Power supply circuit

Details Power supply circuit Power supply circuit

2000-11-29

2002-02-05

Nguyen, Matthew (Department: 2838)

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

C363S056090, C363S056120

Reexamination Certificate

active

06344982

ABSTRACT:

THIS APPLICATION IS A U.S. NATIONAL PHASE APPLICATION OF PCT INTERNATIONAL APPLICATION PCT/JP00/00548.
FIELD OF THE INVENTION
The present invention relates to a power supply circuit employed in a various kind of electronic appliances, telecommunications equipment, and the like, for generating a voltage pulse by resonance effect of a primary side of transformer, and outputting the voltage pulse from a secondary side after raising a potential thereof.
BACKGROUND OF THE INVENTION
With reference to accompanying figures, a power supply circuit of the prior art will be described hereafter.
FIG. 16
represents a circuit diagram illustrating a power supply circuit of the prior art, and
FIG. 17
is a drawing of waveforms showing changes in voltage, current, and switch pulse in the power supply circuit with time.
The power supply circuit of the prior art shown in
FIG. 16
is intended to stabilize an output voltage of high potential applied by a transformer to a display. Its composition has been such that it comprises a driving power supply
403
connected to one side of terminals of a primary coil
402
of the transformer
401
, and a switching element
404
, a capacitor
405
and a diode
406
connected to the other side of the terminals of the primary coil
402
.
The switching element
404
is comprised of a MOS type field-effect transistor (MOS FET) that has an internal diode. This MOS type field-effect transistor is disposed in a manner that a drain is connected to the other side terminal of the primary coil
402
, a source is connected to a ground side, and a gate is connected to a PWM control circuit
407
, which generates a pulse wave for controlling the switching element
404
. It contains the internal diode with its anode connected to the ground side, and a cathode to the other side terminal of the primary coil
402
. The capacitor
405
has its one end connected to the other side terminal of the primary coil
402
, and the other end connected to the ground side. The diode
406
has its cathode connected to the other side terminal of the primary coil
402
, and anode connected to the ground side. In addition, the cathode of the diode
406
and the one end of the capacitor
405
are connected to a point where the drain of the switching element
404
and the primary coil
402
make connection.
A display
409
(CRT) having high horizontal and vertical scanning frequency is connected to a secondary coil
408
of the transformer
401
.
Furthermore, waveforms of voltage, current and switch pulse in this power supply circuit, as they change with a lapse of time are shown in FIG.
17
.
In
FIG. 17
, a reference letter (a) represents a waveform illustrating a time series of change in value of voltage induced in the primary coil
402
of the transformer
401
taken at a point “O” in the power supply circuit; a letter (b) a waveform illustrating a time series of change in amount of current flowing at the point “O” in the power supply circuit; and a letter (c) a waveform illustrating a time series of change in shape of an output wave of the PWM control circuit fed to the switching element
404
.
During a period of A to B in
FIG. 17
, when a pulse wave (the output wave) of a predetermined duration shown by the waveform (c) is input from the PWM control circuit
407
to the switching element
404
, making the switching element
404
into an ON state, amount of electric current in the point “O” increases with time in proportion to a duration of the ON state of the switching element
404
as shown by the waveform (b), and thereby energy is charged into the primary coil
402
.
During a period of B to C, when input of the pulse wave from the PWM control circuit
407
to the switching element
404
is ceased, as shown by the waveform (c), to turn the switching element
404
into an OFF state, the energy charged in the primary coil
402
begins to be charged into the capacitor
405
, and amount of the current in the point “O” decreases with time, as shown by the waveform (b). The voltage of the primary coil
402
reaches its peak value as shown by the waveform (a), upon completion of the charge.
During a period of C to D, after completion of the charge into the capacitor
405
, the energy charged in the capacitor
405
begins to be recharged into the primary coil
402
again, and amount of the current in the point “O” decreases with time, as shown by the waveform (b). The voltage of the primary coil
402
becomes zero as shown by the waveform (a), when the charge is completed.
During a period of D to E, when the charge to the primary coil
402
is completed, the energy charged in the primary coil
402
is about to start being recharged into the capacitor
405
again, and this recharge of the capacitor
405
is to begin through the ground side due to an effect of a positive-negative relation in polarity of the voltage across the primary coil
402
. However, the capacitor
405
is not charged, but a current flows through the diode
406
having a low impedance, since the diode
406
is placed between the other side terminal of the primary coil
402
and the ground with the anode connected to the ground side. Therefore, although amount of the current flowing in the point “O” increases with time as shown by the waveform (b), the voltage of the primary coil
402
remains zero as shown by the waveform (a), since no energy is charged into the capacitor
405
.
During a period of E to F, since the energy charged in the primary coil
402
has been discharged by the flow of current through the diode
406
, amount of the current shown by the waveform (b) in the point “O” shall now remain theoretically zero, unless the switching element
404
is turned into an ON state with the waveform (c). In reality, however, amount of the current through the point “O” increases for a certain period of time as shown by the waveform (b).
A certain amount of energy is therefore charged in the primary coil
402
due to the increase of current through the point “O”.
Subsequently, during a period of F to G, the energy charged into the primary coil
402
begins to be charged to the capacitor
405
in the same manner as above, after the charge to the primary coil
402
is completed. Thus, amount of the current in the point “O” decreases with time, as shown by the waveform (b), and voltage of the primary coil
402
reaches its peak value as shown by the waveform (a), when the charge is completed.
During a period of G to H, after completion of the charge into the capacitor
405
, the energy charged in the capacitor
405
begins to be recharged into the primary coil
402
again, and amount of the current in the point “O” decreases with time, as shown by the waveform (b). The voltage of the primary coil
402
becomes zero as shown by the waveform (a), when the charge is completed.
During a period of H to I, when the charge into the primary coil
402
is completed, the energy charged in the primary coil
402
is about to start being recharged into the capacitor
405
again. While amount of the current flowing in the point “O” increases with time as shown by the waveform (b), the voltage of the primary coil
402
remains zero as shown by the waveform (a), since no energy is charged into the capacitor
405
.
During a period of I to J, amount of the current in the point “O” again increases for a certain period of time in the same manner as described above, as shown by the (b), and energy is hence charged in the primary coil
402
.
During a period of J to K (A), after the charge to the primary coil
402
is completed, the energy charged in the primary coil
402
begins to be charged into the capacitor
405
. Amount of the current in the point “O” decreases with time, as shown by the waveform (b), and the voltage of the primary coil
402
reaches its peak value as shown by the waveform (a), when the charge is completed. Since the switching element
404
is turned into an ON state during this period, as shown by the waveform (c), this becomes a new starting point and the same steps as above are repeated over again.
In the above compositio

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