Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
2002-01-17
2004-01-13
Vu, Bao Q. (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S282000, C323S285000
Reexamination Certificate
active
06677733
ABSTRACT:
BACKGROUND AND SUMMARY OF THE INVENTION
The present invention relates to a DC/DC converter, comprising inductive electrical energy storage means, switching means and control means, wherein the control means are arranged for selectively operating the switching means for transferring an amount of electrical energy from the energy storage means to an output of the DC/DC converter, for providing a desired output voltage.
A DC/DC converter of this type is known from International patent application WO95/34121 in the name of applicant.
In practice, a DC/DC converter of the above type can be operated in a continuous or PWM (Pulse Width Modulation) mode, wherein electrical energy is continuously stored in the energy storage means, or in a discontinuous or PFM (Pulse Frequency Modulation) mode, wherein the energy storage means may become completely discharged.
In a single output DC/DC converter operated in PWM mode, a typical switching cycle comprises a first phase wherein energy is stored in the energy storage means and a second phase wherein energy is transferred from the energy storage means to the output of the converter. The output power of a DC/DC converter operated in PWM mode is controlled by its duty cycle, which is the ratio of the length of the first phase and the total length of the switching cycle, i.e. the sum of the first and second phases.
For controlling the output voltage of the known DC/DC converter a voltage window is required, comprising an upper output voltage reference level and a lower output voltage reference level. Controlling the output voltage using such a voltage window, causes a random low frequency ripple in the output voltage and, of course, a spread in the output voltage. These effects can be reduced by reducing the voltage window, however this reduction is limited due to process spreading in voltage comparators used.
The size of the ripple is directly related to the current by which the energy storage means are charged and discharged, and relates directly to the duty cycle with which the converter is operated. A high duty cycle, implying that a relatively large amount of electrical energy is stored in the energy storage means and discharged therefrom, increases the current and thereby the output ripple, whereas a low duty cycle, implying less energy transfer, decreases the current and, accordingly, the low frequency ripple at the output voltage. A relatively high voltage drop in the output voltage occurs during the second phase of the switching cycle, if the energy storage means are discharged with a relatively high current. When the output voltage, for control purposes, is measured during this second phase, the duty cycle and the discharge current will have a direct negative influence on the accuracy of the measurement.
It is an object of the present invention to provide a DC/DC converter of the above-mentioned type, using a single voltage reference level for controlling the output voltage, thereby reducing the dependency of the voltage measurement on the ripple voltage.
This object is solved in a DC/DC converter according to the present invention, in that the control means are configured for operatively controlling the switching means for transferring electrical energy in accordance with a two-state switching cycle comprising a minimum and a maximum duty cycle.
The present invention is based on the insight that, while the output voltage is above its desired value, set by a reference voltage, the converter is not so heavily loaded, such that during the subsequent switching cycle less energy has to be transferred to the energy storage means, thereby reducing the voltage ripple at the output voltage as disclosed above. Only, in the case that the output voltage drops below its desired value, a greater amount of electrical energy has to be stored in the energy storage means during the subsequent switching cycle, in order to restore the output voltage at its required level. As a result, the overall voltage ripple is reduced while the control means can be of a relatively simple design, using a single reference voltage and a two-state duty cycle control, providing a very stable control of the converter.
In a preferred embodiment of the invention, the DC/DC converter comprises:
first and second input terminals for receiving an input voltage Vin;
first and second output terminals for providing an output voltage Vout;
a coil, having first and second connection ends, wherein the first connection end connects to the first input terminal;
first switching means operatively connected to provide a conduction path from the second connection end of the coil to the second input terminal;
second switching means operatively connected to provide a conduction path from the second connection end of the coil to the first output terminal;
diode means, parallel connected to the second switching means, and providing a conduction path from the second connection end of the coil to the first output terminal;
capacitor means connected between the first and second output terminals;
control means arranged for operatively switching the first and second switching means into their closed or conductive state and their open or non-conductive state, and
comparator means, configured for comparing the output voltage Vout with a reference voltage Vref for providing a control signal to the control means for switching the switching means in accordance with the minimum and maximum duty cycle.
Preferably, switching means constructed as MOS (Metallic Oxide Semiconductor) transistor means are used, having their control terminal (gate) connected with the control means for controlling the conductive or non-conductive state of the transistors.
The DC/DC converter according to the invention is of particular advantage if applied in a portable electronic appliance, such as but not limit to battery powered appliances.
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patent: 5625279 (1997-04-01), Rice et al.
patent: 5914865 (1999-06-01), Barbehenn et al.
patent: 6265854 (2001-07-01), Neuteboom
patent: 6275014 (2001-08-01), Sudo
patent: 6348779 (2002-02-01), Sluijs
patent: 6348781 (2002-02-01), Midya et al.
patent: 6356063 (2002-03-01), Brooks
patent: 6366070 (2002-04-01), Cooke et al.
patent: 6369551 (2002-04-01), Blumenkrantz et al.
patent: 6452368 (2002-09-01), Basso et al.
patent: 9534121 (1995-12-01), None
patent: WO9844622 (1998-03-01), None
Groeneveld Dirk Wouter Johannes
Sluijs Ferdinand Jacob
Biren Steven R.
Vu Bao Q.
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