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CN-122026829-A - Overcurrent protection system and method for push-pull output circuit

CN122026829ACN 122026829 ACN122026829 ACN 122026829ACN-122026829-A

Abstract

The invention discloses an overcurrent protection system and method of a push-pull output circuit, wherein the system comprises an amplifier output stage circuit, an offset voltage generating circuit and an overcurrent protection circuit, the amplifier output stage circuit is provided with a transconductance linear ring, output pipes MP1 and MN1 and clamping pipes MP2 and MN2 respectively connected with the transconductance linear ring, the output pipes MP1 and MN1 IN series, the offset voltage generating circuit mirrors the current IN an offset generator through current sources IP1 and IN1, the overcurrent protection circuit adopts MOS pipes MP3, MP4, MN3 and MN4 of a diode connection method to form an offset branch, when an output node has a short circuit fault, the grid source voltage of the clamping pipe is adaptively changed, so that the maximum output current of the output pipe is reduced to be consistent with the maximum output current of the clamping pipe, a current limiting value is formed, and the output current is rapidly limited. The invention ensures the stability and reliability of the circuit under extreme working conditions, and obviously improves the safety and service life of the push-pull output circuit.

Inventors

  • LIU WEIZHONG
  • WANG LANGYUAN
  • CHEN XIANLIANG

Assignees

  • 共模半导体技术(苏州)有限公司

Dates

Publication Date
20260512
Application Date
20260413

Claims (9)

  1. 1. The overcurrent protection system of the push-pull output circuit is characterized by comprising an amplifier output stage circuit, a bias voltage generating circuit and an overcurrent protection circuit, wherein the amplifier output stage circuit is connected with an amplifier pre-stage circuit; The amplifier output stage circuit comprises a transconductance linear ring, MOS tubes MP1 and MN1 and clamping tubes MP2 and MN2 which are respectively connected with the MOS tubes MP1 and MN1 in series, wherein the input end of the transconductance linear ring is connected with the output end of the amplifier pre-stage circuit, the output end of the transconductance linear ring is respectively connected with the grid electrodes of the MOS tubes MP1 and MN1, the drain electrodes of the MOS tubes MP1 and MN1 are respectively connected with the source electrodes of the clamping tubes MP2 and MN2 in series, the source electrodes of the MOS tubes MP1 and MN1 are respectively connected with a power supply and a ground, the drain electrodes of the clamping tubes MP2 and MN2 are connected to form an output node Vout, and the grid electrodes of the clamping tubes MP4 and MN4 are respectively connected with the grid electrodes of the amplifier pre-stage circuit; The bias voltage generating circuit comprises a bias generator and current sources IP1 and IN1, wherein the current sources IP1 and IN1 mirror currents IN the bias generator, and the current sources IP1 and IN1 respectively output currents to MOS tubes MP3 and MP4 and MOS tubes MN3 and MN4; The overcurrent protection circuit comprises MOS tubes MN3, MN4, MP3 and MP4, wherein the MOS tubes MN3, MN4, MP3 and MP4 all adopt diode connection, the current source IP1 flows into the MOS tubes MP3 and MP4 to generate grid bias voltage of a clamp tube MP2, and the current source IN1 flows into the MOS tubes MN3 and MN4 to generate grid bias voltage of the clamp tube MN 2.
  2. 2. The overcurrent protection system of the push-pull output circuit according to claim 1, wherein the gate bias voltage of the clamp MP2 limits the maximum current of the branches of the MOS transistor MP1 and the clamp MP2, and the gate bias voltage of the clamp MN2 limits the maximum current of the branches of the MOS transistor MN1 and the clamp MN 2.
  3. 3. The overcurrent protection system of the push-pull output circuit according to claim 1, wherein in the overcurrent protection circuit, all of the MOS transistors MN3, MN4, MP3 and MP4 adopt diode connection, specifically; The source electrode of the MOS tube MP3 is connected with the source electrode of the MOS tube MP1, the drain electrode of the MOS tube MP3 is connected with the grid electrode and is connected with the source electrode of the MOS tube MP4, and the drain electrode of the MOS tube MP4 is connected with the grid electrode and is connected with the grid electrode of the clamp tube MP2 and the current source IP1; The source electrode of the MOS tube MN3 is connected with the source electrode of the MOS tube MN1, the drain electrode of the MOS tube MN3 is connected with the grid electrode and is connected to the source electrode of the MOS tube MN4, and the drain electrode of the MOS tube MN4 is connected with the grid electrode and is connected with the grid electrode of the clamping tube MN2 and the current source IN1.
  4. 4. The overcurrent protection system of the push-pull output circuit according to claim 1, wherein the overcurrent protection circuit further comprises a temperature sensor, and MOS transistors MN5 and MP5, wherein sources of the MOS transistors MN5 and MP5 are respectively connected with sources of the MOS transistors MP1 and MN1, drains of the MOS transistors MN5 and MP5 are respectively connected with gates of the MOS transistors MP3 and MN3, and the temperature sensor is used for monitoring temperatures of the MOS transistors MP1 and MN1 in real time.
  5. 5. The overcurrent protection system of the push-pull output circuit according to claim 4, wherein when the detected temperature exceeds a preset threshold, the temperature sensor controls the corresponding MOS transistors MP5, MN5 to be turned on, pulls up the gate voltage of the Gao Qianwei transistor MP2, and pulls down the gate voltage of the clamp transistor MN2, further reducing the current limit value.
  6. 6. A method of overcurrent protection for a push-pull output circuit, based on the system of any one of claims 1 to 5, comprising the steps of: S1, a current source IP1 and a current source IN1 IN a bias voltage generating circuit respectively establish voltage drops on an upper bias branch formed by MOS tubes MP3 and MP4 and a lower bias branch formed by MOS tubes MN3 and MN4, and constant grid bias voltage is provided for clamp tubes MP2 and MN 2; S2, under normal working conditions, the transconductance linear loop drives grids of the MOS tubes MP1 and MN1 according to input signals, and output currents are transmitted to an output node Vout through the clamp tubes MP2 and MN 2; S3, when the output node Vout has a low-level short circuit fault, the grid voltage of the MOS tube MP1 is low, the current flowing through the MOS tube MP1 is increased, the same current flows through the clamping tube MP2, the drain voltage of the MOS tube MP1, namely the source voltage of the clamping tube MP2 is increased, so that the grid source voltage of the clamping tube MP2 is increased, and when the maximum output current value of the MOS tube MP1 is reduced to be consistent with the maximum output current value of the clamping tube MP2, the current is not increased any more, so that a current limiting value is formed; S4, when the output node Vout has a high-level short circuit fault, the grid voltage of the MOS tube MN1 is high, the current flowing through the MOS tube MN1 is increased, the clamping tube MN2 flows the same current, the grid source voltage of the clamping tube MN2 is increased due to the fact that the drain voltage of the MOS tube MN1, namely the source voltage of the clamping tube MN2, is reduced, and when the maximum output current value of the MOS tube MN1 is reduced to be consistent with the maximum output current value of the clamping tube MN2, the current is not increased any more, so that a current limiting value is formed.
  7. 7. The overcurrent protection method of the push-pull output circuit according to claim 6, further comprising step S5: S5, temperature sensors monitor the temperatures of the MOS tubes MP1 and MN1 in real time, and when the detected temperatures exceed a preset threshold value, the temperature sensors output control signals to grids of the MOS tubes MP5 and MN 5; switching on the MOS tube MP5 to change the node potential of the upper bias branch, so that the grid voltage of the clamp tube MP2 is increased to reduce the current limit value of the MOS tube MP 1; the turn-on MOS transistor MN5 changes the node potential of the lower bias branch, so that the gate potential of the clamp transistor MN2 is reduced to reduce the current limit of the MOS transistor MN 1.
  8. 8. The overcurrent protection method of the push-pull output circuit according to claim 7, wherein in S5, the reducing the current limiting value of the MOS transistor MP1 includes: The MOS tube MP5 is conducted to pull up the source voltage of the MOS tube MP4, and as the current source IP1 is constant, the gate voltage of the MOS tube MP4 is increased due to the increase of the source voltage, and the gate voltage of the clamping tube MP2 is increased due to the increase of the gate voltage of the MOS tube MP4, so that the current limiting value of the MOS tube MP1 is further reduced.
  9. 9. The method for overcurrent protection of a push-pull output circuit according to claim 7, wherein in S5, the reducing the current limit of the MOS transistor MN1 includes: The MOS tube MN5 is conducted to pull down the source voltage of the MOS tube MN4, and because the current source IN1 is constant, the gate voltage of the MOS tube MN4 is reduced due to the reduction of the source voltage, and the reduction of the gate voltage of the MOS tube MN4 reduces the gate voltage of the clamping tube MN2, so that the current limiting value of the MOS tube MN1 is further reduced.

Description

Overcurrent protection system and method for push-pull output circuit Technical Field The present invention relates to the field of integrated circuit design, and more particularly, to a method for over-current protection of push-pull output circuits. Background Class AB power amplifiers are an important and classical form of application for push-pull output circuits. The output stage is used as a core architecture in an analog circuit and is widely used in key fields such as a power amplifier, an operational amplifier, a power management chip and the like. By setting lower quiescent current, the structure can effectively avoid crossover distortion and maintain higher energy conversion efficiency. However, when the driving is under heavy load or suffers from abnormal working conditions such as output short circuit, the output current may rise sharply, so that the power consumption of the power device is overlarge, the thermal breakdown risk is increased, and even the problems of aggravation of output signal distortion or deterioration of symmetry are caused. Therefore, the over-current protection circuit has become an important means for improving the reliability of the Class AB output stage. In the prior art, a common overcurrent protection scheme is generally to connect a small-resistance sampling resistor in series with an emitter of a power tube, judge whether overcurrent occurs by detecting the voltage drop on the resistor, trigger a protection action when the voltage drop exceeds a threshold value, and limit a driving signal to clamp the output current. For example, patent CN109067368B proposes a power operational amplifier with integrated current limiting protection, which is implemented by introducing a detection transistor and a negative feedback loop to clamp the gate voltage at the output stage, and patent CN222508785U adopts a negative feedback structure composed of a MOS transistor and a triode, which dynamically reduces the gate voltage of the MOS transistor to limit the current when the current flows and automatically recovers when the current falls back, thus forming steady-state current limiting. In addition, the paper 7.7A 3A 20MHz BiCMOS/DMOS Power Operational Amplifier published by ISSCC 2003 proposes a multi-loop feedback current limiting architecture, which realizes high-precision, adjustable and overshoot-free current limiting response through local gain boosting and gate clamping, while the IEEE journal paper A High Current Drive CMOS Output Stage utilizes a current mirror and adjustable bias to realize symmetrical current limiting, and introduces depletion-type MOSFETs to adapt to low-voltage-difference application scenarios. Although the above solution performs the overcurrent protection function to some extent, there are significant drawbacks. Firstly, most of the existing schemes rely on closed loop feedback control, inevitably introduce the problem of loop stability, and need to carry out complex frequency compensation design, thereby not only increasing the complexity of a circuit and the layout area, but also possibly causing oscillation or response delay due to insufficient phase margin or loop delay. Secondly, in order to realize high-precision current limiting, a part of schemes adopt a multi-stage feedback structure or precise components, so that the manufacturing cost and the testing difficulty are greatly improved. Furthermore, the introduction of elements such as a compensation capacitor can delay the protection response speed, and the protection action is possibly delayed in the event of rapid overcurrent or short circuit, so that the current peak cannot be restrained in time, and the protection effect is weakened. In addition, conventional approaches often interfere with the dynamics of the main amplification loop, affecting overall system stability and signal integrity. In view of the foregoing, there is a need for an over-current protection method that has a simple structure, quick response, no need of complex loop compensation, and little influence on the performance of the main circuit, so as to effectively solve the reliability problem of the Class AB output stage under abnormal working conditions. Disclosure of Invention Aiming at the problems of low response speed, complex circuit structure, large influence on the performance of a main loop and the like of a push-pull output circuit in overcurrent protection, the invention provides an overcurrent protection system and method of the push-pull output circuit. The invention skillfully integrates overcurrent and overtemperature protection functions, ensures the stability and reliability of the circuit under extreme working conditions, obviously improves the safety and service life of the push-pull output circuit, and is suitable for the field of electronic equipment with high reliability requirements. The technical scheme of the invention is as follows: In a first aspect, the present invention provides an overcurre