DC-DC converter

Details DC-DC converter DC-DC converter

2001-06-08

2002-03-26

Han, Jessica (Department: 2838)

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

C363S019000, C363S021010, C363S021020

Reexamination Certificate

active

06362984

ABSTRACT:

BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
The present invention relates to a DC-DC converter for converting a DC voltage into a DC output via a transformer and, in particular, to a self-oscillating DC-DC converter that can keep an output voltage constant by providing control as consisting of both frequency and pulse-width modulation in response to variations in an input voltage or a load.
FIG. 8
shows a conventional example of a self-commutated resonant converter. As shown in this FIGURE, a DC power supply
1
, a capacitor
4
, a primary coil
21
of a transformer
2
, and a semiconductor switching device
91
are connected together in series: a parallel circuit of a semiconductor switching device
92
and a capacitor
5
is connected between the capacitor
4
and the primary coil
21
of the transformer in parallel; diodes
81
and
82
and a filter capacitor
3
are connected to secondary coils
22
and
23
of the transformer
2
; and a DC output is connected to the gates of the semiconductor switching devices
91
and
92
via an output-voltage detection and control circuit
6
, a frequency control circuit
14
, and a high-voltage-resistant driver IC
15
.
FIG. 9
shows an example of the operation of the converter illustrated in FIG.
8
. References v
92
, v
91
, v
4
, and v
21
denote voltage waveforms from the semiconductor switching device
92
, the semiconductor switching device
91
, the capacitor
4
, and the primary coil
21
of the transformer, and references i
92
, i
81
, and i
82
denote current waveforms from the semiconductor switching device
91
, the semiconductor switching device
92
, the diode
81
, and the diode
82
.
During a period {circle around (1)}, when the semiconductor switching device
91
is turned on, the resonant current i
91
flows through the DC power supply
1
→the capacitor
4
→the primary coil
21
of the transformer→the semiconductor switching device
91
to charge the capacitor
4
. At this time, the difference in voltage between the DC power supply and the capacitor
4
is applied to the primary coil
21
of the transformer to charge the filter capacitor
3
via the diode
81
, while supplying power to a load.
During a period {circle around (2)}, when the semiconductor switching device
91
is turned off, the resonant current is commuted to the output capacities of the semiconductor switching devices
91
and
92
and the capacitor
5
, thereby gradually raising or lowering the voltages at the semiconductor switching devices
91
and
92
. During a period {circle around (3)}, once the voltage at the semiconductor switching device
91
reaches the DC power-supply voltage, the resonant current is commuted to a parasitic diode of the semiconductor switching device
92
. At this time, when the semiconductor switching device
92
is turned on, the resonant current i
92
flows through the capacitor
4
→the semiconductor switching device
92
→the primary coil
21
of the transformer to discharge the capacitor
4
. Further, the difference in voltage between the DC power supply and the capacitor
4
is applied to the primary coil
21
of the transformer to charge the filter capacitor
3
via the diode
82
, while supplying power to the load.
During a period {circle around (4)}, when the semiconductor switching device
92
is turned off, the resonant current is commuted to the output capacities of the capacitor
5
and the semiconductor switching devices
91
and
92
, thereby gradually raising or lowering the voltages at the semiconductor switching devices
91
and
92
. During the period, {circle around (1)}, once the voltage at the semiconductor switching device
92
reaches the DC power-supply voltage, the resonant current is commuted to a parasitic diode of the semiconductor switching device
91
. At this time, when the semiconductor switching device
91
is turned on, such an operation is repeated to supply DC output power insulated from the DC power supply. The circuit illustrated in
FIG. 8
operates as illustrated in
FIG. 9
, regardless of its load state (light or heavy load) or input voltage.
In the conventional example illustrated in
FIG. 8
, in response to variations in the load, the output-voltage detection and control circuit and the frequency control circuit are used to modulate the operating frequencies of the semiconductor switching devices, in order to keep the output voltage constant. This method is not based on the current commonly used pulse-width modulation method, and requires relatively expensive high-voltage-resistant driver ICs to drive the semiconductor switching device
92
. Further, the frequency control circuit may be replaced by a pulse-width modulation circuit, and the high-voltage-resistant driver ICs may be replaced by pulse transformers, though the use of pulse transformers hinders size reduction.
It is thus an object of the present invention to eliminate the need for high-voltage-resistant driver ICs or pulse transformers in order to reduce costs.
SUMMARY OF THE INVENTION
To attain this object, the invention set forth in claim
1
provides &Lgr; DC-DC converter for converting DC power from a DC power supply into an arbitrary DC output via a transformer, with the DC-DC converter being characterized in that:
the DC power source, a first capacitor, a primary coil of the transformer, a first semiconductor switching device, and a current-limiting resistor are connected together in series; a parallel circuit of a second semiconductor switching device and a second capacitor is connected between the first capacitor and the primary coil of the transformer in parallel; first and second transformer driving coils are each connected between a gate and a source of the first or second semiconductor switching device, respectively, via a resistor; an activation circuit and a transistor are connected between the gate and source of the first semiconductor switching device; the base of the transistor is connected to a connection between the first semiconductor switching device and the current-limiting resistor via a base resistor; a diode and a filter capacitor are connected to a secondary coil of the transformer; and a DC output is connected to the base of the transistor via an output-voltage detection and control circuit.
The invention set forth in claim
2
provides a DC-DC convertor for converting DC power from a DC power supply into an arbitrary DC output via a transformer, with the DC-DC converter being characterized in that:
the DC power source, a first capacitor, a primary coil of the transformer, a first semiconductor switching device, and a current-limiting resistor are connected together in series; a parallel circuit of a second semiconductor switching device and a second capacitor is connected between the first capacitor and the primary coil of the transformer in parallel; first and second transformer driving coil are each connected between a gate and a source of the first and second semiconductor switching device, respectively, via a resistor; an activation circuit and a transistor are connected between the gate and source of the first semiconductor switching device; the base of the transistor is connected to a connection between the first semiconductor switching device and the current-limiting resistor via a base resistor; a first diode is connected to one terminal of a first secondary coil of the transformer so as to supply power when a positive voltage is applied to the primary coil of the transformer; a second diode is connected to one terminal of a second secondary coil of the transformer so as to supply power when a negative voltage is applied to the primary coil of the transformer; cathodes of the first and second diodes are connected to one terminal of a filter capacitor; the other terminals of the first and second coils of the transformer are both connected to the other terminal of the filter capacitor; and a DC output is connected to the base of the transistor via an output-voltage detection and control circuit.
In the invention set forth in claim
2
, magnetic coupl

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