Abstract:
Disclosed is a solar powered lamp adopting a cold-cathode fluorescent lamp and an auxiliary startup device which can improve the efficiency of the voltaic-photo transformation when lighting the cold-cathode fluorescent lamp. The device comprises a direct current power unit, a DC/AC inverter circuit for generating a high voltage alternating current from the DC voltage to light a CCFL; and an auxiliary startup circuit disposed between the DC power supply unit and the DC/AC inverter circuit for generating across the input terminals of the DC/AC inverter circuit a voltage of about twice of the DC voltage output from the DC power supply unit.

Description:
CROSS REFERENCE OF RELATED APPLICATIONS  
       [0001]     The present application claims the benefit of Chinese application No. 03267219.5 filed on Jul. 2, 2003, entitled solar powered lamp, which is explicitly incorporated herein by reference in its entirety.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     This invention relates to a solar powered lamp, particularly to a solar powered lamp having a cold-cathode fluorescent bulb, and more particularly to a solar powered lamp with a cold-cathode fluorescent bulb and an auxiliary startup device.  
         [0004]     2. Description of the Related Art  
         [0005]     Solar powered lamp has been commonly used in place of the electrically powered lamp to illuminate pathways, yards, parks and other areas, for the purpose of saving existing fuel resources and protecting the environment from pollution.  
         [0006]     U.S. Pat. No. 5,155,668 entitled “Solar Power Lamp Utilizing Cold Cathode Fluorescent Illuminating and Method of Facilitating Same” discloses a solar powered lamp, which utilizes photovoltaic devices to charge batteries which can activate a light source formed by the CCFL, in the absence of sunlight.  
         [0007]     Conventionally, in a device for driving a cold-cathode fluorescent lamp (CCFL), as disclosed in the &#39;668 patent, a direct-current voltage is needed to be converted into a high-tension alternating voltage by a “direct-current voltage/alternating voltage” inverter circuit (hereinafter referred to as a DC/AC inverter circuit). Then the resulting high-tension alternating voltage is supplied to the cold-cathode fluorescent lamp to light it.  
         [0008]     In the cold-cathode fluorescent lamp, the value of the alternating voltage which is required to drive the lamp is about two or three times of the voltage which is required to light the lamp. Therefore, if the DC/AC inverter circuit converts, for example, a DC voltage of 4 volts directly to AC voltage of 1800 volts, and the CCFL operates at about 400 volts, the efficiency of the voltaic-photo transformation will be decreased significantly.  
       SUMMARY OF THE INVENTION  
       [0009]     It is, therefore, an object of the present invention to provide a device for lighting a cold-cathode fluorescent lamp which can overcome the above-mentioned defects in the prior art.  
         [0010]     According to the present invention, the cold-cathode fluorescent lamp lighting device comprises a direct current (DC) power unit, a DC/AC inverter circuit for generating a high voltage alternating current (AC) from the DC voltage to light a CCFL; and an auxiliary startup circuit disposed between the DC power supply unit and the DC/AC inverter circuit for generating across the input terminals of the DC/AC inverter circuit a voltage of about twice of the DC voltage output from the DC power supply unit.  
         [0011]     In one embodiment of the invention, the auxiliary startup circuit comprises a first transistor and a second transistor each having a base, collector and emitter, the emitters are coupled together to one output terminal of the DC power supply unit, the bases are coupled to another output terminal of the DC power supply unit, the collector of the first transistor being coupled to the ground, and the collector of the second transistor being coupled to the DC/AC inverter circuit; and a capacitor coupled between the collector of the first transistor and the emitter of the second transistor.  
         [0012]     Another object of the present invention is to provide a solar powered lamp utilizing the CCFL which can improve the efficiency of the transformer when turning on the CCFL lamp. The solar powered lamp of the present invention is powered by the photovoltaic cells (also referred to as a solar cell array) which charge an electrical storage device, such as a battery for providing power to the CCFL, in the absence of sunlight.  
         [0013]     The solar powered lamp of the present invention comprises a photovoltaic cell receiving sunlight and generating electrical energy; an electrical storage device coupled to the photovoltaic cell for storing the electrical energy generated by the photovoltaic cell and providing low voltage DC; a DC/AC inverter circuit for generating a high voltage alternating current (AC) from the DC voltage to light a CCFL; and an auxiliary startup circuit disposed between the electrical storage device and the DC/AC inverter circuit for generating across the input terminals of the DC/AC inverter circuit a voltage of about twice of the DC voltage output from the electrical storage device.  
         [0014]     Another object of the present invention is to provide a method for activating the CCFL which comprises a first step of generating across the input terminals of the DC/AC inverter circuit a voltage of about twice of the DC voltage output from a DC power supply device, a second step of generating a high AC voltage to startup the CCFL from the generated voltage, and a third step of providing the DC/AC inverter circuit with the DC output from the DC power supply device after the CCFL is started.  
         [0015]     The nature, principle and utility of the invention will become more apparent from the following detailed description together with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]      FIG. 1  is a perspective exploded view showing an exemplary solar powered lamp utilizing a CCFL lighting device according to the invention; and  
         [0017]      FIG. 2  is a schematic diagram of the circuitry of the CCFL lighting device according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0018]      FIG. 1  is a perspective exploded view of an exemplary solar powered lamp  10  utilizing the CCFL lighting device in accordance with an embodiment of the present invention. The solar powered lamp may be positioned at any desired location for any desired application.  
         [0019]     As shown in  FIG. 1 , a solar powered lamp  10  comprises a solar cell array plate  1  for converting solar power into electricity power, a CCFL  5  for illuminating, and a storage battery  7  for storing the electricity power from the solar cell plate  1  and powering the CCFL  5 , and a circuit plate  3  for implementing power transmission, all of which are electrically connected with each other.  
         [0020]     Specifically, a seat  2  composed of an upper cover  21 , a translucent mask  22 , a mid cover  23  and a lower cover  24  forms the main body of the solar powered lamp  10 . A bracket  8  is fixed at the bottom of the main body for supporting the main body of the lamp  10 . One end of the bracket  8  supports the main body and the other end of the same is preferably to be in the form of a sharp tip. In this way, the lamp  10  maybe easily inserted into the ground of any desired locations, for instance, into a garden, roadside, etc.  
         [0021]     The translucent mask  22  is cylindraceous for accommodating an illumination device, e.g. a CCFL  5  and is fixed between the upper cover  21  and mid cover  23 . The mid cover  23  is detachably attached to the lower cover  24 . The solar cell array plate  1  is positioned at the top of the upper cover  21  in the form of exposure to sunlight.  
         [0022]     The CCFL  5  is positioned within the translucent mask  22 . A sleeve  4  comprising an upper lid  41  and a lower lid  42  is used for protecting the CCFL  5 . A supporting pole  6  may be provided for supporting the CCFL at an appropriate position. Low efficacy of lighting and the short lamp life will be resulted when the CCFL works under the ambient condition of frostiness. According to a preferred embodiment of the invention, a translucent casing  25  can be provided between the CCFL  5  and the cylindraceous translucent mask  22 . In this case, when the CCFL bulb is started, the temperature of the air inside the casing is heated by the irradiation of the bulb and the casing prevents the heat inside the casing from escaping outside, thereby protecting the bulb and improving the life of the CCFL.  
         [0023]     Furthermore, a plurality of ribs  26  can be provided on the sidewall of the cylindraceous translucent mask  22  as shown in  FIG. 1 , or on the side wall of the casing  25  (not shown) to thereby diffuse the light and effect the soft sense of the light.  
         [0024]     A storage battery  7  is placed inside an appropriate location of the main body of the lamp  10 , for instance, between the mid cover  23  and lower cover  24 . In the daytime, the solar cell array plate  1  is exposed to sunlight for converting the solar power into electricity power to charge the storage battery  7 . When the sunlight is not sufficient, the storage battery  7  begins to discharge for powering the CCFL  5 .  
         [0025]      FIG. 2  schematically shows a preferred embodiment of the circuit plate  3  used in the solar-powered lamp according to the invention, which comprises five blocks: a circuit  31  for protecting the battery from over-discharging, a circuit  32  for automatically switching on/off the lamp according to the ambient light condition, a circuit  33  for boosting the output from the battery  7  when starting the CCFL  5 , a DC/AC inverter circuit  34  for generating an AC high voltage from the DC voltage to light the CCFL, and a main power supply circuit  35  for providing the current output from the battery  7  to the DC/AC inverter circuit  34 , all of which will be described in detail in the following by ways of example for the purpose of illustration of the invention, and these illustrations are not intended to constitute any limitation to the invention.  
         [0026]     The circuit  31  comprises an operational amplifier U 1 A configured as a comparator. The operational amplifier U 1 A can be a LM393, known to those skilled in the art. A resistor R 1  is connected between the positive terminal of the battery  7  and a voltage stabilizer U 2 . The junction between the resistor R 1  and the voltage stabilizer U 2  is connected to the non-inverter input terminal A of the U 1 A to form a voltage reference source Vref coupled to the terminal A. The voltage stabilizer U 2  can be formed by an IC circuit such as a TL431, known to those skilled in the art. The value of the voltage reference source Vref is selected depending on the type of the battery  7 . For example, Vref can be 3.5-3.6 volts in case the rated voltage output from the battery  7  is 4 volts. The junction of the resistors R 2  and R 3  is connected to the inverter input terminal B of the operational amplifier U 1 A. Exemplary resistance values for resistors R 1 , R 2  and R 3  are 10K, 24K and 12K ohms, respectively.  
         [0027]     The circuit  31  further comprises a switching circuit composed of a transistor Q 1 . A resistor R 4  is coupled between the emitter of the transistor Q 1  and the output of the operational amplifier U 1 A and operates as a pull-up resistor for the transistor Q 1 . A resistor R 5  connected between the output of the operational amplifier U 1 A and the base of the transistor Q 1  is a limiting resistor for preventing the transistor Q 1  from being damaged by the overwhelming current through the base. A capacitor C 1  in parallel with the resistor R 5  is a speedup capacitor for temporarily increasing the current flowing through the transistor Q 1  when turning on the transistor Q 1 . Exemplary resistance values for resistors R 4  and R 5  are 51K and 3 K ohms, respectively. The capacitor C 1  has an exemplary capacitance value of 0.01 μF.  
         [0028]     When the battery  7  is in a normal condition, i.e., the voltage output of the battery  7  is constant at its rated voltage level, the potential level at the terminal B 1  produced by dividing the voltage output from the battery by resistors R 2  and R 3  is higher than that at the non-inverter terminal A 1 . The operational amplifier U 1 A outputs the low level to turn on the transistor Q 1 , a PNP bipolar transistor in this embodiment such as a 8550 known in the art, resulting in the current flowing through the CCFL bulb  5 . On the other hand, when the output voltage of the battery  7  drops below the rated value due to the exhaust of the energy, the potential level at the non-inverter terminal A 1  is higher than that at the inverter terminal B 1 , the operational amplifier U 1 A will output a high level to turn off the transistor Q 1 , thereby cutting off the current output from the battery  7  to prevent it from over-discharging.  
         [0029]     Although the output voltage of the battery is used to indicate the condition of the battery in the above embodiment, it should be readily apparent to those skilled in the art that other electrical characteristics of the battery, such as a current, may also be used to provide an indication of the condition of the battery.  
         [0030]     The circuit  32  comprises an operational amplifier U 1 B which is also configured as a comparator. The operational amplifier U 1 B in this embodiment is an LM393 known in the art. A resistor R 6  is connected between the collector of the transistor Q 1  and a photo-resistor RES. The junction of the resistor R 6  and the photo-resistor RES is connected to the inverter terminal B 2  of the operational amplifier U 1 B. The non-inverter terminal A 2  of the operational amplifier U 1 B is connected with the junction of resistors R 7  and R 8 . Exemplary resistance value for the resistor R 6  is 51K ohms, and for R 7  and R 8  is 20K ohms.  
         [0031]     The resistance value of the photo-resistor RES is lower, e.g. 2K ohms in the daylight and will be increased when the ambient light is not sufficient, e.g. 200K ohms in the evening. Therefore, when the potential at the inverter terminal B 2  of the operational amplifier U 1 B is lower than that at the non-inverter terminal A 2  in the daylight, the operational amplifier U 1 B outputs high level to turn off the PNP-type transistors Q 2  and Q 3 , and hence the CCFL  5 . When the ambient light weakens, the resistance value of the increases above a critical value, 51K ohms in this embodiment, the output of the operational amplifier U 1 B will be reversed to a low level to turn on the transistors Q 2  and Q 3 , and hence the CCFL  5 .  
         [0032]     The circuit  33 , also referred to as an auxiliary startup circuit, comprises transistors Q 2  and Q 3 , both of which are PNP-type bipolar transistors in the embodiment and can be of 8550 type as known in the art. One end of resistor R 9  is coupled the emitter of the transistor Q 2  and the collector of the transistor Q 1 . Another end of resistor R 9  is connected to the output of the operational amplifier U 1 B. A resistor R 10  and a capacitor C 2  both of which are connected in parallel are connected between the junction of R 9  and the output of the operational amplifier U 1 B and the bases of the transistors Q 2  and Q 3  through resistors R 11  and R 12 , respectively. The resistors R 9 , R 10  have exemplary resistance values of 51K and 100K ohms, respectively. The resistors R 11  and R 12  have the same resistance value of 3.3K ohms. The capacitor C 2  has an exemplary capacitance value of 47 μF.  
         [0033]     The resistor R 9  functions as a pull-up resistor for both the transistors Q 2  and Q 3 . The resistor R 10  functions as the current-limiting resistor. The capacitor C 2  operates as a speedup capacitor, which is similar to the capacitor C 1 . Since the output of the operational amplifier U 1 B drives two transistors Q 2  and Q 3  simultaneously, the resistance value of the resistor R 10  is different from that of the resistor R 5 , and the capacitance value of the capacitor C 2  is different from that of the capacitor C 1 , as will be readily understood by those skilled in the art.  
         [0034]     A diode D 2  is connected at its anode with the collector of the transistor Q 1  and at its cathode with one end of a capacitor C 3  connected between the collector of the transistor Q 2  and the emitter of the transistor Q 3 . The Diode D 2  provides a main current channel for charging the capacitor C 3  and for keeping on the electrical power supply to a DC/AC inverter circuit  34  which will be described later after the capacitor C 3  discharges completely. As is well known in the art, the mentioned DC/AC inverter circuit is employed to convert direct-current voltage output from the battery  7  into an alternating voltage to drive the CCFL  5 .  
         [0035]     In the illustrated embodiment, the capacitor C 3  is an electrolytic capacitor of an exemplary capacitance value of 470 μF, with its positive end connected to the cathode of the diode D 2  and its negative end to the collector of the transistor Q 2 .  
         [0036]     As previously discussed, the operational amplifier U 1 B outputs high level when the ambient light is sufficient. In this situation, both of the transistors Q 2  and Q 3  are turned off. The capacitor C 3  is charged by the battery  7  through the diode D 2  to Vcc, the voltage across the battery.  
         [0037]     An exemplary DC/AC inverter circuit  34  will now be described in the following with reference to  FIG. 2 . As shown in  FIG. 2 , the DC/AC inverter circuit  34  comprises an inductor L 1  with one end connected to the collector of the transistor Q 3  and another end coupled to the bases of a pair of transistors Q 6  and Q 7  through resistors R 16  and R 17 , respectively, to positively biases each of those transistors causing them to start conducting. Both the transistors Q 1  and Q 2  are NPN-type transistor in this embodiment.  
         [0038]     A transformer T 1  having a primary winding T 1 A, a secondary winding T 1 B and a tertiary or feedback winding  64  is electrically connected to transistors Q 6  and Q 7 . Transistors Q 6  and Q 7  act as switches alternately connecting the low voltage of approximately 4 volts DC across the primary winding T 1 A.  
         [0039]     The feedback winding T 1 C is arranged in such a way that the base of the conducting transistor is negative whereas the base of the non-conducting transistor is positive. The feedback winding T 1 C is electrically connected between the bases of transistors Q 6  and Q 7 , as a result of which one of the transistors Q 6  and Q 7  conducts more than the other. If transistor Q 6  is conducting, the feedback winding T 1 C electrically connected thereto more positively biases transistor Q 6  with respect to transistor Q 7 , causing transistor Q 6  to turn on fully and transistor Q 7  to turn off. When transistor Q 6  is conducting, current flows from the battery  7  through an inductor L 1  to a center tap of the primary winding T 1 A, through an upper half T 1 A 2  of the primary winding T 1 A. The current flows through the transistor Q 6  from the collector to the emitter and returns to the negative terminal of the battery  7 .  
         [0040]     The flow of current along this path continues until the transformer T 1  begins to saturate and the polarity of the feedback winding T 1 C between the bases of transistors Q 6  and Q 7  is reversed. Transistor Q 6  is turned off and transistor Q 7  starts conducting. When transistor Q 7  is conducting, current flows from the battery  7  through an inductor L 1  to the center tap of the primary winding T 1 A, through a lower half T 1 A 2  of the primary winding T 1 A. The current flows through the transistor Q 7  from the collector to the emitter and returns to the negative terminal of the battery  7 , thus creating flow in the opposite direction through transistor Q 7 .  
         [0041]     This switching continues in the manner described above to convert the low voltage of approximately 4 volts DC provided by the battery  7  to approximately 350 volts AC. A capacitor C 5  connected in parallel with the primary winding T 1 A of the transformer T 1  between the collectors of transistor Q 6  and Q 7  produces a parallel resonant LC circuit which helps control the frequency of oscillation.  
         [0042]     The inductor L 1  together with the transformer T 1  creates a resonant inverter circuit which provides a sine wave output voltage. The inductor L 1  builds charge when the current flows through at a given direction, and when flow reverses, discharges back through the transformer T 1  to aid in generating a sine wave. The inductor L 1 , of conventional design, preferably has 90 turns. The transformer T 1 , also of a type known to those skilled in the art, has 18 turns in its primary winding T 1 A, 2 turns in its feedback winding T 1 C and 1450 turns in its secondary winding T 1 B. The saturation characteristic of the transformer T 1  causes the switching to occur. A capacitor C 6  electrically connected between the secondary winding T 1 B of the transformer T 1  and the CCFL  5  is the series output capacitor.  
         [0043]     The DC/AC inverter circuit  34  in the present invention can also be constituted in the manner as well known in the art.  
         [0044]     Referring to  FIG. 2 , according to a preferred embodiment of the invention, a main power supply circuit  35  is provided in consideration of the fact that since the voltage drop on the transistors Q 1  and Q 3 , and especially on the diode D 2 , which is about 0.3 to 0.7 volts, the voltage across the input terminals of the DC/AC inverter circuit  34  will be lower than the voltage provided by the battery  7 . The main power supply circuit  35  comprises two transistors Q 4  and Q 5 , a resister R 15  connected between the base of Q 5  and the collector of Q 4 . A delay circuit formed by a resistor R 14  and a capacitor C 4  is also provided as shown. The circuit  35  is set In the illustrated embodiment, the transistors Q 4  is an NPN-type transistor of 8050 type known in the art, and the transistor Q 5  is a PNP-type transistor of 8550 type. Exemplary resistance values for the resistor R 14  and R 15  are 47K and 3.3K ohms and exemplary capacitance value for the capacitor C 4  is 1 μF.  
         [0045]     The operations of the circuits  33  and  35  will be described below.  
         [0046]     As mentioned above, the transistors Q 2  and Q 3  are turned off due to the high output from the operational amplifier U 1 B when the ambient light is sufficient, and thus the transistors Q 4  and Q 5  are also turned off. With ambient light weakens gradually, the resistance value of the resistor RES increases to be greater than that of the resistor R 6 , the output of the operational amplifier U 1 B becomes low and thus turns on the transistors Q 2  and Q 3 . The turning on of the transistors Q 2  will then render the turning on of the transistors Q 4  and Q 5  after a delay caused by the delay circuit formed by the resistor R 14  and the capacitor C 4 . After the transistor Q 2  and Q 3  are turned on, the diode D 2  is turned off, and the capacitor C 3  will discharge to the input terminals of the DC/AC inverter circuit  34  through the transistor Q 3 . In this case, the battery  7  is connected in series with the fully charged capacitor C 3  to supply a DC voltage output Vout of about 2Vcc to the input terminals of the DC/AC inverter circuit  34 . According to the experiment of the inventors, in case that the voltage Vcc is about 4 volts, a voltage Vout on the input terminals of the DC/AC inverter circuit  34  is about 7.7 volts.  
         [0047]     After the transistors Q 4  and Q 5  are turned on after the delay, the battery  7  supplies the electrical power through the transistor Q 5  to the DC/AC inverter circuit  34  to keep the CCFL  5  lighting.  
         [0048]     Although the present invention has been described in connection with the preferred embodiments thereof, it will be obvious to those skilled in the art that various changes and modifications may be made. Therefore, the appended claims are intended to cover all such changes and modifications as fall within the true spirit and scope of the invention.