Constant current control circuit, constant current driving system and over power protection method

Abstract

The application provides a constant current control circuit, a constant current driving system and a power over protection method, comprising: a constant current control module for constant current control of an LED load; a charging current control module for generating a corresponding compensation voltage based on a negative voltage of the LED load and adjusting a charging current of an output capacitor based on the compensation voltage; and a compensation voltage locking module for locking the compensation voltage when the constant current control circuit is powered off and restarted, so as to realize power over protection of a charging and discharging MOS tube. The application adopts a loop compensation circuit to meet the requirements of high PF, high efficiency and no flicker; through a low voltage locking or power off detection module, the maximum conduction current of the charging and discharging MOS tube is limited when the system is restarted after being powered off, so as to prevent the charging and discharging MOS tube from being broken down by power over during the instant start-up when the charging and discharging MOS tube is repeatedly switched on and off, and the application range is wider and the reliability is higher; the compensation voltage locking module only works when the system is powered off, and does not affect the working state of the system under normal conditions.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of integrated circuit design, in particular to a constant current control circuit, a constant current driving system and an over-power protection method. BACKGROUND

[0002] LED is a characteristic sensitive semiconductor device, and also has a negative temperature characteristic, so that in the application process, it needs to be stabilized by a driving control circuit, and protection is realized. The LED device is almost rigorous to the driving control circuit, and needs to meet many requirements such as power factor (PF), harmonic, efficiency, and frequency flash; the more requirements are met, the more complex the circuit structure is, and the working environment of each device in the driving control circuit is also more complex, and the device is easy to be damaged and fail.

[0003] Therefore, how to protect the internal device while meeting various requirements of the driving control circuit, and then ensure the stability of the driving control circuit, has become one of the problems to be solved by the person skilled in the art. SUMMARY

[0004] In view of the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide a constant current control circuit, a constant current driving system and an over-power protection method, which are used to solve the problem that the electronic device in the driving control circuit is easy to be damaged in the prior art.

[0005] To achieve the above-mentioned purpose and other related purposes, the present application provides a constant current control circuit, which at least comprises:

[0006] A constant current control module connected to the negative electrode of an LED load, for constant current control of the LED load;

[0007] A charging current control module connected to the negative electrode of the LED load and the lower plate of the output capacitor, for generating a corresponding compensation voltage based on the negative electrode voltage of the LED load, and adjusting the charging current of the output capacitor based on the compensation voltage;

[0008] A compensation voltage locking module connected to the charging current control module, for locking the compensation voltage when the constant current control circuit is powered off and restarted, so as to realize over-power protection of the charge-discharge MOS tube in the charging current control module.

[0009] Optionally, the constant current control module comprises a constant current MOS tube, a first sampling unit and a first operational amplifier unit; the drain electrode of the constant current MOS tube is connected to the negative electrode of the LED load, and the source electrode is grounded through the first sampling unit; the input terminals of the first operational amplifier unit are respectively connected to the source electrode of the constant current MOS tube and a reference voltage, the output terminal is connected to the gate electrode of the constant current MOS tube, and the current flowing through the LED load is controlled based on the difference between the sampling voltage and the reference voltage.

[0010] Optionally, the constant current control module further comprises a dimming unit connected to the first operational amplification unit, the dimming unit receives a dimming control signal, adjusts the size of the reference voltage based on the dimming control signal, and thereby realizes dimming control.

[0011] Optionally, the charging current control module comprises a charge-discharge MOS tube, a second sampling unit, a detection unit, a compensation unit, a third sampling unit and a second operational amplification unit.

[0012] The drain of the charge-discharge MOS tube is connected to the lower plate of the output capacitor, and the source is grounded via the second sampling unit.

[0013] The detection unit is connected to the negative electrode of the LED load, judges the discharge voltage of the output capacitor based on the negative electrode voltage of the LED load, and obtains a control signal.

[0014] The compensation unit is connected to the output end of the detection unit, and generates the compensation voltage based on the output signal of the detection unit.

[0015] The third sampling unit is connected between the bus voltage and the source of the charge-discharge MOS tube, and outputs a sampling signal of the bus voltage.

[0016] The input end of the second operational amplification unit is connected to the output end of the compensation unit and the third sampling unit respectively, and the output end is connected to the gate of the charge-discharge MOS tube, so as to adjust the charging current of the output capacitor.

[0017] More optionally, the detection unit is further connected to the gate of the constant current MOS tube in the constant current control module, and when the gate voltage of the constant current MOS tube is greater than a set value, the compensation voltage is rapidly increased.

[0018] More optionally, the compensation voltage locking module comprises a low voltage locking unit, and the low voltage locking unit is connected to the bus voltage, and when the bus voltage is lower than a set value, the compensation voltage is locked at a lower limit value of the compensation voltage.

[0019] More optionally, the compensation voltage locking module comprises a power-down judgment unit and a locking unit, the power-down judgment unit is connected to the sampling end of the constant current control module and the compensation voltage, detects whether the LED constant current driving circuit is powered down based on the sampling voltage and the compensation voltage, and the locking unit is connected to the output end of the power-down judgment unit, and when it is detected that the LED constant current driving circuit is powered down, the compensation voltage is locked at a lower limit value of the compensation voltage.

[0020] More optionally, the power-off judging unit comprises a first operational amplifier, a second operational amplifier and an AND gate; the input ends of the first operational amplifier are connected with the sampling end of the constant current control module and a preset current respectively, and output a detection signal of the current flowing through the LED load; the input ends of the second operational amplifier are connected with the compensation voltage and a preset voltage respectively, and output a detection signal of the compensation voltage; the input ends of the AND gate are connected with the output ends of the first operational amplifier and the second operational amplifier respectively, and output a power-off detection signal after AND operation.

[0021] To achieve the above object and other related objects, the present application provides a constant current driving system, which at least comprises:

[0022] a rectifier circuit receiving an alternating current power supply, rectifying the alternating current power supply to obtain a bus voltage;

[0023] an LED load, the positive electrode of which is connected with the bus voltage;

[0024] an output capacitor, the upper plate of which is connected with the positive electrode of the LED load;

[0025] and the above constant current control circuit, which is connected with the LED load and the output capacitor to realize constant current control of the LED load.

[0026] To achieve the above object and other related objects, the present application provides a power over protection method, which is realized based on the above constant current control circuit, and at least comprises:

[0027] generating a corresponding compensation voltage based on the negative electrode voltage of the LED load, and adjusting the charging current of the output capacitor based on the compensation voltage to control the LED load to realize no flicker when the output capacitor is discharging;

[0028] locking the compensation voltage at a lower limit value of the compensation voltage when the constant current control circuit is powered off and restarted, limiting the instantaneous power of the charge-discharge MOS tube in the charging current control module, and protecting the charge-discharge MOS tube.

[0029] Optionally, the bus voltage is detected, and when the bus voltage is lower than a set value, the compensation voltage is locked at a lower limit value of the compensation voltage; wherein the set value is lower than the turn-on voltage of the LED load.

[0030] More optionally, when the voltage on the output capacitor is greater than the set value, the power consumption of the charge-discharge MOS tube satisfies:

[0031]

[0032] When the voltage on the output capacitor is less than the set value, the power consumption of the charge-discharge MOS tube satisfies:

[0033]

[0034] PQ2= (Vin_max-VCo) * (VComp-VComp_low) / Rs

[0035] Optionally, the current flowing through the LED load and the compensation voltage are detected, and when the current flowing through the LED load is less than a preset current and the compensation voltage is greater than a preset voltage, the compensation voltage is locked at the lower limit of the compensation voltage.

[0036] More optionally, before triggering the lock, the power consumption of the charge-discharge MOS tube satisfies:

[0037]

[0038] After triggering the lock, the power consumption of the charge-discharge MOS tube satisfies:

[0039]

[0040] PQ2= (Vin_max-VCo) * (VComp-VComp_low) / Rs

[0041] As described above, the constant current control circuit, the constant current driving system and the over-power protection method of the present application have the following beneficial effects:

[0042] 1. The constant current control circuit, the constant current driving system and the over-power protection method of the present application meet the high PF, high efficiency and no flicker requirements of ERP requirements by using a loop compensation circuit.

[0043] 2. The constant current control circuit, the constant current driving system and the over-power protection method of the present application trigger the loop compensation circuit when the power is turned off and turned on again by the low voltage lock or power down detection module, limit the maximum conduction current of the charge-discharge MOS tube, prevent the charge-discharge MOS tube from being broken down by the over-power at the moment of starting up when the power is repeatedly turned on and off, have a wider application range and higher reliability.

[0044] 3. The constant current control circuit, constant current drive system and over-power protection method of the present application, the compensation voltage locking module only works when the system is detected to power down, and does not affect the working state of the system under normal conditions. BRIEF DESCRIPTION OF DRAWINGS

[0045] Figure 1 A structure schematic diagram of the linear LED drive circuit is shown.

[0046] Figure 2 A distribution schematic diagram of the safe working area of the MOS tube is shown.

[0047] Figure 3 A structure schematic diagram of the constant current control circuit and constant current drive system of the present application is shown.

[0048] Figure 4 Another structure schematic diagram of the constant current control circuit and constant current drive system of the present application is shown.

[0049] Element number explanation

[0050] 1. Linear LED drive circuit

[0051] 11. Detection module

[0052] 12. Compensation module

[0053] 2. Constant current control circuit

[0054] 21. Constant current control module

[0055] 211. First operational amplifier unit

[0056] 212. Dimming unit

[0057] 22. Charging current control module

[0058] 221. Detection unit

[0059] 222. Compensation unit

[0060] 222a. Compensation voltage generation circuit

[0061] 223. Second operational amplifier unit

[0062] 23. Compensation voltage locking module

[0063] 231. Low voltage locking unit

[0064] 232. Power down judgment unit

[0065] 232a. First operational amplifier

[0066] 232b. Second operational amplifier

[0067] 232c AND gate

[0068] 233 locking unit

[0069] 24 power factor adjustment module

[0070] 25 operating voltage generation module DETAILED DESCRIPTION

[0071] The present application is herein described, by way of example only, with the comprehension that the advantages and utility thereof are not confined thereto. It will be clear that, in light of the foregoing disclosure, additional embodiments of the present application will be suggested to those of ordinary skill in the art, and such embodiments are intended to be within the scope of the present application. The embodiments described hereinbefore and hereinafter are intended to be merely exemplary and are not intended to limit the scope of the application. Various modifications of the application in addition to those shown herein will become apparent to those skilled in the art from the foregoing description. Such modifications are intended to fall within the scope of the appended claims. It is further understood by those skilled in the art that they can readily apply the principles of the present application to other embodiments without departing from the spirit and scope of the application as set forth in the following claims.

[0072] Reference will now be made to the drawings, wherein Figures 1-4 It is to be understood that the above description is intended to be illustrative, and not restrictive. Many other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the application should, therefore, be determined not with reference to the above description, but instead with reference to the appended claims, along with their full scope of equivalents.

[0073] With the implementation of the enterprise resource planning (ERP) standard, the LED drive increases the requirement of the stroboscopic under the requirement of the power factor (PF), the harmonic, the efficiency and so on. A linear LED drive circuit 1 is provided, as shown in Figure 1 The feedback signal is obtained by sampling the drain and gate voltage of the MOS tube Q1, to control the charging control of the MOS tube Q2 to the output capacitor Co, so that the output capacitor Co has enough power when discharging, so that the MOS tube Q1 controls the LED constant current output to realize no stroboscopic; the MOS tube Q1 can make the average working voltage of the drain be the lowest when the MOS tube Q1 constant current output discharges the output capacitor Co, to reduce the loss of the MOS tube Q1 and improve the system efficiency; the MOS tube Q2 reduces the charging current when the bus voltage Vin is high, to reduce the loss of the MOS tube Q2 and improve the overall efficiency of the system, and the control of the charging current of the MOS tube Q2 can also improve the PF of the system, so as to meet the requirements of the ERP standard of PF, efficiency, no stroboscopic and the like.

[0074] As shown in Figure 2As shown, in practical applications, MOS tubes have a safe working area (SOA) limit. If a high voltage appears at the drain of the MOS tube while a large current flows through it, and the current and voltage duration is too long, the MOS tube will overheat and be damaged once it exceeds the safe working area.

[0075] Figure 1 As shown in the linear LED driving circuit, the loop control of the detection module 11 and the compensation module 12 ensures that the bus voltage Vin at the bottom of the power frequency cycle can still guarantee the non-flickering output of the LED. Therefore, when the input voltage is low, the charging peak current of the MOS tube Q2 is increased to compensate for the loop. This will encounter a problem. When the system is powered off, the LED will no longer be turned on after the bus voltage Vin is lower than the LED turn-on voltage. At this time, since the chip (linear LED driving circuit 1) can still work by the residual amount of the output capacitor Co, the loop will cause the compensation voltage to rise until it is limited by the internal circuit. At this time, the MOS tube Q2 will try to output the maximum current to maintain the loop operation. If the input is suddenly powered on to the highest bus voltage at this time, since the voltage of the output capacitor Co cannot change abruptly, it is equivalent to a short circuit at the moment, and therefore a high voltage (Vin_max-VCo) will appear at the drain of the MOS tube Q2, where Vin_max is the maximum bus voltage, and VCo is the voltage on the output capacitor. At this time, the instantaneous power of the MOS tube Q2 is where VComp_max is the maximum value of the compensation voltage, and Rs is the resistance value of the MOS tube Q2 source sampling resistor. If VCo is relatively low, PQ2 will be large, and once this power exceeds the bearing capacity of the MOS tube Q2, it will cause the MOS tube Q2 to be damaged. For the MOS tube Q1, its power is where Vin_max is the maximum bus voltage, VLED is the turn-on voltage of the LED, Vref is the reference voltage, and Rcs is the resistance value of the MOS tube Q1 source sampling resistor. The maximum power consumption of the MOS tube Q1 will be limited, and it is much smaller than the maximum power consumption of the MOS tube Q2, and it is not easy to be damaged. Therefore, when the voltage of the output capacitor Co is relatively low, the system is suddenly powered on, and the MOS tube Q2 is easily damaged, which can cause the system to malfunction.

[0076] Meanwhile, the linear LED driving power load is LED, the LED on voltage is about 250V, the bus voltage is higher than the LED on voltage, the LED is on and emits light, the bus voltage is lower than the LED on voltage, the LED is off and does not emit light (after the electrolytic capacitor voltage is discharged to be lower than the LED on voltage). When the bus voltage is lower than the LED on voltage after the power is turned off, the LED does not emit light, but due to the existence of the input electrolytic capacitor, the bus voltage cannot be discharged through the LED, but can only be discharged through the static current of the control chip itself (or a discharging resistor connected in parallel to the electrolytic capacitor), and the working voltage can be as low as 10V (the working voltage is directly connected to the bus) due to the small static current of the chip (the discharging resistor is large), according to C*△V=I*△t, the discharging time can be obtained, assuming that C=10uF,△V=200V, the static current I of the chip is 200uA, and the discharging time t is 10s, that is, the chip can stop working completely after the switch is turned off for 10s.

[0077] In order to ensure the constant current of the LED, the control loop will bring loop compensation control, so that the output current does not change when the bus voltage changes in a certain range. When the bus voltage is lower than the LED on voltage, the input signal of the feedback loop is zero, so the compensation output signal is the highest. When the switch is turned on again before the chip completely stops working after the switch is turned off, the compensation control loop will work in the maximum output current state, and if this happens at the highest bus voltage, the MOS tube Q2 will work in the state of the highest voltage and the maximum current, and at this time, over-power damage is easy to occur.

[0078] One way to limit the current is to limit the compensation voltage, set VComp_Limit<VComp_max, at this time the peak current of the MOS tube Q2 is So that the maximum instantaneous power of the MOS tube Q2 is limited: But the compensation voltage determines the range of the system loop, and once it is limited, the adjustable range of the system will be reduced, which will lead to the fact that the loop cannot be adjusted under certain input voltage conditions, so that the no flicker output of the LED cannot be guaranteed, and the application conditions will be limited.

[0079] Another way to limit the gate drive voltage of the MOS tube Q2 is to limit the peak current through the output characteristics of the MOS itself, so as to limit the instantaneous power consumption of the MOS tube Q2 and prevent over-power damage of the MOS tube Q2, and the instantaneous power consumption satisfies: Here, IQ2_Limit is the peak current limit value of MOSFET Q2. However, the gate threshold voltage of a MOSFET is affected by temperature, so the maximum output current of the MOSFET will change at different temperatures. If the change is too large, it may sometimes fail to provide reliable protection, or the output current may be insufficient, causing the output LED to flicker. Furthermore, the threshold voltage of different MOSFETs is also different, and the current limit value will be inconsistent, which will also limit the application.

[0080] Based on the above reasons, this invention proposes a constant current control circuit that, while meeting the requirements of power factor, harmonics, efficiency, and flicker, also provides over-power protection for the charging and discharging MOSFET to prevent damage to the MOSFET. The following is a detailed description.

[0081] Example 1

[0082] like Figure 3 As shown, this embodiment provides a constant current control circuit 2, which includes:

[0083] Constant current control module 21, charging current control module 22 and compensation voltage lockout module 23.

[0084] like Figure 3 As shown, the constant current control module 21 is connected to the negative terminal of the LED load and is used to perform constant current control on the LED load.

[0085] Specifically, in this embodiment, the constant current control module 21 includes a constant current MOSFET Q1, a first sampling unit Rcs, and a first operational amplifier unit 211. The drain of the constant current MOSFET Q1 is connected to the negative terminal of the LED load, the source is grounded via the first sampling unit Rcs, and the gate is connected to the output terminal of the first operational amplifier unit 211. As an example, the first sampling unit Rcs is implemented using a sampling resistor. In actual use, any structure that can achieve the sampling function is applicable to this invention and is not limited to this embodiment. The input terminal of the first operational amplifier unit 211 is connected to the source of the constant current MOSFET Q1 and a reference voltage Vref, respectively, and the output terminal is connected to the gate of the constant current MOSFET Q1. The current flowing through the LED load is controlled based on the difference between the sampled voltage Vcs and the reference voltage Vref. As an example, the inverting input terminal of the first operational amplifier unit 211 is connected to the source of the constant current MOSFET Q1, and the non-inverting input terminal is connected to the reference voltage Vref. In actual use, the polarity of the input terminal of the first operational amplifier unit and the relationship with the corresponding input signal can be adjusted as needed, and this embodiment is not the limitation.

[0086] Specifically, as another implementation form of the present application, the constant current control module 21 further comprises a dimming unit 212 connected to the first operational amplifier unit 211. The dimming unit 212 receives a dimming control signal DIM, adjusts the size of the reference voltage Vref based on the dimming control signal DIM, and thus realizes dimming control.

[0087] As shown in FIG. 2, the charging current control module 22 is connected to the negative electrode of the LED load and the lower plate of the output capacitor Co, generates a corresponding compensation voltage VComp based on the negative electrode voltage of the LED load, and adjusts the charging current of the output capacitor Co based on the compensation voltage VComp. Figure 3

[0088] Specifically, in the present embodiment, the charging current control module 22 comprises a charge-discharge MOS tube Q2, a second sampling unit Rs, a detection unit 221, a compensation unit 222, a third sampling unit and a second operational amplifier unit 223.

[0089] More specifically, the drain of the charge-discharge MOS tube Q2 is connected to the lower plate of the output capacitor Co, the source is grounded via the second sampling unit Rs, and the gate is connected to the output of the second operational amplifier unit 223. As an example, the second sampling unit Rs is implemented by a sampling resistor.

[0090] More specifically, the detection unit 221 is connected to the negative electrode of the LED load, judges the discharge voltage of the output capacitor Co based on the negative electrode voltage of the LED load, and obtains a control signal. As an example, the negative electrode voltage of the LED load is compared with a preset voltage to judge the size of the negative electrode voltage of the LED load, and a control signal for reducing the compensation voltage VComp is generated when the negative electrode voltage of the LED load is greater than a first preset voltage, and a control signal for increasing the compensation voltage VComp is generated when the negative electrode voltage of the LED load is less than a second preset voltage, wherein the first preset voltage is greater than or equal to the second preset voltage. In the present embodiment, the input of the detection unit 221 is also connected to the gate of the constant current MOS tube Q1, and a control signal for rapidly increasing the compensation voltage VComp is generated when the gate voltage of the constant current MOS tube Q1 is greater than a set value. The speed of increasing the compensation voltage by the gate voltage of the constant current MOS tube Q1 is greater than the speed of increasing the compensation voltage by the negative electrode voltage of the LED load.

[0091] It should be noted that any circuit structure capable of detecting the discharge voltage of the output capacitor Co and generating a corresponding control signal for adjusting the charging current of the output capacitor Co is applicable to the present application, and is not limited to the present embodiment.

[0092] ​More specifically, the compensation unit 222 is connected to the output terminal of the detection unit 221, and generates the compensation voltage VComp based on the output signal of the detection unit 221. As an example, the compensation unit 222 includes a compensation voltage generating circuit 222a and a compensation capacitor Ccomp, one end of the compensation voltage generating circuit 222a is connected to the output terminal of the detection unit 221, and the other end is connected to the upper plate of the compensation capacitor Ccomp; the lower plate of the compensation capacitor Ccomp is grounded. The compensation capacitor Ccomp can be arranged outside the chip, or integrated into the chip by digital filtering technology to reduce peripheral components and simplify the system.

[0093] More specifically, the third sampling unit is connected between the bus voltage Vin and the source of the charge-discharge MOS tube Q2, and outputs a sampling signal of the bus voltage Vin; as an example, the third sampling unit includes a first sampling resistor R1 and a second sampling resistor connected in series between the bus voltage Vin and the source of the charge-discharge MOS tube Q2, and the connection node of the first sampling resistor R1 and the second sampling resistor outputs a sampling signal (see Figure 1 ) As another implementation manner of the present application, the constant current control circuit 2 further includes a power factor regulation module 24, one end of the power factor regulation module 24 is connected to the bus voltage Vin, and the other end is connected to the first sampling resistor R1, and the power factor regulation resistor Rpf is further connected outside, and the voltage at the output end of the third sampling unit is adjusted through the power factor regulation resistor Rpf, thereby realizing high power factor, at this time, the second sampling resistor is integrated in the power factor regulation module 24 or obtained by equivalent of internal devices of the power factor regulation module 24.

[0094] More specifically, the input terminals of the second operational amplifier unit 223 are respectively connected to the output terminal of the compensation unit 222 and the second end of the third sampling unit R1, and the output terminal is connected to the gate of the charge-discharge MOS tube Q2, so as to realize adjustment of the charging current of the output capacitor Co. As an example, the non-inverting input terminal of the second operational amplifier unit 223 is connected to the output terminal of the compensation unit 222, and the inverting input terminal is connected to the second end of the third sampling unit R1; in actual use, the correspondence between the input terminal polarity and the input signal can be adjusted, which will not be described one by one here.

[0095] As shown in Figure 3 , the compensation voltage locking module 23 is connected to the charging current control module 22, and locks the compensation voltage VComp when the constant current control circuit 2 is powered off and restarted, so as to realize over-power protection of the charge-discharge MOS tube Q2 in the charging current control module 23.

[0096] Specifically, in the embodiment, the compensation voltage locking module 23 comprises a low voltage locking unit 231. The low voltage locking unit 231 connects the bus voltage Vin, and locks the compensation voltage VComp at a compensation voltage lower limit value VComp_low when the bus voltage Vin is lower than a set value. The compensation voltage lower limit value VComp_low can be set according to actual needs, and is not limited herein.

[0097] As shown in Figure 3 As another implementation manner of the application, the constant current control circuit 2 further comprises a working voltage generating module 25 connected to the bus voltage Vin, which obtains power supply from the bus voltage Vin and converts it into working voltage to supply power to the modules in the constant current control circuit 2. As an example, a resistor R3 is further connected between the output end of the working voltage generating module 25 and the input end of the dimming unit 212.

[0098] As shown in Figure 3 The method for realizing over power protection of the constant current control circuit 2 in the embodiment is as follows:

[0099] 1) A corresponding compensation voltage is generated based on the negative voltage of the LED load, and the charging current of the output capacitor is adjusted based on the compensation voltage to control the LED load to realize flicker-free when the output capacitor Co discharges.

[0100] Specifically, when the bus voltage Vin is less than the turn-on voltage of the LED, the output capacitor Co discharges the LED load, and the LED load is controlled by the constant current control module 21; when the bus voltage Vin is greater than the turn-on voltage of the LED, the bus voltage Vin supplies power to the LED load, and the LED load is controlled by the constant current control module 21, while the bus voltage Vin charges the output capacitor Co; when the bus voltage Vin is less than the voltage of the output capacitor Co, the output capacitor Co discharges the LED load, and the LED load is controlled by the constant current control module 21.

[0101] Specifically, the charging current control module 22 reduces the compensation voltage VComp when the negative voltage of the LED load is large, so as to reduce the charging current of the output capacitor Co; the charging current control module 22 increases the compensation voltage VComp when the negative voltage of the LED load is small, so as to increase the charging current of the output capacitor Co; so that the output capacitor Co has enough power to make the constant current MOS tube Q1 control the LED load to realize constant current output and flicker-free when discharging.

[0102] 2) Lock the compensation voltage VComp at the compensation voltage lower limit value VComp_low when the constant current control circuit 2 is restarted under power down, limit the instantaneous power of the charge-discharge MOS Q2 in the charge current control module 22, and protect the charge-discharge MOS Q2.

[0103] Specifically, in the present embodiment, the bus voltage Vin is detected, and when the bus voltage Vin is lower than the set value Vin_low, the low voltage locking unit 231 locks the compensation voltage VComp at the compensation voltage lower limit value VComp_low, without affecting the working state under normal application conditions. The set value satisfies: Vin_low < VLED, and VLED is the on voltage of the LED load.

[0104] If the system is suddenly input to the highest voltage when powered down, since the output capacitor Co still has a residual voltage, when VCo > Vin_low, the power consumption of the charge-discharge MOS Q2 satisfies:

[0105]

[0106] When VCo < Vin_low, the current flowing through the charge-discharge MOS Q2 is locked to: If the voltage VCo on the output capacitor Co is very low, the power consumption of the charge-discharge MOS Q2 satisfies:

[0107]

[0108] Where PQ2 is the power consumption of the charge-discharge MOS Q2, Vin_max is the maximum value of the bus voltage, VCo is the voltage on the output capacitor, VComp_max is the maximum value of the compensation voltage, Rs is the sampling resistance value of the current flowing through the output capacitor, Vin_low is the set value of the bus voltage, and VComp_low is the compensation voltage lower limit value. By setting appropriate Vin_low and VComp_low, the instantaneous power consumption of the charge-discharge MOS Q2 does not exceed the safe operating area (SOA) of the MOS, thereby avoiding over-power damage to the charge-discharge MOS Q2.

[0109] It should be noted that there is no explicit sequence for steps 1) and 2). The power-down protection of the present application occurs when the bus voltage Vin is lower than the LED on voltage, at which time the residual voltage of the electrolytic capacitor can still be more than 200 volts. In the present embodiment, once the set value Vin_low is determined, it is not possible to switch applications under the input conditions of 120Vac / 220Vac, and only fixed input voltage applications can be made.

[0110] Embodiment Two

[0111] As Figure 4 shown in the figure, the embodiment provides a constant current control circuit 2, which is different from the first embodiment in that the implementation manner of the compensation voltage locking module 23 is different.

[0112] As Figure 4 shown, the compensation voltage locking module 23 includes a power-down judging unit 232 and a locking unit 233.

[0113] Specifically, the power-down judging unit 232 is connected to the sampling end of the constant current control module 21 and the compensation voltage VComp, and detects whether the LED constant current driving circuit 2 is powered down based on the sampling voltage Vcs and the compensation voltage VComp. As an example, the power-down judging unit 232 includes a first operational amplifier 232a, a second operational amplifier 232b, and an AND gate 232c. The input ends of the first operational amplifier 232 are respectively connected to the sampling end CS of the constant current control module 21 and a preset current Io_L, and output a detection signal of the current flowing through the LED load; as an example, the inverting input end of the first operational amplifier 232 is connected to the sampling end CS of the constant current control module 21, and the non-inverting input end is connected to the preset current Io_L. The input ends of the second operational amplifier 232b are respectively connected to the compensation voltage VComp and a preset voltage Comp_H, and output a detection signal of the compensation voltage; as an example, the non-inverting input end of the second operational amplifier 232b is respectively connected to the compensation voltage VComp, and the inverting input end is connected to the preset voltage Comp_H. The input ends of the AND gate 232c are respectively connected to the output ends of the first operational amplifier 232a and the second operational amplifier 232b, and output a power-down detection signal after AND operation.

[0114] It should be noted that the input end polarity of the first operational amplifier 232a and the second operational amplifier 232b and the corresponding relationship with the input signal can be adjusted according to actual needs, as long as the power-down state can be detected, and the embodiment is not limited. Any circuit structure that can detect the power-down state is applicable to the present application, and will not be described here.

[0115] Specifically, the locking unit 233 is connected to the output end of the power-down judging unit 232, and when it is detected that the LED constant current driving circuit 2 is powered down, the compensation voltage VComp is locked at the lower limit value VComp_low of the compensation voltage.

[0116] It should be noted that other circuit structures are the same as those of the first embodiment, and will not be described here.

[0117] As Figure 4 shown, the method for implementing over-power protection of the constant current control circuit 2 of the embodiment is as follows:

[0118] 1) Based on the negative voltage of the LED load, a corresponding compensation voltage is generated, and based on the compensation voltage, the charging current of the output capacitor is adjusted to control the LED load to achieve flicker-free when the output capacitor Co is discharged.

[0119] For specific principles, see Example 1, which is not repeated here.

[0120] 2) Lock the compensation voltage VComp at the lower limit of the compensation voltage VComp_low when the constant current control circuit 2 is restarted, limit the instantaneous power of the charge-discharge MOS tube Q2 in the charging current control module 22, and protect the charge-discharge MOS tube Q2.

[0121] Specifically, in this embodiment, the current flowing through the LED load and the compensation voltage VComp are detected, and when the bus voltage Vin decreases, the compensation voltage VComp will increase under loop control, and when the compensation voltage VComp rises to the preset voltage Comp_H, and the current flowing through the LED load decreases to the preset current Io_L, it is determined that the system is powered down, triggering the locking unit 233 to lock the compensation voltage VComp at the lower limit of the compensation voltage VComp_low. The limit condition of power-down judgment is VCo=VLED, at this time if the bus voltage decreases without triggering the locking unit 233 to lock it again, the power on the charge-discharge MOS tube Q2 before triggering the lock is:

[0122]

[0123] After triggering the lock, the power consumption of the charge-discharge MOS tube Q2 satisfies:

[0124]

[0125] Where PQ2 is the power consumption of the charge-discharge MOS tube, Vin_max is the maximum value of the bus voltage, VCo is the voltage on the output capacitor, VComp is the compensation voltage, Rs is the sampling resistance value of the current flowing through the output capacitor, VComp_max is the maximum value of the compensation voltage, VLED is the on-voltage of the LED load, and VComp_low is the lower limit of the compensation voltage.

[0126] The transient power of the charge-discharge MOS Q2 can be limited so as not to be broken by over-power. The compensation voltage locking module 23 only works when the system is powered off, and does not affect the working state of the system under normal conditions. If a de-compensation capacitor is used, the compensation signal is controlled in a digital manner, so that the digital signal can be directly controlled to prevent the charge-discharge MOS Q2 from being broken by over-power, and the circuit structure of the compensation voltage locking module 23 is adjusted accordingly, which is not described here.

[0127] Embodiment three

[0128] As shown in Figure 3 and Figure 4 , the embodiment provides a constant current driving system, which comprises:

[0129] a rectifier circuit 3, an LED load, an output capacitor Co and a constant current control circuit 2.

[0130] As shown in Figure 3 and Figure 4 , the rectifier circuit 3 receives an alternating current power supply AC, and rectifies the alternating current power supply AC to obtain a bus voltage Vin. As an example, the rectifier circuit 3 adopts a rectifier bridge structure, and in actual use, any circuit structure capable of realizing rectification function is applicable.

[0131] As shown in Figure 3 and Figure 4 , the anode of the LED load is connected to the bus voltage Vin, and the cathode is connected to the drain of a constant current MOS Q1 in the constant current control circuit 2.

[0132] As shown in Figure 3 and Figure 4 , the upper plate of the output capacitor Co is connected to the anode of the LED load, and the lower plate is connected to the drain of a charge-discharge MOS Q2 in the constant current control circuit 2; for discharging the LED load when the bus voltage Vin is less than the voltage on the output capacitor Co.

[0133] As shown in Figure 3 and Figure 4 , the constant current control circuit 2 is connected to the LED load and the output capacitor Co to realize constant current control of the LED load. The constant current control circuit 2 is the structure of embodiment one or embodiment two, which is not described here.

[0134] In summary, the application provides a constant current control circuit, a constant current driving system and a over-power protection method, comprising: a constant current control module connected to the negative electrode of an LED load, for performing constant current control on the LED load; a charging current control module connected to the negative electrode of the LED load and the lower plate of the output capacitor, for generating a corresponding compensation voltage based on the negative electrode voltage of the LED load, and adjusting the charging current of the output capacitor based on the compensation voltage; and a compensation voltage locking module connected to the charging current control module, for locking the compensation voltage when the constant current control circuit is powered off and restarted, so as to realize over-power protection of the charge-discharge MOS tube in the charging current control module. The constant current control circuit, the constant current driving system and the over-power protection method of the application meet the requirements of high PF, high efficiency and no flicker of ERP by using a loop compensation circuit; by means of a low-voltage locking or power-off detection module, the loop compensation circuit is triggered when the system is restarted after shutdown, the maximum conduction current of the charge-discharge MOS tube is limited, and the charge-discharge MOS tube is prevented from being broken down by over-power at the instant of starting up when being repeatedly switched on and off, so that the application range is wider and the reliability is higher; the compensation voltage locking module only works when the system is powered off, and does not affect the working state of the system under normal conditions. Therefore, the application effectively overcomes the various shortcomings in the prior art and has high industrial utilization value.

[0135] The above embodiments only exemplarily illustrate the principles and effects of the application, and are not used to limit the application. Any person skilled in the art can modify or change the above embodiments without departing from the spirit and scope of the application. Therefore, all equivalent modifications or changes completed by those skilled in the art without departing from the spirit and technical thought of the application should be covered by the claims of the application.

Claims

1. A constant current control circuit, characterized by comprising: The constant current control circuit at least comprises: a constant current control module connected to a negative electrode of an LED load for constant current control of the LED load; a charging current control module connected to the negative electrode of the LED load and a lower plate of an output capacitor, for generating a corresponding compensation voltage based on the negative electrode voltage of the LED load and adjusting the charging current of the output capacitor based on the compensation voltage; a compensation voltage locking module connected to the charging current control module, for locking the compensation voltage when the constant current control circuit is powered off and restarted, so as to realize over-power protection of a charge-discharge MOS tube in the charging current control module; wherein the compensation voltage locking module comprises a power-off judging unit and a locking unit; the power-off judging unit is connected to a sampling end of the constant current control module and the compensation voltage, detects whether the constant current control circuit is powered off based on a sampling voltage and the compensation voltage; the power-off judging unit comprises a first operational amplifier, a second operational amplifier and an AND gate; the input ends of the first operational amplifier are respectively connected to the sampling end of the constant current control module and a preset current, and output a detection signal of the current flowing through the LED load; the input ends of the second operational amplifier are respectively connected to the compensation voltage and a preset voltage, and output a detection signal of the compensation voltage; the input ends of the AND gate are respectively connected to the output ends of the first operational amplifier and the second operational amplifier, and output a power-off detection signal after AND operation; the locking unit is connected to the output end of the power-off judging unit, and locks the compensation voltage at a lower limit value of the compensation voltage when it is detected that the constant current control circuit is powered off.

2. The constant current control circuit according to claim 1, characterized by: the constant current control module comprises a constant current MOS tube, a first sampling unit and a first operational amplification unit; the drain of the constant current MOS tube is connected to the negative electrode of the LED load, and the source is grounded via the first sampling unit; the input ends of the first operational amplification unit are respectively connected to the source of the constant current MOS tube and a reference voltage, and the output end is connected to the gate of the constant current MOS tube, for controlling the current flowing through the LED load based on the difference between the sampling voltage and the reference voltage.

3. The constant current control circuit of claim 2, wherein: the constant current control module further comprises a dimming unit connected to the first operational amplification unit; the dimming unit receives a dimming control signal, adjusts the size of the reference voltage based on the dimming control signal, and thus realizes dimming control.

4. The constant current control circuit of claim 1, wherein: the charging current control module comprises a charge-discharge MOS tube, a second sampling unit, a detection unit, a compensation unit, a third sampling unit and a second operational amplification unit; the drain of the charge-discharge MOS tube is connected to the lower plate of the output capacitor, and the source is grounded via the second sampling unit; the detection unit is connected to the negative electrode of the LED load, judges the discharge voltage of the output capacitor based on the negative electrode voltage of the LED load, and obtains a control signal; the compensation unit is connected to the output end of the detection unit, and generates the compensation voltage based on the output signal of the detection unit; the third sampling unit is connected between a bus voltage and the source of the charge-discharge MOS tube, and outputs a sampling signal of the bus voltage; The input end of the second operational amplifier unit is connected to the output end of the compensation unit and the third sampling unit respectively, and the output end is connected to the gate of the charge-discharge MOS tube to realize the adjustment of the charging current of the output capacitor.

5. The constant current control circuit of claim 4, wherein: The detection unit is also connected to the gate of the constant current MOS tube in the constant current control module, and when the gate voltage of the constant current MOS tube is greater than a set value, the compensation voltage is rapidly increased.

6. A constant current driving system characterized by comprising: The constant current driving system at least includes: a rectifier circuit receiving an alternating current power supply, rectifying the alternating current power supply to obtain a bus voltage; an LED load, the positive electrode of which is connected to the bus voltage; an output capacitor, the upper plate of which is connected to the positive electrode of the LED load; and the constant current control circuit according to any one of claims 1-5, which is connected to the LED load and the output capacitor to realize the constant current control of the LED load.

7. A method of over-power protection, implemented based on the constant current control circuit according to any one of claims 1-5, characterized in that, The over-power protection method at least includes: generating a corresponding compensation voltage based on the negative electrode voltage of the LED load, and adjusting the charging current of the output capacitor based on the compensation voltage to control the LED load to realize no flicker when the output capacitor is discharged; locking the compensation voltage at a lower limit value of the compensation voltage when the constant current control circuit is powered off and restarted, limiting the instantaneous power of the charge-discharge MOS tube in the charging current control module, and protecting the charge-discharge MOS tube; wherein the current flowing through the LED load and the compensation voltage are detected, and when the current flowing through the LED load is less than a preset current and the compensation voltage is greater than a preset voltage, the compensation voltage is locked at a lower limit value of the compensation voltage.

8. The over-power protection method of claim 7, wherein: Before triggering the lock, the power consumption of the charge-discharge MOS tube satisfies: After triggering the lock, the power consumption of the charge-discharge MOS tube satisfies: wherein PQ2 is the power consumption of the charge-discharge MOS tube, Vin_max is the maximum value of the bus voltage, VCo is the voltage on the output capacitor, VComp is the compensation voltage, Rs is the sampling resistance value of the current flowing through the output capacitor, VComp_max is the maximum value of the compensation voltage, VLED is the on-voltage of the LED load, and VComp_low is the lower limit value of the compensation voltage.

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