Abstract:
Methods and apparatuses are disclosed for power conversion in fuzes for projectiles. Fuze electronics in the projectile control detonation of the projectile. A rectifier converts pulses from a setter signal to a DC power source signal. A voltage monitor coupled to the power source signal generates a source voltage indicator and a current monitor coupled to the power source signal generates a source current indicator. A combiner generates a supplied power level indicator in response to a combination of the source voltage indicator and the source current indicator. A DC-DC converter uses the supplied power level indicator when converting the power source signal to a power output signal to adjust a current level of the power output for efficient charging of a charge storage device and delivery of power to the fuze electronics.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     The U.S. Government has a paid-up license in this invention and the right in limited circumstances to require the patent owner to license others on reasonable terms as provided for by the terms of Contract No. W15QKN-06-C-0130 awarded by the Department of Defense. 
    
    
     TECHNICAL FIELD 
     Embodiments of the present invention relate generally to providing energy to fuzes for explosive projectiles and, more particularly, to controlling delivery of inductive power to charge storage devices and fuze electronics. 
     BACKGROUND 
     The following background description is provided to assist the understanding of the reader. None of the information provided or references cited in this background section is admitted to be prior art to the present invention. 
     Fuzes for explosive projectiles often receive programming information from a message coil in a projectile launcher that uses alternating current (AC) signals through inductive transfer to a receiver coil in the fuze to receive the message. This inductive message transfer device is often referred to as an inductive setter. In some fuzes, power may be extracted from the AC message to power the fuze, charge capacitors, or combinations thereof. 
       FIG. 1  illustrates a fuze circuitry used to extract power from an inductive setter  10 . The AC signal on from the inductive setter  10  feeds a rectifier  20  including a full-wave diode bridge rectifier for converting the AC signal to a DC signal  25 . A capacitor  30  may be used to filter the rectified voltage to create a more stable DC signal. The DC signal may drive fuze power circuitry  40  that may further condition and regulate the DC signal to provide power at varying loads to the fuze electronics. Excess power not used by the fuze power circuitry  40  may be captured by a capacitor in a capacitor charging circuit  50 . The capacitor charging circuit  50  may provide power to the fuze electronics after the messaging has completed and the inductive setter  10  is no longer providing an AC signal. Generally, in such a configuration, the power output from the inductive setter  10  must be maintained at or below a specified average power level. 
     However, the energy storage capacitor starts to charge from zero volts, which appears as a virtual short circuit to a DC power source. As a result, current to the capacitor  30  must be limited to avoid exceeding the average power limit of the inductive setter  10 . Previous designs limited the current to the capacitor  30  to a preset constant value until the storage capacitor was fully charged. 
       FIG. 2  illustrates a constant current power ramp  80  to a storage capacitor. Line  60  indicates a power limit for the inductive setter  10  ( FIG. 2 ). As the capacitor voltage increases over time and with constant current, the power going into the capacitor increases linearly as illustrated by line  80  and reaches its maximum power level only when the capacitor is fully charged at time  70 . Actual energy captured by the storage capacitor is illustrated by shaded area  90 . Thus, the inductive setter  10  outputs its power limit  60  only at the very end of the capacitor charging period, limiting the energy capture efficiency to only 50%. 
     In addition, as the fuze load changes during the setting operation, (e.g., components are powered down after their data transfer is complete) there is no redirection of available energy to the storage capacitor. This means that the constant current value must be conservatively set at a level to account for the maximum fuze power draw, even though this may only occur over a brief portion of the entire setting operation. 
     There is a need to improve the efficiency of power delivery to charge storage devices and fuze electronics with power supplies and power needs that vary over time. 
     BRIEF SUMMARY 
     Embodiments of the present invention comprise apparatuses and methods to improve the efficiency of power delivery to charge storage devices and fuze electronics with power supplies and power needs that vary over time. 
     An embodiment of the invention comprises a fuze power conversion circuit for a projectile. A voltage monitor is operably coupled to a power source signal and is configured to generate a source voltage indicator. A current monitor is operably coupled to the power source signal and is configured to generate a source current indicator. A combiner is operably coupled to the source voltage indicator and the source current indicator and is configured to generate a current adjustment signal in response to at least one of the source voltage indicator and the source current indicator. A DC-DC converter is configured to convert the power source signal to a power output signal and to adjust a current level of the power output signal responsive to the current adjustment signal. 
     Another embodiment of the invention comprises a fuze for a projectile, which includes a rectifier configured for converting an AC input from a setter signal to a DC input signal. Fuze electronics are configured for controlling detonation of the projectile and receiving power from the DC input signal. A fuze power conversion circuit includes a power input determiner and a power converter. The power input determiner is configured for generating a current adjustment signal in response to determining a power amount on the DC input signal from sensing a current and a voltage on the DC input signal. The power converter is configured for converting the DC input signal to a DC output signal wherein the current adjustment signal modifies a current output on the DC output signal to maintain a power level of the DC input signal substantially near a predefined level. 
     Another embodiment of the invention comprises a method for converting power for a fuze in a projectile. The method includes converting a DC source signal to a DC output signal responsive to at least one PWM signal. A charge storage device is charged with at least some power from the DC output signal. A voltage and a current of the DC source signal are sensed and a power input on the DC source signal is determined responsive to a combination of the sensed voltage and current of the DC source signal. The at least one PWM signal is generated in response to the determined power input to maintain the power input substantially near a predefined level. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  illustrates a fuze circuitry used to extract power from an inductive setter; 
         FIG. 2  illustrates a constant current power ramp to a storage capacitor; 
         FIG. 3  is a simplified block diagram of a fuze power conversion circuit according to one or more embodiments of the present invention; 
         FIG. 4  is a simplified block diagram illustrating additional detail of the switching regulator and combiner of the faze power conversion circuit of  FIG. 3 ; 
         FIGS. 5A and 5B  are simplified block diagrams illustrating possible embodiments of a power input determiner; 
         FIG. 6A  illustrates plots of various signals for the fuze power conversion circuit of  FIG. 3 ; and 
         FIG. 6B  illustrates the plots of  FIG. 6A  with noise and oscillations removed to better see the average DC signals for the fuze power conversion circuit of  FIG. 3 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice the invention. It should be understood, however, that the detailed description and the specific examples, while indicating examples of embodiments of the invention, are given by way of illustration only and not by way of limitation. From this disclosure, various substitutions, modifications, additions rearrangements, or combinations thereof within the scope of the present invention may be made and will become apparent to those skilled in the art. 
     In accordance with common practice the various features illustrated in the drawings may not be drawn to scale. The illustrations presented herein are not meant to be actual views of any particular method, device, or system, but are merely idealized representations that are employed to describe various embodiments of the present invention. Accordingly, the dimensions of the various features may be arbitrarily expanded or reduced for clarity. In addition, some of the drawings may be simplified for clarity. Thus, the drawings may not depict all of the components of a given apparatus (e.g., device) or method. In addition, like reference numerals may be used to denote like features throughout the specification and figures. 
     It should be understood that any reference to an element herein using a designation such as “first,” “second,” and so forth does not limit the quantity or order of those elements, unless such limitation is explicitly stated. Rather, these designations may be used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements may be employed there or that the first element must precede the second element in some manner. Also, unless stated otherwise a set of elements may comprise one or more elements. 
     Embodiments of the present invention comprise apparatuses and methods to improve the efficiency of power delivery to charge storage devices and fuze electronics with power supplies and power needs that vary over time. 
       FIG. 3  is a simplified block diagram of a fuze power conversion circuit  100  according to one or more embodiments of the present invention. A setter signal  105  from a launch apparatus (not shown) is conveyed by an inductive setter. From the setter signal  105 , an AC signal  115  is generated by a coil assembly  110 . The AC signal  115  may be used by a message extractor  128  to extract fuze programming and other information from the AC signal  115 . For example, the AC signal  115  may include amplitude modulated or frequency modulated signals on the base AC signal  115  as the message. 
     The AC signal  115  feeds a rectifier  120  (such as, for example, a full-wave diode bridge) to convert the AC signal  115  to a Direct Current (DC) signal  125  (may also be referred to herein as a rectifier output  125 ). A capacitor C 1  may be used to filter the rectified voltage to create a more stable and smooth DC signal  125 . A resistor R 1  causes a small voltage drop between the DC signal  125  and a power source signal  135  (may also be referred to herein as a DC source signal  135  or a DC input signal  135 ). 
     A current monitor  140  coupled to the DC signal  125  and the power source signal  135  may be used to sense the voltage drop across the resistor R 1  and thus evaluate a current on the power source signal  135 . As a non-limiting example, the current monitor  140  may be an amplifier coupled between the DC signal  125  and the power source signal  135  to generate a source current indicator  145  as a voltage correlated to the current on the power source signal  135 , which may be indicated by the voltage drop across the resistor R 1 . Of course, other current monitors  140  may also be used, such as, for example, a current monitor  140  that can directly sense the current on the power source signal  135  without requiring resistor R 1  and the voltage drop therefrom. 
     A voltage monitor  150  coupled to the DC signal  125  or the power source signal  135  ( FIG. 3  illustrates a connection to the DC signal  125 ) may be used to sense a voltage on the power source signal  135 . As a non-limiting example, the voltage monitor  150  may be a simple resistor divider network (not shown) to generate a source voltage indicator  155  as a voltage correlated to the voltage on the power source signal  135 . Of course, other voltage monitors  150  may also be used, such as, for example, a buffer or an amplifier coupled to the resistor divider network or to the power source signal  135 . 
     The power source signal  135  feeds a DC-DC converter  200  (may also be referred to herein as a power converter  200 ) for generating a power output signal  185  (may also be referred to herein as a DC output signal  185 ). As a non-limiting example, the DC-DC converter  200  may be a buck converter that uses a switching regulator  250  and pulse-width modulation of currents through an inductor L 1 . 
     The power output signal  185  may operably couple to a charge storage device C 2 , such as, for example, a capacitor, a bank of capacitors, a super-capacitor, or a bank of super-capacitors. The charge storage device C 2  may be used to store energy produced by the DC-DC converter  200  for later use by the fuze electronics  190  (may also be referred to herein more generically as a load  190 ). In addition, the charge storage device C 2  may assist in filtering the power output signal  185  to produce a smoother and more stable DC output. Of course, while not shown, a person of ordinary skill in the art will recognize that other passive components such as resistors and additional capacitors (not shown) may be used in filtering the power output signal  185 . 
     An output voltage monitor  170  may be included to sense a voltage on the power output signal  185 . The output voltage monitor  170  may be embodied as a simple resistor divider network (not shown) to generate an output voltage indicator  175  as a voltage correlated to the voltage on the power output signal  185 . Of course, as with the voltage monitor  150 , the output voltage monitor  170  may be configured in many different ways. As non-limiting examples, a buffer may be used or an amplifier coupled to a resistor divider network may be used. Moreover, the output voltage indicator  175  may be conditioned with processes, and apparatuses configured to perform the processes, such as filtering or voltage level adjustments up or down to achieve a substantially smooth voltage correlated to the power output signal  185  and at a level for use by a combiner  300 . 
     As will be explained more fully below with reference to  FIGS. 4 ,  5 A, and  5 B, the combiner  300  may combine one or more of the source current indicator  145 , the source voltage indicator  155 , and the output voltage indicator  175 , to generate a current adjustment signal  395  to the switching regulator  250 . 
     In the buck converter embodiment illustrated in  FIG. 3 , a switched power output  183  drives the inductor L 1  and the charge storage device C 2  to create the power output signal  185 . A high sense signal  184  coupled to the inductor L 1  may feed back to the switching regulator  250  as an indication of the voltage produced by the DC-DC converter  200 . In addition, a feedback resistor R 2  may be coupled between the high sense signal  184  and the power output signal  185  to create a small voltage drop between the high sense signal  184  and the power output signal  185 . The power output signal  185  may be coupled to the switching regulator  250  as a low sense signal  188  such that the voltage drop across feedback resistor R 2  indicates an amount of current being supplied by the power output signal  185 . 
     In some embodiments, the power output signal  185  may be coupled to the charge storage device C 2  and the fuze electronics  190  to share the current produced by the DC-DC converter  200 . In such a configuration, power not used by the fuze electronics  190  as a fuze power input  195  will charge the charge storage device C 2 . Thus, when power is no longer being supplied by the setter signal  105 , and as a result, the DC-DC converter  200 , the fuze electronics  190  may draw from the charge storage device C 2  to provide additional power. 
     In other embodiments, the power source signal  135  may be used as the fuze power input  195 . In such a configuration, the amount of power available to the DC-DC converter  200  may be reduced by the amount of power used by the fuze power input  195 . The power output signal  185  will charge the charge storage device C 2 . In such a configuration, when power is no longer being supplied by the setter signal  105 , the fuze electronics  190  may draw from the charge storage device C 2  to provide additional power on an additional fuze power input  198 . 
     As non-limiting examples for one embodiment, the voltage level on the power output signal  185  may be in a range of about 10-25 volts while the voltage level on the power source signal  135  may be in a range of about 28-32 volts. 
     Conventional DC-DC converters generally track a voltage on the output and feed this voltage back to a pulse-width-modulation control to adjust pulse widths of the current through the inductor L 1  to control overall voltage levels on the output. Generally, DC-DC converters don&#39;t track input voltages and input currents because those parameters are usually less important, or well known, in the overall system and the important factor for the DC-DC converter is to create a stable output at a specified voltage. However, with fuze electronics  190  powered by inductive setters  105 , the amount of power available is very limited. As a result, it is desirable to capture as much of that energy as possible. In addition, the amount of current or power that may be drawn from the inductive setter is required to be maintained at or below a predefined limit. As discussed above, with reference to  FIG. 1 , for many DC-DC converters with a power limit on the input, the energy capture efficiency may be only 50% for charging a capacitor. 
     Accordingly, to substantially optimize charging of the charge storage device C 2 , it may be useful to track the input to the DC-DC converter  200  as a function of voltage, current, or power to better deliver current to the charge storage device C 2  for storing energy to be used later by the fuze electronics  190 . Embodiments of the present invention provide more efficient energy capture for inductive fuzing applications. The embodiments monitor output power from the inductive setter  105  and draw substantially near the maximum available power until the charge storage device C 2  is fully charged. As the fuze electronics  190  power requirements fluctuate (i.e., present a time-varying load), the increased or decreased available energy for the charge storage device C 2  is detected and excess energy is re-directed into the charge storage device C 2  in response to the detected available energy. In other words, the energy capture process for inductive fuzing applications increases power capture efficiency by dynamically throttling the charging current to the charge storage device C 2  based on the amount of available energy from the inductive setter  105 . 
     The switching regulator  250  may be configured to have a current limit (e.g., based on the high sense signal  185  and the low sense signal  188 ) that is used to limit the cycle by cycle maximum current through the inductor L 1  as well as a maximum limit for any component in series with the charging current. This current limit may be set well above the peak storage capacitor charging current such that current is available for both the charge storage device C 2  and the fuze electronics  190 . 
     In addition, the charge storage device C 2  may have a voltage charging limit at which it is fully charged. Once the charge storage device C 2  reaches this predetermined voltage threshold, the combiner  300  may use the output voltage indicator  175  to control the current adjustment signal  395  to substantially reduce the amount of power produced by the DC-DC converter  200 . The reduced power from the DC-DC converter  200  is sufficient because only a trickle power is needed to maintain the charge storage device C 2  at full charge or the power output need is substantially reduced because there is only a need to supply power to the fuze electronics  190 . 
     The buck converter and the switching regulator  250  described herein use an example of a synchronous buck converter using a forward current switch (i.e., P 1 ) and a reverse current switch (i.e., N 1 ). However, other embodiments, such as a basic buck converter (which uses a reverse bias diode in place of the reverse current switch) or a boost converter may also be used in embodiments of the present invention. In addition, the switching regulator  250  described herein uses a constant off-time type control for the pulse-width modulation. Other pulse-width modulation may be used with embodiments of the present invention, such as, for example, a constant period type control.  FIG. 4  is a simplified block diagram illustrating additional detail of the switching regulator  250  and the combiner  300  of the fuze power conversion circuit  100  of  FIG. 3 . Both  FIGS. 3 and 4  are used in much of the description of operation of the switching regulator  250  and the combiner  300 . A comparator  280  compares the difference in voltages on the low sense signal  188  and the high sense signal  184 , which are connected across the feedback resistor R 2 . A p-channel transistor P 1  is coupled between the power source signal  135  and the switched power output  183 . An n-channel transistor N 1  is coupled in series between the p-channel transistor P 1  and ground. When the voltage drop across the feedback resistor R 2  reaches a high threshold value, a pulse-width-modulation (PWM) control circuit  290  negates PWM signal  295 P to turn off the p-channel transistor P 1  and asserts the PWM signal  295 N to turn on the n-channel transistor N 1 . In other words, the current on the power output signal  185  has reached a high enough level that the increasing current storing energy in the inductor L 1  should be reversed through the n-channel transistor N 1  to extract the stored energy in the inductor L 1 . 
     An off timer  270  tracks the voltage on the low sense signal  188  to estimate when a voltage level on the power output signal  185  has fallen below a low threshold value. At that time, the PWM control circuit  290  asserts the PWM signal  295 P to turn on the p-channel transistor P 1  and negates the PWM signal  295 N to turn off the n-channel transistor N 1 . In other words, the current on the power output signal  185  has reached a low enough level that sufficient energy stored in the inductor L 1  has been extracted and current should be supplied to the inductor L 1  to begin storing energy in the inductor L 1 . This process of reversing current through the inductor L 1  is repeated such that the voltage drop across the feedback resistor R 2  oscillates between the high threshold and the low threshold. 
     A voltage level adjuster  260  coupled between the comparator  280  and the high sense signal  184  may be used to adjust the high threshold value at which the PWM control circuit  290  shuts off the p-channel transistor P 1 . In a baseline configuration, a gain stage  255  drives resistor R 3  to create a baseline voltage for the voltage level adjuster  260 . A feedback voltage  251  may be compared to a reference voltage  252  by the gain stage  255  to create the baseline voltage. As a non-limiting example, the reference voltage  252  may be set to about 1.25 volts and the feedback voltage  251  may be coupled to a voltage divider coupled to the low sense signal  188 , such that at a steady state condition on the feedback voltage  251  is substantially near the reference voltage  252 . In this configuration, as the current on the power output signal  185  increases, the voltage on the power output signal  185  will decrease slightly, which will cause the gain stage  255  to slightly increase the comparator threshold at the comparator  280 . 
     The combiner  300  may further modify the comparator threshold through the current adjustment signal  395 . Reverse bias Zener diodes D 1  and D 2  may be configured with a reverse breakdown voltage near or above the baseline voltage produced by the gain stage  255  and resistor R 3 . 
     As stated earlier, the output voltage indicator  175  may be configured to produce a voltage correlated to the predetermined voltage threshold at which the charge storage device C 2  is fully charged. At that point, the output voltage monitor  170  may be configured to place a low enough voltage on the output voltage indicator  175  to drive the current adjustment signal  395  lower. The lower current adjustment signal  395  will change the comparator threshold at the comparator  280  via the voltage level adjuster  260 , such that the current output on the power output signal  185  is throttled back to a much lower level. 
     As another control path, a power input determiner  320  may generate a current level adjustment signal  325  to lower the compartor threshold at the comparator  280  via the voltage level adjuster  260 . The power input determiner  320  uses the source current indicator  145  and the source voltage indicator  155  to generate the current level adjustment signal  325 . Thus, the power input determiner  320  can make adjustments to the amount of current produced on the power output signal  185 , via the current level adjustment signal  325 , in response to the amount of power being delivered on the power source signal  135 . 
       FIGS. 5A and 5B  are simplified block diagrams illustrating two example embodiments for the power input determiner  320 . In  FIG. 5A , a digital embodiment of the power input determiner  320 A includes an analog-to-digital converter  330  to convert the source current indicator  145  to a digital current value  345 . Another analog-to-digital converter  340  converts the source voltage indicator  155  to a digital voltage value  335 . A digital multiplier  350  multiplies together the digital voltage value  335  and the digital current value  345  to arrive at a digital power value  355 . A digital-to-analog converter  360  converts the digital power value  355  back to an analog signal as the current level adjustment signal  325 . A signal conditioner  380 A may be included to adjust the current level adjustment signal  325  to appropriate levels for the voltage level adjuster  260  ( FIG. 4 ) by filtering, adjusting the voltage level, or a combination thereof. The digital multiplier  350  may be included in a controller  390  configured for performing additional functions for the fuze electronics  190  ( FIG. 3 ). In some embodiments, the analog-to-digital converters  330  and  340  may be included in the controller  390  ( FIG. 3 ). In other embodiments, the analog-to-digital converters  330  and  340  may be discrete parts. Moreover, a single analog-to-digital converter ( 330  or  340 ) may be time multiplexed to provide the digital voltage value  335  from the source voltage indicator  155  and provide the digital current value  345  from the source current indicator  145 . In addition, the digital-to-analog converter  360  may be a discrete part or included in the controller  390 . When included in the controller  390 , the signal conditioner  380 A may perform its functions digitally before or after the digital-to-analog conversion. 
     In  FIG. 5B , an analog embodiment of the power input determiner  320 B is illustrated. An analog multiplier  370  may be configured to perform a multiplication of the source current indicator  145  and the source voltage indicator  155  to generate an analog power output  375 . A signal conditioner  380 B may be included to adjust the current level adjustment signal  325  to appropriate levels for the voltage level adjuster  260  by filtering, adjusting the voltage level, or a combination thereof. 
     To mitigate the impact of short term transient behavior, both the source current indicator  145  and the source voltage indicator  155  may be averaged over a sliding time window to determine an average value for the appropriate indicator over the time window. The averaging may be performed in the analog domain, such as, for example, by appropriate low-pass filtering circuitry The averaging may also be performed in the digital domain by averaging multiple samples of the digital current value  345  and the digital voltage value  355  ( FIG. 5A ) over the sliding time window. Providing average values may assist in generating a more stable power output by removing noise or other undesired transients from the raw signals. Of course, the length of the sliding time window may be adjusted depending on the application, the expected variations in signals, and the response time of the feedback loops in the DC-DC converter  200  ( FIG. 3 ). 
     In some embodiments, the rectifier output ( 125  in  FIG. 3 ) may vary over a wide voltage range. In such embodiments, it may be best to use a current control system that is responsive to the overall input power as a product of the source voltage indicator  155  and the source current indicator  145 , as described above. These embodiments may be referred to herein as input-power responsive systems. 
     In other embodiments, it may be appropriate to control the current on the power output signal  185  in response to only the source voltage indicator  155  or only the source current indicator  145 . In such embodiments, the multiplier may be configured to multiply the appropriate indicator (voltage  155  or current  145 ) by a constant or unity. 
     In an input-voltage responsive system, the power input determiner  320  would generate a voltage indication. Thus, the DC-DC converter  200  can throttle current to the charge storage device C 2  by pulling the rectified voltage down to a minimum level. In other words, a voltage level on the power source signal  135  can be monitored. As more power is drawn from the inductive setter  105 , the voltage level on the power source signal  135  will decrease. The DC-DC converter  200  will pull as much power as possible from the inductive setter  105  until the voltage level on the power source signal  135  is pulled down to a preset level and then throttle the current on the power output signal  185 , via the current level adjustment signal  325 , to maintain the voltage level on the power source signal  135  at or near the preset level. 
     In an input-current responsive system, the power input determiner  320  would generate a current indication to throttle the DC-DC converter  200 . In other words, The DC-DC converter  200  will increase the current on the power output signal  185  until the average current on the power source signal  135  reaches a preset maximum level. Then, the DC-DC converter  200  can throttle the current on the power output signal  185 , via the current level adjustment signal  325 , to draw at or near the maximum specified current for the power source signal  135 . 
       FIG. 6A  illustrates plots of various signals for the fuze power conversion circuit of  FIG. 3  when configured in an input-power responsive system.  FIG. 6B  illustrates the plots of  FIG. 6A  with noise and oscillations removed to better see the average DC signals for the fuze power conversion circuit of  FIG. 3 .  FIG. 3  will also be referred to in discussing  FIGS. 6A and 6B . Line  610  illustrates “voltage in” on the power source signal  135 . Line  620  illustrates “current in” on the power source signal  135 . Line  660  illustrates “voltage out” on the power output signal  185  and line  670  illustrates “current out” on the power source signal  135 . Line  630  illustrates “power in” on the power source signal  135  as a product of the voltage in  610  and the current in  620 . 
     The voltage in  610  is shown in ×10 volts and the voltage out  660  is shown in volts. The current in  620  and the current out  670  are shown in amps. The power in  630  is shown in watts. 
     At time  605 , power is applied at the inductive setter  105  and the power in line  630  rises rapidly. This rapid rise is opposed to a conventional system as illustrated in  FIGS. 1 and 2  wherein the power rises slowly. Once the power in line  630  reaches a specified power level, the DC-DC converter  200  begins to throttle the current on the power output signal  185  to maintain the power in line  630  at or near the specified power level. When the charge storage device C 2  reaches a full charge, the voltage out line  660  will go over the predetermined voltage threshold indicating the charge storage device C 2  is fully charged. At that point, indicated by time  695 , the feedback path with the output voltage monitor  170  will substantially reduce the current output on the power output signal  185 , which also causes the voltage in line  610 , the current in line  620 , and the voltage out line  660  to drop. 
     Input-current responsive systems would operate similar to the curves shown in  FIGS. 6A and 6B  except that there would be no need to monitor the power in line  630  and the current in line  620  would be held near the predefined level for input current. Similarly, input-voltage responsive systems would operate similar to the curves shown in  FIGS. 6A and 6B  except that there would be no need to monitor the power in line  630  and the voltage in line  610  would be held near the predefined level for input voltage. 
     Although the present invention has been described with reference to particular embodiments, the present invention is not limited to these described embodiments. Rather, the present invention is limited only by the appended claims and their legal equivalents.