Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
1998-06-17
2001-04-03
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S097000, C363S061000
Reexamination Certificate
active
06212082
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to supply circuits of the type including a rectifier and a storage capacitor, for supplying a load via a regulation circuit such as a switched-mode circuit.
2. Discussion of the Related Art
At the present time, many devices electrically supplied from the mains include a switched-mode power supply. The power is extracted from the network in the form of current peaks of short duration. These current peaks disturb the network efficiency. The effects of these current peaks worsen with the number of devices connected to the network and incorporating a switched-mode power supply. Accordingly, electric distribution companies have imposed several standards to improve the power factor of power supplies.
FIG. 1
shows a conventional diagram of provision of a d.c. power supply from the mains. Terminals X and Y of the a.c. supply are connected to input terminals of a rectifying bridge
1
, output terminals A and B of which are connected to a storage capacitor C
1
and to a load L. It will be assumed that load L incorporates a regulation circuit, for example, a switched-mode power supply, connected to a load. Further, a resistor r of low value for limiting the current surges of the system upon power-on is often to be found in series with capacitor C
1
.
FIG. 2A
shows, as a function of time, rectified mains voltage V
XY
and voltage V
A
B, between terminals A and B (neglecting the effect of resistor r). It is assumed that at a time t
0
, the voltage across capacitor C
1
is higher than the mains voltage. Then, the voltage between terminals A and B corresponds to the voltage across capacitor C
1
which progressively discharges into load L. From a time t
1
, the rectified mains voltage becomes higher than the voltage across the capacitor, and the mains ensures the supply of load L and the recharge of capacitor C
1
. From a time t
2
, the voltage on the capacitor becomes higher than the mains voltage and, again, the capacitor supplies the load. This is repeated at the next halfwave (times t
3
and t
4
).
FIG. 2B
shows the shape of the current extracted from the mains between times t
1
-t
2
and t
3
-t
4
. Theoretically, the current has a substantially triangular shape. In practice and as illustrated in
FIG. 2B
, the current is substantially sinusoidal due to the mains impedances and, more specifically, it corresponds to a sine wave peak, that is, its shape is substantially parabolic. The current peaks are symmetrical with respect to their maximum and this maximum can be relatively high.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a load supply circuit which limits the amplitude and increases the angle of the current peaks extracted from the mains.
Another object of the present invention is to provide such a supply circuit in which the current peaks extracted from the mains are asymmetrical. The present invention also aims at enabling these current peaks, in case of need, to exhibit a maximum at the beginning of each peak.
The present invention also aims at providing a supply circuit in which the charge current of the storage capacitor is controllable independently from the type of load supplied.
To achieve these and other objects, the present invention provides a supply circuit with a storage capacitor including, across a rectifying bridge, a storage capacitor associated with a charge path and with a discharge path, the charge path including a controllable current source and the circuit including means of control of the current source so that, at least in steady state, the charge periods of the storage capacitor have a predetermined duration.
According to an embodiment of the present invention, the circuit includes a means of detection of the charge and discharge periods of the storage capacitor, and a comparator assembly controlling the value of the current provided by the source, to control the charge periods of the capacitor with a reference value.
According to an embodiment of the present invention, the comparator compares the mean value of a detection signal having two states, indicative of the charge and discharge periods of the storage capacitor, with a predetermined reference voltage.
According to an embodiment of the present invention, the comparator is formed by an operational amplifier, connected as an integrator of the detection signal provided by a bipolar transistor controlled by the voltage across the current source.
According to an embodiment of the present invention, the base of the bipolar transistor is connected, via a resistor, to a first output terminal of the current source, the detection signal being taken from the collector of the bipolar transistor, the emitter of which is connected to a second terminal of the current source.
According to an embodiment of the present invention, the current source is an N-channel MOS transistor.
According to an embodiment of the present invention, the intrinsic diode of the MOS transistor forms the discharge path for the storage capacitor.
The present invention also provides a method of control of a supply circuit with a storage capacitor including, across a rectifying bridge, a storage capacitor associated with a charge path and with a discharge path, this method including setting, at least at steady state, the duration of charge periods of the storage capacitor to a predetermined duration.
According to an embodiment of the present invention, the method includes controlling the value of a charge current of the storage capacitor to maintain, at each halfwave and at least at steady state, the charge duration of the storage capacitor to the predetermined value.
According to an embodiment of the present invention, the predetermined duration is at minimum 2.17 ms, preferably 2.67 ms, for an a.c. supply frequency of the rectifying bridge of 50 hertz.
According to an embodiment of the present invention, the predetermined duration is at minimum 1.81 ms, preferably 2.23 ms, for an a.c. supply frequency of the rectifying bridge of 60 hertz.
The foregoing objects, features and advantages of the present invention will be discussed in detail in the following non-limiting description of specific embodiments in connection with the accompanying drawings.
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patent: 2 742 010 (1997-06-01), None
French Search Report for French Application No. 0708165, filed Jun. 24, 1997.
Patent Abstracts from Japan vol. 007, No. 32 (E-180), Jun. 9, 1983 & JP 58 04686803/18/83.
Patent Abstracts from Japan vol. 018, No. 570 (E1623), Oct. 31, 1994 & JP 06 209574.
Galanthay Theodore E.
Morris James H.
Patel Rajnikant B.
SGS-Thomson Microelectronics S.A.
Wolf Greenfield & Sacks P.C.
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