CN114765913A

CN114765913A - Switching buck type LED constant current controller, control system and control method

Info

Publication number: CN114765913A
Application number: CN202011634032.9A
Authority: CN
Inventors: 谢飞; 尤勇; 卢圣晟; 李国成
Original assignee: CRM ICBG Wuxi Co Ltd
Current assignee: CRM ICBG Wuxi Co Ltd
Priority date: 2020-12-31
Filing date: 2020-12-31
Publication date: 2022-07-19
Anticipated expiration: 2040-12-31
Also published as: CN114765913B

Abstract

The invention provides a switch buck LED constant current controller, a control system and a control method, wherein the controller comprises: the device comprises a current control module, a clock oscillation module, a PWM logic control module, an output preceding stage driving module, a power supply detection module, a duty ratio comparison module and an overcurrent protection module; through the design of a current control module, a conducting signal is obtained by utilizing integration, ramp compensation and ramp voltage comparison, and the conducting signal and a clock signal with fixed frequency are subjected to logic processing to obtain a logic control signal, so that the conduction and the disconnection of a power switch tube are controlled, the output average current is consistent with the set current, and the constant current control is realized; the system short circuit detection and protection are realized through the power supply detection module, the duty ratio comparison module, the overcurrent protection module and the design, and the problems that the system short circuit cannot be detected by the controller, the output ripple is large, and the output average current and the set current have certain deviation are solved.

Description

Switch buck type LED constant current controller, control system and control method

Technical Field

The invention relates to the field of LED lighting, in particular to a switching step-down LED constant current controller, a control system and a control method.

Background

The switching buck type LED controller usually adopts a control mode of peak current detection, the output ripple is large, and a certain deviation exists between the output average current and the set current. Moreover, the protection circuit is single, and only aiming at overcurrent protection when large current is output, namely when the output current is larger than the overcurrent protection base, the system quickly turns off the whole circuit and enters a short-circuit hiccup mode; however, when the positive and negative levels of the LED string are short-circuited, that is, when the system is short-circuited, the output short-circuit current is not large enough to trigger the internal over-current comparator to flip, and at this time, the controller is still in the normal PWM switching period, and cannot enter the short-circuit hiccup mode. Meanwhile, in order to maintain output of large current, the large current flows through the peripheral freewheeling diode for a long time, so that the power consumption of the freewheeling diode is increased, the problems of overhigh local temperature rise, device loss and the like are caused, and the environment temperature condition of practical application is harsh.

Disclosure of Invention

In view of the above disadvantages, an object of the present invention is to provide a switching buck LED constant current controller, a control system and a control method, which are used to solve the problems that the switching buck LED constant current controller cannot detect a system short circuit and that a peak current detection method is adopted, so that an output ripple is large and an output average current has a certain deviation from a set current.

To achieve the above and other related objects, the present invention provides a switching buck LED constant current controller, including:

the current control module is used for carrying out integral processing on the output current sampling signal and the constant current reference signal to obtain a loop reference voltage, and carrying out ramp voltage comparison on the loop reference voltage and the output current sampling signal subjected to ramp compensation to obtain a conducting signal;

the clock oscillation module is used for generating a clock signal with fixed frequency;

the PWM logic control module is connected to the output ends of the current control module and the clock oscillation module and is used for carrying out logic processing on the conducting signal and the clock signal to obtain a logic control signal;

the output preceding-stage driving module is connected to the output end of the PWM logic control module and used for converting the logic control signal into a gate driving signal to be output so as to control the conduction and the disconnection of a power switching tube;

the power supply detection module is used for detecting the voltage of an input power supply;

the duty ratio comparison module is connected with the output ends of the power supply detection module and the PWM logic control module, and is used for generating a duty ratio signal according to the output of the power supply detection module and generating a system short circuit fault signal when the duty ratio of the logic control signal is smaller than the duty ratio of the duty ratio signal;

the overcurrent protection module is connected to the output end of the duty ratio comparison module and is used for generating a turn-off signal when the output current sampling signal is greater than an overcurrent protection reference or the system short-circuit fault signal is effective; after the turn-off signal is generated, the PWM logic control module receives the turn-off signal and generates a turn-off logic control signal according to the turn-off signal, and the output preceding-stage driving module converts the turn-off logic control signal into a turn-off gate driving signal so as to control the turn-off of the power switching tube.

Optionally, the current control module comprises:

the integration unit is used for performing integration processing on the output current sampling signal and the constant current reference signal to obtain the loop reference voltage;

the oblique wave compensation unit is used for performing oblique wave compensation on the output current sampling signal to obtain oblique wave compensation voltage;

and the ramp voltage comparison unit is connected with the output ends of the integration unit and the ramp compensation unit and is used for performing ramp voltage comparison on the loop reference voltage and the ramp compensation voltage to obtain the conduction signal.

Optionally, the current control module further comprises: the blanking unit is connected with the input ends of the integration unit and the ramp compensation unit or connected with the output end of the ramp compensation unit; when the blanking unit is connected to the input ends of the integrating unit and the ramp wave compensating unit, the blanking unit is used for blanking the output current sampling signal for a set time; and when the blanking unit is connected to the output end of the ramp compensation unit, the blanking unit is used for carrying out blanking processing on the ramp compensation voltage for a set time.

Optionally, the integration unit comprises: the constant current reference signal is accessed to the non-inverting input end of the operational amplifier, the output current sampling signal is accessed to the inverting input end of the operational amplifier through the first resistor, the first capacitor is connected between the inverting input end of the operational amplifier and the output end of the operational amplifier, and the output end of the operational amplifier is used as the output end of the integrating unit.

Optionally, the power detection module includes: the power supply detection module comprises (n +1) divider resistors and n hysteresis comparators, wherein the (n +1) divider resistors are connected between an input power supply and the ground in series to form n resistor divider ends, the non-inverting input ends of the n hysteresis comparators are connected with the n resistor divider ends in a one-to-one correspondence manner, the inverting input ends of the n hysteresis comparators are connected with detection reference voltages, and the output ends of the n hysteresis comparators are used as the output ends of the power supply detection module; wherein n is a positive integer greater than 1.

Optionally, the duty ratio comparing module includes:

the duty ratio signal generating unit is connected to the output end of the power supply detection module and is used for correspondingly generating a duty ratio signal according to the output of the power supply detection module;

and the time comparison unit is connected with the output ends of the duty ratio signal generation unit and the PWM logic control module, and is used for comparing the duty ratio of the duty ratio signal and the duty ratio of the logic control signal at least once and generating a system short circuit fault signal when the duty ratio of the logic control signal is smaller than the duty ratio of the duty ratio signal.

Optionally, the time comparing unit includes: the input end of the phase inverter is connected with the output end of the PWM logic control module, the output end of the phase inverter is connected with the data input end of the DFF trigger, the clock input end of the DFF trigger is connected with the output end of the duty ratio signal generating unit, the reset end of the DFF trigger is connected with the inverted signal of the turn-off signal, and the data output end of the DFF trigger is used as the output end of the time comparing unit.

Optionally, when the number of the DFF flip-flops is greater than 1, the data input end of the first DFF flip-flop is connected to the output end of the inverter, the data input ends of the remaining DFF flip-flops are connected to the data output end of the previous DFF flip-flop, the data output end of the last DFF flip-flop is used as the output end of the time comparison unit, the clock input ends of all the DFF flip-flops are connected to the output end of the duty ratio signal generation unit, and the clear ends of all the DFF flip-flops are connected to the inverted signal of the turn-off signal.

Optionally, the overcurrent protection module includes: the overcurrent protection device comprises an overcurrent comparator, a NOR gate and a delay unit, wherein the in-phase input end of the overcurrent comparator is connected with the output current sampling signal, the reverse phase input end of the overcurrent comparator is connected with the overcurrent protection reference, the output end of the overcurrent comparator is connected with one input end of the NOR gate, the other input end of the NOR gate is connected with the output end of the duty ratio comparison module, the output end of the NOR gate is connected with the input end of the delay unit, and the output end of the delay unit serves as the output end of the overcurrent protection module.

Optionally, the overcurrent protection module further includes: the input end of the counter is connected with a clock signal, the zero clearing end of the counter is connected with the output end of the RS trigger, the output end of the counter is connected with one input end of the NAND gate and one input end of the RS trigger, the other input end of the NAND gate is connected with the output end of the delay unit, and the output end of the NAND gate is connected with the other input end of the RS trigger; at this time, the output end of the RS flip-flop replaces the output end of the delay unit to serve as the output end of the over-current protection module.

Optionally, the switching buck LED constant current controller further includes: and the voltage stabilizer module is used for converting the voltage of the input power supply to generate a low-voltage power supply and supplying power to the switching step-down LED constant current controller.

The invention also provides a switch buck type LED constant current control system, which comprises: the switching step-down LED constant current controller, the LED lamp string, the output filter capacitor, the inductor, the freewheeling diode, the power switch tube and the sampling resistor are arranged in the circuit board; the output filter capacitor is connected in parallel to two ends of the LED lamp string, the positive electrode of the LED lamp string is connected to an input power supply and the cathode of the freewheeling diode, the negative electrode of the LED lamp string is connected to one end of the inductor, the other end of the inductor is connected to the drain electrode of the power switch tube and the anode of the freewheeling diode, the source electrode of the power switch tube is grounded through the sampling resistor, the source electrode of the power switch tube is further connected to the current detection sampling port of the switch buck-type LED constant current controller, and the grid electrode of the power switch tube is connected to the drive output port of the switch buck-type LED constant current controller.

The invention also provides a constant current control method of the switching buck LED, which comprises the following steps:

sampling the output current of a branch circuit where the LED lamp string is located, performing integral processing on an output current sampling signal and a constant current reference signal to obtain a loop reference voltage, and performing ramp voltage comparison on the loop reference voltage and the output current sampling signal subjected to ramp compensation to obtain a conducting signal;

logic processing is carried out on the conducting signal and a clock signal with fixed frequency to obtain a logic control signal, the logic control signal is converted into a gate driving signal to be output, so that the conducting and the cut-off of the power switch tube are controlled, the output average current is consistent with the set current, and therefore constant current control is achieved;

in the process of the constant-current control,

comparing an output current sampling signal with an overcurrent protection reference, and generating a turn-off signal when the output current sampling signal is greater than the overcurrent protection reference so as to control the power switch tube to be turned off, thereby realizing overcurrent protection when a large current is output;

detecting the voltage of an input power supply, and correspondingly generating a duty ratio signal according to the detected voltage; and comparing the duty ratio of the duty ratio signal with that of the logic control signal, generating a system short-circuit fault signal when the duty ratio of the logic control signal is smaller than that of the duty ratio signal, and generating a turn-off signal to control the power switch tube to be turned off so as to realize overcurrent protection when the system short circuit occurs.

As described above, according to the switching buck type LED constant current controller, the control system and the control method of the present invention, by designing the current control module, the output average current is completely consistent with the set current, and the output ripple is small; meanwhile, through the design of the power supply detection module, the duty ratio comparison module and the overcurrent protection module, the overcurrent protection of the system short circuit is realized, so that the electric leakage on the input power supply is reduced, the input power consumption is reduced to the greatest extent, and the problems of overhigh local temperature rise, device loss and the like caused by the fact that a large current flows through a freewheeling diode for a long time are avoided.

Drawings

Fig. 1 shows a schematic circuit structure diagram of an exemplary switching buck-type LED constant current control system.

Fig. 2 is a schematic circuit diagram of an exemplary switching buck LED constant current controller.

Fig. 3 is a schematic circuit diagram of an overcurrent protection module in an exemplary switching buck LED constant current controller.

Fig. 4 shows a timing diagram of relevant signals when an overcurrent is encountered in the exemplary switching buck LED constant current control system.

Fig. 5 is a timing diagram showing relevant signals when a system short circuit occurs in the exemplary switching buck-type LED constant current control system.

Fig. 6 is a schematic circuit diagram of a switching buck LED constant current controller according to an embodiment.

Fig. 7 is a schematic circuit diagram of a current control module in the switching buck LED constant current controller according to an embodiment.

Fig. 8 is a timing diagram of signals related to the constant current controller of the switching buck LED during constant current control according to an embodiment.

Fig. 9 is a schematic diagram of a current path of the switching buck LED constant current control system when the power switch tube is turned on.

Fig. 10 is a schematic diagram of a current path of the switching step-down LED constant current control system when the power switch tube is turned off.

Fig. 11 is a schematic circuit diagram of a power detection module in the switching buck LED constant current controller according to an embodiment.

Fig. 12 is a schematic circuit diagram of a duty ratio comparison module in the switching buck LED constant current controller according to an embodiment.

Fig. 13 is a schematic circuit diagram of an overcurrent protection module in the switching buck LED constant current controller according to an embodiment.

Fig. 14 is a timing diagram of signals related to the switching buck LED constant current controller during a system short circuit in an embodiment.

Fig. 15 is a schematic circuit diagram of a switching buck LED constant current control system according to an embodiment.

Description of the element reference

1 exemplary switching buck LED constant current controller

11 peak current comparison module

12 clock oscillation module

13 PWM logic control module

14 output preceding stage driving module

15 overcurrent protection module

151 overcurrent comparator

152 delay unit

153 counter

154 NAND gate

155 RS trigger

2-switch buck LED constant current controller

21 current control module

211 integration unit

212 ramp compensation unit

213 ramp voltage comparing unit

214 blanking unit

22 clock oscillation module

23 PWM logic control module

24 output pre-stage driving module

25 power supply detection module

26 duty ratio comparison module

261 duty ratio signal generating unit

262 time comparison unit

27 overcurrent protection module

271 overcurrent comparator

272 nor gate

273 delay unit

274 counter

275 nand gate

276 RS trigger

28 voltage stabilizer module

Detailed Description

The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention.

Please refer to fig. 1 to 15. It should be noted that the drawings provided in the present embodiment are only for schematically illustrating the basic idea of the present invention, and although the drawings only show the components related to the present invention and are not drawn according to the number, shape and size of the components in actual implementation, the form, quantity and proportion of each component in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.

An exemplary switching buck LED constant current control system includes: the switching buck type LED constant current controller 1, a power switching tube Q, a sampling resistor Rsense, a freewheeling diode D, an inductor L, LED lamp string, and an output filter capacitor Cout (the specific connection relationship is shown in fig. 1, in the figure, the LED lamp string only includes two LEDs as an example), wherein the switching buck type LED constant current controller 1 includes: a peak current comparison module 11, a clock oscillation module 12, a PWM logic control module 13, an output pre-driver module 14, and an overcurrent protection module 15 (the specific connection relationship is shown in fig. 2).

The switching buck type LED constant current controller 1 is powered by a low-voltage power supply VDD, after the power is supplied, an output current sampling signal (namely, a voltage generated by the output current ILED through a sampling resistor Rsense) enters a peak current comparison module 11 through a current detection sampling port CS, the peak current comparison module 11 generates a conducting signal Ton when the output current sampling signal is greater than a peak reference signal, the conducting signal Ton and a clock signal CLK generated by a clock oscillation module 12 are processed by a PWM logic control module 13 to generate a logic control signal PREDRV, and then a gate driving signal DRV is generated by an output pre-stage driving module 14 to control the conduction and the disconnection of a power switching tube Q, so that the current (mainly controlling the current peak value and ripple) flowing through an LED lamp string is controlled; meanwhile, the output current sampling signal enters the overcurrent protection module 15 through the current detection sampling port CS, the overcurrent protection module 15 generates a shutdown signal STB (generally, the overcurrent protection reference is set to be 2 to 3 times of the normal working current, and if the normal working current is 200mV, the overcurrent protection reference is set to be 550mV) when the output current sampling signal exceeds the overcurrent protection reference VOCP, and the shutdown signal STB generates a shutdown gate driving signal to shut down the power switching tube Q to reduce the input power consumption after passing through the PWM logic control module 13 and the output preceding stage driving module 14.

The exemplary overcurrent protection module 15 includes: when the output generates a large current due to a similar inductance short circuit, the output current sampling signal CS and the over-current protection reference VOCP are compared by the over-current comparator 151 to output a high-level over-current protection signal OCPOUT, which triggers the counter 153 to operate after a certain time delay (e.g., 200ns for filtering glitch noise), the over-current protection module 15 generates a high-level shutdown signal STB within the hiccup delay signal (e.g., 1ms) counted by the counter 153, the shutdown signal STB is initialized to a low level, the system is restarted, and the next over-current protection detection is performed (the timing sequence of each signal is shown in fig. 4).

When the positive and negative electrodes of the LED lamp string are short-circuited, namely a system short circuit occurs, the output current is not so large, the voltage of the current detection sampling port CS is not higher than the over-current protection reference VOCP, so that over-current protection cannot be triggered, and the switching step-down LED constant current controller 1 is still in a normal PWM switching period; the inductor current IL is already larger than the current Ipref corresponding to the peak reference signal, but is still smaller than the current IOCP corresponding to the overcurrent protection reference, and the high level of the logic control signal PREDRV is the minimum on-time Ton _ min, so that the freewheeling diode D flows a large current for a long time (the timing of the signals is shown in fig. 5).

It can be seen that the overcurrent protection module 15 has the advantages that: when a large current is generated in output, the whole circuit is quickly turned off in a short circuit hiccup mode to enter a standby mode, so that the current on an input power Vin is effectively reduced, and the method can be used for detecting two faults of overlarge external set current or short circuit of an inductor; the disadvantages are: when the positive and negative electrodes of the LED light string are short-circuited, that is, a system short-circuited, the over-current protection module 15 cannot detect a fault and respond, thereby causing unnecessary leakage of the input power, and meanwhile, in order to maintain the output of a large current, a large current (see ID in fig. 5) flows through the freewheeling diode for a long time, which causes problems of excessive local temperature rise, device loss, and the like.

As shown in fig. 6, the present embodiment provides a switching buck LED constant current controller, where the switching buck LED constant current controller 2 includes:

the current control module 21 is configured to perform integration processing on the output current sampling signal CS and the constant current reference signal Vref1 to obtain a loop reference voltage VLOOP, and perform ramp voltage comparison on the loop reference voltage VLOOP and the output current sampling signal CS subjected to ramp compensation to obtain a conduction signal Ton;

a CLOCK oscillation module 22, configured to generate a CLOCK signal CLOCK with a fixed frequency;

a PWM logic control module 23, connected to the output ends of the current control module 21 and the CLOCK oscillation module 22, and configured to perform logic processing on the conducting signal Ton and the CLOCK signal CLOCK to obtain a logic control signal PREDRV;

an output pre-driving module 24, connected to the output end of the PWM logic control module 23, for converting the logic control signal PREDRV into a gate driving signal output DRV to control the on/off of the power switching transistor;

a power detection module 25 for detecting the voltage of the input power Vin;

a duty ratio comparison module 26, connected to the output ends of the power detection module 25 and the PWM logic control module 23, for generating a duty ratio signal TD according to the output of the power detection module 25, and generating a system short circuit fault signal SCP when the duty ratio of the logic control signal PREDRV is smaller than the duty ratio of the duty ratio signal TD;

an overcurrent protection module 27, connected to the output end of the duty ratio comparison module 26, and configured to generate a shutdown signal STB when the output current sampling signal CS is greater than the overcurrent protection reference VOCP or the system short-circuit fault signal SCP is valid; after the shutdown signal STB is generated, the PWM logic control module 23 receives the shutdown signal STB and generates a shutdown logic control signal PREDRV according to the shutdown signal STB, and the output pre-stage driving module 24 converts the shutdown logic control signal PREDRV into a shutdown gate driving signal DRV to control the power switching tube to be turned off.

As an example, as shown in fig. 6, the switching buck LED constant current controller 2 further includes: and the voltage stabilizer module 28 is used for performing voltage conversion on the input power Vin to generate a low-voltage power supply VDD and supplying power to the switching buck type LED constant current controller 2. In this example, the purpose of reducing the number of chip ports is achieved by embedding the voltage regulator module 28 in the switching buck LED constant current controller 2, that is, the number of chip ports is reduced from original 5 (an input power Vin port, a low voltage power VDD port, a current detection sampling port CS, a driving output port DRV, and a ground reference port GND) to 4 (an input power Vin port, a current detection sampling port CS, a driving output port DRV, and a ground reference port GND).

As an example, as shown in fig. 7, the current control module 21 includes:

the integrating unit 211 is configured to integrate the output current sampling signal CS and the constant current reference signal Vref1 to obtain the loop reference voltage VLOOP;

a ramp compensation unit 212, configured to perform ramp compensation on the output current sampling signal CS to obtain a ramp compensation voltage CS _ comp;

the ramp voltage comparing unit 213 is connected to the output ends of the integrating unit 211 and the ramp compensating unit 212, and configured to perform ramp voltage comparison on the loop reference voltage VLOOP and the ramp compensating voltage CS _ comp to obtain the on signal Ton.

In fact, the current control module 21, the PWM logic control module 23 and the output pre-driver module 24 together form a closed loop system, and this example uses the current control module 21 to perform integration, ramp compensation and ramp voltage comparison in the closed loop system to realize closed loop current control, so as to ensure that the output average current is consistent with the set current; the timing of each signal in the constant current control is shown in fig. 8.

Specifically, as shown in fig. 7, the integrating unit 211 includes: the constant current reference circuit comprises a first resistor R1, a first capacitor C1 and an operational amplifier OP, wherein the constant current reference signal Vref1 is connected to the non-inverting input end of the operational amplifier OP, the output current sampling signal CS is connected to the inverting input end of the operational amplifier OP through the first resistor R1, the first capacitor C1 is connected between the inverting input end of the operational amplifier OP and the output end of the operational amplifier OP, and the output end of the operational amplifier OP is used as the output end of the integrating unit 211. In this example, the integration unit 211 is composed of an operational amplifier OP, and a first resistor R1 and a first capacitor C1 connected in series to an inverting input terminal of the operational amplifier OP, and the integration unit obtains the loop reference voltage VLOOP by using an error between the output current sampling signal CS and the constant current reference signal Vref 1; the loop reference voltage VLOOP satisfies the following equation:

wherein, R1 is the resistance of the first resistor, C1 is the capacitance of the first capacitor, Vref1 is the voltage of the constant current reference signal, and Vcs is the voltage of the output current sampling signal.

Specifically, the ramp compensation unit 212 is any one of the existing circuits capable of performing voltage ramp compensation, and the specific circuit configuration thereof is not limited in this example. In this example, the slope compensation unit 212 is designed to ensure the stability of the output inductor current when the duty ratio is greater than 50%.

Specifically, as shown in fig. 7, the ramp voltage comparing unit 213 is implemented by a ramp voltage comparator, a non-inverting input terminal of which is connected to the output terminal of the ramp compensating unit 212, an inverting input terminal of which is connected to the output terminal of the integrating unit 211, and an output terminal of which is used as the output terminal of the current control module 21. In this example, the ramp voltage comparator compares the loop reference voltage VLOOP with the ramp compensation voltage CS _ complete, and generates the on-time Ton when the ramp compensation voltage CS _ complete is greater than the loop reference voltage VLOOP.

Specifically, the current control module 21 further includes: a blanking unit 214, connected to the input ends of the integrating unit 211 and the ramp compensation unit 212, and configured to perform blanking processing on the output current sample signal CS for a set time, so as to prevent a switching transient glitch of the output current sample signal CS caused at an instant when the power switch is turned on, thereby avoiding an integration error caused by the switching transient glitch, and further ensuring consistency between an output average current and a set current (specifically, as shown by a dashed-line frame in fig. 7). Of course, the blanking unit 214 may also be disposed at the output end of the ramp compensation unit 212, and is used for performing a blanking process for a set time on the ramp compensation voltage CS _ complete (specifically, as shown in the solid-line box portion in fig. 7). It should be noted that the design position of the blanking unit 214 should be adjusted according to the actual application, and in the actual application, if the glitch of the switching instant of the output current sampling signal caused by the instant when the power switch is turned on is large, the blanking unit 214 is disposed at the input ends of the integrating unit 211 and the ramp compensation unit 212; otherwise, the blanking unit 214 is set at the output end of the ramp compensation unit 212; furthermore, the blanking time of the blanking unit 214 should also be set according to the specific application. Optionally, in this example, the blanking unit 214 is disposed at an output end of the ramp compensation unit 212.

The clock oscillation module 22 is any conventional circuit capable of generating a clock signal with a fixed frequency, and the specific circuit configuration is not limited in this example. In fact, the CLOCK oscillation module 22 generates a CLOCK signal CLOCK with a fixed frequency to ensure the input power voltage Vin and the output voltage (i.e. the voltage drop V across the LED string) in this example_LED) Is varied with the duty cycle D.

Specifically, in the switching step-down LED constant current control system, the current paths of the power switching tube Q are different when the power switching tube Q is turned on and off;

as shown in fig. 9, the Q-switch of the power switch tubeDuring the on period, the increase amount of the inductor current satisfies the following formula:

wherein, Δ IL (+) is the increment of the inductive current, L is the inductance value, Vin is the input power voltage, VLED is the output voltage, Ton is the on-time of the power switch tube;

as shown in fig. 10, when the power switch Q is turned off, the decrease amount of the inductor current satisfies the following formula:

wherein, Δ IL (-) is the reduction of the inductive current, L is the inductance, VLED is the output voltage, Toff is the turn-off time of the power switch tube;

under the steady state condition, the increment Δ IL (+) of the inductor current in the on state of the power switch tube Q is equal to the decrement Δ IL (-) of the inductor current in the off state, and according to the volt-second balance principle, the two equations can be obtained:

VLED is an output voltage, Vin is an input power voltage, Ton is an on-time of the power switch tube, Toff is an off-time of the power switch tube, Ts is a switching period, and D is a duty cycle.

It can be seen that when the frequency of the clock signal is fixed, the ratio between the output voltage VLED and the input power voltage Vin varies with the duty ratio D, so that the output voltage VLED is within an adjustable range, and the minimum adjustable output voltages of different input power voltages are different. When the positive and negative electrodes of the LED light string are short-circuited, that is, when a system short circuit occurs, there are an inductor L and a parasitic resistor of the power switch tube Q, LED in the loop of the system, and these series resistors inevitably generate a certain fixed voltage through the output current, for example, a voltage drop of 1.2V is generated when the total parasitic impedance of 400m Ω passes through the output current of 3A, if the input power voltage is 12V, the duty ratio is 1.2/12 ═ 10%, and for the input power voltage of 60V, the duty ratio becomes 2%; that is, when the input power voltage is 12V, if the duty ratio is less than 10%, it means that a system short circuit occurs, and when the input power voltage is 60V, it means that the system short circuit occurs when the duty ratio is less than 2%; therefore, a theoretical basis is provided for the system short-circuit fault detection by the power detection module 25 and the duty ratio comparison module 26 in the embodiment.

As an example, as shown in fig. 11, the power detection module 25 includes: (n +1) divider resistors and n hysteresis comparators, wherein the (n +1) divider resistors are connected in series between an input power Vin and the ground to form n resistor voltage dividing ends, non-inverting input ends of the n hysteresis comparators are connected with the n resistor voltage dividing ends in a one-to-one correspondence manner, inverting input ends of the n hysteresis comparators are all connected with a detection reference voltage, and output ends of the n hysteresis comparators serve as output ends of the power detection module 25; wherein n is a positive integer greater than 1. Specifically, the resistance values of the (n +1) voltage dividing resistors are equal.

In practical application, the size of n needs to be set by integrating detection precision and circuit complexity; for convenience of illustration, in this example, n is equal to 5, that is, the power detection module 25 in this example includes 6 voltage dividing resistors (Rd1-Rd6) and 5 hysteresis comparators (Comp1-Comp5), where the 5 hysteresis comparators compare the voltage at the voltage dividing ends of the 5 resistors with the detection reference voltage Vref2 respectively to determine a value range of the input power voltage Vin according to comparison results of the 5 hysteresis comparators, so as to obtain a setting voltage value corresponding to the value range. If the setting voltages corresponding to the 5 hysteretic comparators (Comp1-Comp5) are respectively 12V, 24V, 36V, 48V and 60V, when the outputs of the 5 hysteretic comparators (Comp1-Comp5) are all low, it is indicated that the value of the input power voltage Vin is lower than 12V, and since the voltage is generally not lower than 8V, it is determined that the value of the input power voltage Vin is between 8V and 12V, and at this time, the power detection module outputs the corresponding setting voltage value of 8V; when the output of the hysteresis comparator Comp1 is at a high level and the outputs of the remaining 4 hysteresis comparators (Comp2-Comp5) are all at a low level, it indicates that the value of the input power voltage Vin is between 12V and 24V, and the power detection module outputs a corresponding set voltage value of 12V; when the outputs of the hysteresis comparators Comp1 and Comp2 are at high level and the outputs of the remaining 3 hysteresis comparators (Comp3-Comp5) are at low level, it indicates that the value of the input power voltage Vin is between 24V-36V, and the power detection module outputs a corresponding set voltage value of 24V; when the outputs of the hysteresis comparators Comp1-Comp3 are all at high level, and the outputs of the remaining 2 hysteresis comparators (Comp4-Comp5) are all at low level, it indicates that the value of the input power voltage Vin is between 36V-48V, and the corresponding set voltage value output by the power detection module is 36V at this time; when the outputs of the hysteresis comparators Comp1-Comp4 are all at high level and the output of the hysteresis comparator Comp5 is at low level, it indicates that the value of the input power voltage Vin is between 48V-60V, and the power detection module outputs a corresponding set voltage value of 48V; when the outputs of the 5 hysteresis comparators are all at a high level, it indicates that the value of the input power voltage Vin is higher than 60V, and at this time, the power detection module outputs a corresponding set voltage value of 60V (see table 1). It should be noted that the setting voltage corresponding to the hysteresis comparator may be set according to the magnitude of the input power voltage and the number of the hysteresis comparators in practical application, which is not limited in this example.

As an example, as shown in fig. 12, the duty ratio comparison module 26 includes:

the duty ratio signal generating unit 261 is connected to the output end of the power detection module 25, and is configured to generate a duty ratio signal TD according to the output of the power detection module 25;

and a time comparing unit 262, connected to the output ends of the duty ratio signal generating unit 261 and the PWM logic control module 23, for comparing the duty ratio of the duty ratio signal TD and the logic control signal PREDRV at least once, and generating a system short-circuit fault signal SCP when the duty ratio of the logic control signal PREDRV is smaller than the duty ratio of the duty ratio signal TD.

Specifically, if the duty ratio TD of the duty ratio signal is equal to the system short circuit setting voltage/the power detection module outputs the corresponding setting voltage value, for example, the system short circuit setting voltage is 1.2V, and if the power detection module outputs the corresponding setting voltage value of 8V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is equal to 1.2V/8V, which is equal to 15%, that is, D0 is equal to 15%; if the power detection module outputs a corresponding set voltage value of 12V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is 1.2V/12V-10%, that is, D1 is 10%; if the power detection module outputs a corresponding set voltage value of 24V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is equal to 1.2V/24V, which is equal to 5%, that is, D2 is equal to 5%; if the power detection module outputs a corresponding set voltage value of 36V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is 1.2V/36V, which is 3.3%, that is, D3 is 3.3%; if the power detection module outputs a corresponding set voltage value of 48V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is 1.2V/48V-2.5%, that is, D4 is 2.5%; if the power detection module outputs the corresponding set voltage value of 60V, the duty ratio TD of the duty ratio signal generated by the duty ratio signal generation unit 261 is 1.2V/60V is 2%, that is, D5 is 2% (see table 1). It should be noted that the system short circuit setting voltage must be strictly set according to the actual application environment, and a certain margin is left to avoid that the system short circuit is mistaken to perform overcurrent protection during normal operation. Optionally, the duty ratio signal generating unit 261 may be implemented by using a multi-channel gating switch and a plurality of memories, for example, a system short circuit setting voltage and a setting voltage corresponding to each hysteresis comparator in the power detection module are preset according to specific applications, so as to obtain a plurality of duty ratio signals, each duty ratio signal is pre-stored in the corresponding memory, and then the gating switch is controlled by the output of the power detection module 25, so as to output the corresponding duty ratio signal from the corresponding memory; of course, the duty ratio signal generating unit 261 may also directly calculate the duty ratio according to the output of the power detection module, so as to generate the corresponding duty ratio signal.

TABLE 1

Specifically, as shown in fig. 12, the time comparing unit 262 includes: an input end of the inverter is connected to an output end of the PWM logic control module 23, an output end of the inverter is connected to a data input end of the DFF flip-flop, a clock input end of the DFF flip-flop is connected to an output end of the duty ratio signal generation unit 261, a clear end of the DFF flip-flop is connected to an inverted signal of the off signal STB, and a data output end of the DFF flip-flop is used as an output end of the time comparison unit 262.

More specifically, in order to avoid misjudgment, the number of DFF flip-flops in the time comparing unit 262 in this example is greater than 1; when the number of the DFF flip-flops is greater than 1, the data input end of the first DFF flip-flop is connected to the output end of the inverter, the data input ends of the other DFF flip-flops are connected to the data output end of the previous DFF flip-flop, the data output end of the last DFF flip-flop is used as the output end of the time comparison unit, the clock input ends of all the DFF flip-flops are connected to the output end of the duty ratio signal generation unit 261, and the zero clearing ends of all the DFF flip-flops are connected to the inverted signal of the off signal STB. Optionally, in this example, the number of DFF flip-flops is 3. It should be noted that when the number of DFF flip-flops is greater than 1, it is necessary to ensure that the duty cycle of the logic control signal PREDRV is smaller than the duty cycle of the duty cycle signal TD at each comparison, so as to enable the system short fault signal SCP.

As an example, as shown in fig. 13, the overcurrent protection module 27 includes: an overcurrent comparator 271, a nor gate 272, and a delay unit 273, wherein a non-inverting input terminal of the overcurrent comparator 271 is connected to the output current sampling signal CS, an inverting input terminal of the overcurrent comparator 271 is connected to the overcurrent protection reference VOCP, an output terminal of the overcurrent comparator 271 is connected to an input terminal of the nor gate 272, another input terminal of the nor gate 272 is connected to an output terminal of the duty ratio comparison module 26, an output terminal of the nor gate 272 is connected to an input terminal of the delay unit 273, and an output terminal of the delay unit 273 serves as an output terminal of the overcurrent protection module 27. In this example, the over-current comparator 271 compares the output current sampling signal CS with the over-current protection reference VOCP, and generates an over-current protection signal OCPOUT when the output current sampling signal CS is greater than the over-current protection reference VOCP; the nor gate 272 performs a logical nor operation on the over-current protection signal OCPOUT and the system short-circuit fault signal SCP, and then performs a logical nor operation through the delay unit 273, so that the over-current protection module 27 can generate the shutdown signal STB when the over-current protection signal OCPOUT or the system short-circuit fault signal SCP is valid.

As an example, as shown in fig. 13, the overcurrent protection module 27 further includes: the input end of the counter 274 is connected to a CLOCK signal CLOCK, the clear end of the counter 274 is connected to the output end of the RS flip-flop 276, the output end of the counter 274 is connected to one input end of the nand gate 275 and one input end of the RS flip-flop 276, the other input end of the nand gate 275 is connected to the output end of the delay unit 273, and the output end of the nand gate 275 is connected to the other input end of the RS flip-flop 276; at this time, the output terminal of the RS flip-flop 276 replaces the output terminal of the delay unit 273 to serve as the output terminal of the over-current protection module 27. Specifically, as shown in fig. 13, the counter 274 is formed by a plurality of divide-by-two dividers, wherein each divide-by-two divider is implemented by a DFF flip-flop; of course, the number of the two frequency dividers is related to the set hiccup delay time, in practical application, the number of the two frequency dividers can be set according to the hiccup delay time, and the hiccup delay time can be set according to the actual power consumption requirement. In the present example, the shutdown signal STB is used to trigger the counter 274 to operate, and thus the system enters a short-circuit hiccup mode, so as to implement overcurrent protection of the system; and after hiccup delay time is over, the shutdown signal STB is invalid, and the system is restarted, gets into next overcurrent detection, has avoided the process of power-on again.

Fig. 14 is a timing chart of signals when a system short-circuit fault occurs, and it can be seen from the diagram that: when the duty ratio of the logic control signal PREDRV is continuously lower than the duty ratio of the duty ratio signal TD for three times, the system short-circuit fault signal SCP is effective, the turn-off signal STB becomes high level, and the system enters overcurrent protection; after the hiccup delay time, the initialization of the shutdown signal STB becomes low level, and the system is restarted and enters the next overcurrent protection detection.

Correspondingly, as shown in fig. 15, the present embodiment further provides a switching buck-type LED constant current control system, where the switching buck-type LED constant current control system includes: the switching step-down type LED constant current controller 2 comprises an LED lamp string, an output filter capacitor Cout, an inductor L, a freewheeling diode D, a power switch tube Q and a sampling resistor Rsense; the output filter capacitor Cout is connected in parallel to two ends of the LED lamp string, the positive electrode of the LED lamp string is connected to the input power Vin and the cathode of the freewheeling diode D, the negative electrode of the LED lamp string is connected to one end of the inductor L, the other end of the inductor L is connected to the drain of the power switch tube Q and the anode of the freewheeling diode D, the source of the power switch tube Q is grounded via the sampling resistor Rsense, the source of the power switch tube Q is further connected to the current detection sampling port CS of the switch buck-type LED constant current controller 2, and the gate of the power switch tube Q is connected to the drive output port DRV of the switch buck-type LED constant current controller 2.

Correspondingly, the embodiment also provides a constant current control method for the switching buck type LED, and the constant current control method comprises the following steps:

in the process of the constant-current control,

comparing an output current sampling signal with an overcurrent protection reference, and generating a turn-off signal when the output current sampling signal is greater than the overcurrent protection reference so as to control the power switch tube to be turned off and realize overcurrent protection when a large current is output;

In summary, according to the switching step-down LED constant current controller, the control system and the control method of the present invention, through the design of the current control module, the output average current is completely consistent with the set current, and the output ripple is small; meanwhile, through the design of the power supply detection module, the duty ratio comparison module and the overcurrent protection module, the overcurrent protection of the system short circuit is realized, so that the electric leakage on the input power supply is reduced, the input power consumption is reduced to the greatest extent, and the problems of overhigh local temperature rise, device loss and the like caused by the fact that a large current flows through a freewheeling diode for a long time are avoided. Therefore, the present invention effectively overcomes the aforementioned disadvantages and is highly industrially applicable.

The foregoing embodiments are merely illustrative of the principles and utilities of the present invention and are not intended to limit the invention. Those skilled in the art can modify or change the above-described embodiments without departing from the spirit and scope of the present invention. Accordingly, it is intended that all equivalent modifications or changes which can be made by those skilled in the art without departing from the spirit and technical spirit of the present invention be covered by the claims of the present invention.

Claims

1. The switch buck LED constant current controller is characterized by comprising:

the PWM logic control module is connected to the output ends of the current control module and the clock oscillation module and is used for performing logic processing on the conduction signal and the clock signal to obtain a logic control signal;

the overcurrent protection module is connected to the output end of the duty ratio comparison module and is used for generating a turn-off signal when the output current sampling signal is greater than an overcurrent protection reference or the system short-circuit fault signal is effective; after the turn-off signal is generated, the PWM logic control module receives the turn-off signal and generates a turn-off logic control signal according to the turn-off signal, and the output preceding-stage drive module converts the turn-off logic control signal into a turn-off gate drive signal so as to control the turn-off of the power switching tube.

2. The switched buck LED constant current controller according to claim 1, wherein the current control module comprises:

3. The switching buck LED constant current controller according to claim 2, wherein the current control module further comprises: the blanking unit is connected with the input ends of the integration unit and the ramp compensation unit or connected with the output end of the ramp compensation unit; when the blanking unit is connected to the input ends of the integrating unit and the ramp wave compensating unit, the blanking unit is used for carrying out blanking processing on the output current sampling signal for set time; and when the blanking unit is connected to the output end of the ramp compensation unit, the blanking unit is used for carrying out blanking processing on the ramp compensation voltage for a set time.

4. The switched buck LED constant current controller of claim 2, wherein the integration unit comprises: the non-inverting input end of the operational amplifier is connected with the constant current reference signal, the inverting input end of the operational amplifier is connected with the output current sampling signal through the first resistor, the first capacitor is connected between the inverting input end of the operational amplifier and the output end of the operational amplifier, and the output end of the operational amplifier serves as the output end of the integrating unit.

5. The switching buck LED constant current controller according to claim 1, wherein the power detection module includes: the power supply detection module comprises (n +1) divider resistors and n hysteresis comparators, wherein the (n +1) divider resistors are connected between an input power supply and the ground in series to form n resistor divider ends, the non-inverting input ends of the n hysteresis comparators are connected with the n resistor divider ends in a one-to-one correspondence manner, the inverting input ends of the n hysteresis comparators are connected with detection reference voltages, and the output ends of the n hysteresis comparators are used as the output ends of the power supply detection module; wherein n is a positive integer greater than 1.

6. The switched buck LED constant current controller of claim 1, wherein the duty cycle comparison module comprises:

7. The switching buck LED constant current controller according to claim 6, wherein the time comparison unit includes: the input end of the inverter is connected with the output end of the PWM logic control module, the output end of the inverter is connected with the data input end of the DFF trigger, the clock input end of the DFF trigger is connected with the output end of the duty ratio signal generating unit, the zero clearing end of the DFF trigger is connected with the inverted signal of the turn-off signal, and the data output end of the DFF trigger is used as the output end of the time comparing unit.

8. The switching buck-type LED constant current controller according to claim 7, wherein when the number of the DFF flip-flops is greater than 1, a data input terminal of a first DFF flip-flop is connected to an output terminal of the inverter, data input terminals of the remaining DFF flip-flops are connected to a data output terminal of a previous DFF flip-flop, a data output terminal of a last DFF flip-flop is used as an output terminal of the time comparison unit, clock input terminals of all the DFF flip-flops are connected to an output terminal of the duty ratio signal generation unit, and clear terminals of all the DFF flip-flops are connected to an inverted signal of the off signal.

9. The switching buck-type LED constant current controller according to claim 1, wherein the over-current protection module comprises: the overcurrent protection device comprises an overcurrent comparator, a NOR gate and a delay unit, wherein the in-phase input end of the overcurrent comparator is connected with the output current sampling signal, the reverse phase input end of the overcurrent comparator is connected with the overcurrent protection reference, the output end of the overcurrent comparator is connected with one input end of the NOR gate, the other input end of the NOR gate is connected with the output end of the duty ratio comparison module, the output end of the NOR gate is connected with the input end of the delay unit, and the output end of the delay unit serves as the output end of the overcurrent protection module.

10. The switching buck LED constant current controller according to claim 9, wherein the over-current protection module further comprises: the input end of the counter is connected with a clock signal, the zero clearing end of the counter is connected with the output end of the RS trigger, the output end of the counter is connected with one input end of the NAND gate and one input end of the RS trigger, the other input end of the NAND gate is connected with the output end of the delay unit, and the output end of the NAND gate is connected with the other input end of the RS trigger; at this time, the output end of the RS flip-flop replaces the output end of the delay unit to serve as the output end of the over-current protection module.

11. The switching buck LED constant current controller according to any one of claims 1 to 10, further comprising: and the voltage stabilizer module is used for converting the voltage of the input power supply to generate a low-voltage power supply and supplying power to the switch buck LED constant current controller.

12. The switch buck LED constant current control system is characterized by comprising: the switched buck LED constant current controller as claimed in any one of claims 1 to 11, an LED string, an output filter capacitor, an inductor, a freewheeling diode, a power switch tube and a sampling resistor; the output filter capacitor is connected in parallel to two ends of the LED lamp string, the positive electrode of the LED lamp string is connected to an input power supply and the cathode of the freewheeling diode, the negative electrode of the LED lamp string is connected to one end of the inductor, the other end of the inductor is connected to the drain electrode of the power switch tube and the anode of the freewheeling diode, the source electrode of the power switch tube is grounded through the sampling resistor, the source electrode of the power switch tube is further connected to the current detection sampling port of the switch buck-type LED constant current controller, and the grid electrode of the power switch tube is connected to the drive output port of the switch buck-type LED constant current controller.

13. A constant current control method for a switching buck LED is characterized by comprising the following steps:

in the process of the constant-current control,