Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
1999-12-23
2001-07-17
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S127000
Reexamination Certificate
active
06262903
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a direct-current power supply circuit associated with a coil or equivalent thereof which receives an incoming signal. An output signal of this coil is rectified and smoothed. The direct-current voltage obtained through the rectifying and smoothing operation is controlled to a predetermined constant voltage by a clamp circuit so as to produce a power supply voltage.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a direct-current power supply circuit which includes a rectifying circuit and a smoothing capacitor for rectifying and smoothing an alternating-current input signal entered through a coil.
An object of the present invention is to provide a direct-current power supply circuit which further includes a clamp circuit for controlling the rectified and smoothed direct-current voltage to a preset voltage.
An object of the present invention is to prevent the power supply voltage produced from the direct-current power supply circuit from suddenly decreasing when the alternating-current signal entered through the coil is temporarily interrupted due to amplitude modulation.
In order to accomplish the above and other related objects, the present invention provides a first direct-current power supply circuit comprising a signal receiving section for receiving an alternating-current signal from the outside of the direct-current power supply circuit. A rectifying section rectifies an output of the signal receiving section. A smoothing section is provided for smoothing an output of the rectifying section. A first control section controls the operation of a switching section to produce a constant voltage. The switching section changes a voltage level of an output of the smoothing section. And, a second control section is connected between the signal receiving section and the first control section for prohibiting the switching operation of the switching section in accordance with a signal condition of the alternating-current signal received by the signal receiving section. In this case, the prohibition of the second control section has priority over the control of the first control section.
Preferably, the second control section prohibits the switching operation of the switching section in response to a change of amplitude modulation of the alternating-current signal received by the signal receiving section.
For example, the alternating-current signal received by the signal receiving section is an amplitude-modulated signal changeable up to 100% in the degree of amplitude modulation. In this case, the second control section prohibits the switching operation of the switching section in response to 100% amplitude modulation of the alternating-current signal received by the signal receiving section.
Preferably, the first control section is an analog circuit and the second control section is a digital circuit.
According to preferred embodiments of the present invention, the direct-current power supply circuit is incorporated in an IC card to or from which information is written or read, and the constant voltage produced by the first control section is used to activate a semiconductor integrated circuit accommodated in the IC card.
Furthermore, the present invention provides a second direct-current power supply circuit comprising a coil for receiving an alternating-current signal from the outside of the direct-current power supply circuit, a rectifying circuit for rectifying an output of the coil, a capacitor for smoothing an output of the rectifying circuit, and a clamp circuit for controlling the operation of a switching element to produce a constant voltage when the switching element controls the charging and discharging operations of the capacitor. And, a switching operation control circuit is connected between the coil and the clamp circuit for executing an turning-off operation of the switching element in accordance with a signal condition of the alternating-current signal received by the coil. In this case, the turning-off operation of the switching element is performed prior to the control of the clamp circuit.
Preferably, the switching operation control circuit executes the turning-off operation of the switching element in response to a change of amplitude modulation of the alternating-current signal received by the coil.
For example, the alternating-current signal received by the coil is an amplitude-modulated signal changeable up to 100% in the degree of amplitude modulation. In this case, the switching operation control circuit executes the turning-off operation of the switching element in response to 100% amplitude modulation of the alternating-current signal received by the coil.
Preferably, the clamp circuit is an analog circuit and the switching operation control circuit is a digital circuit.
According to the preferred embodiments of the present invention, the direct-current power supply circuit is incorporated in an IC card to or from which information is written or read, and the constant voltage produced by the clamp circuit is used to activate a semiconductor integrated circuit accommodated in the IC card.
Moreover, the present invention provides a third direct-current supply circuit comprising a coil for receiving an alternating-current signal from the outside of the direct-current power supply circuit, a rectifying circuit for rectifying an output of the coil, a smoothing capacitor for smoothing an output of the rectifying circuit, and a clamp circuit for controlling a terminal voltage of the smoothing capacitor to a predetermined constant voltage. The clamp circuit includes an output transistor connected in parallel with the smoothing capacitor. Furthermore, the clamp circuit includes a short-circuit preventing circuit which prevents the output transistor from short-circuiting both ends of the smoothing capacitor when an electric potential difference between both ends of the coil is smaller than a predetermined value.
Preferably, the short-circuit preventing circuit forcibly turns off the output transistor when the electric potential difference between both ends of the coil is smaller than the predetermined value.
Preferably, the short-circuit preventing circuit comprises an auxiliary transistor connected in series with the output transistor. The auxiliary transistor and the output transistor are connected in parallel with the smoothing capacitor. And, the short-circuit preventing circuit turns off the auxiliary transistor when the electric potential difference between both ends of the coil is smaller than the predetermined value.
According to the preferred embodiments of the present invention, the direct-current power supply circuit is incorporated in an IC card to or from which information is written or read. The coil receives an amplitude-modulated signal for data communication through electromagnetic coupling with an external apparatus. And, the direct-current power supply circuit produces a power supply voltage for activating a semiconductor integrated circuit accommodated in the IC card.
Preferably, the short-circuit preventing circuit is a logic circuit.
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Fujihashi Yoshinori
Harada Takuya
Kitamura Tetsuyasu
Denso Corporation
Pillsbury & Winthrop LLP
Sterrett Jeffrey
LandOfFree
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