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.