Method and Apparatus for Selectable DC to DC Conversion

This invention relates in general to a method and apparatus for DC to DC conversion. More particularly, this invention relates to a method and apparatus for capacitive DC to DC conversion with high efficiency and low battery voltage operation.

Portable receivers such as selective call receivers, pagers, personal messaging units (PMUs), and the like generally utilize a single cell battery for operation. These devices may contain components, such as a microprocessor which requires higher operating voltage than is available from the single cell battery. Accordingly, such devices require DC to DC conversion to provide the operating voltage needed for the components, such as the microprocessor, controller or LCD panel. DC to DC converters are used to boost the battery voltage to a converted voltage high enough to operate these components.

Inductive DC to DC converters have been used in the industry. One such converter is illustrated in U.S. Pat. No. 5,028,861 to Pace, assigned to the assignee of the present invention and incorporated herein by reference and generally described below. The DC to DC converter regulates the maximum current through an inductor. It operates within a paging receiver and boosts a voltage from a 1.4V DC single cell battery to substantially 3.1V DC in order to operate the circuits which require more voltage than a single cell battery.

Some of the disadvantages of using inductive DC to DC converters versus capacitive DC to DC converters are that inductors are less efficient, larger, and cost more than capacitors. Inductors are also less reliable, since they are more susceptible to shock and vibration. Furthermore, inductors are affected by other signals which occur in the receiver.

One solution to the problems associated with inductive DC to DC converters is realized in current CMOS capacitive voltage doublers (DC-DC converters) which use two external capacitors and alternate precharge and dump phases to generate double the battery voltage. For battery voltage VBB, the doubler increases this voltage to 2VBB. A voltage regulator may then be used to lower this voltage to the required level for operating the various components. For a voltage doubler, efficiency E is calculated by the equation E=Vout/2VBB. In a purely efficient operation (E=1.0), Vout would equal 2VBB. Accordingly, if it is desired to produce Vout=2.1V, with a battery initially charged to 1.55V, then the voltage doubler would produce a maximum of 2.times.1.55V=3.1V, which would need to be regulated down to 2.1V. The battery will slowly discharge over time and, upon reaching 1.05V, it will be at maximum efficiency, Vout=2VBB (2.1V=2.times.1.05V). After that point, Vout will no longer be sufficient to power the components and the battery should be replaced. Accordingly, the VBB "low level" would be limited at 1.05V. In this scenario, the efficiency is calculated to be between 0.68 and 1.00 (with 1.00 being the maximum at VBB=1.05V). The average efficiency is 0.83.

One problem with these CMOS capacitive voltage doublers, is that, as the battery discharges with usage over time, the operating voltage falls below suitable levels (e.g., 1.05V) and the battery would need to be replaced, even though it may still be supplying a reduced level of power. Specifically, the microprocessor can no longer operate when the doubled voltage fails below 2.1V in a pager. So, even though the battery has not completely discharged, it would need to be replaced. This results in higher costs to the end user in replacing the battery and may also lead to a greater risk of mechanical failure with the continued opening of the battery compartment. If the device is designed to be water resistant, frequent opening of the battery compartment may destroy or damage the water seal.

One solution to this problem would be to extend the battery life beyond the limits set by voltage doublers so that, for example, a pager can still operate for a time after the battery voltage falls below 1.05V.

Thus, there is a need in the art to extend the battery life beyond the limits set by voltage doublers that is efficient, reliable, economical and small sized.

FIG. 1 is a block diagram of a pager operating in accordance with the present invention.

FIG. 2 is a circuit diagram of the doubler configuration for a capacitive DC to DC converter.

FIG. 3 is a circuit diagram of the tripler configuration for a capacitive DC to DC converter.

FIG. 4 is a flow diagram representing the operation of the DC to DC converter in accordance with a preferred embodiment of the invention.

FIG. 5 is a graphical representation of voltage over time of Vout, VDD and VBB.

FIG. 6 is a timing diagram representing the operative stages of the various doubler and tripler configurations.

FIG. 7 is a block and circuit diagram of the multiplier and configurations of the capacitors for the DC to DC conversion.

FIG. 8 is a graphical representation of voltage over time of Vout, VDD and VBB with HLVBB on for a period of time in an alternate embodiment of the invention.

FIG. 9 is a timing diagram representing the operative stages of the various doubler and tripler configurations in an alternate embodiment of the invention.

FIG. 10 is a block diagram showing the operating control for the DC to DC configurations in an alternate embodiment of the invention.

FIG. 11 is a flow diagram representing the operation of the DC to DC converter in accordance with an alternate embodiment of the invention.

Referring initially to FIG. 1, a block diagram of a pager 100 operating in accordance with the present invention is shown. Paging signals are received by an antenna 110 and demodulated by a receiver 112. The paging signals may then be decoded by pager circuitry 114 controlled by a controller 124, such as a microprocessor. The receiver 112 is powered by a single cell battery 116 which generates a voltage VBB, typically a 1.4V battery which has a maximum voltage of substantially 1.55V which decreases as the battery discharges over time.

Receiving and decoding paging signals is well known in the art. The paging signals may be received on any of a plurality of paging protocols such as the GSC, POGSAG, or other protocols. In response to the reception of the paging signals, the receiver 112 is periodically activated. Additionally, the decoder operates in a low power mode while the receiver 112 is inactive and operates in a high power mode while the receiver 112 is active. The decoder searches the paging signal for an address which matches an address stored in memory 118. In response to detecting the address, an alert 120 may be generated, such as a tone or vibration which causes an increased load on the circuitry. Furthermore, the LCD display may include a light 122 which also loads the circuitry. Thus, it can be appreciated that the power consumption may vary dramatically.

The pager 100 includes a capacitive DC to DC converter 130 which can be configured into various multipliers (N) (e.g., N=2=doubler, N=3=tripler, etc.) by adding extra external capacitors. A voltage regulator 132 is then utilized to decrease the voltage level, Vout, to a required level for operation, VDD. The configuration of the DC to DC converter 130 is dependent, in part, on the battery voltage VBB and, in part, on the load. A voltage detector 152 (shown in FIG. 7) within the selector circuitry 134 is used to determine when the DC to DC converters 130 should be switched between the various configurations.

Referring generally to FIG. 1, the preferred embodiment of the invention generally includes, a voltage detector 152 for detecting a voltage level in a circuit; first DC to DC converter configuration of the DC to DC converter 130 (e.g., voltage doubler) for converting a first DC voltage, (e.g., the battery voltage, VBB) to a first converted DC voltage, (e.g., Vout); second DC to DC converter configuration of the DC to DC converter 130 (e.g., voltage tripler) for converting the first DC voltage, VBB, to a second converted DC voltage, (e.g., Vout); selector circuitry 134 responsive to the voltage detector 152 for selectively enabling the first or the second converters; and a voltage regulator 132 for regulating the first and second converted DC voltage (e.g., Vout) to a predetermined regulated voltage, VDD. The selector circuitry 134 initially enables the first converter configuration, and then disables the first converter configuration and enables the second converter configuration when the voltage level drops below a reference voltage, VREF, substantially equal to a minimum required voltage to adequately drive a load.

FIG. 2 shows the preferred configuration for a multiplier where N=2, i.e., doubler, in its precharge and dump stages. The preferred circuitry for switching between these stages is detailed in FIG. 7. These stages are controlled by a clock circuit which continuously alternates the capacitor configurations between precharge and dump. VBB is the battery voltage. During the precharge phase, capacitor Cp (pump-capacitor) is charged. Once Cp is fully charged, VCp=VBB, then during the dump phase, Cp is in series with VBB to produce Vout=VCp+VBB=2VBB. A filter capacitor, Cf, is used to smooth the output voltage.

FIG. 3 shows the preferred configuration for a multiplier where N=3, i.e., tripler, in its precharge and dump stages. Again, the preferred circuitry for switching between these stages is detailed in FIG. 7. During the precharge phase, capacitors Cp1 and Cp2 are connected in parallel to VBB and are thereby charged. Once the capacitors are fully charged, VCp1=and VCp2=VBB. Accordingly, at the dump phase, Vout=VCp1+VCp2+VBB=3VBB. A filter capacitor, Cf, is used to smooth the output voltage.

For the tripler, efficiency E is calculated by the equation E=Vout/3VBB. At maximum efficiency VBB=Vout/3 Accordingly, if it is desired to produce Vout .gtoreq.2.1V, with a battery 1.55V.gtoreq.VBB.gtoreq.0V, then the tripler would produce a maximum of 3.times.1.55V=4.65V, which would need to be regulated down to VDD=2.1V. Maximum efficiency would be reached when VBB=Vout/3=2.1V/3=0.7V. After that point, Vout will no longer be sufficient to power the components and the battery should be replaced. For the tripler, the VBB low level would not be limited until 0.7V. Thus, a tripler would increase the usable battery life by 12% compared to using only a doubler.

For maximum efficiency, in a preferred embodiment of the invention, the doubler would be used when VBB.gtoreq.1.05V, then the tripler would be activated for 1.05V>VBB.gtoreq.0.7V. The efficiency for the tripler, in this scenario, is between 0.67 and 1.00 (with 1.00 being the maximum at VBB=0.7V). The average efficiency is 0.82.

One skilled in the art would recognize configurations for larger multipliers, and the efficiency thereof, depending on the desired output voltage based on the input voltage.

In the preferred operation of the present invention, the microprocessor controls the switching between the doubler and the tripler configurations, which depends, in part, on relative voltages affected by VBB, for maximum efficiency, as illustrated in the example below. The value of VBB constantly decreases as the battery discharges over time.

If, for example, a 1.4V battery (VBB) is used and a load requires a minimum operating voltage of VREF=2.1V, initially the battery voltage (VBB) would need to be doubled by a doubler. The output of the doubler (Vout=2VBB), could then be regulated down to VDD=VREF=2.1V. As the voltage of the battery decreases over time through discharge, the output of the doubler, Vout, decreases proportionately. As long as the doubled battery voltage (2VBB) is greater than or equal to the minimum operating voltage VREF, the doubler configuration is sufficient to operate the load. However, once the doubled battery voltage is no longer high enough to operate the load (2VBB=Vout<VREF), a tripler configuration will be necessary to provide sufficient voltage to operate the load.

In a tripler configuration, the battery voltage (VBB) is tripled by a tripler. The output of the tripler (Vout=3VBB), is then regulated down to VDD=VREF=2.1V. As long as the tripled battery voltage (3VBB) is greater than or equal to the minimum operating voltage of VREF=2.1V, the tripler configuration will be sufficient to operate the load. However, once the tripled battery voltage is no longer high enough to operate the load (3VBB=Vout<VREF), the minimum operating voltage can no longer be sustained, and the battery should be replaced.

As shown in the flow diagram of FIG. 4, initially when VBB is greater than or equal to VREF/2, the doubler will be enabled, as illustrated by block 410. Vout will equal 2VBB during this time. Vout is then regulated down to the desired operating voltage VDD. For the above example, the doubler will be enabled when VBB.gtoreq.1.05V (VREF/2). If VBB is not less than VREF/2, the doubler will remain enabled. If VBB drops below VREF/2 (1.05V) as illustrated by decision block 412, VDD will fall below the minimum operating voltage of 2.1V and the doubler will be disabled and the tripler will be enabled, as illustrated by block 414. Vout will equal 3VBB during this time, which is then regulated down to the desired operating voltage VDD. Accordingly, in this example, the tripler will be active when 1.05V(VREF/2)>VBB. If VBB drops below 0.7V (VREF/3), as illustrated by decision block 416, VDD will fall below the minimum operating voltage of 2.1V and the battery should be replaced, as illustrated in block 418. If necessary, further multipliers could be utilized to produce Vout=NVBB, where N=multiplier value.

In short, as shown in the graphs of FIG. 5, the battery voltage VBB is shown as a line (dash-dotted line) having segments 510, 512 and 514 as it decreases over time as it discharges. Vout is represented as a solid line having segments 500,502 and 503. The value of Vout decreases proportionately to VBB ("resetting" at the intersection of point 501). VDD is represented as a dashed line having segments 520 and 522. Initially, the doubler configuration is enabled and the value of VDD is regulated to the reference voltage VREF=2.1V, segment 520. When VBB reaches VREF/2 (e.g., 1.05V), at point 511 of the graph, Vout will equal VDD, at point 501 of the graph. At this point, no regulation is necessary and the operation is at maximum efficiency.

After that point, a controller, such as a voltage management controller or microprocessor, will disable the doubler configuration and enable the tripler configuration of the DC to DC converter 130. Again Vout decreases proportionate to VBB over time, shown in segment 502. The value of VDD is again regulated to the reference voltage VREF=2.1V, shown in segment 522. When VBB reaches VREF/3 (e.g., 0.7V), at point 513 of the graph, Vout (and VDD) will continue to decrease, both shown as segment 503, until the system limit voltage is reached, at point 505 of the graph, VSM (e.g., 1.8V). Usually upon reaching the system limit voltage, the decoder (microprocessor and support chip) will reset.

In the timing diagrams of FIG. 6, (with reference to FIG. 5), the DC to DC converter has three modes of operation. First, when VBB.gtoreq.VREF/2, segment 510, the doubler is enabled, segment 530, the tripler is disabled, segment 540, Vout=2VBB, segment 500, and VDD is regulated to 2.1V, segment 520. Second, when VREF/2>VBB.gtoreq.VREF/3, segment 512, the tripler is enabled, segment 542, and the doubler is disabled, segment 532. Vout=3VBB, segment 502, and VDD is regulated down to 2.1V, segment 522. Third, VBB<VREF/3, segment 514, the doubler remains disabled, segment 534, and although the tripler remains enabled, segment 544, Vout =3VBB<VREF, segment 503, and VDD can no longer be regulated to 2.1V. Furthermore, when VDD falls below a system limit of, for example, VSM=1.8V, segment 505, the decoder (microprocessor and support chip) will reset. Generally, when VREF/(N-1)>VBB.gtoreq.VREF/N, then only the N-multiplier is enabled. In this scenario, the DC-DC conversion circuitry includes a voltage detector for detecting a voltage level in a circuit; a number of converters for converting a first DC voltage (e.g., battery voltage) to a number of converted DC voltages (Vout). Each of the converters include a voltage multiplier (N). A selector responsive to the voltage detector selectively (e.g., sequentially) enables each of the converters. A voltage regulator is used to regulate the converted DC voltages to a regulated voltage (VDD).

In operation, the selector initially enables a first converter having a voltage multiplier (N), wherein N is substantially equal to two (i.e., doubler). Then the selector disables the first converter (doubler), and sequentially enables each of the converters up to the plurality (tripler, quadrupler, etc.) each time the voltage level drops below a reference voltage. The reference voltage is substantially equal to a minimum required voltage to adequately drive a load. Each of the converters include the voltage multiplier (N), which has at least N-1 capacitors charged by a voltage source (e.g., battery) having a voltage level VBB. The capacitors are configured to provide a voltage substantially equal to N multiplied by VBB.

The DC to DC conversion circuitry and selector circuitry are detailed in FIG. 7. The selector circuitry 134 includes a two-phase non-overlap clock generator 162 and the precharge and dump generators, 129, 131, for the DC to DC conversion circuit configurations, 130. Selector logic switches, 134a-d, and 134f, and numerous gates, 137a-h, control the various configurations for the DC to DC conversion circuits, 130. The multiplier selector 156 controls the activation of the switches, 134a-d, and 134f, in response to the voltage detector 152. Capacitors CP1 and CP2 are charged depending on the activated gates. A filter capacitor Cf is used to smooth the output.

In operation, as illustrated in FIG. 7, to configure the doubler DC to DC conversion circuit, the multiplier selector 156 closes switch 134f to select gate 137f. Gates 137e, 137g and 137h are directly connected without switches and, therefore, are always selected in this configuration. In the precharge phase, gates 137e and 137g (directly) are connected to the precharge generator 129 such that CP1 is charged to VBB. During the dump phase, gates 137h (directly) and 137f (through switch 134f) are connected to the dump generator 131 such that Vout=VBB+VCP1.

To configure the tripler, as illustrated in FIG. 7, the selector closes switches 134a, 134b, 134c, 134d, (switch 134f is open) to select gates 137a, 137b, 137c and 137d. Gates 137e, 137g and 137h are directly connected without switches. In the precharge phase, gates 137a and 137c (through switches 134a and 134c) and gates 137e and 137g (directly) are connected to the precharge generator 129 to charge CP1 and CP2 to VBB. During the dump phase, gates 137b, 137d (through switches 134b and 134d) and gate 137h (directly) are connected to the dump generator 131, such that Vout=VBB+VCP1+VCP2.

This arrangement is applicable when VBB decreases constantly over time. To control the switching of configurations, a voltage detector 152 compares an input voltage VIN (e.g., VDD or VBB) to a value related to the reference voltage, VREF, to determine the appropriate times to switch configurations (e.g., when VREF/2>VBB.gtoreq.VREF/3, the multiplier selector 156 can signal the tripler to be enabled, gates 137a, 137b, 137c, 137d, 137e, 137g, 137h, and the doubler to be disabled).

Alternately, since the values of Vout and VDD depend, in part, on VBB, these voltages may be compared directly to the reference voltage VREF by the voltage detector 152 to determine the appropriate times to switch configurations (e.g., when Vout<VREF or when VDD can no longer be regulated to equal VREF, the multiplier selector 156 can signal to switch to the next higher multiplier). Accordingly, depending on the desired configuration, one of the inputs to the voltage detector VIN can equal VBB or VDD, depending on the value of the chosen reference voltage VREF.

Since there may be instances when the voltage may experience a sharp momentary decrease due to another load, (see segment 721 of FIG. 8) such as when a user utilizes a light or when a device signals with an alert, in an alternate embodiment, a control bit is used to signal the selector that the decrease in voltage is due to the load and not the discharge in the battery. After the load is disabled, VBB returns to its appropriate level (see segment 714 of FIG. 8). When VBB is no longer subject to the load, the appropriate multiplier needs to be enabled. The representative voltages for this situation are illustrated in the graph of FIG. 8 and discussed in detail hereafter.

Accordingly, the alternate embodiment of the invention further includes, a control bit, HLVBB 150 (shown as dashed line 150 in FIG. 7) input to the multiplier selector 156 which the controller 124 activates just before the high battery current load is activated, shown in FIG. 10. Control logic 154 will signal the switch selector 157 depending on the inputs from the voltage detector 152, which compares a voltage (Vout or VDD) to VREF, and from the HLVBB 150. Accordingly, the configuration of the DC to DC converter depends on (1) the constantly decreasing battery voltage VBB as illustrated above and (2) the sharp decreases in voltage due to loading.

Generally, the controller 124 in the alternate embodiment generates a high load signal HLVBB 150 (HLVBB=1) upon activation of a high load. The multiplier selector 156 initially enables the first converter (doubler configuration, gates 137e, 137f, 137g, and 137h), and, upon receipt of the high load signal 150 (HLVBB=1), and VDD<VREF the multiplier selector 156 temporarily disables the first converter (doubler configuration, gates 137e, 137f, 137g, and 137h) and temporarily enables the second converter (tripler configuration, gates 137a, 137b, 137c, 137d, 137e, 13g, 137h) until the high load signal 150 is inactive (HLVBB=0).

As in the preferred embodiment, when the voltage level drops below the reference voltage due to battery discharge over time, the multiplier selector 156 disables the first converter (doubler configuration, gates 137e, 137f, 137g, and 137h) and enables the second converter (tripler configuration, gates 137a, 137b, 137c, 137d, 137e, 137g, 137h).

Specifically, for example, the controller 124 will set a control bit to "1" (HLVBB=1) before it turns on the light for the display and will clear the control bit to "0" (HLVBB=0) after it turns off the light. The voltage detector 152 continues to monitor the input voltage VIN (e.g., VDD or Vout) with respect to the reference voltage VREF to determine whether the voltage is out of regulation, namely less than the desired voltage. The outputs of the voltage detector 152 and the HLVBB signal 150 are supplied to control logic 154 which controls the switch selector 157 for selecting the appropriate DC to DC converter configurations.

The switching between the configurations relative the voltage levels, in accordance with the alternate embodiment is shown in FIGS. 8 and 9. In short, as shown in the graphs of FIG. 8, the battery voltage VBB decreases over time as it discharges, illustrated in the dashed-dotted line shown by segments 710, 714, 716 and 718. The output voltage from the DC to DC converters, Vout, is shown as the solid line having segments 700, 702, 704, 706, and 708. Normally, the value of Vout decreases in proportion with the battery voltage, with a sharp increase in voltage when the configuration switches from doubler to tripler, point 705. The regulated voltage VDD is illustrated in the dashed line having segments 720, 722, 724, 726, and (solid line segment 708). VDD is regulated to equal VREF.

As in the preferred embodiment, when VBB reaches VREF/2 (e.g., 1.05V), point 715 of the graph, Vout will equal VDD, point 705 of the graph. At this point no regulation is necessary and the operation is at maximum efficiency. After that point, the microprocessor will disable the doubler and enable the tripler. Again VBB decreases over time as it discharges, segments 716 and 718. Vout decreases in proportion to VBB over time, segments 706 and 708. VDD again is regulated to equal VREF, segment 726. Finally, when VBB reaches VREF/3 (e.g., 0.7V), point 717, the battery power is no longer sufficient to power the circuitry, and Vout and VDD decrease, segment 708, until a system limit is reached, VSM (e.g., 1.8V), point 709. At that point the microprocessor resets and the battery should be replaced.

When a user utilizes a light or when a device signals with an alert VDD will experiences a sharp momentary decrease, segment 721. At that point, Vout, segment 701 also decreases momentarily due to this load. The battery voltage VBB may also experience a decrease in voltage, segment 712, during the load. At this point, in the alternate embodiment, the controller will signal the selector to temporarily enable the tripler to provide increased voltages for Vout, segment 702, and VDD, segment 722. VDD, therefore, has sufficient voltage to drive the load until the power drain is discontinued. Then, after the load is discontinued, the controller will signal the selector to return the DC to DC converter to the doubler configuration, and continue therefrom until either the battery discharges to a power level requiring the tripler, point 715, or another load forces temporary enabling of the tripler.

In short, as shown in the timing diagram of FIG. 9, (with reference to FIG. 8), when VBB.gtoreq.VREF/2, segments 710, 714, the doubler is enabled, segment 730, and the tripler is disabled, segment 740, and HLVBB is off, segment 750. VDD is regulated to 2.1V, segment 720.

When a high battery current load component, such as a light, is to be activated, the controller 124 first sets the HLVBB bit to "1", segment 752. Then the controller 124 turns on the high battery current load component which lowers the battery level, segment 712, and in turn lowers Vout and VDD levels, segments 701, 721. If VDD drops below the required regulated voltage, VREF, then VDD is then "out of regulation" as measured by the voltage detector 152. The DC--DC conversion circuits 130 are switched from doubler configuration (doubler disabled, segment 732) to tripler configuration (tripler enabled, segment 742) to bring VDD back to regulation, segment 722. After the controller 124 turns off the high battery current load components, VBB goes back to its previous level, segment 714. The controller 124 then clears the HLVBB bit, segment 754, which directs the multiplier selector 156 to switch back from the tripler (tripler disabled, segment 744) to the doubler (doubler enabled, segment 734) to achieve high efficiency and prolong the battery life. VDD again is regulated to 2.1V, segment 724.

When VREF/2>VBB.gtoreq.VREF/3, segment 716, the tripler is enabled, segment 746, and the doubler is disabled, segment 736. Again VDD is regulated down to 2.1V, segment 726. HLVBB is off, segment 756. Once VBB<VREF/3, segment 718, VDD can no longer be regulated to 2.1V, segment 708. Accordingly, the doubler remains disabled, segment 738, and the tripler is unchanged, segment 748. HLVBB remains off, segment 758. Upon reaching a system limit VSM (e.g., 1.8V), point 709, the microprocessor resets.

The method of operation can be described, generally as the steps of: (1) enabling a first converter (doubler configuration, gates 137e, 137f, 137g, and 137h) for converting a first DC voltage to a first converted DC voltage and regulating the first converted DC voltage to a regulated voltage; (2) detecting a voltage level in a circuit with a voltage detector 152; (3) setting a high load signal HLVBB 150 when a high power load is to be enabled and temporarily disabling the first converter (doubler configuration, gates 137e, 137f, 137g, and 137h) and temporarily enabling a second converter (tripler configuration, gates 137a, 137b, 137c, 137d, 137e, 137g, 137h) for converting the first DC voltage to a second converted DC voltage and regulating the second converted DC voltage to the regulated voltage, while the high load signal is active; (then returning to step 1), and (4) disabling the first converter (doubler configuration, gates 137e, 137f, 137g, and 137h) and enabling the second converter (tripler configuration, gates 137a, 137b, 137c, 137d, 137e, 137g, 137h) for converting the first DC voltage to the second converted DC voltage and regulating the second converted DC voltage to the regulated voltage responsive to the voltage detector when the voltage level drops below a reference voltage substantially equal to a minimum required voltage to adequately drive a load.

The steps of operation are shown in FIG. 11. Initially, the doubler is enabled, block 910, to double VBB to produce Vout=2VBB. Vout is then regulated down by conventional means to the desired regulated voltage VDD (e.g., 2.1V). A voltage detector 152 will monitor the regulated voltage VDD to determine whether the regulated voltage drops below the required level, VREF. If VDD drops below the required regulated level (VDD<VREF), decision block 912, then if the HLVBB=1 (high battery current load component in use), decision block 914, the multiplier is switched from the doubler to the tripler (doubler disabled; tripler enabled block 916). The tripler remains enabled until HLVBB=0 (high battery current load component no longer in use), decision block 918. Once HLVBB=0, the tripler is disabled, block 920, and the doubler is enabled, block 910, as it initially was.

If, however, VDD drops below the required regulated level (VDD<VREF) and HLVBB=0 (high battery current load component not in use), decision block 914, then the multiplier selector 156 switches the configurations from the doubler to the tripler, block 922, and will remain in the tripler configuration until the battery completely discharges (or drops below a usable range), block 924.

As illustrated above, a number of multipliers may be utilized. In this case, the multiplier selector initially enables one of a number of converters having a voltage multiplier (N), wherein N is substantially equal to two, (doubler). Each time the voltage level drops below a reference voltage, provided the high load signal is inactive, the selector disables the first converter, and selectively (e.g., sequentially) enables each of the subsequent converters up to the plurality. Upon receipt of the high load signal, the selector temporarily disables a currently enabled converter having a voltage multiplier (N), and temporarily enables the next converter having a voltage multiplier (N +1), until the high load signal is inactive.

A number of advantages arise from practice of this method and apparatus for DC to DC conversion. The invention provides for increased battery life by utilizing selector circuitry which changes multiplier configurations depending upon voltage levels, thereby allowing the circuitry to operate even after the battery voltage has dropped below limits set by using only a doubler. The invention also determines whether a decrease in voltage is due to a high load or from usage over time, and switches the multiplier configurations accordingly to obtain high efficiency.

Thus, it is apparent that there has been provided, in accordance with the invention, a method and apparatus for DC to DC conversion. While the invention has been described and illustrated with reference to specific embodiments thereof, it is not intended that the invention be limited to these illustrative embodiments. Those skilled in the art will recognize, after review of the foregoing description, that variations and modifications differing from the illustrative embodiments are possible. It is intended that all such variations and modifications as fall within the spirit and scope of the invention be included within the appended claims.