Electric power conversion systems – Current conversion – Including automatic or integral protection means
Reexamination Certificate
1999-12-17
2001-06-12
Riley, Shawn (Department: 2838)
Electric power conversion systems
Current conversion
Including automatic or integral protection means
C363S053000, C323S303000
Reexamination Certificate
active
06246597
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to non-isolated power supplies for supplying a load with a low D.C. voltage obtained from a high A.C. voltage. Such A.C./D.C. converters are found in most electric household appliances to supply low-voltage components such as, for example, logic circuits (microprocessors, programmable logic), electromechanical actuators (relay) or electronic actuators (triacs).
2. Discussion of the Related Art
In such applications intended for being supplied by the mains, the converters must respect electromagnetic compatibility standards (in particular, standards EN 55022, EN 55014, IEC 1000-4-11, IEC 1000-4-5).
Two solutions capable of fulfilling these standards while providing a sufficient power (on the order of one watt) for the supply of most electronic cards are known.
FIG. 1
very schematically illustrates a first conventional A.C./D.C. converter. Such a converter is based on the use of a so-called “class X” high voltage capacitor C connected, in series with a zener diode DZ, between two terminals E
1
, E
2
that receive a high A.C. voltage Vac (for example, the 240V/50 Hz or 110V/60 Hz mains). A resistor R of small value (on the order of one hundred ohms) is generally connected between terminal E
1
and a first terminal of capacitor C, the other terminal of which is connected to cathode K of diode DZ. The anode of diode DZ is connected to terminal E
2
. The function of resistor R is to limit the current upon circuit power-on. The junction point K of capacitor C with diode DZ is connected, via a rectifying diode D, to the positive terminal of a low voltage capacitor C′ across which is sampled a D.C. output voltage Vs that supplies a load Q between respectively positive and reference output terminals S
1
and S
2
. In the present case of a non-isolated power supply, terminal S
2
is confounded with terminal E
2
to which is connected the negative terminal of capacitor C′.
High voltage capacitor C behaves as a reactive inductance enabling limiting the current in the load. During positive halfwaves of voltage Vac, capacitor C lets a current run through diode D and, accordingly, through filtering capacitor C′ and into the load. As soon as the amplitude of voltage Vac becomes greater than the threshold voltage of diode DZ (neglecting the voltage drop in resistor R), the current of capacitor C is shunted by diode DZ, which thus enables regulating output voltage Vs to the value of this threshold voltage. During the negative halfwaves of voltage Vac, diode D is reverse biased and the load is supplied by the power stored in capacitor C′.
It should be noted that the example of
FIG. 1
, described in relation with an A.C. voltage Vac and a halfwave rectification by means of diode D, may also be implemented by placing a rectifying bridge between terminals K and E
2
. Filtering capacitor C′ is used to make voltage Vs across load Q substantially constant.
FIG. 2
illustrates, still very schematically, a second conventional example of a converter from an A.C. high voltage to a D.C. low voltage.
As previously, a high A.C. voltage Vac is applied between two input terminals E
1
, E
2
of the converter. In the example of
FIG. 2
, the converter is formed from a low frequency transformer T, that is, a transformer operating at the frequency of the system supplying A.C voltage Vac. The two terminals of a primary winding L
1
of transformer T are connected to terminals E
1
and E
2
. The two terminals of a secondary winding L
2
of transformer T provide a low A.C. voltage Vi, the peak amplitude of which corresponds, in this example, to the value of D.C. voltage Vs desired across output terminals S
1
, S
2
of the converter to supply load Q. As in the example of
FIG. 1
, voltage Vs is sampled across a low voltage filtering capacitor C′.
A.C. low voltage Vi is applied to two A.C. input terminals
2
,
3
, of a diode bridge D
1
, D
2
, D
3
, D
4
, the rectified output terminals
4
,
5
, of which are connected to terminals S
1
and S
2
. As previously, this is a non-isolated power supply, terminals E
2
and S
2
forming a single terminal.
In the example of
FIG. 2
, the value of output voltage Vs is determined by the transformation ratio, that is, by the ratio between the number of spirals of windings L
1
and L
2
of transformer T.
The above-described solutions are relatively simple to implement due to the small number of components that they use. Further, the components can be sized so that the converters fulfill the requirements of electromagnetic interference standards. Moreover, these solutions allow direct control of bidirectional switches (for example, triacs) since they have a common point with the supply system.
However, the two conventional solutions described here-above have the essential drawback of being bulky and expensive.
The high cost of the first solution is linked to the use of a class X capacitor having to withstand the voltage of the supply system. Such a capacitor is also characterized by a large bulk. For these reasons, converters implementing this solution are generally limited to small currents (under 30 mA).
For the second solution, the high cost and the large volume result from the use of a transformer. Further, this second solution has the disadvantage of generating significant losses due to the use of the transformer. This second solution is more specifically intended for converters meant to provide larger currents (between 30 and 80 mA).
SUMMARY OF THE INVENTION
The present invention aims at providing a novel solution to make a converter from a high A.C voltage into a low D.C. voltage which overcomes the disadvantages of known solutions.
The present invention aims, in particular, at providing a novel solution, with a reduced or minimized bulk. The present invention also aims at having the provided solution respect electromagnetic compatibility constraints.
The present invention also aims at providing a novel converter which automatically adapts to the current demand of the load. More specifically, the present invention aims at providing a solution adapted to a large range of currents, that is, which enables, if necessary, providing currents substantially larger than the conventional solutions using capacitors, without generating the losses associated with the operation of a transformer.
The present invention further aims at having the converter protect the load against overcurrents upon power-on and maintain the load supply even in case of a microfailure of the A.C. supply voltage.
Further, the present invention aims at improving the regulation of the converter output voltage. On this regard, it should be noted that, according to the present invention, the reference to an output voltage corresponds, in fact and unless otherwise specified, to a regulated D.C. voltage, that is, a voltage of substantially constant value.
To achieve these and other objects, the present invention provides a converter of a high A.C. voltage into a low D.C. voltage, including a one-way switch between a first terminal of application of the A.C. voltage and a first positive output terminal, and means for controlling the output voltage to a desired value, the one-way switch being controlled in linear mode.
According to an embodiment of the present invention, the converter includes no high voltage passive component.
According to an embodiment of the present invention, the control means include a first element for setting a reference voltage and comparing this reference voltage with the output voltage, a second element for setting a reference current, and a first means for modifying a current of linear control of the one-way switch upon closing and opening.
According to an embodiment of the present invention, the first element generates an error signal only when the output voltage is greater than the reference voltage.
According to an embodiment of the present invention, the first means is, at the beginning and at the end of each halfwave of the A.C. power supply, activated and deactivated i
Galanthay Theodore E.
Morris James H.
Riley Shawn
STMicroelectronics S.A.
Wolf Greenfield & Sacks P.C.
LandOfFree
A.C./D.C. converter having a linearly controllable one-way... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with A.C./D.C. converter having a linearly controllable one-way..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and A.C./D.C. converter having a linearly controllable one-way... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2538225