CN115134970A

CN115134970A - Low-voltage constant-current driving circuit

Info

Publication number: CN115134970A
Application number: CN202211037084.7A
Authority: CN
Inventors: 不公告发明人
Original assignee: Suzhou Baker Microelectronics Co Ltd
Current assignee: Suzhou Baker Microelectronics Co Ltd
Priority date: 2022-08-29
Filing date: 2022-08-29
Publication date: 2022-09-30
Anticipated expiration: 2042-08-29
Also published as: CN115134970B

Abstract

The invention discloses a low-voltage constant current driving circuit, belonging to the technical field of LED driving, and comprising: the circuit comprises a first power supply, a first switch tube, a second switch tube, a first comparison unit, a switch control circuit and a first capacitor; the first power supply, the second switch tube and the first switch tube are sequentially connected in series and then grounded; the junction of the second switch tube and the first switch tube is connected with the first end of the first capacitor, and the second end of the first capacitor is grounded; the input end of the switch control circuit is connected with the first end of the first capacitor, and the output end of the switch control circuit is respectively connected with the controlled ends of the first switch tube and the second switch tube; one input end of the first comparison unit is connected with the first end of the first capacitor; the other input end of the first comparing unit is connected with the linear dimming signal or the pulse dimming signal, and the output end of the first comparing unit outputs a driving signal of the LED light-emitting circuit. The driving circuit provided by the invention can be simultaneously suitable for linear dimming and pulse dimming.

Description

Low-voltage constant-current driving circuit

Technical Field

The invention relates to the technical field of LED driving, in particular to a low-voltage constant-current driving circuit.

Background

In recent years, Light Emitting Diodes (LEDs) are more and more widely used, and currently, commonly used LED dimming methods are classified into linear dimming and pulse dimming, where the linear dimming method is simple and low in cost, but is not suitable for occasions requiring constant color temperature, and the pulse dimming can accurately control the current of the LEDs, so that the LED dimming method is suitable for occasions requiring constant color temperature, but peripheral circuits of the LEDs are complex and high in cost. Moreover, due to the difference of the control methods caused by the difference of the dimming manners, the control chip of the LED driving circuit is usually designed separately according to the dimming manner, that is, the control chip of a single LED driving circuit can only be applied to linear dimming or only pulse dimming, thereby greatly limiting the application occasions of the LED driving circuit. In addition, the conventional LED driving circuit requires a high input voltage, and thus, cannot normally operate when the input voltage is low.

Disclosure of Invention

In view of this, embodiments of the present invention provide a low-voltage constant-current driving circuit to solve the problem that an existing LED driving circuit is only applicable to one dimming mode (linear dimming or pulse dimming) and cannot work normally when an input voltage is low.

An embodiment of the present invention provides a driving circuit, including: a PWM generator, the PWM generator comprising: the circuit comprises a first power supply, a first switch tube M3, a second switch tube M4, a first comparison unit A6, a switch control circuit and a first capacitor C4;

the first power supply, the second switch tube M4 and the first switch tube M3 are sequentially connected in series and then grounded;

the junction of the second switch tube M4 and the first switch tube M3 is connected to the first end of the first capacitor C4, and the second end of the first capacitor C4 is grounded;

the input end of the switch control circuit is connected with the first end of the first capacitor C4, and the output end of the switch control circuit is respectively connected with the controlled ends of the first switch tube M3 and the second switch tube M4;

the switch control circuit outputs a first control signal for controlling the second switch tube M4 to be turned on and the first switch tube M3 to be turned off when the voltage at the first end of the first capacitor C4 is less than or equal to a first fixed voltage, and outputs a second control signal for controlling the second switch tube M4 to be turned off and the first switch tube M3 to be turned on when the voltage at the first end of the first capacitor C4 is greater than or equal to a second fixed voltage; the first fixed voltage is less than the second fixed voltage;

an input terminal of the first comparing unit a6 is connected with a first terminal of the first capacitor C4;

the other input end of the first comparing unit a6 is connected to a linear dimming signal, and the voltage of the linear dimming signal is greater than the first fixed voltage and less than the second fixed voltage; or the other input end of the first comparing unit a6 is connected to a pulsed dimming signal, the high voltage of the pulsed dimming signal is greater than the second fixed voltage, and the low voltage is less than the first fixed voltage;

the output end of the first comparing unit a6 is used as the output end of the PWM generator, and the output PWM signal is used as the driving signal of the LED lighting circuit.

Optionally, the driving circuit further includes: a first current source I1 and a second current source I2, the first current source I1 and the second current source I2 output currents with equal and constant sizes;

the first current source I1 is connected in series between the first power supply and the second switch tube M4, and the second current source I2 is connected in series between the first switch tube M3 and ground.

Optionally, the switch control circuit includes: a second comparing unit a4, a third comparing unit a5 and a first flip-flop E2;

one input end of the second comparing unit A4 is connected with the first end of the first capacitor C4, and the other input end of the second comparing unit A4 is connected with the second fixed voltage;

one input end of the third comparing unit A5 is connected with the first end of the first capacitor C4, and the other input end of the third comparing unit A5 is connected with the first fixed voltage;

two input terminals of the first flip-flop E2 are respectively connected to the output terminal of the second comparing unit a4 and the output terminal of the third comparing unit a5, and the output terminal of the first flip-flop E2 serves as the output terminal of the switch control circuit.

Optionally, the driving circuit further includes: the switch boosting circuit and the constant current control circuit;

the output voltage of the switch boosting circuit is used as the power supply voltage of the LED light-emitting circuit;

the constant current control circuit is used for controlling the on-off of a switch in the switch boosting circuit during the period that the switch boosting circuit outputs the power supply voltage to the LED light-emitting circuit, so that the current output by the switch boosting circuit to the LED light-emitting circuit is constant, and the output voltage of the switch boosting circuit is larger than the input voltage.

Optionally, the constant current control circuit includes:

the first current sampling resistor R1 is used for collecting the current output by the switching booster circuit and converting the current into a voltage signal;

a fourth comparing unit a2, configured to compare a voltage signal output by the first current sampling resistor R1 with a preset reference voltage, and output a comparison result signal;

and the control unit is used for controlling the on-off of a switch in the switch booster circuit according to the comparison result signal.

Optionally, the control unit controls on/off of a switch in the switch boosting circuit according to the comparison result signal and the driving signal.

Optionally, the constant current control circuit further includes: an oscillator and second flip-flop E1;

one input terminal of the second flip-flop E1 is connected to the oscillator, and the other input terminal of the second flip-flop E1 is connected to an electrical signal obtained based on the comparison result signal; the output end of the second trigger E1 is connected with one input end of the control unit, so that the control unit can control the on-off of a switch in the switch boosting circuit according to the comparison result signal;

the output of the second flip-flop E1 changes only if one of the inputs is low and the other input is high.

Optionally, the constant current control circuit further includes: the circuit comprises a fifth comparison unit A3, a slope compensator F1, a second current sampling resistor R2 and a first resistor R5;

a first input terminal of the fifth comparing unit A3 is connected to the comparison result signal, a second input terminal of the fifth comparing unit A3 is connected to a first terminal of the slope compensator F1, a second terminal of the slope compensator F1 is connected to a first terminal of the second current sampling resistor R2 through the first resistor R5, a third terminal of the slope compensator F1 is connected to a slope compensation current, the second current sampling resistor R2 is connected in series between a switch in the switch boosting circuit and ground, and the first terminal of the second current sampling resistor R2 is connected to the switch in the switch boosting circuit;

the output of the fifth comparator a3 is connected to the input of the control unit.

Optionally, the constant current control circuit further includes: a controllable current source G1 and a second resistor R4;

one control terminal of the controllable current source G1 is connected to the output terminal of the fourth comparing unit a2, the other control terminal of the controllable current source G1 is connected to a preset fixed voltage, the output terminal of the controllable current source G1 is connected to the first input terminal of the fifth comparing unit A3, one end of the second resistor R4 is connected to the first input terminal of the fifth comparing unit A3, and the other end is grounded.

Optionally, the constant current control circuit further includes: a third resistor R3 and a second capacitor C3;

one end of the third resistor R3 is connected to the output end of the fourth comparing unit a2, the other end of the third resistor R3 is connected to one end of the second capacitor C3, and the other end of the second capacitor C3 is grounded.

The driving circuit provided by the embodiment of the invention comprises the PWM generator, and the PWM generator can enable the driving circuit to be suitable for linear dimming and pulse dimming, so that the application occasions of the LED driving circuit are greatly increased.

The driving circuit provided by the embodiment of the invention is also provided with the constant current control circuit, the constant current control circuit can ensure that the current flowing to the LED light-emitting circuit is constant, the light-emitting stability of the LED can be greatly improved, and the constant current control circuit is particularly suitable for driving the white light LED.

The driving circuit provided by the embodiment of the invention realizes the application of the LED driving circuit in the low input voltage occasion through the matching design of the PWM generator, the switch boosting circuit and the constant current control circuit.

Drawings

The features and advantages of the present invention will be more clearly understood by reference to the accompanying drawings, which are schematic and are not to be understood as limiting the invention in any way, and in which:

fig. 1 is a schematic circuit structure diagram of a PWM generator in a driving circuit according to an embodiment of the present invention;

fig. 2 is a schematic circuit diagram of another circuit structure of the PWM generator in the driving circuit according to the embodiment of the present invention;

fig. 3 is a schematic voltage waveform diagram of each important node when the driving circuit is linearly dimmed according to the embodiment of the present invention;

fig. 4 is a schematic voltage waveform diagram of each important node when the driving circuit performs pulse dimming according to an embodiment of the present invention;

fig. 5 is a schematic circuit structure diagram of a driving circuit according to an embodiment of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are 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.

It is to be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other like elements in a process, method, article, or apparatus that comprises the element. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. In the description of the following examples, "plurality" means two or more unless specifically limited otherwise.

Referring to fig. 1, an embodiment of the invention provides an LED driving circuit, including: a PWM generator, the PWM generator comprising: the circuit comprises a first power supply VCC, a first switch tube M3, a second switch tube M4, a first comparison unit A6, a switch control circuit and a first capacitor C4;

the first power supply VCC, the second switch tube M4 and the first switch tube M3 are sequentially connected in series and then grounded;

when the voltage at the first end of the first capacitor C4 is less than or equal to a first fixed voltage V1, the switch control circuit outputs a first control signal for controlling the second switching tube M4 to be turned on and the first switching tube M3 to be turned off, and when the voltage at the first end of the first capacitor C4 is greater than or equal to a second fixed voltage V2, the switch control circuit outputs a second control signal for controlling the second switching tube M4 to be turned off and the first switching tube M3 to be turned on; the first fixed voltage V1 is less than the second fixed voltage V2;

the other input end of the first comparing unit a6 is connected with a linear dimming signal, the voltage of the linear dimming signal is greater than the first fixed voltage V1 and less than the second fixed voltage V2; or, the other input end of the first comparing unit a6 is connected to a pulse dimming signal, the high voltage of the pulse dimming signal is greater than the second fixed voltage V2, and the low voltage is less than the first fixed voltage V1;

the output end of the first comparing unit a6 is used as the output end of the PWM generator, and the output PWM signal is used as the driving signal of the LED lighting circuit 101.

Specifically, the first comparison unit a6 may be an operational amplifier. The input terminal of the first comparing unit a6 connected to the first terminal of the first capacitor C4 may be an inverting input terminal, and the input terminal of the linear dimming signal or the pulse dimming signal of the first comparing unit a6 may be a non-inverting input terminal. The first switch transistor M3 may be an NMOS transistor, and has a gate connected to the output terminal of the switch control circuit as a controlled terminal, a drain connected to the second switch transistor M4, and a source grounded. The first switch tube M3 may also be an NPN type triode, with a base connected to the output terminal of the switch control circuit as a controlled terminal, a collector connected to the second switch tube M4, and an emitter grounded. The second switch transistor M4 may be a PMOS transistor, the gate of which is connected to the output terminal of the switch control circuit as the controlled terminal, the drain of which is connected to the first switch transistor M3, and the source of which is connected to the first power VCC. The second switch tube M4 may also be a PNP type triode, whose base is connected to the output terminal of the switch control circuit as a controlled terminal, whose collector is connected to the first switch tube M3, and whose emitter is connected to the first power VCC.

The first capacitor C4 may be integrated with other components of the PWM generator or may be provided separately. If the first capacitor C4 is separately provided, a RAMP pin is required to be provided on an integrated circuit formed by other components of the PWM generator to connect the first capacitor C4. If the first capacitor C4 is integrated with other components of the PWM generator, the RAMP pin is not required.

The working principle of the driving circuit provided by the embodiment of the invention is as follows:

in an initial state, the voltage V0 at the first end of the first capacitor C4 is smaller than the first fixed voltage V1, and at this time, the switch control circuit controls the second switching tube M4 to turn on and controls the first switching tube M3 to turn off based on the voltage at the first end of the first capacitor C4 (smaller than or equal to the first fixed voltage V1), the first power VCC charges the first capacitor C4 through the second switching tube M4, and the voltage V0 at the first end of the first capacitor C4 gradually rises, that is, the voltage V0 at the input end (which may be the inverting input end of the first comparing unit A6) where the first comparing unit A6 is connected to the first end of the first capacitor C4 gradually rises;

after the voltage V0 at the first end of the first capacitor C4 rises to be greater than or equal to the second fixed voltage V2, at this time, the switch control circuit controls the second switching tube M4 to turn off and controls the first switching tube M3 to turn on based on the voltage at the first end of the first capacitor C4 (greater than or equal to the second fixed voltage V2), the first capacitor C4 discharges through the first switching tube M3, and the voltage V0 at the first end of the first capacitor C4 gradually decreases, that is, the voltage V0 at the input end (which may be the inverting input end of the first comparing unit A6) where the first comparing unit A6 is connected with the first end of the first capacitor C4 gradually decreases;

when the voltage V0 at the first end of the first capacitor C4 decreases to be less than or equal to the first fixed voltage V1, at this time, the switch control circuit controls the second switching tube M4 to be turned on and controls the first switching tube M3 to be turned off based on the voltage at the first end of the first capacitor C4 (less than or equal to the first fixed voltage V1), the first power VCC charges the first capacitor C4 through the second switching tube M4, and the voltage V0 at the first end of the first capacitor C4 gradually increases, that is, the voltage V0 at the input end (which may be the inverting input end of the first comparing unit A6) where the first comparing unit A6 is connected to the first end of the first capacitor C4 gradually increases;

then, the voltage V0 at the first end of the first capacitor C4, that is, the voltage V0 at the input end (which may be the inverting input end of the first comparing unit a 6) of the first comparing unit a6 connected to the first end of the first capacitor C4 enters a cycle of gradually decreasing after increasing to be greater than or equal to the second fixed voltage V2, and gradually increasing after decreasing to be less than or equal to the first fixed voltage V1.

When a linear dimming signal is input to the linear/pulse pin, that is, the other input terminal of the first comparing unit a6 is connected to a linear dimming signal, the input linear dimming voltage V5 is compared with the input voltage V0 of the inverting input terminal of the first comparing unit a6, when V0> V5, the first comparing unit a6 outputs a low level, and when V0< V5, the first comparing unit a6 outputs a high level;

when the linear/pulse pin inputs a pulse dimming signal, that is, the other input terminal of the first comparing unit A6 is connected to a pulse dimming signal, the high voltage of the pulse dimming signal is greater than the second fixed voltage V2, and the low voltage is less than the first fixed voltage V1), the input pulse dimming voltage V5 is compared with the input voltage V0 at the inverting input terminal of the first comparing unit A6, when V0> V5, the first comparing unit A6 outputs a low level, and when V0< V5, the first comparing unit A6 outputs a high level.

As can be seen from the above, the driving circuit provided in the embodiment of the present invention, by setting the PWM generator, can implement that a single LED driving circuit is simultaneously suitable for linear dimming and pulse dimming, i.e., the driving circuit is suitable for both linear dimming and pulse dimming, thereby greatly increasing the application occasions of the LED driving circuit.

In some embodiments, referring to fig. 2, the driving circuit further includes: a first current source I1 and a second current source I2, the current output by the first current source I1 and the current output by the second current source I2 are equal in magnitude and constant;

the first current source I1 is connected in series between the first power source VCC and the second switch tube M4, and the second current source I2 is connected in series between the first switch tube M3 and ground.

Specifically, the input end of the first current source I1 is connected to the first power VCC, and the output end of the first current source I1 is connected to the input end of the second switch tube M4. The input end of the second current source I2 is connected to the output end of the first switch tube M3, and the output end of the second current source I2 is grounded.

In the embodiment of the present invention, the first current source I1 connected in series between the first power source VCC and the second switching tube M4, and the second current source I2 connected in series between the first switching tube M3 and the ground, and the currents output by the first current source I1 and the second current source I2 are equal and constant, so that the charging current and the discharging current of the first capacitor C4 are equal and constant, and further, the voltage V0 at the first end of the first capacitor C4, that is, the voltage V0 at the input end (which may be the inverting input end of the first comparing unit A6) where the first comparing unit A6 is connected to the first end of the first capacitor C4, rises or falls controllably and is stable, for example, fig. 3 and 4 show a waveform diagram of the voltage V0.

In some embodiments, referring to fig. 2, the switch control circuit includes: a second comparing unit a4, a third comparing unit a5 and a first flip-flop E2;

one input end of the second comparison unit A4 is connected with the first end of the first capacitor C4, and the other input end of the second comparison unit A4 is connected with the second fixed voltage V2;

one input end of the third comparing unit A5 is connected with the first end of the first capacitor C4, and the other input end of the third comparing unit A5 is connected with the first fixed voltage V1;

Specifically, the output of the first flip-flop E2 changes only when one of the input terminals is low and the other input terminal is high. When a voltage V0 at a first end of the first capacitor C4 is less than or equal to a first fixed voltage V1, one of the second comparison unit a4 and the third comparison unit a5 outputs a low level and the other outputs a high level, when a voltage V0 at a first end of the first capacitor C4 is greater than or equal to a second fixed voltage V2, one of the second comparison unit a4 and the third comparison unit a5 outputs a low level and the other outputs a high level, and when a voltage V0 at a first end of the first capacitor C4 is greater than the first fixed voltage V1 and less than the second fixed voltage V2, both the second comparison unit a4 and the third comparison unit a5 output a high level.

The second comparing unit a4 and the third comparing unit a5 may be operational amplifiers.

The specific structure (including components and parts and connection modes) of the switch control circuit is not limited to the above, and the switch control circuit may be in other forms as long as the following functions are realized: when the voltage at the first end of the first capacitor C4 is less than or equal to a first fixed voltage V1, a first control signal for controlling the second switch tube M4 to be turned on and the first switch tube M3 to be turned off is output, and when the voltage at the first end of the first capacitor C4 is greater than or equal to a second fixed voltage V2, the switch control circuit outputs a second control signal for controlling the second switch tube M4 to be turned off and the first switch tube M3 to be turned on.

The working principle of the PWM generator will be described below by taking the PWM generator shown in fig. 2 as an example.

Specifically, in fig. 2, the first switch transistor M3 is an NMOS transistor, a gate thereof is connected to the output terminal of the switch control circuit as a controlled terminal, a drain thereof is connected to the second switch transistor M4, and a source thereof is grounded through a second current source I2. The second switch tube M4 is a PMOS tube, the gate of which is connected to the output terminal of the switch control circuit as the controlled terminal, the drain of which is connected to the first switch tube M3, and the source of which is connected to the first power VCC through the first current source I1. The second comparing unit A4 and the third comparing unit A5 are operational amplifiers. The non-inverting input terminal of the second comparing unit a4 is connected to the second fixed voltage V2, the inverting input terminal thereof is connected to the first terminal of the first capacitor C4, the non-inverting input terminal of the third comparing unit a5 is connected to the first terminal of the first capacitor C4, and the inverting input terminal thereof is connected to the first fixed voltage V1. The first flip-flop E2 is an RS flip-flop, and a reset terminal (R terminal) thereof may be connected to the output terminal of the third comparing unit a5, and a set terminal (S terminal) thereof may be connected to the output terminal of the second comparing unit a 4.

Referring to fig. 2 to 4, in an initial state, the non-inverting input terminal of the third comparing unit a5 and the inverting input terminal of the second comparing unit a4 are both low, so the output V3 of the third comparing unit a5 is low, the output V4 of the second comparing unit a4 is high, and when the S input of the first flip-flop E2 is high and the R input is low, the Q output of the first flip-flop E2 is low, therefore, in the initial state, the Q output of the first flip-flop E2 is low, the second switch M4 is turned on, the first switch M3 is turned off, the first current source I1 charges the first capacitor C4 through the second switch M4, and the input voltage V0 of the inverting input terminal of the first comparing unit A6 gradually rises;

when the input voltage V0 at the inverting input terminal of the first comparing unit a6 rises to be greater than or equal to the second fixed voltage V2, the output V3 of the third comparing unit a5 is at a high level, the output V4 of the second comparing unit a4 is at a low level, when the input at the S terminal of the first flip-flop E2 is at a low level and the input at the R terminal is at a high level, the output at the Q terminal of the first flip-flop E2 is at a high level, so at this time, the output at the Q terminal of the first flip-flop E2 becomes at a high level, the second switching tube M4 is turned off, the first switching tube M3 is turned on, the first capacitor C4 is discharged through the first switching tube M3 and the second current source I2, and the input voltage V0 at the inverting input terminal of the first comparing unit a6 gradually decreases;

when the input voltage V0 at the inverting input terminal of the first comparing unit a6 is reduced to be less than or equal to the first fixed voltage V1, the output V3 of the third comparing unit a5 is at a low level, and the output V4 of the second comparing unit a4 is at a high level, so that at this time, the output at the Q terminal of the first flip-flop E2 becomes at a low level, the second switching tube M4 is turned on, the first switching tube M3 is turned off, the first current source I1 charges the first capacitor C4 through the second switching tube M4, and the input voltage V0 at the inverting input terminal of the first comparing unit a6 gradually rises;

then the input voltage V0 at the inverting input terminal of the first comparing unit a6 enters the working mode of the next cycle.

When a linear dimming signal is input to the linear/pulse pin, that is, when the other input terminal of the first comparing unit a6 is connected to the linear dimming signal, the input linear dimming voltage V5 is compared with the input voltage V0 at the inverting input terminal of the first comparing unit a6, when V0> V5, the first comparing unit a6 outputs a low level, and when V0< V5, the first comparing unit a6 outputs a high level, so that the waveform of the output terminal output voltage POUT of the first comparing unit a6 is as shown in fig. 3;

when a pulse dimming signal is input to the linear/pulse pin, that is, the other input terminal of the first comparing unit A6 is connected to a pulse dimming signal, the high voltage of the pulse dimming signal is greater than the second fixed voltage V2, the low voltage of the pulse dimming signal is less than the first fixed voltage V1, the input pulse dimming voltage V5 is compared with the input voltage V0 at the inverting input terminal of the first comparing unit A6, when V0> V5, the first comparing unit A6 outputs a low level, and when V0< V5, the first comparing unit A6 outputs a high level, so that the waveform of the output voltage POUT at the output terminal of the first comparing unit A6 is as shown in fig. 4.

Specifically, the driving signal output by the PWM generator is used to control the on/off of the controllable switch M1 connected in series on the LED lighting circuit 101.

Referring to fig. 5, the LED lighting circuit 101 may include one or more LEDs connected in series, and a controllable switch M1 connected in series with the one or more LEDs, and the brightness of the LEDs can be adjusted by adjusting the on duty ratio of the controllable switch M1. The controlled terminal of the controllable switch M1 is connected to the output terminal of the PWM generator. The controllable switch M1 may be a triode, a MOS transistor, a silicon controlled Switch (SCR), a turn-off thyristor (GTO), an Insulated Gate Bipolar Transistor (IGBT), a magnetic controlled switch, or the like.

That is, the PWM generator provided in the embodiment of the present invention may be used as an LED driving circuit, or may be applied to an LED driving circuit.

As can be known from fig. 3 and 4, when linear dimming is performed, the higher the input voltage V5 is, the larger the PWM duty ratio is, the longer the time that the current flows through the LED lamp bead is, the higher the LED brightness is; when pulse dimming is performed, the duty ratio of the input voltage V5 is larger, the PWM duty ratio is larger, the time for the LED lamp beads to flow current is longer, and the LED brightness is higher.

In addition, according to the driving requirement, the output end of the PWM generator may be directly connected to the LED lighting circuit 101, or may be indirectly connected to the LED lighting circuit 101, for example, the output end of the PWM generator may be connected to the controlled end of the controllable switch connected in series to the LED lighting circuit 101 through the driving amplifier.

In some specific embodiments, the driving circuit further includes: a switching boost circuit 102 and a constant current control circuit 103;

the output voltage of the switch boosting circuit 102 is used as the power supply voltage of the LED light-emitting circuit 101;

the constant current control circuit 103 is configured to, during a period in which the switching boost circuit 102 outputs the supply voltage to the LED light-emitting circuit 101, control on/off of a switch M2 in the switching boost circuit 102 so that a current output from the switching boost circuit 102 to the LED light-emitting circuit 101 is constant and an output voltage of the switching boost circuit is greater than an input voltage.

Specifically, the input terminal of the switch voltage boost circuit 102 is connected to the power supply VIN, and is configured to boost the voltage of the power supply VIN, that is, the voltage output by the switch voltage boost circuit 102 is greater than the voltage of the input terminal (i.e., the power supply VIN). The output terminal of the switch boosting circuit 102 is connected to the power input terminal of the LED lighting circuit 101 to supply power to the LED lighting circuit 101. Of course, the output terminal of the switching boost circuit 102 is not necessarily directly connected to the power input terminal of the LED lighting circuit 101, but may also be indirectly connected to the power input terminal of the LED lighting circuit 101, for example, in some specific embodiments, the output terminal may also be connected to the power input terminal of the LED lighting circuit 101 through the first current sampling resistor R1.

Referring to fig. 5, the switching boost circuit 102 may specifically include an inductor L1, a diode D3, a switch M2 (specifically, a controllable switch), and a third capacitor C2, a first end of the inductor L1 is connected to the power supply VIN, a second end of the inductor L1 is connected to an anode of the diode D3 and a first end of the switch M2, a cathode of the diode D3 is used as an output end of the switching boost circuit 102, one end of the third capacitor C2 is connected to a cathode of the diode D3, the other end of the third capacitor C2 is grounded, and a second end of the switch M2 is grounded. The switch boost circuit 102 may further include a third capacitor C1, one end of which is connected to the power supply VIN (i.e., connected to the first end of the inductor L1), and the other end of which is grounded.

For a specific example, the switch M2 in the switching boost circuit 102 may be a switching device, please refer to a switching device used in the switching boost circuit 102 in the related art, which is not described herein again.

Under the same working voltage, the forward conduction voltage drop of the LED presents certain difference due to the influence of process discreteness, so that the constant current control circuit 103 is designed in the driving circuit provided by the embodiment of the invention, the constant current control circuit 103 can make the current flowing to the LED light-emitting circuit 101 constant, the stability of LED light emission can be greatly improved, and the driving circuit is particularly suitable for driving a white light LED.

In addition, in the related art, generally, the voltage required for driving the LED is higher, and the driving circuit provided by the embodiment of the invention includes the switching boost circuit 102, so that the LED light-emitting circuit 101 can be normally driven even if the output voltage of the power supply VIN is lower.

In some specific embodiments, the constant current control circuit 103 includes:

the first current sampling resistor R1 is used for collecting the current output by the switching boost circuit 102 and converting the current into a voltage signal; the current output by the switching boost circuit 102 is the current on the LED light-emitting circuit 101;

a fourth comparing unit a2, configured to compare a voltage signal output by the first current sampling resistor R1 with a preset reference voltage BG, and output a comparison result signal; the fourth comparing unit a2 is an operational amplifier;

and the control unit is used for controlling the on-off of the switch M2 in the switch boosting circuit 102 according to the comparison result signal.

In the embodiment of the invention, the current of the LED light-emitting circuit 101 is converted into a voltage signal through the first current sampling resistor R1 to be compared with the preset reference voltage BG, and then the control unit (specifically, the PWM controller shown in fig. 5) controls the on/off of the switch M2 in the switch boosting circuit 102 according to the comparison result between the voltage signal converted from the current of the LED light-emitting circuit 101 and the preset reference voltage BG, so that the current of the LED light-emitting circuit 101 can be constant. The resistance value of the first current sampling resistor R1 and the preset reference voltage BG can be reasonably selected according to the current requirement on the LED light-emitting circuit 101.

In other optional specific embodiments, the constant current control circuit 103 further includes an operational amplifier a1, and the operational amplifier a1 is configured to amplify the voltage signal output by the first current sampling resistor R1, for example, the voltage signal may be amplified by 20 times. Specifically, two input ends of the operational amplifier a1 are respectively connected to two ends of the first current sampling resistor R1, an output end of the operational amplifier a1 is connected to one input end of the fourth comparing unit a2, and the other input end of the fourth comparing unit a2 is connected to the preset reference voltage BG. In an embodiment of the present invention, the voltage signal output by the first current sampling resistor R1 is not directly compared with the preset reference voltage BG, but is amplified and then compared with the preset reference voltage BG. The resistance value of the first current sampling resistor R1, the preset reference voltage BG and the amplification factor of the operational amplifier A1 can be reasonably set as required.

In some specific embodiments, the control unit controls on/off of a switch in the switch boosting circuit 102 according to the comparison result signal and the driving signal.

Referring to fig. 5, the control unit is a PWM controller shown in the figure, and a signal (i.e., an output voltage POUT) output by the PWM generator is amplified by the driving amplifier and then input to the PWM controller (i.e., the control unit) as a driving signal of the LED light emitting circuit 101.

In the embodiment of the present invention, during the period that the driving signal controls the LED light emitting circuit 101 to be turned off, the control unit also controls the switch in the switch boosting circuit 102 to be continuously turned off.

In some specific embodiments, the constant current control circuit 103 further includes: an oscillator and second flip-flop E1;

one input end of the second flip-flop E1 is connected with the oscillator, and the other input end of the second flip-flop E1 is connected with an electric signal obtained based on the comparison result signal; the output end of the second trigger E1 is connected to one input end of the control unit, so that the control unit can control the on/off of the switch in the switch boosting circuit 102 according to the comparison result signal; the other input terminal of the second flip-flop E1 is connected to an electrical signal obtained based on the comparison result signal, for example, the other input terminal of the second flip-flop E1 is indirectly (i.e., through other components) connected to the output terminal of the fourth comparing unit a 2;

the output of the second flip-flop E1 changes only if one of the inputs is low and the other input is high. The output of the second flip-flop E1 may be high or low.

In the embodiment of the present invention, the control unit not only controls the on/off of the switch in the switch boosting circuit 102 according to the comparison result between the voltage signal converted by the current on the LED light emitting circuit 101 and the preset reference voltage BG, but also controls the on/off of the switch in the switch boosting circuit 102 according to the electrical signal output by the oscillator. Specifically, even if the current on the LED lighting circuit 101 increases or decreases, causing the comparison result signal output by the fourth comparing unit a2 to change, the control unit (i.e., the PWM controller shown in fig. 5) does not necessarily change the on-off state of the switch M2, but rather, when the level state (high or low) of the oscillator output is appropriate, the control unit (i.e., the PWM controller shown in fig. 5) changes the on-off state of the switch M2. When the circuit reaches a steady state, when the level state of the oscillator output is high, the switch M2 is turned on, and then the level state of the oscillator output is switched to low, at this time, as long as the output signal of the fifth comparing unit A3 changes, the switch M2 is immediately turned off, so that the switching frequency of the switch M2 can be controlled.

In some specific embodiments, the constant current control circuit 103 further includes: the circuit comprises a fifth comparison unit A3, a slope compensator F1, a second current sampling resistor R2 and a first resistor R5;

a first input terminal of the fifth comparing unit A3 is connected to the comparison result signal, a second input terminal of the fifth comparing unit A3 is connected to a first terminal of the slope compensator F1, a second terminal of the slope compensator F1 is connected to a first terminal of the second current sampling resistor R2 through the first resistor R5, a third terminal of the slope compensator F1 is connected to a slope compensation current Islope, the second current sampling resistor R2 is connected in series between a switch in the switch boosting circuit and ground, and the first terminal of the second current sampling resistor R2 is connected to the switch in the switch boosting circuit;

the output of the fifth comparison unit a3 is connected to the input of the control unit. Specifically, the output terminal of the fifth comparing unit A3 is connected to the input terminal of the control unit through the second flip-flop E1, and the output terminal of the fifth comparing unit A3 may be connected to the R terminal of the second flip-flop E1.

In some specific embodiments, the constant current control circuit 103 further includes: a controllable current source G1 and a second resistor R4;

one control terminal of the controllable current source G1 is connected to the output terminal of the fourth comparing unit a2, the other control terminal of the controllable current source G1 is connected to a preset fixed voltage V6, the output terminal of the controllable current source G1 is connected to the first input terminal of the fifth comparing unit A3, one end of the second resistor R4 is connected to the first input terminal of the fifth comparing unit A3, and the other end is grounded.

In addition, the power supply input of the controllable current source G1 is connected to a reference power supply VREF.

In some specific embodiments, the constant current control circuit 103 further includes: a third resistor R3 and a second capacitor C3;

In the embodiment of the present invention, the series connection structure of the third resistor R3 and the second capacitor C3 is used for performing phase compensation on the output of the fourth comparing unit a 2.

In the embodiment of the present invention, during the period when the PWM is at the high level, the current magnitude on R1 is adjusted by adjusting the on duty cycle of M2, during the period when M2 is off, the current on R2 (the charging current of the inductor) should be 0, and during the period when M2 is on, the current on R2 is not 0.

The operation principle of the constant current control circuit 103 is specifically described below.

The operational amplifier a1 detects a voltage across the first current sampling resistor R1, where the voltage reflects a current flowing through the first current sampling resistor R1, and the voltage across the first current sampling resistor R1 is amplified by the operational amplifier a1 and then input to the fourth comparing unit a2 together with a preset reference voltage BG for comparison and calculation.

The fourth comparing unit a2 outputs a comparison result signal (which is a voltage signal) to the positive input terminal of the controllable current source G1, the negative input terminal of the controllable current source G1 is connected to the preset fixed voltage V6, the output current of the controllable current source G1 is adjusted by the difference between the comparison result signal output by the fourth comparing unit a2 and the preset fixed voltage V6, and the output current of the controllable current source G1 is input to the second resistor R4 and then flows to the ground. The voltage of the second resistor R4 is indicative of the output current of the controllable current source G1, and the voltage of the second resistor R4 is inputted to the inverting input terminal of the fifth comparing unit A3. Meanwhile, the slope compensation current Islope flows to the ground through the slope compensator F1 and the first resistor R5 and the second current sampling resistor R2, the current on the control switch M2 flows to the ground through the second current sampling resistor R2, the voltage input to the non-inverting input terminal of the fifth comparing unit A3 is equal to the sum of the voltage corresponding to the slope compensation current Islope and the voltage corresponding to the current on the control switch M2, the fifth comparing unit a3 outputs a voltage signal to the R terminal of the second flip-flop E1 after calculation, the S terminal of the second flip-flop E1 is connected to the oscillator to control the switching frequency of the switch M2, and then the Q terminal of the second flip-flop E1 outputs an SWON signal to the PWM controller, meanwhile, the PWM controller also receives the PWM signal generated by the PWM generator, so that at this time, the PWM controller outputs a control signal to the switch M2 in the switch boosting circuit 102 according to the SWON signal and the PWM signal, thereby controlling the on/off of the switch M2.

From the above connection structure:

when the current flowing through the first current sampling resistor R1 is small, the preset reference voltage BG is greater than the voltage output by the operational amplifier a1, and the fourth comparing unit a2 outputs a high level, at this time, the output current of the controllable current source G1 becomes large, the voltage across the second resistor R4 becomes large, that is, the voltage at the inverting input terminal of the fifth comparing unit A3 becomes large, at this time, the non-inverting input terminal of the fifth comparing unit A3 is not changed temporarily, the fifth comparing unit A3 outputs a low level, that is, the R input of the second flip-flop E1 is at a low level, and when the S input of the second flip-flop E1 is at a high level (i.e., when the oscillator outputs a high level), the Q output of the second flip-flop E1 is at a high level, the switch M2 is continuously turned on, and the on duty ratio of the switch M2 is increased, at this time, as is clear from the principle of the boost circuit, the on duty of the switch M2 is proportional to the current, and therefore the current at the control switch M2 increases.

When the current on the control switch M2 increases to a certain value, the voltage input to the non-inverting input terminal of the fifth comparing unit A3 increases to a certain value, so that the voltage at the non-inverting input terminal of the fifth comparing unit A3 is greater than the voltage at the inverting input terminal of the fifth comparing unit A3 after increasing, the fifth comparing unit A3 outputs a high level, and when the oscillator outputs a low level, the switch M2 is turned off, and the inductor L1 is in a discharging state. At this time, since the current flowing through the control switch M2 has increased to a certain value, the amount of charge in the inductor L1 also increases, and the current flowing through the first current sampling resistor R1 increases.

When the current flowing through the first current sampling resistor R1 is large, the preset reference voltage BG is smaller than the voltage output by the operational amplifier a1, and the fourth comparing unit a2 outputs a low level, at this time, the output current of the controllable current source G1 becomes small, the voltage across the second resistor R4 becomes small, that is, the voltage across the inverting input terminal of the fifth comparing unit A3 becomes small. At this time, the non-inverting input terminal of the fifth comparing unit A3 is not changed temporarily, the fifth comparing unit A3 outputs a high level, that is, the R terminal input of the second flip-flop E1 is a high level, when the S terminal input of the second flip-flop E1 is a low level (that is, the oscillator outputs a low level), the Q terminal output of the second flip-flop E1 is a low level, the switch M2 is turned off, the on duty cycle of the switch M2 is reduced, and therefore, the current on the control switch M2 is reduced.

When the current on the control switch M2 is reduced to a certain value, the voltage input to the non-inverting input terminal of the fifth comparing unit A3 is reduced to a certain value, so that the voltage at the non-inverting input terminal of the fifth comparing unit A3 is smaller than the voltage at the inverting input terminal of the fifth comparing unit A3, the fifth comparing unit A3 outputs a low level, and when the oscillator outputs a high level, the switch M2 is turned on, and the inductor L1 is in a charging state. At this time, since the current flowing through the control switch M2 has decreased to a certain value, the amount of charge on the inductor L1 also decreases, and the current flowing through the first current sampling resistor R1 decreases.

Finally, as can be seen from the pseudo-short characteristic of the operational amplifier (i.e., the fourth comparing unit a 2), the voltage output by the operational amplifier a1 is finally adjusted to be equal to the preset reference voltage BG, i.e., the constant current control is realized by the constant current control circuit 103. And the voltage input into the LED lamp bead is higher than the input power supply voltage VIN, so that the application under low input voltage is realized.

The preset reference voltage BG, the preset fixed voltage V6 and the reference power source VREF are generated by a voltage generator.

Under the scene that one input end of the PWM controller is connected with the SWON signal and the other input end is connected with the PWM signal, when the PWM is at a high level, the controllable switch M1 connected in series on the LED lighting circuit 101 is in a conducting state, the switch M2 in the switch boosting circuit 102 is in a normal switching state, the current flowing through the first current sampling resistor R1 is a constant value, when the PWM is at a low level, the controllable switch M1 connected in series on the LED lighting circuit 101 and the switch M2 in the switch boosting circuit 102 are both in a normal switching state, and no current flows in the driving circuit.

The embodiments in the present specification are described in a progressive manner, and the same and similar parts among the embodiments are referred to each other, and each embodiment focuses on the differences from the other embodiments. The above description is only an example of the present application and is not intended to limit the present application. Various modifications and changes may occur to those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the scope of the claims of the present application.

Claims

1. A driver circuit, comprising: a PWM generator, the PWM generator comprising: the circuit comprises a first power supply, a first switch tube M3, a second switch tube M4, a first comparison unit A6, a switch control circuit and a first capacitor C4;

an input terminal of the first comparing unit a6 is connected with the first terminal of the first capacitor C4;

2. The driving circuit according to claim 1, further comprising: a first current source I1 and a second current source I2, the first current source I1 and the second current source I2 output currents with equal and constant sizes;

3. The drive circuit according to claim 1, wherein the switch control circuit comprises: a second comparing unit a4, a third comparing unit a5 and a first flip-flop E2;

one input end of the second comparison unit A4 is connected with the first end of the first capacitor C4, and the other input end of the second comparison unit A4 is connected with the second fixed voltage;

one input end of the third comparison unit A5 is connected with the first end of the first capacitor C4, and the other input end of the third comparison unit A5 is connected with the first fixed voltage;

4. The driving circuit according to claim 1, further comprising: the switch boosting circuit and the constant current control circuit;

the constant current control circuit is used for controlling the on-off of a switch in the switch boosting circuit when the switch boosting circuit outputs power supply voltage to the LED light-emitting circuit, so that the current output by the switch boosting circuit to the LED light-emitting circuit is constant, and the output voltage of the switch boosting circuit is larger than the input voltage.

5. The drive circuit according to claim 4, wherein the constant current control circuit comprises:

6. The driving circuit according to claim 5, wherein the control unit controls on/off of a switch in the switch boosting circuit according to the comparison result signal and the driving signal.

7. The drive circuit according to claim 5, wherein the constant current control circuit further comprises: an oscillator and second flip-flop E1;

one input end of the second flip-flop E1 is connected with the oscillator, and the other input end of the second flip-flop E1 is connected with an electric signal obtained based on the comparison result signal; the output end of the second trigger E1 is connected with one input end of the control unit, so that the control unit can control the on-off of a switch in the switch boosting circuit according to the comparison result signal;

8. The drive circuit according to claim 5, wherein the constant current control circuit further comprises: the circuit comprises a fifth comparison unit A3, a slope compensator F1, a second current sampling resistor R2 and a first resistor R5;

9. The drive circuit according to claim 8, wherein the constant current control circuit further comprises: a controllable current source G1 and a second resistor R4;

10. The drive circuit according to any one of claims 5 to 8, wherein the constant current control circuit further includes: a third resistor R3 and a second capacitor C3;