Current control circuit

The present invention provides a current control circuit for a driving circuit system of a LED assembly, wherein the driving circuit system includes a current module, a rectifier, and a thyristor, the thyristor is connected in series between an AC power supply and the rectifier, the rectifier rectifies an input AC voltage provided by the thyristor and provides a rectified voltage to an anode of the LED assembly, and an input terminal of the current module and a cathode of the LED assembly are connected to set a current flowing through the LED assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of China Patent Application No. 201610237713.9, filed on Apr. 15, 2016, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an electronic circuitry and in particular to a current control circuit of a driving circuit system of an LED assembly.

Description of the Related Art

With the development of the LED lighting, the technology of the LED lighting dimming is also changing. Because many families have gradually become used to being able to dim their lights since the era of the light bulb, thyristor dimming switches are installed in their thyristors to provide dimming control.

In order to make a thyristor perform linear dimming on a driven LED assembly, the thyristor needs to be maintained in a conductive state. That is, in the LED lighting system working state, it is hoped that the working current flowing through the thyristor is always more than the holding current of the thyristor.

FIG. 1shows a traditional thyristor dimmer driving circuit. As shown inFIG. 1, due to the different holding currents of the various thyristors, the traditional thyristor dimmer driving circuit usually needs to set a larger conductive current of the LED assembly so that the thyristor can maintain a conductive state in order to apply to the maximum variety type of the thyristors. However, a power consumption increases because the conductive current of the LED assembly is set higher.

In addition, according to the conduction principle of the LED assembly, the LED assembly is turned on only when the input voltage is more than the non-inverting conduction voltage of the LED assembly. As a result, in order to turn on the thyristor using the lower voltage, the number of the LED assemblies in the first LED assembly is decreased so that the non-inverting conduction voltage of the first LED assembly becomes smaller. However, when the AC voltage is decreased to less than the non-inverting conduction voltage of the first LED assembly (for example: the non-inverting conduction voltage of the first LED assembly is 60V, and when the AC voltage is decreased to less than 60V), the LED circuit is still turned off, the operating current of the thyristor cannot be maintained (the operating current of the thyristor is less than the holding current of the thyristor), and the thyristor does not work properly, and a flash of the thyristor occurs. The dimming lenity of the thyristor is also influenced because the thyristor works abnormally.

In addition, the traditional thyristor dimmer driving circuit adopts the way of setting the conductive current or the conduction voltage of the LED assembly, so it is difficult for the traditional thyristor dimmer driving circuit to apply for the various types of thyristors equipped with different holding currents.

BRIEF SUMMARY OF THE INVENTION

In view of this, the technical problem to be solved in the present invention is providing a current control circuit with low power consumption and can be applied to various types of the thyristors so that the flash of the thyristor can be avoided.

The present invention provides a current control circuit for a driving circuit system of a LED assembly, wherein the driving circuit system comprises a current module202, a rectifier203, and a thyristor204, the thyristor204is connected in series between an AC power supply and the rectifier203, the rectifier203rectifies an input AC voltage provided by the thyristor and provides a rectified voltage to an anode of the LED assembly201, and an input terminal of the current module202and a cathode of the LED assembly are connected to set a current flowing through the LED assembly, and the current control circuit comprises: a first transistor M1and a transistor control circuit205, wherein a drain of the first transistor M1is connected to the anode of the LED assembly, a gate of the first transistor is connected to a control voltage output terminal of the transistor control circuit205, the first transistor M1is turned on or turned off according to a control voltage provided by the control voltage output terminal of the transistor control circuit, and the drain current of the first transistor M1and the current flowing through the LED assembly determine a feedback voltage VBL for the transistor control circuit; wherein the feedback voltage VBL enables the transistor control circuit to turn on the first transistor and the drain current of the first transistor provides a compensation current for the thyristor when the current flowing through the LED assembly is less than a preset current; wherein the feedback voltage enables the transistor control circuit to turn off the first transistor, when the current flowing through the LED assembly is more than or equal to the preset current; wherein the preset current is set according to the holding current of the thyristor.

In one embodiment of the present invention, the transistor control circuit comprises a first operational amplifier (OP1), a first resistor (RBL), and a second resistor (RCS); wherein a non-inverting input terminal of the first operational amplifier (OP1) receives a first reference voltage (VREF1), an inverting input terminal of the first operational amplifier (OP1) and the drain of the first transistor M1are connected to receive the feedback voltage VBL, an output terminal of the first operational amplifier (OP1) serves as the control voltage output terminal of the transistor control circuit2051and is connected to the gate of the first transistor M1; wherein one terminal of the first resistor (RBL) is connected to a source of the first transistor M1, and the other terminal of the first resistor (RBL) is connected to the ground; wherein one terminal of the second resistor (RCS) is connected to an output terminal of the current module202, and the other terminal of the second resistor (RCS) is connected to the source of the first transistor M1.

In one embodiment of the present invention, the transistor control circuit comprises a first operational amplifier (OP1), a first resistor (RBL), and a second resistor (RCS); wherein an inverting input terminal of the first operational amplifier (OP1) receives a first reference voltage (VREF1), an output terminal of the first operational amplifier (OP1) serves as the control voltage output terminal2051and is connected to the gate of the first transistor M1; wherein one terminal of the second resistor (RCS) is connected to an output terminal of the current module202, the other terminal of the second resistor (RCS) is connected to a terminal of the first resistor (RBL) and a source of the first transistor M1; wherein the terminal of the first resistor (RBL) is connected to the ground, and the other terminal of the first resistor (RBL) is connected to a non-inverting input terminal of the first operational amplifier (OP1) to provide the feedback voltage VBL.

In one embodiment of the present invention, the transistor control circuit comprises a first operational amplifier (OP1), a first resistor (RBL), and a second resistor (RCS); wherein an inverting input terminal of the first operational amplifier (OP1) receives a first reference voltage REF1, and an output terminal of the first operational amplifier (OP1) serves as the control voltage output terminal2051and is connected to the gate of the first transistor M1; wherein one terminal of the second resistor (RCS) is connected to an output terminal of the current module202and a source of the first transistor, and the other terminal of the second resistor (RCS) is connected to one terminal of the first transistor (RBL); wherein said terminal of the first resistor (RBL) is connected to the ground, and the other terminal of the first resistor (RBL) is connected to the non-inverting input terminal of the first operational amplifier (OP1) to provide the feedback voltage VBL.

In one embodiment of the present invention, the current module comprises a second operational amplifier (OP2) and a second transistor M2; wherein a non-inverting input terminal of the second operational amplifier (OP2) receives a second reference voltage VREF2, an inverting input terminal of the second operational amplifier (OP2) is connected to a source of the second transistor M2, and an output terminal of the second operational amplifier (OP2) is connected to a gate of the second transistor M2; wherein a drain of the second transistor M2is connected to an input terminal of the current module202, and the source of the second transistor M2is connected to an output terminal of the current module202.

In one embodiment of the present invention, the first transistor M1is turned on when the voltage on said terminal VBL of the first resistor (RBL) is less than the first reference voltage (VREF1), and the first transistor M1is turned off when the voltage on said terminal of the first resistor is more than the first reference voltage.

In one embodiment of the present invention, the first transistor M1is turned on when the voltage of the other terminal VBL of the first resistor (RBL) is more than the first reference voltage (VREF1), and the first transistor M1is turned off when the voltage of the other terminal VBL of the first resistor (RBL) is less than the first reference voltage (VREF1).

In one embodiment of the present invention, the current I1flowing through the first transistor M1is decreased with the same amount of the increase of the current flowing through the LED assembly when the first transistor is turned on.

In one embodiment of the present invention, the driving circuit system comprises a plurality of LED assemblies and a plurality set of current module arranged to set conductive currents for the plurality of LED assemblies respectively, output terminals of the current modules are connected to a common source output terminal CS.

In one embodiment of the present invention, the preset current is IDS=|VREF1|/RBL, wherein VREF1is the first reference voltage, and RBL is a resistance of the first resistor.

In one embodiment of the present invention, the current control circuit of the present invention turns on the transistor M1when the current flowing through the LED assembly is less than the preset current so that the transistor M1provides the compensation current for the thyristor of the driving circuit system and turns off the transistor M1when the current flowing through the LED assembly is more than or equal to the preset current so that the transistor M1does not provide the compensation current for the thyristor of the driving circuit system to reduce the power consumption. The preset current is set based on the different types of holding current of the thyristors. In such a control method, the thyristor maintains on the conductive state in the whole AC period to prevent flash state. The current control system of the present invention can decrease the power consumption because it does not need to set a higher LED assembly conductive current.

The present invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be discussed in detail in the examples of a variety of methods described. However, it should be noted that many viable concepts provided by the present invention may be implemented in a variety of specific ranges. These specific examples are merely illustrative of the manufacturing and the usage method of the present invention, but they are not intended to limit the scope of the present invention.

Here dedicated word “exemplary” means “serving as an example, embodiments or illustrative.” Any implementation described herein as an “exemplary” is not necessarily to be construed as preferred or advantageous over other implementations.

In addition, in order to illustrate the present invention better, numerous specific details are shown as the embodiments below. It should be understood that those skilled in the art can implement the present invention without the specific details. In some instances, the methods, tools, components, and circuits known by people skilled in the art have not been described in detail to highlight the spirit of the invention.

FIG. 2is a schematic diagram of a current control circuit according to an embodiment of the present invention, and the current control circuit is used in the driving circuit system of the LED assembly.

As shown inFIG. 2, the driving circuit system comprises a current module202, a rectifier203, and a thyristor204. The thyristor204is connected in series between an AC power supply and the rectifier203, the rectifier203rectifies an input AC voltage provided by the thyristor204and provides the rectified voltage to a cathode of a LED assembly201, and an input terminal VIN of the current module202and a cathode of the LED assembly201are connected to set a current I2flowing through the LED assembly201.

In one embodiment of the present invention, the current module202has a similar structure inFIG. 2. The current module202is composed of an operational amplifier OP2and a transistor M2. A non-inverting input terminal of the operational amplifier OP2receives a reference voltage VREF2, an inverting input terminal of the operational amplifier OP2is connected to a source of a transistor M2, and an output terminal of the operational amplifier OP2is connected to a gate of the transistor M2. A drain of the transistor M2is connected to the input terminal of the current module202, and a source of the transistor M2is connected to the output terminal of the current module202. For example, the transistor M2is a MOSFET. As shown inFIG. 2, the transistor M2is an n-type MOSFET. People skilled in the art should understand that the n-type MOSFET can be substituted by other type of the transistor for the same option in switching. The detailed structure of the current module202can be equipped with different designs according to the actual needs, so the above embodiment is only an example and does not limit the scope of the present invention.

In one embodiment of the present invention, as shown inFIG. 2, the current control circuit mainly comprises: a transistor M1and a transistor control circuit205. A drain of the transistor M1is connected to an anode of the LED assembly201, a gate of the transistor M1is connected to a control voltage output terminal2051of the control circuit205, the transistor M1is turned on or off according to a control voltage provided by the control voltage output terminal2051, and a drain current I1of the transistor M1and a current I2flowing through the LED assembly determine a feedback voltage VBL of the transistor control circuit205.

When the current I2flowing through the LED assembly is less than a preset current, the feedback voltage allows the transistor control circuit205to turn on the transistor M1and a drain current of the transistor provides a compensation current for the thyristor.

The feedback voltage allows the transistor control circuit205to turn off the transistor M1when the current I2flowing through the LED assembly is more than or equal to the preset current. The preset current is set according to a holding current of the thyristor. For example, the preset current is set to be more than the holding current of the thyristor.

In one embodiment of the present invention, as shown inFIG. 2, the current control circuit mainly comprises: an operational amplifier OP1, the resistor RBL, and the resistor RCS. A non-inverting input terminal of the operational amplifier OP1receives a reference voltage VREF1, an inverting input terminal of the operational amplifier OP1is connected to the source of the transistor M1, and an output terminal of the operational amplifier OP1serves as the control voltage output terminal2051and is connected to the gate of the transistor M1. A terminal of the resistor RBL is connected to the source of the transistor M1, the other terminal of the resistor RBL is connected to the ground, a terminal of the resistor of the resistor RCS is connected to an output terminal of the current module202, and the other terminal of the resistor RCS is connected to the source of the transistor M1.

It is noticed that the rectifier ofFIG. 2can be a half-wave rectifier, a full wave rectifier, or a bridge rectifier, but it is not limited to the present invention. In addition, a dashed line with pots of theFIG. 2is an embodiment of a circuit packaging, internal parts of the dashed line with pots represent the circuit elements integrated on a single chip, and circles VIN, GND, BLCS, CS on the dashed line with pots represent chip pins. People skilled in the art should realize that the circuit packaging inFIG. 2or shown in the other figures are only examples, and the circuit packaging can be implemented according to real demands. For example, the resistor RBL and the resistor RCS can be integrated with the operational amplifier OP1in the same chip, so the above embodiment is only an example and it is not limited thereto.

FIG. 3AandFIG. 3Bare voltage-current operation timing charts of the current control circuit shown inFIG. 2. TakeFIG. 2for example,FIG. 3AandFIG. 3Bare combined to explain the working of the current control circuit of the present invention.

As shown inFIG. 2, the reference voltage VREF1and the reference voltage VREF2are set by the system, the relationship of the voltages is VREF2>VREF1>0, and a preset current IDS is determined by the reference voltage VREF1and the resistance of the resistor RBL.
IDS=|VREF1|/RBL(1)

The rectifier203performs a full-wave rectification for an AC voltage VAC and generates an output voltage V1when the system is turned on. As shown inFIG. 3A, when the system is turned on (t=0), the output voltage V1is zero and is not enough for the LED assembly201being turned on. At this moment, the current I2flowing through the LED assembly is zero, the feedback voltage VBL on the pin BLCS is zero, the operational amplifier OP1outputs a high voltage level (HIGH), the transistor M1starts to be turned on, a loop P1is composed of the reference voltage VREF1, the operational amplifier OP1, the transistor M1, and the resistor RBL. When the output voltage V1further increases but is not enough to turn on the LED assembly (during the time period t1), the drain current I1of the transistor M1is increased due to the operational amplifier OP1, and the feedback voltage VBL on the pin BLCS is increased to the reference voltage VREF1because the LED assembly201is not turned on. At this moment, the relationship of the voltage VCS on one terminal of the resistor RCS can be represented as VCS=VBL=VREF1<VREF2because the LED assembly201is not turned on. Even though the transistor M2is turned on, the current I2flowing through the LED assembly201is zero, and the current ICS flowing through the resistor RCS can be represented as ICS=I2=0. As a result, the current IBL flowing through the resistor RBL (the current flowing through the thyristor) is equal to the drain current I1of the transistor M1, and the current IBL can be represented as IBL=I1=VREF1/RBL=IDS. As shown inFIG. 3A, the drain current I1of the transistor M1provides the compensation current for the thyristor.

As shown inFIG. 3A, due to the increase of the voltage V1(during the time period t2), the LED assembly201is turned on, a loop P2is composed of the reference voltage VREF2, the operational amplifier OP2, the transistor M2, and the resistor RCS. The current I2flowing through the LED assembly (the current flowing through the transistor M2, the current flowing through the resistor RCS) is increased due to the operational amplifier OP2. At the same time, the drain current I1of the transistor M1is decreased with the reduction of the same amount of current I2due to the operational amplifier OP1. The current IBL flowing through the resistor RBL is the sum of the drain current I1of the transistor M1and the current I2flowing through the LED assembly201, wherein the feedback voltage VBL is generated by the current IBL flowing through the resistor RBL. During the time period t2, the current I2is related to the reference voltage VREF2. If the current I2flowing through the LED assembly201is more than or equal to the preset current IDS during the time period t2, the feedback voltage VBL is more than or equal to the reference voltage VREF1, the operational amplifier OP1outputs a low voltage level (LOW), the transistor M1is turned off, and the drain current I1of the transistor M1is zero. If the current I2flowing through the LED assembly201is less than the preset current IDS during the time period t2, the feedback voltage VBL follows the reference voltage VREF1, the operational amplifier OP1still outputs a high voltage level (HIGH), the transistor M1is still turned on, and the drain current I1of the transistor M1still provides the compensation current for the thyristor.

The situations wherein the current I2flowing through the LED assembly is more than or equal to the preset current IDS and the current I2flowing through the LED assembly is less than the preset current IDS during the time period t2are described in the following.

As shown inFIG. 3B, the LED assembly201is turned on with the increase of the voltage V1(during the time period t2) if the current I2flowing through the LED assembly is more than or equal to the preset current IDS. When the drain current I1of the transistor M1is decreased to zero, the feedback voltage VBL on the pin BCLS can be represented as VBL=I2*RBL≥VREF1, and the operational amplifier OP1outputs a low voltage level (LOW) to turn off the transistor M1. The voltage VCS on a terminal of the resistor RCS at the pin CS follows the reference voltage VREF2, and the current I2flowing through the LED assembly can be represented as I2=ICS=VREF2/(RCS+RBL). At this moment, the current IBL flowing through the resistor RBL can be represented as IBL=I2=ICS because the drain current I1is zero. Similarly, when the voltage V1enters a decreasing period (during the time period t3) and the current I2flowing through the LED assembly is decreased to be less than the preset current IDS, the transistor M1is turned on again. The drain current I1is increased in the same amount with the decrement of the current I2before the drain current I1is increased to the current IDS (I1=VREF1/RBL=IDS).

The transistor M1is still turned on and the drain current I1of the transistor M1still provides the compensation current for the thyristor if the current I2flowing through the LED assembly is less than the preset current IDS during the time period t2. As shown inFIG. 3A, the LED assembly201is turned on and the voltage VCS on a terminal of the resistor RCS at the pin CS follows the reference voltage VREF2with the increase of the voltage V1(during the time period t2). As a result, the current I2flowing through the LED assembly can be represented as I2=ICS=(VREF2−VREF1)/RCS, and the current IBL flows through the resistor RBL is the sum of the drain current I1of the transistor M1and the current I2flowing through the LED assembly201(IBL=I1+I2). Similarly, the drain current I1is increased in the same amount with the decrement of the current I2when the voltage V1enters the decreasing period (during the time period t3).

In an embodiment of the present invention,FIG. 4is a schematic diagram of a current control circuit according to a first modified embodiment of the present invention. Different from the embodiment shown inFIG. 2, an inverting input terminal of the operational amplifier OP1of the transistor control circuit205receives the reference voltage VREF1, one terminal of the resistance RBL is connected to the ground, and the other terminal of the resistance RBL is connected to the non-inverting input terminal of the operational amplifier OP1. The reference voltage VREF1and the reference voltage VREF2are set by the system, the relationship of the voltages can be represented as VREF2>0>VREF1. The operational amplifier OP1outputs a high voltage level (HIGH) and the transistor M1is turned on, when the feedback voltage VBL of the other terminal of the resistor RBL at pin BCLS is more than the reference voltage VREF1. The transistor M1is turned off when the feedback voltage VBL of the other terminal of the resistor RBL at pin BCLS is less than or equal to the reference voltage VREF1.

The operational principle of the modified embodiment ofFIG. 4is the same as the operational principle of the embodiment shown inFIG. 2. When the transistor M1is turned on, the drain current I1of the transistor M1is decreased with the same amount of the increase of the current I2flowing through the LED assembly. The present invention does not repeat the description here for simplicity.

In an embodiment of the present invention,FIG. 5is a schematic diagram of a current control circuit according to a second modified embodiment of the present invention. Different from the embodiment shown inFIG. 2, an inverting input terminal of the operational amplifier OP1of the transistor control circuit205receives the reference voltage VREF1, one terminal of the resistance RBL is connected to the ground, the other terminal of the resistance RBL is connected to the non-inverting input terminal of the operational amplifier OP1, and the source of the transistor M1is connected to the pin (common source output terminal) CS. The reference voltage VREF1and the reference voltage VREF2are set by the system, the relationship of the voltages can be represented as VREF2>0>VREF1. The operational amplifier OP1outputs a high voltage level (HIGH) and the transistor M1is turned on, when the feedback voltage VBL of the other terminal of the resistor RBL at pin BCLS is more than the reference voltage VREF1. The transistor M1is turned off when the feedback voltage VBL of the other terminal of the resistor RBL at pin BCLS is less than or equal to the reference voltage VREF1.

The operational principle of the modified embodiment ofFIG. 5is the same as the operational principle of the embodiment shown inFIG. 2. When the transistor M1is turned on, the drain current I1of the transistor M1is decreased with the same amount of the increase of the current I2flowing through the LED assembly. The present invention does not repeat the description here for simplicity.

In an embodiment of the present invention,FIG. 6is a schematic diagram of a current control circuit according to a third modified embodiment of the present invention. Different from the embodiment shown inFIG. 2, the number of the LED assembly inFIG. 2is one and the number of the current module corresponding to the LED assembly inFIG. 2is one, respectively. However, the number of the LED assemblies inFIG. 6is more than one and the number of the current modules corresponding to the LED assembly inFIG. 2is more than one, respectively (for example: four or an arbitrary number, according to need).

As shown in the modified embodiment inFIG. 6, the reference voltages VREF1, VREF2, VREF3, VREF4, and VREF5are set by the system, the relationship of the voltage can be represented as VREF5>VREF4>VREF3>VREF2>VREF1>0, and the output terminals of the current modules are connected to the pin (common source output terminal) CS.

When the voltage V1is small and not enough for turning on a first LED assembly, the transistors M2, M3, M4, and M5are all turned on. However, no current passes through the transistors M2, M3, M4, and M5because the voltage V1is less than a first LED conduction voltage. With the increase of the voltage V1, when the first LED assembly is turned on, the first LED assembly and the transistor M2form a current path, the current flowing through the resistor RCS is equal to the current I2flowing through the LED assembly, and the voltage VCS follows the voltage VREF2. With the further increase of the voltage V1, when the second LED conduction voltage is turned on, the first LED assembly, the second LED assembly and the transistor M3form a current path, and the current flowing through the resistor RCS is equal to the current I3flowing through the LED assembly. If the current I3flowing through the LED assembly is more than the current IDS, the voltage VCS on one terminal of the resistor RCS at pin CS is increased with the increase of the current I3. Because the drain current I1of the transistor M1is decreased with the same amount of the increase of the current I3, and then the current I3is increased when the drain current I1is decreased to zero. At this moment, the feedback voltage VBL on pin BCLS can be represented as VBL=I2*RBL>VREF1. The operational amplifier OP1outputs a low voltage (LOW) to turn off the transistor M1due to the operation of the operational amplifier OP1. The voltage VCS follows the reference voltage VREF3, and the transistor M2is turned off because the relationship of the reference voltages is VREF3>VREF2. When the further increase of the voltage V1turns on the third LED assembly, the transistor M4, the first LED assembly, the second LED assembly and the third LED assembly form a current path, and the current flowing through the resistor RCS is equal to the current I4flowing through the LED assembly. The voltage VCS follows the reference voltage VREF4, and the transistor M3is turned off because the relationship of the reference voltages is VREF4>VREF3. When the further increase of the voltage V1turns on the fourth LED assembly, the transistor M5, the first LED assembly, the second LED assembly, the third LED and the fourth LED assembly form a current path, and the current flowing through the resistor RCS is equal to the current flowing through the LED assembly. The voltage VCS follows the reference voltage VREF5, and the transistor M4now is turned off because the relationship of the reference voltages is VREF5>VREF4. The above processes are inverted when the voltage V1is decreased.

In other words, the embodiment inFIG. 2shows that the current control circuit is provided by a single-section LED assembly, while the modified embodiment inFIG. 6shows that the current control circuit is provided by a multiple-section LED assembly (four-section LED assembly). The operational principle of the modified embodiment of theFIG. 6is the same as the operational principle of the embodiment shown inFIG. 2. The present invention does not repeat the description here for simplicity.

FIG. 7AandFIG. 7Bare voltage-current operation timing charts of a current control circuit shown inFIG. 6. The voltage-current operation timing chart of the current control circuit is shown asFIG. 7Aif the current I2flowing through the LED IDS and the current I3flowing through the LED assembly upon the first LED assembly and the second LED assembly being turned on is more than the preset current IDS. The voltage-current operation timing chart of the current control circuit is shown asFIG. 7Bif the current I2flowing through the LED assembly upon the first LED assembly being turned on is more than the preset current IDS.

FIG. 7AandFIG. 7Bare voltage-current operation timing charts of a current control circuit shown inFIG. 6.FIG. 3AandFIG. 3Bare voltage-current operation timing charts of a current control circuit shown inFIG. 2. The operational principle of theFIG. 7AandFIG. 7Bis the same as the operational principle of theFIG. 3AandFIG. 3B. The present invention does not repeat the description here for simplicity.

FIG. 8is a schematic diagram of a current control circuit according to a fourth modified embodiment of the present invention. The embodiment inFIG. 4shows that the current control circuit is provided by a single-section LED assembly, while the modified embodiment inFIG. 8shows that the current control circuit is provided by a multiple-section LED assembly (four-section LED assembly). The operational principle of the modified embodiment of theFIG. 8is the same as the operational principle of the embodiment of theFIG. 4andFIG. 6. The present invention does not repeat the description here for simplicity.

FIG. 9is a schematic diagram of a current control circuit according to a fifth modified embodiment of the present invention. The embodiment inFIG. 5shows that the current control circuit is provided by a single-section LED assembly, while the modified embodiment inFIG. 9shows that the current control circuit is provided by a multiple-section LED assembly (four-section LED assembly). The operational principle of the modified embodiment of theFIG. 8is the same as the operational principle of the embodiment ofFIG. 5andFIG. 6. The present invention does not repeat the description here for simplicity.

Based on the above description, the current control circuit of the present invention turns on the transistor M1when the current flowing through the LED assembly is less than the preset current so that the transistor M1provides the compensation current for the thyristor of the driving circuit system and turns off the transistor M1when the current flowing through the LED assembly is more than or equal to the preset current so that the transistor M1does not provide the compensation current for the thyristor of the driving circuit system to decrease the power consumption. The preset current is set by the different types of holding current of the thyristors. The thyristor maintains on the conductive state in the whole AC period to prevent flash state. The current control system of the present invention can decrease the power consumption because the current control system of the present invention does not need to set a higher LED assembly conductive current.

Furthermore, the compensation current for the thyristor provided by the current control system of the present invention decreases correspondingly with the increase of the conductive current of the LED assembly when the first LED assembly is turned on (does not produce brightness).