CN113518491A

CN113518491A - LED constant current drive circuit and controller

Info

Publication number: CN113518491A
Application number: CN202110387804.1A
Authority: CN
Inventors: 牟在鑫
Original assignee: MAXIC TECHNOLOGY (BEIJING) CO LTD
Current assignee: MAXIC TECHNOLOGY (BEIJING) CO LTD
Priority date: 2021-04-09
Filing date: 2021-04-09
Publication date: 2021-10-19

Abstract

The invention provides an LED constant current drive circuit and a controller, wherein the LED constant current drive circuit comprises: the LED driving circuit comprises a first switch circuit, a constant-current detection circuit, a control circuit and a second switch circuit, wherein the first end of the first switch circuit is externally connected with a PWM driving signal, and the second end of the first switch circuit is connected with a target LED load; the input end of the constant-pass detection circuit is respectively connected with the first end of the first switch circuit and the first input end of the control circuit, and the output end of the constant-pass detection circuit is connected with the second input end of the control circuit; the output end of the control circuit is connected with the first end of the second switch circuit, the second end of the second switch circuit is connected with the target LED load, and the control circuit is used for generating a control signal according to the detection result and the PWM driving signal so as to control the working state of the second switch circuit. By implementing the invention, the second switch circuit is controlled to be switched off, the equivalent impedance of the circuit is increased, the LED current is reduced, and the purpose of avoiding the overshoot of the LED current is achieved.

Description

LED constant current drive circuit and controller

Technical Field

The invention relates to the technical field of electronic circuits, in particular to an LED constant current driving circuit and a controller.

Background

The LED lamp has the advantages of low energy consumption, long service life, low pollution and the like, and is rapidly developed in the lighting industry. With the popularization of LED light sources, higher requirements are put forward on LED constant current drive control, the LED constant current precision is required to be higher, and the LED drive cost is required to be reduced. The prior art is usually realized by a hysteresis type switch controller, and has the advantages of high constant current precision, low chip cost and large driving current. However, when the input voltage is close to the LED voltage, the hysteretic switch controller will be in a constant on state, which causes the LED current to be about 15% higher than the rated current, and a current overshoot phenomenon will occur, which is unacceptable for battery-powered applications, especially for automotive lights, and the LED current 15% higher than the rated current will affect the life of the LED.

Disclosure of Invention

Based on this, the present invention provides an LED constant current driving circuit and a controller, which overcome the defect that in the prior art, when the input voltage of an LED driving circuit using a hysteresis type switch controller is close to the LED voltage, the LED current will overshoot.

In order to achieve the purpose, the invention provides the following technical scheme:

in a first aspect, an embodiment of the present invention provides an LED constant current driving circuit, including: the LED driving circuit comprises a first switch circuit, a constant-current detection circuit, a control circuit and a second switch circuit, wherein a first end of the first switch circuit is externally connected with a PWM driving signal, and a second end of the first switch circuit is used for being connected with a target LED load; the input end of the constant-pass detection circuit is respectively connected with the first end of the first switch circuit and the first input end of the control circuit, the output end of the constant-pass detection circuit is connected with the second input end of the control circuit, and the constant-pass detection circuit is used for performing constant-pass detection on the PWM driving signal and sending a detection result to the control circuit; the output end of the control circuit is connected with the first end of the second switch circuit, the second end of the second switch circuit is used for being connected with the target LED load, and the control circuit is used for generating a control signal according to the detection result and the PWM driving signal so as to control the working state of the second switch circuit.

Optionally, the constant-pass detection circuit includes: the CMOS circuit comprises a CMOS circuit and a delay circuit, wherein the input end of the CMOS circuit is connected with the first end of the first switch circuit, the output end of the CMOS circuit is connected with the first end of the delay circuit, the power supply end of the CMOS circuit is externally connected with a first power supply, and the grounding end of the CMOS circuit is grounded after being connected with the second end of the delay circuit.

Optionally, the delay circuit includes: one end of the first capacitor is connected with the output end of the CMOS circuit; the other end of the first capacitor is connected with the grounding end of the CMOS circuit and then grounded.

Optionally, the constant-pass detection circuit further includes: the input end of the first inverter is respectively connected with the output end of the CMOS circuit and one end of the delay circuit, and the output end of the first inverter is connected with the input end of the second inverter; and the output end of the second phase inverter is connected with the second input end of the control circuit.

Optionally, the control circuit includes: the first input end of the AND logic gate is connected with the first end of the first switch circuit, the second input end of the AND logic gate is connected with the output end of the constant-current detection circuit, and the output end of the AND logic gate is connected with the input end of the drive circuit; and the output end of the driving circuit is connected with the first end of the second switch circuit.

Optionally, the LED constant current driving circuit further includes: the current sampling circuit, the first input of current sampling circuit is connected with outside second power, the second input of current sampling circuit is connected with the one end of target LED load, the output of current sampling circuit target LED load both ends voltage.

Optionally, the LED constant current driving circuit further includes: the comparison circuit, comparison circuit's first input with current sampling circuit's output is connected, the external first electric current of comparison circuit's second input limits the threshold value, the external second electric current of comparison circuit's third input limits the threshold value, comparison circuit's output respectively with constant pass detection circuitry's input, control circuit's first input reaches first switch circuit's first end is connected, control circuit is used for the comparison to generate PWM drive signal, and will PWM drive signal send to constant pass detection circuitry's input, control circuit's first input and first switch circuit's first end.

Optionally, the first switching circuit comprises: a first controllable switch, the second switching circuit, comprising: and a first end of the second controllable switch is connected with the output end of the driving circuit, a second end of the second controllable switch is connected with a second end of the first controllable switch, and a third end of the second controllable switch is grounded.

Optionally, the LED constant current driving circuit further includes: the LED load circuit comprises a first resistor, a second capacitor, a first inductor and a first diode, wherein one end of the first resistor is respectively connected with an external second power supply, one end of the second capacitor and a cathode of the first diode, and the other end of the first resistor is connected with one end of a target LED load; one end of the first inductor is connected with the other end of the target LED load, and the other end of the first inductor is respectively connected with the anode of the first diode, the second end of the first controllable switch and the second end of the second controllable switch; the other end of the second capacitor is grounded.

In a second aspect, an embodiment of the present invention provides a controller, including: the LED constant current driving circuit according to the first aspect of the embodiment of the present invention.

The technical scheme of the invention has the following advantages:

according to the LED constant current driving circuit, the constant-pass detection circuit, the control circuit and the second switch circuit are additionally arranged, so that when the LED current is overshot, the constant-pass detection circuit is used for carrying out constant-pass detection on the PWM driving signal, and the first control signal with constant low level is generated. And then inputting the first control signal with constant low level and the PWM driving signal into the control circuit, and outputting the first driving signal with constant low level. And then the second switch circuit is controlled to be switched off by using the first driving signal which is constant at low level. When the LED current overshoots, the second switch circuit is turned off, so that the equivalent impedance of the circuit can be increased, the LED current can be reduced, and the purpose of avoiding the LED current overshooting is achieved.

The invention provides a controller which comprises the LED constant current driving circuit and a target LED load. When the LED current overshoots, the LED constant current driving circuit is utilized to control the internal circuit to be turned off so as to increase the equivalent impedance of the LED constant current driving circuit. And further, the LED current of the target LED load is reduced, so that the target LED load is prevented from generating overshoot.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and other drawings can be obtained by those skilled in the art without creative efforts.

Fig. 1 is a schematic diagram of an exemplary hysteretic switch controller according to an embodiment of the present invention; (ii) a

Fig. 2 is waveforms of electrical quantities during operation of a typical hysteretic switch controller according to an embodiment of the present invention;

FIG. 3 is a graph of the output current versus the input voltage of an LED according to an embodiment of the present invention;

fig. 4 is a schematic block diagram of a specific example of an LED constant current driving circuit according to an embodiment of the present invention;

fig. 5 is a diagram of another specific example of an LED constant current driving circuit according to an embodiment of the present invention;

FIG. 6 is a circuit diagram of an example of a constant pass detection circuit provided by an embodiment of the present invention;

FIG. 7 is a circuit diagram of one example of a control circuit provided by an embodiment of the present invention;

FIG. 8 is a circuit diagram of one example of a current sampling circuit provided by an embodiment of the present invention;

fig. 9 is a circuit diagram of an example of a comparison circuit provided in an embodiment of the present invention.

Detailed Description

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

In the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; the two elements may be directly connected or indirectly connected through an intermediate medium, or may be communicated with each other inside the two elements, or may be wirelessly connected or wired connected. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.

In addition, the technical features involved in the different embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

Fig. 1 shows a typical hysteresis type switch controller in the prior art. The control circuit consists of current sampling, threshold comparison and a first controllable switch M0. Wherein the power switch is exemplified by NMOS. Its advantages are high constant current precision, low chip cost and high drive current. However, when the input voltage is close to the LED voltage, the hysteretic switch controller will be in a constant on state, resulting in a current of the LED that is about 15% higher than the rated current. This is unacceptable for battery powered applications, particularly automotive lighting, and the like, and LED current 15% greater than rated current can have an impact on LED life.

Fig. 2 is a schematic diagram of the output current of the hysteretic switch control. The hysteretic switch controller defines the peak and valley values of the inductor current by 2 different threshold values, respectively. Wherein VRH limits the peak value of the inductive current, that is, when the inductive current sampling value reaches VRH, the PWM signal is low, the power switch is turned off, and the inductive current is reduced. When the inductor current sampling value reaches VRL, the PWM signal is high, and the power switch is closed. Therefore, the inductor current average value can be set by VREF being (VRH + VRL)/2, and the magnitude ILED of the LED current being (VRH + VRL)/(2 × RS) being VREF/RS. Considering inductance of the inductor, accuracy of volume and current sampling, and operating efficiency, generally, VRH is 1.15 × VREF, and VRL is 0.85 × VREF.

FIG. 3 is a graph of fixed LED voltage, output current versus input voltage. As can be seen from fig. 3, when VIN is much larger than VLED, the output current Iout is constant. However, when VIN approaches VLED +. DELTA.V, where Δ V is about 1.15 × VREF, the output current increases to 1.15 × Iout. The reason for this is that when VIN is close to VLED and the power switch is closed, ILED is (VIN-VLED)/(RS + Rdson), where Rdson is the impedance when the power switch is closed. If ILED × RS is less than or equal to VRH, the power switch is not turned off, and the current is maintained to be (VIN-VLED)/(RS + Rdson), the power inductor L will not store energy any more, which is equivalent to a wire. Since VRH is 1.15 × VREF, i.e., i.i.e., i., i.e., i., i.e., i., i.e., i., i.e., i., i.e., i., i.e., i., i, i.e., i., i.e., i., i, v., i, i.e., i., i.e., i, i., i, i.e., i., i, i.e., i, i., i.e., i., i.e., i, i.e., i., i.e., i, i.e., i. It can be seen that when VIN is close to VLED, the ILED current will overshoot by 15%. And the overshoot is proportional to VRH/VREF, i.e. the larger VRG, the larger the overshoot. This is an inherent architectural problem with hysteretic switch controllers.

Therefore, in order to solve the above-mentioned disadvantage of generating an overshoot current when VIN is close to VLED in the prior art, an embodiment of the present invention provides an LED constant current driving circuit. As shown in fig. 4, the LED constant current driving circuit includes: the circuit comprises a first switch circuit 1, a constant-current detection circuit 2, a control circuit 3 and a second switch circuit 4. Wherein, the first end of the first switch circuit 1 is externally connected with a PWM driving signal. The second terminal of the first switching circuit 1 is used for connecting with a target LED load.

The input end of the constant-current detection circuit 2 is connected with the first end of the first switch circuit 1 and the first input end of the control circuit 3 respectively. The output end of the constant-flux detection circuit 2 is connected with the second input end of the control circuit 3. The constant-pass detection circuit 2 is used for performing constant-pass detection on the PWM driving signal and sending a detection result to the control circuit 3. An output terminal of the control circuit 3 is connected to a first terminal of a second switching circuit 4. A second terminal of the second switching circuit 4 is for connection with a second terminal of the target LED load. The control circuit 3 is configured to generate a control signal according to the detection result and the PWM driving signal to control the operating state of the second switch circuit 4.

In one embodiment, when VIN is far from VLED, the LED constant current driving circuit is a normal hysteretic switch controller. The PWM driving signal is a pulse waveform with a variable duty ratio. The PWM drive signal at this time outputs a first control signal which is constantly high after passing through the constant-on detection circuit 2. Then, the first control signal and the PWM drive signal, which are always high, are input to the control circuit 3, and the first drive signal, which is in phase with the PWM drive signal, is output. The PWM driving signal is used to control the operating state of the first switching circuit 1. The first drive signal is used to control the operating state of the second switching circuit 4. Since the first drive signal is in phase with the PWM drive signal. Therefore, in the normal hysteretic switch control state, the first switch circuit 1 and the second switch circuit 4 operate synchronously to ensure the normal operation of the LED load.

When VIN is close to VLED, the LED current will overshoot, and the PWM driving signal is a constant high waveform signal. The PWM drive signal outputs a first control signal that is constantly low after passing through the constant-on detection circuit 2. Then, the first control signal and the PWM driving signal which are constantly low are input to the control circuit 3, and the first driving signal which is constantly low is output. Because the first driving signal is constantly low, the second switch circuit 4 can be controlled to be turned off, so that the equivalent impedance of the circuit is increased, the current is reduced, and the purpose of avoiding the overshoot of the LED current is achieved.

In the embodiment of the present invention, as shown in fig. 5, the first switch circuit 1 includes: a first controllable switch M0. The first end of the first controllable switch M0 is externally connected with a PWM driving signal for adjusting the light intensity of the LED load according to the PWM driving signal. Specifically, the first controllable switch M0 may be an NMOS, which is only used as an example and not limited thereto. In addition, the second switch circuit 4 includes: a second controllable switch M1. A first terminal of the second controllable switch M1 is connected to an output terminal of the control circuit 3. A second terminal of the second controllable switch M1 is connected to a second terminal of the first controllable switch M0. The third terminal of the second controllable switch M1 is connected to ground. The second controllable switch M1 is used for turning off according to the first driving signal when the LED current overshoots, so as to increase the impedance and reduce the current, thereby achieving the purpose of avoiding the overshoot of the LED current. Specifically, the second controllable switch M1 may be an NMOS, for example only, and is not limited thereto.

According to the LED constant current driving circuit, the constant-pass detection circuit, the control circuit and the second switch circuit are additionally arranged, so that when the LED current is overshot, the constant-pass detection circuit is used for carrying out constant-pass detection on the PWM driving signal, and the first control signal with constant low level is generated. And then inputting the first control signal which is constant at a low level and the PWM driving signal into the control circuit. The control circuit outputs a first drive signal which is at a low level constantly. And then the second switch circuit is controlled to be switched off by using the first driving signal which is constant at low level. When the LED current overshoots, the second switch circuit is turned off, so that the equivalent impedance of the circuit can be increased, the LED current can be reduced, and the purpose of avoiding the LED current overshooting is achieved.

In one embodiment, as shown in fig. 6, the constant-pass detection circuit 2 includes: a CMOS circuit 21 and a delay circuit 22. Wherein the input terminal of the CMOS circuit 21 is connected to the first terminal of the first switching circuit 1. An output terminal of the CMOS circuit 21 is connected to a first terminal of the delay circuit 22. The power source terminal of the CMOS circuit 21 is externally connected to a first power source. The ground terminal of the CMOS circuit 21 is connected to the second terminal of the delay circuit 22 and then grounded.

In one embodiment, the delay circuit 22 includes: a first capacitor C1. One end of the first capacitor C1 is connected to the output terminal of the CMOS circuit 21. The other end of the first capacitor C1 is connected to the ground terminal of the CMOS circuit 21 and then grounded.

In the embodiment of the invention, when VIN is greatly different from VLED, the LED constant current driving circuit is a normal hysteretic switch controller. The PWM driving signal is a pulse waveform with a variable duty ratio. The PWM drive signal at this time outputs a first control signal which is constantly high after passing through the constant-on detection circuit 2. Specifically, when the PWM drive signal is low level, the PWM drive signal is input to the gate of the PMOS in the CMOS circuit 21. The first power supply outputs a high level signal through the drain of the PMOS. When the PWM drive signal is at a high level, the PWM drive signal is input to the gate of the NMOS in the CMOS circuit 21, so that the first capacitor C1 in the delay circuit 22 is discharged until the stored electric energy is exhausted and a low level is output to the control circuit 3. However, when the low level output by the constant-pass detection circuit 2 is not yet supplied to the control circuit 3, the PWM low-level driving signal is supplied to the gate of the PMOS in the CMOS circuit 21, so that the low level cannot be supplied to the control circuit 3, and the constant-pass detection circuit 2 outputs the first control signal which is constantly high.

Further, when VIN is close to VLED, the LED current will overshoot, and the PWM driving signal is a constant high waveform signal. The PWM drive signal outputs a first control signal that is constantly low after passing through the constant-on detection circuit 2. Specifically, when the PWM drive signal is at a high level, the PWM drive signal is input to the gate of the NMOS in the CMOS circuit 21, so that the first capacitor C1 in the delay circuit 22 is discharged until the stored electric energy is exhausted and a low level is output to the control circuit 3. By providing the delay circuit 22 in the constant-pass detection circuit 2, when the PWM driving signal is constantly at the high level, the inverted low-level signal can be output with a delay, and the distortion rate of the waveform of the first control signal can be reduced.

In one embodiment, as shown in fig. 6, the constant-current detection circuit 2 further includes: a first inverter 23 and a second inverter 24. The input terminal of the first inverter 23 is connected to the output terminal of the CMOS circuit 21 and one terminal of the delay circuit 22, respectively. The output of the first inverter 23 is connected to the input of the second inverter 24. The output of the second inverter 24 is connected to a second input of the control circuit 3. Since the high and low level signals output by the CMOS circuit 21 are not the standard level signals in the circuit or the waveforms are not ideal, two inverters are usually provided to shape the waveforms to make them the standard level signals output in order to provide the correct signals to the input of the control circuit 3.

In one embodiment, as shown in fig. 7, the control circuit 3 includes: and logic gate 31 and driver circuit 32. Wherein a first input of the and logic gate 31 is connected to a first terminal of the first switching circuit 1. A second input of the and logic gate 31 is connected to an output of the constant-pass detection circuit 2. An output of the and logic gate 31 is connected to an input of the driver circuit 32. An output terminal of the drive circuit 32 is connected to a first terminal of the second switch circuit 4.

In one embodiment, when the LED constant current driving circuit is a normal hysteretic switch controller, the PWM driving signal is a pulse waveform with a variable duty ratio and the constant-on detection circuit 2 outputs the first control signal with a constant high level. At this time, after the PWM driving signal is phase-inverted with the first control signal, the first driving signal with the same phase as the PWM driving signal is obtained, and then the driving circuit 32 controls the second controllable switch M1 in the second switch circuit 4 to act in phase with the first controllable switch M0 in the first switch circuit 1.

Further, when VIN is close to VLED, the PWM driving signal is a constant high waveform signal and the constant on detection circuit 2 outputs a first control signal that is constant low. At this time, after the phase of the PWM driving signal and the first control signal is inverted, the first driving signal with a constant low level is obtained, and then the driving circuit 32 controls the second controllable switch M1 in the second switch circuit 4 to turn off, so that the equivalent impedance of the whole circuit is increased.

In an embodiment, as shown in fig. 5, the LED constant current driving circuit further includes: a current sampling circuit 5. A first input terminal of the current sampling circuit 5 is connected to an external second power supply. A second input terminal of the current sampling circuit 5 is connected to one terminal of the target LED load. The output end of the current sampling circuit 5 outputs the voltage across the target LED load.

In one embodiment, as shown in fig. 8, the current sampling circuit 5 includes: the circuit comprises a second resistor R1, a third resistor R2, a fourth resistor R3, a first switching tube Q1, a second switching tube Q2, a third switching tube Q3, a first current load I1 and a second current load I2. Two ends of the second resistor R1 are connected with two ends of the first resistor RS. A first end of the second resistor R1 is connected to a first end of the first switch Q1 through a third resistor R2. A second end of the second resistor R1 is connected to the first end of the second switch Q2 through a fourth resistor R3. The second terminal of the first switch Q1 is grounded through the first current load I1, and is grounded to the control terminal of the third switch Q3. A first end of the second switching tube Q2 is connected to a first end of the third switching tube Q3, a second end of the second switching tube Q2 is grounded through a second current load I2, and a control end of the second switching tube Q2 is connected to a control end of the first switching tube Q1. The second terminal of the third switch Q3 is grounded through a fourth resistor R4, and outputs a voltage VSN across the LED load.

By adopting the current sampling circuit 5, the current signal can be directly processed, and the voltage at two ends of the LED load with better linearity can be output under the condition of not influencing the output current VIN.

In one embodiment, as shown in fig. 5, the LED constant current driving circuit further includes: and a comparison circuit 6. A first input of the comparison circuit 6 is connected to an output of the current sampling circuit 5. The second input terminal of the comparison circuit 6 is externally connected with the first current limiting threshold. The third input terminal of the comparison circuit 6 is externally connected with a second current limiting threshold. The output end of the comparison circuit 6 is respectively connected with the input end of the constant-current detection circuit 2, the first input end of the control circuit 3 and the first end of the first switch circuit 1. The comparison circuit 6 is configured to compare and generate a PWM driving signal, and send the PWM driving signal to the input end of the constant-current detection circuit 2, the first input end of the control circuit 3, and the first end of the first switch circuit 1.

In one embodiment, as shown in fig. 9, the comparison circuit 6 includes: a first comparator COMP1, a second comparator COMP2, a first NAND gate U1, a second NAND gate U2, and a first NAND gate U3. In the embodiment of the present invention, a non-inverting input terminal of the first comparator COMP1 inputs a preset high threshold voltage URH (first current limit threshold). The current VSN across the LED load is input to the inverting input terminal of the first comparator COMP 1. An output terminal of the first comparator COMP1 is connected to a first input terminal of a first nand logic gate U1. A non-inverting input terminal of the second comparator COMP2 inputs a voltage of the power line. The preset low threshold voltage URL (second current limit threshold) is input to the inverting input terminal of the second comparator COMP 2. An output terminal of the second comparator COMP2 is connected to a first input terminal of a second nand logic gate U2. A second input of the first nand logic gate U1 is connected to an output of the second nand logic gate U2. The output of the first nand logic gate U1 is connected to the input of the first nand logic gate U3. A second input of the second nand logic gate U2 is connected to an output of the first nand logic gate U1. The output of the first not logic gate U3 outputs a PWM drive signal. Wherein, the preset high voltage threshold VRH is higher than the preset low voltage threshold VRL.

By adopting the comparison circuit 6, the invention compares the voltage VSN at two ends of the LED load with the preset high threshold voltage URH and the preset low threshold voltage URL. When the voltage VSN at the two ends of the LED load reaches VRH, a low level PWM driving signal is output, and the first controllable switch M0 is further controlled to be turned off, thereby achieving the purpose of reducing the current of the LED load. When the voltage VSN at the two ends of the LED load reaches VRL, a high level PWM driving signal is output, and the first controllable switch M0 is further controlled to be turned off, thereby increasing the LED load current.

In one embodiment, as shown in fig. 5, the LED constant current driving circuit further includes: the circuit comprises a first resistor RS, a second capacitor C2, a first inductor L and a first diode D. One end of the first resistor RS is connected to an external second power supply, one end of the second capacitor C2, and the cathode of the first diode D, respectively. The other end of the first resistor RS is connected with one end of the target LED load. One end of the first inductor L is connected to the other end of the target LED load. The other end of the first inductor L is connected to the anode of the first diode D, the second end of the first controllable switch M0 and the second end of the second controllable switch M1, respectively. The other terminal of the second capacitor C2 is connected to ground.

In an embodiment, the current sampling circuit 5 is connected to two ends of the first resistor RS, so as to collect current at two ends of the LED load, and further obtain voltage VSN at two ends of the LED load. When VIN is close to VLED, the LED current will overshoot, and to avoid the overshoot, the embodiment of the present invention increases the equivalent impedance of the whole circuit by turning off the second controllable switch M1, thereby reducing the LED current. The following formula is specifically illustrated:

the LED output current ILED is:

in the formula, ILED is an LED output current, VIN is a sampling circuit input voltage, VLED is an LED voltage, RS is a sampling resistor resistance value, Rdson is a circuit equivalent impedance when the first controllable switch M0 and the second controllable switch M1 are closed, and Rdson1 is a circuit equivalent impedance when the first controllable switch M0 and the second controllable switch M1 are turned off.

As can be seen from equation (1), it is only necessary to set the equivalent impedance Rdson1 of the entire circuit when the second controllable switch M1 is turned off, so that ((RS + Rdson)/(RS + Rdson1)) (1/1.15). The LED output current ILED is still VREF/RS. And such that ((RS + Rdson)/(RS + Rdson1)) < (1/1.15), the ILED is guaranteed to be free of overshoot.

An embodiment of the present invention further provides a controller, including: the LED constant current driving circuit is provided.

In an embodiment, the controller provided by the present invention includes the LED constant current driving circuit and a target LED load. When the LED current overshoots, the LED constant current driving circuit is utilized to control the internal circuit to be turned off so as to increase the equivalent impedance of the LED constant current driving circuit. And further, the LED current of the target LED load is reduced, so that the target LED load is prevented from generating overshoot.

It should be understood that the above examples are only for clarity of illustration and are not intended to limit the embodiments. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. And obvious variations or modifications of the invention may be made without departing from the spirit or scope of the invention.

Claims

1. An LED constant current driving circuit, comprising: a first switch circuit (1), a constant-current detection circuit (2), a control circuit (3) and a second switch circuit (4),

a first end of the first switch circuit (1) is externally connected with a PWM (pulse-width modulation) driving signal, and a second end of the first switch circuit (1) is used for being connected with a target LED load;

the input end of the constant-pass detection circuit (2) is respectively connected with the first end of the first switch circuit (1) and the first input end of the control circuit (3), the output end of the constant-pass detection circuit (2) is connected with the second input end of the control circuit (3), and the constant-pass detection circuit (2) is used for performing constant-pass detection on the PWM driving signal and sending a detection result to the control circuit (3);

the output end of the control circuit (3) is connected with the first end of the second switch circuit (4), the second end of the second switch circuit (4) is used for being connected with the target LED load, and the control circuit (3) is used for generating a control signal according to the detection result and the PWM driving signal so as to control the working state of the second switch circuit (4).

2. The LED constant current drive circuit according to claim 1, wherein the constant-current detection circuit (2) comprises: a CMOS circuit (21) and a delay circuit (22), wherein,

the input end of the CMOS circuit (21) is connected with the first end of the first switch circuit (1), the output end of the CMOS circuit (21) is connected with the first end of the delay circuit (22), the power supply end of the CMOS circuit (21) is externally connected with a first power supply, and the grounding end of the CMOS circuit (21) is connected with the second end of the delay circuit (22) and then grounded.

3. The LED constant current drive circuit according to claim 2, wherein the delay circuit (22) comprises: a first capacitor (C1), one end of the first capacitor (C1) being connected to the output terminal of the CMOS circuit (21); the other end of the first capacitor (C1) is connected with the grounding end of the CMOS circuit (21) and then grounded.

4. The LED constant current drive circuit according to claim 2, wherein the constant-current detection circuit (2) further comprises: a first inverter (23) and a second inverter (24), wherein,

the input end of the first inverter (23) is respectively connected with the output end of the CMOS circuit (21) and one end of the delay circuit (22), and the output end of the first inverter (23) is connected with the input end of the second inverter (24);

the output end of the second phase inverter (24) is connected with the second input end of the control circuit (3).

5. The LED constant current drive circuit according to claim 1, wherein the control circuit (3) comprises: and a logic gate (31) and a driver circuit (32), wherein,

a first input end of the AND logic gate (31) is connected with a first end of the first switch circuit (1), a second input end of the AND logic gate (31) is connected with an output end of the constant-current detection circuit (2), and an output end of the AND logic gate (31) is connected with an input end of the drive circuit (32);

the output end of the driving circuit (32) is connected with the first end of the second switch circuit (4).

6. The LED constant current drive circuit according to claim 1, further comprising: the LED lamp comprises a current sampling circuit (5), wherein a first input end of the current sampling circuit (5) is connected with an external second power supply, a second input end of the current sampling circuit (5) is connected with one end of a target LED load, and the output end of the current sampling circuit (5) outputs voltages at two ends of the target LED load.

7. The LED constant current drive circuit according to claim 6, further comprising: comparison circuit (6), the first input of comparison circuit (6) with the output of current sampling circuit (5) is connected, the external first electric current of the second input of comparison circuit (6) prescribes a limit to the threshold value, the external second electric current of the third input of comparison circuit (6) prescribes a limit to the threshold value, the output of comparison circuit (6) respectively with the input of permanent expert detection circuitry (2), the first input of control circuit (3) and the first end of first switch circuit (1) is connected, control circuit (3) are used for comparing and generating PWM drive signal, and will PWM drive signal send to the input of permanent expert detection circuitry (2), the first input of control circuit (3) and the first end of first switch circuit (1).

8. The LED constant current drive circuit according to claim 5, the first switch circuit (1) comprising: -a first controllable switch (M0), characterized in that said second switching circuit (4) comprises: a second controllable switch (M1), a first terminal of the second controllable switch (M1) is connected with the output terminal of the driving circuit (32), a second terminal of the second controllable switch (M1) is connected with a second terminal of the first controllable switch (M0), and a third terminal of the second controllable switch (M1) is grounded.

9. The LED constant current drive circuit according to claim 8, further comprising: a first Resistor (RS), a second capacitor (C2), a first inductor (L), a first diode (D), wherein,

one end of the first Resistor (RS) is respectively connected with an external second power supply, one end of the second capacitor (C2) and the cathode of the first diode (D), and the other end of the first Resistor (RS) is connected with one end of a target LED load;

one end of the first inductor (L) is connected with the other end of the target LED load, and the other end of the first inductor (L) is respectively connected with the anode of the first diode (D), the second end of the first controllable switch (M0) and the second end of the second controllable switch (M1);

the other end of the second capacitor (C2) is grounded.

10. A controller, comprising: the LED constant current drive circuit according to any one of claims 1 to 9.