CN112469165B - LED driving circuit and method - Google Patents
LED driving circuit and method Download PDFInfo
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- CN112469165B CN112469165B CN201910866127.4A CN201910866127A CN112469165B CN 112469165 B CN112469165 B CN 112469165B CN 201910866127 A CN201910866127 A CN 201910866127A CN 112469165 B CN112469165 B CN 112469165B
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Abstract
The invention provides an LED driving circuit and a method, wherein the LED driving circuit comprises: a buck module; the peak control module outputs a turn-off control signal when the current flowing through the LED lamp segment reaches a set peak value; the turn-off time control module is used for adjusting turn-off time of the power switch tube; and a drive control module for generating a drive signal based on the output signals of the peak control module and the off-time control module. A fixed peak value is adopted to turn off a control power switch tube; the turn-off time is reduced when the output current is smaller, and the turn-off time is increased when the output current is larger, so that the turn-off time of the power switch tube is self-adaptively adjustable. The invention adopts fixed peak current to turn off, the output will not overshoot in the loop control, and can be started quickly; the output current after average value current detection has high precision, the turn-off time is internally adjusted, external setting is not needed, external pins and elements can be reduced, and the system cost is reduced; the LED ripple current is internally fixed and is not influenced by external conditions and element parameters.
Description
Technical Field
The invention relates to the field of LED driving, in particular to an LED driving circuit and an LED driving method.
Background
In the DC-DC high power LED constant current driving scheme, a step-down circuit (Buck) is generally adopted, and as shown in fig. 1, a current detection resistor R1' is directly connected in series to the LED, so that the output current can be accurately detected and controlled. Since switch SW is at the high side bus voltage, PMOS devices are typically required, but once the input voltage Vin is relatively high, PMOS options are relatively small and cost is relatively high; if NMOS device is adopted, the buck control module needs to be driven at high voltage, the chip needs to adopt a high-voltage process, and the cost is increased.
The LED can be arranged at a high-end output, the switch SW is arranged at a ground wire end for control, the switch SW adopts an NMOS device, a chip does not need a high-voltage driving process, and the cost can be reduced, as shown in figure 2. But at this time, the current detection resistor R1'The LED current cannot be directly sampled, the current at the on time can only be indirectly sampled through the switch SW, then the CCM continuous operation mode is adopted, and the output current meets the following conditions:
wherein V is CS To sample voltage, R 1 For external sense resistor, V LED For LED load voltage, T OFF For external capacitance C OFF The set off time, L1, is the inductance.
From the above, the output current accuracy depends on the sampling voltage V CS LED load voltage V LED Off time T OFF And an inductance L1 (the current detection resistor R1' employs an external high-precision resistor, and the precision is usually ensured by 1%, so that its influence can be ignored). Wherein the voltage V is sampled CS Mainly relates to sampling errors caused by the inversion delay of an internal comparator (on one hand, errors of delay per se and errors caused by the change of different current slopes in the same time), and LED load voltage V LED The turn-off time T can change under different current and temperature conditions (and the load voltage caused by different LED lamp bead numbers is changed more greatly) OFF By an external capacitor C OFF Set and the external capacitance C OFF The accuracy of the inductor L1 is typically 5% -10%, and the accuracy of the inductor L1 is typically 10% -20%, so that the output current is greatly affected by the parameter variation of the peripheral element. The output current ripple satisfies:
the influence of the peripheral component parameter variation is also relatively large.
Therefore, how to reduce the influence of the peripheral devices on the output current and the output current ripple, improve the output current precision, and reduce the cost has become one of the problems to be solved by those skilled in the art.
Disclosure of Invention
In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide an LED driving circuit and method for solving the problems of the prior art that the peripheral element of the LED driving circuit has a large influence on the output current and the output current ripple, the output current precision is low, and the cost is high.
To achieve the above and other related objects, the present invention provides an LED driving circuit, including at least:
the LED lamp section is positioned at the high-voltage end of the voltage reducing module, and the power switch tube is positioned at the low-voltage end of the voltage reducing module;
the peak control module is used for receiving the sampling voltage of the voltage reducing module and outputting a turn-off control signal of the power switch tube when the current flowing through the LED lamp section reaches a set peak current;
the turn-off time control module is used for receiving the sampling voltage of the voltage reduction module, adjusting the turn-off time of the power switch tube based on the sampling voltage, reducing the turn-off time when the time of the sampling voltage smaller than the reference voltage is longer than the time of the sampling voltage larger than the reference voltage, and increasing the turn-off time when the time of the sampling voltage smaller than the reference voltage is shorter than the time of the sampling voltage larger than the reference voltage;
and the driving control module is connected to the output ends of the peak control module and the turn-off time control module, and generates a driving signal of the power switch tube based on the output signals of the peak control module and the turn-off time control module.
Optionally, the step-down module further comprises a power input unit, an inductor, a diode and a sampling unit;
the positive electrode of the LED lamp section is connected with the output end of the power input unit, the negative electrode of the LED lamp section is connected with the first end of the inductor, the second end of the inductor is connected with the positive electrode of the diode, and the negative electrode of the diode is connected with the positive electrode of the LED lamp section; the drain electrode of the power switch tube is connected with the second end of the inductor, the source electrode of the power switch tube is grounded through the sampling unit, and the grid electrode of the power switch tube is connected with the output end of the driving control module.
More optionally, the LED driving circuit further includes an operating voltage generating module, and the operating voltage generating module is connected to an output end of the power input unit, and is configured to generate an operating voltage.
More optionally, the peak control module includes a first comparator, a first input end of the first comparator is connected to the sampling voltage, a second input end of the first comparator is connected to a set peak voltage, and an output end of the first comparator is connected to the driving control module.
More optionally, the peak control module further comprises a leading edge blanking unit connected between the sampled voltage and the first input of the first comparator.
More optionally, the off-time control module includes a second comparator, a first constant current source, a second constant current source, a first capacitor, an inverter, and a first off-time generating unit;
the first input end of the second comparator is connected with the sampling voltage, the second input end of the second comparator is connected with the reference voltage, the output end of the second comparator is connected with the input end of the inverter, and the control end of the inverter is connected with the output end of the drive control module;
the input end of the first constant current source is connected with the working voltage, the output end of the first constant current source is connected with the input end of the second constant current source, and the output end of the second constant current source is grounded; the control end of the first constant current source is connected with the output end of the second comparator, and the control end of the second constant current source is connected with the output end of the inverter;
the upper polar plate of the first capacitor is connected with the input end of the second constant current source, and the lower polar plate is grounded;
the first turn-off time generating unit is connected to the upper polar plate of the first capacitor and adjusts the turn-off time of the power switch tube based on the voltage value of the first capacitor.
More optionally, the off-time control module includes a transconductance amplifier, a first switch, a second switch, a third switch, a first resistor, a second capacitor, and a second off-time generating unit;
one end of the first switch is connected with the sampling voltage, the other end of the first switch is connected with the first input end of the transconductance amplifier, and the first input end of the transconductance amplifier is grounded through the first resistor;
one end of the second switch is connected with the reference voltage, the other end of the second switch is connected with the second input end of the transconductance amplifier, and the second input end of the transconductance amplifier is grounded through the second resistor;
the output end of the transconductance amplifier is connected with the upper polar plate of the second capacitor through the third switch, and the lower polar plate of the second capacitor is grounded;
the second turn-off time generation unit is connected to the upper polar plate of the second capacitor, and the turn-off time of the power switch tube is adjusted based on the voltage value of the second capacitor;
the control ends of the first switch, the second switch and the third switch are connected with the driving signal, and when the driving signal is in a high level, the first switch, the second switch and the third switch are conducted.
To achieve the above and other related objects, the present invention also provides an LED driving method, including at least:
sampling the current flowing through a power switch tube to obtain a sampling voltage, and turning off the power switch tube when the sampling voltage reaches a set peak voltage;
reducing turn-off time when the time of the sampling voltage is smaller than the reference voltage is longer than the time of the sampling voltage is larger than the reference voltage, increasing turn-off time when the time of the sampling voltage is smaller than the reference voltage is shorter than the time of the sampling voltage is larger than the reference voltage, and keeping the turn-off time of the power switch tube unchanged until the time of the sampling voltage is smaller than the reference voltage and the time of the sampling voltage is larger than the reference voltage is equal;
wherein the reference voltage is less than the set peak voltage.
Optionally, the method for reducing the turn-off time or increasing the turn-off time includes: and detecting the magnitude relation between the sampling voltage and the reference voltage, discharging a capacitor when the sampling voltage is smaller than the reference voltage, charging the capacitor when the sampling voltage is larger than the reference voltage, wherein the smaller the voltage value of the capacitor is, the shorter the turn-off time of the power switch tube is.
More optionally, the LED current satisfies: i LED ＝V ref /R CS Wherein V is ref For the reference voltage, R CS Is the resistance of the sampling unit.
As described above, the LED driving circuit and method of the present invention have the following advantages:
1. the LED driving circuit and the method have the advantages that the LED current precision is high, and the influence of peripheral element parameters is avoided.
2. The LED driving circuit and the method have the advantages that the turn-off time is internally adjusted, external arrangement is not needed, external pins and elements can be reduced, and the system cost is reduced.
3. In the LED driving circuit and the method, the LED current ripple is internally fixed and is not influenced by external element parameters.
Drawings
Fig. 1 is a schematic diagram of an LED driving circuit with a step-down structure in the prior art.
Fig. 2 is a schematic diagram of an LED driving circuit with another voltage reducing structure in the prior art.
Fig. 3 is a schematic structural diagram of an embodiment of an LED driving circuit according to the present invention.
Fig. 4 is a schematic diagram illustrating the operation of the LED driving circuit according to the present invention.
Fig. 5 is a schematic structural diagram of another embodiment of the LED driving circuit of the present invention.
Description of element reference numerals
1 LED driving circuit
11. Step-down module
111. Power input unit
12. Peak control module
121. First comparator
122. Leading edge blanking unit
13. Shut-down time control module
131. Second comparator
132. Inverter with a high-speed circuit
133. First off-time generating unit
134. Transconductance amplifier
135. Second off-time generation unit
14. Drive control module
15. Operating voltage generating module
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.
Please refer to fig. 3-5. It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.
Example 1
As shown in fig. 3, the present embodiment provides an LED driving circuit 1, the LED driving circuit 1 including:
the step-down module 11, the peak control module 12, the off-time control module 13 and the drive control module 14.
As shown in fig. 3, the step-down module 11 performs step-down processing on the input voltage to provide electric energy for the LED lamp segment.
Specifically, in this embodiment, the step-down module 11 includes a power input unit 111, an LED segment LED, an inductor L, a diode D, a power switch Q, and a sampling unit.
More specifically, in the present embodiment, the power input unit 111 includes a dc power V DC And an input capacitor Cin, the DC power supply V DC Obtained by means including, but not limited to, rectification of an ac power source. The power input unit 111 may provide a dc input voltage, and the implementation manner is not limited to the embodiment, and is not described herein.
More specifically, the positive electrode of the LED light segment LED is connected to the output end of the power input unit 111, and the negative electrode of the LED light segment LED is connected to the first end of the inductor L. The LED lamp section LEDs comprise a plurality of LED lamps which are connected in series, the specific number of the LED lamps can be set according to the needs, and the LED lamps are not limited in one-to-one mode.
More specifically, the second end of the inductor L is connected to the positive electrode of the diode D, and the negative electrode of the diode D is connected to the positive electrode of the LED light segment LED. The inductor L is used for providing electric energy for the LED lamp section LEDs when the power switch tube Q is turned off, and the diode D is used for providing a current path when the power switch tube Q is turned off.
More specifically, the drain electrode of the power switch Q is connected to the second end of the inductor L, the source electrode is grounded via the sampling unit, and the gate electrode is connected to the output end of the driving control module 14. The power switch tube Q controls the current flowing through the LEDs of the LED lamp section through turn-off and turn-on, and in the embodiment, the power switch tube Q adopts an NMOS device.
More specifically, one end of the sampling unit is connected to the source electrode of the power switch tube Q, and the other end is grounded. In this embodiment, the sampling unit includes a sampling resistor Rcs. In practical use, any circuit structure capable of realizing current sampling is suitable for the sampling unit of the invention.
It should be noted that, the structure of the voltage reducing module 11 is not limited to the examples in this embodiment, any structure that can achieve the voltage reducing function, and the LED lamp section is located at the high voltage end of the voltage reducing module 11 and the power switch Q is located at the low voltage end of the voltage reducing module 11 is suitable for the present invention.
As shown in fig. 3, the peak control module 12 receives the sampled voltage V of the buck module 11 CS And outputting a turn-off control signal of the power switch tube Q when the current flowing through the LED lamp segment LED reaches a set peak current.
Specifically, in this embodiment, the peak control module 12 includes a first comparator 121, where an inverting input terminal of the first comparator 121 is connected to the sampling voltage Vcs, a non-inverting input terminal is connected to the set peak voltage Vpeak, and an output terminal is connected to the driving control module 14.
The sampling voltage V CS The voltage of the sampling current of the voltage reduction module 11 on the sampling resistor Rcs is based on the sampling voltage V CS The magnitude of the sampling current may be determined. The correspondence between the input signal and the polarity of the input terminal of the first comparator 121 may be exchanged through an inverter, so long as the logic relationship of the present invention can be implemented, and the present invention is not limited to this embodiment.
As an implementation manner of the present invention, the peak control module 12 further includes a leading edge blanking unit 122, where the leading edge blanking unit 122 is connected between the sampling voltage Vcs and the inverting input terminal of the first comparator 121, and is configured to perform leading edge blanking when the power switch Q is turned on and generates the pulse peak current instantaneously, so as to avoid generating a false triggering action due to a peak of the pulse leading edge, and improve stability.
As shown in fig. 3, the off-time control module 13 receives the sampling voltage Vcs of the voltage step-down module 11, and adjusts the off-time T of the power switch Q based on the sampling voltage Vcs OFF The off-time T is reduced when the time when the sampling voltage Vcs is smaller than the reference voltage Vref is longer than the time when the sampling voltage Vcs is larger than the reference voltage Vref OFF The off-time T is increased when the time when the sampling voltage Vcs is smaller than the reference voltage Vref is shorter than the time when the sampling voltage Vcs is larger than the reference voltage Vref OFF 。
Specifically, in the present embodiment, the off-time control module 13 includes a second comparator 131, a first constant current source I1, a second constant current source I2, a first capacitor C1, an inverter 132, and a first off-time generation unit 133.
More specifically, the second comparator 131 has a non-inverting input terminal connected to the sampling voltage Vcs, an inverting input terminal connected to the reference voltage Vref, and compares the sampling voltage Vcs with the reference voltage Vref to obtain a charge-discharge control signal. The reference voltage Vref is smaller than the set peak voltage Vpeak, and specific values may be set as needed, which is not limited herein.
It should be noted that, the correspondence between the input signal and the polarity of the input end of the second comparator 131 may be exchanged through an inverter, so long as the logic relationship of the present invention can be implemented, and the present invention is not limited to the embodiment.
More specifically, the input end of the first constant current source I1 is connected to the working voltage VDD, the output end is connected to the input end of the second constant current source I2, and the output end of the second constant current source I2 is grounded. The control end of the first constant current source I1 is connected with the charge and discharge control signal, the control end of the second constant current source I2 is connected with the inversion signal of the charge and discharge control signal through the inverter 132, and the control end of the inverter 132 is connected with the output end of the driving control module 14. Namely, when the power switch tube Q is conducted, the control signals of the first constant current source I1 and the second constant current source I2 are opposite; when the power switch tube Q is turned off, the first constant current source I1 and the second constant current source I2 do not work. In this embodiment, the first constant current source I1 and the second constant current source I2 have equal currents.
It should be noted that the operating voltage VDD may be generated by the operating voltage generating module 15 of the present embodiment, or may be provided by an external signal through a port, which is not limited to the present embodiment.
More specifically, the upper plate of the first capacitor C1 is connected to the output end of the first constant current source I1 and the input end of the second constant current source I2, and the lower plate of the first capacitor C1 is grounded. The first capacitor C1 is charged when the first constant current source I1 is turned on, and the first capacitor C1 is discharged when the second constant current source I2 is turned on. Since the currents of the first constant current source I1 and the second constant current source I2 are small and the operating frequency of the system is high, the capacity of the first capacitor C1 is relatively small, and in this embodiment, the first capacitor C1 is integrated inside the chip.
More specifically, the first off-time generating unit 133 is connected to the upper plate of the first capacitor C1, and adjusts the off-time T of the power switch Q based on the voltage value VC1 of the first capacitor C1 OFF . The larger the voltage value VC1 of the first capacitor C1 is, the switch-off time T is OFF The longer the voltage value VC1 of the first capacitor C1 is, the smaller the turn-off time T is OFF The shorter.
The off time T OFF By internal adjustment, external pins and elements are not needed for setting, and the system cost is saved.
As shown in fig. 3, the driving control module 14 is connected to the output ends of the peak control module 12 and the off-time control module 13, and generates the driving signal of the power switch Q based on the output signals of the peak control module 12 and the off-time control module 13.
Specifically, the driving control module 14 outputs a driving signal of the power switching tube Q, and when the peak control module 12 outputs a turn-off control signal, the driving signal controls the power switching tube Q to be turned off; and off time T OFF Is determined by the output signal of the off-time control module 13. Off time T OFF And after the end, the driving signal is used for controlling the power switch tube Q to be conducted again.
As shown in fig. 3, as an implementation manner of the present invention, the LED driving circuit 1 further includes an operating voltage generating module 15, where the operating voltage generating module 15 is connected to an output end of the power input unit 111, and is configured to generate an operating voltage VDD. The generating manner of the operating voltage VDD includes, but is not limited to, the present embodiment, and any manner of generating the operating voltage VDD is applicable to the present invention.
As shown in fig. 3, as an implementation of the present invention, the peak control module 12, the off-time control module 13, the driving control module 14, and the operating voltage generation module 15 are integrated in a chip.
As shown in fig. 3, as another implementation manner of the present invention, the power switching tube Q, the peak control module 12, the off-time control module 13, the driving control module 14, and the operating voltage generating module 15 are integrated in a chip.
The present embodiment also provides an LED driving method, in this embodiment, the LED driving method is implemented based on the LED driving circuit 1, and in actual use, any hardware or software that accords with the logic of the method is applicable, and is not limited to this embodiment. The LED driving method comprises the following steps:
sampling the current flowing through the power switch tube Q to obtain a sampling voltage Vcs, and turning off the power switch tube Q when the sampling voltage Vcs reaches a set peak voltage Vpeak;
reducing the off-time T when the sampled voltage Vcs is less than the reference voltage Vref longer than the sampled voltage Vcs is greater than the reference voltage Vref OFF Increasing the turn-off time T when the time when the sampling voltage Vcs is smaller than the reference voltage Vref is shorter than the time when the sampling voltage Vcs is larger than the reference voltage Vref OFF The turn-off time T of the power switch tube Q is equal to the time when the sampling voltage Vcs is smaller than the reference voltage Vref and the time when the sampling voltage Vcs is larger than the reference voltage Vref OFF Remain unchanged; wherein, the reference voltage Vref is smaller than the set peak voltage Vpeak.
Specifically, the LED driving method employs a fixed peak off, when the sampling voltage Vcs reaches a set peak voltage Vpeak (i.e., LED current I LED Reaching a set peak current Ipeak) turns off the power switch Q. And then the sampling voltage V CS Comparing with the reference voltage Vref, when the sampling voltage V CS When the reference voltage Vref is lower than the reference voltage Vref, the second constant current source I2 is controlled to discharge the first capacitor C1 (the first constant current source I1 is turned off at the moment), and when the sampling voltage V is lower than the reference voltage Vref, the second constant current source I2 is controlled to discharge the first capacitor C1 CS Above saidThe first constant current source I1 is controlled to charge the first capacitor C1 at the reference voltage Vref (the second constant current source I2 is turned off at this time). When the power switch tube Q is turned off, the first constant current source I1 and the second constant current source I2 are turned off, the first capacitor C1 is neither charged nor discharged, the voltage VC1 on the first capacitor C1 is kept unchanged, and the voltage VC1 on the first capacitor C1 at the moment determines the turn-off time T OFF 。
More specifically, if the LED current I LED Higher, the sampling voltage V CS The time when the voltage is higher than the reference voltage Vref is longer than the sampling voltage V CS The voltage is lower than the reference voltage Vref for a long time, the charging time of the first constant current source I1 is longer than the discharging time of the second constant current source I2, the voltage VC1 on the first capacitor C1 can rise, and the corresponding turn-off time T OFF Will increase, so that the time for discharging the inductor L is prolonged, and the sampling voltage V is in the next switching period due to the fixed peak value turn-off CS The starting point of (1) decreases so that the LED current I LED Down to reciprocate until equilibrium is re-reached. If the LED current I LED Low, the sampling voltage V CS A time lower than the reference voltage Vref is less than the sampling voltage V CS The voltage is higher than the reference voltage Vref for a long time, the second constant current source I2 discharges for a longer time than the first constant current source I1 charges, the voltage value VC1 of the first capacitor C1 drops, and the corresponding turn-off time T OFF Will decrease, so that the time for discharging the inductor L is shortened, and the sampling voltage V is in the next switching period due to the fixed peak value being turned off CS Will rise from the starting point of (1), so the LED current I LED Will rise and thereby reciprocate until equilibrium is re-reached. When the system reaches equilibrium, the charging time of the first constant current source I1 is equal to the discharging time of the second constant current source I2, so that the sampling voltage V CS Is equal to the reference voltage Vref, thus enabling detection of the output average current.
At this time, the LED current satisfies: i LED ＝V ref /R CS Wherein，V ref For the reference voltage, R CS The resistance value of the sampling resistor; the accuracy of the current depends on the consistency of the first constant current source I1 and the second constant current source I2 and the accuracy of the second comparator 131, and the input voltage Vin and the output voltage V LED Irrespective of the inductance L and independently of the peripheral conditions and variations in the component parameters. In addition, the invention adopts fixed peak value turn-off, so that the LED peak current is controlled in each turn-on period, overshoot of the normal loop response does not occur, and the LED current ripple is controlled at 2 (V peak -V ref )/R CS Within, wherein V peak For the set peak voltage, V ref For the reference voltage, R CS The resistance of the sampling resistor is also not affected by the parameters of the peripheral elements.
As shown in fig. 3 to 4, at time t0, the power switch Q is turned on, at this time, the input voltage Vin passes through the LED of the LED lamp section, the power switch Q, and the sampling resistor R CS And charging the inductor L. Before time t1, vcs<When Vref, the first capacitor C1 is in a discharge state (the voltage value VC1 of the first capacitor C1 is 0 at start-up, corresponding to the minimum off time T OFF ). Vcs after time t1>Vref, the first capacitor C1 is in a charging state, and the VC1 voltage starts to rise. At time T2, vcs reaches Vpeak value, switching tube Q1 is turned off, C1 is neither charged nor discharged, voltage value VC1 of first capacitor C1 remains unchanged, and voltage value VC1 of first capacitor C1 determines the off time T at this time OFF . An off time T set by a voltage value VC1 of the first capacitor C1 OFF And after reaching the time t3, the power switch tube Q is opened again. If the last period is the turn-off time T OFF Is relatively short (the off time T at start-up) OFF Relatively short and therefore can be started quickly), the inductor lrischarge time is also short, when Vcs>And Vref, wherein the first capacitor C1 is in a charging state, and the voltage value VC1 of the first capacitor C1 continuously rises. Until time t4, when the sampling voltage Vcs reaches the set peak voltage Vpeak again, the power switch Q is turned off, and the first capacitor C1 is powered onThe pressure value VC1 remains unchanged. An off time T set by a voltage value VC1 of the first capacitor C1 OFF After reaching time t5, a new switching cycle starts, and the operation is continued according to the set mode (t 5-t 7) until the system reaches the equilibrium state (t 8-t 13).
Example two
As shown in fig. 5, this embodiment provides an LED driving circuit, which is different from the first embodiment in that the implementation manner of the off-time control module 13 is different.
Specifically, the off-time control module 13 includes a transconductance amplifier 134, a first switch S1, a second switch S2, a third switch S3, a first resistor R1, a second resistor R2, a second capacitor C2, and a second off-time generating unit 135.
More specifically, one end of the first switch S1 is connected to the sampling voltage Vcs, the other end is connected to the non-inverting input terminal of the transconductance amplifier 134, and the non-inverting input terminal of the transconductance amplifier 134 is grounded via the first resistor R1; one end of the second switch S2 is connected to the reference voltage Vref, the other end is connected to the inverting input terminal of the transconductance amplifier 134, and the inverting input terminal of the transconductance amplifier 134 is grounded via the second resistor R2. The control ends of the first switch S1 and the second switch S2 are connected to the driving signal, when the power switch tube is turned on, the first switch S1 and the second switch S2 are turned on, and the transconductance amplifier 134 generates a charging signal based on the sampling voltage Vcs and the reference voltage Vref.
It should be noted that, the correspondence between the input signal and the polarity of the input terminal of the transconductance amplifier 134 may be exchanged through an inverter, so long as the logic relationship of the present invention can be implemented, and the present invention is not limited to this embodiment.
More specifically, the output end of the transconductance amplifier 134 is connected to the upper plate of the second capacitor C2 via the third switch S3, the lower plate of the second capacitor C2 is grounded, the control end of the third switch S3 is connected to the driving signal, when the power switch Q is turned on, the third switch S3 is turned on, and the output signal of the transconductance amplifier 134 charges the second capacitor C2.
More specifically, the second off-time generating unit 135 is connected to the upper plate of the second capacitor C2, and adjusts the off-time T of the power switch Q based on the voltage value of the second capacitor C2 OFF . The second capacitor C2 has the same operation principle as the first capacitor C1 in the first embodiment, and the second off-time generating unit 135 has the same structure and function as the first off-time generating unit 133 in the first embodiment, which are not described in detail herein.
The principle of the LED driving circuit of the present embodiment is the same as that of the first embodiment, and will not be described in detail here. In this embodiment, the transconductance amplifier 134 is used to charge the capacitor, so that the influence caused by the errors of the first constant current source I1 and the second constant current source I2 in the first embodiment can be reduced, and higher output accuracy can be obtained.
In summary, the present invention provides an LED driving circuit and method, including: the step-down module is used for controlling the LED lamp section to be positioned at a high voltage end and the power switch tube to be positioned at a low voltage end; the peak control module is used for receiving the sampling voltage of the voltage reducing module and outputting a turn-off control signal of the power switch tube when the current flowing through the LED lamp section reaches a set peak value; the turn-off time control module is used for receiving the sampling voltage of the voltage reduction module, adjusting the turn-off time of the power switch tube based on the sampling voltage, reducing the turn-off time when the time of the sampling voltage smaller than the reference voltage is longer than the time of the sampling voltage larger than the reference voltage, and increasing the turn-off time when the time of the sampling voltage smaller than the reference voltage is shorter than the time of the sampling voltage larger than the reference voltage; and the driving control module is connected with the output ends of the peak control module and the turn-off time control module, and generates a driving signal of the power switch tube based on the output signals of the peak control module and the turn-off time control module. The LED driving circuit and the method adopt fixed peak value turn-off, the output cannot overshoot in loop control, and the LED driving circuit and the method can be started quickly; the output current after the average value is used for detection has high precision and is not influenced by the parameters of peripheral elements; the turn-off time is internally adjusted, external setting is not needed, external pins and elements can be reduced, and the system cost is reduced; the LED ripple current is internally fixed and is not influenced by external conditions and element parameters. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.
The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.
Claims (9)
1. An LED driving circuit, comprising at least:
the LED lamp section is positioned at the high-voltage end of the voltage reducing module, and the power switch tube is positioned at the low-voltage end of the voltage reducing module;
the peak control module is used for receiving the sampling voltage of the voltage reducing module and outputting a turn-off control signal of the power switch tube when the current flowing through the LED lamp section reaches a set peak current;
the turn-off time control module is used for receiving the sampling voltage of the voltage reduction module, adjusting the turn-off time of the power switch tube based on the sampling voltage, reducing the turn-off time when the time of the sampling voltage smaller than the reference voltage is longer than the time of the sampling voltage larger than the reference voltage, and increasing the turn-off time when the time of the sampling voltage smaller than the reference voltage is shorter than the time of the sampling voltage larger than the reference voltage; discharging a capacitor when the sampling voltage is smaller than the reference voltage, charging the capacitor when the sampling voltage is larger than the reference voltage, wherein the smaller the voltage value of the capacitor is, the shorter the turn-off time of the power switch tube is;
and the driving control module is connected to the output ends of the peak control module and the turn-off time control module, and generates a driving signal of the power switch tube based on the output signals of the peak control module and the turn-off time control module.
2. The LED driving circuit according to claim 1, wherein: the voltage reduction module further comprises a power input unit, an inductor, a diode and a sampling unit;
the positive electrode of the LED lamp section is connected with the output end of the power input unit, the negative electrode of the LED lamp section is connected with the first end of the inductor, the second end of the inductor is connected with the positive electrode of the diode, and the negative electrode of the diode is connected with the positive electrode of the LED lamp section; the drain electrode of the power switch tube is connected with the second end of the inductor, the source electrode of the power switch tube is grounded through the sampling unit, and the grid electrode of the power switch tube is connected with the output end of the driving control module.
3. The LED driving circuit according to claim 2, wherein: the LED driving circuit further comprises a working voltage generating module, wherein the working voltage generating module is connected with the output end of the power input unit and used for generating working voltage.
4. The LED driving circuit according to claim 1 or 2, characterized in that: the peak control module comprises a first comparator, wherein a first input end of the first comparator is connected with the sampling voltage, a second input end of the first comparator is connected with a set peak voltage, and an output end of the first comparator is connected with the driving control module.
5. The LED driving circuit of claim 4, wherein: the peak control module further includes a leading edge blanking unit connected between the sampled voltage and a first input of the first comparator.
6. The LED driving circuit according to claim 1 or 2, characterized in that: the turn-off time control module comprises a second comparator, a first constant current source, a second constant current source, a first capacitor, an inverter and a first turn-off time generation unit;
the first input end of the second comparator is connected with the sampling voltage, the second input end of the second comparator is connected with the reference voltage, the output end of the second comparator is connected with the input end of the inverter, and the control end of the inverter is connected with the output end of the drive control module;
the input end of the first constant current source is connected with the working voltage, the output end of the first constant current source is connected with the input end of the second constant current source, and the output end of the second constant current source is grounded; the control end of the first constant current source is connected with the output end of the second comparator, and the control end of the second constant current source is connected with the output end of the inverter;
the upper polar plate of the first capacitor is connected with the input end of the second constant current source, and the lower polar plate is grounded;
the first turn-off time generating unit is connected to the upper polar plate of the first capacitor and adjusts the turn-off time of the power switch tube based on the voltage value of the first capacitor.
7. The LED driving circuit according to claim 1 or 2, characterized in that: the turn-off time control module comprises a transconductance amplifier, a first switch, a second switch, a third switch, a first resistor, a second capacitor and a second turn-off time generation unit;
one end of the first switch is connected with the sampling voltage, the other end of the first switch is connected with the first input end of the transconductance amplifier, and the first input end of the transconductance amplifier is grounded through the first resistor;
one end of the second switch is connected with the reference voltage, the other end of the second switch is connected with the second input end of the transconductance amplifier, and the second input end of the transconductance amplifier is grounded through the second resistor;
the output end of the transconductance amplifier is connected with the upper polar plate of the second capacitor through the third switch, and the lower polar plate of the second capacitor is grounded;
the second turn-off time generation unit is connected to the upper polar plate of the second capacitor, and the turn-off time of the power switch tube is adjusted based on the voltage value of the second capacitor;
the control ends of the first switch, the second switch and the third switch are connected with the driving signal, and when the driving signal is in a high level, the first switch, the second switch and the third switch are conducted.
8. An LED driving method, comprising at least:
sampling the current flowing through a power switch tube to obtain a sampling voltage, and turning off the power switch tube when the sampling voltage reaches a set peak voltage;
reducing turn-off time when the time of the sampling voltage is smaller than the reference voltage is longer than the time of the sampling voltage is larger than the reference voltage, increasing turn-off time when the time of the sampling voltage is smaller than the reference voltage is shorter than the time of the sampling voltage is larger than the reference voltage, and keeping the turn-off time of the power switch tube unchanged until the time of the sampling voltage is smaller than the reference voltage and the time of the sampling voltage is larger than the reference voltage is equal; wherein the method for reducing the turn-off time or increasing the turn-off time comprises the following steps: detecting the magnitude relation between the sampling voltage and the reference voltage, discharging a capacitor when the sampling voltage is smaller than the reference voltage, charging the capacitor when the sampling voltage is larger than the reference voltage, wherein the smaller the voltage value of the capacitor is, the shorter the turn-off time of the power switch tube is;
wherein the reference voltage is less than the set peak voltage.
9. The LED driving method according to claim 8, wherein: the LED current satisfies: i LED ＝V ref /R CS Wherein V is ref For the reference voltage, R CS Is the resistance of the sampling unit.
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| CN115296259B (en) * | 2022-09-27 | 2022-12-20 | 深圳利普芯微电子有限公司 | Overvoltage protection circuit and LED drive power supply |
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