Supply circuit for an electronic circuit connected to an...

Electric power conversion systems – Phase conversion without intermediate conversion to d.c. – By dynamoelectric machine converter

Reexamination Certificate

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C323S351000

Reexamination Certificate

active

06639817

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a supply circuit for an electronic circuit connected to a switched mode power supply (SMPS) converter operating at low output voltage. In particular, the invention relates to a supply circuit for an integrated circuit operating as a switch of an SMPS converter having a circuit topology of the buck (step down or forward) type or of the buck-boost (step up/down or flyback) type.
2. Description of the Related Art
As is known, SMPS converters having a circuit topology of the buck type or the buck-boost type use inductive components, the charging and discharging of which are controlled by switches that operate switching between a saturation condition and an inhibition condition (ON/OFF).
For a more detailed treatment of SMPS converters of the type referred to above, see, for example, J. G. Kassakian, M. F. Schlecht, G. C. Verghese “Principles of Power Electronics,” Addison Wesley.
At present, the aforesaid supply circuits are connected to the output of the converter and are able to operate only when the output voltage of the converter has a value greater than a preset value (8-9 V). For a better understanding, see for example the supply circuit provided in a standard buck converter illustrated in FIG.
1
.
In
FIG. 1
, a buck converter comprises an integrated circuit
2
, forming a controlled power switch, an inductor
3
, a first diode
4
, a first capacitor
5
, and a supply circuit
6
. The converter
1
moreover has a first input pin
10
receiving an input voltage Vin, a second input pin
11
connected to a ground line
12
, a first output pin
13
supplying an output voltage Vo, which is positive with respect to the ground line
12
and has a value lower than that of the input voltage Vin, and a second output pin
14
, connected to the ground line
12
.
In detail, the integrated circuit
2
, typically formed by an NMOS power transistor and a control circuit, has a first terminal (drain) connected to the first input pin
10
, a second terminal (source) connected to a first intermediate node
18
, and a supply input
19
receiving a supply voltage Vcc. The inductor
3
has a first terminal connected to the first intermediate node
18
and a second terminal directly connected to the first output pin
13
.
The first diode
4
has its cathode connected to the first intermediate node
18
and its anode connected to the ground line
12
.
The first capacitor
5
has a first terminal connected to the first output pin
13
and a second terminal connected to the second output pin
14
.
The supply circuit comprises a second diode
20
and a second capacitor
21
. The second diode
20
has its anode connected to the first output pin
13
and its cathode connected to the supply input
19
of the integrated circuit
2
. The second capacitor
21
is connected between the first intermediate node
18
and the supply input
19
of the integrated circuit
2
.
In a known way, the integrated circuit
2
performs a power conversion between the first input pin
10
and the first intermediate node
18
. The voltage on the first intermediate node
18
is filtered by the inductor
3
and by the first capacitor
5
. The first diode
4
enables recirculation of the current of the inductor
3
when the integrated circuit
2
opens, disconnecting the first intermediate node
18
from the first input pin
10
.
The second diode
20
connects the first output pin
13
to the supply input
19
of the integrated circuit
2
and discharges the second capacitor
21
during opening of the integrated circuit
2
. The second capacitor
21
filters the output voltage Vo and stabilizes it.
The supply circuit
6
of
FIG. 1
can be used if the output voltage Vo is higher than the supply voltage Vcc of the integrated circuit
2
, since
Vcc=Vo−V
D
where V
D
is the voltage drop on the second diode
20
.
Consequently, the supply circuit
6
of
FIG. 1
is limited in its application.
In order to extend the range of output voltage of the converter
1
of
FIG. 1
, one known solution is to provide a double winding on the inductor
3
, as shown in
FIG. 2
, wherein a second winding
3
a
is connected between the first intermediate node
18
and the anode of a second diode
20
′, so as to take and supply to the integrated circuit
2
the voltage present on the first intermediate node
18
, which is higher than the voltage present on the first output pin
13
when the integrated circuit
2
is closed.
The above solution is advantageous only in insulated converters, wherein a high-frequency transformer is already available, as in the case, for example, of a flyback converter provided with transformer, in which the introduction of an additional winding does not affect costs very much.
Instead, this solution is not economically advantageous in non-insulated converters using a standard inductor insulated in lacquer.
BRIEF SUMMARY OF THE INVENTION
The disclosed embodiments of the present invention provide a supply circuit for an electronic circuit connected to an SMPS converter operating at a low output voltage that does not present the drawbacks previously described.
According to the embodiments of the present invention, there is provided an SMPS converter having a first input receiving an input voltage, an output supplying an output voltage, a controlled switch connected between said first input and an intermediate node, a first component connected between said intermediate node and said output, a second component connected between said intermediate node and a reference-potential line, one of said first component and said second component comprising an inductive element, and another of said first and second components comprising a unidirectional current-conducting element, and a supply circuit connected to said inductive element and having an output pin that supplies a supply voltage, the supply circuit having an energy taking element connected to said inductive element, an energy accumulation element connected to said energy taking element and storing an electric voltage, and a voltage transfer element connected between said energy accumulation element and said output pin of said supply circuit.


REFERENCES:
patent: 4016461 (1977-04-01), Roland
patent: 4347474 (1982-08-01), Brooks et al.
patent: 4725768 (1988-02-01), Watanabe
patent: 4736151 (1988-04-01), Dishner
patent: 4864213 (1989-09-01), Kido
patent: 5045771 (1991-09-01), Kislovski
patent: 5119013 (1992-06-01), Sabroff
patent: 5389871 (1995-02-01), Otake
patent: 5532577 (1996-07-01), Doluca
patent: 5847553 (1998-12-01), Beaudoin et al.
patent: 5886513 (1999-03-01), Appeltans et al.
patent: 5969515 (1999-10-01), Oglesbee
patent: 6369558 (2002-04-01), Umemoto

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