Abstract:
A control circuit for an electrical load in an electronic device includes a voltage divider, a current measurement circuit, a variable-current-output switch and a comparison circuit, the voltage entering the load and the voltage (and thus current) exiting from the load being monitored and compared to a reference voltage, any difference causing the switch to dynamically adjust the level of current being supplied, to protect the load from sudden variations in power supply and ensure a stable and constant supply of power.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates to an electronic device and a control circuit applied to the electronic device. 
         [0003]    2. Description of Related Art 
         [0004]    Electronic devices are usually driven by a constant current. However, external factors or internal factors may cause the voltage provided to the electronic devices or the current flowing through the electronic devices to increase abruptly, which will damage the electronic devices or may affect stability and service life of the electronic devices. Many types of control circuits are often employed in the electronic devices to adjust the current flowing through the load. However, these control circuits have a complicated structure and are expensive. 
         [0005]    Therefore, there is room for improvement within the art. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the embodiments can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
           [0007]      FIG. 1  is a block diagram of a control circuit which is employed in an electronic device, according to an embodiment. 
           [0008]      FIG. 2  is an exemplary circuit diagram of the control circuit of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Referring to  FIG. 1 , an electronic device  100  includes a power source  10 , a control circuit  20  and a load  30 . In the embodiment, the load  30  is an LED light source including multiple LED units L1˜Ln connected in series (as shown in  FIG. 2 ). The control circuit  20  monitors the voltage input to the load  30  and the current flowing through the load  30  as it flows through the load  30 , and dynamically adjusts the value of the current flowing through the load  30  according to the monitoring, in order to provide a stable constant current for the load  30 . 
         [0010]    In the embodiment, the control circuit  20  includes an alternating current and direct current (AC/DC) rectifying circuit  201 , a voltage measurement circuit  202 , a current measurement circuit  203 , a comparison circuit  204  and a switch unit  205 . The AC/DC rectifying circuit  201  converts an alternating current power source  10  into direct current, and provides the direct current to the load  30 . 
         [0011]    The voltage measurement circuit  202  is coupled to an input of the load  30 , and samples a voltage input to the load  30  so as to obtain a first sampling voltage. The current measurement circuit  203  is coupled to an output of the load  30 , and samples a current flowing through the load  30  so as to obtain a second sampling voltage. The switch unit  205  is coupled to a current path of the load  30 , and the comparison circuit  204  is coupled to the voltage measurement circuit  202 , to the current measurement circuit  203  and to the switch unit  205 . 
         [0012]    Specifically, as shown in  FIG. 2 , the voltage measurement circuit  202  is a simple voltage divider circuit. In the embodiment, the voltage divider circuit includes a first resistor R1 and a second resistor R2 connected in series. A first node A1 is formed between the first resistor R1 and the second resistor R2. The first resistor R1 is connected between the output of the load  30  and the first node A1, the second resistor R2 is connected between the first node A1 and a ground terminal, and the first node A1 is coupled to an input R of the comparison circuit  204  via a first diode D1. In the embodiment, the first sampling voltage is taken from the first node A1 and then provided to the comparison circuit  204 . 
         [0013]    The switch unit  205  includes a control terminal G coupled to an output C of the comparison circuit  204  via a resistor R5, a first path terminal D coupled to the output of the load  30 , and a second path terminal S coupled to the current measurement circuit  203 . In the embodiment, the switch unit  205  is selected from a group consisting of a metal oxide semiconductor (MOS) transistor and a bipolar junction transistor (BJT). 
         [0014]    The current measurement circuit  203  includes a third resistor R3. A second node A2 is formed between the third resistor R3 and the second path terminal S of the switch unit  205 . In the embodiment, the third resistor R3 is coupled between the second node A2 and the ground terminal, and the second node A2 is coupled to the input R of the comparison circuit  204  via a second diode D2. The second sampling voltage is taken from the second node A2 and then provided to the comparison circuit  204 . 
         [0015]    The comparison circuit  204  includes a comparator D3. In the embodiment, the comparator D1 is a three-terminal voltage regulator, and includes the input R and the output C. In use, the first sampling voltage and the second sampling voltage are input to the input R of the comparator D3, and the comparator D3 compares the first sampling voltage and the second sampling voltage with a predetermined threshold voltage. In the embodiment, the predetermined threshold voltage is preset to be equal to an interior reference voltage of the comparator D3. The comparator D3 further outputs a control signal based on the result of comparison, to control the switch unit  205  to allow a certain level of current conduction, in order to adjust the value of the current flowing through the load  30 , and provide a stable constant current for the load  30 . 
         [0016]    Specifically, if external factors cause the voltage provided to the load  30  to increase abruptly, the first sampling voltage is therefore increased; if internal factors cause the current flowing through the load  30  to increase or to decrease abruptly, the second sampling voltage is therefore increased or decreased accordingly. For each of these events, the comparator D3 compares the changed first sampling voltage or the changed second sampling voltage with the predetermined threshold voltage, and outputs a control signal based on the result of comparison, to control the switch unit  205  to switch to different levels of conduction. In the embodiment, the switch unit  205  is selectively switchable to one of different levels of conduction, by selectively applying one of different internal resistances. Thereby, the current flowing through the load  30  can be adjusted dynamically, and a stable constant current is provided to the load  30 , insulating the load  30  from damage caused by high voltages or high currents. 
         [0017]    Moreover, it is to be understood that the disclosure may be embodied in other forms without departing from the spirit thereof. Thus, the present examples and embodiments are to be considered in all respects as illustrative and not restrictive, and the disclosure is not to be limited to the details given herein.