Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2000-06-09
2001-01-30
Berhane, Adolf Deneke (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S285000
Reexamination Certificate
active
06181120
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to DC/DC converters.
BACKGROUND OF THE INVENTION
As the complexity and clock speed of CPUs continue to rise, greater demands are placed on the power supplies (DC/DC converters) that supply the operating voltage to the CPUs. Typically, the operating voltage of CPUs is specified with a relatively tight tolerance to ensure proper operation of the CPU. The tight tolerances on CPU operating voltages are being further narrowed as CPU clock and CPU bus speeds increase, and CPU operating voltages decrease. The decrease in permissible tolerances on CPU operating voltages has resulted in a corresponding increase in the regulation specifications of power supplies that supply operating voltages to CPUs.
The current drawn by a CPU generally undergoes frequent variation and rapid changes of substantial magnitude. For example, the current a CPU draws from a power supply may change by as much as 10-75 Amps per microsecond. These frequently varying and rapidly changing demands for substantial amounts of current are referred to as load transients. These extreme load transients cause a corresponding voltage transient on voltage output of the power supply, thereby making it very difficult for a power supply to comply with tight power supply regulation specifications. Many power supplies incorporate very large capacitors to reduce the effect of these large and rapid load transients, and thereby lessen the resultant corresponding voltage transients on the output voltage of the power supply to an acceptable level. However, the use of large capacitors adds significantly to the cost, size and weight of the power supply.
In order to reduce the number and size of capacitors needed to lessen the effect of a given load transient on power supply output voltage, a technique known as “droop” is employed. Normally, power supplies are designed to have an output voltage that is essentially independent of the load current. However, in applications where a power supply will be required to comply with tight regulation specifications in a high-load-transient environment, there is an advantage in carefully controlling and/or adjusting the output impedance of the power supply to thereby cause the power supply output voltage to decrease by a predetermined amount in response to an increase in current demanded by or being supplied to the load.
In conventional current-mode DC/DC converters, the duty cycle of the DC/DC converter is modulated by a negative-feedback voltage loop to maintain the desired output voltage. The feedback voltage loop has a DC voltage gain which determines the amount of “droop” in the output impedance of the power supply. The DC voltage gain of the feedback loop is, therefore, designed to be relatively low in order to achieve a relatively small amount of droop and thereby maintain a substantial degree of voltage regulation to comply with the tight tolerances placed upon the operating voltage supplied to the CPU.
The low DC gain in the feedback loop, however, results in any variations or offsets in the voltages within the DC/DC converter being reflected in a corresponding error in the output voltage of the converter. The only known solution to this problem is to design precise circuitry using components having tight tolerances in order to achieve low-offset voltages and/or precise internal voltages within the DC/DC converter. The inclusion of such precise circuitry adds substantially to the cost and complexity of the converter.
Therefore, what is needed in the art is a converter that maintains voltage regulation in a high-load-transient environment.
Furthermore, what is needed in the art is a converter which does not depend upon large capacitors to maintain voltage regulation in a high-load transient environment, and is therefore less expensive to build, smaller in size and lighter in weight.
Moreover, what is needed in the art is a converter which achieves voltage regulation in a high-load transient environment without the use of precision circuitry, and is therefore less complex and less expensive to build.
SUMMARY OF THE INVENTION
The present invention provides a DC/DC converter having a controlled output impedance and which provides for a controlled droop in the output voltage in response to load transients.
The invention comprises, in one form thereof, a DC/DC converter having an output voltage and sourcing an output current to a load. The DC/DC converter includes an error amplifier with a reference input and a summing input. The reference input is electrically connected to a reference voltage. The summing input is electrically connected to the output voltage and the output current. The summing input is configured for adding together the output voltage and the output current. The error amplifier issues an error signal and adjusts the error signal dependent at least in part upon the output voltage and the output current. A comparator receives the error signal. The comparator has a ramp input electrically connected to a voltage ramp signal. The comparator issues an output signal that is based at least in part upon said error input. A power switch has an on condition and an off condition, and supplies dc current to the load when in the on condition. The power switch has a control input electrically connected to the comparator output signal. The power switch is responsive to the control input to change between the on condition and the off condition to thereby adjust the output current of the DC/DC converter.
An advantage of the present invention is that droop in the output voltage of the converter in response to a load transient is controlled and reduced.
Another advantage of the present invention is that the need for a plurality of large capacitors to maintain regulation of the output voltage in a high-load transient environment is eliminated, and therefore the present invention is less expensive to manufacture, is of a lighter weight and smaller in size than conventional DC/DC converters.
A further advantage of the present invention is that it is essentially immune to errors in internal reference and offset voltages.
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Hawkes Charles E.
Isham Robert H.
Walters Michael M.
Berhane Adolf Deneke
Intersil Corporation
Jaeckle Fleischmann & Mugel LLP
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