Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2003-06-10
2004-09-28
Han, Jessica (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C363S021160, C363S097000
Reexamination Certificate
active
06798671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a self-excitation type switching power supply unit for supplying a stabilized D.C. voltage to an electronic apparatus for industrial use or consumer use.
2. Description of the Related Art
FIG. 2
is a circuit diagram schematically showing a configuration of an example of an electronic apparatus which is adapted to be operated with an A.C. power supply. In the figure, as an A.C. voltage Vac of an A.C. power supply
11
, there are a 100 V system (e.g., in the range of 90 V to 130 V) and a 200 V system (e.g., in the range of 180 V to 260 V). Thus, as for electronic apparatuses as well, there are an electronic apparatus having a corresponding power supply voltage of the 100 V system, an electronic apparatus having a corresponding power supply voltage of the 200 V system, and a worldwide compatible electronic apparatus corresponding to both the power supply voltage of the 100 V system and the power supply voltage of the 200 V system.
Next, the configuration of the apparatus shown in
FIG. 2
will be described. An A.C. voltage Vac supplied from an A.C. power supply
11
is converted into a D.C. voltage Vin in a rectification portion
12
. The rectification portion
12
includes a diode D
10
for rectification, and a capacitor C
10
for rectification. Moreover, the D.C. voltage Vin is converted into a D.C. voltage Vout necessary for the operation of an electronic apparatus
13
in a D.C./D.C. conversion portion
10
. A switching power supply unit is often used as the D.C./D.C. conversion portion
10
.
In addition, as for the electronic apparatus
13
adapted to be operated by being supplied with the D.C. voltage Vout, there are many cases where the apparatus is provided with a control portion
14
using a microcomputer or the like. In one example of the control performed in the control portion
14
, a switch
15
is controlled to change over ON and OFF of the D.C. voltage to be supplied to the electronic circuit
16
. Then, for example, the control portion
14
which has received a signal from a remote control transmitter (not shown) cuts off the D.C. voltage to be applied to the electronic circuit
16
(standby state), or applies the same (operation state). Thus, the power supply is turned ON/OFF by the remote control transmitter.
FIG. 3
is a circuit diagram showing a configuration of a switching power supply unit of an RCC (Ringing Choke Converter) system which is conventionally used in relatively small electronic apparatuses. Note that, as a conventional example of this sort, JP 7-7940 A is given.
In the figure, a switching power supply unit
2
is provided with a transformer T having a primary winding N
1
, a primary auxiliary winding N
2
and a secondary winding N
3
the polarities of which are indicated by black circle symbols in the figure. The primary winding N
1
side of the transformer T corresponds to a so-called D.C. voltage input side. Then, a main switching element Q
1
comprised of a power MOS FET is operatively connected in series with the primary winding N
1
. One end of the primary winding N
1
is operatively connected to an input terminal A on a high potential side of a D.C. voltage, and a drain of the main switching element Q
1
is operatively connected to an input terminal GND on a low potential side of the D.C. voltage. In addition, a starting resistor R
1
is operatively connected between an input terminal A and a gate of the main switching element Q
1
.
In addition, series-connected resistor R
2
and capacitor C
1
are operatively connected between one end of the primary auxiliary winding N
2
and the gate of the main switching element Q
1
. In a control circuit including an NPN type transistor Q
2
and an NPN type phototransistor PT, a collector of the transistor Q
2
is operatively connected to the gate of the switching element Q
1
, while an emitter of the transistor Q
2
is operatively connected to an input terminal GND. An emitter of the phototransistor PT is operatively connected to abase of the transistor Q
2
, and a collector of the phototransistor PT is operatively connected to the primary auxiliary winding N
2
through a resistor R
3
. In addition, the base of the transistor Q
2
is operatively connected to one end of a capacitor C
2
which will be described later.
In an overcurrent protection circuit including a resistor R
6
, a Zener diode D
3
and a capacitor C
2
, the resistor R
6
and the capacitor C
2
are connected in series with each other with one end of the capacitor C
2
is operatively connected to the input terminal GND. The entirety of the overcurrent protection circuit is operatively connected in parallel with the primary auxiliary winding N
2
. The Zener diode D
3
and the resistor R
6
are operatively connected in parallel with each other. In addition, a node between the resistor R
6
and the capacitor C
2
is operatively connected to the base of the above-mentioned transistor Q
2
.
The secondary winding N
3
side of the transformer T corresponds to a so-called rectification output side (output portion). The diode D
2
for rectification is connected in series with the secondary winding N
3
of the transformer T. A cathode side of the diode D
2
and one end of the secondary winding N
3
are operatively connected to an output terminal B and an output terminal GND, respectively. A smoothing capacitor C
3
is operatively connected between the output terminal B and the output terminal GND, and a voltage detection circuit is provided in the after stage of the smoothing capacitor C
3
.
The voltage detection circuit includes voltage division resistors R
4
and R
5
, a light emitting diode LED, and a shunt regulator IC
1
. The voltage division resistors R
4
and R
5
are connected in series with each other between the output terminal B and the output terminal GND, and are connected in parallel with the light emitting diode LED constituting a photocoupler together with the phototransistor PT, and the shunt regulator IC
1
. The light emitting diode LED and the shunt regulator IC
1
are also connected in series with each other between the output terminal B and the output terminal GND. In addition, a node between the voltage division resistors R
4
and R
5
is operatively connected to a terminal R of the shunt regulator IC
1
.
The description will hereinbelow be given with respect to the operation of the switching power supply unit having the above-mentioned configuration. First of all, upon application of the D.C. voltage Vin across the input terminal A and the input terminal GND, a voltage which is equal to or larger than a threshold voltage is applied to the gate of the main switching element Q
1
through the starting resistor R
1
, and the main switching element Q
1
is turned ON. As a result, the D.C. voltage Vin is applied to the primary winding N
1
of the transformer T. Upon application of the D.C. voltage Vin to the primary winding N
1
, a voltage in the same direction as that of the primary winding N
1
is induced in the primary auxiliary winding N
2
. Then, the induced voltage is applied to the gate of the main switching element Q
1
through the capacitor C
1
and the resistor R
2
, so that the main switching element Q
1
is held in an ON state.
During the turn-ON time period of the main switching element Q
1
, the capacitor C
2
is charged with electricity originated from currents which are caused to flow through a path having the resistor R
2
, the capacitor C
1
and the phototransistor PT, and a path having the resistor R
6
and the Zener diode D
1
, respectively. Thus, the capacitor C
2
is charged with electricity in accordance with a time constant based on constants of the elements forming the above-mentioned paths. Then, at the time when a base-to-emitter voltage of the transistor Q
2
has been increased up to a level equal to or higher than a threshold voltage (e.g., 0.6 V), the transistor Q
2
is turned ON so that a voltage at the gate of the switching element Q
1
is rapidly decreased to turn OFF the main switching element Q
1
. Then, the
A. Marquez, Esq. Juan Carlos
Fisher Esq. Stanley P.
Han Jessica
Orion Electric Company Ltd.
Reed Smith LLP
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