Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2001-02-15
2001-08-14
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S283000
Reexamination Certificate
active
06275016
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to buck-boost switched voltage regulators (also referred to as buck-boost DC—DC voltage converters), and more particularly to improvements therein which reduce power dissipation, provide smooth transitions between buck mode and boost mode, and provide stable operation during fast switching of the load current.
So-called Cuk and Sepic switching topologies are known for buck-boost voltage regulation, and are described in “Dynamic Analysis of the Switch-Mode DC/DC Converters”, by Andre Kislovski et al., Van Nostrand Reinold, New York, pp. 177-203. The Cuk and Sepic topologies include two inductors. This nearly doubles the amount of circuit board area, the cost, and the amount of EMI (electromagnetic interference) produced by the regulator. Another typical prior art buck-boost switching voltage regulator includes two power switches, two diodes (or synchronous rectifiers), one inductor, and a load capacitor. Such typical prior art buck-boost switching voltage regulators are described in U.S. Pat. Nos. 4,395,675, 4,578,630, 5,528,125, 5,734,258 and 5,602,463. These buck-boost topologies typically include two simultaneously switching power transistors and two diodes or synchronous rectifiers operating invert each clock or oscillation cycle. This essentially doubles the power dissipation of the regulator in most of its operating modes.
U.S. Pat. No. 5,734,258 discloses complex inductor coupling arrangements in a buck-boost switching regulator, wherein switching decisions are based on the relationship between the unregulated input voltage and the output voltage. This technique does not allow fast response to rapid changes in the load. Furthermore, the operation of circuitry within the buck-boost switching regulator is unpredictable when the output voltage is nearly equal to the unregulated input voltage. Furthermore, products using complex custom inductor arrangements and transformer arrangements are unsuitable for high-volume production.
Prior buck-boost switched voltage regulators typically use a comparator to determine whether the input voltage or the regulated output voltage is larger, and use that information to control only one of the switches. This approach is often slow because too much “cycling” is required. Furthermore, if the unregulated input voltage goes significantly below the regulated output voltage, that may cause serious circuit stability problems.
Therefore, there is an unmet need for a low-cost, fast-responding integrated circuit buck-boost switching voltage regulator having stable circuit operation despite large differences between the unregulated input voltage and the regulated output voltage.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an economical buck-boost switched voltage regulator having low power dissipation.
It is another object of the invention to provide an economical buck-boost switched voltage regulator that provides smooth transitions between buck mode and boost mode operation.
It is another object of the invention to provide an economical buck-boost switched voltage regulator that provides fast, stable circuit operation despite rapid changes in the load to which the regulated output voltage is applied.
It is another object of the invention to provide an economical buck-boost switched voltage regulator that avoids inaccuracies and/or circuit instability resulting from switching decisions based on use of a comparator to determine which of the unregulated input voltage and the regulated output voltage is greater.
Briefly described, and in accordance with one embodiment thereof, the invention provides a voltage regulator (
1
) including a first switch (S
1
) coupled between an input conductor (
2
) and a first terminal (
4
) of an inductor (
5
), a second switch (S
2
) coupled between the first terminal of the inductor and a common conductor (
3
), a third switch coupled between an output conductor (
7
) and a second terminal (
6
) of the inductor, and a fourth switch (S
4
) coupled between the second terminal of the inductor and the common conductor (
3
). A first signal (V
32
) representative of the difference between an output voltage (V
OUT
) is produced on the output conductor (
7
) by the voltage regulator and a reference voltage. A pulse width modulated signal (PWM) is produced by comparing the first signal to a reference voltage. The first (S
1
) and fourth (S
4
) switches are controlled in response to the pulse width modulated signal and first (Q
23
) and second (Q
27
) state signals representative of prior states of the first (S
1
) and fourth (S
4
) switches. In one embodiment, a signal (I
MEAS
) is produced representative of current through the inductor (
5
). A signal is produced representing a combination of the first signal and the second signal and is compared to the reference voltage to produce the pulse width modulated signal.
REFERENCES:
patent: 4395675 (1983-07-01), Toumani
patent: 4578630 (1986-03-01), Grosch
patent: 4974141 (1990-11-01), Severinsky et al.
patent: 5528125 (1996-06-01), Marshall et al.
patent: 5602463 (1997-02-01), Bendall et al.
patent: 5734258 (1998-03-01), Esser
patent: 5831418 (1998-11-01), Kitagawa
“Dynamic Analysis of the Switch-Mode DC/DC Converters” by Andre Kislovski et al., Van Nostrand Reinold, New York, pp. 177-203, No date.
Brady W. James
Riley Shawn
Swayze, Jr. W. Daniel
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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