CN-121985447-A - Circuit for improving on-off performance of LED driving chip

CN121985447ACN 121985447 ACN121985447 ACN 121985447ACN-121985447-A

Abstract

The invention relates to the technical field of LED driving circuits and discloses a circuit for improving the on-off performance of an LED driving chip. The voltage transient detection module detects whether the voltage of an VOUT pin exceeds a first voltage threshold value through a first voltage stabilizing diode to establish a current bypass channel, the current limiting charging module controls the size of bypass current through a current limiting resistor, the protection triggering module enables the ISET voltage to rise by utilizing the bypass current to trigger the internal overcurrent protection of the chip to turn off the ultrahigh voltage MOSFET, the clamping control module clamps the ISET voltage in a safe range through a second voltage stabilizing diode, and the accumulation charging module realizes gradual charging of the electrolytic capacitor in a plurality of alternating current periods. The invention can effectively prevent the chip from thermal breakdown caused by high-voltage and high-current impact at the moment of starting up, and improve the reliability and the service life of the LED driving system.

Inventors

HUANG CHAOWU
XU YUANZHE
XIA ZHONGQI
HUANG YIPING

Assignees

芯源创科技(深圳)有限公司

Dates

Publication Date: 20260505
Application Date: 20260331

Claims (10)

1. A circuit for improving the power on/off performance of an LED driver chip, comprising: The voltage transient detection module is used for acquiring a starting transient input voltage signal and obtaining an output pin high-voltage state judgment result by adopting a voltage threshold detection method; The current-limiting charging module is used for obtaining the charging current of the controlled electrolytic capacitor by adopting a current bypass channel establishment and current-limiting control method based on the high-voltage state judgment result; The protection triggering module is used for obtaining the turn-off state of the ultrahigh voltage MOSFET by adopting an internal overcurrent protection triggering method of the chip based on the rising characteristic of ISET pin voltage; the clamping control module is used for obtaining the limitation of ISET pin voltage and the stable control of bypass current by adopting a second voltage-stabilizing diode clamping method based on the current bypass state after MOSFET is turned off; The accumulation charging module is used for obtaining a charging curve of gradually increasing the capacitor voltage to the LED on voltage by adopting an alternating current period accumulation effect based on the progressive charging process of the electrolytic capacitor; And the shutdown protection module is used for obtaining the safety confirmation of the shutdown process and the complete working period of the protection circuit based on the voltage and current characteristics of the system shutdown process by adopting an energy release analysis method.
2. The circuit for improving the on-off performance of an LED driver chip of claim 1, wherein said voltage transient detection module comprises: Determining a first voltage threshold based on the safety operating region characteristics of the LED driving chip and the operating voltage range of the LED string lights; Comparing the voltage of the VOUT pin monitored in real time with a first voltage threshold by adopting a voltage comparison method to obtain a high-voltage state judgment signal; The first voltage threshold is realized through a first voltage stabilizing diode, the cathode of the first voltage stabilizing diode is connected to the VOUT pin, the anode of the first voltage stabilizing diode is connected to the ISET pin through a current limiting resistor, and when the VOUT voltage exceeds the first voltage threshold, the first voltage stabilizing diode is conducted, and a current bypass channel is established.
3. The circuit for improving the on-off performance of an LED driver chip of claim 2, wherein said voltage transient detection module further comprises: based on the time sequence characteristic of the high-voltage state judging signal, analyzing the time point and the frequency of protection triggering in the starting process; In an alternating current mains supply LED system, an input voltage shows periodic fluctuation, when the voltage rises to exceed a first voltage threshold value, a first voltage stabilizing diode is conducted, a protection circuit is started, when the voltage drops below the first voltage threshold value, the first voltage stabilizing diode is cut off, the protection circuit is stopped, and the protection circuit works near a voltage peak value of each period.
4. The circuit for improving the on-off performance of an LED driver chip according to claim 2, wherein the current limiting charging module comprises: establishing a current bypass channel from the VOUT pin to the ISET pin based on the turn-on characteristics of the first zener diode; When the first zener diode is conducted, a new current path is formed between VOUT and ISET, current flows to the anode through the cathode of the first zener diode, flows to one end of the current limiting resistor from the anode, flows to the other end through the current limiting resistor, the other end of the current limiting resistor is connected to the ISET pin, current flows to the ground from the ISET pin through the external setting resistor, and the new path bypasses the ultra-high voltage MOSFET inside the chip.
5. The circuit for improving the on-off performance of an LED driver chip of claim 4, wherein said current limiting charging module further comprises: Determining a current limiting parameter of the bypass channel based on the relation between the resistance value of the current limiting resistor and the current flowing through the bypass channel; The functional targets of the current limiting resistor include limiting the size of bypass current to prevent overload of the first zener diode and the current limiting resistor, generating enough voltage drop to enable ISET voltage to rise to a threshold value for triggering chip protection, and realizing effective current limiting of all charging currents of the load electrolytic capacitor after the chip protection is triggered; When the ISET voltage exceeds a preset current control threshold, the control logic in the chip determines an overcurrent state, and the MOSFET is immediately turned off for protection.
6. The circuit for improving the on-off performance of an LED driver chip according to claim 1, wherein the protection triggering module comprises: Calculating a real-time voltage value of an ISET pin based on a voltage drop relation between the bypass current and the current limiting resistor; When the bypass channel is established, bypass current is injected into an ISET node, the voltage of the ISET is changed, and the voltage drop relationship from VOUT to ISET through the first voltage-stabilizing diode is that the voltage of VOUT minus the breakdown voltage of the first voltage-stabilizing diode is equal to the voltage of the ISET plus the voltage drop of the current-limiting resistor, and the voltage drop of the bypass current generated by the current-limiting resistor greatly increases the voltage of the ISET.
7. The circuit for improving the power on/off performance of an LED driver chip of claim 6, wherein said protection triggering module further comprises: Comparing the ISET pin voltage with a chip internal current control threshold value by adopting a voltage comparison method to generate an overcurrent judgment signal; The current control circuit integrated in the driving chip comprises a voltage comparator, the ISET pin voltage is compared with an internal reference voltage, when the ISET pin voltage is higher than the reference voltage, the comparator outputs a high level to indicate that the output current exceeds a set value or an abnormality occurs, and the control logic immediately reduces the conduction degree of the MOSFET or completely turns off the MOSFET to realize overcurrent protection.
8. The circuit for improving the power on/off performance of an LED driver chip of claim 7, wherein said protection triggering module further comprises: based on the overcurrent determination signal, a control logic driving method is adopted to output a MOSFET grid turn-off control signal; the control logic unit in the chip receives the overcurrent judging signal output by the comparator, generates a drive signal of the MOSFET grid according to the overcurrent judging signal, when the overcurrent judging signal is received, the control logic immediately enters a protection mode, outputs a turn-off signal to the grid drive circuit of the MOSFET, the drive circuit pulls down the grid voltage to force the MOSFET to turn off, the current between the drain electrode and the source electrode of the MOSFET is blocked after the MOSFET is turned off, and the total power consumption of the chip is greatly reduced.
9. The circuit for improving the on-off performance of an LED driver chip of claim 1, wherein said clamp control module comprises: determining a second voltage threshold based on the withstand voltage limit of the ISET pin and the clamping characteristic of the second zener diode; The setting of the second voltage threshold is required to be lower than the maximum withstand voltage of ISET and higher than the current control threshold of the chip, so that the protection function is not influenced; The second voltage threshold is realized through a second zener diode, the cathode of the second zener diode is connected to the ISET pin, the anode of the second zener diode is connected to the ground, and when the ISET voltage rises to the breakdown voltage of the second zener diode, the second zener diode is conducted to clamp the ISET voltage at the breakdown voltage value, so that the continuous rising is prevented.
10. The circuit for improving the on-off performance of an LED driver chip of claim 1, wherein said accumulating charging module comprises: Based on the capacitance charging characteristics in a single alternating current period, a calculation model of capacitance voltage increment is established; During the operation of the protection circuit, the electrolytic capacitor is charged by limited current, when the voltage exceeds a first voltage threshold value, the first voltage stabilizing diode is conducted, the protection circuit works, the charging current flows through the bypass channel and is limited by the current limiting resistor, and the basic relationship of capacitor charging is that the change amount of the voltage at two ends of the capacitor is equal to the charging charge amount divided by the capacitance value of the capacitor, and the charging charge amount is equal to the charging current multiplied by the charging time; and calculating a time sequence change curve of the capacitor voltage in a plurality of alternating current periods by adopting a recursive accumulation method, wherein the capacitor voltage rises in a step shape, and the capacitor voltage steadily rises to the LED conduction voltage through gradual charging of a plurality of periods.

Description

Circuit for improving on-off performance of LED driving chip Technical Field The invention relates to the technical field of LED driving circuits, in particular to a circuit for improving the on-off performance of an LED driving chip. Background In an LED lighting system, a linear LED driving chip is widely applied to the fields of commercial lighting and household lighting due to the advantages of simple structure, low cost, no electromagnetic interference and the like. A typical linear LED driving scheme adopts alternating current commercial power to directly drive an LED lamp string after being rectified by a rectifier bridge, and constant current control is realized through an ultrahigh voltage MOSFET inside a driving chip. The scheme has the characteristic of high power factor, meets the energy efficiency requirement of a lighting system, and plays an important role in the market. However, linear LED driver chips face severe reliability challenges at power-on instants. When the system is powered on, the initial voltage of the electrolytic capacitor connected in parallel with the LED is zero, and the peak value of the rectified input voltage can reach 311V. In the initial stage that the LED is not conducted yet, the electrolytic capacitor is charged through the ultra-high voltage MOSFET inside the driving chip, and the charging current can reach 2A or even higher. At this time, the MOSFET is simultaneously subjected to high voltage and high current, the instantaneous power consumption exceeds 600W, and the safe operating area of the microchip is far limited. This high voltage, high current surge causes the MOSFET junction temperature to rise sharply, exceeding the maximum junction temperature limit within a few milliseconds, causing thermal breakdown failure. Under the application scene of frequent switching of the intelligent lighting system, the driving chip fails after hundreds of switching cycles, the failure rate is up to 15%, and the reliability and the user satisfaction of the lighting system are seriously affected. In the prior art, the method for solving the problem mainly comprises two approaches of chip internal improvement and external current limiting. The internal chip improvement scheme turns off the MOSFET when overcurrent or overtemperature is detected by adding a complex protection circuit and control logic, but the scheme increases the complexity and cost of chip design, and the response speed is limited by the delay of the detection circuit. The external current limiting scheme limits the charging current through the series connection of large-value resistors, but can lead to increased power consumption and reduced efficiency during normal operation. Therefore, a protection scheme which is simple and reliable, low in cost and does not affect normal working performance is needed, and the technical problem of thermal breakdown at the moment of starting up the linear LED driving chip is solved. Disclosure of Invention The invention provides a circuit for improving the on-off performance of an LED driving chip, which solves the technical problems that the linear LED driving chip in the related art is in thermal breakdown failure of an ultrahigh voltage MOSFET caused by high-voltage and high-current impact at the moment of starting up, and the existing protection scheme has low response speed and high cost and influences the normal working performance. The invention provides a circuit for improving the on-off performance of an LED driving chip, which comprises: The voltage transient detection module is used for acquiring a starting transient input voltage signal and obtaining an output pin high-voltage state judgment result by adopting a voltage threshold detection method; The current-limiting charging module is used for obtaining the charging current of the controlled electrolytic capacitor by adopting a current bypass channel establishment and current-limiting control method based on the high-voltage state judgment result; The protection triggering module is used for obtaining the turn-off state of the ultrahigh voltage MOSFET by adopting an internal overcurrent protection triggering method of the chip based on the rising characteristic of ISET pin voltage; the clamping control module is used for obtaining the limitation of ISET pin voltage and the stable control of bypass current by adopting a second voltage-stabilizing diode clamping method based on the current bypass state after MOSFET is turned off; The accumulation charging module is used for obtaining a charging curve of gradually increasing the capacitor voltage to the LED on voltage by adopting an alternating current period accumulation effect based on the progressive charging process of the electrolytic capacitor; And the shutdown protection module is used for obtaining the safety confirmation of the shutdown process and the complete working period of the protection circuit based on the voltage and current characteristics of th