CIRCUIT D'ABSORPTION D'IMPULSIONS POUR CIRCUIT D'ALIMENTATION

PULSE ABSORPTION CIRCUIT FOR POWER SOURCE CIRCUIT

Abrégé anglais

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Abstract of the Disclosure
A pulse absorbing circuit for a power source
circuit for absorbing an abnormal pulse when an input
current at a primary winding of an output transformer
in a switching power source is cut off, has: a
capacitor, one end of which is connected to a primary
winding output terminal of a transformer in a phase
opposite to a primary winding input terminal thereof; a
first rectifying element, an anode of which is
connected to the other end of said capacitor and a
cathode of which is connected to an output terminal of
a rectifying circuit arranged at a secondary winding
side of said transformer; a second rectifying element,
a cathode of which is connected to a junction between
said first rectifying element and said capacitor; and a
conductor inserted between a ground terminal and said
second rectifying element. The conductor has, for
example, a coil for absorbing and effectively
reutilizing abnormal pulse energy.

Revendications

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What is claimed is:
1. A pulse absorption circuit for a switching
power source circuit for supplying or cutting off an
input current at a primary winding of a transformer
upon ON/OFF operation of a switching element, and for
rectifying and smoothing an output of a secondary
winding of said transformer by means of a diode and a
smoothing capacitor, comprising: a capacitor, one end
of which is connected to a primary winding output
terminal of the transformer in a phase opposite to a
primary winding input terminal thereof; a first
rectifying element, an anode of which is connected to
the other end of said capacitor and a cathode of which
is connected to an output terminal of a rectifying
circuit arranged at a secondary winding side of said
transformer; a second rectifying element, a cathode of
which is connected to a junction between said first
rectifying element and said capacitor; and a conductor
inserted between a ground terminal and said second
rectifying element.
2. A pulse absorption circuit according to claim
1, wherein said conductor comprises a coil.

Description

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Background of the Invention
(1) Field of the Invention
The present invention relates to a pulse absorption
circuit for absorbing an abnormal pulse generated at a
secondary winding when an input current is cut off at a
primary winding of an output transformer in a switching
power source.
In some conventional pulse absorption circuits,
pulse energy is absorbed by a circuit loss, thereby
degrading efficiency of the power source.
It is an object of the present invention to provide
a pulse absorption circuit for properly absorbing an
abnormal pulse and reutilizing absorbed energy, thereby
improving efficiency of a power source voltage.
According to the present invention there is provided
a pulse absorption circuit for a switching power source
circuit for supplying or cutting off an input current
at a primary winding of a transformer upon ON/OFF open-
anion of a switching element, and for rectifying and
smoothing an output of a secondary winding of said
transformer by means of a diode and a smoothing capacitor,
comprising: a capacitor, one end of which is connected
to a primary winding output terminal of the transformer
in a phase opposite to a primary winding input terminal
thereof; a first rectifying element, an anode of which
is connected to the other end of said capacitor and a
cathode of which is connected to an output terminal of
a rectifying circuit arranged at a secondary winding
side of said transformer; a second rectifying element,
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a cathode of which is connected to a junction between
said first rectifying element and said capacitor; and a
conductor inserted between a ground terminal and said
second rectifying element.
Brief Description of the Drawings
Figs. 1 to 4 are circuit diagrams showing convent
tonal pulse absorption circuits for a power source
circuit, respectively;
Fig. 5 is a circuit diagram of a pulse absorption
circuit for a power source circuit according to an em-
bodiment of the present invention; and
Fig. 6 is a circuit diagram of a pulse absorption
circuit for a power source circuit according to another
embodiment of the present invention.
Description of the Prior Art
Conventionally, a pulse absorption circuit is arranged
in an output transformer of a switching power source. In
typical conventional pulse absorption circuits S shown
in Figs. 1 to 4, each circuit S is connected between a
ground side terminal To of a primary winding of a trays-
former T and a ground terminal El i.e., between the
collector and emitter of a switching transistor Q. In
the arrangement shown in Fig. 1, a snubber comprises a
series circuit of a capacitor C and a resistor R. In
the arrangement shown in Fig. I varister B is used to
constitute a pulse absorption circuit. In the arrange-
mint shown in Fig. 3, a Zoner diode Z is used to absorb
a pulse component having a voltage exceeding a predator-
mined voltage. In the arrangement shown in Fig. 4, a clamp

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circuit is arranged wherein a diode D is connected in
series wit a capacitor C, and a common junction there-
between is connected to a ground terminal E through a
resistor R.
In these conventional pulse absorption circuits,
pulse energy is absorbed by a circuit loss, thereby
degrading efficiency of the power source.
Detailed Description of the Preferred Embodiments
A pulse absorption circuit according to an embody-
lo mint of the present invention will be described with
reference to Fig. 5.
Referring to Fig. 5, reference symbol T denotes a
transformer; and Q, a switching transistor for supplying
or cutting off a current with respect to a primary winding
Lo. Reference symbols Lo and Lo denote secondary windings
of the transformer T. An output from the secondary winding
Lo is rectified and smoothed through a rectifying diode
Do, a choke coil Lo and a smoothing capacitor Of. Refer-
once numeral l denotes a pulse absorption circuit. The
pulse absorption circuit l comprises: a capacitor C2,
one end of which is connected to a primary winding output
terminal P of the
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transformer T in a phase opposite to a primary winding
input terminal thereof; a diode Do as a first
rectifying element, an anode of which is connected to
the other end of the capacitor C2 and a cathode of
which is connected to an output terminal OUT of a
rectifying circuit arranged at a secondary winding side
of the transformer T; a diode Do as a second rectifying
element, a cathode of which is connected to a junction
between the diode Do and the capacitor C2; and a
conductor inserted between a ground terminal E and the
rectifying element Do. The conductor comprises a coil
Lo.
The operation of the pulse absorption circuit will
be described hereinafter. When an electromotive force
is generated at the secondary winding Lo of the
transformer 1' in such a manner that the diode Do is
reverse biased, the capacitor C2 is charged by the
electromotive force at the winding Lo through the coil
Lo and the diode Do. In this case, the coil Lo is
operated to reduce pulse noise by slowly charging the
capacitor C2. Louvre, the coil Lo may be omitted.
When the coil Lo is omitted, the anode of the diode Do
is directly connected to the ground terminal E.
Thereafter, when the polarity of the output voltage at
the winding Lo is inverted, the capacitor C2 is
discharged through the diode Do since a voltage of the
winding Lo causes the output terminal P to be set at a

~26~9~
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positive potential. The discharge voltage thus appears
at the output terminal OUT. The pulse noise generated
at the side of the winding Lo can be absorbed by the
capacitor C2. In addition, the pulse noise energy can
be effectively utilized to improve efficiency of the
power source voltage.
Fig. 6 shows another embodiment of the present
invention. Only a winding Lo is provided as a
secondary winding of a transformer T. In this
embodiment, pulse noise energy is supplied to the
secondary winding only when a switching transistor Q is
turned off. The arrangement of the pulse absorption
circuit 1 is the same as that of the previous
embodiment (Fig. 5), except that one end of a capacitor
C2 is connected to one end (secondary output terminal P
having a phase opposite to the primary input terminal)
of the winding Lo.
When an electromotive force is generated in the
winding Lo in such a manner that a diode Do is reverse
biased, the capacitor C2 is charged through a coil Lo
and a diode Do. Thereafter, when the polarity of the
secondary winding output is inverted upon OFF operation
of a transistor Q, a smoothing capacitor C1 is charged
through the diode Do. In this case, the charge at the
capacitor C2 is supplied to the output terminal OUT
through the diode Do. In the same manner as in the
first embodiment, the pulse generated at the winding Lo

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is absorbed by the capacitor C2. In addition, when the
transistor Q is on, the energy charged in the capacitor
C2 can be effectively utilized.
According to the pulse absorption circuit for a
power source circuit of the present invention, the abnormal
pulse generated when the input current at the primary
winding of the output transformer in the switching power
source is cut off can be absorbed at the secondary winding
side. In addition, absorbed energy can be effectively
utilized to greatly improve the power source voltage.
There has been described a pulse absorbing circuit
for a power source circuit for absorbing an abnormal
pulse when an input current at a primary winding of an
output transformer in a switching power source is cut
off, comprising: a capacitor, one end of which is connect-
Ed to a primary winding output terminal of the transformer
in a phase opposite to a primary winding input terminal
thereof; a first rectifying element, an anode of which
is connected to the other end of said capacitor and a
cathode of which is connected to an output terminal of
a rectifying circuit arranged at a secondary winding
side of said transformer; a second rectifying element, a
cathode of which is connected to a junction between said
first rectifying element and said capacitor; and a con-
doctor inserted between a ground terminal and said second rectifying element. The conductor comprises, for example,
a coil for absorbing the abnormal pulse to effectively
reutilize abnormal pulse energy.