Abstract:
A control circuit for regulating current supplied from a power source to at least one load. The control circuit has a current mirror circuit electrically coupled between the power source and the at least one load, and being capable of regulating current supplied from the power source to the at least one load at different levels; a real-time clock (RTC) circuit adapted for recording real time; and a micro control unit (MCU) electrically coupled between the RTC circuit and the current mirror circuit, and configured such that when the real time changes from a first time period to a second time period, the MCU generates control signals to trigger the current mirror circuit to regulate current supplied from the power source to the at least one load from a first level corresponding to the first time period to a second level corresponding to the second time period.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to solar powered street-lamps, and particularly to a control circuit capable of automatically controlling brightness of a solar powered street-lamp according to an environmental condition. 
         [0003]    2. Description of Related Art 
         [0004]    Nowadays, with the earth resources being depleted day by day, the cost of investment for energy increases significantly. Solar energy has drawn great attention from the energy industry as an alternative source of energy, and has found widespread applications in a variety of fields. For example, solar powered street-lamps are used in many countries. 
         [0005]    A conventional solar powered street-lamp typically includes a solar energy operated absorption board, a storage battery, and a lamp. The solar energy operated absorption board absorbs solar energy and converts it into electric energy, which is used to recharge the storage battery. The storage battery supplies power to the lamp. However, the lamp typically works at a constant maximum power, i.e., the brightest state at all times. Therefore, the conventional solar powered street-lamp unnecessarily consumes a great deal of energy, thereby increasing costs and shortening its life span. 
         [0006]    What is needed is a solar powered street-lamp control circuit for automatically controlling the brightness of the street-lamp according to environmental conditions. 
       SUMMARY OF THE INVENTION 
       [0007]    In one aspect, the present invention relates to a control circuit for regulating current supplied from a source of power to at least one load. In one embodiment, the source of power is a storage battery rechargeable from a solar energy operated absorption board. The at least one load includes at least one street lamp. In one embodiment, the control circuit has a current mirror circuit electrically coupled between the source of power and the at least one load, and being capable of regulating current supplied from the source of power to the at least one load at different levels; a real-time clock (RTC) circuit adapted for recording real time; and a micro control unit (MCU) electrically coupled between the RTC circuit and the current mirror circuit, and configured such that when the real time changes from a first time period to a second time period, the MCU generates one or more control signals to trigger the current mirror circuit to regulate current supplied from the source of power to the at least one load from a first level corresponding to the first time period to a second level corresponding to the second time period. 
         [0008]    In one embodiment, the current mirror circuit has a resistor having a first terminal and a second terminal, wherein the first terminal is connected to the source of power and a first terminal of the at least one load, and a first transistor having a base, a collector, and an emitter, wherein the collector is electrically coupled to both the base and the second terminal of the resistor, and the emitter is grounded. The current mirror circuit has N second transistors, N being a positive integer. Each second transistor has a base, a collector, and an emitter. The base of each second transistor is electrically coupled to the base of the first transistor, and the collector of each second transistor is electrically coupled to a port that is electrically coupled to a second terminal of the at least one load. Furthermore, the current mirror circuit has N electric switch elements, each electric switch element having a gate, a source, and a drain, wherein the drain of each electric switch element is electrically coupled to the emitter of a corresponding second transistor, and the source of each electric switch element is electrically coupled to a port that is grounded, and the gate of each electric switch element is electrically coupled to a corresponding output port of the MCU. In one embodiment, N=4. Each of the first transistor and the N second transistors is an NPN transistor. Each electric switch element is an N-MOS transistor. 
         [0009]    In one embodiment, the generated one or more control signals are output to the gates of corresponding one or more electric switch elements to individually turn on or turn off the corresponding one or more electric switch elements. The current, I 0 , supplied from the source of power to the at least one load is regulated according to a formula: 
         [0000]        I 0= M *[( V−Vbe )/ R ]*[β/(β+1+ M )], 
         [0000]    wherein R is a resistance of the resistor, V is a voltage of the source of power, Vbe is a voltage difference between the base and the emitter of the first transistor, β is a gain of each second transistor, and M=0, 1, 2, . . . N is the amount of electric switch elements turned on. 
         [0010]    In another aspect, the present invention relates to a solar powered street-lamp system. In one embodiment, the solar powered street-lamp system includes a storage battery rechargeable from a solar energy operated absorption board, and at least one lamp. In one embodiment, the at least one lamp has a plurality of light-emitting diodes (LEDs). The solar powered street-lamp system further includes a current mirror circuit electrically coupled between the storage battery and the at least one lamp, and being capable of regulating current supplied from the storage battery to the at least one lamp at different levels, an RTC circuit adapted for recording the real time, and an MCU electrically coupled between the RTC circuit and the current mirror circuit, and configured such that when the real time changes from a first time period to a second time period, the MCU generates one or more control signals to trigger the current mirror circuit to regulate current supplied from the source of power to the at least one load from a first level corresponding to the first time period to a second level corresponding to the second time period. 
         [0011]    In yet another aspect, the present invention relates to a control circuit for regulating current supplied from a source of power to at least one load to operate in an area thereof responsive to an environmental condition in the area. The source of power has an anode and a cathode being grounded, and is rechargeable from a solar energy operated absorption board. The at least one load has a first terminal electrically coupled to the anode of the source of power and a second terminal. In one embodiment, the at least one load comprises at least one street lamp. The environmental condition comprises a plurality of states. Each state of the environmental condition is associated with a corresponding period of time in a day. 
         [0012]    In one embodiment, the control circuit comprises a current mirror circuit. The current mirror circuit includes a resistor having a first terminal and a second terminal, wherein the first terminal is connected to the anode of the source of power; a first transistor having a base, a collector, and an emitter, wherein the collector is electrically coupled to both the base and the second terminal of the resistor, and the emitter is grounded; N second transistors, N being a positive integer, each second transistor having a base, a collector, and an emitter, wherein the base of each second transistor is electrically coupled to the base of the first transistor, and the collector of each second transistor is electrically coupled to a port that is electrically coupled to the second terminal of the at least one load; and N electric switch elements, each electric switch element having a gate, a source, and a drain, wherein the drain of each electric switch element is electrically coupled to the emitter of a corresponding second transistor, and the source of each electric switch element is electrically coupled to a port that is grounded. 
         [0013]    Furthermore, the control circuit comprises an MCU at least having N output ports, wherein each output port is electrically coupled to the gate of a corresponding electric switch element, and wherein the MCU is configured such that when the environmental condition in the area changes from one state to another state, the MCU generates one or more control signals selectively outputting to the gates of corresponding one or more electric switch elements to individually turn on or turn off the corresponding one or more electric switch elements, thereby regulating current supplied from the source of power to the at least one load responsive to the environmental condition in the area. 
         [0014]    Additionally, the control circuit comprises a timer coupled to the MCU and configured to record the real time in the area, thereby identifying a state of the environmental condition thereof. 
         [0015]    These and other aspects of the present invention will become more apparent from the following detailed description of the preferred embodiments taken in conjunction with the accompanying drawings, although variations and modifications therein may be affected without departing from the spirit and scope of the novel concepts of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a block diagram of a solar powered street-lamp control circuit according to one embodiment of the present invention; and 
           [0017]      FIG. 2  is a circuit diagram of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    The description will be made as to the embodiments of the present invention in conjunction with the accompanying drawings in  FIGS. 1 and 2 . In accordance with the purposes of this invention, as embodied and broadly described herein, this invention, in one aspect, relates to a control circuit for regulating current supplied from a source of power to at least one load to operate in an area thereof responsive to an environmental condition in the area. In one embodiment, the source of power is a storage battery rechargeable from a solar energy operated absorption board. The at least one load is a street-lamp. The environmental condition may correspond to the time when the street-lamp operates. Accordingly, the control circuit is adapted for controlling the brightness of the solar powered street-lamp according to the time when the solar powered street-lamp operates. 
         [0019]    Referring to  FIGS. 1 and 2 , a solar powered street-lamp control circuit in accordance with a preferred embodiment of the present invention is provided for controlling brightness of a solar powered street-lamp having a lamp  50  with power supplied from a storage battery  40 . The control circuit includes a current mirror circuit  10 , an RTC circuit  20 , and an MCU  30 . The storage battery  40  supplies power to the lamp  50  of the solar powered street-lamp via the current mirror circuit  10 . The MCU  30  controls current of the lamp  50  from the current mirror circuit  10  according to the RTC circuit  20 , thereby controlling brightness of the lamp  50 . In this embodiment, the storage battery  40  is rechargeable from a solar energy operated absorption board (not shown). The lamp  50  includes twelve LEDs, where each four LEDs are connected in parallel to form a parallel circuit  52 . The three parallel circuits  52  are connected in parallel. Other numbers of LEDs and/or types of electric load(s) can also be utilized in same or different configurations to practice the present invention. 
         [0020]    In this exemplary embodiment, the current mirror circuit  10  includes a resistor R 1  having two terminals, a first transistor Q 1 , four second transistors Q 2 , and four electric switch elements Q 3 . Each of the first transistor Q 1  and the four second transistors Q 2  has a base, a collector, and an emitter. Each of the four electric switch elements Q 3  has a gate, a source and a drain. The first transistor Q 1  and second transistors Q 2  are NPN transistors. The electric switch elements Q 3  are N-MOS transistors. Other numbers and types of the transistors and electric switch elements can also be utilized to practice the present invention. 
         [0021]    The storage battery  40  has a cathode that is grounded, and an anode that is electrically coupled to an anode of the lamp  50 . The anode of the storage battery  40  is also electrically coupled to one terminal of the resistor R 1 . The other terminal of the resistor R 1  is electrically coupled to the collector of the first transistor Q 1 . The emitter of the first transistor Q 1  is grounded, and the base of the first transistor Q 1  is electrically coupled to the collector of the first transistor Q 1 . Additionally, the base of the first transistor Q 1  is also electrically coupled to the base of each second transistor Q 2 . The collectors of the second transistors Q 2  are electrically coupled together and then electrically coupled to a cathode of the lamp  50 . The emitter of each second transistor Q 2  is electrically coupled to the drain of a corresponding electric switch element Q 3 . The sources of the electric switch elements Q 3  are grounded. The gate of each electric switch element Q 3  is electrically coupled to a corresponding general purpose input/output (GPIO) pin of the MCU  30 . If one of the GPIO pins of the MCU  30  outputs a high voltage control signal to the corresponding electric switch element Q 3 , the corresponding electric switch element Q 3  will be turned on. If one of the GPIO pins of the MCU  30  outputs a low voltage control signal to the corresponding electric switch element Q 3 , the corresponding electric switch element Q 3  will be turned off. In operation, the MCU  30  generates one or more control signals according to an environmental condition such as the time when the street-lamp operates. The generated one or more control signals are output into the gates of corresponding one or more electric switch elements Q 3  to turn on or turn off (i.e., control work status of) the one or more electric switch elements Q 3 , thereby regulating the current supplied from the storage battery  40  to the lamp  50 . The RTC circuit  20  is electrically coupled to the MCU  30  for recording the real time when the street-lamp operates and supplying the recorded real-time clock signals thereto. Thus, in the embodiment as shown in  FIGS. 1 and 2 , the RTC circuit  20  records real time and supplies a real-time clock signal to the MCU  30 , which in turn generates one or more control signals accordingly. 
         [0022]    For example, when the MCU  30  responsively generates control signals (i.e., the four GPIO pins of the MCU  30  all output high voltage control signals) to turn all the four electric switch elements Q 3  on, the following relationships are satisfied: 
         [0000]        I =( V−Vbe )/ R;    
         [0000]        I 1= I 2= I 3= I 4 =I [β/(β+1+4)]; and 
         [0000]        I 0= I 1+ I 2+ I 3+ I 4. 
         [0000]      Then  I 0=4[( V−Vbe )/ R ]*[β/(β+1+4)], 
         [0000]    where R is a resistance of the resistor R 1 , I is a current passing from the resistor R 1 , V is a voltage of the storage battery  40 , Vbe is a voltage difference between the base and emitter of the first transistor Q 1 , I 1 -I 4  are current passing from the collectors of the four second transistors Q 2 , respectively, I 0  is a regulated current passing from the lamp  50 , β is a gain of each second transistor Q 2 . 
         [0023]    When the MCU  30  responsively generates control signals (i.e., three of the four GPIO pins of the MCU  30  output high voltage control signals, the other one GPIO pin of the MCU  30  outputs low voltage control signal) to turn three of the four electric switch elements Q 3  on, the regulated current I 0  passing from the lamp  50  is obtained in the form of: 
         [0000]        I 0=3[( V−Vbe )/ R ]*[β/(β+1+3)]. 
         [0024]    When the MCU  30  responsively generates control signals (i.e., two of the four GPIO pins of the MCU  30  output high voltage control signals, the other two GPIO pins of the MCU  30  output low voltage control signals) to turn two of the four electric switch elements Q 3  on, the regulated current I 0  passing from the lamp  50  is obtained in the form of: 
         [0000]        I 0=2[( V−Vbe )/ R ]*[β/(β+1+2)]. 
         [0025]    When the MCU  30  responsively generates control signals (i.e., one of the four GPIO pins of the MCU  30  outputs high voltage control signal, the other three GPIO pins of the MCU  30  output low voltage control signals) to turn one of the four electric switch elements Q 3  on, the regulated current I 0  passing from the lamp  50  is obtained in the form of: 
         [0000]        I 0=[( V−Vbe )/ R ]*[β/(β+1+1)]. 
         [0026]    When the MCU  30  responsively generates control signals (i.e., the four GPIO pins of the MCU  30  all output low voltage control signals) to turn all the four electric switch elements Q 3  off, the regulated current I 0 =0. 
         [0027]    In general, for a control circuit having one first transistor, N second transistors Q 2  and N electric switch elements Q 3 , the current, I 0 , supplied from the source of power to the at least one load is regulated in the form of: 
         [0000]        I 0= M *[( V−Vbe )/ R ]*[β/(β+1 +M )], 
         [0000]    where R is a resistance of the resistor, V is a voltage of the source of power, Vbe is a voltage difference between the base and the emitter of the first transistor, β is a gain of each second transistor, and M=0, 1, 2, . . . N is the amount of which electric switch elements are turned on. 
         [0028]    In the embodiment as shown in  FIGS. 1 and 2 , the brightness of the lamp  50  can be characterized with three brightness states, which are a first brightness state, a second brightness state, and a third brightness state, respectively, and a darkness state. The brightness of the lamp  50  when it operates at the first brightness state is brighter than that of the second brightness state which, in turn, is brighter than that of the third brightness state. When the brightness of the lamp  50  is in the darkness state, the lamp  50  emits no light. Specifically, when all of the four electric switch elements Q 3  are turned on, the lamp  50  operates at the first brightness state. When three of the four electric switch elements Q 3  are turned on, the lamp  50  operates at the second brightness state. When two of the four electric switch elements Q 3  are turned on, the lamp  50  operates at the third brightness state. When all of the four electric switch elements Q 3  are turned off, the lamp  50  operates at the darkness state. Each state may be associated with a period of time when the lamp  50  operates. For examples, the first brightness state, the second brightness state, the third brightness state, and the darkness state may correspond to the brightness of the lamp  50  operating at different time periods of a day: 19:00-01:30, 01:30-04:00, 04:00-05:30, and 05:30-19:00, respectively. 
         [0029]    In one embodiment, the MCU  30  is programmably configured such that when the time is at 05:30, which is recorded by the RTC circuit  20  and the RTC circuit  20  supplies a corresponding real-time clock signal to the MCU  30 , the MCU  30  accordingly transmits a control signal to the electric switch elements Q 3  via the GPIO pins of the MCU  30  to turn all the electric switch elements Q 3  off, the lamp  50  works at the darkness state and continuously works at this state until 19:00. When the time is at 19:00, which is recorded by the RTC circuit  20  and the RTC circuit  20  supplies a corresponding real-time clock signal to the MCU  30 , the MCU  30  accordingly transmits a control signal to the electric switch elements Q 3  via the GPIO pins of the MCU  30  to turn all the electric switch elements Q 3  on, the lamp  50  transits from the darkness state to work at the first brightness state and continuously works at this state until 01:30. When the time is at 01:30, which is recorded by the RTC circuit  20  and the RTC circuit  20  supplies a corresponding real-time clock signal to the MCU  30 , the MCU  30  accordingly transmits a control signal to the electric switch elements Q 3  via the GPIO pins of the MCU  30  to turn three of the electric switch elements Q 3  on, the lamp  50  transits from the first brightness state to work at the second brightness state and continuously works at this state until 04:00. When the time is at 04:30, which is recorded by the RTC circuit  20  and the RTC circuit  20  supplies a corresponding real-time clock signal to the MCU  30 , the MCU  30  accordingly transmits a control signal to the electric switch elements Q 3  via the GPIO pins of the MCU  30  to turn two of the electric switch elements Q 3  on, the lamp  50  transits from the second brightness state to work at the third brightness state and continuously works at this state until 05:30. Then another working circle begins. Accordingly, the solar powered street-lamp saves energy effectively, and prolongs life span thereof. 
         [0030]    The configuration of the MCU  30  as disclosed above can be changed and/or adjusted according to some other environmental conditions such as weather, season, locality and so on. The brightness states of the lamp  50  can also be adjusted via selecting properly the resistance of the resistor, the amount of the second transistors Q 2 , and the gain of the second transistors Q 2 . Additionally, according to the present invention, the source of power can be any types of power sources, a solar-powered battery, a non-solar powered battery, or the like. The at least one load can also be a room lamp, an appliance, or the like. 
         [0031]    The foregoing description of the exemplary embodiments of the invention has been presented only for the purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many modifications and variations are possible in light of the above teaching. 
         [0032]    The embodiments were chosen and described in order to explain the principles of the invention and their practical application so as to enable others skilled in the art to utilize the invention and various embodiments and with various modifications as are suited to the particular use contemplated. Alternative embodiments will become apparent to those skilled in the art to which the present invention pertains without departing from its spirit and scope. Accordingly, the scope of the present invention is defined by the appended claims rather than the foregoing description and the exemplary embodiments described therein.