LED driving system

Abstract

The invention provides an LED driving system which comprises a transformer, an LED driving chip, a minimum brightness control resistor and a sampling adjustment circuit. The LED driving chip comprises a power switch tube, the drain electrode of the power switch tube is connected to the primary winding of the transformer, and the source electrode of the power switch tube is connected to the circuit reference ground through the lowest brightness control resistor. The sampling adjusting circuit comprises a basic adjusting resistor, a plurality of current sensing resistors and a plurality of dial dimming switches, and the basic adjusting resistor is connected between the source electrode of the power switch tube and the current sensing terminal of the LED driving chip; any current sensing resistor in the plurality of current sensing resistors is connected in series with a corresponding dial dimming switch in the plurality of dial dimming switches to form a current sensing unit which is connected between the current sensing terminal of the LED driving chip and the circuit reference ground. A current sensing terminal of the LED driving chip is used for receiving a current sensing signal representing a primary side current flowing through a primary side winding of the transformer.

Description

Technical Field

[0001] The present invention relates to the field of circuits, and more particularly to an LED driving system. Background Art

[0002] With the development of light-emitting diode (LED) lighting related technologies, LED lighting has gradually replaced traditional lighting and is widely used in various fields such as home lighting, outdoor landscape lighting, industrial lighting, commercial lighting, and automotive lighting. Generally, LED driver chips used in the field of LED lighting are non-dimming applications and cannot meet the user's needs for brightness adjustment of LED lights. For example, for indoor lighting, if users can adjust the brightness of LED lights to achieve appropriate light brightness, it can not only improve the user experience and comfort, but also improve energy utilization and save energy. Summary of the invention

[0003] According to an embodiment of the present invention, the LED driving system includes a transformer, an LED driving chip, a minimum brightness control resistor, and a sampling adjustment circuit, wherein: the LED driving chip includes a power switch tube, the drain of the power switch tube is connected to the primary winding of the transformer, and the source of the power switch tube is connected to the circuit reference ground via the minimum brightness control resistor; the sampling adjustment circuit includes a basic adjustment resistor, a plurality of current sensing resistors, and a plurality of dip-code dimming switches, the basic adjustment resistor is connected between the source of the power switch tube and the current sensing terminal of the LED driving chip, any one of the plurality of current sensing resistors is connected in series with a corresponding one of the plurality of dip-code dimming switches to form a current sensing unit and is connected between the current sensing terminal of the LED driving chip and the circuit reference ground, and the current sensing terminal of the LED driving chip is used to receive a current sensing signal representing the primary current flowing through the primary winding of the transformer. BRIEF DESCRIPTION OF THE DRAWINGS

[0004] The present invention can be better understood from the following description of specific embodiments of the present invention in conjunction with the accompanying drawings, in which:

[0005] Figure 1 The invention is a circuit diagram showing a conventional dial-code dimming solution used in an LED driving system.

[0006] Figure 2 FIG. 4 is a circuit diagram illustrating a dial-code dimming solution used in an LED driving system according to an embodiment of the present invention.

[0007] Figure 3 The diagram shows Figure 2 The circuit schematic diagram of the functional modules related to the dial dimming in the LED driver chip shown.

[0008] Figure 4 The diagram shows Figure 2 The schematic diagram of the working waveforms of the voltage at the CS terminal of the LED driver chip and the gate voltage of the power switch tube M1 is shown. DETAILED DESCRIPTION

[0009] The features and exemplary embodiments of various aspects of the present invention will be described in detail below. In the detailed description below, many specific details are proposed to provide a comprehensive understanding of the present invention. However, it is obvious to those skilled in the art that the present invention can be implemented without the need for some of these specific details. The following description of the embodiments is only to provide a better understanding of the present invention by illustrating examples of the present invention. The present invention is by no means limited to any specific configuration and algorithm proposed below, but covers any modification, replacement and improvement of elements, parts and algorithms without departing from the spirit of the present invention. In the accompanying drawings and the following description, known structures and technologies are not shown to avoid unnecessary ambiguity in the present invention. In addition, it should be noted that the term "A is connected to B" used here can mean "A is directly connected to B" and can also mean "A is indirectly connected to B via one or more other elements".

[0010] Figure 1 FIG. 1 is a circuit diagram showing a conventional dial-code dimming solution used in an LED driving system. Figure 1As shown, the LED driving system 100 includes an LED driving chip 102 and a sampling and adjusting circuit 104, wherein: the sampling and adjusting circuit 104 includes current sensing resistors Rcs1 and Rcs2 and dip-code dimming switches S1 and S2; the current sensing resistor Rcs1 and the dip-code dimming switch S1 are connected in series to form a first current sensing unit; the current sensing resistor Rcs2 and the dip-code dimming switch S2 are connected in series to form a second current sensing unit; the first current sensing unit and the second current sensing unit are connected in parallel between the current sensing terminal (i.e., the CS terminal, used to receive the current sensing signal Vcs representing the primary current flowing through the primary winding Lp of the transformer T) of the LED driving chip 102 and the circuit reference ground; when the dip-code dimming switch S1 is in the on state and the dip-code dimming switch S2 is in the off state, the brightness of the LED lamp is low; when the brightness of the LED lamp needs to be increased, the dip-code dimming switch S2 is changed from the off state to the on state while the dip-code dimming switch S1 is kept in the on state. Here, the essence of adjusting the brightness of the LED lamp is to increase the primary current flowing through the primary winding Lp of the transformer T by reducing the current sensing resistor Rcs while controlling the average voltage Vref at the CS terminal of the LED driver chip 102 to remain unchanged (when the dip dimming switch S1 is in the on state and the dip adjustment resistor S2 is in the off state, Rcs=Rcs1, when the dip dimming switches S1 and S2 are both in the on state, Rcs=(Rcs1+Rcs2) / (Rcs1×Rcs2)), thereby increasing the current flowing through the secondary winding Ln of the transformer T (that is, increasing the average output current ILED flowing through the LED lamp).

[0011] exist Figure 1 In the LED driving system 100 shown, when the dip switch S1 is in the on state and the dip switch S2 is in the off state, the average output current ILED flowing through the LED lamp can be expressed as:

[0012]

[0013] In addition, when the dip switches S1 and S2 are both in the on state, the average output current ILED flowing through the LED lamp can be expressed as:

[0014]

[0015] Wherein, N is the turns ratio of the primary winding Lp and the secondary winding Ln of the transformer T, and Vref is the reference voltage of the error amplifier for performing constant current control on the average output current ILED flowing through the LED lamp.

[0016] exist Figure 1In the LED driving system 100 shown, the average output current ILED flowing through the LED lamp is largely limited by the absolute value of the resistance value of the current sensing resistors Rcs1 and Rcs2. When the resistor manufacturing process deviation is large, the average output current ILED flowing through the LED lamp varies greatly, which results in poor accuracy of the average output current ILED flowing through the LED lamp and poor brightness consistency of the LED lamp in the case of actual multi-lamp applications (i.e., applications including multiple LED driving systems 100 and multiple strings of LED lamps driven by these LED driving systems). In addition, in actual applications, the LED driver chip 102 is generally sealed in the middle of the plastic shell, and the dip switches S1 and S2 are mostly set on both sides of the plastic shell for the convenience of user adjustment, which results in the dip switches S1 and S2 being far away from the LED driver chip 102 and needing to be connected to the corresponding terminals of the LED driver chip 102 through a long printed circuit board trace, which greatly reduces the anti-interference ability of the entire circuit system.

[0017] In view of the above situation, an LED driving system according to an embodiment of the present invention is proposed, which can improve the accuracy of the average output current flowing through the LED lamps in the case of multiple lamps, thereby improving the brightness consistency of the LED lamps.

[0018] Figure 2 1 is a circuit diagram showing a dial-code dimming solution used in an LED driving system according to an embodiment of the present invention. Figure 2As shown, the LED driving system 200 includes a transformer T, an LED driving chip 202, a minimum brightness control resistor Rs, and a sampling adjustment circuit 204, wherein: the LED driving chip 202 includes a power switch tube M1, the drain of the power switch tube M1 is connected to the primary winding Lp of the transformer T via the drain terminal (i.e., the Drain terminal) of the LED driving chip 202, and the source of the power switch tube M1 is connected to the circuit reference ground via the source terminal (i.e., the Source terminal) of the LED driving chip 202 and the minimum brightness control resistor Rs; the sampling adjustment circuit 204 includes a basic adjustment resistor RH, current sensing resistors RL1 to RLn, and the dip-code dimming switches S1 to Sn (where n is an integer greater than 1), the basic adjustment resistor RH is connected between the Source terminal and the current sensing terminal (i.e., the CS terminal, for receiving the current sensing signal Vcs representing the primary current flowing through the primary winding Lp of the transformer T) of the LED driver chip 202, and any current sensing resistor RLk (where k is an integer greater than or equal to 1 and less than or equal to n) among the current sensing resistors RL1 to RLn and a corresponding dip-code dimming switch Sk among the dip-code dimming switches S1 to Sn are connected in series to form a current sensing unit and connected between the CS terminal of the LED driver chip 202 and the circuit reference ground. It should be noted that the sampling adjustment circuit 204 can be located inside or outside the LED driver chip 202, and the minimum brightness control resistor Rs can be located inside or outside the LED driver chip 202. Here, for the sake of clarity, the sampling adjustment circuit 206 and the minimum brightness control resistor Rs are both located outside the LED driver chip 202 as an example for explanation.

[0019] exist Figure 2 In the LED driving system 200 shown, when the dip switches S1 to Sn are all in the off state, the brightness of the LED lamp is the lowest; when the number of the dip switches S1 to Sn in the on state increases, the brightness of the LED lamp increases.

[0020] Figure 3 The diagram shows Figure 2 The circuit schematic diagram of the functional modules related to the dial dimming in the LED driver chip shown in FIG. Figure 3As shown, the LED driver chip 202 includes a constant current control circuit 2022 and a gate drive circuit 2024 in addition to the power switch tube M1, wherein: the constant current control circuit 2022 is configured to generate an error amplification signal Vdiff representing the difference between the current sensing signal Vcs and the reference voltage Vref based on the current sensing signal Vcs representing the primary current flowing through the primary winding Lp of the transformer T and the reference voltage Vref, and to generate a comparison result signal Vcomp representing the size comparison relationship between the error amplification signal Vdiff and the threshold voltage Vth based on the error amplification signal Vdiff and the threshold voltage Vth, And based on the comparison result signal Vcomp, a turn-off control signal Vctrl_off for controlling the power switch tube M1 to change from the on state to the off state or a turn-on control signal Vctrl_on for controlling the power switch tube M1 to change from the off state to the on state is generated; the gate drive circuit 2024 is configured to generate a turn-off drive signal Vgate_off for driving the power switch tube M1 to be in the off state based on the turn-off control signal Vctrl_off, and to generate a turn-on drive signal Vgate_on for driving the power switch tube M1 to be in the on state based on the turn-on control signal Vctrl_on. It should be noted that the turn-off drive signal Vgate_off and the turn-on drive signal Vgate_on can be collectively referred to as the gate drive signal Vgate for driving the power switch tube M1 to be turned on and off.

[0021] like Figure 3 As shown, in some embodiments, the constant current control circuit 2022 may include an error amplifier, a differential control unit, and a logic control unit, wherein: the error amplifier is configured to generate an error amplification signal Vdiff by performing error amplification on the current sensing signal Vcs and the reference voltage Vref; the differential control unit is configured to generate a comparison result signal Vcomp by comparing the error amplification signal Vdiff with the threshold voltage Vth; the logic control unit is configured to perform a logic operation based on the comparison result signal Vcomp to generate a shutdown control signal Vctrl_off or a conduction control signal Vctrl_on. For example, the logic control unit may be configured to generate a shutdown control signal Ctrl_off when the comparison result signal Vcomp indicates that the error amplification signal Vdiff is greater than the threshold voltage Vth, and to generate a conduction control signal Ctrl_on when the comparison result signal Vcomp indicates that the error amplification signal Vdiff is not greater than the threshold voltage Vth.

[0022] like Figure 2 and Figure 3As shown, when the LED driving system 200 is just powered on, the primary current flowing through the primary winding Lp of the transformer T is equal to the current flowing through the power switch tube M1, and the dip switches S1 to Sn are all in the off state. At this time, since the input of the error amplifier is high impedance, no current flows through the basic adjustment resistor RH, the current flowing through the power switch tube M1 is equal to the current flowing through the minimum brightness control resistor Rs, and the source voltage Vsource of the power switch tube M1 is equal to the voltage Vcs (i.e., the current sensing signal Vcs) at the CS terminal of the LED driving chip 202, i.e.

[0023]

[0024] Vsource = Vcs (Equation 4)

[0025] like Figure 2 and Figure 3 As shown, when the LED driver chip 202 works normally, the power switch tube M1 switches between the on state and the off state. Figure 4 2 is a schematic diagram showing the working waveforms of the voltage Vcs at the CS terminal of the LED driver chip 202 and the gate voltage Vgate of the power switch tube M1. Figures 2 to 4 As shown in, when the gate voltage Vgate (i.e., the gate drive signal Vgate) of the power switch tube M1 is at a high level, the power switch tube M1 is in the on state, and the voltage Vcs at the CS terminal of the LED driver chip 202 increases; when the voltage Vcs at the CS terminal of the LED driver chip 202 increases to the preset peak voltage Vcspeak, the power switch tube M1 changes from the on state to the off state; when the duration of the power switch tube M1 in the off state reaches the demagnetization time Tdem of the primary winding Lp of the transformer T and the quasi-resonant delay time QR delay preset inside the LED driver chip 202, the power switch tube M1 changes from the off state to the on state; a complete switching cycle of the power switch tube M1 Tsw = Ton + Tdem + QR delay, where Ton is the duration of the power switch tube M1 in the on state. The average value of the voltage Vcs at the CS terminal of the LED driver chip 202 in the entire switching cycle of the power switch tube M1 is:

[0026]

[0027] exist Figure 3 In the constant current control circuit 2022 shown in FIG. 1 , the function of the error amplifier is to make the proportion (Ton / Tsw) of the voltage Vcs at the CS terminal of the LED driver chip 202 in the entire switching cycle of the power switch tube M1 equal to the reference voltage Vref, that is,

[0028]

[0029] When the dip switches S1 to Sn are all in the off state, the average value of the current flowing through the power switch tube M1 during the entire switching cycle of the power switch tube M1 is:

[0030]

[0031] When the DIP dimming switches S1 to Sn are all in the off state, the average output current flowing through the LED lamp during the entire switching cycle of the power switch tube M1 is:

[0032]

[0033] like Figure 2 and Figure 3 As shown, when the brightness of the LED lamp needs to be increased, the dip switch S1 can be changed from the off state to the on state and the dip switches S2 to Sn can be kept in the off state. At this time, the current flowing through the power switch tube M1 is equal to the sum of the current flowing through the minimum brightness control resistor Rs and the current flowing through the basic adjustment resistor RH. Since the usual situation in actual engineering applications is RH>RL1>>Rs, the current flowing through the power switch tube M1 is approximately equal to the current flowing through the minimum brightness control resistor Rs, and the current flowing through the basic adjustment resistor RH is equal to the current flowing through the current sensing resistor RL1, so the following relationship can be obtained:

[0034]

[0035] From equation 10, we can get Similarly, the average output current ILED flowing through the LED lamp is:

[0036]

[0037] Compared with the case where the dip-code dimming switches S1 to Sn are all in the off state, the average output current flowing through the LED lamp when the dip-code dimming switch S1 is in the on state and the dip-code dimming switches S2 to Sn are all in the off state increases The average output current ILED flowing through the LED lamp has nothing to do with the absolute values ​​of the resistances of the basic adjustment resistor RH and the current sensing resistor RL1 (it is only related to the ratio between them).

[0038] By analogy, when more of the dip-code dimming switches S1 to Sn are turned on, Thereby, more levels of brightness adjustment for the LED lamp can be achieved.

[0039] In summary, in the LED driving system 200 according to the embodiment of the present invention, when the dip dimming switches S1 to Sn are all in the off state, the peak value of the source voltage Vsource of the power switch tube M1 is controlled to be fixed and equal to the peak voltage at the CS terminal of the LED driving chip 202, the peak primary current flowing through the primary winding Lp of the transformer T is fixed and is related to the reference voltage Vref preset inside the LED driving chip 202 under the duty cycle in the entire switching cycle of the power switch tube M1, the average output current ILED flowing through the LED lamp remains unchanged, and the brightness of the LED lamp is the lowest at this time; when one or more of the dip dimming switches S1 to Sn are in the on state, the sampling and adjustment circuit 202 doubles the source voltage Vsource of the power switch tube M1, and compared with the case where the dip dimming switches S1 to Sn are all in the off state, under the condition that the duty cycle of the switching cycle of the power switch tube M1 remains unchanged, the average primary current flowing through the primary winding Lp of the transformer T doubles, thereby increasing the average output current ILED flowing through the LED lamp, and the brightness of the LED lamp increases at this time.

[0040] In the LED driving system 200 according to the embodiment of the present invention, the average output current ILED flowing through the LED lamp is only related to the ratio of the basic adjustment resistor RH to the current sensing resistor Rcs (i.e., the parallel resistance of one or more of the current sensing resistors RL1 to RLn) and has nothing to do with the absolute values ​​of their resistance values. Figure 1 The LED driving system 100 shown can improve the accuracy of the average output current flowing through the LED lamp. In addition, when all the dip switches S1 to Sn are in the off state, the average output current flowing through the LED lamp is only related to the lowest brightness control resistor Rs flowing near the LED driving chip 202, so compared Figure 1 The LED driving system 100 shown is more excellent in anti-interference capability.

[0041] The present invention can be implemented in other specific forms without departing from its spirit and essential features. For example, the algorithms described in the specific embodiments can be modified, and the system architecture does not depart from the basic spirit of the present invention. Therefore, the current embodiments are regarded as exemplary and non-restrictive in all aspects, and the scope of the present invention is defined by the appended claims rather than the above description, and all changes falling within the meaning and equivalent scope of the claims are thus included in the scope of the present invention.

Claims

1. An LED driving system, comprising a transformer, an LED driving chip, a minimum brightness control resistor, and a sampling adjustment circuit, wherein: The LED driver chip comprises a power switch tube, the drain of the power switch tube is connected to the primary winding of the transformer, and the source of the power switch tube is connected to the circuit reference ground via the minimum brightness control resistor; The sampling and adjustment circuit includes a basic adjustment resistor, a plurality of current sensing resistors, and a plurality of dip-code dimming switches. The basic adjustment resistor is connected between the source of the power switch tube and the current sensing terminal of the LED driver chip. Any one of the plurality of current sensing resistors is connected in series with a corresponding one of the plurality of dip-code dimming switches to form a current sensing unit and is connected between the current sensing terminal of the LED driver chip and a circuit reference ground. The current sensing terminal of the LED driver chip is used to receive a current sensing signal representing the primary current flowing through the primary winding of the transformer.

2. The LED driving system according to claim 1, wherein: The LED driver chip is configured as: generating an error amplified signal representing a difference between the current sensing signal and the reference voltage based on the current sensing signal and the reference voltage; Based on the error amplification signal and the threshold voltage, generating a comparison result signal representing a magnitude comparison relationship between the error amplification signal and the threshold voltage; as well as Based on the comparison result signal, a shut-down control signal for controlling the power switch tube to change from the on state to the off state or a shut-down control signal for controlling the power switch tube to change from the off state to the on state is generated.

3. The LED driving system according to claim 2, wherein: The LED driver chip is further configured as: generating the shutdown control signal when the comparison result signal indicates that the error amplified signal is greater than the threshold voltage; as well as In a case where the comparison result signal indicates that the error amplified signal is not greater than the threshold voltage, the conduction control signal is generated.

4. The LED driving system according to claim 2, wherein: The LED driver chip is further configured as: Based on the shutdown control signal, generating a shutdown drive signal for driving the power switch tube to be in a shutdown state; and Based on the conduction control signal, a conduction drive signal for driving the power switch tube to be in a conduction state is generated.

5. The LED driving system according to claim 2, wherein: The LED driver chip further comprises: an error amplifier configured to generate the error amplified signal by error-amplifying the current sensing signal and the reference voltage; a differential control unit configured to generate the comparison result signal by comparing the error amplified signal with the threshold voltage; and A logic control unit is configured to generate the shutdown control signal or the conduction control signal by performing a logic operation based on the comparison result signal.

6. The LED driving system according to claim 5, wherein: The LED driver chip further comprises: The gate driving circuit is configured to generate a turn-off driving signal for driving the power switch tube to be in a turn-off state based on the turn-off control signal, and to generate a turn-on driving signal for driving the power switch tube to be in a turn-on state based on the turn-on control signal.

7. The LED driving system according to claim 1, wherein: The minimum brightness control resistor is located inside or outside the LED driver chip.

8. The LED driving system according to claim 1, wherein: The sampling adjustment circuit is located inside or outside the LED driver chip.

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