GB2163908A - A transformer - Google Patents

Abstract

A transformer has a number of single turn primary windings 5 formed by printed circuit tracks on a flexible bendable sheet which is wrapped around a core of the transformer. The primary windings are connected to output terminals 12 of an enclosure 1 of the transformer by another printed circuit board 8 having further conductive tracks on opposite sides thereof to form balanced transmission lines whose impedance is matched to the impedance of the primary windings. A secondary winding may surround the primary windings. A similar arrangement of primary and secondary windings may be provided on another limb of the core. <IMAGE>

Description

SPECIFICATION A transformer This invention relates to a transformer having a number of primary windings. The invention arose in the design of a particular pulse modulator for feeding high voltage pulses to the output tube of a radar. In this particular pulse modulator it is proposed that a number of simultaneous pulses be fed to individual single turn primary windings of the transformer and it is important to provide transmission lines connecting directly with the primarys and matched to the impedance of the primarys.

According to the invention there is provided a transformer having a number of primary windings formed by conductive tracks on an insulating sheet wound around a core of the transformer.

The use of this technique results in "flat" conductors which have excellent properties of low RF resitance and good cooling properties. Furthermore the fact that the primarys are formed on a single sheet can greatly facilitate assembly of the transformer.

By employing the invention it can become a simple matter to connect the primarys directly to matched impedance lines formed by opposed pairs of conductive tracks on opposite sides of a circuit board. The latter can be arranged to rest against the flexible sheet carrying the primary windings and suitable direct connections can be made between on the one hand the two tracks forming one of the feed lines and, on the other hand, the two ends of a primary winding associated with that feed line.

The circuit board and the conductive tracks on it preferably extend in the same direction as the axis of the primary windings. This arrangement allows a secondary to be wound or otherwise positioned around the primary windings.

One way in which the invention may be performed will now be described by way of example with reference to the accompanying drawings in which: Figure I is a schematic perspective view of a transformer constructed in accordance with the invention, shown in exploded form with its casing partly broken away; and Figure 2 is a view of the outside of the casing as seen in direction II as indicated on Figure 1.

Referring to the drawings the transformer is en closed within an insulating casing of which a small section is shown at 1 and which is filled with oil.

Inside the casing is a closed rectangular magnetic core 2. Around each of two opposite sides of this core 2 is wound an inner primary assembly 3 and an outer seconding 4. One of these secondaries has been removed from the illustrated transformer to reveal the primary assembly under it. Each sec ondary has a low voltage end at the right hand side as seen in the drawing and a high voltage end at the left hand side, the secondaries being wound progressively from one side to the other so as to minimise the effects of high voltages at the left hand side where the feed lines to the primary assembly are located. Each primary assembly is composed of an insulating sheet 4 which is bent around one side of the core 2. The insulating sheet 3 is formed as a printed circuit board and carries a number of conductive tracks 5 each defining a space 6.Where the edges of the sheet 3 overlap, the conductive tracks are soldered so as to bridge the adjacent parts of the conductive tracks. These soldered connections are shown at 7. It is preferred that the conductive tracks be formed on both sides of the sheet 3 but this is not essential. If it is so however a further sheet of insulating material should be interposed between the sheet 4 and the core 2.

From the drawing it will be apparent that the conductive tracks on the insulating sheet 4 form single loop primary circuits. These have to be connected to outside the casing 1 by transmission lines which are matched to the impedance of the respective primarys. The way in which the primarys are formed enables this to be done in a particularly effective manner using a further printed circuit board 8 which rests against the insulating sheet 3 with the inter-position of an insulator 9.

The conductive tracks on the circuit board 8 are formed on opposite sides thereof and define balanced feed lines one of which is indicated by reference numerals 10A and 10B. The right-hand ends of these lines are shaped as shown so as to allow connection to corresponding ends 11A and 11B of an associated primary winding. Suitable holes may be formed through the circuit board 8 and insulator 9 to effect such connections e.g. by soldering.

It will be noted that the gaps 6 between the ends of the primary windings are staggered, being spaced by distances dl around a common axis x-x of the primarys. The distance dl is equal to the distances between the balances line pairs 10A, 10B etc. Also these balanced lines, which extend in the direction of the aforementioned axis, have different lengths. The lengths differ by distances d2 equal to the spacing of the primarys in the direction of the axis so that their right-hand ends are staggered and lie directly on top of the ends (eg 11A & 11B) of the primarys.

The transmission lines and the board 8 on which they are carried extend from the left hand low voltage side of the transformer, in the direction of axis x-x, which is common to the primaries on sheet 4, to studs 12 which extend through the transformer casing 1. These studs are connected to a further circuit board similar to that shown at 8 either di rectly or through the intermediary of an edge con nector (not shown). A method of direct connection is shown on Figure 2 where the studs 12 are con nected to balanced transmission lines 13, 14 and 15 formed by tracks 13A, 13B; 14A, l54B and 15B on an insulating board, not shown. The lines 13, 14 and 15 are connected at their other ends, not shown, in parallel with respective lines connected to the primarys on the lower side of the transformer (which are identical to those on the inner side). The two secondaries are also connected in parallel and their output is connected in this partic ular embodiment of the invention to the output stage of a radar transmitter.

Claims (4)

1. A transformer having a number of primarys formed by inductive tracks on an insulating sheet wound or bent around a core of the transformer.

2. A transformer according to claim 1 including an enclosure and a series of transmission lines for connecting the ends of the primary windings to outside the enclosure, the transmission lines being of matched impedance with respect to the primarys and being formed by conductive tracks on opposite sides of an insulating sheet.

3. A transformer according to claim 2 in which one end of the insulating sheet carrying the transmission lines lies against the insulating sheet carrying the primary.

4. A transformer according to claim 2 in which transmission lines and the insulating sheet on which they are carried extend from the core in the direction of a common axis of the primarys and in which a secondary winding is located over the primary windings.