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CN-122026828-A - Overload protection method for audio power amplifier

CN122026828ACN 122026828 ACN122026828 ACN 122026828ACN-122026828-A

Abstract

The invention discloses an overload protection method for an audio power amplifier, and relates to the field of audio power amplifiers. The invention obtains the reference current which dynamically changes along with the signal by dividing the instantaneous output amplitude signal of the power amplifier by the preset overload threshold impedance, and compares the actual output current with the reference current in real time, so that the protection criterion is converted from a fixed current threshold value into a self-adaptive impedance threshold, thereby realizing the instant identification and disconnection of the low-impedance abnormal load and simultaneously being compatible with the normal output of the high-peak-factor audio signal.

Inventors

  • LUO PINGUI

Assignees

  • 成都宏屹科技有限公司

Dates

Publication Date
20260512
Application Date
20260130

Claims (14)

  1. 1. An overload protection method for an audio power amplifier, comprising the steps of: S1, generating a reference current which changes in real time along with output voltage according to a current instantaneous output amplitude signal of a power amplifier and preset overload threshold impedance; S2, detecting the current actual output current of the power amplifier; S3, comparing the actual output current with the reference current, and controlling the output of the power amplifier according to a comparison result; in the step S1, the reference current generation flow is specifically that the output voltage at the current moment is divided by the preset overload threshold impedance to obtain the reference current, namely: ; Wherein the said Representing a reference current, said Representing an output voltage, said Representing an overload threshold impedance.
  2. 2. The method of claim 1, wherein the output amplitude signal is an output voltage obtained by sampling an actual output voltage of the power amplifier.
  3. 3. The overload protection method of an audio power amplifier according to claim 1, wherein the output amplitude signal is obtained by sequentially compensating for delay of an audio input signal and amplifying the output amplitude signal according to a gain G of the power amplifier.
  4. 4. The method for protecting an overload of an audio power amplifier according to claim 3, wherein in S1, the reference current is generated by dividing an equivalent output amplitude value after delay compensation and gain G expansion by a preset overload threshold impedance to obtain the reference current, namely: ; Wherein the said Representing a reference current, said Representing a delay compensated audio input signal, said Representing the gain of a power amplifier, said Representing an overload threshold impedance.
  5. 5. A method of overload protection for an audio power amplifier according to claim 3, characterized in that the audio input signal is delay compensated in particular by means of an RC circuit or a delay line.
  6. 6. The method of claim 1, wherein the overload threshold impedance is a fixed value and is less than the rated load impedance of the power amplifier.
  7. 7. The overload protection method of an audio power amplifier according to claim 1, wherein in S3, a specific control decision flow for controlling the output of the power amplifier according to the comparison result is as follows: When the actual output current is larger than the reference current, judging that the load is lower than the overload threshold impedance and closing or limiting the output of the power amplifier; and when the actual output current is smaller than or equal to the reference current, judging that the load is higher than the overload threshold impedance, and keeping the normal output of the power amplifier.
  8. 8. An audio power amplifier overload protection circuit, the circuit being implemented on the basis of an audio power amplifier overload protection method as claimed in any one of claims 1 to 7, comprising: the power amplifier comprises an audio signal input end, a power amplifier output end and a load connection end; the input end of the reference current generation branch is coupled to the signal path of the power amplifier and is used for obtaining an instantaneous output amplitude sample, dividing the sample by a preset overload threshold impedance and generating a reference current which changes along with the sample in real time; The load current detection branch is connected in series between the power amplifier output end and the load and is used for detecting actual output current and outputting an actual current signal; the first input end of the comparator is connected with the output end of the reference current generation branch, and the second input end of the comparator is connected with the output end of the load current detection branch and is used for outputting an overload protection signal when the actual current signal is larger than the reference current; And the control end of the turn-off execution element is connected with the output end of the comparator, and the execution end of the turn-off execution element is connected in series with a power supply loop or a signal path of the power amplifier and is used for responding to the overload protection signal to turn off or limit the output of the power amplifier.
  9. 9. An audio power amplifier overload protection circuit as claimed in claim 8, wherein, The reference current generation branch is provided with: a first sampling input end connected with the power amplifier output end for obtaining output voltage sample, or The second sampling input end is connected with the audio signal input end, and outputs an equivalent output amplitude sample after sequentially passing through the delay compensation circuit and the gain G amplifying circuit, wherein the reference current generation branch circuit generates the reference current by adopting the sample provided by the first sampling input end or the second sampling input end.
  10. 10. The audio power amplifier overload protection circuit of claim 9, wherein said reference current generating branch takes output voltage samples through said first sampling input and follows Generating a reference current, wherein the Representing a reference current, said Representing an output voltage, said Representing an overload threshold impedance.
  11. 11. The overload protection circuit of claim 9, wherein the reference current generation branch obtains an equivalent output amplitude sample after delay compensation and gain G amplification through the second sampling input terminal, and follows Generating a reference current, wherein Representing a reference current, said Representing a delay compensated audio input signal, said Representing the gain of a power amplifier, said Representing an overload threshold impedance.
  12. 12. An audio power amplifier overload protection circuit as claimed in claim 11, wherein the delay compensation circuit is formed by an RC network or delay line.
  13. 13. The audio power amplifier overload protection circuit of claim 8, wherein the comparator is configured to: when the actual current signal is larger than the reference current, judging that the load is lower than overload threshold impedance and outputting an overload protection signal, so that the turn-off executing element turns off or limits the output of the power amplifier; when the actual current signal is smaller than or equal to the reference current, the load is judged to be higher than the overload threshold impedance, an overload protection signal is not sent out, and the normal output of the power amplifier is maintained.
  14. 14. A playback device, comprising: The audio power amplifier is used for driving the load to sound; An audio power amplifier overload protection circuit as claimed in claims 8-13, said protection circuit controlling the output of said audio power amplifier to shut down or limit the output of said audio power amplifier when the load is below an overload threshold impedance.

Description

Overload protection method for audio power amplifier Technical Field The invention relates to the field of audio power amplifiers, in particular to an overload protection method for an audio power amplifier. Background An audio signal refers to an electrical signal having a frequency in the range of 20 Hz-20 kHz, typically with a crest factor (peak to effective ratio) of 6-20 dB. Due to the high crest factor, the instantaneous amplitude of the audio signal is much lower than its peak value for most of the time, and the average power is only 1/4-1/100 of the peak power. An audio power amplifier (hereinafter referred to as "power amplifier") is used for amplifying the audio signal to drive a low-impedance load such as a speaker. The power amplifier must meet performance indexes such as distortion, frequency response, signal to noise ratio, and the like, and must also have high reliability and environmental adaptability. However, in the actual use process, the power amplifier output end often has abnormal working conditions of extremely low impedance and even near zero impedance due to load short circuit, line misconnection, speaker unit fault and other reasons. If the power amplifier continuously transmits power to an abnormal load, an output-stage power semiconductor device (hereinafter referred to as a power device) is subjected to overcurrent, overpower and overheat stress, so that secondary breakdown, wire bonding fusing or package thermal mechanical failure are caused, and finally the power amplifier is damaged. To avoid the above risk, the prior art generally adopts an "overcurrent threshold comparison" scheme as a load abnormality protection mechanism, in which a fixed current threshold Ith is set in an output loop, and when the detected current instantaneous value exceeds Ith, protection is triggered, and output is turned off or gain is reduced. To ensure no malfunction under rated load and peak audio signals, the current threshold must be higher than the current corresponding to the audio peak. Because the peak factor of the audio signal is large, the effective value current is far lower than the peak value, and when the load impedance is abnormally reduced, the instantaneous current is obviously higher than the rated value but is often lower than the set high threshold, so that the protection circuit cannot respond. Therefore, the power amplifier works in an overload but unprotected window area for a long time, the device continuously bears excessive thermal-electric stress, and the reliability is obviously reduced. In order to protect the power amplifier from being damaged, the conventional method is forced to improve the safety working area (SOA) allowance of the power device, enlarge the volume of the radiator and enhance the RMS current tolerance capability of the power line, so that the weight, the volume and the cost of the whole power amplifier are synchronously increased, and the hidden trouble of transient breakdown cannot be thoroughly eliminated. In addition, the fundamental disadvantage of the existing fixed current threshold scheme is that its protection reference is static and stiff and cannot accommodate dynamic changes in the audio signal. Therefore, in order to solve the above protection dead zone and the reliability, cost and volume problems caused by the protection dead zone, it is needed in the art to provide an alternative generation method of the reference current to replace the conventional fixed threshold, so as to realize more accurate and timely protection of the low-impedance load. Disclosure of Invention The invention provides an overload protection method of an audio power amplifier, which aims to solve the technical problems that when the existing audio power amplifier adopts a fixed current threshold as an overcurrent protection criterion, the effective value of output current of the existing audio power amplifier is far lower than a peak value due to high peak factor of an audio signal, so that a protection threshold must be set high, and an overload unprotected dead zone is formed when load impedance is abnormally reduced, so that a power device bears excessive thermal-electric stress for a long time and the reliability is reduced. The overload protection method for the audio power amplifier comprises the following steps: S1, generating a reference current which changes in real time along with the output voltage according to a current instantaneous output amplitude signal of a power amplifier and a preset overload threshold impedance; Specifically, the step abandons the traditional method of 'fixed current threshold', divides the current instantaneous output amplitude signal (output voltage or equivalent amplitude compensated by delay) of the power amplifier by the overload threshold impedance which is preset and lower than the rated load in real time to obtain an overload line reference current with constant slope along with signal fluctuation, so that the protectio