuit comprises a high-speed comparator IC11 and a peripheral resistance-capacitance element thereof, wherein,

the inverting input end of the high-speed comparator IC11 is respectively connected with one end of a resistor R63 and one end of a capacitor C42, the other end of the capacitor C42 is connected with a positive feedback pin FB3, the other end of a resistor R63 is respectively connected with one end of a resistor R58, one end of a resistor R62 and a grounded capacitor C46, the other end of a resistor R58 is connected with an output pin OUTT +, the other end of the resistor R62 is connected with an audio signal INT-through a capacitor C43,

the non-inverting input end of the high-speed comparator IC11 is respectively connected with one end of a resistor R71 and one end of a capacitor C54, the other end of the capacitor C54 is grounded, the other end of a resistor R71 is respectively connected with one end of a resistor R70, one end of a resistor R74 and a grounded capacitor C49, the other end of a resistor R74 is grounded, the other end of the resistor R70 is used for inputting an audio signal INT +,829 through a capacitor C4,

pins 5 and 6 of the high-speed comparator IC11 are suspended, pins 1 and 4 are connected with-15B power supply and are grounded through a capacitor C53, and pin 8 is connected with +15B power supply and is grounded through a capacitor C39; pin 7 of the high speed comparator IC11 is the output pin.

7. The full-loop self-oscillating class-D power amplifier circuit according to claim 4, wherein: the trigger shaping module of the bass power amplifier circuit has the same structure as that of the treble power amplifier circuit, and comprises a trigger IC4, a triode Q3, diodes D11, D3, D4, D8, D9 and peripheral resistance capacitance devices thereof, wherein,

the base of the triode Q1 is connected with a-15A power supply, the emitter is connected with the output end of the signal modulation module, the collector is connected with the anode of a diode D11, a pin 1 of a trigger IC4A is respectively connected with a ground resistor R14 and the cathode of a diode D11, the other end of a resistor R14 and a pin 2 of a trigger IC4A are connected with a-30V power supply, a pin 5 of a trigger IC4A is connected with a 5V power supply through a resistor R3, a pin 6 is respectively connected with one end of a resistor R6, the cathode of a diode D8 and a pin 3 of a trigger IC4B, a pin 4 of a trigger IC4B is respectively connected with one end of a resistor R9 and the cathode of a diode D9, the other end of a resistor R6 and the other end of an R9 are respectively connected with different pins of the driving module, the anode of a diode D8 is respectively connected with the anode of a diode D4, the other end of a resistor R6 and one end of a capacitor C10, the anode of a diode D9 is respectively connected with the anode of a resistor R874, the cathodes of the diodes D4 and D3 are connected with a mute pin, and the other ends of the capacitors C10 and C11 are connected with a-30V power supply.

8. The full-loop self-oscillating class-D power amplifier circuit according to claim 7, wherein: the positive phase driving unit of the bass power amplifier circuit comprises a driving chip IC3, the reverse phase driving unit comprises a driving chip IC6, the driving chip IC3 and the driving chip IC6 both adopt MP18021A chips, wherein the other end of the resistor R6 is connected with a pin IL 6 of a driving chip IC3 and a pin IH 5 of a driving chip IC3, and the other end of the resistor R9 is connected with a pin IH 5 of a driving chip IC3 and a pin IL 6 of the driving chip IC 3.

9. The full-loop self-oscillating class-D power amplifier circuit according to claim 8, wherein: the switch amplification unit comprises two switch tubes, wherein the gate of a switch tube Q1 of the first switch amplification unit is connected with a pin 2 of a driving chip IC3, the drain of the switch tube Q1 is connected with a 30V power supply and is grounded through a capacitor C1, the source of the switch tube Q2 is connected with the drain of the switch tube Q2 and the input end of a filter, the gate of the switch tube Q2 is connected with the anode of a diode D10 and one end of a resistor R14, the cathode of the diode D10 and the other end of the resistor R15 are connected with a pin 8 of the driving chip IC3, and the source of the switch tube Q2 is connected with a-30V power supply and is grounded through a capacitor C15.

10. The full-loop self-oscillating class-D power amplifier circuit according to any of claims 1-9, wherein: the low-pass filter of the high-pitch power amplifier circuit comprises an inductor L2 and a capacitor C41, wherein the input end of the inductor L1 is connected with the output end of a switch amplification module, the output end of the inductor L1 is connected with one end of the capacitor C41 and outputs high-pitch audio OUTT +, the other end of the capacitor C41 is grounded, a positive feedback pin FB1 is respectively connected with one end of the capacitors C40 and C141 which are connected in parallel and one end of the resistors R64 and R65 which are connected in parallel, the other end of the capacitors C40 and C141 which are connected in parallel is connected with the output end of the inductor L1, and the other ends of the resistors R64 and R65.

Technical Field

The invention relates to an active sound box circuit, in particular to a full-loop self-oscillation type D-class power amplifier circuit.

Background

The class D power amplifier simply means an amplification mode in which the power amplification element is in a switch operation state. The principle is realized by comparing an audio signal with a high-frequency fixed frequency signal to obtain a modulation signal of the audio signal on a carrier wave with fixed frequency, namely converting the modulation signal into a PWM signal, amplifying the PWM signal into a high-voltage and high-current high-power PWM signal through a switching amplifier, and finally restoring the high-power audio signal through a low-pass filter.

In this way, the amplifying element (generally a transistor) enters a saturation state from the beginning of operation, the transistor is equivalent to a switch which is switched on and directly connects the power supply and the load, and an ideal switching amplifying circuit has no voltage drop, no electric energy loss and no heat generation, and does not need a bulky heat dissipation device. The actual D-type amplifying circuit almost only has transistor saturation voltage drop, so the actual loss is almost only related to the element characteristic of the transistor and is not related to the amplitude of signal output, and the D-type amplifying circuit is particularly suitable for most application occasions of high-power or high-energy-efficiency amplification of audio frequency and small space.

The class-D power amplifier products on the same level on the market usually adopt a fully integrated driving chip, the driving form is relatively fixed, the driving capability is relatively limited, and a perfect and reliable protection circuit is lacked. Meanwhile, the circuit architecture is limited, and large loop negative feedback similar to that commonly used by A/B class power amplifiers cannot be used, so that a larger improvement space does not exist on the distortion factor which is a weak key index of the D class power amplifier.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a full-loop self-oscillation type D class power amplifier circuit.

The invention comprises a bass power amplifier circuit and a treble power amplifier circuit which are independent of each other and are respectively used for driving a treble loudspeaker and a woofer, wherein the bass power amplifier circuit and the tweeter power amplifier circuit are respectively provided with a signal modulation module, a trigger shaping module, a driving module, a switch amplification module and a low-pass filter, the output end of the signal modulation module is connected with the input end of the trigger shaping module, the output end of the trigger shaping module is connected with the input end of the driving module, the output end of the driving module is connected with the input end of the switch amplification module, the output end of the switch amplification module is connected with the input end of the low-pass filter, the output end of the low-pass filter is provided with a positive feedback pin and a negative feedback pin which is simultaneously used as an output pin, and the positive feedback pin and the negative, forming a full loop feedback circuit.

The invention is further improved, the high-pitch power amplifier circuit adopts a half-bridge output stage topological structure, and the low-pitch power amplifier circuit adopts a full-bridge output stage topological structure.

The invention is further improved, the driving module comprises a positive phase driving unit and a reverse phase driving unit, the switch amplifying module comprises two switch amplifying units respectively connected with the output ends of the positive phase driving unit and the reverse phase driving unit, and the output end of the switch amplifying unit is connected with the input end of the low-pass filter.

The invention is further improved, the low-pass filter of the bass power amplifier circuit is a common-mode inductance low-pass filter, and comprises a common-mode inductance L1, a first switch amplification unit is connected with an input pin 4 of a common-mode inductance L1, a second switch amplification unit is connected with an input pin 1 of a common-mode inductance L1, the common-mode inductance low-pass filter further comprises a grounding capacitance C7 and a grounding capacitance C22, an output pin 3 of the common-mode inductance L7 is connected with one end of the grounding capacitance C7 and outputs bass audio OUTW +, an output pin 2 of the common-mode inductance L7 is connected with one end of the grounding capacitance C22 and outputs bass audio OUTW-.

The low-pass filter of the high-pitch power amplifier circuit comprises an inductor L2 and a capacitor C41, wherein the input end of the inductor L1 is connected with the output end of a switch amplification module, the output end of the inductor L1 is connected with one end of the capacitor C41 and outputs high-pitch audio OUTT +, the other end of the capacitor C41 is grounded, a positive feedback pin FB1 is respectively connected with one end of the capacitors C40 and C141 which are connected in parallel and one end of the resistors R64 and R65 which are connected in parallel, the other end of the capacitors C40 and C141 which are connected in parallel is connected with the output end of the inductor L1, and the other ends of the resistors R64 and R65.

The invention is further improved, a differential filter is further arranged between the output end and the output pin of the common mode inductor low-pass filter, the differential filter comprises resistors R73, R75 and a capacitor C18, wherein after the resistors R73 and R75 are connected in parallel, one end of the resistor R73 is connected with the output pin 3 of the common mode inductor L7, the other end of the resistor R73 is connected with one end of a capacitor C18, the other end of the capacitor C18 is connected with the output pin 2 of the common mode inductor L7, the first positive feedback pin is connected with one end of the capacitor C18 through the capacitor C142 and the capacitor C12 which are connected in parallel, and the second positive feedback pin is connected with the other end of the capacitor C18 through the capacitor C143 and the capacitor C21 which.

The invention is further improved, the signal modulation module of the bass power amplifier circuit comprises a high-speed comparator IC5 and a peripheral capacitance-resistance device thereof, wherein,

the inverting input end of the high-speed comparator IC5 is respectively connected with one end of a resistor R8 and one end of a capacitor C5, the other end of the capacitor C5 is connected with a first positive feedback pin FB1, the other end of a resistor R8 is respectively connected with one end of a resistor R5, one end of a resistor R7 and a grounded capacitor C8, the other end of a resistor R5 is connected with an output pin OUTW +, the other end of the resistor R7 is connected with an audio signal INW-through a capacitor C3,

the non-inverting input end of the high-speed comparator IC5 is respectively connected with one end of a resistor R17 and one end of a capacitor C16, the other end of the capacitor C16 is connected with a second positive feedback pin FB2, the other end of a resistor R17 is respectively connected with one end of a resistor R19, one end of a resistor R16 and a grounded capacitor C9, the other end of a resistor R19 is connected with an output pin OUTW-, the other end of the resistor R16 is connected with an audio signal INW + through a capacitor C13,

pins 5 and 6 of the high-speed comparator IC5 are suspended, pins 1 and 4 are connected to-15A power supply and are grounded through a capacitor C19, and pin 8 is connected to +15A power supply and is grounded through a capacitor C4; pin 7 of the high speed comparator IC5 is the output pin,

the signal modulation module of the high-pitch power amplifier circuit comprises a high-speed comparator IC11 and a peripheral resistance-capacitance element thereof, wherein,

the inverting input end of the high-speed comparator IC11 is respectively connected with one end of a resistor R63 and one end of a capacitor C42, the other end of the capacitor C42 is connected with a positive feedback pin FB3, the other end of a resistor R63 is respectively connected with one end of a resistor R58, one end of a resistor R62 and a grounded capacitor C46, the other end of a resistor R58 is connected with an output pin OUTT +, the other end of the resistor R62 is connected with an audio signal INT-through a capacitor C43,

the non-inverting input end of the high-speed comparator IC11 is respectively connected with one end of a resistor R71 and one end of a capacitor C54, the other end of the capacitor C54 is grounded, the other end of a resistor R71 is respectively connected with one end of a resistor R70, one end of a resistor R74 and a grounded capacitor C49, the other end of a resistor R74 is grounded, the other end of the resistor R70 is used for inputting an audio signal INT +,829 through a capacitor C4,

pins 5 and 6 of the high-speed comparator IC11 are suspended, pins 1 and 4 are connected with-15B power supply and are grounded through a capacitor C53, and pin 8 is connected with +15B power supply and is grounded through a capacitor C39; pin 7 of the high speed comparator IC11 is the output pin.

The invention is further improved, the trigger shaping module of the bass power amplifier circuit has the same structure with the trigger shaping module of the treble power amplifier circuit, the trigger shaping module of the bass power amplifier circuit comprises a trigger IC4, a triode Q3, diodes D11, D3, D4, D8, D9 and peripheral resistance-capacitance devices thereof, wherein,

the base of the triode Q1 is connected with a-15A power supply, the emitter is connected with the output end of the signal modulation module, the collector is connected with the anode of a diode D11, a pin 1 of a trigger IC4A is respectively connected with a ground resistor R14 and the cathode of a diode D11, the other end of a resistor R14 and a pin 2 of a trigger IC4A are connected with a-30V power supply, a pin 5 of a trigger IC4A is connected with a 5V power supply through a resistor R3, a pin 6 is respectively connected with one end of a resistor R6, the cathode of a diode D8 and a pin 3 of a trigger IC4B, a pin 4 of a trigger IC4B is respectively connected with one end of a resistor R9 and the cathode of a diode D9, the other end of a resistor R6 and the other end of an R9 are respectively connected with different pins of the driving module, the anode of a diode D8 is respectively connected with the anode of a diode D4, the other end of a resistor R6 and one end of a capacitor C10, the anode of a diode D9 is respectively connected with the anode of a resistor R874, the cathodes of the diodes D4 and D3 are connected with a mute pin, and the other ends of the capacitors C10 and C11 are connected with a-30V power supply.

The invention is further improved, the positive phase driving unit of the bass power amplifier circuit comprises a driving chip IC3, the negative phase driving unit comprises a driving chip IC6, the driving chip IC3 and the driving chip IC6 both adopt MP18021A chips, wherein the other end of the resistor R6 is respectively connected with a pin IL 6 of a pin 3 of the driving chip IC and a pin IH 5 of a pin 3 of the driving chip IC, and the other end of the resistor R9 is respectively connected with a pin IL 5 of a pin 3 of the driving chip IC and a pin IL 6 of a pin 3 of the driving chip IC 3.

The invention further improves, the switch amplifying unit comprises two switch tubes, wherein, the grid of the switch tube Q1 of the first switch amplifying unit is connected with pin 2 of the driving chip IC3, the drain is connected with 30V power supply and is grounded through a capacitor C1, the source is connected with the drain of the switch tube Q2 and the input end of the filter, the grid of the switch tube Q2 is connected with the anode of the diode D10 and one end of the resistor R14, the cathode of the diode D10 and the other end of the resistor R15 are connected with pin 8 of the driving chip IC3, and the source of the switch tube Q2 is connected with-30V power supply and is grounded through a capacitor C15.

The invention is further improved, the low pass filter of the high-pitch power amplifier circuit comprises an inductor L2 and a capacitor C41, wherein the input end of the inductor L1 is connected with the output end of the switch amplification module, the output end of the inductor L1 is connected with one end of the capacitor C41 and outputs high-pitch audio OUTT +, the other end of the capacitor C41 is grounded, a positive feedback pin FB1 is respectively connected with one end of the capacitors C40 and C141 which are connected in parallel and one end of the resistors R64 and R65 which are connected in parallel, the other end of the capacitors C40 and C141 which are connected in parallel is connected with the output end of the inductor L1, and the other ends of the resistors R64 and R65 which are.

Compared with the prior art, the invention has the beneficial effects that: compared with the common D-type power amplifier, the scheme of balanced audio signal feed-in and full-loop self-oscillation type D-type power amplifier can easily introduce large-loop audio negative feedback, greatly reduce the distortion degree, provide high-quality music playback capability and enable the sound to be clearer and more transparent.

Drawings

FIG. 1 is a block diagram of the present invention;

FIG. 2 is a schematic diagram of the circuit of the present invention;

FIG. 3 is a schematic diagram of a bass power amplifier circuit;

FIG. 4 is a schematic diagram of a high pitch power amplifier circuit;

FIG. 5 is a schematic diagram of a peripheral power supply circuit of the present invention;

fig. 6 is a schematic diagram of a peripheral speaker DSP board circuit of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples.

As shown in fig. 2 and fig. 5-6, the input audio signal of the present invention is processed by the DSP board and then output to the full-loop self-oscillation type D power amplifier circuit of the present invention, and the power circuit provides power for the whole speaker circuit, including the power amplifier circuit of this example.

As shown in fig. 1, the present embodiment includes a bass power amplifier circuit and a treble power amplifier circuit, which are independent of each other, and are respectively used for driving a tweeter and a woofer, wherein the bass power amplifier circuit and the tweeter power amplifier circuit are respectively provided with a signal modulation module, a trigger shaping module, a driving module, a switch amplification module and a low pass filter, wherein an output end of the signal modulation module is connected with an input end of the trigger shaping module, an output end of the trigger shaping module is connected with an input end of the driving module, an output end of the driving module is connected with an input end of the switch amplification module, an output end of the switch amplification module is connected with an input end of the low pass filter, an output end of the low pass filter is provided with a positive feedback pin and a negative feedback pin simultaneously serving as an output pin, the positive feedback pin and the negative feedback, forming a full loop feedback circuit.

As shown in fig. 3 and 4, the two power amplifier circuit channels of the present embodiment have basically similar principles, and the modules are designed independently and separately, and two different output stage topologies, namely a half-bridge type and a full-bridge type, are applied due to different power requirements. The present embodiment uses a relatively simple and intuitive treble power amplifier circuit for technical analysis.

As shown in fig. 4, the present embodiment adopts an LM311 high-speed comparator to re-invent the circuit, and utilizes the inherent phase shift characteristic of the LC filter outputted by the class D power amplifier circuit to introduce the LC filter from the final output terminal OUTT + into the inverting input terminal of the comparator for phase inversion at high frequency, so as to form a special phase-shifted oscillator from the large loop of the whole power amplifier circuit, thereby forming a set of novel full-loop self-oscillation class D amplifier circuit. The structure of the circuit is relatively simple, but the conception and the application are skillful, and the specific analysis is as follows:

the inductor L2 and the capacitor C41 at the output end form an LC low-pass filter, the oscillation frequency of the whole power amplifier circuit is mainly determined by the values of the two inductors and capacitors, the inductor L2 takes 22uH, the capacitor C41 takes 1uF, the upper limit cut-off frequency of the low-pass filter is calculated to be set to be 33.9kHz, the LC low-pass filter can generate phase lag offset close to 180 degrees near a 10 times cut-off frequency point (namely 340kHz), and the phase lag is generated by the limitation of the conversion rate and the bandwidth of the IC11 high-speed comparator LM311, and the conduction delays caused by other flip-flop shaping modules, driver modules and switch amplifier modules in the overall loop, also introduce phase lags, the phase of these lags adding up, the phase lag offset around the 10-fold cut-off frequency point of the low-pass filter will be equal to or exceed 180 deg., which is a prerequisite for high frequency self-oscillation of the whole circuit.

The high-precision RC high-pass filter consists of resistors R64 and R65, 464 omega resistors, C40 and C141, 10nF capacitors, the lower limit cut-off frequency of the high-precision RC high-pass filter is set to be 34.3kHz, and audio frequency lower than 20kHz in the whole working frequency band of an output end OUTT + of the LC low-pass filter is filtered; the high-frequency signal of about 340kHz set as described above can be filtered by the LC low-pass filter to obtain a residual sine wave, and then the residual sine wave is connected to the capacitor C42 from the positive feedback pin FB3 and fed back to the inverting input terminal of the high-speed comparator IC11, so that a slight over phase difference is brought to the high-frequency feedback path by the capacitor (but the phase lag brought to the reversed frequency point by the whole loop, particularly the LC filter, does not have obvious influence), and the high-frequency signal is shaped and accelerated to make the modulation oscillation working state of the high-speed comparator IC11 more ideal.

The whole power amplifier loop has a set 180-degree phase reversal at the IC12 trigger shaping module, if the conduction delay caused by the output LC low-pass filter and other circuits in the whole loop is superposed at a set certain higher frequency point, the sum of all phase shifts of phase lag is exactly equal to 180 degrees, the phase of the output end and the phase of the input end of the whole high-frequency conduction loop are the same at the frequency point, namely, the output end and the input end are in a positive feedback mode, the high-frequency alternating current loop of the LM311 high-speed comparator circuit forms a phase-shift oscillator to generate an oscillation square wave signal, and the mechanism is the whole generation mechanism of the high-frequency self-oscillation of the whole power amplifier circuit.

The actual oscillation frequency is reduced from the originally preset frequency of about 340kHz to about 230kHz, which is exactly because the slew rate and bandwidth of the LM311 high-speed comparator IC11 are not high enough, and the conduction delay is increased by the trigger shaping module, the driving module and the switch amplifying module in the loop, so that the superimposed phase lag of the whole loop is shifted to be reduced to the self-oscillation frequency point of 180 ° turnover. As long as the component parameters and the selection of the whole high-frequency conduction path are fixed, the actual self-oscillation frequency of the whole loop can be controlled and stabilized.

If there is no input signal, the non-inverting input terminal of the high-speed comparator IC11 is grounded, and the OUTT + output point is a standard square wave with a self-oscillation 50% duty cycle around 230 kHz. The input of the input end of the LM311 high-speed comparator IC11 is the comparative superposition of an audio signal and an overall loop feedback signal, the change of the audio signal can change the zero crossing point of the comparator, namely the reversed threshold value, further change the duty ratio of the oscillation square wave, ensure that the duty ratio completely follows the change of the audio signal, and the LM311 high-speed comparator IC11 outputs a PWM (pulse width modulation) signal modulated by the audio signal.

The PWM signal output by the pin 7 of the high-speed comparator IC11 is converted into a current direction output by the high-speed comparator through a BC807 triode Q14, then is subjected to accelerated shaping and phase inversion through an SN74LVC2G04 two-way high-speed Schmidt trigger IC12, is converted into a high-low end complementary symmetrical PWM driving signal, is further pushed to work in a working state close to an ideal switch through an IC10 high-speed high-performance half-bridge driver MP18021A, a Q9 and a Q12 two small patch type field effect transistors AON6280 are converted into high-voltage and high-current high-speed high-power PWM signals, and an amplified audio frequency is obtained after filtering through an output LC low-pass filter. The rated output power of the half-bridge type working mode of the power amplifier circuit can reach 50W/8 omega calculated from the power supply voltage.

In this example, the audio feedback loop has a predetermined 180 ° phase flip at the IC12 flip-flop shaping circuit, and in the audio range, the conduction delay caused by the output LC low pass filter and other circuits in the whole loop is small and has only a relatively weak phase shift, so the phase of the whole loop output is opposite to that of the input, i.e., in negative feedback mode. Because of the introduction of the negative feedback of the audio large loop, the output distortion degree can be reduced by one or even several orders of magnitude compared with the common class D power amplifier, so that the power amplifier circuit provides high-quality music playback capability, and the sound is clear and transparent and is restored at a higher degree.

As shown in fig. 3, the bass power amplifier circuit employs a full-bridge output stage topology structure due to a higher power requirement, so that one path of an inverting driving circuit is added to drive the other two AON6280 small patch fets Q4 and Q7, wherein the two paths of driving circuits of the bass power amplifier circuit and the treble power amplifier circuit have the same structure.

The output low-pass filter of the embodiment is changed into a common-mode inductance low-pass filter from an LC low-pass filter, the output LC low-pass filter and a high-frequency RC feedback path fed back to the input end of the comparator are correspondingly increased, and meanwhile, the parameters of elements are re-adapted to match the change of the topological structure of the output stage.

Similarly, the common-mode inductor L1 and the capacitors C7 and C22 at the output end of the present example form an LC common-mode low-pass filter, and a capacitor C18 is connected in parallel to two resistors (load current sampling resistor, which has negligible influence on filter parameters) of 0.03 Ω through R73 and R75 to form a differential filter. The oscillation frequency of the whole power amplifier circuit is mainly determined by the values of the 4 inductance capacitors, the inductance L2 takes the value of 11uH, the capacitors C7 and C22 take the value of 0.47uF, the capacitor C18 takes the value of 1uF, the upper limit cut-off frequency of the low-pass filter is set to be about 35kHz, and phase lag offset close to 180 degrees can be generated near a 10-time cut-off frequency point (namely about 350 kHz); similarly, because of the superposition of conduction delay caused by other trigger shaping modules, two sets of driving units and two sets of switch amplifying units in the whole bass power amplifier loop, the phase lag of the whole loop shifts to 180 degrees, the self-oscillation frequency point turned over is also reduced, and the actual self-oscillation frequency of the bass power amplifier circuit is reduced to about 220kHz from the originally preset about 350 kHz.

The differential output negative terminal OUTW-of the embodiment is also additionally provided with an audio negative feedback path, a complete balanced type large loop negative feedback is formed while the change of the topological structure of the output stage is matched, and the more specific principle structure and calculation analysis of other circuit modules of the low-pitch power amplifier are completely the same as those of the high-pitch part half-bridge type power amplifier and are not repeated any more.

The calculation of the power supply voltage shows that the bass power amplifier circuit of the embodiment adopts a full-bridge output mode, the rated output power can reach 400W/4 omega, and the miniaturized components and the power amplifier component complete machine design can stabilize the normal operation of mass production at the larger output power level, which shows that the optimization design of the split type full-loop self-oscillation type D class power amplifier circuit is very successful and has high product competitiveness.

In conclusion, the class-D power amplifier circuit of the active sound box of the present embodiment has the advantages of novel design, simplicity, high efficiency, and small size, and the core lies in ingeniously utilizing the phase shift characteristic of the LC output low-pass filter inherent in the class-D power amplifier circuit to build a scheme of a full-loop self-oscillation class-D amplifier. The independent split type of each unit circuit and the optimized design of the performance of the driving stage circuit can obtain excellent driving performance so as to reduce the switching loss of an output power tube; the more perfect protection logic ensures that the circuit works more reliably to give full play to the performance of the element, and the element and the power amplifier circuit assembly can be miniaturized as a whole; meanwhile, the balanced type audio signal feed-in and the introduction of the balanced type large loop negative feedback greatly reduce the distortion degree, provide high-quality music playback capability and enable the sound to be clearer and more transparent compared with the common D-type power amplifier.

The above-described embodiments are intended to be illustrative, and not restrictive, of the invention, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.