Electric power conversion systems – Current conversion – With voltage multiplication means
Reexamination Certificate
2000-07-26
2001-05-01
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With voltage multiplication means
C363S060000
Reexamination Certificate
active
06226193
ABSTRACT:
The invention relates to a DC/DC converter operating on the charge pump principle, receiving an input voltage and regulating it into a fixed, predetermined output voltage.
Many electronic circuits require in addition to the supply voltage further voltages sometimes at a level above that of the supply voltage. One low-cost, simple and with respect to converters employing a coil highly compact solution for making these further voltages available are DC/DC converters operating on the charge pump principle. Converters of this kind are described e.g. in the text book “The Art of Electronics” by Paul Horowitz, 2nd edition, Cambridge University Press, New York, 1991 on pages 377 to 379 thereof.
Horowitz also describes a simple DC/DC converter operating on the charge pump principle which may be employed to attain an output voltage corresponding, at the most, to roughly twice the input voltage. The basic circuit of the converter consists substantially of a charge pump capacitor and four controllable switches (e.g. MOSFETs), whereby one electrode of the charge pump capacitor is connectable via the first switch to the input voltage terminal of the converter and via the second switch to ground, and the other electrode of the capacitor is connectable via the third switch to the input voltage terminal and via the fourth switch to the output voltage terminal of the converter. The converter comprises further a control circuit including a clock oscillator which signals the switches so that in a first phase of a clock cycle, the so-called charge phase, the second switch and the third switch are ON whilst the other switches are OFF so that the charge pump capacitor is charged to the input voltage, and in a second phase of a clock cycle, the so-called discharge phase, the first switch and the fourth switch are ON whilst the other switches are OFF so that the charged charge pump capacitor is then connected in series to the input voltage, resulting in a voltage value at a smoothing and storage capacitor located at the output of the circuit corresponding to roughly twice the input voltage.
In the DC/DC converter described, operating in accordance with the charge pump principle, the output voltage undesirably drops off sharply at even small load currents, however. Since in the majority of applications the output voltage, which e.g. in digital electronic circuits is often 3.3 or 5 V, is fixed and is allowed to fluctuate only in a tight range, regulated converters have been developed which set the output voltage to a fixed, desired voltage value.
The regulators of the DC/DC converters comprise as a rule a comparator which compares the actual output voltage or a voltage proportional to the actual output voltage (the proportional voltage being derived e.g. from the output voltage via a voltage divider) to a predetermined reference voltage representing the design output voltage and then, when a deviation is sensed, outputs a control signal, with the aid of which the actual output voltage is adapted to the predetermined design output voltage value.
Described in U.S. Pat. No. 5,680,300 are two types of regulators employed in DC/DC converters operating on the charge pump principle, i.e. the so-called linear regulator and the so-called skip mode regulator.
In the linear regulator the control signal of the comparator changes, e.g. via a gate of one of the MOSFET switches, the ON resistance of the MOSFET so that the drop in voltage across the switch is increased or decreased, resulting in a reduction or increase in the actual output voltage. The linear regulator has, however, the drawback that the losses occurring on switching the charge pump switches are relatively large since the charge pump in the case of the linear regulator is always in operation; it thus being suitable only for relatively large load currents occurring continually.
These drawbacks do not occur in the so-called skip mode regulator since it uses the control signal of the comparator to signal the charge pump alternatingly ON/OFF so that a charge is pumped to a smoothing and storage capacitor located at the output of the circuit only when the voltage connected thereto has dropped below the design output voltage level. The skip mode regulator thus operates in a particularly energy-saving way and is especially suitable for applications in which sometimes small and sometimes large load currents may occur.
One drawback in the described DC/DC converters regulated to a fixed predetermined output voltage operating in accordance with the charge pump principle, however, is that their efficiency is not an optimum over the full input voltage range when changes in the input voltage occur in time, as is typical e.g. in the case of battery-operated devices.
To get round this problem German patent application No. 199 24 047.7 proposed a DC/DC converter comprising, in addition to the circuit array of four switches and a charge pump capacitor employed in the Horowitz converter as described above, a second circuit array configured and switched the same as the first circuit array. In this arrangement a further controllable switch is also provided, via which the two charge pump capacitors of the two circuit arrays may be interconnected. For optimizing the efficiency of the converter in the case of a changing input voltage the control circuit in this arrangement is able to operate the charge pump e.g. in two different modes, i.e. in a first mode in which the charge pump works with a gain factor of 1.5 and in a second mode in which the charge pump works with a gain factor of 2. When the voltage—supplied for instance by a battery—applied to the input of the converter has dropped to a critical value, a changeover is made from the first mode to the second mode. In the first mode the two charge pump capacitors in this arrangement are connected in series between the input of the converter and ground via the switches in the charging phase of the charge pump, whilst in the second mode they are connected in parallel between the input and ground. In the discharge phase of the two modes the two charge pump capacitors are connected in parallel between the input and output of the converter.
In the patent application describing this converter with improved efficiency it is proposed to select the mode by measuring the input voltage and selecting the mode suitable for optimal efficiency as a function of the input voltage.
The disadvantage of this simple solution is that the value of the input voltage is only then independent of the load current of the converter when the ON resistance of the switches of the charge pump is infinitely small. In addition to this, spikes occur in the output current and in the output voltage on changeover between the modes.
In a similar converter of the Company National Semiconductor type LM 3352 described in a product catalog available in June 1999 in Internet under the site address http://www.national.com the value of the output voltage of the converter is additionally made use of to select the suitable gain mode of the converter. However, this approach for selecting the suitable mode has various drawbacks. Thus, the output voltage is not independent of the gain mode. In the described converter the gain mode changes with increasing input voltage and the output voltage drops off. However, the particularly serious disadvantage in this arrangement is that the output voltage also spikes in this case when a change is made from one gain mode to the other. This simultaneously involves a large current spike at the output of the converter system causing heavy electromagnetic interference. This is particularly a nuisance in items of equipment incorporating such charge pump converters as employed in telecommunications applications, e.g. in mobile telephones.
It is thus the object of the present invention to configure a DC/DC converter operating on the charge pump principle, regulated and comprising various gains modes so that the changeover between the modes is improved in avoiding current spikes and voltage overshoots at the output of the DC/DC converter as o
Bayer Erich
Meindl Christian
Schmeller Hans
Berhane Adolf Deneke
Petersen Bret J.
Telecky , Jr. Frederick J.
Texas Instruments Deutschland GmbH
LandOfFree
DC/DC converter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with DC/DC converter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and DC/DC converter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2527697