Abstract:
A rechargeable solar lantern with an improved power control circuit. The power control circuit includes a first switch, actuated by the connection of the solar panel to the battery, to prevent power from being supplied to the light bulb when the battery is charging. The power control circuit also includes a second switch to prevent power from being supplied to the light bulb when the voltage falls below a predetermined unacceptable level. Preferably, the second switch remains tripped until reset by the actuation of the first switch, indicating that the battery is being recharged.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to battery-powered lanterns, and more particularly to rechargeable battery-powered lanterns. 
     Battery-powered lanterns are well known and are used worldwide as portable light sources for a wide variety of work and leisure activities. Such lanterns typically include a base and a fixture mounted on the base. One or more light bulbs are supported within the fixture, and a battery is contained within the base to power the bulbs. 
     As with all battery-powered devices, battery life is a concern. Without a battery tester, determining the remaining life of a battery is difficult. To avoid running out of power, a user either will replace batteries before they are fully used or will carry extra batteries. Particularly in remote areas, extra batteries fill needed space, add weight, and can be hard to procure. 
     Solar-powered lanterns were developed in part to eliminate the need to replace batteries prematurely and/or the need to carry extra batteries. These solar-powered lanterns include a rechargeable battery in the base and a separate solar panel that can be connected to the lantern to recharge the battery. Unfortunately, solar-powered lanterns suffer several disadvantages. First, when the battery fully discharges, the life of the battery is shortened. Second, full discharge degrades the battery, causing the battery to hold less charge each cycle. Third, the lights within the solar lanterns oscillate or flicker when the battery is weak. 
     SUMMARY OF THE INVENTION 
     The aforementioned problems are overcome in the present invention wherein a solar-powered rechargeable lantern includes a power management system to prevent the battery from fully discharging and to prevent the lantern from operating when the battery is charging. 
     In a first aspect of the invention, the power management system terminates power output to the light bulb when the voltage from the battery drops below a specified level. Preferably, power is not restored to the bulb until the charging circuit is reset. The advantages of this technique are numerous. First, the power management system prevents the battery from fully discharging thereby extending the life of the battery. Second, since a rechargeable battery can build some charge after the power is terminated (i.e. with no load on the battery), the power management system prevents the light from turning back on until the charging circuit has been reset. Third, the termination of power until the charging circuit is reset prevents the light bulb from flickering or oscillating near the end of the battery&#39;s cycle. Fourth, power is removed from the lantern control circuitry when the solar panel is connected. 
     In a second aspect of the invention, the power management system prevents operation of the lantern while the battery is recharging. In the preferred embodiment, the connection of the solar panel to the lantern actuates a switch that prevents the light from being powered. Because the charging current is less than the operating current, this technique prevents the operation of the lantern when there is insufficient power to properly do so. 
     These and other objects, advantages, and features of the invention will be more readily understood and appreciated by reference to the detailed description of the preferred embodiment and the drawings. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of the rechargeable lantern of the present invention; 
     FIG. 2 is a block diagram of the rechargeable lantern; 
     FIG. 3 is a schematic circuit diagram of the power management system; and 
     FIG. 4 is a perspective exploded view, similar to FIG. 1 of the lantern. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A solar lantern system constructed in accordance with a preferred embodiment of the invention is illustrated in the drawings and generally designated  1 . The system includes a lantern  10  and a solar panel  20 . The lantern  10  in turn includes a light bulb  12 , a rechargeable battery  30 , and a power management system or power control circuit  50 . The solar panel  20  can be releasably connected to the lantern  10  to charge the battery  30 . The power management system  50  controls the supply of power to the light bulb (1) to prevent operation of the lantern while the battery is charging and (2) to prevent the battery from being drawn below an unacceptably low voltage. 
     The physical configuration of the lantern  10  is generally well known to those skilled in the art. The lantern includes a base  13 , a light housing  15  mounted on the base, and a carrying handle  17  attached to the housing. Each of these components is of a conventional design generally known to those skilled in the art. The base  13  houses the battery  30  and thereby provides a low center of gravity to the lantern  10 . A socket  42  is mounted within the base to provide part of a means for releasably interconnecting the solar panel  30  and the lantern  10 . The light housing  15  protectively supports the light bulb  12 . The carrying handle  17  provides a means of easily grasping and transporting the lantern  10 . 
     The battery  30  can be any rechargeable battery. In the preferred embodiment, the battery  30  is a nickel-metal hydride (NiMH) battery such as those sold by Harding Energy Inc. of Norton Shores, Mich. NiMH batteries eliminate voltage hysteresis effects that progressively reduce NiCD battery capacity over charging cycles. Constant and low discharge rates, as encountered in the present invention, are the worst case for NiCD batteries. Other appropriate rechargeable batteries are and will be know to those skilled in the art. 
     The solar panel  30  can be any solar panel. In the preferred embodiment, the panel  30  is an amorphous silicon solar electric module sold under the UNI-SOLAR trademark by United Solar Systems Corp. of Troy, Mich. The panel  30  includes a cord  41  terminating in a plug  42 , which is releasably or removably received with the socket  42 . 
     The power management system  50 , schematically shown in FIG. 3, interfaces the light bulb  12  with the battery  30 . The power management system  50  contains a circuit  60  which can be divided into four functional parts—the reset  70 , the disconnect  90 , the shutdown  110 , and the level shifter  130 . 
     The shutdown  110  controls when power output to the light bulb should be terminated. The shutdown  110  contains a 191k resistor  112  in series with a 49.9k resistor  116 . The level of resistance in these two resistors determines at what voltage should the power output to the light bulb be terminated. The resistors  112  and  116  comprise a voltage divider configuration. The values of the resistors will be selected depending on the desired cut-off voltage. Interconnected between the 191k resistor  112  and the 49.9k resistor  116  are a diode  118  and a 270 ohm resistor  114  leading to the base terminal  126  of the NPN shutdown transistor  120 . A 100k resistor  124 , and a 0.1 F 25V capacitor  122  connect in parallel between the base terminal  126  of the shutdown transistor  120  and the drain  104  on the disconnect transistor  100 . The collector terminal  128  of the shutdown transistor  120  has a 750k resistor  134  between the battery  30  and the collector  128 . The shutdown  110  controls the level shifter  140 . 
     The level shifter  140  of the circuit  60  connects with a 100k resistor  142  to the collector  128  on the shutdown transistor  120  and the collector  82  on the reset transistor  80 . The level shifter transistor  150  is a pnp transistor. The level shifter  140  is controlled by the shutdown  110 , and in turn the level shifter controls the disconnect  90 . 
     The disconnect  90  contains a field effect transistor (FET)  100 . The collector  156  of the level shifter transistor  150  is attached to the gate  106  of the FET  100 . The gate  106  controls the FET  100  and terminates power between the light bulb  12  and the battery  30  when the voltage at the gate  106  is zero. The gate  106  allows voltage to pass between the source  102  and the drain  104  when the level shifter  150  applies a positive voltage to the gate  106  on the FET  100 . A 150k resistor  92  is located between the gate  106  and the battery  30 . 
     The reset  70  includes a 100k resistor  72 , a npn transistor  80 , a 100k resistor  78 , and a 1M resistor  76  which is in parallel with a 0.1 F 25V capacitor  74 . The NPN reset transistor  80  has a collector  82 , a base  84 , and an emitter  86 . The shutdown  110  causes the circuit  60  to terminate power when the voltage drops below a specified level and the reset  70  forces the shutdown to keep power terminated if the battery regenerates. The reset  70  accomplishes the continual shutdown through a capacitor  74  that keeps voltage on the base terminal  84  of the transistor  80  until the battery  30  is disconnected from the circuit  60  by the switch  40  when a charging means  20  is attached. When power is circumvented from the circuit  60  to the battery  30  by the switch  40 , the capacitor  74  discharges and the reset  70  of the circuit  60  resets the shutdown  110  allowing the light bulb  12  to operate. 
     Operation 
     When the battery  30  is fully charged, the power management system  50  allows power to flow to the light bulb  12 . The power management system  50  also allows the battery  30  to discharge until the battery reaches 5% state of charge (SOC) or 95% depth of discharge (DOD). The termination of power output by the power management circuit  60  at the specified level and/or with an unacceptable range prevents the battery  30  from degenerating. 
     Specifically, the power termination occurs when the base  126  of the shutdown transistor  120  receives about 1.1 V or less. At this level the shutdown transistor  120  no longer allows voltage to flow from the collector  128  to the emitter  132  on the shutdown transistor. The lack of power flowing into the collector  128  on the shutdown transistor  120  activates the collector  156  on the level shifter transistor  150 , which normally gives a positive charge to the gate  106  on the FET  100 , by changing the voltage to zero. When the collector  156  on the level shifter transistor  150  has no voltage, the gate  106  on the FET  100  is switched, activating the disconnect  90  and terminating power output to the light bulb  12 . 
     The capacitor  94  in parallel with the IM resistor keeps charge on the base of the reset  80  preventing the circuit  60  from allowing power to light bulb  12  once power has been terminated. The reset is necessary to prevent the light bulb  12  from turning off and on or flickering, since the rechargeable battery  30  may regenerate and gain charge when there is no load on the battery. When the charging means  20  is plugged into the plug  44 , a switch  40 , normally closed, is opened causing disruption of power to the circuit  60 . The capacitor  74  on the reset  70  then discharges allowing the power management system  50  to return to original operation once the charging means  20  is unplugged and the switch  40  returns to its normally closed position. The integral switch  40  on the plug  44  prevents the lantern from operating when the battery is charging. 
     The above description is that of a preferred embodiment of the invention. Various alterations and changes can be made without departing from the spirit and broader aspects of the invention as set forth in the appended claims, which are to be interpreted in accordance with the principles of patent law including the doctrine of equivalents.