Electricity: power supply or regulation systems – In shunt with source or load – Using choke and switch across source
Reexamination Certificate
1999-01-14
2001-03-20
Riley, Shawn (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using choke and switch across source
C323S286000, C323S282000
Reexamination Certificate
active
06204644
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to technologies to improve an operation speed of a switching element in a PWM control type switching power supply.
BACKGROUND OF THE INVENTION
The switching power supply can set an output voltage to a desired value by controlling ON and OFF operation of the switching element.
FIG. 1
illustrates an example of a circuit using as such a switching power supply.
A circuit as shown in
FIG. 1
is constructed as set forth below. It should be noted that in
FIG. 1
, reference numerals
1
and
2
indicate an input terminal and an output terminal of high potential sides, respectively, and an input terminal and an output terminal of low potential sides are omitted, but each terminal is grounded.
A choke coil L
1
and a switching transistor Q
1
are connected between the input terminal
1
and the ground, a diode D
1
is connected between a connection point of the choke coil L
1
and the switching transistor Q
1
, and the output terminal
2
, and a smoothing capacitor C
2
is connected between the output terminal
2
and the ground. A capacitor C
1
for filter is connected between the input terminal
1
and the ground. A boost chopper circuit is formed by connecting these elements.
In order to operate this boost chopper circuit, a control circuit
3
and a driving circuit
4
a
are arranged, wherein the driving circuit
4
a
is formed of a resistor R
2
, transistors Q
2
and Q
3
which are connected in series, and a resistor R
1
connected between the input terminal
1
and a common connection point of each base of the transistors Q
2
and Q
3
.
A common connection point of each emitter of the transistors Q
2
and Q
3
in the driving circuit
4
a
is connected to a base of the switching transistor Q
1
, and a common connection point of each base of the transistors Q
2
and Q
3
is connected to a pulse output terminal PO of the control circuit
3
. A power supply terminal Vcc of the control circuit
3
is connected to the input terminal
1
, and a terminal GND is grounded. A voltage detecting terminal FB of the control circuit
3
is connected to a mid-connection point of resistors R
3
and R
4
, which are connected in series between the output terminal
2
and the ground.
In the circuit as shown in
FIG. 1
, when pulse signals are supplied from the control circuit
3
, the transistors Q
2
and Q
3
of the driving circuit
4
a
are operated complementarily and drives the switching transistor Q
1
. For example, if the pulse signal which the control circuit
3
outputs is high in voltage value, the transistor Q
2
is in an ON-state and the transistor Q
3
is in an OFF-state. In this case, a forward bias is applied through the resistor R
2
and the transistor Q
2
to the base of the switching transistor Q
1
, thereby the switching transistor Q
1
becomes ON.
On the contrary, if the pulse signal is low in a voltage value, the transistor Q
2
is in an OFF-state and the transistor Q
3
is in an ON-state. In this case, a forward bias is not applied to the base of the switching transistor Q
1
, and the base of the transistor Q
1
is grounded through the transistor Q
3
, so that the switching transistor Q
1
becomes OFF.
In this connection, during an ON-period, positive charges are stored in a base region and negative charges in an emitter region of the switching transistor Q
1
. These stored charges are important in operation. This is because the switching transistor Q
1
is turned to the OFF-state by extinction of the stored charges.
When the switching transistor Q
1
is turned from the ON-state to the OFF-state in
FIG. 1
, the transistor Q
3
becomes ON and short-circuits between the base and emitter of the switching transistor Q
1
. At this time, a discharge path of the stored charges of the base and emitter regions of the switching transistor Q
1
is formed by operation of the transistor Q
3
and extinction of the stored charges is improved, so that turn-off operation of the switching transistor Q
1
is speeded up.
Then, in order to disappear rapidly the stored charges of the base and emitter regions of the switching transistor Q
1
, it is desirable that there is neither electric resistance nor potential difference to disturb a flow of the charges on a discharge path of the charges. As is well known, however, between terminals of a transistor element, the potential difference based on a PN junction thereof is caused. In this connection, in the transistor Q
3
in
FIG. 1
the potential difference (a voltage V
BE
between a base and an emitter) is also caused. For this, in the circuit in
FIG. 1
the potential difference appears, based on a voltage between the base and emitter of the transistor Q
3
, on the discharge path between the base and emitter of the transistor Q
1
, and discharge of the stored charges is disturbed.
SUMMARY OF THE INVENTION
An object of this invention is to obtain a switching power supply in which a switching element is rapid in operation and a device is high in efficiency by eliminating an undesirable effect based on a potential difference caused in a driving circuit.
A switching power supply according to the present invention comprises; a switching element for controlling the amount of current passing through a main current path based on ON and OFF operation of the switching element; a control circuit for detecting an output voltage of a power supply and outputting pulse signals of on-duty according to the output voltage; a driving circuit for driving the switching element according to pulse signals; and an auxiliary bias circuit, connected to the driving circuit, for supplying a reverse bias voltage to a control terminal of the switching element via the driving circuit.
Another switching power supply according to the present invention comprises: a switching element for controlling an amount of current passing through a main current path based on ON and OFF operation of the switching element; a control circuit for detecting an output voltage of a power supply and outputting pulse signals of on-duty according to the output voltage; a driving circuit having a transistor to short-circuit between one terminal of a main current flow pass and a control terminal of the switching element and for driving the switching element according to the pulse signals; and an auxiliary bias circuit for applying a forward bias to the transistor of the driving circuit according to the pulse signals.
In one embodiment for realizing the present invention, the auxiliary bias circuit generating a voltage applying a reverse bias to a base of the switching element is provided to connect an output thereof to the driving circuit of the switching element.
In another embodiment for realizing the present invention, the auxiliary bias circuit generating a voltage applying a forward bias to a transistor in the driving circuit for short-circuiting between the base and emitter of a switching element is provided to connect an output thereof to the control terminal of the transistor.
The input of the auxiliary bias circuit in each embodiment is connected to one terminal of the main current path of the switching element, or one end of a predetermined winding of an inductance part. For example, the auxiliary bias circuit is formed of a circuit combined with two capacitance elements and two diodes, or a circuit combined with two capacitor elements, an inductance element and a diode.
In the switching power supply constructed as set forth above, undesirable potential difference is cancelled or not generated in the driving circuit by means of a voltage supplied from the auxiliary bias circuit. Thereby the stored charges in vicinity of each terminal of the switching element can be discharged without any difficulty. Consequently, the improved switching power supply according to the present invention is obtained in high operation speed of the switching element and high efficiency.
REFERENCES:
patent: 5689178 (1997-11-01), Otake
patent: 9-246932 (1997-09-01), None
patent: 2586788 (1998-10-01), None
Frishauf, Holtz Goodman, Langer & Chick, P.C.
Patel Rajnikant B.
Riley Shawn
Toko Inc.
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