CN114885465B

CN114885465B - LED fault state detection and protection circuit

Info

Publication number: CN114885465B
Application number: CN202210806999.3A
Authority: CN
Inventors: 王琦桀; 刘彬
Original assignee: Shanghai Xinlong Semiconductor Technology Co ltd Nanjing Branch
Current assignee: Shanghai Xinlong Semiconductor Technology Co ltd Nanjing Branch
Priority date: 2022-07-11
Filing date: 2022-07-11
Publication date: 2022-09-27
Anticipated expiration: 2042-07-11
Also published as: CN114885465A

Abstract

The invention discloses an LED fault state detection and protection circuit, wherein a load LED lamp group is formed by connecting a plurality of LEDs in series and parallel, a power supply chip detects the voltage at two ends of the load LED lamp group through a VOUT pin, a first load state detection unit in the power supply chip circuit realizes the function of turning off the power supply chip when the load LED lamp group is short-circuited by a single or a plurality of load LEDs, a second load state detection unit, a load initial state detection unit and a load current reduction unit realize the function of dynamically reducing the output current of the power supply chip when the load LED lamp group is open-circuited by a single LED or a plurality of LEDs, and a fault alarm circuit transmits a high-level signal to monitoring equipment when the load LED lamp group is open-short-circuited by a power supply chip VS pin. The invention realizes the detection and protection of the fault state of the LED, so that maintenance personnel can maintain the LED in time.

Description

LED fault state detection and protection circuit

Technical Field

The invention relates to the technical field of application of LED lamp bank illumination, in particular to an LED fault state detection and protection circuit.

Background

In the application of the BUCK constant current power supply chip to the illumination of the LED lamp bank, the total current of the LED lamp bank can be kept unchanged by the conventional BUCK constant current power supply chip, because the LED lamp bank is usually formed by connecting multiple LEDs in series or in parallel, when the LED lamp bank has a fault state that one or more LEDs are short-circuited, the LED(s) flow through a branch with short circuit (the branch with the short circuit also has normal LEDs, namely the branch is not completely short-circuited) or the branch without the short circuit, the temperature of the LED is easily overhigh when the LED flows through the large current, and the LED can be damaged due to overhigh temperature under severe conditions.

Disclosure of Invention

The invention aims to provide an LED fault state detection and protection circuit which can detect a fault in time and provide protection when an LED lamp bank has a fault state that a single or a plurality of LEDs are open or short-circuited, so that the damage of the remaining normal LEDs due to overhigh temperature when large current passes through the LEDs before maintenance personnel do not maintain the LEDs is avoided.

In order to achieve the technical purpose, the invention provides an LED fault state detection and protection circuit, which comprises a load LED lamp set and a power chip, wherein the load LED lamp set is formed by connecting a plurality of LEDs in series and in parallel, the load LED lamp set has an incomplete open short circuit fault, and the incomplete open short circuit fault is a single or a plurality of load LEDs open short circuit fault, wherein: the power chip detects the voltage at two ends of the load LED lamp bank through a VOUT pin, and comprises: the load fault detection device comprises a first load state detection unit, a second load state detection unit, a fault alarm circuit, a load initial state detection unit and a load current reduction unit; the first load state detection unit realizes the function of turning off the power supply chip when the load LED lamp group is short-circuited by one or more load LEDs, the second load state detection unit, the load initial state detection unit and the load current reduction unit realize the function of dynamically reducing the output current of the power supply chip when the load LED lamp group is open-circuited by one or more LEDs, the fault alarm circuit transmits a high level to a VS pin of the power supply chip when the load LED lamp group is open-short-circuited, and an amplitude VCC signal of the high level of the VS pin is transmitted to the monitoring equipment so as to send the fault state to the monitoring equipment; the power supply chip comprises a power supply chip, a working voltage VDD and a power supply voltage control unit, wherein the power supply voltage VCC of an internal power supply unit of the power supply chip is obtained from VOUT, the high level amplitude of the power supply voltage VCC is smaller than VOUT, the low level is 0V, the working voltage VDD of the internal power supply unit of the power supply chip is obtained from VIN and VOUT, the high level amplitude of the working voltage VDD is between VIN and VOUT, and the low level is 0V; the first load state detection unit avoids more serious consequences by switching off a power chip when the load LED lamp group is in an incomplete short-circuit state, the second load state detection unit detects output voltage VOUT in real time so as to realize the function of monitoring the voltage of the load LED lamp group, the fault alarm circuit sends a fault state to monitoring equipment when the load LED lamp group is in an open short-circuit fault, the load initial state detection unit stores the maximum VOUT1 of the output voltage VOUT at the power-on initial stage of the power chip, and the load current reduction unit reduces the output current of the power chip when the voltage at two ends of LEDs of the remaining branches rises to be more than or equal to a set value, so that the voltage at two ends of the LEDs of the remaining branches gradually falls to be less than the set value.

The invention provides an LED fault state detection and protection circuit, wherein a power supply chip of the LED fault state detection and protection circuit detects the load state of an LED lamp group, when the LED lamp group has a fault state that a single LED or a plurality of LEDs are in open short circuit, the output current of the power supply chip can be dynamically reduced, namely the total current flowing through the LED lamp group is reduced, so that the current flowing through an LED which is not in an open circuit branch circuit is reduced, or the power supply chip is switched off, and the damage of the remaining normal LEDs due to overhigh temperature when passing large current before the maintenance personnel does not maintain the LED lamp group is avoided. Meanwhile, the power supply chip disclosed by the invention can be connected with the monitoring equipment, and when the load LED lamp group has an open short circuit fault, the monitoring equipment can continuously send the fault state signal to maintenance personnel so that the maintenance personnel can maintain the load LED lamp group in time.

As a further improvement, the load LED lamp set is connected in series with a resistor RCS, and when the load LED lamp set is completely short-circuited, the power chip outputs current constantly through the resistor RCS, so as to avoid the power chip from being damaged by a large current during short circuit.

As a further improvement, the VS pin is connected to the monitoring device, and when the VS pin is at a high level, the monitoring device latches the high-level state memory.

As a further improvement, the first load state detection unit compares the voltage VOUT of the load LED lamp set with a control voltage VD, so as to control the main power tube driving control unit and turn off the main power tube by the control voltage VD when the load LED lamp set is not completely short-circuited.

As a further improvement, VOUT ≠ 0V when the load LED lamp set is not completely shorted, and VOUT ≠ 0V when the load LED lamp set is completely shorted.

The power chip in the detection and protection circuit provided by the invention solves the problem that when a single or a plurality of LEDs are turned on for a short time in the process that the BUCK power chip supplies power to the load LED lamp group, the LEDs of the rest branches or the LEDs of the short-circuit branches are damaged due to higher temperature rise caused by the fact that large current flows through the LEDs.

Drawings

FIG. 1 is a schematic diagram of a power chip application circuit;

FIG. 2 is a diagram of an internal circuit of the power chip;

FIG. 3 is a first timing diagram according to the present invention;

FIG. 4 is a second timing diagram according to the present invention.

Reference numerals: the LED monitoring system comprises a power supply chip 1, a first load state detection unit STAGE1, a second load state detection unit STAGE2, a fault alarm circuit STAGE3, a load initial state detection unit STAGE4, a load current reduction unit STAGE5, a load LED lamp group 2, monitoring equipment 3, a power supply 4, a power supply chip input end capacitor CIN, a power supply chip output end capacitor COUT, a freewheeling diode D10 and an inductor L1.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

As shown in fig. 1 and fig. 2, the invention provides an LED fault status detection and protection circuit, which includes a load LED lamp set and a power chip, wherein the load LED lamp set is formed by connecting a plurality of LEDs in series and in parallel, the load LED lamp set has an incomplete open/short circuit fault, and the incomplete open/short circuit fault is an open/short circuit fault of a single or a plurality of load LEDs, wherein: the power chip detects the voltage at two ends of the load LED lamp bank through a VOUT pin, and comprises: a first load state detection unit STAGE1, a second load state detection unit STAGE2, a fault alarm circuit STAGE3, a load initial state detection unit STAGE4 and a load current reduction unit STAGE 5; the first load state detection unit STAGE1 is configured to turn off the power chip when the load LED lamp group is short-circuited by one or more load LEDs, the second load state detection unit STAGE2, the load initial state detection unit STAGE4, and the load current reduction unit STAGE5 are configured to dynamically reduce the output current of the power chip when the load LED lamp group is open-circuited by one or more LEDs, the fault alarm circuit STAGE3 transmits a high level to a VS pin of the power chip when the load LED lamp group is open-short-circuited, and an amplitude VCC signal of the high level of the VS pin is transmitted to the monitoring device to transmit the fault state to the monitoring device; the power supply chip comprises a power supply chip, a working voltage VDD and a power supply voltage control unit, wherein the power supply voltage VCC of an internal power supply unit of the power supply chip is obtained from VOUT, the high level amplitude of the power supply voltage VCC is smaller than VOUT, the low level is 0V, the working voltage VDD of the internal power supply unit of the power supply chip is obtained from VIN and VOUT, the high level amplitude of the working voltage VDD is between VIN and VOUT, and the low level is 0V; the first load state detection unit STAGE1 avoids a more serious consequence by turning off a power supply chip when the load LED lamp group is in an incomplete short-circuit state, the second load state detection unit STAGE2 detects output voltage VOUT in real time, so as to realize a function of monitoring the voltage of the load LED lamp group, the fault alarm circuit STAGE3 sends a fault state to monitoring equipment when the load LED lamp group is in an open-short-circuit fault, the load initial state detection unit STAGE4 stores a maximum value VOUT1 of the output voltage VOUT at the power-on initial STAGE of the power supply chip, and the load current reduction unit STAGE5 reduces the output current of the power supply chip when the voltage at the two ends of the LEDs of the remaining branches rises to be greater than or equal to a set value, so that the voltage at the two ends of the LEDs of the remaining branches gradually falls back to be less than the set value.

As a further improvement, the first load state detection unit STAGE1 compares the voltage VOUT of the load LED lamp set with the control voltage VD, so as to control the main power tube driving control unit and turn off the main power tube by the control voltage VD when the load LED lamp set is not completely short-circuited.

As shown in fig. 1, the present invention provides an LED fault status detection and protection circuit, which includes a power chip 1, a load LED lamp group 2, a monitoring device 3, a power supply 4, a resistor RCS, a power chip input end capacitor CIN, a power chip output end capacitor COUT, a freewheeling diode D10, an inductor L1, and the like. The power supply chip in the detection and protection circuit provided by the invention solves the problem that when a single or a plurality of LEDs are turned on for a short time in the process that the BUCK power supply chip supplies power to the load LED lamp group, the LEDs of the rest branches or the LEDs of the short-circuit branches are damaged due to high temperature rise caused by large current flowing through the LEDs.

Fig. 2 is a circuit diagram of the power chip according to the present invention. The power supply chip is applied to a scheme that a BUCK (voltage reduction) power supply topology supplies power to a load LED lamp bank. The load LED lamp group is formed by connecting a plurality of LEDs in series and in parallel. The power supply chip detects the voltages at two ends of the load LED lamp group through the VOUT pin, when the load LED lamp group is opened by a single LED or a plurality of LEDs, and before a maintenance worker maintains the load LED lamp group, the power supply chip can dynamically reduce the output current of the power supply chip (namely the total current flowing through the LED lamp group so as to reduce the current flowing through the LED of the branch circuit which is not opened) so as to avoid the damage of the LED caused by higher temperature rise due to the fact that the LEDs of the rest branch circuits pass through large current.

When the load LED lamp group is not completely short-circuited (VOUT is not equal to 0V), namely when the load LED lamp group is short-circuited by a single LED or a plurality of LEDs, before a maintenance worker does not maintain the load LED lamp group, the power supply chip can avoid the damage of the short-circuit branch circuit caused by high temperature rise of the rest LEDs on the short-circuit branch circuit due to the large current by switching off the power supply chip.

When the load LED lamp group is in a complete short circuit (VOUT is 0V), the power supply chip can output current constantly through the resistor RCS, and the constant output current IOUT is VCS/RCS, so that the power supply chip is prevented from being damaged by large current in the short circuit.

When the load LED lamp group has an open-short circuit fault, the VS pin of the power supply chip is at a high level, and the amplitude of the high level is VCC-0.7V. The power supply chip VS pin can be connected with the monitoring equipment, when the VS pin is at a high level, the monitoring equipment can memorize and latch the high level state, even if the power supply chip is turned off, the fault state of the load LED lamp group on the monitoring equipment can exist all the time, the monitoring equipment can continuously send the fault state signal to maintenance personnel, and the maintenance personnel reset the fault state on the monitoring equipment until the maintenance personnel maintain the load LED lamp group.

The power supply chip internally comprises: the load current reduction circuit comprises a first load state detection unit (STAGE1), a second load state detection unit (STAGE2), a fault alarm circuit (STAGE3), a load initial state detection unit (STAGE4) and a load current reduction unit (STAGE 5). And the STAGE1 part realizes the function of turning off the power supply chip when the load LED lamp group has a short circuit of single or multiple load LEDs. The STAGE2 part, the STAGE4 part and the STAGE5 part realize the function of dynamically reducing the output current of the power supply chip when a single LED or a plurality of LEDs of the load LED lamp group are in open circuit. And in the STAGE3, when the load LED lamp group has an open short circuit fault, the VS pin is at a high level, the amplitude of the high level VCC is high, and a high-level signal is transmitted to the monitoring equipment. The internal power supply unit VCC takes power from VOUT, the high level amplitude of VCC is less than VOUT, and the low level is 0V. The internal power supply unit VDD is used for getting power from VIN and VOUT, the amplitude of the high level of VDD is between VIN and VOUT, and the low level of VDD is 0V.

STAGE1 part:

the part is a first load state detection unit, when the load LED lamp group is not in a complete short circuit state (VOUT is not equal to 0V) in the working process of the load LED lamp group, a single load LED or a plurality of load LED short circuits occur, and more serious consequences are avoided by turning off a power supply chip.

The voltage signal V5 is connected to the emitter of the transistor Q1 through the voltage follower E1 and the diode D1, and the base of the transistor Q1 is connected to the voltage VOUT across the load LED. The collector of the triode is grounded through a resistor R1, and a voltage signal VC is generated on a resistor R1. E2 is powered by an internal power supply unit VCC.

When the load LED lamp group is not completely short-circuited (VOUT is not equal to 0V), namely when the load LED lamp group is short-circuited by a single LED or a plurality of LEDs, the voltage VOUT of the load LED is reduced by more than or equal to 3V (the LEDs in the invention patent are all conventional white LEDs, the conduction voltage drop of the single white LED is generally considered to be about 3V, so that the VOUT is reduced by more than or equal to 3V when the load LED is short-circuited), at the moment, the triode Q1 is conducted, and when VC is at a high level and the high level amplitude is V5. When VC is at high level and the amplitude of the high level is V5 (the amplitude of the V5 voltage is greater than or equal to 3V), the transistor Q2 is turned on, the VD voltage signal on the resistor R3 is at high level, and the amplitude of the high level is VDD. When the VD voltage is at a high level, the VD voltage controls the main power tube driving control unit through a diode D2, so that the main power tube is turned off.

When the load LED is not short-circuited, the voltage VOUT of the load LED is greater than or equal to the voltage signal V5, the triode Q1 is turned off, and VC is at a low level of 0V. When the VC voltage is low level 0V, the triode Q2 is turned off, the VD voltage on the resistor R3 is also low level 0V, the VD voltage signal can not pass through the diode D2, namely the VD voltage signal does not influence the working state of the main power tube.

E1 is powered by the internal power supply unit VDD.

STAGE2 part:

the partial circuit is a second load state detection unit which detects the output voltage VOUT in real time, so that the function of monitoring the voltage of the load LED is realized.

The gate of the Mos transistor Q3 is connected with a switching signal VA, the high level amplitude of VA is VOUT, and the low level is 0V. The power supply chip is applied to the BUCK topology, so that the SW high level amplitude is VIN and the SW low level is 0V. The switching signal VA and the voltage signal state of the chip SW are the same (the VA and the SW are in a high level state or a low level state at the same time), namely the switching state of the mos transistor Q3 is ensured to be opposite to the switching state of the main power transistor (when the Q3 is switched on, the main power transistor is switched off, and when the Q3 is switched off, the main power transistor is switched on). The drain of the Mos tube Q3 is connected with a pin VOUT of the chip, the VOUT voltage at the power-on initial stage of the power chip charges the capacitor C1 through a body diode of the Mos tube Q3 and the resistor R4, and when the voltage V1 at the two ends of the C1 rises to VGSth, the Mos tube Q3 enters a switch working state. When the mos tube Q3 is conducted, the VOUT voltage charges a capacitor C1 through a resistor R4, proper values of R4 and C1 are set, and the voltage V1 at the two ends of the C1 is guaranteed to be filled to the maximum VOUTmax of the VOUT voltage in a short time. The voltage signal of V1 passes through the voltage follower E2 to output the voltage signal V2, i.e., the voltage of V2 is the maximum value VOUTmax of VOUT voltage. The voltage signal of V2 outputs a voltage signal V3 after passing through an in-phase proportional operational amplifier E3, wherein the voltage of V3 is calculated as follows:

V3＝V2＊(1+R6/R5)＝VOUTmax＊(1+R6/R5)

when the power supply is powered on again, the VIN voltage starts to rise, the VIN voltage is divided into a V0 voltage through the resistors R21 and R22, before the V0 voltage is lower than the V1 voltage, the output voltage VB of the comparator E2 is at a high level, the amplitude of the high level is VCC, the mos tube Q16 is conducted, and the voltage at the two ends of the capacitor C5 is instantly discharged to 0V.

E2 is powered by the internal power supply unit VCC, E3, E4 are powered by the internal power supply unit VDD.

STAGE3 part:

the partial circuit is a fault alarm circuit, and when the load LED lamp group has an open-short circuit fault, the partial circuit sends a fault state to the monitoring equipment.

When the voltage V8 is at a high level, the amplitude of the high level is VCC OR the VD voltage is at a high level, and the amplitude of the high level is VCC, the OR gate OR1 outputs the voltage VS1 at a high level, and the amplitude of the high level is VCC. When the voltage of VS1 is at high level, the inverter NOT2 outputs low level 0V to turn on the mos transistor Q5, the voltage VS1 at both ends of the capacitor C2 is at high level, and the amplitude of the high level is VCC.

VOUT voltage detection timing unit passes through chip VOUT pin detection load LED banks voltage, begins the timing when load LED banks both ends voltage VOUT is 0V, after timing a period of time, load LED banks both ends voltage still is VOUT is 0V, considers load LED banks complete short circuit so, and VOUT voltage detection timing unit output voltage VS2 is the high level, and the high level amplitude is the VCC.

When the load LED lamp group has an open short circuit fault, the voltage of VS1 or VS2 is at a high level, the amplitude of the high level is VCC, and the voltage of VS1 or VS2 is transmitted to the VS pin of the chip through the diode D3 or D4. When the load LED lamp group does not have an open short circuit fault, the voltages of VS1 and VS2 are low level 0V.

The NOT1, NOT2, NOT3 and OR1 are all powered by the internal power supply unit VCC.

STAGE4 part:

the partial circuit is a load initial state detection unit which stores the maximum value VOUT1 of the output voltage VOUT at the power-on initial stage of the power chip.

The gate of the Mos transistor Q10 is connected with the drain of the Mos transistor Q9 through a resistor R10, the source of the Mos transistor Q10 is connected with a pin of a chip VOUT, the output voltage VOUT of the power chip at the initial power-on stage gradually rises, because V4 is low-level 0V, the triode Q6 at the initial power-on stage is turned on, the resistor R8 is high-level, the high-level amplitude VOUT is higher, because VCC amplitude is smaller than VOUT amplitude, the triode Q7 is turned off at this time, and the voltage VE of the resistor R9 is low-level 0V. VE voltage passes through inverter NOT3 and outputs high level, high level amplitude VCC, and mos pipe Q9 switches on this moment, and mos pipe Q9 switches on and makes mos pipe Q10 switch on, and VOUT voltage signal diode D5 and resistance R12 charge electric capacity C4, set up suitable R4 and C4 value, guarantee that C4 both ends voltage V4 fills to VOUT 1-0.7V in short time, namely V4 equals VOUT 1-0.7V.

When the voltage V4 at the two ends of the C4 rises to VOUT 1-0.7V, the transistor Q6 is turned off, the resistor R8 is at a low level of 0V, the transistor Q7 is turned on, the voltage VE on the resistor R9 is at a high level, and the amplitude VCC of the high level is obtained. When VE is high level, the capacitor C3, the inverter NOT3, the mos transistor Q8 and other devices latch VE in high level state, and the high level amplitude VCC. Therefore, the inverter NOT3 always outputs a low level of 0V, the mos transistor Q9 is turned off to turn off the mos transistor Q10, that is, the capacitor C4 is no longer charged, and the voltage V4 across the capacitor C4 is maintained at VOUT 1-0.7V. The voltage signal of V4 passes through the voltage follower E5 to the base of the transistor Q12, the emitter voltage of the transistor Q12 is V5, V5 is V4+0.7V, that is, V5 is VOUT1, and the voltage of V5 is the maximum value VOUT1 of the initial state output voltage VOUT. The voltage signal of V2 outputs a voltage signal V6 after passing through an in-phase proportional operational amplifier E6, wherein the voltage of V6 is calculated as follows:

V6＝V5＊(1+R14/R13)＝VOUT1＊(1+R14/R13)

when the power supply is powered up again, the VIN voltage starts to rise, before the voltage of V0 is lower than the voltage of V1, the output voltage VB of the comparator E2 is at a high level, the amplitude of the high level is VCC, so that the mos transistor Q16 is turned on, and the voltage across the capacitor C5 instantaneously discharges to 0V.

E5, E6 are powered by the internal power supply unit VDD.

STAGE5 part:

the power chip of the invention reduces the output current of the power chip to gradually drop the voltage at the two ends of the LED of the remaining branch by reducing the output current of the power chip when the voltage at the two ends of the LED of the remaining branch rises to a certain value, namely the voltage difference delta V between the voltage at the two ends of the LED of the remaining branch and the initial voltage at the two ends of the LED lamp group is more than or equal to 0.7V R5/(R5+ R6), and finally the delta V is reduced to delta V less than 0.7V R5/(R5+ R6).

When the difference between the voltage of V3 and the voltage of V6 is greater than or equal to 0.7V, the transistor Q13 is turned on, and at this time, the voltage V7 on the resistor R15 is at a high level, and the amplitude V3 of the high level (the voltage of V3 is much greater than 0.7V) is turned on, so that the transistor Q14 is turned on. When the resistors R5 and R6 are set to R13 and R14, the voltage difference Δ V is calculated as follows:

V3－V6＝(1+R6/R5)＊(V2－V5)＝(1+R6/R5)＊(VOUTmax－VOUT1)＝(1+R6/R5)

＊ΔV≥0.7V

ΔV＝VOUTmax－VOUT1≥(0.7V＊R5)/(R5+R6)

after the transistor Q14 IS turned on, the voltage V8 IS low level 0V, so the mos transistor Q15 IS turned on, the constant current source IS2 charges the capacitor C5, and the voltage V9 across the C5 IS calculated as follows:

V9＝IS2/C5＊t

VREF is the reference voltage inside the chip, when the voltage of V9 changes, the feedback voltage VCS also changes, the error amplifier E7 outputs a VG voltage signal to the main power tube driving control part, and the output current is reduced by adjusting the switch state of the main power tube. According to the superposition theorem, the calculation formula between the feedback voltages VCS and V9 is obtained as follows:

VCS＝(VREF＊(R19+R20)－V9＊R20)/R19

E7 is powered by an internal power supply unit VCC.

With reference to fig. 1 and fig. 2, when one or more LEDs in the load LED lamp set have an open-circuit fault, before a maintenance worker does not maintain the load LED lamp set, the power supply chip of the invention can dynamically reduce the output current of the power supply chip, so as to avoid the damage of the remaining LEDs due to high temperature rise of the LEDs caused by a large current.

When the load LED lamp group is not completely short-circuited (VOUT is not equal to 0V), namely when the load LED lamp group is short-circuited by LEDs on a certain branch or a plurality of branches, before a maintenance worker does not maintain the load LED lamp group, the power supply chip can avoid the damage of the short-circuit branch due to high temperature rise of the rest LEDs on the branch caused by large current.

When the load LED lamp group is in a complete short circuit (VOUT is 0V), the power supply chip can output current constantly through the resistor RCS, the constant output current IOUT is VCS/RCS, and before maintenance personnel do not maintain the power supply chip, the power supply chip is prevented from being damaged by large current in the short circuit.

The VS pin of the power supply chip can be connected with the monitoring equipment, when the load LED lamp group has an open short circuit fault, the monitoring equipment can continuously send the fault state signal to maintenance personnel, and the maintenance personnel reset the fault state on the monitoring equipment until the maintenance personnel maintain the load LED lamp group.

Referring to FIG. 3, a timing diagram of the relationship of SW, VA, V2 and other voltage signals, voltage signal V2 equals voltage signal V1.

In the time t1, at the initial power-on stage of the power chip, the VOUT voltage charges the capacitor C1 through the body diode of the mos tube Q3 and the resistor R4, and when the voltage across the C1 rises to VGSth, the mos tube Q3 enters a switch working state.

In the time t2, when the mos transistor Q3 is in a switch working state (the voltage V1 across the C1 is greater than or equal to VGSth), and when VA is at a high level, the mos transistor Q3 is turned off, and the voltage V1 across the C1 capacitor remains unchanged. When VA is low level, mos tube Q3 is conducted, VOUT voltage charges capacitor C1 through resistor R4, proper values of R4 and C1 are set, and voltage V1 at two ends of C1 is guaranteed to be charged to the maximum VOUTmax of VOUT voltage in a short time. The Mos transistor Q3 charges the capacitor C1 at a higher rate when turned on than the capacitor C1 through the body diode and resistor R4.

And in the time t3, the power chip enters a stable working state, and the voltage at the two ends of the capacitor C1 is determined by the maximum value VOUTmax of the VOUT voltage. The voltage signal V1 outputs the voltage signal V2 through the voltage follower E3, so the voltage signal V2 is equal to the voltage signal V1.

As shown in fig. 3, when the main power transistor is in the switch working state, the main power transistor is turned on when the SW voltage is at a high level, and the main power transistor is turned off when the SW voltage is at a low level, that is, the switching state of the mos transistor Q3 is ensured to be opposite to the switching state of the main power transistor (the main power transistor is turned off when Q3 is turned on, and the main power transistor is turned on when Q3 is turned off).

As shown in fig. 4, in a stable operating state of the power chip (time period t3 in fig. 3), when one or more LEDs in the load LED lamp set have an open-circuit fault, the voltage across the LEDs in the remaining branches will rise by a certain value because the current flowing through the LEDs in the remaining branches becomes large. When the voltage difference delta V between the maximum voltage VOUTmax at the two ends of the LED of the remaining branch and the maximum voltage VOUT1 at the two ends of the LED lamp group is more than or equal to 0.7V R5/(R5+ R6), the power supply chip reduces the output current IOUT of the power supply chip, so that the current flowing through the LED of the remaining branch is reduced, the voltage at the two ends of the LED of the remaining branch is gradually dropped after the current flowing through the LED of the remaining branch is reduced, and finally the delta V is reduced to delta V less than 0.7V R5/(R5+ R6).

According to the power supply chip, the LED of the rest branches can be prevented from being damaged due to high temperature rise caused by the fact that large current flows through the LED before maintenance personnel maintain the power supply chip.

As shown in fig. 4, when Δ V is greater than or equal to 0.7V R5/(R5+ R6) (Δ V2-V5-VOUTmax-VOUT 1), VOUTmax is a solid line portion indicated by an arrow in the drawing, VOUT1 is a broken line portion indicated by an arrow in the drawing), the voltage V8 is at a low level of 0V, and the voltage V9 across the capacitor C5 gradually rises, so that the output current IOUT of the power chip gradually decreases. When the delta V is less than 0.7V R5/(R5+ R6), the voltage V8 is at high level, the amplitude value VCC of the high level is high, and the voltage V9 at the two ends of the capacitor C5 is kept unchanged, so that the output current IOUT of the power chip is kept unchanged.

The invention has simple structure and reliable operation, and solves the problem that when a single or a plurality of LEDs are turned on for a short time in the process that the BUCK power supply chip supplies power to the load LED lamp group, the LEDs of the rest branches or the LEDs of the short-circuit branches are damaged due to higher temperature rise caused by the large current flowing through the LEDs.

It is to be understood that the scope of the present invention is not to be limited to the non-limiting embodiments, which are illustrated as examples only. The essential protection sought for the invention is further defined in the scope provided by the independent claims, as well as in the dependent claims.

Claims

1. The utility model provides a LED fault state detects and protection circuit, includes load LED banks and power chip, load LED banks is many LED series-parallel connection and constitutes, load LED banks has the short-circuit fault of opening totally, the short-circuit fault of opening totally not is single or many load LED opens short-circuit fault, its characterized in that:

the power chip detects the voltage at two ends of the load LED lamp bank through a VOUT pin, and comprises: the load fault detection device comprises a first load state detection unit, a second load state detection unit, a fault alarm circuit, a load initial state detection unit and a load current reduction unit;

the first load state detection unit realizes the function of turning off the power supply chip when the load LED lamp group is short-circuited by one or more load LEDs, the second load state detection unit, the load initial state detection unit and the load current reduction unit realize the function of dynamically reducing the output current of the power supply chip when the load LED lamp group is open-circuited by one or more LEDs, the fault alarm circuit transmits a high level to a VS pin of the power supply chip when the load LED lamp group is open-short-circuited, and an amplitude VCC signal of the high level of the VS pin is transmitted to the monitoring equipment so as to send the fault state to the monitoring equipment;

the utility model discloses a power chip's inside power supply unit's supply voltage VCC gets the electricity from VOUT, supply voltage VCC's high level amplitude is less than VOUT, and the low level is 0V, the operating voltage VDD of the inside power supply unit of power chip is got the electricity from VIN and VOUT, operating voltage VDD high level amplitude is between VIN and VOUT, and the low level is 0V:

the first load state detection unit avoids more serious consequences by switching off a power chip when the load LED lamp group is in an incomplete short-circuit state, the second load state detection unit detects output voltage VOUT in real time so as to realize the function of monitoring the voltage of the load LED lamp group, the fault alarm circuit sends a fault state to monitoring equipment when the load LED lamp group is in an open short-circuit fault, the load initial state detection unit stores the maximum VOUT1 of the output voltage VOUT at the power-on initial stage of the power chip, and the load current reduction unit reduces the output current of the power chip when the voltage at two ends of LEDs of the remaining branches rises to be more than or equal to a set value, so that the voltage at two ends of the LEDs of the remaining branches gradually falls to be less than the set value.

2. The LED fault condition detection and protection circuit of claim 1, wherein: the load LED lamp bank is connected with a resistor RCS in series, and when the load LED lamp bank is completely short-circuited, the power supply chip outputs current through the resistor RCS in a constant mode so as to avoid large current during short circuit from damaging the power supply chip.

3. The LED fault condition detection and protection circuit of claim 2, wherein: and the VS pin is connected with the monitoring equipment, and when the VS pin is at a high level, the monitoring equipment can memorize and latch the high level state.

4. The LED fault condition detection and protection circuit of claim 3, wherein: the first load state detection unit compares the voltage VOUT of the load LED lamp group with the control voltage VD so as to control the main power tube driving control unit and turn off the main power tube through the control voltage VD when the load LED lamp group is not completely short-circuited.

5. The LED fault condition detection and protection circuit of claim 4, wherein: VOUT is not equal to 0V when load LED banks are not the dead short circuit 0V when load LED banks are the dead short circuit.