Electronic device

An electronic device is provided. The electronic device includes a plurality of load units, a plurality of serial-parallel switch units and a control module. The control module switches the serial-parallel switch units to a first state or a second state according to a level variation of an input voltage. Connection relations of the load units are correspondingly changed according to the level variation of the input voltage. In this way, the electronic device can be driven by an alternating-current voltage.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority benefit of Taiwan application serial no. 98133560, filed on Oct. 2, 2009. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification.

BACKGROUND

1. Field of the Invention

The invention relates to an electronic device. Particularly, the invention relates to an electronic device capable of switching load units according to an input voltage.

2. Description of Related Art

Since a light emitting diode (LED) has advantages of long service life, small size, high shock resistance, low heat generation and low power consumption, it is widely used as indicators or light sources in various home appliances and equipments. In recent years, the LEDs are developed to have features of multi-color (multicolor) and high brightness, so that application fields thereof have been extended to large outdoor billboards, traffic lights and related fields. In the future, the LEDs could even become main illumination light sources having features of power saving and environmental protection.

Generally, a control circuit of the LED first converts an alternating-current (AC) voltage into a direct-current (DC) voltage or a DC current, and then uses the stable DC voltage or the DC current to control a brightness of the LED. In other words, the conventional control circuit of the LED is generally embedded with an AC-DC converter or equipped with a transformer so as to control the LED through an AC commercial power, though in this case, not only a hardware size of the control circuit of the LED is increased, but also application convenience of the LED is limited.

SUMMARY OF THE INVENTION

The invention is directed to an electronic device, which can control load units through alternating-current (AC) commercial power without using an embedded AC/direct-current (DC) converter or a transformer.

The invention is directed to an electronic device, which has advantages of miniaturization and utilization convenience.

The invention provides an electronic device including N load units, (N−1) serial-parallel switch units and a control module, wherein N is an integer greater than 1. The load units respectively have a first terminal and a second terminal, wherein the first terminal of a first load unit is used for receiving an input voltage, and the second terminal of an N-th load unit is coupled to ground.

Moreover, the serial-parallel switch units respectively have a first terminal to a fourth terminal, wherein the first terminal of each of the serial-parallel switch units is used for receiving the input voltage, the second terminal of an i-th serial-parallel switch unit is coupled to the second terminal of an i-th load unit, the third terminal of the i-th serial-parallel switch unit is coupled to the first terminal of an (i+1)-th load unit, and the fourth terminal of each of the serial-parallel switch unit is coupled to ground, wherein i is an integer and 1≦i≦(N−1).

Moreover, the control module switches the serial-parallel switch units to a first state or a second state according to a level variation of the input voltage. When the i-th serial-parallel switch unit is in the first state, the first terminal thereof is conducted to the third terminal thereof, and the second terminal thereof is conducted to the fourth terminal thereof, and when the i-th serial-parallel switch unit is in the second state, the both first and the fourth terminals thereof are isolated which are not conducted to any other terminals, and the second terminal thereof is conducted to the third terminal thereof.

The invention provides an electronic device including N first load units, (N−1) first serial-parallel switch units, a second serial-parallel switch unit and a control module, wherein N is an integer greater than 1. The first load units respectively have a first terminal and a second terminal, and the first terminal of a 1st first load unit is used for receiving an input voltage.

Moreover, the first serial-parallel switch units respectively have a first terminal to a fourth terminal, wherein the first terminals of the first serial-parallel switch units are coupled to the first terminal of the 1st first load unit, the second terminal of an i-th first serial-parallel switch unit is coupled to the second terminal of an i-th first load unit, the third terminal of the i-th first serial-parallel switch unit is coupled to the first terminal of an (i+1)-th first load unit, and the fourth terminals of the first serial-parallel switch units are coupled to the second terminal of an N-th first load unit, wherein i is an integer and 1≦i≦(N−1).

Moreover, the second serial-parallel switch unit has a first terminal to a fourth terminal. The first terminal of the second serial-parallel switch unit is used for receiving the input voltage, the second terminal of the second serial-parallel switch unit is coupled to the second terminal of the N-th first load unit, and the fourth terminal of the second serial-parallel switch unit is coupled to ground. The control module switches the first serial-parallel switch units and the second serial-parallel switch unit to a first state or a second state according to a level variation of the input voltage. When the i-th first serial-parallel switch unit is in the first state, the first terminal thereof is conducted to the third terminal thereof, and the second terminal is conducted to the fourth terminal thereof, and when the i-th first serial-parallel switch unit is in the second state, the both first and the fourth terminals thereof are isolated which are not conducted to any other terminals, and the second terminal thereof is conducted to the third terminal thereof. When the second serial-parallel switch unit is in the first state, the first terminal thereof is conducted to the third terminal thereof, and the second terminal is conducted to the fourth terminal thereof, and when the second serial-parallel switch unit is in the second state, the both first and the fourth terminals thereof are isolated which are not conducted to any other terminals, and the second terminal thereof is conducted to the third terminals thereof

According to the above descriptions, the states of the serial-parallel switch units are switched according to the level variation of the input voltage, so that connection states of the load units are correspondingly changed along with the level variation of the input voltage. In this way, the electronic device can control the load units through AC commercial power without using an embedded AC/DC converter or a transformer. Therefore, compared to the conventional technique, the electronic device of the invention has advantages of miniaturization and utilization convenience.

DETAILED DESCRIPTION OF DISCLOSED EMBODIMENTS

FIG. 1is a circuit schematic diagram illustrating an electronic device according to an embodiment of the invention. Referring toFIG. 1, the electronic device100includes a rectifier unit110, N load units101-105, (N−1) serial-parallel switch units141-144, and a control module150, wherein N is an integer greater than 1. The control module150includes (N−1) serial-parallel control units161-164and a buck unit170. It should be noticed that the electronic device100is an illumination device, in which the load units101-105are used to produce light sources. Therefore, in an actual structure, the load units101-105respectively include a light emitting diode (LED) string and a shunt control unit, for example, LED strings121-125and N shunt control units131-135. The electronic device100further includes a voltage control unit180, which is used for supplying power required by the shunt control units131-135in the load units101-105.

Referring toFIG. 1, the rectifier unit110is used for rectifying an alternating-current (AC) voltage AC, for example, a full-wave rectification. In this way, the rectifier unit110outputs an input voltage VIN to the LED string121. The load unit101has a first terminal and a second terminal, and includes the LED string121and the shunt control unit131. The LED string121is used for receiving a voltage of the first terminal of the load unit101. Moreover, the LED string121includes M LEDs LED1-LED4, and the LEDs LED1-LED4are connected in series, wherein M is an integer greater than 1. The shunt control unit131is coupled to the LED string121and the second terminal of the load unit101. In view of a whole operation, the shunt control unit131may detect a variation of the input voltage VIN varied along with time to obtain a detection result.

Moreover, the shunt control unit131provides M shunt paths PT1-PT4through which the LEDs LED1-LED4are respectively conducted to the second terminal of the load unit101. Therefore, the shunt control unit131one-by-one turns on the shunt paths PT1-PT4in a sequence started from the first shunt path PT1as the input voltage VIN is increased along with time, and the shunt control unit131one-by-one turns off the shunt paths PT1-PT4in a sequence started from the M-th shunt path PT4as the input voltage VIN is decreased along with time. In this way, during a process that the input voltage VIN is increased along with time, the LEDs LED1-LED4are turned on one-by-one, and currents thereof are maintained around a target current. Comparatively, during a process that the input voltage VIN is decreased along with time, the LEDs LED1-LED4are turned off one-by-one, and currents thereof are still maintained around the target current.

Similarly, the LED strings122-125respectively have the same circuit structure as that of the LED string121. Namely, the LED strings122-125respectively have M LEDs connected in series. On the other hand, the shunt control units132-135respectively have the same circuit structure as that of the shunt control unit131. Therefore, the shunt control unit132may also control a current of each of the LEDs in the LED string122through the M shunt paths. Similarly, the shunt control unit133may also control a current of each of the LEDs in the LED string123through the M shunt paths. Operation mechanisms of the shunt control units134and135can be deduced by analogy.

In an actual application, the LED strings121-125may respectively have a different number of the LEDs. For example, if the LED string121is formed by a plurality of blue LEDs connected in series, and if the LED string122is formed by a plurality of red LEDs connected in series, a number NUM1of the LEDs serially connected in the LED string121can be less that a number NUM2of the LEDs serially connected in the LED string122, for example, NUM1=⅔ NUM2. In this way, cross-voltages (or optimal operating voltages) of the LED strings121and122can be relatively close. Moreover, during an actual application, each of the LEDs in the LED strings121-125can be constituted by a plurality of LEDs which are combined to serve as one unit, i.e. each of the LEDs LED1-LED4can be a plurality of LEDs connected in series, parallel, or a combination thereof.

It should be noticed that in the electronic device100, connection states of the load units101-105can be switched by the serial-parallel switch units141-144. In this way, the electronic device100can adjusts a voltage dropped on each of the LED strings121-125, so that the LED strings121-125can be still maintain to the most effectively operating voltage range and operating current range in case of a large variation range of the rectified input voltage VIN.

For example, the serial-parallel switch units141-144respectively include a first terminal to a fourth terminal TM11-TM14. The first terminals TM11of the serial-parallel switch units141-144are all used to receive the input voltage VIN, and the fourth terminals TM14of the serial-parallel switch units141-144are all coupled to ground. Moreover, the second terminal TM12of the serial-parallel switch unit141is coupled to the second terminal of the load unit101, and the third terminal TM13of the serial-parallel switch unit141is coupled to the first terminal of the load unit102. In addition, the second terminal TM12of the serial-parallel switch unit142is coupled to the second terminal of the load unit102, and the third terminal TM13of the serial-parallel switch unit142is coupled to the first terminal of the load unit103. Connection relations of the serial-parallel switch units143-144and the load units103-105can be deduced by analogy.

In view of a whole operation, when the serial-parallel switch unit141is maintained to a first state, the serial-parallel switch unit141conducts the first terminal TM11and the third terminal TM13, and conducts the second terminal TM12and the fourth terminal TM14. In this way, the load unit101is connected to the load unit102in parallel. Comparatively, when the serial-parallel switch unit141is maintained to a second state, the serial-parallel switch unit141isolates the first terminal TM11and the fourth terminal TM14, but conducts the second terminal TM12and the third terminal TM13. In this way, the load unit101is connected to the load unit102in series. On the other hand, the serial-parallel switch units142-144respectively have the same circuit structure as that of the serial-parallel switch unit141, so as to control the connection relations of the load units102-105.

On the other hand, in the electronic device100, the buck unit170and the serial-parallel control units161-164in the control module150are used to control the states of the serial-parallel switch units141-144. Here, the buck unit170is used to sense the input voltage VIN, and accordingly produces a plurality of trigger signals with reference of the input voltage VIN. Comparatively, the serial-parallel control units161-164control the states of the serial-parallel switch units141-144according to the trigger signals, so as to switch the serial-parallel switch units141-144to the first state or the second state.

In an actual application, initial states of the serial-parallel switch units141-144are maintained to the first state, so that the load units101-105are connected in parallel. In other words, when the input voltage VIN is gradually increased, in the beginning, the LED strings121-125are connected in parallel. Now, the voltage dropped on each of the LED strings121-125is the same, and the shunt control units131-135may adjust the currents of the LED strings121-125, so that each of the LED strings121-125may provide a stable light source. However, when an excessively high voltage is dropped on each of the LED strings121-125, the voltage of the LED strings121-125will exceed a predetermined value, and the LED strings121-125enter a low efficiency operating range. For avoiding the above-mentioned condition, when the input voltage VIN is increased to a certain voltage value, the serial-parallel switch unit141-144of the electronic device100may switch the connection relations of the LED strings121-125.

For example, N=4 is taken as an example, i.e. in case that the electronic device100includes four load units101-104, three serial-parallel switch units141-143and three serial-parallel control unit161-163, in the beginning, the buck unit170does not generate the trigger signal. Now, the serial-parallel switch unit141-144are maintained in the first state, so that the LED strings121-124are connected in parallel.

However, when the input voltage VIN is increased to a certain voltage value, the buck unit170outputs a first trigger signal in case that the lowered input voltage VIN complies with a first predetermined voltage (for example, 40V). Now, the serial-parallel control units161and163switch the serial-parallel switch units141and143to the second state from the first state according to the first trigger signal. In this way, the LED strings121and122are connected in series to form a link string, and the LED strings123and124are connected in series to form another link string. Moreover, the LED strings122and123are maintained in a parallel connection, i.e. the two link strings are connected in parallel. As the LED strings121and122are connected in series and the LED strings123and124are connected in series, the voltage dropped on the LED strings121-124is decreased, so that a number of the LEDs lightened in the LED strings121and122is decreased.

Comparatively, when the input voltage VIN is continually increased to another voltage value, the buck unit170outputs a second trigger signal in case that the lowered input voltage VIN complies with a second predetermined voltage (for example, 80V). Now, the serial-parallel control unit162switches the serial-parallel switch unit142to the second state from the first state according to the second trigger signal, and the serial-parallel control units161and163are still maintained to a triggered state. In this way, the serial-parallel switch units141-143are all maintained to the second state, so that the LED strings121-124are connected in series.

In other words, regarding a whole operation mechanism of the electronic device100, as the input voltage VIN is continually increased, the LED strings121-125are connected in series at the beginning, and then every two stings in the LED strings121-125are connected in series to form a link string, and the link strings are maintained in a parallel connection. Then, when the input voltage VIN is continually increased to another voltage value, every three strings in the LED strings121-125are connected in series to form a link string, and the link strings are maintained in the parallel connection. Deduced by analogy, as the input voltage VIN is continually increased, a number the LED strings connected in series in the link string is gradually increased, and a number of the link strings connected in parallel is gradually decreased until all of the LED strings121-125are connected in series.

Comparatively, when the input voltage VIN is decreased along with time, in the beginning, the LED strings121-125are connected in series, and then the LED strings121-125are divided into two link strings connected in parallel. Then, when the input voltage VIN is continually decreased to another voltage value, the LED strings121-125are divided into three link strings connected in parallel. Deduced by analogy, as the input voltage VIN is continually decreased, a number of the link strings connected in parallel is gradually increased, and a number of the LED strings connected in series in the link string is gradually decreased until the LED strings121-125are connected in parallel.

In this way, as a level of the AC voltage AC is continually varied, the electronic device100can first use the serial-parallel switch units141-144to adjust a number of the LED strings121-125connected in series, so as to roughly tune a current of each of the LED strings121-125. Then, the electronic device100uses the shunt control units131-135to fine-tune a current of each of the LEDs in the LED strings121-125. In this way, the LED strings121-125driven by the AC voltage AC can maintain a stable light source. Comparatively, the electronic device100can control the LED strings121-125through the AC commercial power without using an embedded AC/DC converter or a transformer, so that the electronic device100has advantages of miniaturization and utilization convenience.

It should be noticed that in case that the electronic device100is not embedded with the AC/DC converter, the electronic device100drives its internal circuits by extracting a plurality of node voltages formed by the LED strings121-125. For example, the electronic device100further includes a voltage control unit180, and the voltage control unit180is coupled to the shunt control units131-135. The voltage control unit180produces a reference voltage according to the input voltage VIN, and extracts a plurality of node voltages formed by the LED strings121-125, for example, node voltages V1-V3between the LEDs LED1-LED4in the LED string121. In this way, the voltage control unit180selects a node voltage from a part of the node voltages greater than the reference voltage to serve as a supply voltage VS, and uses the supply voltage VS to drive the corresponding shunt control units131-135. In this way, power consumption of the electronic device100can be effectively reduced.

To fully convey the spirit of the invention to those skilled in the art, internal circuit structures of the shunt control unit131, the serial-parallel switch unit141and the voltage control unit180are further described below.

FIG. 2is a circuit block diagram illustrating a shunt control unit according to an embodiment of the invention. InFIG. 2, the LED string121is further illustrated, and two terminals TM21and TM22of the load unit101are indicated. Referring toFIG. 2, the shunt control unit131includes a voltage sensor210, a reference current generator220, a current controller230and M current controllers241-244. In view of the whole structure, the current controllers241-244are coupled to the LEDs LED1-LED4in the LED string121for providing the shunt paths PT1-PT4through which the LEDs LED1-LED4are conducted to the second terminal TM22of the load unit101. The current controller230is coupled to the voltage sensor210, the reference current generator220and the current controllers241-244.

In view of the whole operation, the voltage sensor210is used for sensing a variation of the input voltage VIN varied along with time, and produces a corresponding sensing voltage variation signal SEV. The reference current generator220is used to generate a reference current signal IREF. The current controller241is used for detecting a current flowing through the shunt path PT1, i.e. a current difference between the LEDs LED1and LED2in the LED string121. Similarly, the current controllers242-244respectively detect currents flowing through the shunt paths PT2-PT4. The current controllers241-244further generate corresponding sensing current signals I21-I24to the current controller230. The sensing current signals I21-I24can be converted into corresponding analog voltages or digital signals for providing to the current controller230.

Now, the current controller230may obtain a current of the LED LED1by accumulating the sensing current signals I21-I24, and obtain a current of the LED LED2by accumulating the sensing current signals I22-I24. Deduced by analogy, the current controller230obtains the current information of the LEDs LED1-LED4according to the sensing current signals I21-I24. Moreover, the current controller230multiplies the reference current signal IREFby a predetermined multiple to generate a target current signal. In this way, the current controller230compares the target current signal with the sensing current signals I21-I24, and limits the currents flowing through the shunt paths PT1-PT4to be lower than a target current through shunt control signals S21-S24. It should be noticed that during the operation of limiting the currents flowing through the shunt paths PT1-PT4, the current controller230can precisely control the shunt paths PT1-PT4with reference of the sensing voltage variation signal SEVgenerated by the voltage sensor210, though the invention is not limited thereto, and those skilled in the art can determine whether the voltage sensor210is used according to an actual design requirement.

Regarding detailed operations of the shunt paths PT1-PT4, when the input voltage VIN is increased from the lowest value to a value that is great enough to light the LED LED1but is not enough to simultaneously light the LEDs LED1and LED2, the current flowing through the shunt path PT1is gradually increased from “0” to the target current. When the input voltage VIN is increased to a value that is great enough to simultaneously light the LEDs LED1and LED2but is not enough to simultaneously light the LEDs LED1-LED3, the current flowing through the shunt path PT2is gradually increased from “0”. When the current controller230detects the sensing current signal I22, the current controller230adjusts the current flowing through the shunt path PT1through the shunt control signal S21, so as to maintain the current flowing through the LED LED1around the target current. Now, the current flowing through the LED LED1is equivalent to the current flowing through the shunt path PT1plus the current flowing through the shunt path PT2.

The current controller230simultaneously controls the current flowing through the shunt path PT2through the shunt control signal S22, so that the current flowing through the shunt path PT2is not higher than the target current. Similarly, when the current controller230detects the sensing current signal I23, the current controller230adjusts the current flowing through the shunt paths PT1and PT2through the shunt control signals S21and S22, so as to maintain the currents flowing through the LEDs LED1and LED2around the target current, and control the current flowing through the shunt path PT3to be not higher than the target current. Now, the current flowing through the LED LED2is equivalent to the current flowing through the shunt path PT2plus the current flowing through the shunt path PT3. Operation mechanisms of the current controllers243-244can be deduced by analogy. In this way, the LED string121can be maintained to operate around the target current, and light up a maximum number of the LEDs “capable of being lighted up” according to the input voltage VIN.

FIG. 3is a circuit schematic diagram illustrating a voltage control unit according to an embodiment of the invention. Referring toFIG. 3, the voltage control unit180includes resistors R1and R2, resistors R31-R33, a Zener diode ZD1, N-type transistors MN1and MN21-MN23, diodes D1and D21-D24, and a capacitor C1. It is assumed that the voltage control unit180extracts the node voltages V1-V3formed by the LED string121to generate the supply voltage VS, wherein V1<V2<V3.

Referring toFIG. 3, first ends of the resistors R1and R2receive the input voltage VIN. A cathode of the Zener diode ZD1is coupled to a second end of the resistor R1, and an anode thereof is coupled to ground. A first terminal of the N-type transistor MN1is coupled to a second end of the resistor R2, and a control terminal thereof is coupled to the cathode of the Zener diode ZD1. An anode of the diode D1is coupled to a second terminal of the N-type transistor MN1, and a cathode thereof is used for generating the supply voltage VS. A first end of the capacitor C1is coupled to the cathode of the anode D1, and a second end thereof is coupled to ground.

On the other hand, anodes of the diodes D21-D23respectively receive the node voltages V1-V3, and first ends of the resistors R31-R33are respectively coupled to cathodes of the diodes D21-D23. Moreover, a first terminal of the N-type transistor MN21is coupled to a second end of the resistor R31, a control terminal of the N-type transistor MN21is coupled to the cathode of the Zener diode ZD1, and a second terminal thereof is coupled to the first end of the capacitor C1. A first terminal of the N-type transistor MN22is coupled to a second end of the resistor R32, a control terminal of the N-type transistor MN22is coupled to the cathode of the Zener diode ZD1, and a second terminal thereof is coupled to the first end of the capacitor C1. A first terminal of the N-type transistor MN23is coupled to a second end of the resistor R33, a control terminal of the N-type transistor MN23is coupled to the cathode of the Zener diode ZD1, and a second terminal thereof is coupled to the first end of the capacitor C1.

In view of a whole operation, the voltage control unit180maintains a voltage of the control terminals of the N-type transistors MN21-MN23to a specific voltage (for example, 5.7V) through the resistor R1and the Zener diode ZD1. In this way, a current loop formed by the resistor R2, the N-type transistor MN1, the diode D1and the capacitor C1can immediately produce a primary supply voltage VS according to the reference voltage in case that the input voltage VIN is excessively low and the N-type transistors MN21-MN23cannot effectively supply power to the C1to establish the supply voltage VS, and accordingly provide the primary supply voltage VS to the shunt control units131-135for utilization. Since the diode D1can provide a voltage difference of 0.6-0.7V, such power supply path with poor energy efficiency can be cut off when any of the N-type transistors is activated.

Moreover, it should be noticed that in the voltage control unit180, layout areas of the N-type transistor MN21-MN23are sequentially decreased, and resistances of the resistors R31-R33are sequentially increased. Therefore, in case that the node voltages V1-V3are all greater than the reference voltage, a current loop formed by the diode D21, the resistor R31and the N-type transistor MN21becomes a main power source. It is known that levels of the node voltages V1-V3are sequentially increased, i.e. V1<V2<V3, so that the voltage control unit180first selects the node voltage V1with the lowest level to serve as the supply voltage VS. In other words, in case that the input voltage VIN and the node voltages V1-V3are all varied, the voltage control unit180selects a node voltage closest to and greater than the reference voltage from the node voltages V1-V3to serve as the supply voltage VS, i.e. selects a path of lowest power consumption to supply power.

FIG. 4is a circuit schematic diagram illustrating a serial-parallel switch unit according to an embodiment of the invention. Referring toFIG. 4, the serial-parallel switch unit141includes a P-type transistor MP1, a diode D3, a N-type transistor MN3, a first potential control unit410and a second potential control unit420. The first potential control unit410includes resistors R4and R5, a Zener diode ZD2and a P-type transistor MP2. The second potential control unit420includes resistors R6and R7, a Zener diode ZD3and a N-type transistor MN4. The serial-parallel switch unit141is controlled by a switch signal S41generated by the serial-parallel control unit161.

As shown inFIG. 4, a first end of the resistor R4is coupled to the first terminal TM11of the serial-parallel switch unit141. The Zener diode ZD2and the resistor R4are connected in parallel to protect the P-type transistor MP2. A first end of the resistor R5is coupled to the first end of the resistor R4. A first terminal of the P-type transistor MP2is coupled to a second end of the resistor R5, and a control terminal of the P-type transistor MP2is coupled to a second end of the resistor R4and is used for receiving the switch signal S41from the serial-parallel control unit161. On the other hand, a first end of the resistor R6is coupled to a second terminal of the P-type transistor MP2, and a second end thereof is coupled to the fourth terminal TM14of the serial-parallel switch unit141. The Zener diode ZD3and the resistor R6are connected in parallel for protecting the N-type transistor MN4. A first terminal of the N-type transistor MN4is coupled to the first terminal TM11of the serial-parallel switch unit141, and a control terminal thereof is coupled to the first end of the resistor R6. A first end of the resistor R7is coupled to a second terminal of the N-type transistor MN4, and a second end thereof is coupled to the second end of the resistor R6.

On the other hand, a first terminal of the P-type transistor MP1is coupled to the first terminal TM11of the serial-parallel switch unit141, a control terminal thereof is coupled to the second end of the resistor R5, and a second terminal thereof is coupled to the third terminal TM13of the serial-parallel switch unit141. A cathode of the diode D3is coupled to the second terminal of the P-type transistor MP1, and an anode thereof is coupled to the second terminal TM12of the serial-parallel switch unit141. A first terminal of the N-type transistor MN3is coupled to the anode of the diode D3, a control terminal thereof is coupled to the first end of the resistor R7, and a second terminal thereof is coupled to the fourth terminal TM14of the serial-parallel switch unit141.

In view of a whole operation, as a level of the switch signal S41is switched, the first potential control unit410and the second potential control unit420synchronously operate, so that the serial-parallel switch unit141is switched to the first state or the second state. When the serial-parallel switch unit141is maintained in the first state, the P-type transistor MP1and the N-type transistor MN3are maintained in a conducting state, so that the first terminal TM11and the third terminal TM13of the serial-parallel switch unit141are electrically connected, and the second terminal TM12and the fourth terminal TM14of the serial-parallel switch unit141are electrically connected. Comparatively, when the serial-parallel switch unit141is maintained in the second state, the P-type transistor MP1and the N-type transistor MN3are maintained in a non-conducting state, and the diode D3is conducted. Now, the second terminal TM12and the third terminal TM13of the serial-parallel switch unit141are electrically connected, and the first terminal TM11and the fourth terminal TM14of the serial-parallel switch unit141are not electrically connected. Now, the load unit101connected to the second terminal TM12of the serial-parallel switch unit141and the load unit102connected to the third terminal TM13of the serial-parallel switch unit141are connected in series.

It should be noticed that the serial-parallel switch unit141ofFIG. 4uses the switch signal S41to control the first potential control unit410, and then the first potential control unit410drives the second potential control unit420, so the first potential control unit410and the second potential control unit420can synchronously operate. However, in an actual application, as shown inFIG. 5, the serial-parallel switch unit can use the switch signal S41to control the second potential control unit420, and then the second potential control unit420drives the first potential control unit410, so as to achieve the synchronous operation of the first potential control unit410and the second potential control unit420. Different to the serial-parallel switch unit141ofFIG. 4, in the serial-parallel switch unit141ofFIG. 5, the second potential control unit420receives the switch signal S41through the control terminal of the N-type transistor MN4, and the first potential control unit410is coupled to the fourth terminal TM14of the serial-parallel switch unit141through the second terminal of the P-type transistor MP2. Moreover, the second potential control unit420is coupled to the control terminal of the P-type transistor MP2in the first potential control unit410through the first terminal of the N-type transistor MN4. It should be noticed that the diode D3shown inFIG. 5can also be implemented by an equivalent circuit with a unidirectional conduction effect or a bi-directional conduction effect. The first potential control unit410and the second potential control unit420can also be implemented by other control circuits.

FIG. 6is a circuit schematic diagram illustrating an electronic device according to another embodiment of the invention. Referring toFIG. 6, the electronic device600includes a plurality of load units611-616, a plurality of serial-parallel switch units621-625, and a control module630. Similar to the embodiment ofFIG. 1, the electronic device600can use the control module630to control states of the serial-parallel switch units621-625, so as to switch connection relations of the load units611-616.

In the embodiment ofFIG. 6, as the connection relation of the load units611-616is varied, different serial-parallel connection effects can be achieved. For example, shown in a table 1 andFIGS. 7A-7D, when the serial-parallel switch units621-625are all in a first state (a parallel state), an effect that the load units611-616are all connected in parallel as that shown inFIG. 7Ais obtained. When the serial-parallel switch units621,623and625are all in a second state (a serial state), and the serial-parallel switch units622and624are all in the first state (the parallel state), an effect that every two of the load units611-616are connected in series as that shown inFIG. 7Bis obtained. When the serial-parallel switch units621,622,624and625are all in the second state (the serial state), and the serial-parallel switch unit623is in the first state (the parallel state), an effect that every three of the load units611-616are connected in series as that shown inFIG. 7Cis obtained. When the serial-parallel switch units621-625are all in the second state (the serial state), an effect that the load units611-616are all connected in series as that shown inFIG. 7Dis obtained.

Moreover, a main difference between the embodiments ofFIG. 6andFIG. 1is that the load units611-616may respectively include a resistor, a capacitor, an inductor, a diode, a bipolar transistor, a field effect transistor, a light emitting diode, a laser diode, a photo sensor, a signal receiver, a signal transmitter, a battery, a DC power supply, or a combination thereof. Therefore, as the components of the load units611-616are different, one or a plurality of the load units611-616can be used to store energy, so as to provide power to the LEDs when external power is inadequate.

Moreover, one or a plurality of the load units611-616can be used for receiving external cable or wireless signals, so as to adjust a reference current value within the control module to a achieve an effect of adjusting a light emitting brightness or chrominance (color). Moreover, one or a plurality of the load units611-616can be used for sending signals to other external control systems, or used for controlling the other LED strings. Moreover, one or a plurality of the load units611-616can be used as a stable power supply for supplying power to other system for utilization.

It should be noticed that when the load units611-616do not require an additional supply voltage, configuration of the voltage control unit180ofFIG. 1in the electronic device600is unnecessary. Moreover, the rectifier unit110ofFIG. 1can also be disposed at an external circuit according to a design requirement, so that the rectifier unit can be selectively configured in the electronic device600. Detailed circuit structures and operation principles of the components in the electronic device600have been described in the aforementioned embodiment, so that detailed descriptions thereof are not repeated.

Further, the first terminals of the serial-parallel switch units ofFIG. 1andFIG. 6are all coupled to the input voltage VIN, i.e. the highest voltage, and the fourth terminals of the serial-parallel switch units are all coupled to ground, i.e. the lowest voltage. However, in an actual application, the serial-parallel switch units and the load units can be coupled according to another approach to achieve the similar switching operation.

For example,FIG. 8is a circuit schematic diagram illustrating an electronic device according to still another embodiment of the invention. The electronic device800includes a plurality of load units811-814, a plurality of serial-parallel switch units821-823and a control module830. A main difference between the embodiment ofFIG. 8and the embodiments ofFIG. 1andFIG. 6is that in the embodiment ofFIG. 8, the load units811-812and the serial-parallel switch unit821are regarded as a whole unit, and the load units813-814and the serial-parallel switch unit823are regarded as another whole unit, and a serial-parallel connection between the two whole units is controlled by the serial-parallel switch unit822. Moreover, regarding detailed connection relations, the fourth terminal of the serial-parallel switch unit821is coupled to the second terminal of the load unit812, and the fourth terminal of the serial-parallel switch unit823is coupled to the second terminal of the load unit814.

Moreover, similar to the embodiments ofFIG. 1andFIG. 6, the electronic device800can use the control module830to control the states of the serial-parallel switch units821-823, so as to switch the connection relations of the load units811-814. For example, in the embodiment ofFIG. 8, as shown in a table 2 andFIGS. 9A-9C, when the serial-parallel switch units821-823are all in a first state (a parallel state), an effect that the load units811-814are all connected in parallel as that shown inFIG. 9Ais obtained. When the serial-parallel switch units821and823are all in a second state (a serial state), and the serial-parallel switch unit822is in the first state (the parallel state), an effect that every two of the load units811-814are connected in series as that shown inFIG. 9Bis obtained. When the serial-parallel switch units821-823are all in the second state (the serial state), an effect that the load units811-814are all connected in series as that shown inFIG. 9Cis obtained.

Moreover, the load units811-814shown inFIG. 8may respectively include different passive devices, active devices, or a combination of the passive devices or the active devices. In addition, a rectifier unit and a voltage control unit can also be selectively configured in the electronic device800according to a design requirement. Detailed circuit structures and operation principles of the components in the electronic device800have been described in the aforementioned embodiment, so that detailed descriptions thereof are not repeated.

It should be noticed that regardless whether the coupling method of the serial-parallel switch units and the load units ofFIG. 1andFIG. 6is used, or the coupling method ofFIG. 8is used, a serial-parallel switch unit and a capacitor can be added to further increase a performance of the electronic device.

For example, it is assumed that a serial-parallel switch unit801and a capacitor C81are added to the electronic device800ofFIG. 8, and the load units811-814have the same circuit structure as that of the load units101-105ofFIG. 1, i.e. the load units811-814respectively include a LED string and a shunt control unit, and the electronic device800is additional configured with a voltage control unit to provide a voltage source required by the shunt control units of the load units811-814. Moreover, it is further assumed that an operating voltage of the LED strings in the load units811-814is more than 12V, and is preferably between 20V and 40V to achieve an optimal operating efficiency.

In this case, at the beginning, the load units811-814are all connected in parallel. Then, during a process that the input voltage VIN is increased from 0V to 12V for the first time, the input voltage VIN cannot light the LED strings in the load units811-814, but the input voltage VIN can continually charge the capacitor C81, so that the capacitor C81may have an electricity quantity of 12V. When the input voltage VIN reaches 12V for the first time and is lower than 20V, the LED strings in the load units811-814are lightened, though the LED strings are not in the optimal voltage operating range, and now the electricity quantity stored in the capacitor C81is gradually increased to 20V. When the input voltage VIN reaches 20V for the first time and is lower than 40V, the LED strings in the load units811-814are in the optimal voltage operating range, and the electricity quantity stored in the capacitor C81is gradually increased to 40V.

When the input voltage VIN reaches 40V for the first time and is lower than 80V, the serial-parallel switch units821,823and801are switched to the second state (the serial state), and now the LED strings in the load units811-814are changed to a connection state that every two of the LED strings connected in series, and a cross-voltage of each of the LED strings is ½ of the input voltage VIN. Now, the cross-voltage of each of the LED strings is gradually increased from 20V (a half of 40V) to 40V (a half of 80V), so that the LED strings are still in the optimal voltage operating range, though the capacitor C81is isolated from external, and is maintained to 40V.

When the input voltage VIN reaches 80V, the serial-parallel switch units821˜823and801are all switched to the second state (the serial state), and the LED strings are all connected in series, and a cross-voltage of each of the LED strings is ¼ of the input voltage VIN. Now, the cross-voltage of each of the LED strings is between 20V (¼ of 80V) and 39V (¼ of a highest voltage155obtained after the 110V AC voltage is rectified), so that the LED strings are still in the optimal voltage operating range. Moreover, the capacitor C81is still isolated from external, and is maintained to 40V.

When the input voltage VIN is decreased to be lower than 80V but higher than 40V, the serial-parallel switch unit822is switched to the first state (the parallel state), and now the LED strings are changed back to the connection state that every two of the LED strings are connected in series, and the respective cross-voltage is changed back to ½ of the input voltage VIN. Now, the cross-voltage of each of the LED strings is between 20V and 40V, so that the LED strings are still in the optimal voltage operating range. Moreover, the capacitor C81is still isolated from external, and is maintained to 40V.

When the input voltage VIN is decreased to be lower than 40V, the serial-parallel switch units821-823are all switched to the first state (the parallel state), and now the LED stings are connected in parallel, and are connected to the capacitor C81in parallel. Now, the input voltage VIN is lower than the voltage of the capacitor C81, so that the capacitor C81replaces the input voltage VIN to become the power source for the LED strings. Here, as long as the capacitance of the capacitor C81is enough, it can maintain the LED strings in the optimal voltage operating range (>20V) until a next voltage increasing cycle for more than 20V. In this way, the LED strings can be maintained in a light up state, so as to eliminate a flicking problem of the light source.

It should be noticed that in the electronic device800ofFIG. 8, two load units and one serial-parallel switch unit are regarded as a whole unit, and another serial-parallel switch unit is used to switch the serial-parallel connection of the whole structure. However, in the actual application, those skilled in the art can extend the whole structure ofFIG. 8to a plurality of load units and a plurality of serial-parallel switch units.

For example,FIG. 10is a circuit schematic diagram illustrating an electronic device according to yet another embodiment of the invention. The electronic device1000includes a plurality of load units1100_1-1100—nand1200_1-1200—n,a plurality of serial-parallel switch units1300_1-1300—m,1400,1500_1-1500mand1600, and a control module1700. InFIG. 10, the load units1100_1-1100—nand the serial-parallel switch units1300_1-1300—mare regarded as a whole structure, and the load units1200_1-1200—nand the serial-parallel switch units1500_1-1500—mare regarded as another whole structure, and the serial-parallel connection between the two whole structures are controlled by the serial-parallel switch unit1400. Similarly, a third terminal of the serial-parallel switch unit1600can be used to connect another whole structure. Deduced by analogy, the electronic device1000can be formed by a plurality of whole structures. Moreover, the control module1700is used for controlling the states of the serial-parallel switch units1300_1-1300—m,1400,1500_1-1500—mand1600, so that the connection relations of the load units1100_1-1100—nand1200_1-1200—nare correspondingly varied long with a level variation of the input voltage VIN. Detailed circuit structures and operation principles of the components in the electronic device1000have been described in the aforementioned embodiment, so that detailed descriptions thereof are not repeated.

In summary, the serial-parallel switch units are used to switch the connection states of the load units, which are performed according to a level variation of the input voltage. In this way, the electronic device of the invention can be directed operated under the AC voltage without additionally configuring an AC/DC converter or using a transformer. Therefore, the electronic device of the invention has advantages of miniaturization and utilization convenience.