LED driving system, feedback control circuit and method for LED driving

Abstract

This invention provides an LED driving system, a feedback control circuit and method for LED driving, including detecting the output current and obtaining a feedback voltage; when the feedback voltage is less than a first threshold, setting a preset voltage to a first preset value and increasing the feedback voltage; when the feedback voltage is greater than a second threshold, setting the preset voltage to a second preset value and decreasing the feedback voltage; when the feedback voltage is between the first and second thresholds, maintaining the preset voltage in its previous state and not adjusting the feedback voltage; adjusting the output current based on the comparison result between the feedback voltage and the preset voltage and a dimming signal to achieve dimming control. This invention can still have sufficient current detection capability at low current output, improving detection accuracy and meeting the application of dimming to very low current output; preventing flickering caused by output current jumps; preventing oscillation caused by mode switching; increasing the current adjustment range; and integrating it inside the chip to simplify the peripheral circuitry and reduce costs.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit design, and in particular to an LED driving system, a feedback control circuit for LED driving, and a method thereof. Background Technology

[0002] Dimming refers to adjusting the brightness of a light source by changing its luminous flux and illuminance level. It is an important means of controlling lighting. Common dimming circuits use the CS pin to feed back the voltage of a current sensing resistor. An external DIM dimming pin is used to input a dimming signal to change the operational amplifier's reference, thus achieving a dimming current output. This dimming signal can be a PWM signal or an analog signal. At large dimming ratios, if analog dimming is used, the voltage at the CS pin will be very small when adjusting to a low current output. The operational amplifier will be unable to accurately control this due to the offset voltage. Therefore, low current output (for example, <10% output) is usually achieved using PWM dimming. However, PWM dimming can cause flickering, noise, and EMI (Electromagnetic Interference) problems due to the dimming frequency and switching effects.

[0003] Another common dimming feedback circuit uses a sense MOS (sensing MOSFET) proportional to the main MOS to detect current and provide feedback. The detection module converts the current signal of the sense MOS into a voltage signal, which is then compared with a reference voltage to control the output current. However, the same problem exists when dimming to a low current output: the feedback current signal is too small, making detection and control difficult.

[0004] In analog dimming applications, since the output current feedback detection is fixed, a small current output will inevitably result in a weak feedback signal, for which there is currently no good solution. Therefore, how to solve the problem of detection and control difficulties under small current output has become one of the urgent problems to be solved by those skilled in the art. Summary of the Invention

[0005] In view of the shortcomings of the prior art described above, the purpose of this invention is to provide an LED driving system, a feedback control circuit and method for LED driving, to solve the problem of difficulty in detection and control when the output current is small in the prior art.

[0006] To achieve the above and other related objectives, the present invention provides a feedback control method for an LED driver, the feedback control method for the LED driver comprising at least:

[0007] The output current is detected, and the feedback voltage of the output current is obtained; when the feedback voltage is less than a first threshold, the preset voltage is set to a first preset value, and the feedback voltage is increased; when the feedback voltage is greater than a second threshold, the preset voltage is set to a second preset value, and the feedback voltage is decreased; when the feedback voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the preset voltage remains at the preset value of the previous state, and the feedback voltage is not adjusted.

[0008] The output current is adjusted based on the comparison result between the feedback voltage and the preset voltage and the dimming signal to achieve dimming control; wherein the first threshold, the first preset value, the second preset value and the second threshold increase sequentially.

[0009] Optionally, the feedback voltage can be adjusted by changing the sampling resistor of the output current.

[0010] Alternatively, at least two resistors are connected in parallel, and the resistance value of the sampling resistor is changed by adjusting the resistance of the circuit.

[0011] Optionally, the feedback voltage can be adjusted by changing the sampling current of the output current.

[0012] Alternatively, a current detection power transistor and at least two main power transistors are provided, with each main power transistor and the current detection power transistor connected in parallel. The current flowing through the current detection power transistor is changed by adjusting the main power transistor connected to the circuit, and the current flowing through the current detection power transistor is used as the sampling current.

[0013] Alternatively, a main power transistor and at least two current detection power transistors are provided. The main power transistor and each current detection power transistor are connected in parallel. The current flowing through each current detection power transistor is changed by adjusting the current detection power transistor connected to the circuit. The sum of the currents flowing through all current detection power transistors is used as the sampling current.

[0014] To achieve the above and other related objectives, the present invention provides a feedback control circuit for an LED driver, implementing the aforementioned feedback control method for an LED driver. The feedback control circuit for the LED driver includes at least:

[0015] Feedback voltage adjustment module, hysteresis comparator, dimming control module, operational amplifier and first main power transistor;

[0016] The feedback voltage adjustment module detects the output current of the feedback control circuit of the LED driver to obtain the feedback voltage of the output current, and adjusts the feedback voltage based on the output signal of the hysteresis comparator.

[0017] The hysteresis comparator is connected to the output of the feedback voltage adjustment module, compares the value of the feedback voltage with the first threshold and the second threshold, and outputs the corresponding comparison result.

[0018] The dimming control module is connected to the output of the hysteresis comparator and receives the dimming signal. It generates a preset voltage based on the output signal of the hysteresis comparator and the dimming signal.

[0019] The operational amplifier is connected to the output terminals of the feedback voltage adjustment module and the dimming control module, and controls the first main power transistor based on the difference between the feedback voltage and the preset voltage.

[0020] The output current flows into the drain of the first main power transistor, and the gate is connected to the output terminal of the operational amplifier. The output current is adjusted based on the output signal of the operational amplifier.

[0021] Optionally, the feedback voltage adjustment module includes a first resistor and a first switching transistor; one end of the first resistor is connected to the source of the first main power transistor, and the other end is grounded; the first switching transistor is connected in parallel with the first resistor, and its control terminal is connected to the output terminal of the hysteresis comparator; when the feedback voltage is less than the first threshold, the first switching transistor is turned off; when the feedback voltage is greater than the second threshold, the first switching transistor is turned on; when the feedback voltage is between the first threshold and the second threshold, the first switching transistor maintains the previous state.

[0022] Alternatively, the feedback control circuit for the LED driver may further include a second resistor, which is connected in series with the first switching transistor and then in parallel across the two ends of the first resistor.

[0023] Alternatively, the feedback control circuit for the LED driver further includes a first mode selection module and at least one second switch; the first mode selection module is connected to the output of the hysteresis comparator, and is also connected to the dimming control module, the gate of the first switch, and the gates of each second switch, adjusting the preset voltage based on the output signal of the hysteresis comparator, and controlling the on and off of the first switch and each second switch respectively; the second switch is connected in parallel with the first switch.

[0024] Alternatively, the feedback voltage adjustment module is located inside the chip; the feedback control circuit of the LED driver further includes a first setting resistor located outside the chip, one end of the first setting resistor is connected to the dimming control module, and the other end is grounded, for setting the reference voltage.

[0025] Optionally, the feedback voltage adjustment module includes a second main power transistor, a first current-sensing power transistor, a third switching transistor, and a first current-sensing unit; the second main power transistor and the first current-sensing power transistor are connected in parallel with the first main power transistor; the first current-sensing unit is connected to the source of the first current-sensing power transistor and converts the current flowing through the first current-sensing power transistor into the feedback voltage; the gate of the first current-sensing power transistor is connected to the output terminal of the operational amplifier; the gate of the second main power transistor is connected to the output terminal of the operational amplifier via the third switching transistor, the control terminal of the third switching transistor is connected to the output terminal of the hysteresis comparator, the third switching transistor is turned off when the feedback voltage is less than the first threshold, the third switching transistor is turned on when the feedback voltage is greater than the second threshold, and the third switching transistor maintains the previous state when the feedback voltage is between the first threshold and the second threshold.

[0026] Alternatively, the feedback voltage adjustment module further includes a second mode selection module and at least one third main power transistor; the second mode selection module is connected to the output of the hysteresis comparator, and is also connected to the dimming control module, the gate of the second main power transistor, and the gates of each third main power transistor, adjusting the preset voltage based on the output signal of the hysteresis comparator, and controlling the on and off states of the second main power transistor and each third main power transistor respectively; the third main power transistor is connected in parallel with the first main power transistor.

[0027] Optionally, the feedback voltage adjustment module includes a second current-sensing power transistor, a third current-sensing power transistor, a fourth switch, an adder, and a second current-sensing unit; the second current-sensing power transistor and the third current-sensing power transistor are connected in parallel with the first main power transistor; the adder is connected to the source of the second current-sensing power transistor and the third current-sensing power transistor; the second current-sensing unit is connected to the output of the adder, converting the sum of the currents flowing through the second current-sensing power transistor and the third current-sensing power transistor into the feedback voltage; the gate of the second current-sensing power transistor is connected to the output of the operational amplifier; the gate of the third current-sensing power transistor is connected to the output of the operational amplifier via the fourth switch, the control terminal of the fourth switch is connected to the output of the hysteresis comparator, the fourth switch is turned on when the feedback voltage is less than the first threshold, the fourth switch is turned off when the feedback voltage is greater than the second threshold, and the fourth switch remains in the previous state when the feedback voltage is between the first threshold and the second threshold.

[0028] Alternatively, the connection relationship of the fourth switch can be replaced as follows: one end of the fourth switch is connected to the source of the third current-sensing power transistor, and the other end is connected to the input of the adder; the gate of the third current-sensing power transistor is connected to the output of the operational amplifier.

[0029] Alternatively, the feedback voltage adjustment module is located inside the chip; the feedback control circuit of the LED driver further includes a second setting resistor located outside the chip, one end of the second setting resistor is connected to the dimming control module, and the other end is grounded, for setting the reference voltage.

[0030] To achieve the above and other related objectives, the present invention provides an LED driving system, the LED driving system comprising at least:

[0031] LED light strings and the feedback control circuit of the aforementioned LED driver;

[0032] The positive terminal of the LED string receives the input voltage, and the negative terminal is connected to the drain of the first main power transistor in the feedback control circuit of the LED driver.

[0033] The feedback control circuit of the LED driver controls the current flowing through the LED string.

[0034] As described above, the LED driving system, LED driving feedback control circuit, and method of the present invention have the following beneficial effects:

[0035] 1. The LED driving system, LED driving feedback control circuit and method of the present invention, by changing and increasing the feedback amount, can still have sufficient current detection capability when the current output is small, improve the detection accuracy, and meet the application of dimming to a very small current output.

[0036] 2. The LED driving system, LED driving feedback control circuit and method of the present invention change the reference while changing the feedback quantity to prevent the output current from jumping and causing flickering.

[0037] 3. The LED driving system, LED driving feedback control circuit and method of the present invention prevent oscillation caused by mode switching by setting an appropriate hysteresis voltage.

[0038] 4. The LED driving system, LED driving feedback control circuit and method of the present invention adopts the parallel connection of multiple MOS to increase the current adjustment range, and the integration inside the chip can simplify the peripheral circuit and cost. Attached Figure Description

[0039] Figure 1 The diagram shown is a first structural schematic of the feedback control circuit for LED driving according to the present invention.

[0040] Figure 2 The diagram shows a waveform of the feedback control circuit for LED driving according to the present invention.

[0041] Figure 3 The diagram shown is a second structural schematic of the feedback control circuit for LED driving according to the present invention.

[0042] Figure 4 The diagram shown is a third structural schematic of the feedback control circuit for LED driving according to the present invention.

[0043] Figure 5 The diagram shown is a fourth structural schematic of the feedback control circuit for LED driving according to the present invention.

[0044] Figure 6 The diagram shown is a fifth structural schematic of the feedback control circuit for LED driving according to the present invention.

[0045] Figure 7 The diagram shown is a sixth structural schematic of the feedback control circuit for LED driving according to the present invention.

[0046] Figure 8 The diagram shown is a seventh structural schematic of the feedback control circuit for LED driving according to the present invention.

[0047] Figure 9 The diagram shown is a flowchart illustrating the feedback control method for LED driving according to the present invention.

[0048] Component designation explanation

[0049] 1 Feedback control circuit for LED driver

[0050] 11 Feedback Voltage Adjustment Module

[0051] 111 First Inverter

[0052] 112 First Current Detection Unit

[0053] 113 Second Inverter

[0054] 114 Adders

[0055] 115 Second Current Detection Unit

[0056] 12 Hysteresis Comparator

[0057] 13 Dimming Control Module

[0058] 131 dimming units

[0059] 132 Preset voltage generation unit

[0060] 14 Operational Amplifier

[0061] 15 Power Module

[0062] 16 First Mode Selection Module

[0063] 17 Second Mode Selection Module

[0064] 18 Driver Modules Detailed Implementation

[0065] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0066] Please see Figures 1-9 It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0067] Example 1

[0068] like Figure 1 As shown, this embodiment provides a feedback control circuit 1 for an LED driver, the feedback control circuit 1 for the LED driver includes:

[0069] Feedback voltage adjustment module 11, hysteresis comparator 12, dimming control module 13, operational amplifier 14 and first main power transistor Q1.

[0070] like Figure 1 As shown, the feedback voltage adjustment module 11 detects the output current of the feedback control circuit 1 driving the LED to obtain the feedback voltage Vcs of the output current, and adjusts the feedback voltage Vcs based on the output signal of the hysteresis comparator 12.

[0071] Specifically, in this embodiment, the feedback voltage adjustment module 11 adjusts the feedback voltage Vcs by changing the sampling resistor. As an example, the feedback voltage adjustment module 11 includes a first resistor R1, a second resistor R2, and a first switch Q_1. One end of the first resistor R1 is connected to the source of the first main power transistor Q1, and the other end is grounded. The second resistor R2 is connected in series with the first switch Q_1 and then in parallel across the first resistor R1. The control terminal of the first switch Q_1 is connected to the output terminal of the hysteresis comparator 12. When the feedback voltage Vcs is less than the first threshold Vs_L, the first switch Q_1 is turned off; when the feedback voltage Vcs is greater than the second threshold Vs_H, the first switch Q_1 is turned on; when the feedback voltage Vcs is between the first threshold Vs_L and the second threshold Vs_H, the first switch Q_1 is turned on. When the value Vs_H is between the first threshold Vs_L and the second threshold Vs_H (the feedback voltage Vcs is greater than or equal to the first threshold Vs_L and less than or equal to the second threshold Vs_H), the first switch Q_1 maintains the previous state. In this example, the first switch Q_1 is implemented using NMOS. The drain of the first switch Q_1 is connected to the second resistor R2, the source is grounded, and the gate is connected to the output of the hysteresis comparator 12 via the first inverter 111. In actual use, the appropriate device type can be selected as needed, and whether to set an inverter to adjust the signal polarity relationship can be selected, as long as it meets the logic of this invention.

[0072] like Figure 1 As shown, the hysteresis comparator 12 is connected to the output terminal of the feedback voltage adjustment module 11, compares the value of the feedback voltage Vcs with the first threshold Vs_L and the second threshold Vs_H, and outputs the corresponding comparison result; wherein, the first threshold Vs_L is less than the second threshold Vs_H.

[0073] Specifically, in this embodiment, the inverting input terminal of the hysteresis comparator 12 is connected to the feedback voltage Vcs, and the non-inverting input terminal is connected to either the first threshold Vs_L or the second threshold Vs_H. In practical use, the relative relationship between the input signal and the polarity of the input terminal of the hysteresis comparator 12 can be adjusted according to actual needs, and is not limited to this embodiment.

[0074] like Figure 1 As shown, the dimming control module 13 is connected to the output of the hysteresis comparator 12 and receives the dimming signal DIM. Based on the output signal of the hysteresis comparator 12 and the dimming signal DIM, it generates a preset voltage Vset.

[0075] Specifically, the dimming control module 13 generates the preset voltage Vset based on the dimming signal DIM, and adjusts the first main power transistor Q1 based on the operational amplifier 14 to achieve dimming control; simultaneously, the dimming control module 13 also adjusts the value of the preset voltage Vset based on the output signal of the hysteresis comparator 12 to prevent output current jumps. When the feedback voltage Vcs is less than the first threshold Vs_L, the preset voltage Vset is adjusted to the second preset value Vset_H; when the feedback voltage Vcs is greater than the second threshold Vs_H, the preset voltage Vset is adjusted to the first preset value Vset_L; when the feedback voltage Vcs is between the first threshold Vs_L and the second threshold Vs_H, the output signal of the hysteresis comparator 12 does not affect the value of the preset voltage Vset; wherein, the first preset value Vset_L is less than the second preset value Vset_H, the second preset value Vset_H is less than the second threshold Vs_H, and the first threshold Vs_L is less than the first preset value Vset_L.

[0076] More specifically, as an example, the dimming control module 13 includes a dimming unit 131 and a preset voltage generation unit 132. The dimming unit 131 generates a control signal based on the dimming signal DIM. The preset voltage generation unit 132 is connected to the output terminal of the dimming unit 131 and the hysteresis comparator 12, and generates the preset voltage Vset based on the control signal and the output signal of the hysteresis comparator 12.

[0077] like Figure 1 As shown, the operational amplifier 14 is connected to the output terminals of the feedback voltage adjustment module 11 and the dimming control module 13, and the first main power transistor Q1 is based on the difference between the feedback voltage Vcs and the preset voltage Vset.

[0078] Specifically, in this embodiment, the non-inverting input terminal of the operational amplifier 14 is connected to the preset voltage Vset, and the inverting input terminal is connected to the feedback voltage Vcs, outputting an amplified signal representing the difference between the two. In practical use, the correspondence between the input signal and the polarity of the input terminal of the operational amplifier can be interchanged, as long as the logic of the present invention can be implemented, and it is not limited to this embodiment.

[0079] like Figure 1 As shown, the output current flows into the drain of the first main power transistor Q1, and the gate is connected to the output terminal of the operational amplifier 14. The output current is adjusted based on the output signal of the operational amplifier 14.

[0080] Specifically, in this embodiment, the first main power transistor is an NMOS.

[0081] It should be noted that, in this embodiment, the hysteresis comparator 12, the dimming control module 13, the operational amplifier 14, and the first main power transistor Q1 are disposed within the chip, while the feedback voltage adjustment module 11 (as an example, wherein the first inverter 111 is disposed within the chip) is disposed outside the chip. In actual use, each module can be disposed within or outside the chip as needed, and is not limited to this embodiment.

[0082] like Figure 1 and Figure 2 As shown, the working principle of the feedback control circuit 1 for LED driving is as follows:

[0083] During normal high-current output, the hysteresis comparator 12 detects the feedback voltage Vcs at the CS terminal and outputs a low level, turning on the first switch Q_1 through the first inverter 111. At this time, the current sensing resistor becomes a parallel combination of the first resistor R1 and the second resistor R2 (ignoring the influence of the on-resistance RDSon of the first switch Q_1). When dimming to low-current output, if the feedback voltage Vcs is lower than the first threshold Vs_L (at this time I... o <V S_L If (R1 / / R2) is true, then the hysteresis comparator 12 outputs a high level, which turns off the first switch Q_1 through the first inverter 111. The current sensing resistor becomes the first resistor R1, and its resistance value is increased compared to the original (R1>R1 / / R2). Therefore, the feedback voltage Vcs also increases accordingly (V CS =I O *R1>I O *(R1 / / R2)), To prevent deviations in the output current caused by changes in the sensing resistor, the preset voltage Vset needs to be increased accordingly. In this embodiment, the second preset value of the preset voltage Vset is set to Vset_H(V set_H =R1 / (R1 / / R2)*V S_L >V S_L At this point, the increased feedback voltage Vcs is beneficial for detection when the output current is small. As the output current increases, if it reaches the other switching voltage of the hysteresis comparator 12 (the second threshold Vs_H > Vset_H), the output current I... O >V S_H When the hysteresis comparator 12 outputs a low level, the first inverter 111 turns on the first switch, and the detection resistor becomes the parallel connection of the first resistor R1 and the second resistor R2 (R1 / / R2). At this time, the feedback voltage Vcs decreases (V S =I O *(R1 / / R2)<I O*R1), the feedback voltage Vcs should not be too large, which would increase system losses and exceed the detection or adjustment control range. In this case, the value of the preset voltage Vset also needs to be reduced accordingly. In this embodiment, the first preset value of the preset voltage Vset is set to Vset_L(V set_L = (R1 / / R2) / R1*V S_H >V S_L ).

[0084] When the output current Io decreases, switching from Vs_L to Vset_H will not trigger Vs_H. When the output current Io increases, switching from Vs_H to Vset_L will not trigger Vs_L. In this way, the switching conditions for entering another mode will not be met after each mode switch, thus avoiding oscillations caused by switching back and forth.

[0085] like Figure 2 The diagram shows the working waveform. When the output current Io decreases to Io_L, the feedback voltage Vcs touches the first threshold Vs_L, the first switch Q_1 turns off, the sensing resistor becomes R1, and the preset voltage Vset correspondingly rises to the second preset value Vset_H. The feedback voltage Vcs is also raised to meet the detection requirements. When the output current Io increases to Io_H, the feedback voltage Vcs touches the second threshold Vs_H (Vs_H>Vset_H), the first switch Q_1 turns on, the sensing resistor becomes a parallel connection of R1 and R2, and the preset voltage Vset correspondingly decreases to the first preset value Vset_L (>Vs_L). The feedback voltage Vcs decreases to reduce system losses. When the output current is between Io_L and Io_H, the feedback voltage may have two different values, the specific value of which is determined by the current output signal SET state of the hysteresis comparator 12. Figure 2 (The dashed lines indicated by the arrows SET_L and SET_H). During dimming, the dimming signal DIM is usually related to the output current Io, so the dimming signal DIM can be used instead of detecting the output current Io.

[0086] In this embodiment, by switching the feedback quantity, the minimum output ratio of the original 10% can be adjusted to [(R1 / / R2) / R1]*10% while keeping the minimum detection value unchanged. The actual needs can be met by setting appropriate resistance values ​​of R1 and R2, which are not limited here.

[0087] Example 2

[0088] like Figure 3 As shown, this embodiment provides a feedback control circuit 1 for LED driving. The difference from the first embodiment is that the feedback voltage adjustment module 11 is disposed inside the chip.

[0089] Specifically, in Embodiment 1, the values ​​of the first preset value Vset_L and the second preset value Vset_H of the preset voltage Vset are related to the first resistor R1 and the second resistor R2, which is inconvenient to use. In this embodiment, the feedback voltage adjustment module 11 is disposed inside the chip; the feedback control circuit 1 for the LED driver also includes a first setting resistor Rset1 disposed outside the chip, one end of the first setting resistor Rset1 is connected to the dimming control module 13, and the other end is grounded, used to set the reference voltage.

[0090] It should be noted that the feedback control circuit 1 of the LED driver in this embodiment has the same other structure and working principle as the feedback control circuit 1 of the LED driver in Embodiment 1, and will not be described in detail here.

[0091] Example 3

[0092] This embodiment provides a feedback control circuit 1 for LED driving. The difference from Embodiment 1 and Embodiment 2 is that the second resistor R2 is not included. The first switch Q_1 is connected in parallel with the first resistor R1. The on-resistance RDSon of the first switch Q_1 is used to replace the second resistor R2. The specific structure and principle are not described in detail here.

[0093] Example 4

[0094] like Figure 4 As shown, this embodiment provides a feedback control circuit 1 for an LED driver. The difference between this circuit and embodiments one through three is that a smaller and more precise current output is achieved through the parallel connection of multiple switching transistors. The feedback control circuit 1 for the LED driver also includes a first mode selection module 16 and n second switching transistors (denoted as Q_21, Q_22…Q_2n, respectively), where n is a natural number greater than or equal to 1.

[0095] like Figure 4 As shown, each of the second switching transistors is connected in parallel with the first switching transistor Q_1.

[0096] Specifically, in this embodiment, each of the second switching transistors is an NMOS transistor. As another example, each of the second switching transistors is also connected in series with a resistor, which will not be described in detail here.

[0097] like Figure 4 As shown, the first mode selection module 16 is connected to the output terminal of the hysteresis comparator 12, and is connected to the dimming control module 13 and the gates of each switch (the first switch Q_1 and each second switch). Based on the output signal of the hysteresis comparator 12, the preset voltage Vset is adjusted, and the conduction and turn-off of each switch are controlled respectively.

[0098] Specifically, the first mode selection module 16 generates a control signal (output to the dimming control module 13) based on the output signal of the hysteresis comparator 12 to control and adjust the preset voltage Vset. It also generates control signals for the first switch Q_1 and each of the second switches based on the output signal of the hysteresis comparator 12. By selecting different combinations of the first switch Q_1 and each of the second switches, precise current control is achieved. For the case with one first switch Q_1 and n second switches, the first mode selection module 16 can output 2... n+1 A combination of states.

[0099] Example 5

[0100] like Figure 5 As shown, this embodiment provides a feedback control circuit 1 for LED driving. The difference between this circuit and embodiments one to four is that the feedback voltage adjustment module 11 adjusts the feedback voltage Vcs by controlling the number of connected main power transistors to change the sampling current.

[0101] like Figure 5 As shown, as an example, the feedback voltage adjustment module 11 includes a second main power transistor Q2, a first current detection power transistor Qs1, a third switching transistor SW1, and a first current detection unit 112.

[0102] Specifically, the second main power transistor Q2 and the first current-sensing power transistor Qs1 are connected in parallel with the first main power transistor Q1. In this example, the first main power transistor Q1, the second main power transistor Q2, and the first current-sensing power transistor Qs1 are all implemented using NMOS. In actual use, the appropriate device type can be selected according to actual needs. The first current-sensing unit 112 is connected to the source of the first current-sensing power transistor Qs1, converting the current flowing through the first current-sensing power transistor Qs1 into the feedback voltage Vcs. The gate of the first current-sensing power transistor Qs1 is connected to the output terminal of the operational amplifier 14. The gate of the second main power transistor Q2 is connected to the output of the operational amplifier 14 via the third switch SW1. The control terminal of the third switch SW1 is connected to the output of the hysteresis comparator 12. When the feedback voltage Vcs is less than the first threshold Vs_L, the third switch SW1 is turned off; when the feedback voltage Vcs is greater than the second threshold Vs_H, the third switch SW1 is turned on; and when the feedback voltage Vcs is between the first threshold Vs_L and the second threshold Vs_H, the third switch SW1 maintains the previous state. In this example, the control terminal of the third switch SW1 is connected to the output signal of the hysteresis comparator 12 via the second inverter 113. In actual use, the polarity of the input signal can be adjusted according to the logic of the specific application, which will not be elaborated here. Furthermore, the third switch SW1 can be implemented using any controllable switching device, including but not limited to a MOSFET.

[0103] like Figure 5 As shown, in another implementation of the present invention, the feedback voltage adjustment module 11 is disposed within the chip; the feedback control circuit 1 for the LED driver further includes a second setting resistor Rset2 disposed outside the chip, one end of the second setting resistor Rset2 being connected to the dimming control module 13, and the other end being grounded, for setting the reference voltage. In practical use, the feedback voltage adjustment module 11 can be disposed outside the chip, and the second setting resistor Rset2 can be ignored.

[0104] like Figure 5 As shown, the working principle of the feedback control circuit 1 for LED driving is as follows:

[0105] The current signal flowing through the first main power transistor Q1 is I1, the current signal flowing through the second main power transistor Q2 is I2, and the current signal flowing through the first current detection power transistor Qs1 is Is1. Is1 is proportional to I1 and I2, where I1 = K1 * Is1 and I2 = K2 * Is1. K1 and K2 are related to the size ratio of each power transistor, which will not be elaborated here. When detecting a large current output, the hysteresis comparator 12 outputs a low level, which turns on the third switch transistor SW1 through the second inverter 113. At this time, the first main power transistor Q1 and the second main power transistor Q2 are connected in parallel and conduct, and the output current is Io = (1 + K1 + K2) * Is1. When the output current decreases to the first threshold Vs_L, the hysteresis comparator 12 outputs a high level, which turns off the third switch SW1 through the second inverter 113, thereby turning off the second main power transistor Q2. Current can only flow through the first main power transistor Q1 and the first current detection power transistor Qs1, Io = (1+K1)*Is1. The current detection signal increases to the original (1+K1+K2) / (1+K1). At this time, the corresponding preset voltage Vset needs to be raised (V set_H =[(1+K1+K2) / (1+K1)]*V S_L When the output current increases to the second threshold Vs_H, the hysteresis comparator 12 outputs a low level, which turns on the third switch SW1 through the second inverter 113. At this time, the second main power transistor Q2 turns on, and the current detection signal decreases to the original (1+K1) / (1+K1+K2). Correspondingly, the preset voltage Vset needs to be reduced (V set_L =[(1+K1) / (1+K1+K2)]*V S_H ).

[0106] In this embodiment, the first main power transistor Q1 and the second main power transistor Q2 are equivalent to the first main power transistor Q1 in Embodiment 1 and Embodiment 2. Therefore, the first main power transistor Q1 and the second main power transistor Q2 in this embodiment are both smaller than the first main power transistor Q1 in Embodiment 1 and Embodiment 2. Compared with Embodiment 1 and Embodiment 2, this embodiment will switch to only the first main power transistor Q1 (the smaller power transistor) being turned on and having current flowing when the output current is small. It is easier to achieve detection and control than the high-power S-transistor in Embodiment 1 and Embodiment 2 working in a low-current working state. The operating range of the power transistor and the system can be wider.

[0107] Example 6

[0108] like Figure 6As shown, this embodiment provides a feedback control circuit 1 for LED driving. The difference from Embodiment 5 is that multiple parallel main power transistors are used to obtain a smaller and more precise current output. The feedback voltage adjustment module 11 also includes a second mode selection module 17 and m third main power transistors (denoted as Q31…Q3m), where m is a natural number greater than or equal to 1.

[0109] like Figure 6 As shown, each of the third main power transistors is connected in parallel with the first main power transistor Q1.

[0110] Specifically, in this embodiment, each of the third main power transistors is an NMOS transistor. The current flowing through each third main power transistor is denoted as I31…I3m.

[0111] like Figure 6 As shown, the second mode selection module 17 is connected to the output terminal of the hysteresis comparator 12, and is connected to the dimming control module 13, the second main power transistor Q2 and the gates of each third main power transistor. Based on the output signal of the hysteresis comparator 12, the preset voltage Vset is adjusted, and the conduction and turn-off of the second main power transistor Q2 and each third main power transistor are controlled respectively.

[0112] Specifically, the second mode selection module 17 generates a control signal (output to the dimming control module 13) based on the output signal of the hysteresis comparator 12 to control and adjust the preset voltage Vset. It also generates control signals for the second main power transistor Q2 and each of the third main power transistors based on the output signal of the hysteresis comparator 12. As an example, the second mode selection module 17 obtains the gate drive signals of the second main power transistor Q2 and each of the third main power transistors from the output of the operational amplifier 14 (in actual use, the gate drive signals can be obtained from a suitable location as needed), and achieves precise current control by selecting different combinations of the main power transistors. For a case with one first main power transistor Q1, one second main power transistor Q2, and m third main power transistors, the second mode selection module 17 can output 2... m+1 A combination of states.

[0113] Specifically, as another implementation of the present invention, the output signal of the second mode selection module 17 is applied to the gate of each power transistor through the driving module 18.

[0114] Example 7

[0115] like Figure 7As shown, this embodiment provides a feedback control circuit 1 for LED driving. The difference between this circuit and embodiments one to six is ​​that the feedback voltage adjustment module 11 adjusts the feedback voltage Vcs by controlling the number of connected current detection power transistors to change the sampling current.

[0116] like Figure 7 As shown, the feedback voltage adjustment module 11 includes a second current detection power transistor Qs2, a third current detection power transistor Qs3, a fourth switch transistor SW2, an adder 114, and a second current detection unit 115.

[0117] Specifically, the second current-sensing power transistor Qs2 and the third current-sensing power transistor Qs3 are connected in parallel with the first main power transistor Q1. In this example, the first main power transistor Q1, the second current-sensing power transistor Qs2, and the third current-sensing power transistor Qs3 are all implemented using NMOS. In actual use, the appropriate device type can be selected according to actual needs. The adder 114 is connected to the source of the second current-sensing power transistor Qs2 and the third current-sensing power transistor Qs3 to obtain the sum of the currents flowing through the second current-sensing power transistor Qs2 and the third current-sensing power transistor Qs3. The second current-sensing unit 115 is connected to the output of the adder 114 to convert the sum of the currents flowing through the second current-sensing power transistor Qs2 and the third current-sensing power transistor Qs3 into the feedback voltage Vcs. The gate of the second current-sensing power transistor Qs2 is connected to the output of the operational amplifier 14. The gate of the third current-sensing power transistor Qs3 is connected to the output of the operational amplifier 14 via the fourth switch SW2. The control terminal of the fourth switch SW2 is connected to the output of the hysteresis comparator 14. When the feedback voltage Vcs is less than the first threshold Vs_L, the fourth switch SW2 is turned on; when the feedback voltage Vcs is greater than the second threshold Vs_H, the fourth switch SW2 is turned off; and when the feedback voltage Vcs is between the first threshold Vs_L and the second threshold Vs_H, the fourth switch SW2 remains in the previous state. In practical use, the polarity of the input signal can be adjusted according to the logic of the specific application, which will not be elaborated here.

[0118] like Figure 7 As shown, the working principle of the feedback control circuit 1 for LED driving is as follows:

[0119] In this embodiment, the current feedback is the sum of the currents flowing through the second current-sensing power transistor Qs2 and the third current-sensing power transistor Qs3, i.e., Is2 + Is3. The current I1 flowing through the first main power transistor Q1 is proportional to Is1 and Is2, I1 = K3 * Is2, Is3 = K4 * Is2. The output current is Io = I1 + Is2 + Is3 = (1 + K3) * Is2 + K4 * Is2. K3 and K4 are related to the size ratio of each power transistor, which will not be elaborated here. During normal high-current output, the hysteresis comparator 12 outputs a low level, the fourth switch SW2 is turned off, the third current-sensing power transistor Qs3 is turned off, and the feedback current is only Is2. When the output current decreases to the feedback voltage Vcs being equal to the first threshold Vs_L, the hysteresis comparator 12 outputs a high level, turning on the fourth switch SW2. The third current detection power transistor Qs3 also turns on, and the feedback current is Is2 + Is3 = (1 + K4)Is2. The feedback quantity is (1 + K4) times the original, which is beneficial for detection. Correspondingly, the preset voltage Vset also needs to be increased (V... set_H = (1+K4)*V S_L When the output current increases to the second threshold Vs_H of the feedback voltage Vcs, the hysteresis comparator 12 outputs a low level, turning off the fourth switch SW2 and the third current detection power transistor Qs3. The feedback current is reduced to Is2, ensuring the test value does not exceed the range. Correspondingly, the preset voltage Vset also needs to be reduced (V... set_L =V S_H / (1+K4)).

[0120] Example 8

[0121] like Figure 8 As shown, this embodiment provides a feedback control circuit 1 for LED driving. The difference from embodiment seven is that the third current detection power transistor Qs3 is always on, and its feedback current is sent to adder 114 through a switch.

[0122] Specifically, the connection relationship of the fourth switch SW2 is replaced as follows: one end of the fourth switch SW2 is connected to the source of the third current detection power transistor Qs3, and the other end is connected to the input terminal of the adder 114; the gate of the third current detection power transistor Qs3 is connected to the output terminal of the operational amplifier 14.

[0123] The other structures and principles are the same as in Example 7, and will not be described in detail here.

[0124] Example 9

[0125] like Figure 1 , Figures 3-8As shown, the present invention provides an LED driving system, the LED driving system comprising:

[0126] Feedback control circuit for LED light strings and LED drivers 1.

[0127] like Figure 1 , Figures 3-8 As shown, the positive terminal of the LED string receives the input voltage Vin, and the negative terminal is connected to the drain of the first main power transistor Q1 in the feedback control circuit 1 of the LED driver.

[0128] like Figure 1 , Figures 3-8 As shown, the feedback control circuit 1 of the LED driver controls the current flowing through the LED string.

[0129] Specifically, the feedback control circuit 1 for the LED driver can adopt any one of the structures in Embodiments 1 to 8, which will not be described in detail here. The feedback control circuit 1 for the LED driver is located inside the chip, and a power module 15 is also provided inside the chip. The power module obtains electrical energy from the positive terminal of the LED string and provides operating voltage to each module inside the chip.

[0130] Example 10

[0131] like Figure 9 As shown, the present invention provides a feedback control method for an LED driver, the feedback control method for the LED driver comprising:

[0132] The output current is detected, and the feedback voltage of the output current is obtained; when the feedback voltage is less than a first threshold, the preset voltage is set to a first preset value, and the feedback voltage is increased; when the feedback voltage is greater than a second threshold, the preset voltage is set to a second preset value, and the feedback voltage is decreased; when the feedback voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the preset voltage remains at the preset value of the previous state, and the feedback voltage is not adjusted.

[0133] The output current is adjusted based on the comparison result between the feedback voltage and the preset voltage and the dimming signal to achieve dimming control; wherein the first threshold, the first preset value, the second preset value and the second threshold increase sequentially.

[0134] Specifically, the feedback voltage is adjusted by changing the sampling resistor of the output current. As an example, at least two resistors are connected in parallel, and the resistance value of the sampling resistor is changed by adjusting the resistor connected to the circuit. In this embodiment, the method is implemented using any one of the circuit structures in Embodiments 1 to 4. In practical use, any method of adjusting the feedback voltage by changing the sampling resistor of the output current is applicable to this invention and is not limited to this embodiment.

[0135] Specifically, the feedback voltage is adjusted by changing the sampling current of the output current. As an example, at least two main power transistors and one current-sensing power transistor are configured, with each main power transistor and the current-sensing power transistor connected in parallel. The current flowing through the current-sensing power transistor is changed by adjusting the main power transistor connected to the circuit, and the current flowing through the current-sensing power transistor is used as the sampling current. In this embodiment, the method is implemented using any one of the circuit structures in Embodiments 5 and 6. As another example, at least two current-sensing power transistors and one main power transistor are configured, with each main power transistor and the current-sensing power transistor connected in parallel. The current flowing through each current-sensing power transistor is changed by adjusting the current connected to the circuit, and the sum of the currents flowing through all current-sensing power transistors is used as the sampling current. In this embodiment, the method is implemented using any one of the circuit structures in Embodiments 7 and 8. In practical use, any method of adjusting the feedback voltage by changing the sampling current of the output current is applicable to this invention and is not limited to this embodiment.

[0136] In summary, this invention provides an LED driving system, an LED driving feedback control circuit, and a method, including detecting an output current and acquiring a feedback voltage of the output current; when the feedback voltage is less than a first threshold, setting a preset voltage to a first preset value and increasing the feedback voltage; when the feedback voltage is greater than a second threshold, setting the preset voltage to a second preset value and decreasing the feedback voltage; when the feedback voltage is greater than or equal to the first threshold and less than or equal to the second threshold, maintaining the preset voltage of the previous state and not adjusting the feedback voltage; adjusting the output current based on the comparison result of the feedback voltage and the preset voltage and a dimming signal to achieve dimming control; wherein the first threshold, the first preset value, the second preset value, and the second threshold increase sequentially. The LED driving system, LED driving feedback control circuit, and method of this invention, by changing and increasing the feedback quantity, can still maintain sufficient current detection capability at low current output, improving detection accuracy and meeting the application requirements of dimming to very low current output. The LED driving system, LED driving feedback control circuit, and method of this invention change the reference while changing the feedback quantity, preventing flickering caused by jumps in output current. The LED driving system, LED driving feedback control circuit, and method of this invention prevent oscillations caused by mode switching by setting an appropriate hysteresis voltage. The LED driving system, LED driving feedback control circuit, and method of this invention, by using parallel connection of multiple MOS stages, can increase the current adjustment range, and integration within the chip simplifies the external circuitry and reduces costs. Therefore, this invention effectively overcomes the various shortcomings of the prior art and has high industrial applicability.

[0137] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A feedback control method for LED driving, characterized in that, The feedback control method for the LED driver includes at least the following: The output current is detected, and the feedback voltage of the output current is obtained; when the feedback voltage is less than a first threshold, the preset voltage is set to a first preset value, and the feedback voltage is increased; when the feedback voltage is greater than a second threshold, the preset voltage is set to a second preset value, and the feedback voltage is decreased; when the feedback voltage is greater than or equal to the first threshold and less than or equal to the second threshold, the preset voltage remains at the preset value of the previous state, and the feedback voltage is not adjusted. The output current is adjusted based on the comparison result between the feedback voltage and the preset voltage and the dimming signal to achieve dimming control; wherein, the first threshold, the first preset value, the second preset value and the second threshold increase sequentially; The feedback voltage can be adjusted by changing the sampling resistor of the output current, wherein the feedback voltage is increased by increasing the sampling resistor and decreased by decreasing the sampling resistor; or the feedback voltage can be adjusted by changing the sampling current of the output current, wherein the feedback voltage is increased by increasing the sampling current of the output current and decreased by decreasing the sampling current of the output current.

2. The feedback control method for LED driving according to claim 1, characterized in that: When adjusting the feedback voltage by changing the sampling resistor of the output current, at least two resistors are set in parallel, and the resistance value of the sampling resistor is changed by adjusting the resistor connected to the circuit.

3. The feedback control method for LED driving according to claim 1, characterized in that: When the feedback voltage is adjusted by changing the sampling current of the output current, a current detection power transistor and at least two main power transistors are set up, with each main power transistor and the current detection power transistor connected in parallel. The current flowing through the current detection power transistor is changed by adjusting the main power transistor connected to the circuit, and the current flowing through the current detection power transistor is used as the sampling current.

4. The feedback control method for LED driving according to claim 1, characterized in that: When the feedback voltage is adjusted by changing the sampling current of the output current, a main power transistor and at least two current detection power transistors are set up. The main power transistor and each current detection power transistor are connected in parallel. The current flowing through each current detection power transistor is changed by adjusting the current detection power transistor connected to the circuit. The sum of the currents flowing through all current detection power transistors is used as the sampling current.

5. A feedback control circuit for an LED driver, implementing the feedback control method for an LED driver as described in any one of claims 1-4, characterized in that, The feedback control circuit for the LED driver includes at least: Feedback voltage adjustment module, hysteresis comparator, dimming control module, operational amplifier and first main power transistor; The feedback voltage adjustment module detects the output current of the feedback control circuit of the LED driver to obtain the feedback voltage of the output current, and adjusts the feedback voltage based on the output signal of the hysteresis comparator. The hysteresis comparator is connected to the output of the feedback voltage adjustment module, compares the value of the feedback voltage with the first threshold and the second threshold, and outputs the corresponding comparison result. The dimming control module is connected to the output of the hysteresis comparator and receives the dimming signal. It generates a preset voltage based on the output signal of the hysteresis comparator and the dimming signal. The operational amplifier is connected to the output terminals of the feedback voltage adjustment module and the dimming control module, and controls the first main power transistor based on the difference between the feedback voltage and the preset voltage. The output current flows into the drain of the first main power transistor, and the gate is connected to the output terminal of the operational amplifier. The output current is adjusted based on the output signal of the operational amplifier.

6. The feedback control circuit for LED driving according to claim 5, characterized in that: When the feedback voltage is adjusted by changing the sampling resistor of the output current, the feedback voltage adjustment module includes a first resistor and a first switching transistor; one end of the first resistor is connected to the source of the first main power transistor, and the other end is grounded; the first switching transistor is connected in parallel with the first resistor, and its control terminal is connected to the output terminal of the hysteresis comparator. When the feedback voltage is less than the first threshold, the first switching transistor is turned off; when the feedback voltage is greater than the second threshold, the first switching transistor is turned on; when the feedback voltage is between the first threshold and the second threshold, the first switching transistor maintains the previous state.

7. The feedback control circuit for LED driving according to claim 6, characterized in that: The feedback control circuit for the LED driver also includes a second resistor, which is connected in series with the first switching transistor and then in parallel across the two ends of the first resistor.

8. The feedback control circuit for LED driving according to claim 6, characterized in that: The feedback control circuit for the LED driver further includes a first mode selection module and at least one second switching transistor. The first mode selection module is connected to the output of the hysteresis comparator and to the dimming control module, the gate of the first switching transistor, and the gates of each second switching transistor. It adjusts the preset voltage based on the output signal of the hysteresis comparator and controls the on and off states of the first switching transistor and each second switching transistor respectively. The second switching transistor is connected in parallel with the first switching transistor.

9. The feedback control circuit for LED driving according to any one of claims 6-8, characterized in that: The feedback voltage adjustment module is located inside the chip; the feedback control circuit of the LED driver also includes a first setting resistor located outside the chip, one end of the first setting resistor is connected to the dimming control module, and the other end is grounded, for setting the reference voltage.

10. The feedback control circuit for LED driving according to claim 5, characterized in that: When the feedback voltage is adjusted by changing the sampling current of the output current, the feedback voltage adjustment module includes a second main power transistor, a first current detection power transistor, a third switch transistor, and a first current detection unit; the second main power transistor and the first current detection power transistor are respectively connected in parallel with the first main power transistor; the first current detection unit is connected to the source of the first current detection power transistor and converts the current flowing through the first current detection power transistor into the feedback voltage; the gate of the first current detection power transistor is connected to the output terminal of the operational amplifier; the gate of the second main power transistor is connected to the output terminal of the operational amplifier via the third switch transistor, the control terminal of the third switch transistor is connected to the output terminal of the hysteresis comparator, the third switch transistor is turned off when the feedback voltage is less than the first threshold, the third switch transistor is turned on when the feedback voltage is greater than the second threshold, and the third switch transistor maintains the previous state when the feedback voltage is between the first threshold and the second threshold.

11. The feedback control circuit for LED driving according to claim 10, characterized in that: The feedback voltage adjustment module further includes a second mode selection module and at least one third main power transistor; the second mode selection module is connected to the output of the hysteresis comparator, and is also connected to the dimming control module, the gate of the second main power transistor, and the gates of each third main power transistor. It adjusts the preset voltage based on the output signal of the hysteresis comparator and controls the on and off states of the second main power transistor and each third main power transistor respectively; the third main power transistor is connected in parallel with the first main power transistor.

12. The feedback control circuit for LED driving according to claim 5, characterized in that: When the feedback voltage is adjusted by changing the sampling current of the output current, the feedback voltage adjustment module includes a second current detection power transistor, a third current detection power transistor, a fourth switching transistor, an adder, and a second current detection unit; the second current detection power transistor and the third current detection power transistor are respectively connected in parallel with the first main power transistor; the adder is connected to the source of the second current detection power transistor and the third current detection power transistor; The second current detection unit is connected to the output of the adder and converts the sum of the currents flowing through the second current detection power transistor and the third current detection power transistor into the feedback voltage. The gate of the second current detection power transistor is connected to the output of the operational amplifier. The gate of the third current detection power transistor is connected to the output of the operational amplifier via the fourth switch. The control terminal of the fourth switch is connected to the output of the hysteresis comparator. When the feedback voltage is less than the first threshold, the fourth switch is turned on. When the feedback voltage is greater than the second threshold, the fourth switch is turned off. When the feedback voltage is between the first threshold and the second threshold, the fourth switch remains in the previous state.

13. The feedback control circuit for LED driving according to claim 12, characterized in that: The connection relationship of the fourth switch is replaced as follows: one end of the fourth switch is connected to the source of the third current-sensing power transistor, and the other end is connected to the input of the adder; the gate of the third current-sensing power transistor is connected to the output of the operational amplifier.

14. The feedback control circuit for LED driving according to any one of claims 10-13, characterized in that: The feedback voltage adjustment module is located inside the chip; the feedback control circuit of the LED driver also includes a second setting resistor located outside the chip, one end of which is connected to the dimming control module and the other end is grounded, for setting the reference voltage.

15. An LED driving system, characterized in that, The LED driving system includes at least: LED light strings and the feedback control circuit for LED driving as described in any one of claims 5-14; The positive terminal of the LED string receives the input voltage, and the negative terminal is connected to the drain of the first main power transistor in the feedback control circuit of the LED driver. The feedback control circuit of the LED driver controls the current flowing through the LED string.

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