Flashlight with hybrid battery and electronic control circuit

A flashlight has a hybrid battery pack consisting of a primary-cell battery (ex: an Alkaline battery) and an auxiliary rechargeable battery of low internal resistance (ex: a Ni--Cad battery). Connected in circuit between the batteries and the flashlight's light bulb is a slide switch and an electronic control circuit. The slide switch has an OFF-position, an ON-position, and a spring-loaded variable BOOST-position. In full BOOST, the electronic control circuit operates such as to apply a voltage of about 1.5 times normal magnitude to the light bulb; thereby increasing the flashlight's light output by a factor of about 4.0 above normal. However, at that degree of BOOST, if indeed maintained on a continuous basis, the life of the light bulb will be shortened to about 15 minutes versus about 50 hours when used in the normal ON-position. The function of the auxiliary battery, which is controllably charged by the primary-cell battery, is that of permitting the size of the primary-cell battery to be much smaller than otherwise would be required to provide the increased power associated with the BOOST-position.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to flashlights and similar battery-powered 
light sources. 
2. Background of the Invention 
Flashlights are well known products; which, in many situations provide much 
less light than might be wanted. 
SUMMARY OF THE INVENTION 
Objects of the Invention 
An object of the present invention is the provision of cost-effective means 
whereby the light output from a battery-powered light source, such as a 
flashlight, might be boosted beyond what normally would be obtained. 
Another object is that of providing for a special battery pack comprising a 
combination of a more-or-less ordinary primary-cell battery with a 
rechargeable battery having low internal resistance. 
These as well as other objects, features and advantages of the present 
invention will become apparent from the following description and claims. 
Brief Description 
A flashlight has a hybrid battery pack consisting of a primary-cell battery 
(such as an ordinary Alkaline battery) and an auxiliary rechargeable 
battery of low internal resistance (such as a collection of ordinary 
Ni--Cad cells). Connected in circuit with the batteries and the 
flashlight's light bulb is a slide switch and an electronic control 
circuit. The slide switch has an OFF-position, an ON- position, and a 
spring-loaded variable BOOST-position. In full BOOST, the electronic 
control circuit operates such as to apply a voltage of about 1.5 times 
normal magnitude to the light bulb; thereby increasing the flashlight's 
light output by a factor of about 4.0 above normal. However, at that 
degree of BOOST, if indeed maintained on a continuous basis, the life of 
the light bulb will be shortened to about 15 minutes versus about 50 hours 
when used in the normal ON-position. 
The function of the auxiliary battery, which is controllably charged on 
command from the primary-cell battery, is that of permitting the size of 
the primary-cell battery to be much smaller than otherwise would have been 
required to provide the increased power associated with the BOOST-position 
.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Details of Construction 
FIG. 1 schematically illustrates a basic embodiment of the invention in the 
form of an electrical circuit diagram. 
In FIG. 1, a battery B has a B+ terminal and a B- terminal. The B+ terminal 
is connected with a switch terminal ST1 of a slide switch SW; which switch 
terminal, in turn, is connected with a slideable arm SA of slide switch 
SW. Slideable arm SA is connected with a spring S, and has first and 
second slide contactors SC1 and SC2, as well as a slide conductor SC and a 
slide resistor SR. Slide conductor SC and slide resistor SR are both 
mounted on a back board BB; in which back board there is a first detent 
D1. Slide conductor SC, in which there is a second detent D2, is connected 
with a switch terminal ST2. Slide resistor SR has a first terminal point 
TP1 and a second terminal point TP2; which second terminal point is 
connected with a switch terminal ST3. 
An energy-storing inductor L is connected between switch terminal ST2 and a 
first junction J1; and a light bulb LB is connected between first junction 
J1 and a second junction J2. 
A forward converter means FCM has: (i) a common terminal CT, which is 
connected with second junction J2; (ii) a power control terminal PCT, 
which is connected with first junction J1; and (iii) a control input 
terminal CIT, which is connected with switch terminal ST3. 
FIG. 2 diagrammatically illustrates a forward converter of a type suitable 
for use in the basic embodiment of FIG. 1. 
In FIG. 2, battery B and battery terminals B+ and B- are equivalent to the 
corresponding elements of FIG. 1. However, slide switch SW of FIG. 1 has 
been replaced with a switch means SM; which has a first switch terminal 
ST1', a second switch terminal ST2', and a third switch terminal ST3'. 
Within switch means SM is: (i) an ON-OFF switch OOS connected between 
switch terminals ST1' and ST2'; (ii) a BOOST switch BS connected between 
switch terminal ST2' and a junction Js; and (iii) an adjustable resistor 
AR connected between junction Js and switch terminal ST3'. 
An energy-storing inductor L', corresponding to energy-storing inductor L 
of FIG. 1, is connected between switch terminal ST2' and a first junction 
J1'; which energy-storing inductor has an auxiliary winding AW, whose 
terminals are connected between the anode of diode Dx and a junction Jx. 
A transistor Q is connected with its emitter to a second junction J2', 
and--by way of a first primary winding PW1 of a saturable current 
transformer SCT--is connected with its collecter to junction J1'. The base 
of transistor Q is connected with switch terminal ST3' by way of secondary 
winding SW of saturable current transformer SCT. 
A resistor Rx is connected with the cathode of diode Dx by way of a second 
primary winding PW2 of saturable current transformer SCT. Another resistor 
Ry and a capacitor Cx are both connected between switch terminal ST3' and 
junction J2'. 
Light bulb LB is connected between junctions J1' and J2'. 
FIG. 3 illustrates a flashlight FL made in accordance with the invention. 
In FIG. 3, an ON/OFF/BOOST control means OOBM--which corresponds to slide 
switch SW of FIG. 1--has a slide lever SL slideably movable in a slide 
slot SS between markings OFF, ON, BOOST and MAX. 
FIG. 5 schematically illustrates an alternative embodiment of the 
invention. In FIG. 5, a battery B' has B+' and B-' terminals. A 
three-position switch TPS has: (i) a first switch terminal ST1", Which is 
connected with the B+ terminal; (ii) a second switch terminal ST2", which 
is connected with a first junction J1"; and (iii) a third switch terminal 
ST3", which is connected with a first IC terminal ICT1 of an integrated 
circuit IC. 
A second IC terminal ICT2 is connected with first junction J1". A third IC 
terminal ICT3 is connected with a second junction J2"; which is also 
connected with the B-' terminal. A fourth IC terminal ICT4 is connected 
with second junction J2" by way of an adjustable resistor AR'. A light 
bulb LB' is connected between junctions J1" and J2". 
FIG. 7 illustrates the preferred embodiment of the invention in the form of 
a schematic electric circuit diagram. 
In FIG. 7, a first battery B"l is connected with its negative terminal to a 
negative bus NB" and with its positive terminal to a positive bus PB". 
Positive bus PB" is connected with a first switch terminal ST"l of a switch 
means SM". A second switch terminal ST"2 of switch means SM" is connected 
with a first terminal T"l of an integrated circuit IC". A second terminal 
T"2 of integrated circuit IC" is connected with negative bus NB". 
A second battery B"2 is connected with its positive terminal to a third IC 
terminal T"3 of integrated circuit IC". A light bulb LB" is connected with 
its two terminals between negative bus NB" and a fourth terminal T"4 of 
integrated circuit IC". 
An adjustable resistor AR" is connected between negative bus NB" and a 
fifth terminal T"5 of integrated circuit IC". 
A momentary switch MS" is connected between positive bus PB" and a sixth 
terminal T"6 of integrated circuit IC". 
An adjustable voltage sensor AVS" is connected between negative bus NB", 
terminal T"4 and a seventh terminal T"7 of integrated circuit IC". 
Explanation of Waveforms 
FIG. 4 shows some of the current and voltage waveforms associated with the 
arrangement of FIG. 1. 
FIG. 4(a) shows the waveform of the voltage V1 provided across light bulb 
LB under a condition of providing a moderate amount of BOOST; while FIG. 
4(b) shows the waveform of the corresponding current I1 flowing through 
inductor L. 
FIG. 4(c) shows the waveform of the voltage V2 provided across light bulb 
LB under a condition of providing maximum amount of BOOST; while FIG. 4(d) 
shows the waveform of the corresponding current I1 flowing through 
inductor L. 
FIG. 6 shows some of the current and voltage waveforms associated with the 
arrangement of FIG. 5. 
FIG. 6(a) shows the waveform of the voltage V1' provided across light bulb 
LB' under a condition of providing a moderate amount of BOOST; while FIG. 
6(b) shows the waveform of the voltage V2' provided across light bulb LB' 
under the condition of providing the maximum amount of BOOST. 
Details of Operation 
In the arrangement of FIG. 1, with slideable arm SA in the position shown, 
battery B is disconnected and no power flows through light bulb LB. With 
slideable arm SA moved from its first (or OFF) detent D1 and into its 
second (or ON) detent D2, the full battery voltage gets applied to light 
bulb LB via slide conductor SC. However, connection is not yet made with 
slide resistor SR; and forward conversion means FCM constitutes an open 
circuit between terminals PCT and CT. 
Moving slideable arm SA past its ON-detent causes connection to be made 
between the B+ terminal and slide resistor SR, thereby causing a control 
current to flow into control input terminals CIT. This control current 
will cause forward conversion means FCM to start operating such as to 
cause a short circuit to occur intermittently between junctions J1 and J2. 
With reference to FIG. 4, forward conversion means FCM causes a relatively 
brief short circuit to occur periodically between junctions J1 and J2 (see 
FIG. 4a or 4c). During each such brief period of short circuit, the DC 
voltage of battery B is applied directly across energy-storing inductor L; 
which means that whatever current was flowing through that inductor just 
prior to the onset of the short circuit will increase rapidly (see FIG. 4b 
or 4d). At the end of each brief period of short circuit, the by-now 
larger-magnitude inductor current will be switched to flow through light 
bulb LB. Thereafter, its magnitude will decay in an exponential manner 
toward the level determined by the ratio of the magnitude of the DC 
voltage and the magnitude of the resistance of the light bulb. 
As a result, the RMS magnitude of the voltage V1 resulting across the light 
bulb will be larger that it was without the action of the forward 
conversion means. That is, the reduction in RMS magnitude resulting from 
the periodic brief short circuits is more than compensated-for by the 
increase in RMS magnitude resulting from the extra energy imparted to the 
energy-storing inductor during the periods when the short circuit is 
present and released during the periods when the short circuit is not 
present. 
Without the action of the forward converter means, the current flowing from 
the battery would simply be at the level indicated by the minimum points 
of waveform I1. As a result of the action of the forward converter means, 
the average magnitude of the current drawn from the battery increases; 
which increased flow of current simply translates into increased power 
drawn from the battery; which increased power has no other place to go but 
into the light bulb. 
By varying the duration of the short circuit period, the amount of power 
applied to the light bulb will vary correspondingly. FIG. 4c indicates a 
situation where the RMS magnitude of the voltage applied across the light 
bulb has been increased by about 50%. 
Forward conversion means FCM may be made in many different ways. For 
instance, it could be made in the form of a custom integrated circuit 
expressly designed to perform the function herein specified. Or, it could 
be made in the manner illustrated by FIG. 2; which shows a 
self-oscillating single transistor oscillator. 
In the circuit of FIG. 2, when switches OOS and BS are both closed, current 
flows through adjustable resistor AR, thereby to charge capacitor Cx. 
Eventually, the voltage on Cx reaches a magnitude high enough to cause 
transistor Q to become conductive, at which point current will start 
flowing into the collector of transistor Q and thereby through primary 
winding PW1 of saturable current transformer SCT as well. In turn, this 
flow of collector current will cause additional base current to be 
provided to the base of transistor Q; and, by means of positive feedback, 
transistor Q now becomes fully conductive: sufficiently so to constitute 
an effective short circuit between junctions J1 and J2. 
After a brief period of time, such as about 10 micro-seconds, saturable 
current transformer SCT saturates, thereby stopping the flow of base 
current; which therefore causes transistor Q to stop conducting. Now, the 
increased inductor current will flow into the light bulb; and, as a 
result, a voltage is induced across auxiliary winding AW; which voltage, 
by way of diode Dx and secondary winding PW2, is used for resetting 
saturable current transformer SCT, thereby to make it ready for a new 
cycle. 
While secondary winding SW provided base current for transistor Q, this 
base current actually flowed out of capacitor Cx and therefore caused the 
voltage at terminal ST3' to become quite negative; which, as long as this 
negative voltage does indeed exist, prevents transistor Q from entering 
another cycle of positive-feedback-maintained conduction. However, current 
flowing through adjustable resistor AR will gradually cause the voltage at 
terminal ST3' again to become positive and to cause transistor Q to start 
conducting; whereafter transistor Q, with the help of saturable current 
transformer SCT, will initiate another positive-feedback-maintained period 
of conduction. 
The lower be the magnitude of the resistance of adjustable resistor AR, the 
shorter be the time it takes for the negative voltage at terminal ST3' to 
be dissipated; and the shorter become the duration of the periods of 
transistor non-conduction versus the duration of the periods of transistor 
conduction. 
For additional information with respect to the operation of single-ended 
self-oscillating transistor oscillators, reference is made to U.S. Pat. 
No. Re. 32,155 to Ole Nilssen. 
With respect to the operation of flashlight FL of FIG. 3, it is sufficient 
to mention that the light output from this flashlight is controlled as 
follows. 
With slide lever SL in the OFF-position, no light is provided. With the 
slide lever in the ON-position, an ordinary amount of light is provided. 
Both the OFF-position and the ON-position are detented. 
Pushing slide lever SL past the detented ON-position, light output 
increases in approximate proportion to the degree to which the slide lever 
is pushed past the ON-position. When the slide lever is pushed all the way 
to the indicated MAX-position, the light output will be about four times 
higher than it is in the normal-output ON-position. 
The slide lever is spring-loaded in such manner that, when pushed past the 
ON-position and without expressly holding it there, it will automatically 
return to the detented ON-position. 
Whereas the arrangement of FIG. 1 is intended for a situation where the 
light bulb is designed to operate in its normal mode of light output, as 
well as to have an ordinary life expectancy, when powered with the full 
voltage available from the battery; the arrangement of FIG. 5 is intended 
for a situation where the light bulb is designed to have an unusually high 
level of light output, as well as an unusually short life expectancy, when 
powered with the full voltage of the battery. 
Thus, while the task of forward conversion means FCM of FIG. 1 is that of 
increasing the RMS magnitude of the voltage applied to the light bulb, 
thereby to get increased light output in exchange for reduced bulb life 
expectancy; the task of integrated circuit IC of FIG. 5 is that of 
decreasing the RMS magnitude of the voltage applied to the light bulb, 
thereby to get increased bulb life expectancy in exchange for reduced 
light output. 
Thus, in the arrangement of FIG. 5, operating the light bulb so as to 
attain an ordinary level of light output in combination with an ordinary 
life expectancy, requires a reduction of the RMS magnitude of the voltage 
available directly from the battery. By way of integrated circuit IC, this 
reduction in RMS magnitude is simply attained by connecting/disconnecting 
the light bulb from the battery in a rapid periodic manner, thereby to 
reduce the RMS magnitude of the voltage applied to tile light bulb in 
proportion to the square root of the duty cycle. That is, compared with a 
100% or unity duty cycle (where the light bulb is continuously connected 
with the battery) a 50% of 0.5 duty cycle (where the light bulb is 
connected with the battery only 50% of the time) gives rise to a reduction 
of RMS magnitude by a factor equal to the square root of 0.5, or equal to 
about 0.7. 
While the arrangement of FIG. 1 requires an energy-storing inductor in 
order to attain a voltage magnitude boost; the arrangement of FIG. 5 does 
not require such an energy-storing means since it does not need to attain 
a voltage magnitude boost. 
The function of the circuit of FIG. 5 is illustrated by the voltage 
waveforms of FIG. 6. 
The voltage waveform of FIG. 6b indicates a situation of near maximum 
BOOST; where the full battery voltage is applied to the light bulb with 
nearly 100% duty cycle. The voltage waveform of FIG. 6a indicates a 
situation where the full battery voltage is applied to the light bulb with 
less than 50% duty cycle, such as to cause the RMS magnitude of the 
voltage applied to the light bulb to be only about two thirds of the full 
battery voltage, thereby providing for about one fourth the light output 
and 200 times longer life expectancy as compared with providing the light 
bulb with the full battery voltage. 
The operation of the circuit arrangement of FIG. 7 is substantially the 
same as that of FIG. 5, except for three important features. 
(1) The first of these features relates to the use of two separate 
batteries in combination to form a hybrid battery pack: first battery B"1 
and second battery B"2; 
(2) the second of these features relates to an automatic procedure by which 
to charge second battery B"2 (which is a rechargeable battery) from first 
battery B"l (which is a primary battery); and 
(3) the third of these features relates to means for automatically 
regulating the RMS magnitude of the voltage provided to light bulb LB" 
First battery B"l is a more-or-less ordinary Alkaline primary battery; 
second battery B"2 is a more-or-less ordinary Nickel-Cadmium rechargeable 
battery. 
The purpose of second battery B"2 is that of operating as an energy-storing 
buffer; which is to say: it is used much like an energy-storing capacitor 
of extremely high capacitance. This energy-storing buffer battery B"2 is 
charged from primary battery B"l over a relatively long period of time 
(and therefore quite efficiently). Once charged, however, buffer battery 
B"2 will permit--for brief periods at a time--an extra high rate of power 
output to be provided to light bulb LB", much higher than could possibly 
have been provided by primary battery B"l alone. The reason for this is 
that the internal resistance of an ordinary Nickel-Cadmium battery is very 
much lower than that of an ordinary Alkaline battery of similar size. 
To automatically charge buffer battery B"2 by a predetermined amount of 
energy (or for a predetermined length of time), it is only necessary to: 
(i) close switch means SM"; and (ii) momentarily depress momentary switch 
MS". During this charging procedure, which may last for a few of minutes, 
adjustable voltage sensor AVS" should be so set as to call for no more 
than a nominal RMS magnitude of the voltage provide to light bulb LB". 
Any time after buffer battery B"2 is charged, adjustable voltage sensor 
AVS" may be used for the purpose of providing the BOOST function. 
The function of adjustable voltage control AVC" is that of permitting 
manual control of the RMS magnitude of the output voltage (i.e. the 
voltage provided between terminal T"4 and negative bus NB", which is 
voltage provided to the terminals of light bulb LB"). When adjustable 
voltage sensor AVS" is set at its one extreme position, the RMS magnitude 
of the output voltage is substantially zero; when it is set at its other 
extreme position, the RMS magnitude of the output voltage is at its 
maximum level; which maximum level is adjustable by the setting of 
adjustable resistor AR" and is generally such as to provide for a 
substantial boost in the light output of light bulb LB" as compared with 
that light bulb's normal light output. 
That is, even if the magnitude of the DC voltage supplied from first 
battery B"l may vary from time to time (such as may occur as first battery 
B"l gets discharged), or even if different light bulbs were to be used, 
the RMS magnitude of the output voltage is regulated to be substantially 
constant at whatever level is called-for by the position of adjustable 
voltage sensor AVS". 
Additional Comments 
(a) The arrangement of FIG. 1 corresponds to a situation of merely adding 
the indicated electronic circuitry to an otherwise ordinary flashlight 
having a common (ex: 3 Volt, two-cell) battery and a matching ordinary 
(ex: 3 Volt, 50 hour) light bulb. 
(b) The arrangement of FIG. 5 corresponds to a situation of either: (i) 
using an ordinary-voltage (ex: 3 Volt, two-cell) battery in combination 
with a lower-voltage (ex: 2 Volt, 50 hour) light bulb; or (ii) using a 
higher-voltage (ex: 4.5 Volt, three-cell) battery in combination with an 
ordinary-voltage (ex: 3 Volt, 50 hour) light bulb; or (iii) using an 
ordinary-voltage (ex: 3 Volt, two-cell) battery in combination with a 
matching short-life/high-efficacy (ex: 15 minutes life) light bulb; etc. 
(c) It is important to realize that in incandescent lamps, such as ordinary 
light bulbs for flashlights, there is a clear and consistent relationship 
between luminous efficacy and lamp life. By increasing the RMS magnitude 
of the voltage applied to a given lamp, the lamp's luminous efficacy 
increases while its life expectancy decreases. Conversely, by reducing the 
RMS magnitude of the voltage applied to the lamp, the lamp's luminous 
efficacy decreases while its life expectancy increases. 
(d) Clearly, in the arrangement of FIG. 5, instead of reducing the RMS 
magnitude provided to the light bulb by way of duty-cycling the connection 
between the light bulb and the battery, a variable resistor means could be 
used for attaining such a reduction. However, efficiency (and thereby 
battery life) would then be severely compromised. 
(e) In light of instant disclosure, it is clear that the BOOST feature may 
be also be attained--although only in a non-variable manner--either: (i) 
by powering a given light bulb with a two-cell battery and then, to attain 
a fixed-level BOOST, to switch-in an auxiliary cell such as to increase 
the RMS magnitude of the voltage applied to the light bulb; or (ii) by 
connecting to a given battery either one or the other of two light bulbs: 
one designed for normal operation on the voltage from the given battery, 
the other designed to provide high-efficacy/short-life operation on that 
same voltage. 
Also, the effect of two light bulbs could be attained by using a light bulb 
with two filaments. 
(f) Just as is the case with forward conversion means FCM of FIG. 1, 
integrated circuit IC of FIG. 5 may--in the form of a custom integrated 
circuit made to function in accordance with the functional specifications 
provided herein--readily and routinely be obtained from a semiconductor 
manufacturer. 
(g) The basic BOOST feature herein disclosed is applicable to various types 
of battery-powered lighting means, including those wherein the light 
output is provided by gas discharge lamps. 
(h) Clearly, the BOOST feature is basically intended to be used for only a 
small percentage of the total usage time of a flashlight. Normally, a 
flashlight with the BOOST feature would have a light bulb that would have 
a life expectancy of about 50 hours if used continuously in the 
ON-position and about 15 minutes if used continously in the MAX-BOOST 
position. 
In actual usage, it is expected that the flashlight will be used in the 
plain ON-position most of the time, and in the MAX-BOOST-position for only 
a small fraction of the time. What is important to understand is that each 
minute of usage on the MAX-BOOST-position is equivalent--as far as wear of 
the light bulb is concerned--to over three hours of usage in the plain 
ON-position. However, due partly to the much increased luminous efficacy 
associated with the MAX-BOOST-position, battery life will be much less 
affected by use of the MAX-BOOST-position: continuous operation in the 
MAX-BOOST-position would only shorten battery life by a factor of two or 
so; yet, the total net resulting light output (in Lumen-hours) attained 
from the battery would have doubled. 
(i) The word "lamp" is herein defined to include various forms and types of 
incandescent light bulbs (ex: light bulbs for battery-powered hand-held 
flashlights) as well as gas discharge lamps (ex: fluorescent lamps for 
camper lanterns). 
(j) In light of the invention herein disclosed, is it clear that the 
circuit arrangement illustrated by FIGS. 5 and 6 can be used for light 
DIMMING as well as for light BOOSTING. That is, it would readily be 
feasible to power the light bulb (in an adjustable manner) at less than 
the normal amount of power, thereby attaining longer than normal lamp life 
expectancy. 
Also, while provisions are made for spring-loaded automatic return to 
regular ON-position after having used the BOOST-position, a similar 
automatic return from a DIM-position would not be necessary. Hence, in 
some lighting products it would be anticipated that the light control 
function include a detented OFF-position, a continuous DIMMING-range, a 
detented ON-position, an automatic-return BOOSTING-range, and an 
automatic-return MAX-BOOST-position. 
(k) Also, by slight modification of the circuit arrangement of FIG. 5, 
mechanical switch means (such as TPS) may be entirely eliminated. Instead, 
integrated circuit IC may be made in such manner as to provide for all the 
required switching functions, for instance by way of a simple 
high-resistance potentiometer; which would provide both for the ON/OFF 
function as well as for the continuous-range DIMMING/BOOSTING function. 
(1) By using a simple photo-sensor to sense the luminous output from the 
light bulb, and to feed the output from this photo-sensor back to 
integrated circuit IC, it is simple to provide for automatic control of 
luminous output, thereby to compensate for reduced battery output voltage 
with wear as well as for diminished luminous efficacy as the light bulb 
ages. 
Of course, any changes in battery voltage can be automatically 
compensated-for merely by so specifying the IC. 
(m) It is anticipated that it be desirable in some cases to filter the 
current provided to the light bulb, thereby to avoid possible mechanical 
resonances in the filament due to the high frequency content of the 
chopped voltage. In the arrangement of FIG. 5, this filtering would not 
need to consist of more than a filter capacitor connected in parallel with 
the light bulb and a filter inductor connected in series with the 
parallel-combination of the light bulb and the filter capacitor. 
(n) In the arrangement of FIG. 7, the nominal voltage of first battery B"l 
is somewhat higher than that of second battery B"2, thereby making the 
charging of the second battery by the first battery particularly simple. 
However, by using a forward conversion arrangement, as in FIGS. 1 and 2, 
the nominal voltages of the two batteries do not have to match one 
another. 
(o) In situation where initial battery cost would be of lesser importance, 
a Lithium battery might be particularly appropos as first battery B"I. For 
a given size, a Lithium battery would have more energy available than an 
ordinary Alkaline battery. However, the internal resistance of a Lithimum 
battery is substantially higher than that of an Alkaline battery; which 
would therefore make the use of a Nickel-Cadmium battery particularly 
appropos as a buffer for such a Lithium battery. 
(p) As energy is drained from it, the terminal voltage of an ordinary 
Alkaline primary battery gradually diminishes. Typically, a nominal 6 Volt 
Alkaline battery loaded at 0.5 Ampere provides an output voltage of 5.5 
Volt when it is new, but provides only about 3.5 Volt after half the 
available energy is consumed. Thus, the amount of light provided by a 
flashlight powered by such a battery diminishes drastically as the battery 
is used. In all probability, before the battery is even halfway 
discharged, the light output would be so diminished (by a factor of more 
than three to one) as to cause the ordinary user to assume that the 
battery must be replaced. Hence, the feature of regulating the RMS 
magnitude of the voltage provided to the light bulb in a flashlight 
provides for a major de facto increase in useful battery life. 
(q) Whereas an Alkaline (or a Lithium) battery may be stored for years 
without losing a significant portion of its energy, a charged 
Nickel-Cadmium battery loses its energy after but a few months. Thus, in 
at least some applications, it is important not to arrange for the 
Alkaline battery to charge the Nickel-Cadmium battery on a continuous 
basis. Instead, as is indeed provided-for in the arrangement of FIG. 7, 
the Nickel-Cadmium battery receives only a pre-determined modest amount of 
charge at a time, and then only after having been expressly called-for (as 
by momentarily depressing momentary switch MS") by the user of the 
flashlight. 
(r) Clearly, the combination hybrid battery pack herein described may be 
useful in applications other than flashlights. For instance, instead of 
light bulb LB" in FIG. 7, a portable radio may be the load; and 
arrangements can be made whereby the Nickel-Cadmium battery is being 
programmably charged whenever the radio is in use. That way, a far higher 
peak audio power level may be provided than would be possible to provide 
from the Alkaline batteries alone. 
(s) In the arrangement of FIGS. 1 and 2, it should be noted that the RMS 
magnitude of the voltage provided across the terminals of light bulb LB is 
higher than that of the DC voltage provided by battery B. 
(t) It is believed that the present invention and its several attendant 
advantages and features will be understood from the preceeding 
description. However, without departing from the spirit of the invention, 
changes may be made in its form and in the construction and/or 
interrelationships of its component parts, the form herein presented 
merely representing the currently preferred embodiment.