Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-01-10
2002-04-09
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021030
Reexamination Certificate
active
06370043
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a switching power supply circuit which may be used as a power supply for electronic apparatus.
A switching power supply circuit which includes a switching converter of a voltage resonance type is a soft switching power supply circuit. In such circuit, a switching output pulse voltage and switching output current produced by the switching converter and supplied to an insulating converter transformer may have smooth waveforms. As a result, the switching converter may generate relatively low noise. Furthermore, such switching converter may be formed from a relatively small number of parts.
FIG. 11
illustrates a switching power supply circuit of the voltage resonance type. Such switching power supply circuit is operable with a commercial ac power supply AC of 100 V which may be available in Japan or the United States and is usable with a maximum load power of 150 W or more.
The switching power supply circuit shown in
FIG. 11
includes a rectifier smoothing circuit for rectifying and smoothing the commercial ac power supply AC. The rectifier smoothing circuit is formed as a voltage multiplying rectifier circuit composed of a pair of rectifier diodes Di
1
and Di
2
and a pair of smoothing capacitors Ci
1
and Ci
2
. The voltage multiplying rectifier circuit may produce a dc input voltage equal to approximately twice a dc input voltage Ei which is equal to a peak value of the ac input voltage VAC. For example, if the ac input voltage VAC is 144 V, then the dc input voltage 2Ei is approximately 400 V
The voltage multiplying rectifier circuit is adopted as the rectifier smoothing circuit so as to enable a relatively heavy load from the ac input voltage of 100 V and the maximum load power of 150 W or more. In other words, the dc input voltage is set to twice the normal voltage to suppress the amount of inflow current to a switching converter in the next stage so as to improve the reliability of the components of the switching power supply circuit.
An inrush current limiting resistor Ri is inserted in a rectifier current path of the voltage multiplying rectifier circuit shown in FIG.
11
. As a result, inrush current which may flow into the smoothin capacitors during the initial supply of power may be suppressed.
The switching power supply circuit of
FIG. 11
may include a switching converter of the voltage resonance type having a self-excited construction and including a single switching element Q
1
. Such switching element may be a high voltage withstanding bipolar transistor (BJT: junction transistor). The collector of the switching element Q
1
is connected to an end of a primary winding N
1
of an insulating converter power isolation transformer (PIT), and the emitter of the switching element Q
1
is grounded. The base of the switching element Q
1
is coupled to the positive electrode side of the smoothing capacitor Ci
2
(rectified smoothed voltage Ei) through a starting resistor RS. As a result, during a starting operation, the current supplied to the base of the switching element Q
1
may be rectified and smoothed. Further, a resonance circuit for self-excited oscillation is connected between the base of the switching element Q
1
and the primary side ground and is formed from a series connection of an inductor LB, a resonance capacitor CB, a detection driving winding NB, and a damping resistor RB. The detection driving winding NB is wound on the insulating converter PIT and together with the inductor LB provides the inductance for setting a switching frequency.
A clamp diode DD is arranged between the base of the switching element Q
1
and the primary side ground and forms a path for damper current which flows when the switching element Q
1
is off.
A resonance capacitor Cr is connected in parallel between the collector and the emitter of the switching element Q
1
. Based on the capacitance of the resonance capacitor Cr and a combined inductance (L
1
and LR) obtained from a series connection of the primary winding N
1
of the insulating converter transformer PIT and a controlled winding NR of an orthogonal control power regulating transformer (PRT), the resonance capacitor Cr forms a resonance circuit of a voltage resonance type converter. When the switching element Q
1
is off, a voltage resonance type operation may be obtained by the resonance circuit which causes the voltage Vcr across the resonance capacitor Cr to exhibit a pulse wave of a sine waveform.
One end of the primary winding N
1
of the PIT is connected to the collector of the switching element Q
1
, and the other end of the primary winding N
1
is connected to the controlled winding NR of the PRT.
The PIT transmits a switching output of the switching element Q
1
to the secondary side.
On the secondary side of the insulating converter transformer PIT, an alternating voltage induced by the primary winding N
1
appears in the secondary winding N
2
. A secondary side parallel resonance capacitor C
2
is connected in parallel to the secondary winding N
2
so as to form a parallel resonance circuit. The alternating voltage induced in the secondary winding N
2
is converted into a resonance voltage by the parallel resonance circuit. Such resonance voltage is supplied to two half-wave rectifier circuits in which one such half-wave rectifier circuit includes a rectifier diode D
01
and a smoothing capacitor C
01
and the other half-wave rectifier circuit includes a rectifier diode D
02
and a smoothing capacitor C
02
. The two half-wave rectifier circuits produce two different dc output voltages E
01
and E
02
. The rectifier diodes D
01
and D
02
may be high-speed type rectifier diodes so as to rectify the alternating voltage of a switching period.
The control circuit
1
is an error amplifier which may compare a dc output voltage of the secondary side with a reference voltage and supply a dc current corresponding to an error therebetween as a control current to the control winding NC of the orthogonal control transformer PRT. Here, the dc output voltage E
01
and the dc output voltage E
02
may be supplied to the control circuit
1
as a detection voltage and as an operation power supply, respectively.
As an example, if the dc output voltage E
02
of the secondary side varies in response to a variation of the ac input voltage VAC or the load power, then the control current which is to flow through the control winding NC may be varied within the range of 10 mA to 40 mA by the control circuit
1
. As a result, the inductance LR of the controlled winding NR may vary within the range of 0.1 mH to 0.6 mH.
Since the controlled winding NR forms a resonance circuit which may perform a voltage resonance type switching operation as previously described, the resonance condition of the resonance circuit may vary with respect to the switching frequency which is fixed. Across the parallel circuit of the switching element Q
1
and the resonance capacitor Cr, a resonance pulse of a sine waveform may appear due to the resonance circuit corresponding to an off period of the switching element Q
1
and the width of the resonance pulse may be variably controlled by the variation of the resonance condition of the parallel resonance circuit. As such, a pulse width modulation (PWM) control operation for a resonance pulse may be obtained. The PWM control of the resonance pulse width may occur during the off period of the switching element Q
1
and, as a result, the on period of the switching element Q
1
is variably controlled in the condition wherein the switching frequency is fixed. Since the on period of the switching element Q
1
is variably controlled in this manner, the switching output transmitted from the primary winding N
1
(which forms the parallel resonance circuit to the secondary side) varies, and the level or levels of the dc output voltages E
01
and E
02
of the secondary side vary. Consequently, the secondary side dc output voltage E
01
or E
02
is controlled to a constant voltage. Such constant voltage control method is hereinafter referred to as an inductan
Frommer William S.
Frommer & Lawrence & Haug LLP
Smid Dennis M.
Sony Corporation
Sterrett Jeffrey
LandOfFree
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