TWI587744B - Driving circuit for light emitting diode - Google Patents

Description

Light-emitting diode driving circuit

The invention provides a light emitting diode driving circuit, in particular to a driving circuit for driving a light emitting diode unit according to a voltage level of a control node in the driving circuit and controlling the current of the light emitting diode unit.

With the rise of environmental awareness, people began to advocate environmental protection policies such as energy conservation and carbon reduction. Among them, reducing the power consumption of lighting fixtures is one example of environmental protection policy. At present, the light-emitting element having better energy-saving efficiency is a Light Emitting Diode (LED). Because of its energy saving, environmental protection, long life and durability, LEDs are gradually replacing traditional lamps and gradually expanding to various applications.

For a driving circuit that drives an LED with an AC power source, the voltage supplied to the LED by the AC power source changes with time, that is, when the voltage value of the AC voltage rises, the LED that is driven is driven. The number of polar bodies is large, and when the voltage value of the alternating voltage is lowered, the number of light-emitting diodes that can be driven is small. Therefore, when the driving power source for driving the light-emitting diodes changes in size over time, the number of light-emitting diodes that can be driven by the power source changes with time, and the current flowing through the light-emitting diodes also follows. Time changes.

The invention provides a light-emitting diode driving circuit, such that the number of driven light-emitting diodes and the current flowing through the driven light-emitting diodes will change with the voltage of the alternating current power source, thereby driving the light-emitting two more efficiently. The polar body avoids the phenomenon that the current flowing through the light-emitting diode is excessively large and the light-emitting diode is burned out.

The light emitting diode driving circuit disclosed in the present invention drives the first light emitting diode unit and the second light emitting diode unit with an alternating current power source. The first light emitting diode unit is electrically connected between the alternating current power source and the first node, the second light emitting diode unit is electrically connected to the first light emitting diode and the control node, and the first node is located at the first light emitting diode Between the unit and the second light emitting diode unit. The LED driving circuit has a first switching unit, a first current source, a second current source, and a current control unit. The first switch unit is electrically connected between the first node and the control node, and turns on the first node and the control node according to the voltage level of the control node. The first current source is electrically connected to the control node, and when the first LED unit is turned on, the first current is supplied to the control node according to the first control signal. The second current source is electrically connected to the control node, and selectively supplies the second current to the control node according to whether the first switching unit is turned on. The current control unit is configured to generate a first control signal.

According to the LED driving circuit disclosed in the present invention, the number of the conducting diode units is controlled according to the voltage level of the control node, and the first current source and the second current source are controlled to provide the flow through the two LEDs. The current of the polar body unit enables the light-emitting diode to be driven efficiently, and effectively controls the current flowing through the light-emitting diode to prevent the current flowing through the light-emitting diode from being excessively large, thereby making the light-emitting diode Burnt phenomenon.

The above description of the disclosure and the following description of the embodiments of the present invention are intended to illustrate and explain the spirit and principles of the invention, and to provide further explanation of the scope of the invention.

The detailed features and advantages of the present invention are set forth in the Detailed Description of the Detailed Description of the <RTIgt; </ RTI> <RTIgt; </ RTI> </ RTI> </ RTI> <RTIgt; The objects and advantages associated with the present invention can be readily understood by those skilled in the art. The following examples are intended to describe the present invention in further detail, but are not intended to limit the scope of the invention.

Please refer to FIG. 1. FIG. 1 is a schematic diagram of a light emitting diode driving circuit according to an embodiment of the invention. As shown in FIG. 1, the LED driving circuit 10 drives the first light emitting diode with an AC power source 11. The body unit Xa1 and the second light emitting diode unit Xa2. In one embodiment, the AC power source 11 is converted into a power that does not change the direction of the current with time through a rectifier or a filter, and is provided to drive the first LED unit Xa1 and the second LED unit Xa2.

In this embodiment, the first LED unit Xa1 is electrically connected between the AC power source 11 and the first node a1, and the second LED unit Xa2 is electrically connected to the first LED unit Xa1 and the control node. Between ax, the first node a1 is located between the first light emitting diode unit Xa1 and the second light emitting diode unit Xa2. The LED driving circuit 10 has a first switching unit 12, a first current source 13, a second current source 14, and a current control unit 15.

The first switch unit 12 is electrically connected between the first node a1 and the control node ax, and turns on the first node a1 and the control node ax according to the voltage level of the control node ax. In one embodiment, the first switch unit 12 can be implemented by a transistor switch. The first end of the first switch unit 12 is electrically connected to the first node a1, and the second end of the first switch unit 12 is electrically connected to the control node ax. . The control terminal of the first switching unit 12 is electrically connected to the first comparing unit 16 or other suitable components, so that the first switching unit 12 turns on the first node a1 and the control node ax according to the voltage level of the control node ax. Taking the first comparison unit 16 as an example, the first comparison unit 16 is, for example, an operational amplifier. The forward input terminal of the first comparison unit 16 receives the first preset voltage Vpre1, and the reverse input terminal of the first comparison unit 16 is electrically The output of the first comparison unit 16 is electrically connected to the control end of the first switching unit 12. The first comparison unit 16 compares the voltage level of the control node ax with the voltage level of the first preset voltage Vpre1, and outputs the first according to whether the voltage level of the control node ax is less than the voltage level of the first preset voltage Vpre1. The signal Hg1 is compared to control the first switching unit 12 to conduct the first node a1 and the control node ax.

The first current source 13 is electrically connected to the control node ax, and is configured to provide a first current flowing through the control node ax according to the first control signal SC1 when the first LED unit Xa1 is turned on. In one embodiment, the first current source 13 is implemented by, for example, a transistor switch, and the first end of the first current source 13 is electrically connected to the control node ax, and the second end is electrically connected to the low voltage level, and the control terminal is electrically connected. The current controller 15 is connected.

The second current source 14 is electrically connected to the control node a1 for selectively providing the second current to flow through the control node ax according to whether the first switching unit 12 is turned on. When the second current source 14 is implemented by a transistor switch, the first end of the second current source 14 is electrically connected to the control node ax, and the second end is electrically connected to the low voltage level. In one embodiment, the LED driving circuit 10 further has a first auxiliary control unit 17 electrically connected to the control end of the second current source 14. The first auxiliary control unit 17 generates a second according to whether the first switching unit 12 is turned on. The control signal SC2 is controlled, and the second current source 14 provides a second current flowing through the control node ax according to the second control signal SC2.

Specifically, the first auxiliary control unit 17 has a comparator 171 and a multiplexer 172. The forward input terminal of the comparator 171 receives the reference voltage Vref1, and the inverting input terminal of the comparator 171 receives the first comparison signal Hg1. The output end of the 171 is electrically connected to the data selection end of the multiplexer 172. The first data input end of the multiplexer 172 is electrically connected to the current controller 15, and the second data input end is electrically connected to the low voltage level. The multiplexer 172 selects one of the signals received according to the first data input terminal or the second data input terminal according to the comparison result D1 of the comparator 171 for the voltage level of the first comparison signal Hg1 and the reference voltage Vref1, and outputs the second control. Signal SC2 to second current source 14.

The current control unit 15 is configured to generate the first control signal SC1. In one implementation In the example, the current control unit 15 has a first control switch 151, a second control switch 152, and an output controller 153. The first control switch 151 and the second control switch 152 form a current mirror, that is, the first end of the first control switch 151 is electrically connected to the first end of the second control switch 152, and the control end of the first control switch 151 is electrically connected. The second control switch 152 is controlled. The second end of the second control switch 152 generates a mirror current according to the control current of the first control switch 151 on the second end. The output controller 153 is electrically connected to the second end of the second control switch 152. The output controller 153 generates the first control signal SC1 according to the mirror current of the second control switch at the second end, and according to whether the first switch unit 12 is turned on. The first control signal SC1 is selectively output.

In more detail, the output controller 153 has a voltage selector 154, an operational amplifier 155, and a third control switch 156. The first end of the third control switch 156 is electrically connected to the second end of the second control switch 152, and the control end of the third control switch 156 is electrically connected to the output end of the operational amplifier 155. The forward input terminal of the operational amplifier 155 is electrically connected to the first end of the third control switch 156, and the inverting input terminal of the operational amplifier 155 is electrically connected to the output terminal of the voltage selector 154. The voltage selector 154 selects and outputs the first preset voltage Vpre1 to the operational amplifier 155 according to the comparison result D1 output by the comparator 171, so that the operational amplifier 155 sets the voltage level of the first end of the third control switch 156 according to the first preset voltage Vpre1. quasi. Furthermore, the operational amplifier 155 controls the output of the first control signal SC1 to turn on the third control switch 156 and the first current source 13.

Next, the driving method of the light emitting diode driving circuit 10 will be explained. In order to facilitate the description of the driving manner of the LED driving circuit 10, the following first current source 13 and second current source 14 are exemplified by a transistor switch, but are not limited thereto. In actual operation, when the power supply provided by the AC power source 11 is insufficient to drive the first LED unit Xa1 and the second LED unit Xa2, the voltage levels of the first node a1 and the control node ax are low at 0V. The voltage value of the first preset voltage Vpre1. The first comparison unit 16 outputs the first comparison signal Hg1 according to the voltage level of the control node ax and the first preset voltage Vpre1, so that the first switching unit 12 is turned on. The comparator 171 outputs a comparison result D1 according to the voltage levels of the first comparison signal Hg1 and the reference voltage Vref1. The multiplexer 172 outputs the second control signal SC2 according to the comparison result D1 of the comparator 171. To control the second current source 14 to be non-conducting.

At this time, the voltage selector 154 selects to output the first preset voltage Vpre1 to the inverting input terminal of the operational amplifier 155 according to the comparison result D1 of the comparator 171 for the voltage level of the first comparison signal Hg1 and the reference voltage Vref1. The voltage level of the first end of the third control switch 156 is set by the operational amplifier 155 to be equal to or slightly smaller than the voltage level of the first preset voltage Vpre1.

When the power supply provided by the AC power source 11 is gradually increased until the power supply provided by the AC power source 11 can drive the first LED unit Xa1, but is insufficient to drive the second LED unit Xa2, and the voltage level of the control node ax remains When the voltage level is lower than the first preset voltage Vpre1, the first switching unit 12 continues to be turned on. The first current source 13 provides a first current flowing through the control node ax that is increasingly larger depending on the voltage level at which the control node ax is gradually increasing. However, due to the voltage value setting of the first comparison unit 16 at the forward input terminal, the voltage level of the first end of the first current source 13 is set to be lower than the voltage of the first preset voltage Vpre1 before the first switching unit 12 is turned off. The level, that is, the voltage level of the first end of the third control switch 156, is such that the magnitude of the first current generated by the first current source 13 is limited to be no greater than the magnitude of the current on the third control switch 156.

When the power supply provided by the AC power source 11 is gradually increased, until the power supply provided by the AC power source 11 can drive the first LED unit Xa1 and the second LED unit Xa2, the voltage level of the control node ax is greater than the first preset. The voltage level of the voltage Vpre1, the first comparison signal Hg1 output by the first comparison unit 16 controls the first switching unit 12 to be turned off. The comparator 171 outputs the comparison result D1 according to the first comparison signal Hg1 being smaller than the voltage level of the reference voltage Vref1, so that the multiplexer 172 outputs the second control signal SC2 according to the first control signal SC1, and controls the second current source 14 to be turned on, providing the first Two currents flow through the control node ax.

In the foregoing embodiment, the first control signal SC1 is, for example, a voltage level at the control end of the third control switch 156. That is, when the third control switch 156 receives the mirror current of the second control switch 152 at the second end, between the first end and the second end of the third control switch 156 The voltage difference and the voltage difference between the control terminal and the second terminal are determined, and the voltage level of the first terminal of the third control switch 156 is set by the operational amplifier 155 to determine the voltage level of the control terminal of the third control switch 156. quasi. The control terminal of the first current source 13 is electrically connected to the control terminal of the third control switch 156, and receives the voltage level of the control terminal of the third control switch 156 to be turned on according to the voltage level of the control terminal of the third control switch 156, and is The difference between the voltage level at the control terminal of the third control switch 156 and the control node ax voltage level produces a first current. Similarly, the voltage level of the second control signal SC2 may also be equal to or less than the voltage level of the first control signal SC1, and the second current source 14 may be based on the voltage level of the control terminal of the third control switch 156 and the control node ax. The difference in voltage level produces a second current. This embodiment is not limited.

It can be understood from the foregoing that the magnitude of the mirror current of the second control switch 152 at the second end will affect the magnitude of the current of the first current and the second current. Therefore, in one embodiment, as shown in FIG. The unit 15 further has a variable resistor Ra and a voltage controller 157 at the second end of the first control switch 151. The voltage controller 157 controls the voltage difference across the variable resistor Ra according to the set voltage Vset to adjust the magnitude of the control current. Further, the magnitudes of the currents of the first current and the second current are adjusted.

In another embodiment, please refer to FIG. 2. FIG. 2 is a schematic diagram of a light emitting diode driving circuit according to another embodiment of the present invention. In FIG. 2, a second switching unit 12' and a second comparing unit 16' are further disposed between the second LED unit Xa2 and the control node ax', and the second switching unit 12' and the second LED There is a second node a2 between the units Xa2, and the second switching unit 12' turns on the second node a2 and the control node ax' according to the voltage level of the control node ax'. In this embodiment, the second switch unit 12' is implemented by a transistor switch. The first end of the second switch unit 12' is electrically connected to the second node a2, and the second end of the second switch unit 12' is electrically connected. Control node ax'. The control end of the second switching unit 12' is electrically connected to the output end of the second comparing unit 16', and the forward input end of the second comparing unit 16' receives the second preset voltage Vpre2, and the reverse of the second comparing unit 16' The input terminal is electrically connected to the control node ax'. The second comparing unit 16' compares the voltage level of the control node ax' with the voltage level of the second predetermined voltage Vpre2, And according to whether the voltage level of the control node ax' is smaller than the voltage level of the second preset voltage Vpre2, the second comparison signal Hg2 is output to control the second switching unit 12' to turn on the second node a2 and the control node ax'.

The operation mode of the LED driving circuit 10' of FIG. 2 is substantially the same as that of the LED driving circuit 10 of FIG. 1. Unlike the embodiment of FIG. 1, the first LED unit Xa1 and the second The LEDs Xa2 are driven, and the comparison result D1 output by the comparator 171 causes the multiplexer 172 to output the second control signal SC2 according to the first control signal SC1, and the voltage selector 154 compares the comparator 171 with respect to the first comparison. The comparison result D1 of the signal Hg1 and the reference voltage Vref1 voltage level is selected to output the second preset voltage Vpre2 to the inverting input terminal of the operational amplifier 155, and the voltage level of the first end of the third control switch 156 is used by the operational amplifier 155. It is set to be equal to or slightly smaller than the voltage level of the second preset voltage Vpre2. At this time, the voltage level of the first end of the first current source 13 and the first end of the second current source 14 is set to be lower than the voltage level of the second preset voltage Vpre2, that is, less than the third control switch 156. The voltage level at one end, therefore, the magnitude of the first current generated by the first current source 13 and the magnitude of the second current generated by the second current source 14 are controlled to be no greater than the magnitude of the current on the third control switch 156.

Referring to FIG. 3 and FIG. 4 together, FIG. 3 is a schematic diagram of a light emitting diode driving circuit according to another embodiment of the present invention, and FIG. 4 is a light emitting diode according to the embodiment of FIG. A timing diagram of the voltage level of the driving circuit and the number of driving LEDs. As shown in the figure, the LED driving circuit 20 drives three or more LED units, such as LED units Xb1 to Xbn, with an AC power source 21, wherein each of the LED units may have a different number. The light emitting diodes are not limited in this embodiment. For convenience of explanation, the light-emitting diode unit Xb1, the light-emitting diode unit Xb2, and the light-emitting diode unit Xbn will be described below as an example.

The AC power source 21 is converted into a power that does not change the direction of the current with time by a rectifier or a filter, and is supplied to drive the LED units Xb1 to Xbn. The light-emitting diode unit Xb1 and the light-emitting diode unit Xb2 have a node b1 between the light-emitting diode unit Xb2 and the light-emitting diode unit Xb3 and the light-emitting diode unit Xb3, and so on. Light-emitting diode driving circuit 20 has a switching unit 221 22 22n, a current source 231 ~ 23n and a current control unit 25, wherein the switch unit 221 is electrically connected between the node b1 and the control node bx, and the switch unit 222 is electrically connected to the node b2 and the control node bx The switching unit 22n is electrically connected between the node bn and the control node bx. The switching units 221 to 22n respectively turn on the nodes b1 to bn and the control node bx according to the voltage level of the control node bx. In this embodiment, the switch units 221 22 22 n are implemented by a transistor switch, and the first ends of the switch units 221 22 22 n are electrically connected to the nodes b1 bn bn and the second ends of the switch units 221 22 22 n are electrically connected. Node bx.

The control terminal of the switch unit 221 is electrically connected to the output terminal of the comparison unit 241, the forward input terminal of the comparison unit 241 receives the preset voltage Vpre1', and the reverse input terminal of the comparison unit 241 is electrically connected to the control node bx. The comparing unit 241 compares the voltage level of the control node bx with the voltage level of the preset voltage Vpre1', and outputs a comparison signal Hg1' according to whether the voltage level of the control node bx is less than the voltage level of the preset voltage Vpre1'. Whether the switch unit 221 turns on the node b1 and the control node bx. Similarly, the control end of the switch unit 222 is electrically connected to the output end of the comparison unit 242, the control end of the switch unit 22n is electrically connected to the output end of the comparison unit 24n, and the forward input terminals of the comparison unit 242 and the comparison unit 24n are respectively received. The preset voltage Vpre2' and the preset voltage Vpren' are electrically connected to the control node bx of the comparison unit 242 and the comparison unit 24n to compare the voltage level of the control node bx with the preset voltage Vpre2' and the preset The voltage level of the voltage Vpren' is output to the comparison signal Hg2' and the comparison signal Hgn', respectively, to control the switching unit 222 and the switching unit 22n.

The current source 231 is electrically connected to the control node bx, and provides a first control current according to the control signal SD1 output by the current controller 25. The current source 232 is electrically connected to the control node bx, and provides a second control current according to the control signal SD2 output by the auxiliary control unit 261. The current source 23n is electrically connected to the control node bx, and the nth control current is supplied according to the control signal SD3 output from the auxiliary control unit 26n. The auxiliary control unit 261 compares the voltage levels of the reference voltage Vref1' and the comparison signal Hg1', and outputs the control signal SD2 to the current source according to the control signal SD1 when the voltage level of the comparison signal Hg1' is less than the voltage level of the reference voltage Vref1'. 232. The current source 232 is turned on to provide a second control current flowing through the control node bx. Similarly, the auxiliary control unit 26n compares the voltage levels of the reference voltage Vref(n-1)' and the comparison signal Hg(n-1)', and the voltage level of the comparison signal Hg(n-1)' is smaller than the reference. When the voltage level of the voltage Vref(n-1)' is output, the control signal SDn is outputted to the current source 23n according to the control signal SDn _-1 , so that the current source 23n is turned on to provide the nth control current flowing through the control node bx. The circuit of the current control unit 25 is substantially the same as the current control unit 15 shown in FIG. 1, and will not be described again.

Next, a driving method of the light emitting diode driving circuit 20 will be described. In actual operation, when the power supplied from the AC power source 21 is insufficient to drive the LED units Xb1 to Xbn, the voltage level of the node bn is 0V. The switching unit 22n is turned on so that the voltage of the control node bx and the voltage level of the node bn are also 0V. The voltage level of the control node bx is lower than the preset voltage Vpre1' and the preset voltage Vpre2' voltage value, so the comparison unit 241 outputs the comparison signal Hg1' to control the switch according to the voltage level of the control node bx and the preset voltage Vpre1'. The unit 221 is turned on, and the comparing units 242~24(n-1) output the comparison signal Hg2'~Hg(n-1) according to the voltage level of the control node bx and the preset voltage Vpre2'~Vpre(n-1)'. 'The control switch units 222 to 22 (n-1) are turned on.

At this time, the auxiliary control unit 261 compares the voltage levels of the reference voltage Vref1' and the comparison signal Hg1', and outputs a control signal SD2 to control the current source 232 not to provide when the comparison signal Hg1' is higher than the voltage level of the reference voltage Vref1'. Current. Similarly, the auxiliary control units 262~26(n-1) compare the voltage levels of the reference voltages Vref2'~Vref(n-1)' and the comparison signals Hg2'~Hg(n-1)', respectively, and output them separately. The control signals SD3 to SDn control the current sources 233 to 23n to supply no current. The voltage selector 254 selects the output preset voltage Vpre1' to the inverting input terminal of the operational amplifier 255 according to the comparison result D1' of the comparison signal Hg1' and the reference voltage Vref1' voltage level, so that the first end of the third control switch 256 The voltage level is set by the operational amplifier 255 to be equal to or slightly less than the voltage level of the preset voltage Vpre1'.

When the power supplied from the AC power source 21 is gradually increased until the power supplied from the AC power source 21 can drive the LED unit Xb1, it is insufficient to drive the LED unit Xb2. When ~Xbn, the voltage level of the control node bx also increases with the voltage level of the node b1, but the voltage level of the control node bx is still less than the voltage level of the preset voltage Vpre1', and the switching units 221~22n are still turned on. . The current source 231 provides a first control current flowing through the control node bx that is increasingly larger depending on the voltage level at which the control node bx is gradually increasing. However, due to the voltage value setting of the comparison unit 211 at the forward input terminal, before the switch unit 221 is turned off, the voltage level of the first end of the current source 231 is less than the voltage level of the preset voltage Vpre1', and the third control switch 256 is based on The mirror current and the preset voltage Vpre2' generate a current, and the magnitude of the first control current generated by the first current source 231 is limited to be no greater than the magnitude of the current on the third control switch 256.

When the power supply provided by the AC power source 21 is gradually increased, and the voltage level of the control node bx is also increased with the voltage level of the node b1, the power supply provided by the AC power source 21 can drive the LED unit Xb1 and the LED unit. When Xb2 is insufficient to drive the LED units Xb3 to Xbn, the voltage level of the control node bx is greater than the voltage level of the preset voltage Vpre1', and the comparison unit 241 controls the switching unit 221 to be turned off. The auxiliary control unit 261 determines that the comparison signal Hg1' is lower than the voltage level of the reference voltage Vref1', and outputs the control signal SD2 according to the control signal SD1 to control the current source 232 to supply current. The auxiliary control units 262~26(n-1) respectively judge that the comparison signal Hg2'~Hg(n-1)' is still higher than the voltage level of the reference voltages Vref2'~Vref(n-1)', so continue to control signals The SD3~SDn control current sources 233~23n do not supply current.

At this time, the voltage selector 254 selects an output preset according to the comparison result D1' of the reference voltage Vref1' and the comparison signal Hg1' voltage level, and according to the comparison result D2' of the reference voltage Vref2' and the comparison signal Hg2' voltage level. The voltage Vpre2' is to the inverting input of the operational amplifier 255, and the voltage level of the first terminal of the third control switch 256 is set by the operational amplifier 255 to be equal to or slightly smaller than the voltage level of the second predetermined voltage Vpre2'. At this time, before the switching unit 222 is turned off, the voltage level of the first end of the current source 231 and the first end of the current source 232 is less than the voltage level of the preset voltage Vpre2', and the third control switch 256 is based on the mirror current and the pre- The voltage Vpre2' is set to generate a current, and the first control generated by the current source 231 and the second control current generated by the current source 232 are limited to a magnitude greater than the magnitude of the current on the third control switch 256.

Similarly, when the power supply provided by the AC power source 21 is gradually increased until the power supply provided by the AC power source 21 can drive the LED units Xb1 to Xbn, the voltage level of the control node bx is greater than the preset voltage Vpre(n-1). The voltage level of ', the comparison units 241 to 24 (n-1) control the switching units 221 to 22 (n-1) are turned off. The auxiliary control units 261~26(n-1) determine that the comparison signals Hg1'~Hg(n-1)' are lower than the voltage levels of the reference voltages Vref1'~Vref(n-1)', and are output controlled according to the control signal SD1. Signals SD2~SDn provide current through control node bx with control current sources 232~23n.

At this time, the voltage selector 254 selects the output preset voltage Vpren' to calculate according to the comparison result D(n-1)' of the reference voltage Vref(n-1)' and the comparison signal Hg(n-1)' voltage level. The inverting input of the amplifier 255 causes the voltage level at the first end of the third control switch 256 to be set by the operational amplifier 255 to be equal to or slightly less than the voltage level of the preset voltage Vpren'. At this time, the voltage level of the first end of the current sources 231~23n is less than the voltage level of the preset voltage Vpren', and the third control switch 256 generates a current according to the mirror current and the preset voltage Vpren', and the current sources 231~23n are generated. The current will be limited to no more than the current on the third control switch 256.

In this embodiment, the control signals SD2~SDn are generated according to the control signal SD1, and the control signal SD1 is, for example, the voltage level of the control terminal of the third control switch 256. That is, when the third control switch 256 receives the mirror current of the second control switch 252 at the second end, the voltage difference between the first end and the second end of the third control switch 256 and the control end and the second end The voltage difference between the two is determined by the operational amplifier 255, and the voltage level of the first terminal of the third control switch 256 is set to determine the voltage level of the control terminal of the third control switch 256. The control terminal of the current source 231 is electrically connected to the control end of the third control switch 256, and receives the voltage level of the control terminal of the third control switch 256 to be turned on according to the voltage level of the control terminal of the third control switch 256, and according to the third The difference between the voltage level at the control terminal of control switch 256 and the voltage level at control node bx produces a first control current.

To facilitate the timing diagram display of FIG. 4, the timing diagram of FIG. 4 is exemplified by three light-emitting diode units, that is, the value of n in the foregoing embodiment is equal to three. As can be seen from Figure 4, at the time point At t1, the light emitting diode unit Xb1 is driven. At the time point t2, the switching unit 221 is turned off, and the light emitting diode unit Xb1 and the light emitting diode unit Xb2 are driven. At time t3, the switching units 221 to 222 are turned off, and the light-emitting diodes Xb1 to Xb3 are driven, and the number of driven light-emitting diode units increases and decreases with the voltage value of the alternating voltage.

In summary, the embodiment of the present invention provides a light-emitting diode driving circuit that controls whether a switching unit is turned on by controlling a voltage level of a node to control the number of conduction of the light-emitting diode unit. Furthermore, by controlling whether the switching unit is turned on, the first current source and the second current source are controlled to provide a current flowing through the light emitting diode unit, so that the light emitting diode can be efficiently driven and the flow can be effectively controlled. The current of the light-emitting diode avoids the phenomenon that the current flowing through the light-emitting diode is excessively large and the light-emitting diode is burned out.

Although the present invention has been disclosed above in the foregoing embodiments, it is not intended to limit the invention. It is within the scope of the invention to be modified and modified without departing from the spirit and scope of the invention. Please refer to the attached patent application for the scope of protection defined by the present invention.

10, 10', 20‧‧‧Lighting diode driving circuit

11, 21‧‧‧ AC power supply

12‧‧‧First switch unit

12’‧‧‧Second switch unit

13‧‧‧First current source

14‧‧‧second current source

15, 25‧‧‧ Current Control Unit

151, 251‧‧‧ first control switch

152, 252‧‧‧ second control switch

153, 253‧‧‧ Output controller

154, 254‧‧‧ voltage selector

155, 255‧‧‧Operational Amplifier

156, 256‧‧‧ third control switch

157, 257‧‧‧ voltage controller

16‧‧‧ first comparison unit

16’‧‧‧Second comparison unit

17‧‧‧First Auxiliary Control Unit

171‧‧‧ comparator

172‧‧‧Multiplexer

221~22n‧‧‧Switch unit

231~23n‧‧‧current source

241~24n‧‧‧Comparative unit

261~26(n-1)‧‧‧Auxiliary Control Unit

Hg1‧‧‧ first comparison signal

Hg2‧‧‧ second comparison signal

Hg1’~Hgn’‧‧‧ comparison signal

Vpre1‧‧‧ first preset voltage

Vpre2‧‧‧ second preset voltage

Vpre1’~Vpren’‧‧‧Preset voltage

Vref1‧‧‧ first reference voltage

Vref2‧‧‧second reference voltage

Vref1'~Vref(n-1)'‧‧‧ reference voltage

Vset, Vset’‧‧‧ set voltage

D1, D2, D1'~D2'‧‧‧ comparison results

Ra, Rb‧‧‧Variable Resistors

Xa1‧‧‧first light-emitting diode unit

Xa2‧‧‧Second light-emitting diode unit

Xb1~Xbn‧‧‧Lighting diode unit

A1‧‧‧first node

A2‧‧‧second node

Ax‧‧‧ control node

B1~bn‧‧‧ nodes

Bx‧‧‧ control node

T0, t1, t2, t3‧‧‧ time points

FIG. 1 is a schematic diagram of a light emitting diode driving circuit according to an embodiment of the invention. 2 is a schematic diagram of a light emitting diode driving circuit according to another embodiment of the present invention. FIG. 3 is a schematic diagram of a light emitting diode driving circuit according to still another embodiment of the present invention. 4 is a timing diagram of the voltage level of the LED driving circuit and the number of LEDs driven according to the embodiment of FIG. 3.

10‧‧‧Lighting diode drive circuit

11‧‧‧AC power supply

12‧‧‧First switch unit

13‧‧‧First current source

14‧‧‧second current source

15‧‧‧ Current Control Unit

151‧‧‧First control switch

152‧‧‧Second control switch

153‧‧‧Output controller

154‧‧‧Voltage selector

155‧‧‧Operational Amplifier

156‧‧‧ third control switch

157‧‧‧Voltage controller

16‧‧‧ first comparison unit

17‧‧‧First Auxiliary Control Unit

171‧‧‧ comparator

172‧‧‧Multiplexer

Hg1‧‧‧ first comparison signal

Vpre1‧‧‧ first preset voltage

Vref1‧‧‧ first reference voltage

Vset‧‧‧Set voltage

D1‧‧‧ comparison results

Ra‧‧‧Variable resistor

Xa1‧‧‧first light-emitting diode unit

Xa2‧‧‧Second light-emitting diode unit

A1‧‧‧first node

Ax‧‧‧ control node

Claims (13)

A light-emitting diode driving circuit drives an first light-emitting diode unit and a second light-emitting diode unit with an AC power source, and the first light-emitting diode unit is electrically connected to the AC power source and a first node The second light emitting diode unit is electrically connected to the first light emitting diode unit and a control node, and the first node is located at the first light emitting diode unit and the second light emitting diode unit The LED driving circuit includes: a first switching unit electrically connected between the first node and the control node, and the first node and the control are turned on according to a voltage level of the control node a first current source electrically connected to the control node, when the first light emitting diode unit is turned on, providing a first current flowing through the control node according to a first control signal; a second current source, Electrically connecting the control node, selectively providing a second current through the control node according to whether the first switch unit is turned on; and a current control unit for generating the first control signal. The illuminating diode driving circuit of claim 1, further comprising a first comparing unit for comparing a voltage level of the control node with a first predetermined voltage level and a voltage level at the control node When the first predetermined voltage level is less than the first predetermined voltage level, a first comparison signal is output to control the first switching unit to turn on the first node and the control node. The illuminating diode driving circuit of claim 2, further comprising a second switching unit electrically connected between the second illuminating diode unit and the control node, the second switching unit and the second illuminating There is a second node between the diode units, and the second switch unit turns on the second node and the control node according to the voltage of the control node. The illuminating diode driving circuit of claim 3, further comprising a second comparing unit for comparing a voltage level of the control node with a second predetermined voltage level and a voltage level at the control node When the second predetermined voltage level is less than the second predetermined voltage level, a second comparison signal is output to control the second switching unit to turn on the second node and the control node. The illuminating diode driving circuit of claim 2, further comprising a first auxiliary control unit, wherein the first auxiliary control unit selectively selects whether the voltage level of the first comparison signal is less than a reference voltage level, A second control signal is output to control the second current source to provide the second current. The illuminating diode driving circuit of claim 5, wherein the first auxiliary control unit generates the second control signal according to the first control signal when the voltage level of the first comparison signal is less than the reference voltage level When the second current source supplies the second current, the second current source further adjusts the magnitude of the second current according to the voltage level of the second control signal. The illuminating diode driving circuit of claim 5, further comprising a third illuminating diode unit, a third switching unit and a third current source, wherein the third illuminating diode unit is electrically connected to the first Between a node and a third node, the third node is located between the second LED unit and the third LED unit, and the third switch unit is electrically connected to the third node and the third node Between the control nodes, the third switch unit turns on the third node and the control node according to the voltage of the control node, and the third current source is electrically connected to the control node, and is selected according to whether the third switch unit is turned on. A third current is provided to flow through the control node. The illuminating diode driving circuit of claim 7, further comprising a third comparing unit for comparing the voltage level of the control node with a third predetermined voltage level and the voltage level of the control node When it is less than the third preset voltage level, a third comparison signal is output to control the third switching unit to turn on the third node and the control node. The illuminating diode driving circuit of claim 8 further includes a second auxiliary control unit, wherein the second auxiliary control unit selects whether the voltage level of the third comparison signal is less than a second reference voltage level. A third control signal is outputted to control the third current source to provide the third current. The illuminating diode driving circuit of claim 9, wherein when the voltage level of the third comparison signal is less than the second reference voltage level, the second auxiliary control unit generates the third according to the second control signal And controlling the signal, when the third current source provides the third current, the third current source further adjusts the magnitude of the third current according to the voltage level of the third control signal. The illuminating diode driving circuit of claim 1, wherein the current control unit has a first control switch, a second control switch and an output controller, and the second control switch forms a first control switch a current mirror, the current mirror generates a mirror current at a second end of the second control switch according to a control current on a second end of the first control switch, and the output controller is electrically connected to the first The second control terminal of the second control switch, the output controller generates the first control signal according to the mirror current of the second control switch at the second end, the first current source is further based on the voltage level of the first control signal The size of the first current is adjusted. The illuminating diode driving circuit of claim 11, wherein the output controller selectively outputs the first control signal according to whether the first switching unit is turned on. The illuminating diode driving circuit of claim 11, wherein the current control unit further has a variable resistor and a voltage controller, and the variable resistor and the voltage controller are electrically connected to the first control switch At the second end, the voltage controller controls a voltage difference across the variable resistor to adjust the magnitude of the control current.