Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2002-07-08
2004-06-29
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S267000, C323S271000, C363S060000
Reexamination Certificate
active
06756772
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This is the first application filed for the present invention.
MICROFICHE APPENDIX
Not applicable.
TECHNICAL FIELD
The present invention relates to voltage converters and, in particular, to a dual-output voltage converter that provides a regulated low voltage output as well as an auxiliary high voltage output.
BACKGROUND OF THE INVENTION
Many computer peripherals are powered from a single fixed DC voltage power supply and use step-down switching voltage regulators to supply lower voltages for driving logic circuits. A step-down switching voltage regulator, more commonly known in the art as a “buck” converter, converts an applied input voltage to a lower output voltage. The output stage of a synchronous buck converter typically includes a pair of switches coupled in series across the input voltage supply. One switch, the voltage switch, is coupled to the voltage supply and the other switch is connected to ground. An output filter typically including an inductor and a capacitor is connected to a junction formed by the pair of switches. The capacitor is responsible for reducing the ripple content in voltage across it, whereas the inductor smoothes the current passing through it. The combined action of the LC filter, therefore, reduces the ripple content in the output voltage supplied to a load connected to the buck converter. Typically, feedback from the output of the LC filter is provided to a controller which drives the switches to connect the output filter to the voltage supply or to ground in order to maintain the output voltage at some predetermined low voltage level.
At the same time, however, some applications require a higher voltage than available from the voltage supply to power linear (analog) devices. In this respect, battery-powered equipment use DC/DC step-up converters to generate auxiliary supply voltages for internal circuits that require higher voltages than the available battery voltage. The conventional approach is to use either a switched capacitor voltage booster (i.e. charge pump) or an inductive step-up converter (also called boost converter). Boost converters have a high efficiency over the entire input voltage range. Charge pumps, on the other hand, provide a high efficiency over selected input voltage ranges. Since their design does not require any knowledge of magnetics, charge pumps are much easier to design and implement. In either case, however, such auxiliary high voltage generators usually require the use of a dedicated integrated circuit to provide the boosted voltages.
FIG. 1
illustrates a simplified schematic of a conventional voltage converter
10
used for providing a regulated low voltage output (RLVO) as well as an auxiliary high voltage output (AHVO) from a single applied DC input voltage V
IN
. The input voltage V
IN
is received at an input terminal
11
and supplied separately to a step-down or “buck” integrated circuit voltage regulator VR
1
and to a charge pump voltage doubler circuit VR
2
. The step-down integrated circuit voltage regulator VR
1
includes a circuit block
12
, which includes a pair of switches S
1
and S
2
connected in series between the input terminal
11
and ground. Control circuitry for driving the switches S
1
and S
2
is not shown but understood to be embodied by the circuit block
12
. An output filter that includes an inductor L and a capacitor C is connected at the junction between the pair of switches S
1
and S
2
. The junction between the inductor and capacitor of the output LC filter provides the regulated low voltage output (RLVO). A feedback path
14
is further provided from the output of the LC filter to the circuit block
12
to permit the control circuitry to appropriately drive the switches S
1
and S
2
, so that a constant regulated low voltage output may be maintained.
The charge pump voltage doubler circuit VR
2
includes a circuit block
16
, which includes a pair of switches S
3
and S
4
connected in series between the input terminal
11
and ground. The associated control circuitry for driving the switches S
3
and S
4
is not illustrated but understood to be embodied within the circuit block
16
. A first stage of the charge pump circuit VR
2
includes a first diode D
1
and a first capacitor C
1
. The input terminal
11
is connected via the first diode D
1
to one electrode of the first capacitor while the other electrode of the first capacitor C
1
is connected to a junction between the pair of switches S
3
and S
4
of the circuit block
16
. A second stage of the charge pump circuit VR
2
includes a second diode D
2
and a second capacitor C
2
. A junction between the first diode D
1
and first capacitor C
1
is connected via the second diode D
2
to one electrode of the second capacitor C
2
. The other electrode of the second capacitor C
2
is connected to ground. The junction between the second diode D
2
and second capacitor C
2
of the charge pump circuit VR
2
provides the auxiliary high voltage output (AHVO).
The step-down voltage regulator VR
1
and charge pump VR
2
depicted in
FIG. 1
are standard circuit topologies whose operation is well known to those skilled in the art and, as such, will not be detailed.
As seen in
FIG. 1
, a dedicated switched-capacitor voltage booster or charge pump circuit VR
2
is needed to provide an auxiliary high voltage output from the single input DC voltage V
IN
applied to the step-down voltage regulator VR
1
. Alternatively, an inductive booster may be employed. Either approach, however, requires the use of a dedicated integrated circuit with associated control circuitry to provide an auxiliary boosted voltage from a single applied DC input voltage. This leads to a high component count resulting in higher cost while preventing improvement in integration density.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a voltage converter that integrates the functions of both a step-down voltage regulator and a charge pump into a single device.
A further object of the present invention is to provide a voltage converter capable of generating both a regulated low voltage output as well as an auxiliary high voltage output from a single applied input DC voltage.
Thus, an aspect of the present invention uses the inherent properties of a conventional step-down or “buck” switching voltage regulator with a push-pull output stage to provide an auxiliary output voltage higher than the applied input voltage. Specifically, the push-pull output stage of the step-down voltage regulator is used to drive a charge pump voltage doubler circuit. Advantageously, the novel circuit topology of the present invention provides a low component (i.e. two diodes and two capacitors) count resulting in lower component cost and smaller physical size.
REFERENCES:
patent: 5245524 (1993-09-01), Nakagawa et al.
patent: 5336985 (1994-08-01), McKenzie
patent: 5412308 (1995-05-01), Brown
patent: 5455501 (1995-10-01), Massie
patent: 5532577 (1996-07-01), Doluca
patent: 5635776 (1997-06-01), Imi
patent: 5886508 (1999-03-01), Jutras
patent: 5959442 (1999-09-01), Hallberg et al.
patent: 6222352 (2001-04-01), Lenk
patent: 6479972 (2002-11-01), Chen
patent: 6566846 (2003-05-01), Voo
Article “Simple Design of Low-Ripple DC/DC Boost Converter”, Nikkei Electronics Asia, Dec. 2000.
Website Info “Switch Mode Power Supply”, Power Designers, pp. 1-5 and 1-11.
Article DC-DC Converter Tutorial, 2002, Maxim Integrated Products.
(Ogilvy Renault)
Cogency Semiconductor Inc.
Sterrett Jeffrey
Wood Max R.
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