Coherent light generators – Particular component circuitry – For driving or controlling laser
Reexamination Certificate
1999-07-13
2003-07-15
Ip, Paul (Department: 2828)
Coherent light generators
Particular component circuitry
For driving or controlling laser
C372S038010, C372S038030, C372S038040, C372S038070, C372S038100, C372S037000, C307S419000, C307S415000, C307S106000
Reexamination Certificate
active
06594292
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a saturable reactor having a magnetic switching function which serves to switch between a high inductance state and a low inductance state and a low-inductance conductive function in accordance with the direction of the current flowing therethrough so as to perform high-speed, large-power rectification. It further relates to a power source apparatus for pulse laser utilising the saturable reactor.
2. Description of the Related Art
Saturable reactors comprising a magnetic core of ferrite or amorphous magnetic material have conventionally been used as magnetic switches by utilising the non-linear permeability of the magnetic material. The configuration of these saturable reactors is such that a principal coil is wound a prescribed number of times around the magnetic core. When the electric current I flowing through the principal coil increases, so does the magnetic flux density B as illustrated in FIG.
5
. Once the magnetic flux density B reaches B
0
, the magnetic core becomes a state of saturation in which the constant magnetic flux density B
0
is maintained despite a further increase in the electric current. In this state of saturation, the inductance of the magnetic core is very small. As a result, the saturable reactor fulfils the function of a magnetic switch. Even if the electric current flows through the principal coil in the opposite direction, it still fulfils the same magnetic switching function. The absolute value of the electric current at which the transition from unsaturated to saturated state occurs is the same, as is the magnetic flux density, and the B-H characteristics are in point symmetry with respect to the origin.
Japanese Patent Publication 62-76511 proposes an improved saturable reactor in which a supplementary coil is wound around a saturable iron core in addition to a principal coil. By feeding a bias current to the supplementary coil in accordance with the current in the principal coil, a magnetic switch is provided which performs controllable switching action for the electric current flowing through the principal coil. With this satiable reactor, by altering the amount of current in the supplementary coil, it is possible to switch with the desired timing without regard to the amount of current flowing through the principal coil.
However, conventional saturable reactors with a supplementary coil such as the magnetic switch described in Japanese Patent Publication 62-76511 has the supplementary coil for the purpose of resetting the magnetism.
For instance, in the power source apparatus for pulse laser illustrated in
FIG. 6
, electric charge is stored directly into a capacitor C
11
by a charger
11
which forms a power source for charging. The electric charge stored in this capacitor C
11
begins transferring energy when a switch SW
1
turns on. More particularly, as the switch SW
1
turns on, the voltage generated across a saturable reactor SL
11
increases, and after a predetermined assist time at that voltage, that is, after a product of time and voltage reaches a predetermined value, the saturable reactor SL
11
reaches saturation, turning the saturable reactor SL
11
on. The electric charge stored in the capacitor C
11
is transferred in the form of the current I
11
by way of the saturable reactor SL
11
and the switch SW
1
to the opposite side of the capacitor C
11
. Thereafter, voltage is generated across the saturable reactor SL
12
, turning it on when the saturable reactor SL
12
reaches saturation after a predetermined assist time at that voltage. The electric charge stored in the capacitor C
11
is transferred in the form of the current I
12
to a peaking capacitor CP
1
. The electric charge which has been transferred to the peaking capacitor CP
1
becomes the electric current I
13
, which causes the laser discharge unit LD
1
to discharge, creating laser pulse oscillation.
However, in the power source apparatus for pulse laser illustrated in
FIG. 6
, when the switch SW
1
turns on and the electric charge which has been charged in the capacitor C
11
is transferred, this causes the voltage P
0
across the capacitor C
11
, which has been positive during charging, to reverse polarity and rapidly change into negative. From the point at which the voltage P
0
becomes negative, the electric current I
01
is output from the charger
11
. As a result, it sometimes happens that the charging current flowing out from the charger
11
increases beyond its design value, leading to problems of damage to the charger
11
and inferior accuracy of charging.
Meanwhile, in the power source apparatus for pulse laser illustrated in
FIG. 7
, a charger
12
charges at least a capacitor C
12
by way of a saturable reactor SL
21
. When a switch SW
2
turns on, voltage is generated across the saturable reactor SL
21
. When the saturable reactor SL
21
turns on after a product of time and voltage reaches a predetermined value, electric charge stored in the capacitor C
12
in the form of current
121
is subjected to a reversal of polarity whereby it is transferred to the opposite side of the capacitor C
12
. Thereafter, voltage is generated across a saturable reactor SL
22
, turning it on after a predetermined assist time at that voltage. The electric charge transferred to the, capacitor C
12
in the form of current
122
is transferred to the peaking capacitor CP
2
. The electric charge which has been transferred to a peaking capacitor CP
2
becomes electric current
123
, which causes a laser discharge unit LD
2
to discharge, creating laser pulse oscillation.
However, if there are ripples in the electric current flowing from the charger
12
in the power source apparatus for pulse laser illustrated in
FIG. 7
, when the charger
12
charges the capacitor C
12
by way of the saturable reactor SL
21
, the frequency of these ripples causes the inductance of the saturable reactor SL
21
to increase, inhibiting the charging of the capacitor C
12
, with the result that a surge voltage is generated at point P
1
on the charger
12
side of the saturable reactor SL
21
. This surge voltage is problematic in that it may exceed the withstand voltage of the switch SW
2
and cause it to break, while it also makes it impossible to detect the voltage across the capacitor C
11
with accuracy.
In such a case, if the saturable reactor SL
21
is conductive in the direction of the charging current and has the magnetic switching function for the magnetic compression action of the charged electric charge, the switch SW
2
can be protected because surge voltage is not generated, and also the electric current with ripples can be utilised as the charging current.
SUMMARY OF THE INVENTION
It is an object of the present invention to eliminate such problems as described above, and to provide a saturable reactor having a conductive state and a magnetic switching function corresponding to the direction of the electric current, and a power source apparatus for pulse laser utilising the satiable reactor.
The first aspect of the present invention is a saturable reactor comprising a saturable magnetic core; a principal coil wound around the saturable magnetic core; a subsidiary coil wound around the saturable magnetic core; and a power source which feeds electric current to the subsidiary coil when the transition of the saturable magnetic core from unsaturated state to saturated state is effected by the subsidiary coil, characterised in that the saturable magnetic core becomes saturated state immediately when voltage is applied to the principal magnetic coil in the same direction as the current in the subsidiary magnetic coil, while becoming the saturated state from an initial unsaturated state at the time when a product of the voltage and time reaches a predetermined value if the voltage is applied to the principal magnetic coil in a direction opposite to the current flowing in the subsidiary magnetic coil.
In the first aspect of the invention, the current fed to the subsidiary coil is set to exactly th
Hagiwara Masao
Kawasuji Yasufumi
Matsuki Yasuhiko
Nomura Yoshio
Ip Paul
Komatsu Ltd.
Menefee James
Varndell & Varndell PLLC
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