Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2002-05-23
2004-02-10
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S018000, C363S097000
Reexamination Certificate
active
06690586
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-excited oscillation type switching power source device and, more particularly, to a self-excited oscillation type switching power source device which is provided with a start-stop circuit for controlling the starting and stopping of the device.
2. Description of the Related Art
Self-excited oscillation type switching power source devices of the related art provided with start-stop circuits for controlling the starting and stopping thereof are described, for example, in Japanese Unexamined Utility Model Application Publication No. 63-100993, Japanese Patent Application No. 2000-295203 filed on Sep. 27, 2000, and Japanese Unexamined Patent Application Publication No. 11-341802. In a ringing choke converter (RCC) described in Japanese Unexamined Utility Model Application Publication No. 63-100993, a starting voltage is applied to a switching element using a starting resistor connected between an input power source and a switching element. Also, in a switching power source device for a half-bridge converter described in Japanese Patent Application No. 2000-295203, a starting voltage is applied to a switching element using a starting resistor connected between an input power source and the control terminal of the switching element. Furthermore, in a switching power source device described in Japanese Unexamined Patent Application Publication No. 11-341802 (FIG. 10), a starting voltage is applied to the control terminal of a switching element using a thyristor.
FIG. 11
shows a circuit diagram of the half-bridge converter described in Japanese Patent Application No. 2000-295203. The outline of the configuration of the converter circuit will be described below. A series circuit including a first switching element Q
1
and a second switching element Q
2
is connected in parallel to an input power source Vin. One end of a series circuit including a capacitor C, an inductor L, and a primary winding T
1
of a transformer T is connected to the node between the first and second switching elements Q
1
and Q
2
, and the other end is connected to an input power source Vin. A rectification-smoothing circuit is connected to a secondary winding of the transformer T. The transformer T contains a first drive winding T
3
for developing a voltage that is substantially proportional to a voltage of the primary winding T
1
, and a second drive winding T
4
. A first control circuit A
1
is connected between the first drive winding T
3
and the first switching element Q
1
. A second control circuit A
2
is connected between the second drive winding T
4
and the second switching element Q
2
. The first and second control circuits control the turning on and off of the first and second switching elements so that both of the switching elements are alternately turned on and off, with the time period during which both of the switching elements are off being interposed between the alternate on and off. Thereby, the switching power source device is self-excitedly oscillated.
In the above-descried configuration, the capacitor C is connected in series with each other between the primary winding T
1
and the input power source Vin. Accordingly, this circuit functions as a half-bridge converter.
As a starting circuit, a resistor voltage-dividing circuit including a resistor R
2
connected between the input power source Vin and the control terminal of the first switching element Q
1
, and a resistor R
7
connected between the control terminal and the source terminal is used. That is, when the voltage from the input power source Vin is increased, and the divided voltage obtained by dividing the input power source voltage using the resistors R
2
and R
7
exceeds the threshold voltage of the first switching element Q
1
, the first switching element Q
1
is turned on. When the first switching element Q
1
is turned on, current flows through the primary winding T
1
, and voltage is developed in the first drive winding T
3
and promotes the turn-on of the first switching element Q
1
. Thereafter, a transistor Tr
1
of the first control circuit is turned on, and the first switching element Q
1
is turned off, so that voltage is developed in the second drive winding T
4
, and then, the second switching element Q
2
is turned on. In this way, the first switching element Q
1
and the second switching element Q
2
are controlled so as to be alternately turned on and off. Thus, the self-excited oscillation is carried out.
FIG. 12
is a circuit diagram of the half-bridge converter provided with a circuit similar to the starting circuit using a thyristor described in Japanese Unexamined Patent Application Publication No. 11-341802 (FIG. 10). The basic configuration of this circuit is similar to that of FIG.
11
. The first switching element Q
1
and the second switching element Q
2
are controlled so as to alternately turn on and off. Thus, the self-excited oscillation is carried out. The difference between the configurations of
FIGS. 11 and 12
lies in the starting circuits. In the circuit of
FIG. 12
, a thyristor SR is connected to the control terminal of the first switching element Q
1
. The outline of the operation at starting will be described below.
When the voltage of the input power source Vin is increased, a capacitor C
1
is charged via a resistor R
1
. When the charge voltage exceeds the Zener voltage of a Zener diode Dz, the thyristor SR electrically conducts. Thereby, the charge stored in the capacitor C
1
flows in the gate of the first switching element Q
1
, so that the first switching element Q
1
is turned on. When the first switching element Q
1
is turned on, the charge stored in the capacitor C
1
is shunt-discharged via a resistor R
4
and the first switching element Q
1
. Moreover, current flows in the primary winding T
1
so that voltage is developed in the first drive winding T
3
, and the turn-on of the first switching element Q
1
is promoted. Thereafter, the first switching element Q
1
is turned off, caused by the first control circuit, and then, the second switching element Q
2
is turned on. Thus, the first and second switching elements Q
1
and Q
2
are controlled so as to alternately turn on and off. That is, the self-excited oscillation is carried out.
The above-described configurations of the related art have the following problems caused during starting and stopping of the oscillation.
(1) Self-Excited Oscillation Type RCC Using Starting Resistor
For starting, power is supplied to a load by repeating the starting caused by the starting resistor and the turn-off of the switching element. Accordingly, when the starting time-period from the turn-off of the switching element to the re-starting is long, the power supply per unit time is small. Thus, a predetermined output voltage can not be obtained for a heavy load, and the starting becomes deficient.
Moreover, there are problems with the stopping, in that the oscillation continues until the input voltage becomes low, and therefore, the current peak value of the primary winding becomes high, which causes the transformer to be saturated.
(2) Self-Excited Oscillation Type Half-Bridge Converter Using Starting Resistor
When the voltage from the input power source is slowly increased, the first switching element Q
1
gradually reaches the on-state from its active region. In this case, the change ratio of the current flowing in the transformer becomes small, so that no voltage is generated in the transformer. In this case, the self-excited oscillation is not performed. Thus, the starting is deficient.
If the input voltage becomes low, and the on-duty of the first switching element Q
1
becomes too large in the stopping operation, the first control circuit for controlling the on-off of the first switching element Q
1
may malfunction.
(3) Self-Excited Oscillation Type Half-Bridge Converter Using Thyristor or Diac
No problems are caused in the starting characteristic even if the input voltage is slowly increased. The converter requires thyristors and diacs wh
Hosotani Tatsuya
Takemura Hiroshi
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Patel Rajnikant B.
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