Abstract:
A light emitting diode driving circuit comprising a power supply circuit, a rectifier circuit, a light emitting diode load and a controlling circuit. The rectifier circuit is connected between the power supply circuit and one port of the light emitting diode load. The other port of the light emitting diode load is connected to ground through a transistor. of the controlling circuit. The power supply circuit, the rectifier circuit, the light emitting diode load are connected to the ground when the transistor is turned on and disconnected from the ground when the transistor is turned off. The controlling circuit further comprises a pulse generating unit which controls the turn on/off of the transistor.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure generally relates to light emitting diode driving circuits. 
         [0003]    2. Description of Related Art 
         [0004]    Nowadays, light emitting diodes (LEDs) have been used extensively as light source for illuminating devices due to their high luminous efficiency and low power consumption. In view of currently popularized energy saving and emission reduction, it would be much satisfied to provide an LED illuminating device equipped with a power saving driving circuit. 
         [0005]    Therefore, what is needed is to provide a power saving driving circuit for an LED illuminating device. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    Many aspects of the disclosure 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 disclosure. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the whole view. 
           [0007]      FIG. 1  is a block diagram of a light emitting diode driving circuit of the present disclosure. 
           [0008]      FIG. 2  is a circuit diagram of the light emitting diode driving circuit in accordance with an exemplary embodiment of the present disclosure. 
           [0009]      FIG. 3  is a circuit diagram of the light emitting diode driving circuit in accordance with an alternative embodiment of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    Reference will now be made to the drawing to describe the present light emitting diode driving circuit, in detail. 
         [0011]    Referring to  FIG. 1 , a light emitting diode (LED) driving circuit  10  according to an exemplary embodiment includes a power supply circuit  11 , a rectifier circuit  12 , a light emitting diode load  13  and a controlling circuit  14 . 
         [0012]    The power supply circuit  11  is configured for receiving an alternating current voltage, and converting the alternating current voltage into a working voltage suitable for the light emitting diode load  13 . Referring to  FIG. 2 , in this embodiment, the power supply circuit  11  includes a voltage transformer “T” with a primary winding  110  and a secondary winding  112 . The primary winding  110  is connected to an exterior power supply, thereby receiving an alternating current voltage. The secondary winding  112  is configured for generating the working voltage in condition of receiving an electromagnetic excitation from the primary winding  110 , and output the working voltage to the rectifier circuit  12 . The voltage value generated by the secondary winding  112  can be adjusted according to winding turns ratio of the primary winding  110  and the secondary winding  112 . 
         [0013]    The rectifier circuit  12  is connected to the secondary winding  112 . The rectifier circuit  12  rectifies the work voltage outputted by the secondary winding  112  and successively transforms the work voltage to the light emitting diode load  13  into a form of direct current voltage. In this embodiment, the rectifier circuit  12  includes a rectifier diode “D”. An anode of the rectifier diode “D” is connected to the secondary winding  112 , and a cathode of the rectifier diode “D” is connected to the light emitting diode load  13 . The rectifier circuit  12  can further include a capacitor “C” connected between the cathode of the rectifier diode “D” and ground. The capacitor “C” is configured for filtering noise of the work voltage. 
         [0014]    The light emitting diode load  13  includes a plurality of light emitting diodes “LED 1 ”, “LED 2 ”, . . . , “LEDn”, for receiving the work voltage and emitting light. The plurality of light emitting diodes can be connected together in series connection, parallel connection or series-parallel connection. In the shown embodiment, the light emitting diodes “LED 1 ”, “LED 2 ”, . . . , “LEDn” are connected together in series connection. 
         [0015]    The controlling circuit  14  is configured for controlling the light emitting diode load  13  to emit light periodically. In this embodiment, the controlling circuit  14  includes a pulse generating unit  140  and a switch unit  142 . 
         [0016]    The pulse generating unit  140  is connected to the switch unit  142  and configured for outputting a periodical pulse signal to the switch unit  142 . In this embodiment, the pulse generating unit  140  is a frequency oscillator “U”. The frequency oscillator “U” is connected to the switch unit  142 , thereby outputting a pulse width modulation (PWM) signal to the switch unit  142 . 
         [0017]    The switch unit  142  is configured for receiving the pulse signal output by the pulse generating unit  140 . In condition that the pulse signal has a high electrical level, the switch unit  142  switches on the electrical connection between the light emitting diode load  13  and the ground. In condition that the pulse signal has a low electrical level, the switch unit  142  switches off the electrical connection between the light emitting diode load  13  and the ground. As such, the light emitting diode load  13  emits light periodically according to the electrical level of the pulse signal output by the pulse generating unit  140 . In this embodiment, the switch unit  142  includes a bipolar transistor “Q”. A base terminal of the bipolar transistor “Q” is connected to an output port of the switch unit  142 , thereby receiving the pulse signal output by the pulse generating unit  140 . A collector terminal of the bipolar transistor “Q” is connected to the light emitting diode load  13 . An emitter terminal of the bipolar transistor “Q” is connected to the ground. 
         [0018]    When the frequency oscillator “U” outputs a high electrical level to the base terminal of the bipolar transistor “Q”, the bipolar transistor “Q” is in a conductive state. The light emitting diode load  13  is connected to the ground by the collector terminal and the emitter terminal of the bipolar transistor “Q”. As such, the power supply circuit  11 , the rectifier circuit  12 , the light emitting diode load  13  and the ground together form a closed loop, and hence, the light emitting diode load  13  emits light. 
         [0019]    When the frequency oscillator “U” outputs a low electrical level to the base terminal of the bipolar transistor “Q”, the bipolar transistor “Q” is in a cut off state. Electrical connection between the light emitting diode load  13  and the ground is cut off. As such, the light emitting diode load  13  doesn&#39;t emit light. 
         [0020]    Accordingly, the light emitting diode load  13  periodically emits light with a frequency in accordance with the pulse signal of the frequency oscillator “U”. As long as the frequency of the pulse signal is at least 50 hertz, the periodical turn on/off of the light emitting diode load  13  will not influence human visual sense of the light generated thereby. 
         [0021]    Due to that the light emitting diode load  13  doesn&#39;t emit light all the time, the work time is reduces and effect of power saving is achieved. 
         [0022]    Furthermore, the power supply circuit  11 , the rectifier circuit  12 , the light emitting diode load  13  and the controlling circuit  14  each can have a variety of configurations only if it is capable of achieving the above described function. 
         [0023]    For example, referring to  FIG. 3 , the base terminal of the bipolar transistor “Q” can be connected to the output port of the pulse generating unit  140  by a resistor R 1 , and be connected to the cathode of the rectifier diode “D” by a resistor R 2 . 
         [0024]    In condition that the pulse generating unit  140  has a low level output, the frequency oscillator “U” connects the base terminal of the bipolar transistor “Q” to ground through the resistor R 1 , thereby making the bipolar transistor “Q” be in a cut off state. As such, the power supply circuit  11 , the rectifier circuit  12 , the light emitting diode load  13  and the ground together can&#39;t form a closed loop, and hence, the light emitting diode load  13  doesn&#39;t emit light. 
         [0025]    In condition that the pulse generating unit  140  has a high level output, the frequency oscillator “U” cuts off the connection between the base terminal of the bipolar transistor “Q” and ground, and the resistor R 2  connected to the rectifier diode “D” provides a high level output to the bipolar transistor “Q”. As such, the bipolar transistor “Q” is in a conductive state. The power supply circuit  11 , the rectifier circuit  12 , the light emitting diode load  13  and the ground together form a closed loop, and hence, the light emitting diode load  13  emits light. Due to that the bipolar transistor “Q” is driven by a high electrical level provided by the rectifier circuit  12  instead of the pulse signal provided by the pulse generating unit  140 , the circuit configuration illustrated in  FIG. 3  is much stable than that of  FIG. 2 . 
         [0026]    It is to be understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments without departing from the spirit of the disclosure as claimed. The above-described embodiments illustrate the scope of the disclosure but do not restrict the scope of the disclosure.