the present invention consists of a novel power supply and power management module that is capable of supplying power to computer peripherals that require higher peak power than the main power supply of a portable computer can handle , yet is rechargeable by the main power supply of the portable computer without placing an undue burden on the computer &# 39 ; s power supply . while the following detailed description is directed to a particular embodiment of the present invention adapted to supply power to a packet - switched data radio in combination with a portable personal computer , it should be understood that application of the present invention is not limited to a personal computer / pocket switched data radio combination . the present invention can be adapted for use with a personal computer and any associated peripheral or appliance that has peak power consumption requirements that exceed the capability of power supplies typically used in portable personal computers . packet - switched data radios transmit data in bursts or pulses each of which contains a packet of data . during the transmission of a data packet , the radio uses a relatively high amount of electrical energy over a relatively short period of time . at other periods , particularly when the radio is idle or is in the data receiving mode , the electrical energy used by the radio is substantially lower as compared to that used during the transmission mode . for example , during transmission cycles the radio may require as much as 2 amps of current , whereas it may only require 50 - 100 milliamps during reception cycles and less than 50 milliamps when idle ( e . g ., when the radio is on but is neither transmitting nor receiving data .) as discussed in more detail below in relation to fig4 due to the fact that the radio transmits data in packets or pulses that are relatively short ( e . g ., 0 . 1 to 1 second in duration ) as compared to the time separating successive transmission pulses ( e . g ., 3 seconds or more ), the relatively low power output of the computer &# 39 ; s power supply can provide sufficient power to supply the average power requirements of the radio transmitter . referring to fig1 the present invention 10 comprises a personal computer 12 in combination with a radio 14 . radio 14 is preferably a packet - switched data radio adapted to transmit and receive data packets over radio waves . radio 14 could also comprise a conventional cellular radiotelephone that combines transmission and reception of both voice and data signals . by integrating radio 14 with personal computer 12 , it is possible to transmit and receive data from and to personal computer 12 without the necessity of connecting the computer to a telephone land line , as is the case with the use of a conventional modem , thereby dramatically enhancing the ease of data exchange to and from personal computer 12 . as will be appreciated , these advantages are most significant in relation to portable personal computers , since access to a telephone land line is usually readily available in most environments in which a desk top computer is used . radio 14 can be either an internal radio that forms an integral part of personal computer 12 or it can be a separate device that is external to , and interfaces with , personal computer 12 through input / output ports conventionally incorporated into most personal computers . in either event , radio 14 interfaces with personal computer 12 for transmission of data output by personal computer 12 and input of data received by radio 14 to personal computer 12 . radio 14 comprises a receiver 16 , a transmitter 18 and a power supply and power management module 20 . as discussed above , one of the problems inherent with combining a packet - switched data radio 14 with a portable , battery powered personal computer is the fact that the peak power requirements of such radios during transmission of data packets exceed the power available from most portable personal computers . for example , portable personal computers typically provide power to operate peripherals at 5 volts and within the range of 30 milliamps to 1 amp through a pcmcia or similar connector incorporated into many portable computers . in contrast , the transmitter of a packet - switched data radio typically operates at 6 volts or higher and requires up to 2 amps of current during transmission cycles . the present invention solves this dilemma through the use of a novel power supply and power management module 20 . referring to fig2 module 20 comprises a programmable control means 22 , a first converter means 24 , a second converter means 26 , an energy storage means 28 and a stored energy sensing means 30 . in the preferred embodiment , control means 22 comprises a programmable microprocessor that is separate from the processor that is part of personal computer 12 . however , advances in the art of modern electronic devices may allow the processor of personal computer 12 to carry out internally many of the functions carried out by microprocessor 22 . in the preferred embodiment , first converter means 24 and second converter means 26 each comprise a dc - to - dc converter . in the preferred embodiment , energy storage means 28 comprises a small , lightweight battery with relatively high power capacity . alternatively , energy storage means 28 could comprise a capacitor ( not shown ) of sufficient size and power to provide the anticipated transmitter power requirements of radio 14 . module 20 derives its power from two sources . the first power source is a dc power source 32 . in the preferred embodiment , dc power source 32 comprises a dc power output from personal computer 12 and , more particularly , a dc power output available on a conventional pcmcia card ( not shown ) that is a conventional and integral part of many contemporary portable personal computers . as will be appreciated , the dc output of a pcmcia card of a portable personal computer is powered by the main power supply of the personal computer . power supplies typically used in portable personal computers generally do not have sufficient peak power capacity to supply the level of power needed to power a packet - switched data radio during its transmission cycles . the dc output of a pcmcia card is generally 5 volts and is capable of supplying continuous current in the range of from 30 milliamps to 1000 milliamps . although it is conceivable that the dc output of a pcmcia card might be able to supply peak current approaching that required by radio 14 during transmission cycles , it may cause such a drop in voltage as to endanger the proper operation of personal computer 12 . however , the level of power available from the dc output of most pcmcia cards is generally sufficient to supply the average power requirements of a radio 14 . module 20 also derives power from an ac power source 34 . ac power source 34 can either be the same ac power source utilized by personal computer 12 or some other independent ac power source . as explained in more detail below , all of the components of module 20 derive their power from dc power source 32 , ac power source 34 , and / or its internal battery 28 . referring to fig2 and 3 together , dc power source 32 is coupled to first dc - to - dc converter 24 , which comprises a field effect transistor (&# 34 ; fet &# 34 ;) 36 , an inductor 38 and a diode 40 . the gate of fet 36 is electrically coupled to , and controlled by , a first output 42 of microprocessor 22 . a first input 44 to microprocessor 22 is also coupled to dc power source 32 to detect the presence or absence of power from dc power source 32 . in the preferred embodiment , when microprocessor 22 detects that dc power source 32 is supplying power to module 20 and microprocessor 22 detects that battery 28 needs charging , output 42 of microprocessor 22 drives the gate of fet 36 with a 50 kilohertz pulse width modulated (&# 34 ; pwm &# 34 ;) wave , which causes current to flow through inductor 38 and fet 36 while the signal on line 42 is at a high asserted level ( 5 volts ). when the input at the gate of fet 36 goes to a low asserted level , the current flowing through inductor 38 is diverted through diode 40 , which is coupled through line 46 to battery 28 , thereby charging battery 28 . when an ac power source is used , power management module 20 can contain means for converting power derived from the ac power source . in fig2 and 3 , the means for converting power derived from the ac power source comprise 9 volt dc converter 48 and voltage regulator 50 . the voltage regulator 50 is coupled to second dc - to - dc converter 26 . converter 26 comprises a fet 52 , an inductor 54 and a diode 56 . the gate of fet 52 is coupled to and controlled by a second output 58 of microprocessor 22 . a second input 60 to microprocessor 22 is also coupled to the output of voltage regulator 50 to detect the presence or absence of power from ac power source 34 . in the preferred embodiment , when microprocessor 22 detects that ac power source 34 is supplying power to module 20 and microprocessor 22 detects that battery 28 needs charging , output 58 of microprocessor 22 drives the gate of fet 52 with a 50 kilohertz pwm wave , which causes current to flow through inductor 54 and fet 52 while the signal on line 58 is at a high asserted level . when the input at the gate of fet 52 goes to a low asserted level , the current flowing through inductor 54 is diverted through diode 56 , which is coupled through line 62 to energy storage means 28 , thereby charging energy storage means 28 . converters 24 and 26 also convert the voltage level from 5 volts to 6 volts . schottky diodes 40 and 56 also prevent current from flowing back into either converter 24 or 26 . energy storage means 28 may comprise a 6 volt battery with relatively high peak power capacity . in the preferred embodiment , energy storage means 28 comprises a battery having a peak current capacity of at least 2 amps , being capable of delivering sufficient power to operate radio transmitter 18 for relatively short periods of time and being capable of recharging in a relatively short period of time , preferably in the time between successive transmission cycles . when storage means 28 comprises a battery , it is desirable to include capacitor 88 as shown in fig3 so as to help filter the charging current on line 46 . alternatively , energy storage means 28 can comprise a capacitor ( not shown ) in place of the battery shown at 28 in fig3 . the capacitor should be of sufficient voltage rating and peak power capacity to power transmitter 18 . since the energy storage per unit volume ( e / v ) in a capacitor is greatest when the capacitor voltage is high , the size of the capacitor could be reduced by using a dc - to - dc converter ( not shown ) to convert the voltage from the computer ( typically 5 volts ) to a much higher voltage ( e . g ., 60 volts ), charging the capacitor with the higher voltage , and using another dc -- dc converter ( not shown ) to convert the capacitor voltage back down to the voltage of the radio ( e . g ., 6 volts ). module 20 also incorporates circuitry to monitor the stored energy level or charge of battery 28 and to charge battery 28 when the level of energy stored in battery 28 is below a certain minimum threshold level , which is too low for radio transmission . this is accomplished under the control of microprocessor 22 in combination with stored energy sensing means 30 . in the preferred embodiment , stored energy sensing means 30 comprises resistor 66 and fet 68 . stored energy sensing means 30 and a third input 64 to microprocessor 22 are both coupled to line 46 , which , in turn is coupled to battery 28 . the gate of fet 68 is coupled to , and controlled by , a third output 70 of microprocessor 22 . microprocessor 22 , under the control of its programming , measures or derives the electrical energy level stored in battery 28 whenever the radio is turned on ( e . g ., the radio power switch 74 is switched from the &# 34 ; off &# 34 ; position to the &# 34 ; on &# 34 ; position ). when microprocessor 22 applies a voltage to the gate of fet 68 through line 70 , a test load ( resistor 66 ) is placed on line 46 , which causes a voltage drop on line 46 . it will be appreciated that the amount of voltage drop on line 46 , which is detected by microprocessor 22 through input 64 , will be proportional to the level of electrical energy stored in battery 28 . if the stored energy level of the battery 28 is below the threshold level required to power transmitter 18 , microprocessor 22 initiates the recharging process by enabling converter 24 and / or converter 26 through output lines 42 and / or 58 , respectively . as soon as microprocessor 22 detects that battery 28 has been charged to the point where the stored energy level of battery 28 exceeds the minimum threshold level , microprocessor 22 disables converter 24 and converter 26 so that no further charging of battery 28 occurs . after the initial recharging has been completed , microprocessor 22 controls the recharging function of module 20 to recharge battery 28 after each transmission cycle of radio 14 so as to restore energy to battery 28 in an amount equal to or slightly greater than the amount of energy consumed by radio 14 during such transmission cycle . by monitoring the amount of energy consumed by radio 14 during each transmission cycle , microprocessor 22 can compute the amount of time and power that is necessary for the recharging circuits of module 20 to recharge battery 28 to a stored energy level equal to or slightly greater than its stored energy level immediately prior to the preceding transmission cycle . microprocessor 22 then enables converter 24 and / or 26 through lines 42 and / or 58 , respectively , to charge battery 28 for the amount of time and power computed by microprocessor 22 . as further shown in fig3 battery 28 is coupled to and supplies power to radio transmitter 18 . battery 28 is also coupled to voltage regulator 71 , which steps down the voltage from 6 vdc to 5 vdc , and the output of voltage regulator is coupled to and supplies power to radio receiver 16 . as alluded to above , microprocessor 22 is programmed to monitor the status of , and control the various components of module 20 . microprocessor 22 derives its power from either the 5 volts from dc power source 32 ( the pcmcia connector [ not shown ] of personal computer 12 ) or the regulated 5 volts derived from ac power source 34 . schottky diodes 76 and 78 prevent current from flowing back into either power source . once microprocessor 22 powers up , it determines where the power is coming from and tests the state of the radio power switch 74 ( a slide switch on the side of the radio ), which microprocessor 22 detects through a fourth input 72 . microprocessor 22 then performs the following functions , depending on the state of radio power switch 74 and the state of module 20 , which microprocessor 22 monitors through input lines 44 , 60 , 64 : table i______________________________________radio ac pcmcia &# 34 ; on &# 34 ; power power action______________________________________yes yes x after boot up , put dummy load on battery , observe voltage drop and estimate battery capacity . recharge battery , if necessary , from ac power source . fast , then trickle charge battery . yes no yes same as above , but charge battery from pcmcia power source . replace energy used in transmissions as necessary . yes no no do nothing ( processor will be dead ). no yes x charge battery ( fast at first , then trickle ) from ac power source . no no x do nothing . ______________________________________ in table i , the symbol &# 34 ; x &# 34 ; represents a &# 34 ; don &# 39 ; t care &# 34 ; condition . microprocessor 22 is programmed to monitor inputs 44 , 60 , 64 and 72 and to control fets 36 , 52 and 68 through output lines 42 , 58 and 70 , respectively , in accordance with the truth table set forth above . for example , if the radio is turned on and if power is being supplied to module 20 by either dc power source 32 or ac power source 34 , then microprocessor 22 will recharge battery 28 as necessary . microprocessor 22 also determines which power source to use to recharge battery 28 . in one preferred embodiment line 60 is provided with resistor 84 , capacitor 86 and capacitor 88 connected in parallel with battery 28 . for example , any time microprocessor 22 detects through input line 60 that ac power source 34 is active and supplying power to module 20 , microprocessor 22 will use ac power source 34 ( instead of dc power source 32 ) to recharge battery 28 , when necessary , and will take line 42 low , thereby disabling fet 36 , so that dc power source 32 ( which derives its power from the main battery of computer 12 ) is not drained needlessly . the only time dc power source 32 is used to recharge battery 28 is when the radio power switch is in the &# 34 ; on &# 34 ; position , microprocessor 22 detects through input line 44 that dc power source 32 is active supplying power to module 20 , and microprocessor 22 detects through input line 60 that ac power source 34 is inactive ( e . g ., no power is being supplied to module 20 by ac power source 34 ). when the radio transmitter is turned on , the circuitry allows battery 28 capacitor ( now shown ) to be &# 34 ; initialized .&# 34 ; this initialization comprises charging battery 28 according to some predetermined criteria . for example , micro processor 22 can charge battery 28 for a predetermined time . the charging criteria can also include various types of monitoring . as an additional example , micro processor 22 can charge battery 28 until a predetermined energy level is reached . alternately , micro processor 22 can first measure how much energy is currently stored in battery 28 and then charge battery 28 until it contains a sufficient amount of energy to perform some desired task . as a third alternative , micro processor 22 can initialize battery 28 to a relatively low energy level sufficient to transmit a few packets . this will avoid initial drain on the internal power supply of the computer . after transmission of the packets begins , battery 28 can be further charged to a predetermined energy level . this will ensure sufficient energy is always stored in batter 28 to accomplish its designed task . whenever the radio is turned off , there will not be any appreciable drain on battery 28 . in that case , since there is no need to test the stored energy capacity of battery 28 until the radio is turned back on , microprocessor 22 will take output line 70 low ( and keep it at a low asserted level until the radio is switched on ), thereby disabling fet 68 . microprocessor 22 also monitors the status of the dc power source 32 and adjusts converter 24 if the voltage level of the dc power source 32 ever drops below a predetermined lower limit . during the normal operation of personal computer 12 , varying loads are placed on the computer &# 39 ; s power supply as various internal components of the computer are activated or deactivated in various combinations . by sensing the voltage level of dc power source 32 through input line 44 , microprocessor 22 can determine the load on the power supply of personal computer 12 at any point in time and adjust the additional load added by recharging battery 28 so as to not threaten the proper operation of computer 12 . reference is now made to fig4 which compares the radio current to the stored energy of battery 28 during transmission of a succession of data packets . as graphically depicted in the top line of the graph of fig4 the duration of individual transmission pulses in packet - switched data radios typically range from approximately 0 . 1 to approximately 1 second , and the space of time separating successive transmission pulses is typically no less than 3 seconds . during transmission each successive data packet , radio transmitter 18 draws current from battery 28 , which , as graphically represented in fig4 reduces the energy stored in battery 28 . however , the energy stored in battery 28 is replenished through the recharging circuits described above during the times separating successive transmissions . as depicted by the lower line of the graph of fig4 the rate at which the energy stored in energy storage means 28 is reduced during transmission is generally greater than the rate at which the energy is replenished between transmissions . however , the relatively short duration of the pulses as compared to the relatively long separation of successive transmission pulses makes it possible for personal computer 12 to supply sufficient current to maintain the energy stored in battery 28 to a sufficient level to operate radio 14 . furthermore , the energy stored in battery 28 is maintained at a level well above the minimum threshold level , designated as e in fig4 required to power radio transmitter 18 . in the event the level of energy stored in energy storage means 28 is ever depleted to the point that it approaches e , then microprocessor 22 prevents any further radio transmissions until such time as battery 28 has been recharged to a sufficient level to permit further radio transmissions to occur . microprocessor 22 may also provide a visible and / or audible signal to warn the user of the low charge condition of battery 28 . another embodiment of the present invention overcomes the need to determine the amount of power utilized in the transmission of a packet and then recharging the battery at least as much as , or a little more than that amount , by consistently recharging the radio battery by a predetermined amount after each transmission . this predetermined amount is derived from the greatest energy drain anticipated from the transmission of the packet of data . by consistently recharging the battery with this predetermined amount , this embodiment of the present invention does not need to monitor the amount of energy utilized during the transmission of each packet . it will be understood , that while this embodiment is more simplistic , it is not as efficient as custom tailoring each recharge amount to the energy lost from the transmission of each individual packet . from the foregoing , it will be appreciated that the present invention provides a rechargeable power supply that has sufficient power capacity to supply the electrical power needs of its corresponding peripheral , yet be small , lightweight and rechargeable by the main power supply of a battery powered portable computer without placing an undue burden on the main power supply of the portable computer . the present invention also provides an electrically efficient dc - to - dc recharging circuit powered by a lower power , battery powered power supply to recharge a higher power , battery or capacitor powered power supply . the present invention further provides a rechargeable power supply that would have sufficient power capacity to supply the electrical power needs of a packet - switched data radio , yet be small , lightweight and rechargeable by the main power supply of a battery powered portable computer without placing an undue burden on the power supply of the portable computer . the present invention provides a rechargeable battery or capacitor powered power supply for a packet - switched data radio that is rechargeable by either the main power supply of a battery powered portable computer or by an external ac power source . the present invention also provides an efficient means for testing the status of the rechargeable battery by detecting the level of energy stored in the rechargeable battery . the present invention may be embodied in other specific forms without departing from its spirit or essential characteristics . the described embodiments are to be considered in all respects only as illustrative and not restrictive . the scope of the invention is , therefore , indicated by the appended claims rather than by the foregoing description . all changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope .