Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-11-19
2003-02-04
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S097000
Reexamination Certificate
active
06515875
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switching power supply circuit equipped to various types of equipment as a power supply source.
2. Description of the Related Art
The applicant of this application previously proposed a technique of constructing a composite resonance type converter as a switching power supply circuit by combining a voltage resonance type converter of one stone at a primary side and a half-wave rectifying type voltage resonance circuit at a secondary side, providing an active clamp circuit at the secondary side and stabilizing the DC output voltage thereof by controlling the conduction angle of the switching element of the active clamp circuit.
FIG. 10
is a circuit diagram of a conventional switching power supply circuit which can be constructed on the basis of the invention previously proposed by the applicant of this application.
In the power supply circuit shown in
FIG. 10
, a full-wave rectifying circuit comprising a bridge rectifying circuit Di and a smoothing capacitor Ci is equipped as a rectifying and smoothing circuit to which commercial alternating power (alternating input voltage VAC) is input to achieve a DC input voltage, whereby the rectified and smoothed voltage Ei corresponding to the once level of the alternating input voltage VAC is achieved.
At the primary side of the power supply circuit, a self-excited type is constructed as a voltage resonance type converter circuit which carries out a single-end operation on the basis of a one-stone switching element Q
1
. In this case, a bipolar transistor having high resistance to voltage (BJT; junction type transistor) is used as the switching element Q
1
.
The base of the switching element Q
1
is connected to the anode of the smoothing capacitor Ci (rectified and smoothed voltage Ei) through a starting resistor Rs to achieve base current at the starting time from a rectifying and smoothing line.
A drive winding NB which is provided at the primary side of an insulating converter transformer PIT so as to have a turn number of 1T (turn), and a series resonance circuit for self-excited resonance driving which comprises a series an inductor LB, a resonance capacitor CB and a base current limiting resistor RB is connected between the base of the switching element Q
1
and the earth at the primary side. A switching frequency fs for turning on/off the switching element Q
1
is generated by the self-excited circuit. For example, the switching frequency fs is set to 66 KHz by the series resonance circuit.
A route for clamp current flowing when the switching element Q
1
is turned off is formed by a clamp diode DD
1
inserted between the base of the switching element Q
1
and the cathode (the earth at the primary side) of the smoothing capacitor Ci. The collector of the switching element Q
1
is connected to one end of the primary winding N
1
of the insulating converter transformer PIT, and the emitter thereof is grounded.
A parallel resonance capacitor Cr is connected between the collector and emitter of the switching element Q
1
in parallel. In this case, a primary series resonance circuit of the voltage resonance type converter is formed by the capacitance of the parallel resonance capacitor Cr itself and the leakage inductance L
1
of the primary winding N
1
side of the insulating converter transformer PIT.
The insulating converter transformer PIT transmits the switching output of the switching element Q
1
to the secondary side. The insulating converter transformer PIT is equipped with an EE-type core comprising two E-type cores of ferrite material or the like which are assembled such that both the magnetic legs thereof are confronted to each other, and the primary winding N
1
and the secondary winding N
2
are wound around the center magnetic leg of the EE-type core by using a divisional bobbin so as to be separated from each other. Further, the EE-type core is assembled so that a gap is formed in the center magnetic leg thereof, whereby loose coupling based on a required coupling coefficient is achieved.
One end of the primary winding N
1
of the insulating converter transformer PIT is connected to the switching element Q
1
, and the other end thereof is connected to the anode of the smoothing capacitor Ci (rectified and smoothed voltage Ei). Accordingly, an alternating voltage having the period corresponding to the switching frequency occurs at the primary winding N
1
when the switching output of the switching element Q
1
is supplied to the primary winding Ni.
Further, at the secondary side of the insulating converter transformer PIT, an alternating voltage induced by the primary winding N
1
is generated at the secondary winding N
2
. In this case, a secondary parallel resonance capacitor C
2
is connected to the secondary winding N
2
in parallel, so that a parallel resonance circuit is formed by the leakage inductance L
2
of the secondary winding N
2
and the capacitance of the secondary parallel resonance capacitor C
2
. The parallel resonance circuit sets the alternating voltage induced in the secondary winding N
2
to a resonance voltage, so that a voltage resonance operation can be achieved at the secondary side. That is, the power supply circuit described above has the construction of a “composite resonance type switching converter” in which a parallel resonance circuit for setting the switching operation to a voltage resonance type is provided at the primary side and a parallel resonance circuit for achieving the voltage resonance operation is provided at the secondary side.
The secondary side of the power supply circuit thus constructed is equipped with a half-wave rectifying circuit comprising a secondary rectifying diode D
01
and a smoothing capacitor C
01
which are connected to the secondary winding N
2
, thereby achieving a main secondary DC output voltage E
01
corresponding to substantially the once level as the alternating voltage induced in the secondary winding N
2
.
Further, in this case, an intermediate tap is provided to the secondary winding N
2
, and a half-wave rectifying circuit comprising a rectifying diode D
02
and a smoothing capacitor C
02
is connected to the winding between the tap output line of the secondary winding N
2
and the earth at the secondary side as shown in
FIG. 10
to generate and output a low secondary DC output voltage E
02
.
In the power supply circuit, an active clamp circuit is equipped to the secondary side. That is, an auxiliary switching element Q
2
of MOS-FET, a clamp capacitor C
3
and a clamp diode DD
2
are equipped as the secondary active clamp circuit. Further, a drive winding Ng
1
, a capacitor Cg
1
and a resistor Rg
1
are equipped as a driving circuit system for driving the auxiliary switching element Q
2
.
A clamp diode DD
2
is connected between the drain and source of the auxiliary switching element Q
2
in parallel. As a connection manner, the anode of the clamp diode DD
2
is connected to the source, and the cathode is connected to the drain.
The drain of the auxiliary switching element Q
2
is connected to the connection point between the tap output line of the secondary winding N
2
and the anode of the rectifying diode D
02
through a clamp capacitor C
3
. Further, the source of the auxiliary switching element Q
2
is connected to the earth at the secondary side.
Accordingly, the secondary active clamp circuit is constructed by connecting the clamp capacitor C
3
to the parallel connection circuit comprising the auxiliary switching element Q
2
and the clamp diode DD
2
in series. The circuit thus formed is further connected to the secondary winding N
2
in parallel.
As the driving circuit system of the auxiliary switching element Q
2
, a series connection circuit of a capacitor Cg
1
, a resistor Rg
1
and a drive winding Ng
1
is connected to the gate of the auxiliary switching element Q
2
as shown in FIG.
10
. The series connection circuit forms the self-excited driving circuit for the auxiliary switching element Q
2
. That is, a signal voltage VGS from the se
Berhane Adolf Deneke
Frommer William S.
Frommer & Lawrence & Haug LLP
Sony Corporation
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