Driving circuit, device and electric appliance of light emitting element

Abstract

Provided are a driving circuit, a device, and an electrical appliance of a light emitting element. The driving circuit comprises: at least two adjustable units, which, together with at least two external shunt units, form a variable impedance network; a driving power supply stage, which, together with the variable impedance network and the light emitting element, forms a series path between a power supply and a reference ground, and is used to adjust a driving current flowing through the light emitting element to have a constant current value; and an impedance adjustment circuit, which is used to adjust a voltage difference between a first voltage value on a driving input side of the driving power supply stage and a second voltage value on a driving output side of the driving power supply stage to a preset voltage value by adjusting impedance values of the at least two adjustable units.

Description

Technical Field

[0001] This disclosure relates to the field of circuits, and more specifically, to a driving circuit, apparatus, and electrical device for driving light-emitting elements. Background Technology

[0002] The prior art provides a method such as Figure 1 The driving circuit shown includes a driving circuit 12 connected in series between the power supply 11 and the reference ground, and a light-emitting element 13. The electrical energy generated by the power supply 11 is converted into a driving current with a suitable constant value by the driving circuit 12, and then delivered to one or more light-emitting elements 13 connected in series to drive them. To ensure a constant driving current output, the voltage difference between the driving input side and the driving output side of the driving circuit 12 needs to be greater than a certain value. However, due to fluctuations and deviations in the forward voltage drop of the light-emitting element 13, the output voltage of the power supply 11 needs to have sufficient voltage margin. However, the heat generated by the constant current output by the driving circuit 12, due to the voltage margin and the heat dissipation capacity of the chip package of the driving circuit 12, results in high power consumption, high heat generation, and limited driving capability of the driving circuit 12 in the prior art.

[0003] Therefore, there is a need for a technical solution to the problems of high power consumption, high heat generation, and limited output current capability of the driving circuit of the light-emitting element in the prior art. Summary of the Invention

[0004] According to one aspect of this disclosure, a driving circuit is provided for driving a light-emitting element. The driving circuit includes: at least two adjustable units forming a variable impedance network with at least two external shunt units; a driving power supply stage forming a series path between the variable impedance network and the light-emitting element between a power supply and a reference ground, for adjusting the driving current flowing through the light-emitting element to have a constant current value; and an impedance adjustment circuit for adjusting the voltage difference between the first voltage value and the second voltage value to a preset voltage value by adjusting the impedance values ​​of the at least two adjustable units, based on a first voltage value on the driving input side of the driving power supply stage and a second voltage value on the driving output side of the driving power supply stage.

[0005] According to another aspect of this disclosure, an electrical device is provided, including a light-emitting element and a driving circuit as described above. Attached Figure Description

[0006] Figure 1 A schematic circuit diagram of a driving circuit for a light-emitting element in the prior art is shown.

[0007] Figure 2A schematic circuit diagram of a driving circuit for a light-emitting element according to some embodiments is shown.

[0008] Figure 3A and Figure 3B A schematic circuit diagram of a driving circuit 30 for a light-emitting element according to some embodiments of the present disclosure is shown.

[0009] Figure 4 The illustration schematically depicts the variation of the power supply voltage according to embodiments of the present disclosure. Figure 3A The changes in the associated parameters of the driving circuit are shown.

[0010] Figure 5 The following is also schematically illustrated according to embodiments of the present disclosure, as the power supply voltage changes. Figure 3A The diagram shows the changes in the on-resistance of the first and second adjustable units in the driving circuit.

[0011] Figure 6 An embodiment according to this disclosure is shown. Figure 3A More details of the drive circuit shown.

[0012] Figure 7A A schematic circuit diagram of a voltage compensation circuit according to an embodiment of the present disclosure is shown.

[0013] Figure 7B A schematic circuit diagram of a voltage sampling circuit according to an embodiment of the present disclosure is shown.

[0014] Figure 8 An example structure of a variable impedance network according to an embodiment of the present disclosure is shown.

[0015] Figure 9A and 9B A schematic diagram of a multi-stage control voltage generation method according to an embodiment of the present disclosure is shown. Detailed Implementation

[0016] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0017] Light-emitting elements (LEDs) serve functions such as illumination, indication, and display, and are therefore widely used in various fields. Taking LEDs and their derivatives such as OLEDs as examples, they are widely used in automotive lighting devices due to their advantages such as high brightness, environmental friendliness, small size, fast response speed, and long lifespan. LEDs can also be arranged into pixel circuits to form lighting or display devices for electrical equipment. Stable operation of LEDs requires a driving circuit or device as a "medium," which adjusts and controls the power supply voltage and / or current to drive the LEDs to operate according to a preset mode.

[0018] Taking LEDs as the light-emitting element and LED driver circuits as the driving circuit, the basic function of an LED driver circuit is to provide a constant output current to the LEDs, especially when the power supply voltage or LED voltage drop changes, it should still maintain a constant output current. In addition, the LED driver circuit should maintain low power consumption under a certain output current to ensure a greater output current capability. Meanwhile, as LEDs are a common component of modern automotive lighting systems, considering the increasing personalized needs of automotive lighting applications and the gradually improving requirements for display effects, the number and arrangement density of LEDs have greatly increased, and the required driving current for LEDs has greatly increased. Therefore, it is necessary to control the driving performance and heat generation of the LED driver circuit. Existing constant current driver circuits used to drive multi-LED loads suffer from high power consumption and limited driving capability. One of the objectives of this disclosure is to effectively balance constant current performance and heat generation to improve the output current capability of the driver circuit.

[0019] One embodiment of this disclosure provides an electrical device including a light-emitting element and a light-emitting element driving circuit for driving the light-emitting element. The electrical device may further include a display device formed by the light-emitting element, and the light-emitting element driving circuit is connected to one or more channels (or branches) on the display device to achieve driving. Specifically, the electrical device may be, for example, a car headlight, car taillight, interior ambient light, signal light, or other lighting or signaling device; it may also be a liquid crystal screen, display screen, or any other electrical device that needs to emit light through driving to provide illumination to the outside world, display information, or interact with the user.

[0020] Furthermore, one embodiment of this disclosure provides, as follows: Figure 2 The light-emitting element driving circuit shown can be installed in any of the above-mentioned electrical devices, or exist independently in other application scenarios, for driving the light-emitting element.

[0021] Figure 2 A schematic diagram of a driving circuit 20 for a light-emitting element according to some embodiments is shown.

[0022] like Figure 2 As shown, the driving circuit 20 can be used to provide a driving current with a constant current value to the light-emitting element 21 to drive the light-emitting element 21 to emit light. The light-emitting element 21 may include multiple light-emitting branches, each of which includes, for example, an LED or an LED string. In this case, the driving circuit 20 correspondingly includes multiple driving branches that drive the respective light-emitting branches.

[0023] The driving circuit 20 may include an adjustable unit 201, a driving power stage 202, and an impedance adjustment circuit 203, as well as an optional voltage sampling circuit 204. The adjustable unit 201, the driving power stage 202, and the light-emitting element 21 are connected in series between the power supply VS1 and the reference ground GND. An external shunt unit 22 is also provided between the power supply VS1 and the driving input side of the driving power stage 202. The adjustable unit 201 and the external shunt unit 22 constitute a variable impedance network RVA. The impedance adjustment circuit 203 can change the equivalent impedance value of the variable impedance network RVA by controlling the resistance value of the adjustable unit 201. The driving power stage 202 can convert the electrical energy from the power supply VS1 after passing through the variable impedance network RVA to provide a driving current with a constant current value to the light-emitting element 21, so that the light-emitting element 21 can emit light normally.

[0024] Typically, it is desirable that the voltage difference between the drive input side and the drive output side (i.e., the input terminal of the light-emitting element 21) of the drive power supply stage 202 is greater than or equal to a preset voltage value to achieve normal operation of the drive power supply stage 202. This preset voltage value corresponds to the optimal operating state of the drive power supply stage 202, in which the drive power supply stage 202 can provide the light-emitting element 21 with a drive current of the desired current value (e.g., the rated current value) (even if there are fluctuations in the forward voltage drop of the light-emitting element 21) and with minimal power.

[0025] Impedance adjustment circuit 203 is used to adjust the voltage difference between the drive input side and drive output side of drive power supply stage 202 to a preset voltage value. The voltage value on the drive output side can be a voltage value associated with the output voltage of the drive output side. When the light-emitting element 21 includes a single light-emitting branch, the voltage value on the drive output side of drive power supply stage 202 is the output voltage value of the single drive branch; and when the light-emitting element 21 includes multiple light-emitting branches, the voltage value on the drive output side of drive power supply stage 202 is the maximum voltage value (VOUT1, …VOUTm) among the output voltage values ​​(VOUT1, …VOUTm) of each output terminal of the multiple drive branches. maxIn this way, if the voltage difference between the drive input side and the drive output side is the preset voltage value, then for each drive branch, the voltage difference between the input and output ends will be greater than or equal to the preset voltage value, thus ensuring the normal operation of the drive branch.

[0026] exist Figure 2 In this embodiment, the impedance adjustment circuit 203 can control the impedance value of the adjustable unit 201 based on a feedback control loop, so that its equivalent impedance value after being connected in parallel with the external shunt unit 22 is also adjusted, that is, the equivalent impedance value of the variable impedance network RVA is changed. Figure 2 In the illustrated embodiment, the variable impedance network RVA includes two impedance branches: an external shunt unit 22 and an adjustable unit 201. In some embodiments, the adjustable unit 201 can be a transistor that operates in the variable impedance region. The impedance adjustment circuit 203 can control the on-resistance value of the transistor by controlling its conduction level, thus changing the equivalent impedance value of the variable impedance network RVA. In the context of this disclosure, the transistor can be, for example, an N-type metal-oxide-semiconductor (NMOS) transistor or a P-type metal-oxide-semiconductor (PMOS) transistor, or other types of transistors capable of being turned on and off according to a signal at a control terminal, and having different impedance values ​​depending on the conduction level. In another embodiment, the adjustable unit 201 can also be an adjustable resistor.

[0027] exist Figure 2 In this embodiment, when the power supply voltage VS1 is in the first voltage range [V min VOUT+V headroom +Rshunt I LED When [the impedance of the adjustable unit 201 is adjusted by the impedance adjustment circuit 203, heat sharing is achieved with the external shunt unit 22 outside the drive circuit 20.] min This is the minimum power supply voltage for the drive circuit 20, for example, the minimum value of the rated voltage range, such as 7V. LED VOUT is the constant current value of the drive current on the light-emitting element 21, and VOUT is the voltage value of the drive output side of the drive power supply stage or the maximum voltage value output by multiple drive branches. headroom The preset voltage value is used. The impedance value of the external shunt unit 22 is represented as Rshunt. In this case, the voltage value on the drive input side is VS2 = VOUT + V headroom .

[0028] The heat loss power of the drive circuit 20 can be expressed as: P drv =I LED (VS2-VOUT)+ (VS1-VS2) (I LED -(VS1-VS2) / Rshunt), based on this formula, we can solve for VS1-VS2= Rshunt. I LED / 2, the equivalent impedance of the adjustable unit 201 is equal to the impedance value Rshunt of the external shunt unit (each shares half of the constant current value I). LED When the drive current is / 2), the heat loss power of the drive circuit 20 has a maximum value: P drv_max = I LED 2 Rshunt / 4+V headroom I LED .

[0029] As can be seen, since a portion of the driving current for the light-emitting element 21 flows through the external shunt unit 22 outside the driving circuit 20, the external shunt unit 22 performs a shunt function, reducing the current flowing through the driving circuit 20. This reduces the power consumption of the driving circuit itself, thereby avoiding excessive heat generation and achieving higher driving efficiency and providing a larger output current capability. The external shunt unit 22 can be considered as sharing heat with the adjustable unit 201 and other circuits inside the driving circuit.

[0030] exist Figure 2 In this embodiment, the shunting effect of the external shunt unit 22 is limited by its impedance value. When the power supply voltage VS1 > VOUT + V headroom + Rshunt I LED At that time, since the external shunt unit 22 has already handled the entire drive current I... LED When the voltage that the variable impedance network RVA can handle has reached its maximum value, the excess voltage drop will be borne by the drive power supply stage 202. At this time, the impedance adjustment circuit 203 loses its function of adjusting the impedance.

[0031] Furthermore, there is a contradiction between the thermal sharing adjustment capability and the adjustment range of the drive circuit. For example, when the power supply voltage VS1 is low, the overall power consumption is low. At this time, it is generally desirable for more current to flow through the adjustable unit 201 inside the drive circuit. Therefore, the impedance value of the external shunt unit 22 should be as small as possible so that the equivalent impedance value of the variable impedance network RVA is small enough to share a small voltage drop, ensuring that the voltage difference between the drive input side and the drive output side is basically stable at the preset voltage value. However, as mentioned earlier, the shunt effect of the external shunt unit 22 is limited by its impedance value. If the impedance of the shunt unit 22 is small, the impedance adjustment circuit 203 may lose its impedance adjustment function when the power supply voltage VS1 is not high, thus the adjustment range is very small. On the other hand, when the power supply voltage VS1 is high, it is generally desirable for the external shunt unit 22 to be able to handle a larger voltage drop to ensure low power consumption within the drive circuit. Therefore, the impedance of the external shunt unit 22 should be as large as possible. However, in application scenarios where the power supply voltage VS1 is low, this will reduce efficiency and may even make it impossible to guarantee that the voltage difference across the drive power stage is the preset voltage value, thus affecting the adjustment capability. Therefore, it can be seen that... Figure 2 The proposed solution may be difficult to be compatible with a wide range of heat dissipation and power supply voltages.

[0032] Therefore, as an improvement, Figures 3A-3B A schematic diagram of a driving circuit 30 for a light-emitting element according to some embodiments of the present disclosure is shown. In the context of this disclosure, the same or similar reference numerals refer to the same elements.

[0033] exist Figures 3A-3B In this embodiment, the driving circuit 30 can be used to provide a driving current with a constant current value to the light-emitting element 31 so as to drive the light-emitting element 31 to emit light. The light-emitting element 31 may include multiple light-emitting branches, each of which includes, for example, an LED or an LED string. In this case, the driving circuit 30 correspondingly includes multiple driving branches that drive the respective light-emitting branches.

[0034] like Figures 3A-3B As shown, the drive circuit 30 may include at least two adjustable units 301 (301-1, 301-2, etc.), a drive power supply stage 302, and an impedance adjustment circuit 303.

[0035] Each of the at least two adjustable units 301 can be a transistor (e.g., an NMOS transistor or a PMOS transistor) or a variable resistor, as described above. The at least two adjustable units 301 can form a variable impedance network (RVA) with at least two external shunt units 32 (32-1, 32-2, etc.). The impedance values ​​of each external shunt unit 32 can be the same or different, and this disclosure is not limiting in this regard. Furthermore, two adjustable units 301 and two external shunt units 32 are schematically shown in FIG3 and are illustrated as an example in most embodiments of this disclosure; however, more adjustable units 301 and external shunt units 32 can be provided as needed.

[0036] The drive power stage 302, the variable impedance network RVA, and the light-emitting element 31 form a series path between the power supply VS1 and the reference ground GND, used to regulate the drive current flowing through the light-emitting element 31 to a constant current value. For example, as Figure 3A As shown, the variable impedance network RVA, the driving power supply stage 302, and the light-emitting element 31 are connected in series. Specifically, the driving input side of the driving power supply stage 302 is connected to the adjustable unit 301, and the driving output side of the driving power supply stage 302 is connected to the light-emitting element 31 and provides driving current to it. (The following text refers to...) Figure 3A The circuit structure of the driving circuit shown has been described; however, it should be understood that in other embodiments, the connection order of the variable impedance network RVA, the driving power supply stage 302, and the light-emitting element 31 can be changed, for example... Figure 3B As shown. In Figure 3B In this circuit, the light-emitting element 31, the driving power supply stage 302, and the variable impedance network RVA are connected in series. That is, the driving output side of the driving power supply stage 302 is connected to the adjustable unit 301, and the driving input side of the driving power supply stage 302 is connected to the output terminal of the light-emitting element 31, and controls the driving current flowing through the light-emitting element 31.

[0037] The impedance adjustment circuit 303 is used to adjust the voltage difference between the first voltage value VS2 and the second voltage value VOUT, which are associated with the first voltage value VS2 on the drive input side of the drive power supply stage 302 and the second voltage value VOUT on the drive output side of the drive power supply stage 302, to a preset voltage value by adjusting the impedance values ​​of the at least two adjustable units 301.

[0038] For example, for Figure 3AIn the connection method shown, when the voltage difference between the first voltage value VS2 and the second voltage value VOUT is greater than the preset voltage value, the impedance adjustment circuit 303 adjusts the impedance values ​​of the at least two adjustable units 301 to increase the equivalent impedance value of the variable impedance network RVA. Since the current flowing through the variable impedance network RVA (i.e., the driving current provided to the light-emitting element 21) is constant, the voltage drop on the variable impedance network RVA is increased. As a result, for the current power supply voltage VS1, the voltage value on the driving input side, i.e., the first voltage value VS2, is reduced, and the voltage difference between the driving input side and the driving output side is gradually reduced until the voltage difference is basically equal to the preset voltage value. Conversely, when the voltage difference between the first voltage value VS2 and the second voltage value (VOUT) is less than the preset voltage value, the impedance adjustment circuit 303 adjusts the impedance values ​​of the at least two adjustable units 301 to reduce the equivalent impedance value of the variable impedance network RVA. Since the current flowing through the variable impedance network RVA (i.e. the driving current provided to the light-emitting element 21) is constant, the voltage drop on the variable impedance network RVA is reduced, thereby reducing the first voltage value of the driving input side for the current power supply voltage VS1, and gradually increasing the voltage difference between the driving input side and the driving output side until the voltage difference is basically equal to the preset voltage value.

[0039] Optionally, as described above, in one application scenario, at least two sets of light-emitting branches constituting the light-emitting element 31 are provided at the rear end of the driving power supply stage 302. Thus, the driving power supply stage 302 can correspondingly include at least two sets of driving branches, and each of the at least two sets of driving branches is connected in series with at least two sets of light-emitting branches. Multiple light-emitting channels formed by the driving branches and their corresponding light-emitting branches are connected in parallel between the driving input side and the reference ground terminal GND. The driving branches of the driving power supply stage 302 each output a corresponding output voltage, and the second voltage value on the driving output side is the maximum voltage value (VOUT) among the voltage values ​​(VOUT1, VOUT2, ... VOUTm) of each output terminal of the multiple driving branches. max Based on this, the driving circuit may further include a voltage sampling circuit 304, and specifically, the voltage sampling circuit 304 is disposed between the impedance adjustment branch 303 and the driving output side, and is configured to sample the maximum output voltage of the at least two sets of driving branches as a second voltage value.

[0040] The driving circuit shown in Figure 3 ensures that the first voltage value VS2 on the driving input side and the second voltage value VOUT on the driving output side are equal. max While the voltage difference remains basically stable at the preset voltage value, the variable impedance network RVA includes at least two adjustable units 301 and at least two external resistors 32, compared to Figure 2The two impedance branches in the circuit can include more impedance branches, thus providing a wider range of variable impedance. This allows for adjustment of the appropriate impedance value according to actual conditions, while ensuring... Figure 2 The driving circuit shown can have a wider power supply voltage adjustment range while maintaining its adjustment capability.

[0041] Furthermore, such as Figure 3A As shown in the illustration, as a specific example, the variable impedance network RVA includes a first impedance branch, a second impedance branch, and a third impedance branch connected in parallel. The first impedance branch includes a first external shunt unit 32-1, one of the at least two external shunt units, which has a fixed impedance value, denoted as Rshunt1, and is also the maximum impedance value of the variable impedance network RVA. The second impedance branch includes a first adjustable unit 301-1. The third impedance branch includes a series structure of a second adjustable unit 301-2 and a second external shunt unit 32-2, which also has a fixed impedance value, denoted as Rshunt2.

[0042] Typically, under different power supply voltages VS1, the variable impedance network RVA should be adjusted to have different impedance values ​​to ensure that the voltage difference across the drive power stage is a preset voltage value. For example, as mentioned earlier, when the power supply voltage VS1 is small, the variable impedance network RVA should have a small impedance to produce a small voltage drop, and when the power supply voltage VS1 is large, the variable impedance network RVA should have a large impedance to produce a large voltage drop. Through this impedance adjustment circuit 303, the impedance value of the variable impedance network RVA can be adaptively adjusted for different power supply voltages, and the voltage difference across the drive power stage 302 can be stabilized at a preset voltage value.

[0043] Figure 4 The illustration schematically depicts the variation of the power supply voltage VS1 according to an embodiment of the present disclosure. Figure 3A The changes in the associated parameters of the driving circuit are shown. Figure 5 The diagram also schematically illustrates the effect of varying power supply voltage VS1 according to embodiments of the present disclosure. Figure 3A The on-resistance of the first adjustable unit 301-1 and the second adjustable unit 301-2 in the driving circuit shown.

[0044] Figure 4 The diagram shows the changes in the first current I1 of the first impedance branch, the second current I2 of the second impedance branch, the third current I3 of the third impedance branch, and the changes in the heat loss power of the drive circuit 30. Furthermore, in... Figure 4In this system, the power supply voltage VS1 is dynamically divided into three consecutive intervals that increase sequentially within the allowable range of the power supply voltage.

[0045] It should be noted that Figure 4 and Figure 5 The parameter changes mentioned are for different power supply voltages, and the corresponding parameter values ​​when the drive circuit operates in steady state (i.e., the voltage difference across the drive power supply stage 302 is stable at the preset voltage value and provides a stable drive current).

[0046] like Figure 4 As shown, when the power supply voltage VS1 is in a smaller first voltage range, the drive current flows through the first impedance branch, the second impedance branch, and the third impedance branch. At this time, the impedance value of the first adjustable unit 301-1 is variable, while the impedance value of the second adjustable unit 301-2 is adjusted to be fixed (e.g., the minimum impedance value of the second adjustable unit 301-2 can be ignored). Therefore, the equivalent impedance value of the variable impedance network RVA is adjusted by adjusting the impedance value of the first adjustable unit 301-1. Correspondingly, since the first adjustable unit 301-1 is connected in parallel with two external shunt units (32-1 and 32-2), the equivalent impedance value of the variable impedance network RVA will be less than the impedance value of the second adjustable unit 301-2, thereby providing a smaller voltage drop to adapt to the smaller first voltage range.

[0047] When the power supply voltage VS1 is in the first voltage range, as the power supply voltage VS1 increases, the impedance adjustment circuit 303 can increase the impedance value of the first adjustable unit 301-1, and keep the impedance value of the second adjustable unit 301-2 at a small fixed impedance value R. M2-ON This increases the equivalent impedance of the variable impedance network RVA, thereby increasing the voltage drop. Therefore, it increases the current flowing through the two external shunt units (32-1 and 32-2). Figure 4 (represented as I1 and I3). Since the current flowing through the variable impedance network RVA is constant, the current I2 flowing through the first adjustable unit 301-1 should decrease. Therefore, as... Figure 5 As shown, in the first voltage range, the fixed impedance value R of the second adjustable unit 301-2 is... M2-ON Keep it at a low value, it can be ignored, and the impedance value R of the first adjustable unit M1-ON Gradually increase.

[0048] Figure 4 The currents I1 / I3 increase linearly, and the slope is related to the impedance values ​​of the two external shunt units. In this embodiment, it is assumed that the first external shunt unit 32-1 and the second external shunt unit 32-2 have the same impedance value. Figure 4The slopes of the straight lines corresponding to I1 and I3 are slightly different because the second external shunt unit 32-2 is also connected in series with the second adjustable unit 301-2, which also has a small impedance value. Correspondingly, the current I2 decreases almost linearly.

[0049] As the power supply voltage VS1 increases, when the current I2 flowing through the first adjustable unit 301-1 decreases to 0, the drive current with a constant current value flows entirely through the first impedance branch and the third impedance branch. At this time, the power supply voltage VS1 = VOUT + V headroom + (Rshunt1 / / Rshunt2) I LED , where I LED VOUT is the constant current value of the drive current supplied to the light-emitting element 31, and VOUT is the second voltage value on the drive output side of the drive power supply stage 302. headroom As a preset voltage value, Rshunt1 represents the first resistance value of the first external shunt unit 32-1, and Rshunt2 represents the second resistance value of the second external shunt unit 32-2. Therefore, the first voltage range is [V]. min VOUT+V headroom + (Rshunt1 / / Rshunt2) I LED ], where V min The minimum value of the power supply voltage, for example. Figure 4 The value shown is 7V.

[0050] In other words, if the power supply voltage VS1 is within the first voltage range, the impedance that achieves thermal sharing with the power consumption devices inside the drive circuit 30 (e.g., the second adjustable unit M2, the drive power supply stage, etc.) is represented by the parallel connection of two external shunt units 32-1 and 32-2 (as mentioned before, the very small impedance value R of the second adjustable unit 301-2 is ignored). M2-ON The impedance value is Rshunt2 / / Rshunt1 (i.e., Rshunt1). Rshunt2 / (Rshunt1+Rshunt2)), this resistance value is less than Rshunt1, therefore compared to Figure 2 When the drive circuit only has an external shunt unit 32-1, and for a small, identical power supply voltage VS1, and when the voltage difference across the drive power supply stage needs to be satisfied, the variable impedance network RVA can handle the same voltage drop. Figure 3A The driving circuit shown can have more current flowing out of the driving circuit, therefore compared to Figure 2 The driving circuit can further reduce the heat loss of the chip. Within this first voltage range, the heat loss power of the driving circuit can be expressed as: P drv1 =ILED V headroom +(VS1-VS2) I LED -(VS1-VS2) 2 / (Rshunt2 / / Rshunt1), based on this formula, we obtain that when VS1-VS2=I LED When (Rshunt2 / / Rshunt1) / 2, we obtain the maximum value P. drv_max1 =I LED V headroom +I LED 2 / 4 (Rshunt2*Rshunt1) / (Rshunt2+Rshunt1). VS2 represents the first voltage value on the drive input side of the drive power supply stage 302, and because it stably provides drive current I to the light-emitting element 31. LED At that time, VS2 is basically equal to VOUT + V headroom Furthermore, if multiple light-emitting branches are included, VOUT here represents the maximum voltage value VOUT output by each driving branch. max .

[0051] Continue as Figure 4 As shown, when the power supply voltage VS1 is in a suitable second voltage range, for example, greater than the maximum voltage value of the first voltage range, the drive current flows through the first impedance branch and the third impedance branch. At this time, the impedance value of the first adjustable unit 301-1 is adjusted by the impedance adjustment circuit 303 to make the second impedance branch open. The impedance value of the second adjustable unit 301-2 is variable, so the equivalent impedance value of the variable impedance network RVA is adjusted by adjusting the impedance value of the second adjustable unit 301-2. Correspondingly, since the second adjustable unit 301-2 is connected in series with the second external shunt unit 32-2 and then in parallel with the first external shunt unit 32-1, the equivalent impedance value of the variable impedance network RVA is increased compared to the first voltage range, thereby providing a larger voltage drop to adapt to the suitable second voltage range.

[0052] When the power supply voltage is in the second voltage range, as the power supply voltage VS1 increases, since the impedance adjustment circuit 303 has already adjusted the impedance value of the first adjustable unit 301-1 to disconnect the second impedance branch, it is meaningless to continue adjusting the impedance value of the first adjustable unit 301-1. At this time, the impedance adjustment circuit 303 can increase the impedance value of the second adjustable unit 301-2, thus increasing the equivalent impedance value of the variable impedance network RVA and increasing the provided voltage drop. Therefore, it can increase the current flowing through the first external shunt unit 32-1 (first impedance branch). Figure 4 Represented as I1), since the current flowing through the variable impedance network RVA is constant, the current I3 flowing through the series branch (third impedance branch) of the second adjustable unit 301-2 and the second external shunt unit 32-2 should decrease, and the current flowing through the second impedance branch should remain 0. Similarly, in Figure 4 In this second voltage range, the currents I1 / I3 change essentially linearly. For example... Figure 5 As shown, in the second voltage range, the impedance value R of the second adjustable unit 301-2 is... M2-ON The impedance value R of the first adjustable unit 301-1, which has been gradually increased and is now turned off, is gradually increased. M1-ON When the value is relatively large, the corresponding impedance branch is basically equivalent to an open circuit.

[0053] As the power supply voltage VS1 increases, when the current I3 flowing through the second adjustable unit 301-2 decreases to 0, the entire drive current flows through the first impedance branch. At this time, the power supply voltage VS1 = VOUT + V headroom +Rshunt1 I LED Therefore, the second voltage range is (VOUT + V headroom +(Rshunt1 / / Rshunt2) I LED VOUT+V headroom +Rshunt1 I LED The definitions of each parameter are the same as before.

[0054] In other words, if the power supply voltage VS1 is within the second voltage range, the resistance that achieves thermal sharing with the power-consuming devices inside the drive circuit (e.g., the second adjustable unit M2, the drive power supply stage, etc.) is represented by the first external shunt unit 32-1 and the second external shunt unit 32-2 connected in series with the second adjustable unit M2. Therefore, compared to Figure 2In the driving circuit, since the second external shunt unit 32-2 can share a portion of the voltage with the second adjustable unit M2, the chip's heat loss can be further reduced. Within this second voltage range, the heat loss power of the driving circuit can be expressed as: P drv2 =I LED V headroom +{VS1-VS2-[I LED - (VS1-VS2) / Rshunt1] Rshunt2} (I LED - (VS1-VS2) / Rshunt1), based on this formula, we can solve for VS1-VS2= I LED When (Rshunt1 / 2+(Rshunt1 / / Rshunt2) / 2), the maximum value P is obtained. drv_max2 = I LED V headroom +I LED 2 / 4 (Rshunt1 2 / (Rshunt2 + Rshunt1)). VS2 represents the first voltage value on the drive input side of the drive power stage 302, and because it stably provides drive current I to the light-emitting element 31. LED At that time, VS2 is basically equal to VOUT + V headroom .

[0055] Continue as Figure 4 As shown, when the power supply voltage VS1 is in a larger third voltage range, such as a third voltage range greater than the maximum value of the second voltage range, the impedance adjustment circuit 303 adjusts the impedance values ​​of the first adjustable unit 301-1 and the second adjustable unit M2 to make the corresponding impedance branch open-circuit, such as... Figure 5 As shown, in the third voltage range, both the second adjustable unit 301-2 and the first adjustable unit 301-1 maintain a relatively large impedance value. At this time, the variable impedance network RVA has a fixed impedance value Rshunt1, and the driving current supplied to the light-emitting element 31 flows entirely through the first external shunt unit 32-1. Therefore, the current I1 flowing through the first external shunt unit 32-1 remains unchanged, while I2 and I3 remain 0. Correspondingly, the variable impedance network RVA can provide a fixed, relatively large voltage drop. In this third voltage range, even if the power supply voltage VS1 increases, since the impedance adjustment circuit 303 cannot stabilize the voltage difference across the driving power stage 302 at a preset voltage value, the excess voltage drop will be borne by the driving power stage 302.

[0056] The third voltage range is (VOUT+V) headroom +Rshunt1 I LED V max ], V max The maximum value of the power supply voltage for the drive circuit, for example Figure 4 The 16V shown. That is, if the power supply voltage VS1 is within the third voltage range, the first adjustable unit 301-1 and the second adjustable unit M2 are simultaneously turned off by the impedance adjustment circuit 303. Only the impedance branch containing the first external shunt unit 32-1 bears the entire drive current. Therefore, the excess voltage drop will be borne by the drive power supply stage. At this time, the impedance adjustment circuit has lost its adjustment function, and the heat loss power of the drive circuit can be expressed as: P drv3 = I LED (VS1–Rshunt1 I LED -VOUT). At this time, VS2 is greater than VOUT+V. headroom .

[0057] Through the above combination Figure 4 The relationship between heat loss power and power supply voltage VS1 shows that if Figure 3A The requirements of the drive circuit are the same as Figure 2 If the heat loss power of the drive circuits has the same maximum value, then Figure 3A The first external shunt unit 32-1 and the second external shunt unit 32-2 (assuming they are equal) can take values ​​of... Figure 2 The impedance of the external shunt unit of the drive circuit is twice that of the drive circuit. Therefore, given that the drive circuit has the same heat loss power, Figure 3A The adjustment range supported by the drive circuit will be Figure 2 The drive circuit is twice the size. On the other hand, if Figure 3A The requirements of the drive circuit are the same as Figure 2 The drive circuits have the same adjustment range. Figure 3A The maximum value of the heat loss power of the drive circuit is significantly smaller than Figure 2 The drive circuit can reduce the heat loss power of the drive circuit.

[0058] Figure 6 An embodiment according to this disclosure is shown. Figure 3A More details of the drive circuit shown.

[0059] like Figure 6As shown, the adjustable unit 301 includes a first transistor M1 and a second transistor M2. The external shunt unit 32 includes a first external resistor Rshunt1 and a second external resistor Rshunt2. The first external resistor Rshunt1 has a fixed impedance value, also denoted as Rshunt1, and serves as the first impedance branch. The first transistor M1 serves as the second impedance branch. The series connection of the second transistor M2 and the second external resistor Rshunt2 serves as the third impedance branch. The fixed impedance value of the second external resistor Rshunt2 is also denoted as Rshunt2. The first impedance branch, the second impedance branch, and the third impedance branch are connected in parallel to form a variable impedance network RVA.

[0060] Since each of the first transistor M1 and the second transistor M2 can be turned on and off, and can be considered as having an infinite impedance when turned off, and as a conducting switch when fully turned on, it has a negligible minimum impedance value, and when partially turned on (i.e., not fully turned on), it has an impedance value between the minimum impedance value and the infinite impedance value. The impedance value of each of the first transistor M1 and the second transistor M2 can vary depending on the degree of conduction.

[0061] As mentioned above, the impedance adjustment circuit 303 can adaptively adjust the equivalent impedance value of the variable impedance network RVA for different power supply voltages, so as to stabilize the voltage difference across the drive power stage 302 at a preset voltage value.

[0062] like Figure 6 As shown, the impedance adjustment circuit 303 includes a voltage compensation circuit 3031, an error amplifier 3032, and a control voltage adjustment circuit 3033.

[0063] The first input terminal of the error amplifier 3032 is connected to the drive input side of the drive power supply stage 302, and the second input terminal is connected to the drive output side of the drive power supply stage 302. The output terminal of the error amplifier 3032 is directly connected to the control terminal of the second transistor M2, and is connected to the control terminal of the first transistor M1 via the control voltage adjustment circuit 3034. The voltage compensation circuit 3031 is disposed between the error amplifier 3032 and the drive power supply stage 302, and is configured to generate a third voltage value based on a preset voltage value, and either the first voltage value VS2 on the drive input side or the second voltage value VOUT on the drive output side, and output the third voltage value to either the first input terminal or the second input terminal of the error amplifier 3032.

[0064] For example, in one example, such as Figure 6As shown, the voltage compensation circuit 3031 can perform positive voltage compensation on the second voltage value VOUT on the drive output side based on a preset voltage value to obtain a third voltage value greater than the second voltage value. This third voltage value is then input to the error amplifier 3032 along with the first voltage value VS2 on the drive input side of the drive power supply stage 302. The error amplifier 3032 responds to the difference between the first and third voltage values ​​by outputting a control voltage at its output terminal. For example, although not in... Figure 6 As shown, in another example, the voltage compensation circuit 3031 can perform negative voltage compensation on the first voltage value VS2 on the drive input side based on a preset voltage value to obtain a third voltage value that is less than the first voltage value. This third voltage value is then input to the error amplifier 3032 along with the second voltage value on the drive output side of the drive power supply stage 302. The error amplifier 3032 responds to the difference between the second and third voltage values ​​by outputting a control voltage at its output terminal.

[0065] based on Figure 6 In this embodiment, the error amplifier 3032 outputs a first-stage control voltage based on the difference between the sum of the first voltage value VS2 and a preset voltage value and the second voltage value VOUT. This first-stage control voltage can be further adjusted by the control voltage adjustment circuit 3033 to obtain a second-stage control voltage. Therefore, the impedance adjustment circuit 303 can provide multiple control voltages. As mentioned above, as the power supply voltage VS1 increases, the first transistor M1, which is the first adjustable unit, and the second transistor M2, which is the second adjustable unit, should be turned off sequentially. When both the first transistor M1 and the second transistor M2 are NMOS transistors, the first-stage control voltage output by the error amplifier 3032 is directly provided to the control terminal of the second transistor M2. After being reduced by a voltage value (e.g., 2V) by the control voltage adjustment circuit 3033, the second-stage control voltage is provided to the first transistor M1. Therefore, the second-stage control voltage at the control terminal of the first transistor M1 can make the first transistor M1 be in the variable impedance region while the second transistor M2 is fully turned on, or be turned off before the second transistor M2 (because it drops below the turn-on threshold more quickly).

[0066] Based on this, the error amplifier 3032 outputs different levels of control voltage according to the difference between the sum of the first voltage value VS2 and the preset voltage value and the second voltage value VOUT, so as to automatically adjust the conduction level of at least one of the first transistor M1 and the second transistor M2, thereby adjusting the current flowing through at least one of the first transistor M1 and the second transistor M2. At the end of this adjustment process, the voltage difference between the first voltage value VS2 and the second voltage value VOUT can be adjusted to be approximately equal to the preset voltage value.

[0067] For example, when the second voltage value VOUT is different from the preset voltage value V headroomWhen the sum of the voltage values ​​is less than the first voltage value VS2, the output first-stage control voltage and second-stage control voltage will decrease. This results in: when the power supply voltage VS1 is in the first voltage range, maintaining the current flowing through the second transistor M2 (although the first-stage control voltage decreases, the second transistor M2 can still be kept in the constant current region) and reducing the current flowing through the first transistor M1; or, when the power supply voltage VS1 is in the second voltage range, turning off the first transistor M1 and reducing the current flowing through the second transistor M2 (in the second voltage range). Both of these methods increase the current flowing through the first external resistor Rshunt1, thus reducing the first voltage value VS2, thereby making the second voltage value VOUT equal to the preset voltage value V. headroom The sum of these values ​​is approximately equal to the first voltage value VS2.

[0068] On the other hand, when the second voltage value VOUT is different from the preset voltage value V headroom When the sum of the voltage values ​​is greater than the second voltage value VS2, the voltage values ​​of the first-stage control voltage and the second-stage control voltage output by the error amplifier 3032 will increase. This will cause: when the power supply voltage VS1 is in the first voltage range, the current flowing through the second transistor M2 will be maintained and the current flowing through the first transistor M1 will be increased; or, when the power supply voltage VS1 is in the second voltage range, the first transistor M1 will be turned off (still not exceeding the conduction threshold), and the current flowing through the second transistor M2 (in the second voltage range) will be increased. In both cases, the current flowing through the first external resistor Rshunt1 will decrease, thus increasing the first voltage value VS2, thereby making the second voltage value VOUT equal to the preset voltage value V. headroom The sum of these values ​​is approximately equal to the first voltage value VS2.

[0069] It should be noted that, although in Figure 6 In the example circuit structure, both the first transistor M1 and the second transistor M2 are NMOS transistors, and a feedback control loop based on an error amplifier is designed accordingly. When the first transistor M1 and the second transistor M2 use other switching devices such as PMOS transistors, a similar feedback control loop can also be designed based on the same control logic. For example, the control voltage regulation circuit can increase the first-stage control voltage by a voltage value (e.g., 2V) to obtain the second-stage control voltage, or it can provide the first-stage control voltage to the control terminal of the first transistor, and so on.

[0070] For example, in one specific implementation, suppose the voltage compensation circuit 3031 is as follows: Figure 6 The example shown is used to perform positive voltage compensation on the second voltage value VOUT on the drive output side based on a preset voltage value, such as... Figure 7AAs shown, the voltage compensation circuit 3031 may include a first NMOS transistor 711, a second PMOS transistor 712, a first current source 713, a second current source 714, and a compensation resistor 715.

[0071] The first NMOS transistor 711 and the second PMOS transistor 712 are used to maintain and transmit the first voltage value from the sampling input side 701 and apply it to the compensation resistor 715. The first current source 713 and the second current source 714 are used to generate bias currents corresponding to the first NMOS transistor 711 and the second PMOS transistor 712, respectively. The compensation resistor 715 is used to generate a compensated voltage V with the compensation voltage value at its terminals. headroom The voltage corresponding to the first voltage value formed at one end of the compensation resistor 715 is pulled up and output to the error amplifier 3032.

[0072] Furthermore, the gate of the first NMOS transistor 711 is connected to the drive output side, the drain of the first NMOS transistor 711 is connected to the internal level VCC, and the source of the first NMOS transistor 711 is connected to the gate of the second PMOS transistor 712 and the reference ground GND, respectively. The drain of the second PMOS transistor 712 is connected to the reference ground GND, and the source of the second PMOS transistor 712 is connected to the error amplifier 72. In this way, the expected technical effect can be basically achieved.

[0073] Preferably, a first current source 713 is connected in series between the source of the first NMOS transistor 711 and the reference ground terminal GND, and a second current source 712 is connected in series between the drain of the second PMOS transistor 712 and the reference ground terminal GND, respectively providing the first NMOS transistor 711 and the second PMOS transistor 712 with the same or different bias currents. Simultaneously, a compensation resistor 715 is connected in series between the source of the second PMOS transistor 712 and the error amplifier 72, thereby forming a compensation voltage V. headroom .

[0074] It should be noted that, Figure 7A The transistor configuration shown is merely one implementation of the voltage compensation circuit 3031. Replacing the transistors with switching transistors such as bipolar junction transistors or other electronic components can also achieve the desired technical effect to a certain extent. Furthermore, the specific circuit of the voltage compensation circuit 3031 shown in FIG7 is merely exemplary, and this disclosure does not limit it.

[0075] Meanwhile, since the control circuit adjustment circuit 3033 also performs voltage compensation on the control voltage output by the error amplifier 3032, it can also adopt a circuit structure similar to that of the voltage compensation circuit 3031, for example... Figure 7AAs shown. Of course, the control circuit adjustment circuit 3033 can also be implemented using other circuit structures.

[0076] On the one hand, the voltage sampling circuit 304 included in the driving circuit 30 can also be applied to the embodiment that specifically defines the structure of the voltage compensation circuit 3031 described above. In this embodiment, the voltage compensation circuit 3031 is disposed between the voltage sampling circuit 304 and the error amplifier 3032, and specifically, it can be disposed between the drive output side and the first input terminal of the error amplifier 3032. The voltage sampling circuit 304 is disposed between the voltage compensation circuit 304 and the drive output side, and sends the filtered first voltage value into the voltage compensation circuit 3031.

[0077] Furthermore, such as Figure 7A As shown, the gate of the first NMOS transistor 711 can be connected to the output of the voltage sampling circuit 304 to obtain the filtered first voltage value. The connection is not limited to a direct connection. When the voltage sampling circuit 304 does not include a voltage holding structure, a holding circuit 305 can be included between the voltage sampling circuit 304 and the voltage compensation circuit 3032. The holding circuit 305 may include a follower switch connected in series between the output of the voltage sampling circuit 304 and the error amplifier 3032, and a holding capacitor with one end connected between the two components and the other end grounded. Of course, any holding circuit structure that can be foreseen by those skilled in the art and serves a similar function is within the scope of this disclosure.

[0078] The specific structure of the voltage sampling circuit 304 can be as follows: Figure 7B The structural configuration is shown. In this embodiment, the voltage sampling circuit 304 includes an analog-to-digital converter 751, a digital comparator 752, a register 753, and a digital-to-analog converter 754 connected in series. The input terminal of the analog-to-digital converter 751 is connected to the drive output side 502, and the output terminal of the digital-to-analog converter 754 is connected to the input terminal of the error amplifier. Specifically, the analog-to-digital converter 751 receives the voltage values ​​of multiple light-emitting channels and converts them into digital quantities; the digital comparator 752 compares multiple digital voltage values ​​of the multiple light-emitting channels on the drive output side and filters to obtain the maximum digital voltage value; the register 753 stores the maximum digital voltage value; and the digital-to-analog converter 754 converts the maximum digital voltage value into an analog quantity to obtain a voltage with a first voltage value and outputs this voltage.

[0079] While most embodiments are described with respect to a variable impedance network (RVA) comprising three impedance branches, a variable impedance network (RVA) may also include a greater number of impedance branches, for example, based on more than two adjustable units and more than two external shunt units.

[0080] Figure 8 An example structure of a variable impedance network (RVA) according to an embodiment of this disclosure is shown. Figure 3A and Figure 6 Compared to the driving circuit shown, Figure 8 The variable impedance network RVA associated with the drive circuit 80 includes a greater number of adjustable units and external shunt units.

[0081] like Figure 8 As shown, the adjustable unit 801 may include a first adjustable unit 801-1, a second adjustable unit 801-2, and one or more additional adjustable units 801-n. Each additional adjustable unit 801-n may be connected in series with a corresponding additional external shunt unit 82-n to form an additional impedance branch. Thus, the variable impedance network RVA may include a first impedance branch including the first external shunt unit 82-1, a second impedance branch including the first adjustable unit 801-1, a third impedance branch including the second adjustable unit 801-2 and the second external shunt unit 82-2, and one or more additional impedance branches connected in parallel. The first external shunt unit 82-1 has a fixed impedance value, and the impedance values ​​of each of the second external shunt unit 82-2 and the additional external shunt units may be the same as or different from those of the first external shunt unit 82-1.

[0082] For example, each adjustable unit 801 can also be implemented using a transistor or a variable resistor.

[0083] Since the impedance value of each of the first adjustable unit 801-1, the second adjustable unit 801-2, and these additional adjustable units 801-n can be adjusted between the minimum impedance value and the impedance value that causes the corresponding impedance branch to be open, therefore Figure 8 The variable impedance network RVA shown is compared to Figure 3A or Figure 6 The variable impedance network RVA shown can have a wider range of impedance values, so the impedance adjustment circuit 803 can be adjusted over a wider range of power supply voltages or further reduce the heat loss power of the drive circuit.

[0084] For example, by taking into account the characteristics of the second adjustable unit 801-2 and these additional adjustable units 801-n, as the power supply voltage VS1 increases, the impedance adjustment circuit 803 can sequentially turn off these transistors, thereby increasing the equivalent impedance value of the variable impedance network RVA to form an increased voltage drop on the variable impedance network RVA, so as to stabilize the voltage difference across the drive power supply stage.

[0085] For example, when the power supply voltage VS1 is in a state that depends on Figure 8 The first voltage range [V] of the circuit structure of the variable impedance network RVA shown. minVOUT+V headroom + (Rshunt1 / / Rshunt2 / / …Rshuntn) I LED Within the [unclear context], the impedance value of the first adjustable unit 801-1 is variable, while the second adjustable unit 801-2 and all additional adjustable units 801n are adjusted to have a fixed minimum impedance value (which can be ignored). At this time, the driving current I supplied to the light-emitting element 31 flows through all impedance branches. LED In this case, because the impedances of all impedance branches are connected in parallel, compared to the previous drive circuit, for a smaller supply voltage VS1 and when the voltage difference across the drive power stage needs to be satisfied, the variable impedance network RVA can handle the same voltage drop. Figure 8 The driving circuit shown can allow more current to flow out of the driving circuit, thus further reducing the heat loss of the chip compared to the previous driving circuit.

[0086] When the power supply voltage VS1 is in a state that depends on Figure 8 The second voltage range (VOUT+V) of the circuit structure of the variable impedance network RVA shown. headroom + (Rshunt1 / / Rshunt2 / / …Rshuntn) I LED VOUT+V headroom + (Rshunt1 / / Rshunt3 / / …Rshuntn) I LED Within the first adjustable unit 801-1, the impedance value is adjusted to disconnect the second impedance branch. The impedance value of the second adjustable unit 801-2 is variable, and all additional adjustable units 801-n are adjusted to have a fixed minimum impedance value (which is ignored here). At this time, the driving current I supplied to the light-emitting element 31 flows through the first impedance branch, the third impedance branch, and all additional impedance branches. LED In this case, similarly, since the second external shunt unit 82-2 can share part of the voltage with the second adjustable unit 801-2, and the remaining additional impedance branch can ensure that more current flows out to the outside of the drive circuit, the chip heat loss can be further reduced.

[0087] When the power supply voltage VS1 is in a state that depends on Figure 8 The circuit structure of the variable impedance network RVA shown has a third voltage range (VOUT+V). headroom + (Rshunt1 / / Rshunt3 / / …Rshuntn) I LED VOUT+V headroom+ (Rshunt1 / / Rshunt4 / / …Rshuntn) I LED Within the first adjustable unit 801-1 and the second adjustable unit 801-2, both are turned off. The impedance value of the first additional adjustable unit 801-n in the first additional impedance branch is variable. If there are any remaining additional impedance branches, all the additional adjustable units in the remaining additional impedance branches are adjusted to have a fixed minimum impedance value (which is ignored here). At this time, the driving current I supplied to the light-emitting element 31 flows through the first impedance branch, the first additional impedance branch, and the remaining additional impedance branches. LED If there are no remaining additional impedance branches, the driving current I supplied to the light-emitting element 31 flows through the first impedance branch and the first additional impedance branch. LED .

[0088] Therefore, the additional adjustable units in the additional impedance branches can be adjusted sequentially to disconnect the corresponding impedance branches, and after the last additional impedance branch is disconnected, the variable impedance network RVA reaches the maximum equivalent impedance value, that is, the impedance value of the first external shunt unit 82-1.

[0089] In addition, regarding Figure 8 The maximum heat loss power for each voltage range in the drive circuit shown can also be determined based on the resistance value of each additional external resistor. The specific determination method is as described in the previous reference. Figure 4 and Figure 5 As described, it will not be repeated here.

[0090] based on Figure 8 The drive circuit shown, due to the presence of a greater number of external shunt units, can employ external shunt units with larger impedance values. This satisfies the requirement for smaller external impedance values ​​under lower power supply voltages, while simultaneously meeting the requirement for larger external impedance values ​​under higher power supply voltages so that the impedance adjustment circuit can still function. In other words, given equal heat dissipation power in the drive circuit... Figure 8 The adjustment range supported by the drive circuit is compared to Figure 2 , Figure 3A or Figure 6 The drive circuit is larger. On the other hand, if it is with Figure 2 , Figure 3A or Figure 6 The drive circuits have the same adjustment range, referring to the derivation of the maximum heat loss power above. Figure 8 The maximum value of the heat loss power of the drive circuit will also be significantly smaller than that of the drive circuit. Figure 2 , Figure 3A or Figure 6The drive circuit can reduce the heat loss power of the drive circuit.

[0091] Regarding impedance adjustment circuit 303 Figure 8 The control of the adjustable unit 801 shown is similar to that before. In the impedance adjustment circuit 303, a corresponding control voltage adjustment circuit can be set for the third impedance branch and each additional impedance branch to obtain multi-level control voltage.

[0092] Figure 9A and 9B A schematic diagram illustrating the generation method of multi-stage control voltage is shown, in conjunction with the preceding... Figure 6 The specific circuit structure of the impedance adjustment circuit is as follows: the output terminal of the error amplifier 3032 is directly connected to or connected to the control terminal of the corresponding adjustable unit 801 via one or more control voltage adjustment circuits. The output terminal of the error amplifier 3032 is directly connected to the control terminal of the nth adjustment unit 801-n, and is connected to the control terminals of other adjustable units via multiple control voltage adjustment circuits to provide control voltages at various levels, thereby achieving the sequential shutdown of the impedance branches where these adjustable units are located.

[0093] Assuming the impedance of each adjustable unit decreases as the control voltage increases (e.g., when the adjustable unit is an NMOS transistor), such as Figure 9A and Figure 9B As shown, since the first adjustable unit 801-1 is the first to be turned off, its voltage dVm1, which is lowered relative to the control voltage at the output of the error amplifier 3032, has the largest magnitude. And since the second adjustable unit 801-2 is the second to be turned off, its voltage dVm2, which is lowered relative to the control voltage at the output of the error amplifier 3032, has the second largest magnitude, and so on.

[0094] For example, assuming an additional adjustable unit exists, and still taking each adjustable unit as an NMOS transistor as an example, that is, the first transistor M1 in the second impedance branch, the second transistor M2 in the third impedance branch, and the additional transistor Mn in the additional impedance branch are all NMOS transistors. Since the first transistor M1 is the first to turn off as the power supply voltage VS1 increases (at which point the second transistor M2 and the additional transistor Mn are fully turned on), and then the second transistor M2 and the additional transistor Mn turn off sequentially, the voltage at the output of the error amplifier 3032 can be subtracted from the first preset voltage dVm1 (e.g., -4V) and then supplied to the control terminal of the first transistor M1; the voltage at the output of the error amplifier 3032 can be subtracted from the second preset voltage dVm2 (e.g., -2V) and then supplied to the control terminal of the second transistor M2; and the voltage at the output of the error amplifier 3032 can be directly supplied to the control terminal of the additional transistor Mn. With this configuration, as the power supply voltage VS1 increases, the first transistor M1, the second transistor M2, and the additional transistor Mn can be turned off sequentially.

[0095] Therefore, in Figures 8 to 9B In the illustrated embodiment, by generating multi-level control voltages, one or more impedance branches in the variable impedance network RVA can be automatically adjusted according to the voltage range of the power supply voltage VS1 to ensure the voltage difference across the drive power stage, while having higher regulation capability and a larger regulation range.

[0096] Unless otherwise defined, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains. It should also be understood that terms such as those defined in a common dictionary shall be interpreted as having a meaning consistent with their meaning in the context of the relevant art, and not as being interpreted with an idealized or highly formalized meaning, unless expressly defined herein.

[0097] In this disclosure, the terms "first" and "second," etc., are used only to distinguish various elements and do not indicate any order, importance, or priority.

[0098] Even if a particular combination of features is defined in the claims and / or disclosed in the specification, such combinations are not intended to limit the disclosure of aspects. In fact, many of these features can be combined in ways that are not defined in the claims and / or disclosed in the specification. Although each dependent claim listed below may directly depend on only one claim, the disclosure of aspects includes every dependent claim in combination with every other claim in the claim set.

[0099] The embodiments of this disclosure described above are merely illustrative and not restrictive. Those skilled in the art should understand that various modifications and combinations can be made to these embodiments or their features without departing from the principles and spirit of this disclosure, and such modifications should fall within the scope of this disclosure.

Claims

1. A driving circuit for driving a light-emitting element, the driving circuit comprising: At least two adjustable units, together with at least two external shunt units, form a variable impedance network; The drive power stage, together with the variable impedance network and the light-emitting element, forms a series path between the power supply and the reference ground to regulate the drive current flowing through the light-emitting element to a constant current value. An impedance adjustment circuit is used to adjust the voltage difference between the first voltage value and the second voltage value to a preset voltage value by adjusting the impedance values ​​of the at least two adjustable units, based on the first voltage value on the drive input side of the drive power supply stage and the second voltage value associated with the output voltage on the drive output side of the drive power supply stage.

2. The driving circuit according to claim 1, wherein, A variable impedance network is connected to the input side of the driver, and a light-emitting element is connected to the output side of the driver. When the voltage difference between the first voltage value and the second voltage value is greater than a preset voltage value, the impedance adjustment circuit increases the equivalent impedance value of the variable impedance network by adjusting the impedance values ​​of the at least two adjustable units, and / or When the voltage difference between the first voltage value and the second voltage value is less than the preset voltage value, the impedance adjustment circuit reduces the equivalent impedance value of the variable impedance network by adjusting the impedance values ​​of the at least two adjustable units.

3. The driving circuit according to claim 1, wherein, The variable impedance network consists of a first impedance branch, a second impedance branch, and a third impedance branch connected in parallel. The first impedance branch includes the first external shunt unit of the at least two external shunt units, and the first external shunt unit has a fixed impedance value; The second impedance branch includes the first adjustable unit of the at least two adjustable units; The third impedance branch includes a series structure of the second adjustable unit in the at least two adjustable units and the second external shunt unit in the at least two external shunt units.

4. The driving circuit according to claim 3, wherein: When the power supply voltage is in the first voltage range, the driving current flows through the first impedance branch, the second impedance branch and the third impedance branch, wherein the impedance value of the first adjustable unit is variable and the impedance value of the second adjustable unit is adjusted to be fixed. When the power supply voltage is in the second voltage range, the drive current flows through the first impedance branch and the third impedance branch, wherein the impedance value of the second adjustable unit is variable, and the impedance value of the first adjustable unit is adjusted to make the second impedance branch open. When the power supply voltage is in the third voltage range, the drive current flows through the first impedance branch, wherein the impedance values ​​of both the first and second adjustable units are adjusted to open the corresponding impedance branches. The first voltage range, the second voltage range, and the third voltage range are consecutive ranges that increase sequentially within the allowable range of the power supply voltage.

5. The driving circuit according to claim 4, wherein: When the power supply voltage is in the first voltage range, as the power supply voltage increases, the impedance value of the first adjustable unit increases, and the current flowing through the first impedance branch increases, the current flowing through the second impedance branch decreases, and the current flowing through the third impedance branch increases. When the power supply voltage is in the second voltage range, as the power supply voltage increases, the impedance value of the second adjustable unit increases, the current flowing through the first impedance branch increases, the current flowing through the second impedance branch is 0, and the current flowing through the third impedance branch decreases. When the power supply voltage is in the third voltage range, as the power supply voltage increases, the current flowing through the first impedance branch remains at the constant current value, and the voltage difference between the first voltage value and the second voltage value gradually increases.

6. The driving circuit according to claim 5, wherein: The first voltage range is [V] min VOUT+V headroom +(Rshunt1 / / Rshunt2) I LED ]; The second voltage range is (VOUT+V) headroom +(Rshunt1 / / Rshunt2) I LED V LED +V headroom +Rshunt1 I LED ]; The third voltage range is (VOUT+V) headroom +Rshunt1 I LED V max ], Among them, V min and V max These are the minimum and maximum values ​​of the power supply voltage, I, respectively. LED VOUT is the constant current value of the drive current supplied to the light-emitting element, and V is the voltage value at the drive output terminal. headroom The preset voltage value is defined as follows: Rshunt1 represents the first impedance value of the first external shunt unit, and Rshunt2 represents the second impedance value of the second external shunt unit.

7. The driving circuit according to claim 3, wherein, The variable impedance network also includes one or more additional impedance branches, each of which is connected in parallel with the first impedance branch. Each additional impedance branch includes an additional adjustable unit and an additional external shunt unit connected in series.

8. The driving circuit according to claim 7, wherein, As the power supply voltage increases, the second impedance branch, the third impedance branch, and one or more additional impedance branches are successively disconnected to gradually increase the equivalent impedance value of the variable impedance network.

9. The driving circuit according to claim 2, wherein, The light-emitting element includes at least two sets of light-emitting branches, and The driving power stage includes at least two sets of driving branches, which are connected in series with the at least two sets of light-emitting branches.

10. The driving circuit according to claim 9 further includes a voltage sampling circuit. The voltage sampling circuit is located between the impedance adjustment circuit and the drive output side, and is configured to sample the maximum output voltage of the at least two sets of drive branches as the second voltage value.

11. The driving circuit according to claim 1, wherein the impedance adjustment circuit comprises a voltage compensation circuit, an error amplifier, and one or more control voltage adjustment circuits. The first input terminal of the error amplifier is connected to the drive input side, and the second input terminal is connected to the drive output side; The output of the error amplifier is directly connected to or connected via a control voltage adjustment circuit to the control terminal of one of the at least two adjustable units respectively. The voltage compensation circuit is located between the error amplifier and the drive power supply stage, and is configured to generate a third voltage value based on a preset voltage value and either a first voltage value or a second voltage value, and output it to the first input terminal or the second input terminal of the error amplifier.

12. The driving circuit according to claim 1, wherein, Each of the at least two adjustable units includes a variable resistor or a transistor, and the external shunt unit includes a resistor.

13. The driving circuit according to claim 1, wherein, The preset voltage value is greater than or equal to the voltage value under optimal operating conditions of the drive power supply stage. In the optimal operating state, the driving power supply stage can provide a constant current with the rated current value to the light-emitting element with the minimum power.

14. The driving circuit according to claim 1, wherein the driving circuit is packaged in a driving chip, and the at least two external shunt units are connected to the pins of the driving chip.

15. An electrical device comprising a light-emitting element and a driving circuit as described in any one of claims 1 to 14.

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