Electronic transformer

Details Electronic transformer Electronic transformer

2002-02-27

2003-07-29

Sherry, Michael (Department: 2838)

Electric power conversion systems

Current conversion

Including d.c.-a.c.-d.c. converter

C363S021120, C323S222000

Reexamination Certificate

active

06600667

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to an electronic converter having an input circuit and an output circuit, which are connected to one another via an inductive coupling, with the output circuit having a first and a second output terminal between which an output voltage can be produced, and with the input circuit having a first and a second input terminal for connection of a voltage source which has at least one DC voltage component, a series circuit which is arranged in series between the first input terminal and a first connection of the inductive coupling and comprises an inductance and a capacitor, with the junction point between the inductance and the capacitor being connected via an electronic switch to the second input terminal, and with the inductance being arranged between the junction point and the first input terminal and the capacitor being arranged between the junction point and the inductive coupling, having a sensor resistor which is arranged between the second input terminal and the second connection of the inductive coupling, and having a control circuit to which at least the output voltage and the voltage which is dropped across the sensor resistor can be supplied as input signals, with the control circuit opening and closing the switch as a function of the input signals supplied to it.
The invention furthermore relates to an electronic converter having an input circuit and an output circuit which are connected to one another via an inductive coupling with the output circuit having a first and a second output terminal, between which an output voltage can be produced, and the input circuit having a first and a second input terminal for connection of a voltage source which has at least one DC voltage component, a series circuit, which is arranged in series between the second input terminal and a first connection of a sensor resistor and comprises an inductance and a capacitor, with the junction point between the inductance and the capacitor being connected via a diode to the second connection of the inductive coupling, the second connection of the sensor resistor being connected to the first connection of the inductive coupling, and the inductance being arranged between the junction point and the second input terminal and the capacitor being arranged between the junction point and the first connection of the sensor resistor, an electronic switch which is arranged between the first input terminal and the first connection of the sensor resistor, a storage capacitor which is arranged between the first input terminal and the second connection of the inductive coupling, a control circuit, to which at least the output voltage and the voltage dropped across the sensor resistor can be supplied as input signals, with the control circuit opening and closing the switch as a function of the input signals supplied to it.
Converters such as these are suitable, inter alia, for operation of low-voltage incandescent lamps and optical semiconductors, for example light-emitting diodes (LED) and the like.
BACKGROUND OF THE INVENTION
Circuits such as these are known and are used in the prior art, for example, as DC/DC converters with power levels up to 100 W. The control circuit is generally in the form of a PWM-IC, which monitors current and voltage, while the electronic switch is formed by a vertical power MOSFET.
FIG. 1
shows three embodiments of such topologies, with
FIG. 1
a
showing a so-called BIFRED (Boost Integrated Flyback Rectifier Energy Storage DC/DC Converter) converter,
FIG. 1
b
showing a so-called BIBRED (Boost Integrated Buck Rectifier Energy Storage DC/DC Converter) converter and
FIG. 1
c
showing a so-called PFC Flyback Converter (PFC=Power Factor Correction).
From the year 2001, the mains current harmonics for all lighting devices will have to comply with IEC 1000-3-2. So-called PFC circuits are used for this purpose in the prior art. Described in simple terms, the PFC is adequate, provided the current drawn from the mains is proportional to the mains voltage. The circuits illustrated in
FIGS. 1
a
to
1
c
are merely higher-order single-ended converters, and need to have additional PFC circuits connected to them on the input side for this purpose.
First of all, however, the circuits in
FIGS. 1
a
to
1
c
will be described in more detail. The input side of the BIFRED and BIBRED converters is in this case constructed identically, as follows: an input voltage UE, which has at least a DC voltage component, is applied between two input terminals. The first input terminal is optionally followed by a diode D
1
and an inductance L
1
. A parallel circuit is arranged between a first junction point VP
1
, which follows the inductance L
1
, and a second junction point VP
2
, one branch of which parallel circuit comprises a series circuit formed from an electronic switch S
1
and a shunt resistor RS. The second parallel branch comprises a capacitor C
1
and an inductance L
2
. The shunt resistor RS is used to determine a variable which is approximately proportional to the load current, to be precise in the form of a voltage US which is supplied to the control circuit ST which controls the switch S
1
. Provided the current flowing through RS is greater than a specific value, the switch S
1
is opened, in order to prevent damage to the circuit itself and to circuits connected on the secondary side. The BIFRED converter illustrated in
FIG. 1
a
has an inductance L
3
on its secondary side, and, together with the inductance L
2
, this forms a two-winding storage coil. A diode, D
2
is arranged in series with the inductance L
3
. A voltage U
A
is produced at the output terminals, with a capacitor C
2
being arranged between the output terminals.
The BIBRED converter illustrated in
FIG. 1
b
has an inductance L
3
on its secondary side, and, together with the inductance L
2
, this forms a pure AC transformer. A capacitor C
2
is arranged in series with the inductance L
3
, with the series circuit formed in this way being in parallel with a diode D
2
. The parallel circuit formed in this way is in turn arranged in series with an inductance L
4
. A capacitor C
3
is arranged between the output terminals, at which the output voltage U
A
is produced.
The PFC Flyback Converter illustrated in
FIG. 1
c
likewise comprises an input formed by two input terminals and to which a voltage U
E
is applied. One input terminal is followed by a diode D
1
and an inductance L
1
. The junction point between D
1
and L
1
may be connected via an optional capacitor C
1
to ground. The inductance is followed firstly by the series circuit formed by a diode D
2
and an inductance L
2
, and secondly by a capacitor C
2
. The junction point between D
2
and L
2
is connected via a capacitor C
3
to ground. A diode D
4
may optionally also be connected to this junction point, with its second connection being connected to the junction point between the diode D
1
and the inductance L
1
. The junction point between L
2
and C
2
is connected to ground via a switch Si and a shunt resistor RS. The voltage Us that is dropped across the shunt resistor RS is used as the input signal to a control circuit ST, which in turn controls the switch S
1
. The secondary side of the PFC Flyback Converter comprises an inductance L
3
that, together with the inductance L
2
, forms a two-winding storage coil, with a diode D
3
and a capacitor C
4
likewise being connected in this case, see
FIG. 1
a
, and in which case the voltage which is dropped across the capacitor C
4
can be tapped off as the output voltage U
A
. Alternatively (not illustrated), the secondary side can also be designed in a manner corresponding to the secondary side in
FIG. 1
b
. The respective ground is annotated M is
FIGS. 1
a
to
1
c.
FIG. 2
shows the basic structure, which is known from the prior art, of a PFC: this comprises a capacitor C, an inductance L and a switch S.
SUMMARY OF THE INVENTION
The object of the present invention is to provide electronic converters which do not require any additional contro

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