Electric power conversion systems – Current conversion – Having plural converters for single conversion
Patent
1998-04-17
1999-11-23
Sterrett, Jeffrey
Electric power conversion systems
Current conversion
Having plural converters for single conversion
363126, 363144, H02M 710
Patent
active
059911786
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a miniaturized VHV (Very High Voltage) transformer/rectifier for surface mounting on a screen-printed ceramic substrate.
2. Discussion of the Background
A specific example of an environment in which a VHV transformer/rectifier according to the invention is typically incorporated is represented in the electrical diagram of the attached FIG. 1.
This FIG. 1 concerns a dc step-up voltage converter which, for a dc input voltage VE which is typically a few hundred volts, delivers a dc output voltage Vs which is for example of the order of a few kilovolts.
This circuit includes a chopper 1, in itself very conventional, which includes four static switches of the MOS transistor type, labelled 2 to 5, mounted as a bridge whose input diagonal is supplied with the dc input voltage VE as represented. The four transistors 2, 3, 4, 5 are turned on respectively by the recurrent pulsed signal trains Q1, Q2, Q1, Q2, the signal trains Q1 and Q2 being offset from one another as represented in the attached FIGS. 2A and 2B, and having a high frequency, for example of the order of a few hundred kilohertz.
As a result, on the output diagonal of this bridge, there is a voltage Vp, represented in FIG. 2C, which is made up of a string of relatively short pulses (of width equal to the offset between the pulse trains Q1 and Q2), which are spaced apart and are alternately positive and negative.
To obtain a rectified voltage Vs of absolute value of much greater amplitude (or "VHV") than that of the voltage Vp, use is made of a transformer/rectifier 6 which includes a low-voltage primary winding 7 and a plurality of secondary windings N1, N2, N3, . . . , Nn. Each of these secondary windings supplies a respective diode bridge P1, P2, P3, . . . Pn, the rectified outputs of this plurality of bridges being connected in series as represented in order to obtain the output voltage Vs.
Present-day techniques for constructing transformers do not allow them to be miniaturized without reducing the power which they transmit, on account of problems with the cooling of these transformers.
SUMMARY OF THE INVENTION
The subject of the present invention is a transformer/rectifier, in particular a VHV transformer/rectifier, for surface mounting, which can be miniaturized to the greatest possible extent, while being capable of transmitting a markedly greater power than a conventional transformer of the same volume (or else which is markedly smaller than a conventional transformer of the same power.
In accordance with a characteristic of the invention, a series inductance L of high value is connected in series between the bridge chopper 1 and the transformer 6. In this way, the current Ip, represented in FIG. 2D, which is delivered by the chopper 1 to the primary 7 of the transformer is a sawtooth current, which is alternately positive and negative, the positive half-cycles being symmetric with the negative half-cycles. The transformer 6 consequently operates as a current transformer rather than as a voltage transformer.
The invention proposes to incorporate into a single unit 8 not only the transformer/rectifier 6, hence including the diode bridges P1 to Pn, but also the high series inductance L, this unit 8, surrounded by a dashed line in FIG. 1, moreover being miniaturized and, around an opening made in this plate, the various plates being arranged one beside the other, the magnetic circuit passing through their openings, rectifiers being arranged or formed on each support and linked to the corresponding coil, the directions of coiling being alternated from one plate to the next.
This alternation allows for the simple placing in series of pancake coils directly via the substrate on which they are mounted, this substrate also providing the thermal interconnection between the transformer and an appropriate heat sink, on account of the fact that this substrate can have excellent thermal conduction properties.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention w
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"Thomson-CSF"
Sterrett Jeffrey
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