A LED driving method

Abstract

The present invention provides an LED driving method, comprising: establishing a relationship between a reference voltage and a compensation voltage; when the working voltage is established, the compensation voltage is pulled up to a second compensation setting value, and the reference voltage is correspondingly pulled down to a reference setting value; within a loop adjustment time, the compensation voltage is gradually reduced from the compensation setting value and stabilized, the reference voltage is gradually increased from the reference setting value and stabilized, the output current changes in the same direction as the reference voltage and finally outputs a constant current; when the power is turned off, the compensation voltage is adjusted to a maximum clamping voltage; if the power is turned off and then restarted quickly, within the loop adjustment time, the compensation voltage is gradually reduced from the maximum clamping voltage and stabilized, the reference voltage is gradually increased from the reference setting value and stabilized, the output current changes in the same direction as the reference voltage and finally outputs a constant current. The LED driving method provided by the present invention solves the problems of soft start failure and low voltage input power frequency flickering in the existing driving method when the machine is turned on and off quickly.

Description

Technical Field

[0001] The present invention relates to the field of LED lighting, and in particular to an LED driving method. Background Art

[0002] Figure 1 This is a common LED driver circuit. The alternating current voltage AC is converted into an input voltage Vin after passing through a rectifier bridge module 100 and an input filter capacitor Cin. This voltage is then directly supplied to a constant current control chip 200 via an operating voltage generation module 201. Simultaneously, this input voltage Vin is passed through an LED driver module 300 to drive the LED light string. A current sensing resistor Rs converts the current in the LED light string into a voltage, which is then fed back to the op amp input of the constant current control chip 200. After comparison with a reference voltage Vref by an operational amplifier (GM) 202, the compensation capacitor Ccomp is charged and discharged based on the output of the operational amplifier (GM) 202. This adjusts the compensation voltage Vcomp generated by the compensation voltage generation module 203. Finally, based on this compensation voltage Vcomp, the peak current or duty cycle signal of the LED driver module 300 is controlled by the driver module 204, thereby ensuring that the LED output current reaches a stable equilibrium value, i.e., a set output current. Alternatively, a PF control module 400, controlled by the compensation voltage generation module 203, can be added between the input filter capacitor Cin and ground to regulate the system's power factor.

[0003] exist Figure 1 When performing soft start in the LED driver circuit shown, a relatively large compensation capacitor Ccomp is usually used. Due to the limited output current capability of the operational amplifier (GM) 202, the compensation voltage Vcomp output by the compensation voltage generating module 203 can only rise slowly during startup, causing the output peak current or duty cycle of the LED driver module 300 to also increase slowly, thereby causing the LED output current to rise slowly (see Figure 2 (time period t0-t1).

[0004] In the existing soft-start method using a large compensation capacitor, when the power is turned off, due to the slow discharge of the busbar, after the input voltage Vin is insufficient to maintain the LED output current, the operational amplifier (GM) 202 detects that the voltage of the current detection resistor Rs is too low, and will increase the compensation voltage Vcomp output by the compensation voltage generation module 203 in an attempt to maintain the LED output current (in fact, the LED has no current). If the power supply is turned on quickly at this time, the system will lose the soft-start capability due to the high compensation voltage Vcomp, resulting in output overshoot (see Figure 2 (time periods t3-t4 and t6-t7).

[0005] At the same time, when the input voltage Vin is relatively low, the bus voltage ripple on the input filter capacitor Cin will be relatively large (if the system is equipped with a PF control module 400, it will further increase the bus ripple voltage). From C*ΔV=ILED*t_Discharge (the time when the input voltage Vin is lower than the capacitor voltage is the capacitor discharge time, and since the capacitor voltage depends on the LED lamp voltage, the discharge time t_Discharge is basically unchanged for a certain application), it can be seen that once the bus ripple voltage exceeds ΔV, it will exceed the voltage adjustment range of the LED driver module, and the LED output current will decrease, resulting in power frequency flickering of the LED light string. Summary of the Invention

[0006] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to provide an LED driving method to solve the problems of soft start failure and low voltage input frequency flickering during rapid power on and off in the prior LED driving method.

[0007] To achieve the above-mentioned and other related objectives, the present invention provides an LED driving method, which includes:

[0008] The LED load is subjected to constant current control by a compensation control loop formed by the LED driver module, the LED load and the constant current control module;

[0009] The relationship between the reference voltage and the compensation voltage in the constant current control module is established so that the two satisfy the following relationship:

[0010] Among them, Vref represents the reference voltage, Vcomp represents the compensation voltage, Ref max Indicated as reference stable value, Ref min It represents the reference setting value, VB represents the first compensation setting value, VC represents the second compensation setting value, and VD represents the highest clamping voltage of the compensation control loop;

[0011] When the power supply is powered on and the operating voltage of the constant current control module begins to be established, the compensation voltage is increased to a second compensation setting value, at which time the reference voltage is correspondingly lowered to a reference setting value, and the output current of the LED driver module is minimized;

[0012] During the loop adjustment time of the compensation control loop, the compensation voltage gradually decreases from the second compensation setting value and stabilizes at the compensation stable value, the reference voltage gradually increases from the reference setting value and stabilizes at the reference stable value, and the output current of the LED driver module changes in the same direction as the reference voltage and ultimately achieves constant current output;

[0013] When the power supply is shut down, the compensation voltage is adjusted to the highest clamping voltage under the control of the compensation control loop. At this time, if the power supply is shut down and then quickly restarted, the compensation voltage gradually decreases from the highest clamping voltage and stabilizes at the compensation stable value within the loop adjustment time of the compensation control loop, and the reference voltage correspondingly gradually increases from the reference set value and stabilizes at the reference stable value. The output current of the LED driver module changes in the same direction as the reference voltage and ultimately achieves constant current output.

[0014] Optionally, when the normal working range of the compensation voltage is 0-VA, the first compensation setting value VB is greater than or equal to VA and less than VD, and the second compensation setting value VC is greater than VA and less than VD.

[0015] Optionally, the reference setting value is 0.

[0016] Optionally, within the loop adjustment time of the compensation control loop, the output current changes from low to high and eventually reaches a constant current output, thereby achieving output current soft start.

[0017] Optionally, when the power supply is quickly restarted after being shut down, the output current decreases following the reference voltage, thereby reducing the bus ripple voltage and preventing the LED load from experiencing power frequency flickering.

[0018] Optionally, the loop adjustment time is adjusted by adjusting the capacitance of the compensation capacitor in the constant current control module, thereby adjusting the output current soft start time.

[0019] Optionally, the loop adjustment time is adjusted by the discharge current of the compensation capacitor in the constant current control module, thereby adjusting the output current soft start time.

[0020] Optionally, the loop adjustment time is adjusted by adjusting the clock frequency of the compensation control loop, thereby adjusting the output current soft-start time.

[0021] As described above, an LED driving method of the present invention, through the design of the compensation voltage and the reference voltage, makes it possible that each time the power is turned on, the compensation voltage changes from high to low and reaches stability, and the reference voltage changes from low to high and reaches stability accordingly, and the output current changes in the same direction as the reference voltage, that is, changes from low to high and reaches a constant current output, thereby avoiding the problem of output current overshoot during rapid and repeated power on and off, and the output current soft start function can be achieved each time; even when the AC input voltage is lower than the rated operating voltage, when the compensation control loop raises the compensation voltage to the maximum clamping voltage, the output current will also decrease with the reference voltage, so that the charging and discharging ripple of the input filter capacitor on the bus is reduced, that is, the bus ripple voltage is reduced, thereby ensuring the stability of the output current and avoiding the power frequency flicker phenomenon of the LED load. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Shown is a structural schematic diagram of an existing LED driving circuit.

[0023] Figure 2 The following diagram shows the corresponding signal waveforms when a larger compensation capacitor is used to achieve soft start based on the existing LED drive circuit.

[0024] Figure 3 Shown are the signal waveforms corresponding to the soft start of the LED driving method according to the present invention.

[0025] Figure 4 It shows the linear relationship between the compensation voltage and the reference voltage of the present invention.

[0026] Component number description

[0027] 100 rectifier bridge module

[0028] 200 constant current control chip

[0029] 201 working voltage generation module

[0030] 202 Operational Amplifier

[0031] 203 compensation voltage generation module

[0032] 204 drive control module

[0033] 300 LED driver module

[0034] 400 PF Control Module DETAILED DESCRIPTION

[0035] The following describes the embodiments of the present invention through specific examples. Those skilled in the art will readily understand the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention.

[0036] See also Figures 3 and 4 It should be noted that the illustrations provided in this embodiment are merely schematic illustrations of the basic concept of the present invention. Although the illustrations only show components related to the present invention and are not drawn according to the number, shape, and size of components in actual implementation, the form, quantity, and proportion of each component in actual implementation may be arbitrarily changed, and the component layout may also be more complex.

[0037] like Figure 3As shown, this embodiment provides an LED driving method, the LED driving method comprising:

[0038] The LED load is subjected to constant current control by a compensation control loop formed by the LED driver module, the LED load and the constant current control module;

[0039] The relationship between the reference voltage and the compensation voltage in the constant current control module is established so that the two satisfy the following relationship: Among them, Vref represents the reference voltage, Vcomp represents the compensation voltage, Ref max It is expressed as the reference stable value (that is, the value corresponding to the reference voltage when the compensation control loop reaches stability), Ref min It represents the reference setting value, VB represents the first compensation setting value, VC represents the second compensation setting value, and VD represents the highest clamping voltage of the compensation control loop;

[0040] When the power supply is powered on and the operating voltage of the constant current control module begins to be established, the compensation voltage is increased to a second compensation setting value, at which time the reference voltage is correspondingly lowered to a reference setting value, and the output current of the LED driver module is minimized;

[0041] During the loop adjustment time of the compensation control loop (i.e., the time period corresponding to the start-up of the compensation control loop and before it reaches stability), the compensation voltage gradually decreases from the second compensation setting value and stabilizes at the compensation stable value (i.e., the value corresponding to the compensation voltage when the compensation control loop reaches stability), the reference voltage gradually increases from the reference setting value and stabilizes at the reference stable value, and the output current of the LED driver module changes in the same direction as the reference voltage and ultimately achieves constant current output (e.g., Figure 3 (time period t0-t1);

[0042] When the power supply is shut down, the compensation voltage is adjusted to the highest clamping voltage under the control of the compensation control loop. If the power supply is quickly restarted after being shut down, the compensation voltage gradually decreases from the highest clamping voltage and stabilizes at the compensation stable value within the loop adjustment time of the compensation control loop. The reference voltage correspondingly increases from the reference set value and stabilizes at the reference stable value. The output current of the LED driver module changes in the same direction as the reference voltage and finally achieves constant current output (such as Figure 3 (time periods t3-t4 and t6-t7).

[0043] It should be noted that the constant current control module described in this example not only includes Figure 1The constant current control chip 200 in the circuit shown also includes a current detection resistor Rs and a compensation capacitor Ccomp; the specific circuits of the LED driver module and the constant current control module can be any existing circuit that can achieve constant current regulation of the output current based on the compensation voltage. This example does not limit its specific circuit composition. It is particularly important to note that after the specific circuit of the compensation control loop is determined, the corresponding compensation stability value, reference stability value and maximum clamping voltage are also determined; and the reference set value Ref min The first compensation setting value VB and the second compensation setting value VC are set according to actual application requirements.

[0044] As an example, during the loop adjustment time of the compensation control loop, the output current changes from low to high and ultimately reaches a constant current output, thereby achieving output current soft-start. Even during the loop adjustment time after the power supply is shut down and quickly restarted, the output current soft-start function described in this example remains effective. Moreover, when the power supply is quickly restarted after shutdown, the output current decreases along with the reference voltage, thereby reducing the bus ripple voltage and preventing power frequency flicker in the LED load. This can be inferred from the formula C*ΔV=ILED*t_Discharge. When the capacitance C of the compensation capacitor and its discharge time t_Discharge remain unchanged, the bus ripple voltage ΔV also decreases due to the decrease in the output current ILED.

[0045] Specifically, the loop adjustment time is adjusted by the capacitance of the compensation capacitor in the constant current control module, thereby adjusting the time of the output current soft start; or, the loop adjustment time is adjusted by the discharge current of the compensation capacitor in the constant current control module, thereby adjusting the time of the output current soft start. It should be noted that when adjusting the loop adjustment time by the discharge current of the compensation capacitor, the purpose of adjusting the discharge current of the compensation capacitor can be achieved by selecting a suitable operational amplifier GM. Of course, other methods that can achieve the regulation of the discharge current of the compensation capacitor are also applicable to this example. In practical applications, a digital control circuit (such as a counter or a switching capacitor, etc.) can also be used to replace the operational amplifier GM and the compensation capacitor to achieve the purpose of de-capacitance; in this case, the loop adjustment time can be adjusted by adjusting the clock frequency of the digital control circuit, thereby adjusting the time of the output current soft start.

[0046] As an example, when the normal operating range of the compensation voltage is 0-VA (i.e., after the compensation control loop stabilizes, the compensation voltage stabilizes at the compensation stable value, which is greater than 0 and less than or equal to VA), the first compensation setting value VB is greater than or equal to VA and less than VD, and the second compensation setting value VC is greater than VA and less than VD. It should be noted that once the specific circuit of the compensation control loop is determined, the maximum compensation stable value VA is also determined.

[0047] Specifically, the reference setting value is 0, so that when the power is quickly restarted after shutdown, the reference voltage can gradually increase from 0. At this time, the corresponding minimum output current is smaller than when the reference setting value is non-zero. That is, when the power is quickly restarted after shutdown, the bus ripple voltage is reduced by reducing the output current to a minimum, thereby further preventing the LED load from experiencing power frequency flicker. When the reference setting value is 0, the relationship between the reference voltage and the compensation voltage is as follows:

[0048] In summary, the LED driving method of the present invention, through the design of the compensation voltage and reference voltage, ensures that each time the power is turned on, the compensation voltage changes from high to low and reaches stability, and the reference voltage changes from low to high and reaches stability accordingly. The output current changes in the same direction as the reference voltage, that is, changes from low to high and reaches a constant current output. This avoids the problem of output current overshoot during rapid and repeated power on and off, and can achieve the output current soft start function every time. Even when the AC input voltage is lower than the rated operating voltage, when the compensation control loop raises the compensation voltage to the maximum clamping voltage, the output current will also decrease with the reference voltage, reducing the charging and discharging ripple of the input filter capacitor on the bus, that is, reducing the bus ripple voltage, thereby ensuring output current stability and avoiding power frequency flickering of the LED load. Therefore, the present invention effectively overcomes the various shortcomings of the prior art and has high industrial utilization value.

[0049] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may 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 one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. A LED driving method, characterized in that: The LED driving method comprises: In the process of performing constant current control on the LED load through a compensation control loop formed by an LED driving module, an LED load and a constant current control module; The relationship between the reference voltage and the compensation voltage in the constant current control module is established so that the two satisfy the following relationship: Among them, Vref represents the reference voltage, Vcomp represents the compensation voltage, Ref max Indicated as reference stable value, Ref min It represents the reference setting value, VB represents the first compensation setting value, VC represents the second compensation setting value, and VD represents the highest clamping voltage of the compensation control loop; When the power supply is powered on and the working voltage of the constant current control module begins to be established, the compensation voltage is pulled up to a second compensation setting value, at which time the reference voltage is correspondingly pulled down to a reference setting value, and the output current of the LED driving module is minimum; During the loop adjustment time of the compensation control loop, the compensation voltage gradually decreases from the second compensation setting value and stabilizes at the compensation stable value, the reference voltage gradually increases from the reference setting value and stabilizes at the reference stable value, and the output current of the LED driving module changes in the same direction as the reference voltage and finally realizes constant current output; When the power supply is shut down, the compensation voltage is adjusted to the highest clamping voltage under the control of the compensation control loop; at this time, if the power supply is shut down and then quickly restarted, within the loop adjustment time of the compensation control loop, the compensation voltage gradually decreases from the highest clamping voltage and stabilizes at the compensation stable value, and the reference voltage correspondingly gradually increases from the reference set value and stabilizes at the reference stable value, and the output current of the LED driver module changes in the same direction as the reference voltage and finally achieves constant current output.

2. The LED driving method according to claim 1, characterized in that: When the normal working range of the compensation voltage is 0-VA, the first compensation setting value VB is greater than or equal to VA and less than VD, and the second compensation setting value VC is greater than VA and less than VD, wherein VA represents the maximum compensation stable value.

3. The LED driving method according to claim 1, characterized in that: The reference setting value is 0.

4. The LED driving method according to claim 1, characterized in that: During the loop adjustment time of the compensation control loop, the output current changes from low to high and finally reaches a constant current output, thereby realizing output current soft start.

5. The LED driving method according to claim 4, characterized in that: When the power supply is quickly restarted after being shut down, the output current decreases following the reference voltage, thereby reducing the bus ripple voltage and preventing the LED load from flickering at the power frequency.

6. The LED driving method according to claim 4, characterized in that: The loop adjustment time is adjusted by adjusting the capacitance of the compensation capacitor in the constant current control module, thereby adjusting the output current soft start time.

7. The LED driving method according to claim 4, characterized in that: The loop adjustment time is adjusted by the discharge current of the compensation capacitor in the constant current control module, thereby adjusting the output current soft start time.

8. The LED driving method according to claim 4, characterized in that: The loop adjustment time is adjusted by adjusting the clock frequency of the compensation control loop, thereby adjusting the output current soft start time.

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