Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-03-12
2001-01-23
Nguyen, Matthew (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
Reexamination Certificate
active
06177786
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power supply apparatus provided with a power supply circuit for generating a DC output.
2. Description of the Related Art
A power supply apparatus such as an AC/DC converter, a DC/DC converter, a charger, etc. is popular in various fields. Generally, a power supply apparatus should be small in loss. Particularly, it is very important to reduce loss in a power supply apparatus used in a portable personal computer, a terminal unit in a mobile communications device, etc.
FIG. 1
shows the configuration of the charger or the DC power supply provided in the conventional power supply apparatus. The charger and the DC power supply have the same basic configurations, and each includes an electric power converter
510
and an analog circuit unit
520
. In this example, the DC power supply is a DC/DC converter.
The electric power converter
510
includes a switching element (MOSFET) controlled according to the instruction from the PWM control circuit
524
; a rectifying diode; an inductor for storing/discharging energy; a resistor for detecting an inductor current or an output current; and an output capacitor for smoothing an output. While the switching element is in the ON state, the inductor current ramps up with the electric current provided for the load, thereby storing residual charge in the output capacitor. While the switching element is in the OFF state, the inductor current ramps down and the electric charge stored in the output capacitor is discharged as necessary with the electric current provided for the load.
The analog circuit unit
520
includes an amplifier
521
for amplifying an inductor current; an amplifier
522
for amplifying the difference between the output from the amplifier
521
and a reference voltage Vref
1
; an amplifier
523
for amplifying the difference between the output voltage and a reference voltage Vref
2
; a PWM control circuit
524
for generating a PWM signal for controlling the switching element based on the output from these amplifiers, etc.; and an oscillator
525
for providing a clock at a predetermined frequency for the PWM control circuit
524
.
When the output voltage drops below the reference voltage Vref
2
, the PWM control circuit
524
makes the duty (duty cycle) of the PWM signal to be provided for the switching element higher so that the inductor current can be increased and the output voltage will increase. On the other hand, when the output voltage becomes higher than the reference voltage Vref
2
, the PWM control circuit
524
makes the duty of the PWM signal lower so that the inductor current can be reduced and the output voltage will drop. Thus, the output voltage can be maintained at a constant level. When the PWM control circuit
524
detects an overcurrent based on the output from the amplifier
522
, it reduces the duty of the PWM signal or forcibly turns off the switching element.
Thus, an analog circuit has been used to control the output from a charger provided in the conventional power supply apparatus, or each DC power supply.
As described above, an analog circuit has been used to control the output from the conventional power supply apparatus. Therefore, the characteristics or specification of a power supply circuit cannot be easily changed. If they can be changed, a number of circuits have to be added for amendments. Considering a smaller or a lower cost power supply apparatus, the conventional technology has been impractical and unrealistic. Described below are some of the problems with the conventional power supply apparatus.
(1) Precision in Output Voltage
To control and maintain the output voltage of a power supply circuit, the output voltage is normally used as a feedback signal. However, a transfer function for a feedback system changes with external factors (input voltage, output current, temperature, etc.). Therefore, if such factors are not taken into account, oscillation may occur in the feedback system.
Therefore, in the conventional power supply apparatus, an amplifier for the feedback system is designed for the worst possible case in order to avoid the above described oscillation. However, this design reduces a gain in the normal operation, thereby lowering the precision in control of an output voltage. This problem is due to the characteristic of an amplifier, which cannot be flexibly changed depending on various factor such as input voltage, output current, and temperature, in the conventional analog circuit.
(2) Error in Digitalizing Data
In newly developed technology, the functions of a conventional analog circuit can be replaced with digital control. For example, a power supply apparatus has been designed such that an output voltage as a feedback signal is converted into digital data from which numeral data for control of a switching element is generated, and then, the switching element is controlled according to the numeral data. However, under the control, an unavoidable digital error (quantization error) occurs. The error may cause a ripple in an output voltage.
To reduce the above described error, the quantization step should be reduced. However, reducing the quantization step raises the cost and increases the electric power consumption in the power supply apparatus.
(3) Power Consumption
When an electric current required by a load is small, for example, in the suspense mode of a personal computer, etc., it is particularly important to reduce the power consumption of a power supply apparatus itself. This technology has long been studied, but has not been satisfactorily developed, and therefore should be improved.
SUMMARY OF THE INVENTION
The present invention aims at providing a power supply apparatus for flexibly changing its characteristic or specification. It also aims at improving the precision in output voltage. The present invention further aims at realizing smaller power consumption.
The power supply apparatus according to the present invention includes a power supply circuit for generating DC output according to a given pulse signal; a conversion unit for converting a parameter relating to the output of the power supply circuit into digital data; an amplification unit for amplifying the difference between the digital data obtained from the conversion unit and a reference value; an adjustment unit for adjusting the characteristic of the amplification unit based on the input voltage of the power supply circuit; and a generation unit for generating a pulse signal applied to the power supply circuit according to the amplification unit. The characteristic of the amplification unit can be adjusted by an output current or the temperature around the power supply apparatus in addition to the input voltage.
With the above described configuration, even if various parameters relating to the operation of the power supply apparatus or the vicinal environment are changed, the precision in voltage control can be improved because the gain and the phase of the power supply apparatus can be optimized according to the changes.
The power supply apparatus, according to another aspect of the present invention, is based on the configuration including a power supply circuit in which DC output is controlled by the PWM system. The power supply apparatus includes a computation unit for computing the pulse width of a pulse signal to be provided for the power supply circuit based on a parameter relating to output of the power supply circuit; a correction unit for correcting the pulse width data computed by the computation unit according to a stored carry-over value; a conversion unit for converting the pulse width data corrected by the correction unit into pulse width data that is a predetermined number of digits in length; a generation unit for generating a pulse signal according to the pulse width data converted by the conversion unit, and providing it for the power supply circuit; and a storage unit for storing the difference between the pulse width data corrected by the correction unit and the pulse width data converted by t
Armstrong, Westerman Hattori, McLeland & Naughton
Fujitsu Limited
Nguyen Matthew
LandOfFree
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