Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
2003-01-29
2004-12-14
Han, Jessica (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C323S277000, C323S222000
Reexamination Certificate
active
06831449
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a current determination circuit which detects and determines a current supplied from a power supply device when the power supply device, which converts a voltage by a switching method using, e.g., a semiconductor element, is used by connecting the power supply device to a load such as an electrical device, and an image printing apparatus using a power supply device which incorporates the current determination circuit.
BACKGROUND OF THE INVENTION
A power supply device which is used in many electrical devices and supplies power preferably detects a load current supplied from the power supply device and determines the load state. This is achieved by, e.g., an overcurrent protection circuit incorporated in a widely used power supply device.
A general method of detecting a supplied load current is a method using a “current detection resistor” in which the load current is detected as a voltage drop by a detection resistance component.
In the method using the “current detection resistor”, a larger load current increases the loss by Joule heat generated by the “current detection resistor”. Various methods which solve this problem have been disclosed.
For example, Japanese Patent Laid-Open No. 6-201738 (“Current Detection Circuit”) uses “the ON resistance (Rdon) of a switching MOS transistor” through which the load current flows, instead of the “current detection resistor”. The characteristic of “the ON resistance of the switching MOS transistor” is influenced by variations between switching MOS transistor lots of the same manufacturer, and also readily influenced by the use environment (e.g., temperature).
To employ a method of detecting a load current supplied from the power supply device by using “the ON resistance of the switching MOS transistor”, switching MOS transistors with the same characteristic are desirably stably supplied. For this purpose, it is desirable to freely use switching MOS transistors of not one manufacturer but a plurality of manufacturers.
For the switching MOS transistor having the above-mentioned characteristic, a substitute of a different manufacturer fails to obtain the same characteristic. It is therefore difficult in terms of practical use to adopt the load current detection method using “the ON resistance of the switching MOS transistor” under this restriction.
Another method which does not use any resistance component such as the “current detection resistor” is a method of “detecting a load current as a magnetic component and converting the load current into a physical amount”, i.e., a method of converting a current into a voltage amount via a magnetic component. As an example of this method, a current detection coil called a “current transformer” is used, or a current flowing through a reactor is detected by a Hall element as a magnetic sensor. This method is disclosed in Japanese Patent Laid-Open No. 5-64425 (“Overcurrent Detection Circuit of Step-Up Converter”).
The method of “detecting a load current as a magnetic component and converting the load current into a physical amount” can advantageously decrease the loss caused by Joule heat in comparison with the use of the “current detection resistor”, and increase the current detection precision.
However, the current detection coil and Hall element are expensive and must be mounted at a location where they can detect a magnetic component, resulting in low usability.
As still another method, Japanese Patent Laid-Open No. 5-292742 (“Switching Power Supply Device”) discloses a current detection circuit which is electrically connected to the two terminals of a flywheel diode and constituted by a voltage-dividing resistor, filter capacitor, and voltage amplifier.
According to this method, a current flowing through the flywheel diode in proportion to the load current is extracted in mounting. An unwanted loop antenna may be formed depending on the wiring pattern of a printed circuit board, which poses a serious problem in a power supply which should suppress generation of power noise.
As described in “BACKGROUND OF THE INVENTION”, the method of detecting a load current supplied from a power supply device which is used in an electrical device and supplies power suffers problems: (1) the precision is high, but the detection loss is large; (2) the precision is high, but the cost is high; and (3) noise may be generated.
For this reason, the above-described load current detection method cannot be applied to an energy-saving electrical device such as a recently popular printer (e.g., a large-format printer).
When the current is required to be detected in an electrical device, the absolute precision of a continuous current value is not often measured. In many cases, it is sufficient to detect a current value in a specific load state and determine the load state.
For example, the load current used in an overcurrent protection circuit is detected to detect a current in a load state and determine (decide) the operation start time of the overcurrent protection circuit in order to determine the start point of the overcurrent protect operation. In this case, it suffices to determine whether the load current exceeds a preset current value, and the load current need not be continuously measured at a high precision.
SUMMARY OF THE INVENTION
The present invention has been made to overcome the conventional drawbacks, and has as its object to provide a current determination circuit capable of determining that the current falls within a proper range while preventing an increase in cost in current detection and reducing Joule loss caused by an unwanted resistance component without employing any method such as a method using a current detection resistance, a method using the ON resistance of a switching MOS transistor, or a current detection method using a current detection coil or Hall element when a power supply device which converts a voltage by a switching method using a semiconductor element is connected to a load (electrical device) and it is determined whether a current supplied from the power supply device to the load falls within a proper range.
It is another object of the present invention to provide an image printing apparatus which uses a power supply device having the current determination circuit as a power supply device for supplying power in the image printing apparatus, and even if a printhead error occurs in printing, can detect the error before printing and prevent wasteful printing suffering from the printing error.
To achieve the above objects, a current determination circuit according to an aspect of the present invention has the following arrangement. That is, a current determination circuit which determines a current value supplied to a load from a power supply device having a power supply circuit which converts an input voltage by turning on/off switching means comprises detection means for detecting a predetermined signal on the basis of an ON/OFF signal used to turn on/off the switching means, and current determination means for determining based on the predetermined signal, of a plurality of ranges, a range within which the current value supplied from the power supply device to the load falls.
For example, the plurality of ranges are preferably two ranges including a range in which the current value is not less than a predetermined current value, and a range in which the current value is smaller than the predetermined current value.
For example, the detection means preferably DC-detects the ON/OFF signal to detect a voltage level corresponding to the ON/OFF signal.
For example, the current determination means preferably compares the voltage level with a predetermined voltage level set in advance, and when the voltage level exceeds the predetermined voltage level, determines that the current value supplied from the power supply device to the load is not less than the predetermined value.
For example, the detection means preferably detects a time width corresponding to an ON time of the ON/OFF signal.
For example, the current determination means p
Masuda Kazunori
Nishida Hideyuki
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