Abstract:
A lamp includes a light source, a power tool battery for providing a DC voltage level, and a base for housing the power tool battery. A stem is coupled to the base and supports the light source. A power inverter converts the DC voltage level to an AC voltage level, and a current sensing circuit operatively coupled to the converter or the inverter senses an over-current condition when the converter or the inverter draws more than a predetermined amount of current. The converter or inverter is disabled if the over-current condition continues for more than a predetermined amount of time so that the light source receives the AC voltage level and is illuminated for the predetermined amount of time before power is removed.

Description:
BACKGROUND 
       [0001]    This disclosure relates to lamps. In particular, this disclosure relates to a battery-powered fluorescent lamp. 
         [0002]    Battery-powered lamps may be used when a source of AC power is unavailable or inaccessible. Battery-powered lamps may be convenient when a user is in an outside environment, such as while camping or when otherwise away from buildings or other structures having electricity. Such lamps may be powered by a plurality of standard 1.5 volt D-cell batteries, a 6 volt ganged battery pack, car battery, or other type of battery. 
         [0003]    Some battery-powered lamps may use an incandescent light bulb, while others may use a fluorescent tube. When an incandescent light bulb is used, the batteries must be changed frequently, depending on usage duration, because incandescent light bulbs draw much more power than fluorescent bulbs, thus reducing battery lifetime. The user must have a sufficient supply of batteries on hand to meet lighting demands. 
         [0004]    Some battery-powered lamps are able to interchangeably use an incandescent bulb or a fluorescent bulb. In such lamps, a user may inadvertently install an incandescent light bulb rather than a fluorescent bulb. Inadvertent installation of an incandescent light bulb in a battery-powered lamp designed to use a fluorescent bulb will result in significantly shorter battery life. This results in extra cost for frequent battery replacement. Further, the user may not realize that the shortened battery life is a result of installation of the wrong type of light bulb, and may become dissatisfied with the product. 
       SUMMARY 
       [0005]    According to one specific embodiment, a lamp having a light source includes a power tool battery for providing a DC voltage level and a base for housing the power tool battery. A stem is coupled to the base and supports the light source. A power inverter converts the DC voltage level to an AC voltage level, and a current sensing circuit operatively coupled to the converter or the inverter senses an over-current condition when the converter or the inverter draws more than a predetermined amount of current. The converter or inverter is disabled if the over-current condition continues for more than a predetermined amount of time so that the light source receives the AC voltage level and is illuminated for the predetermined amount of time before power is removed. 
         [0006]    In another specific embodiment, a battery-powered lamp having a light source includes a power tool battery that provides a first DC voltage level, a base for housing the power tool battery, and an electrical socket for receiving the light source. A hollow stem couples the base with the electrical socket, and provides electrical connection between the battery and the electrical socket. A voltage converter converts the first DC voltage level to a second DC voltage level, and a power inverter converts the second DC voltage level to an AC voltage level, where the AC voltage level is provided to the light source. A current sensing circuit operatively coupled to the converter or the inverter issues an over-current signal when the converter or the inverter draws more than a predetermined amount of current or power. A delay circuit receives the over-current signal and disables the converter or the inverter in response to the over-current signal. The delay circuit delays disabling the converter or the inverter for a predetermined amount of time so that the light source receives the AC voltage level and is illuminated for the predetermined amount of time before power is removed. 
         [0007]    In a further specific embodiment, a lamp having a light source includes a power tool battery that provides a first DC voltage level, a base for housing the power tool battery, and a stem coupled to the base. The stem supports the light source. A voltage converter converts the first DC voltage level to a second DC voltage level, and a power inverter converts the second DC voltage level to an AC voltage level. A current sensing circuit operatively coupled to the converter or the inverter issues an over-current signal when the converter or the inverter draws more than a predetermined amount of current or power. A delay circuit disables the converter or the inverter after a predetermined amount of time after receiving the over-current signal so that the light source receives the AC voltage level and is illuminated for the predetermined amount of time before power is removed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a specific embodiment of a battery-powered lamp; 
           [0009]      FIG. 2  is a perspective view of a specific embodiment of a battery and circuit board; 
           [0010]      FIG. 3  is a schematic diagram of a lamp circuit having a DC-to-DC converter; 
           [0011]      FIG. 4  is a schematic diagram of a current sensing circuit; 
           [0012]      FIG. 5  is a schematic diagram of an alternate embodiment of a battery-powered lamp; and 
           [0013]      FIG. 6  is a slide-type power tool battery. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0014]    The invention is described with reference to the drawings in which like elements are referred to by like numerals. The relationship and function of the various elements of this invention are better understood by the following description. Each aspect so defined may be combined with any other aspect or aspects unless clearly indicated to the contrary. The embodiments described below are by way of example only, and the invention is not limited to the embodiments illustrated in the drawings. 
         [0015]      FIG. 1  shows the physical structure of a specific embodiment of a battery powered lamp  100 . The lamp  100  may include a base  110  that may house a power tool battery  120 . The base  110  may have a releasable bottom cover  130  configured to provide access to a battery compartment  134 . A rigid elongated stem  140  may couple the base  110  to a bulb housing  150 , which may contain an electrical socket  160 . The electrical socket  160  may be a standard Edison-type screw-base socket, which accepts a standard compact fluorescent lamp (CFL)  164 . A CFL is a commercially available self-contained fluorescent lamp configured to be received in a standard screw-type 120 volt AC socket, and is powered by a standard output of 110-125 volts AC. The elongated stem  140  may be hollow to facilitate the routing of electrical wiring  165  from a circuit board  170  to the electrical socket  160 . The lamp  100  may include a decorative shade  180 . 
         [0016]    Unlike conventional lamps, which may use a plurality of D-cell batteries, the illustrated lamp or lantern  100  may include a power tool type battery  120 . Power tool batteries may be used with a variety of power tools and may be rechargeable. Because many households have battery powered power tools, a user may be able to conveniently find an available power tool battery to install in the lamp  100 , rather than attempting to locate a large number of D-cell or other types of batteries. Commercially available power tool batteries may be used, which may provide various output voltages, such as 19.2 volts, 18 volts, 14.4 volts, or 12 volts, and other voltage outputs. Such power tool batteries may be lithium-ion or nickel-cadmium batteries. Some suitable batteries may include the Ryobi® One+ Battery™, which may have a power output of about 1.7 ampere-hours. 
         [0017]      FIG. 2  shows a specific embodiment of the power tool battery  120  and the associated circuit board  170 . The power tool battery  120  is generally rectangular in shape and may have a cylindrical stem or mast  210  projecting from a top surface  220  of the power tool battery. The battery  120  may be releasably connectable to the lamp  100  or the lamp base  110 . The stem  210  may an electrical connection when inserted into a power tool. The stem  210  may include two or more metal contacts  230  for providing battery power to a load, such as the power tool or the CFL. The circuit board  170  may be disposed over the top surface  220  of the battery  120 , and may have an aperture  236  configured to receive the mast  210 . Wiring or mechanical contacts  240  may couple the circuit board  170  to the metal contacts  230  to provide battery power to the circuit board. The circuit board  170  may include output terminals  246  configured to deliver the electrical output of the circuit board to terminals of the electrical socket  160  via the wires  165  or other connectors. The circuit board  170  need not necessarily be mounted on the power tool battery  120 , and may be mounted in any suitable location. For example, the circuit board  170  may be mounted to an interior portion of the base  110  using conventional fasteners or mounting hardware. 
         [0018]      FIG. 3  is a schematic diagram of the electronic circuitry that may be mounted on the circuit board  170 . The circuit board  170  may include a voltage converter  310  configured to convert a DC output voltage  314  of the battery to a lower DC voltage  316 . For example, the voltage converter  310  may convert an 18 volt or 19.2 volt DC output voltage to a lower DC voltage level  316  of about between 12 volts to about 14.2 or about 15 volts. The voltage converter  310  may be a commercially available voltage converter, such as a step-down switching regulator no. LM25576 from National Semiconductor of California. Other suitable voltage converters or regulators may be used. 
         [0019]    A power inverter  320  may convert the lower DC voltage level  316  to an AC voltage level  330 . The output voltage  330  of the power inverter  320  may be an AC voltage of about 110 volts to about 130 volts. The power inverter  320  provides the AC voltage output  330  to the electrical socket  160 , and thus provides power to the CFL  164 . The power inverter  320  may be a commercially available power inverter, such as a DC-to-AC Mobile Inverter no. 0900-36 from PowerLine. Other suitable power inverters may be used. 
         [0020]    A current sensing circuit  360  may be coupled between the voltage converter  310  and the power inverter  320 . The current sensing circuit  360  may issue an over-current signal  364  when either the voltage converter  310  or the power inverter  320  draws more than a predetermined amount of current or power. For example, the maximum current draw may be limited to about 1.25 amperes at about 12 volts or about 0.8 amperes at about 19 volts. Such power ratings correspond to about a 15 watt power rating. A 15 watt CFL may provide about the same amount of light output as a corresponding 60 watt incandescent light bulb. The current sensing circuit  360  may issue the over-current signal  364  when a maximum power level or maximum current draw is reached. The over-current signal  364  is shown in dashed lines coupled to the voltage converter to indicate that either the voltage converter  310  or the power inverter  320  may receive the over-current signal. 
         [0021]    A low value sensing resistor  366  may be coupled to the current sensing circuit  360 , where a voltage developed across the sensing resistor may be proportional to the current flowing through the sensing resistor. In this way, the current sensing circuit  360  may determine the value of the current flow. The current sensing circuit  360  may be a commercially available current or power sensing device, such as a high-side current monitor no. ZXCT1010 available from Zetex Semiconductors. Other suitable current or power sensors and monitors may be used. 
         [0022]      FIG. 4  shows a specific embodiment of the current sensing circuit  400 . The current sensing circuit  400  may include an operational amplifier  404  having inputs coupled across the sensing resistor  366 . The operational amplifier  404  may issue an output signal  410  when the maximum permissible current or power draw has been reached. A delay circuit  420  may delay the output signal  410  by a predetermined amount of time, for example by about 0.1 seconds to about 1 second. Other suitable delay times, for example, 1 second to 10 seconds, may be used depending upon the application. The delay circuit  420  may be a monostable vibrator or one-shot, such as a LM555 timer circuit. The output of the delay circuit  420  may drive the base of an output transistor  440 , which in turn, may provide the over-current signal  364 . 
         [0023]    The battery-powered lamp  100  is configured to operate with a CFL rather than an incandescent light bulb. A CFL-type bulb draws much less power than a corresponding incandescent bulb having a similar light output rating. Accordingly, when a CFL is installed in the battery-powered lamp  100 , the current sensing circuit  360  or  400  does not sense an over-current condition and thus does not issue the over-current signal  364 . This conserves battery life and extends the operating time of the battery-powered lamp  100  before the battery requires recharging. However, because both an incandescent lamp and a CFL both fit into the electrical socket  160 , a user may inadvertently install an incandescent light bulb in the battery-powered lamp  100 . Because both types of light bulbs are powered by 120 volts AC, both bulbs could be illuminated using the 120 AC output of the power inverter  320 . If the user inadvertently installs an incandescent bulb, the incandescent bulb will draw more current or power than may be permitted by the current sensing circuit  360  or  400 . Accordingly, the current sensing circuit  360  or  400  will detect the over-current condition and will issue the over-current signal  364  to either the power inverter  320  or the voltage converter  310 . This disables or turns off the power inverter  320  or the voltage converter  310 , respectively. 
         [0024]    The battery-powered lamp is self-restarting. This means that after the current sensing circuit  400  has disabled or turned off the voltage converter  310  or the power inverter  320  due to improper installation of an incandescent light, the CFL will be automatically illuminated upon installation. 
         [0025]    Note that the power inverter  320  or the voltage converter  310  may be capable of providing the excessive current defining the over-current condition without physical damage, but is disabled or turned off to conserve battery life. However, the power inverter  320  or the voltage converter  310  is not disabled immediately upon detection of the over-current condition. Rather, the delay circuit  420  delays such disabling for a predetermined amount of time. The time delay before turning off the power inverter  320  or the voltage converter  310  permits illumination of an installed incandescent light bulb for an amount of time equal to the time delay, for example, about 0.1 seconds to about 1 second. 
         [0026]    The brief illumination of the incandescent light bulb alerts the user that the wrong type of light bulb has been installed, but that the improper type of light bulb, as well as the lamp circuitry, is nonetheless functional. Without such a time delay, the light bulb would not be illuminated at all, or may only be illuminated for an extremely brief period of time not observable by the user. Thus, without the time delay, the user may believe that the replacement light bulb was burnt-out or that the battery-powered lamp  100  was not functioning. This conserves battery life while preventing inadvertent use of incandescent bulbs in the battery-powered lamp  100 . 
         [0027]    Other current sensing circuits or power monitoring circuits may be used. For example, a power monitoring circuit based on thermal conditions or temperature parameters may be used. If an excessive amount of current is drawn, a temperature-based monitor may disable or turn off the voltage converter  310  or the power inverter  320  when an elevated temperature is sensed. Because temperature elevation may require a predetermined amount of time to rise, a temperature-based power monitor may inherently include a time delay. Depending upon the sensitivity of the power monitoring circuit, different time delays may be implemented. 
         [0028]    The current sensing circuits  360  and  400  or temperature-base power monitors may be separate from the voltage converter  310  or the power inverter  320 , or may be incorporated into the voltage converter or the power inverter, respectively. The current sensing circuits  360  and  400  need not necessarily be placed between the voltage converter  310  and the power inverter  320 . Alternatively, the current sensing circuits  360  and  400  may be placed between the battery  120  and the voltage converter  310 . In another embodiment, a current sensing circuit adapted for AC monitoring may be placed between the power inverter  320  and the electrical socket  160 . 
         [0029]    With regard to  FIG. 3 , the power inverter  320  may require an input voltage, for example, between about 10 volts to about 15 volts, which may be less than the battery voltage  314  of, for example, about 18 to 19 volts. Accordingly, the voltage converter  310  may convert or “step-down” the battery voltage  314  to a level suitable for input to the power inverter  320 . However, if the battery  120  provides an output voltage  314  in the range suitable for input to the power inverter  320 , the power converter  310  may be omitted, as shown in  FIG. 5 . In the alternate embodiment of the circuit of  FIG. 5 , the battery voltage  314  is provided to the power inverter  320  with no intermediate voltage conversion. The power inverter of  FIG. 5  may accept an input voltage of about 12 volts to about 25 volts. The power inverter of  FIG. 5 , for example, is a commercially available power inverter. 
         [0030]      FIG. 6  shows a slide type power tool battery  600 , which is known. Stem-type power tool batteries, slide-type power tool batteries, or other styles of power tool batteries may also be used in all of the described embodiments and circuitry. Electrical connection to the circuit board  170  can be made through contacts or wiring. 
         [0031]    While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only exemplary embodiments have been shown and described and do not limit the scope of the invention in any manner. The illustrative embodiments are not exclusive of each other or of other embodiments not recited herein. Accordingly, the invention also provides embodiments that comprise combinations of one or more of the illustrative embodiments described above. Modifications and variations of the invention as herein set forth can be made without departing from the spirit and scope thereof, and, therefore, only such limitations should be imposed as are indicated by the appended claims.