Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Pulse ~ransformer
The invention relates to a pulse transformer for the transformation
of low-voltage pulses to high-voltage pulses, whlch is equipped with
a primary winding suitable for connection to a pulS8 transformer
generating low-voltage pulses, a secondary winding provided with
high-voltage terminals, snd a transformer core, which is at least
partly surrounded by the primary and secondary windings.
This type of pulse transformer can be used in a radar transmitter
for the generation of radar transmit pulses. The transformer is then
placed between a pulse forming network and a high power tube, such
as a magnetron or a klystron. In that application, the transformer
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- is required to transform voltage pulses, generated by the pulse
forming network, of e.g. several hundred volts, thousands of
amperes and a length in the order of microseconds, to voltage
pulses of tens of kilovolts and tens of amperes. The transformed
pulses are applied to the klystron or magnetron for the generation
of microwave pulses.
r~ These microwave pulses must be generated at a certain repetition
rate, the intervals between consecutive pulses being used by a radar
receiver to collect echoes of emittted pulses. However, to enable an
echo to be received immediately after the emission of a pulse, the
pulses need to have steep etg-s.
Pulses having less steep edges may be caused by what is known as the
leakage inductance of the pulse transformer. This occurs if the
coupling between the primary and 4econdary winting of the
;~30 transformer is less than optimal. Then, the electromagnetic fields
~` generated by the primsry and secondary windings are not fully
coupled.
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Supply leads, too, may contribute to the leakage intuctance, as well
as ths non-conducting spacing which, to achieve the necessary
insulation, is present between wind$ngs and core.
From GB-A 2.103.426 a version of this type of pulse transformer is
known, which is equippet with a toroidal core around which is wound
a secondary toroidal winding, the primary winding completely
surrounding this sccondary winding, from which it is separated by an
abundance of insulation material.
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A toroital core with toroidal windings around it will keep the
magnetic flus mainly contained within the core. A disadvantage is
that much interspace is needet for the insulation between the
primary and secondary wintings, the insulation space in turn having
an adverse effect on the coupling between the wintings.
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The pulse transformer according to the invention has for its ob~ect
to provite a transformer exhibitlng little leakage inductance by
limiting to a large extent the spacing between the windings and
between windings and core. To this end ehe pulse transformer is
equipped with connection means between the secondary winding and the
transformer core for connecting the high voltage to the transformer
core, the secondary winding, for at least part of its width, being
surrounded by the entire primary winding.
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Since now the voltage on the~transformer core closely follows the
voltage on the secondary winding, little or no insulation is needed ;~
between the secondary winding and the core. This results in a better
coupl:ing and less leakage inductance.
In one embodiment of the pulse transformer featuring a primary
winding in the form of a foil with conductive material, wound arount
a secondary winding which is al80 in the form of a conducting foil,
~ the potential difference between successive layers is small.
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Conssquently, the required insulation space between the windings is
minimal, further reducing the leakage inductance.
A further reduction of the leaksge inductance is achieved in an
embodiment where the transformer core is clamped, by means of the
primary winding, to an electrically conducting support frame which
comprises insulated parts, a current supplying part and a current
draining part having a contact surface with, respectively, the
conducting side of a current supplying lead and a current draining
lead of the primary winding. Consequently, the space between the
primary and secondary windings can be limited to a minimum and a
well-defined electrical connection i8 obtained.
~;~ The invention will be elucidated with reference to the accompanying
; 15 drawings, of which:
Fig. 1 shows a partial circuit diagram of a radar transmitter with
pulse trsnsformer;
Fig. 2 shows a schematic embodiment of a pulse transforDer with
-~ support; and
Fig- 3 shows a schematic side view of the windings and core of the
`~ pulse transformer of Fig. 2 in the direction of the line A-A.
The pulse transformer according to the invention can be used in a
radar transmit chain as tepicted schematically in Fig. 1. A pulse
generator 2, connected to power supply 1, generates pulses with a
length and at a repetition rate which are suitable for ratar. To
this end, the pulse generator 2 comprises known pulse forming means,
such as networks incorporating delay lines, and switching means
using, e.g. thyristors. The generated pulses are appliet in the
~ 30 usual ~ay via a fast saturable coil 3 to the pulse transformer 4.
The coil 3 blocks the pulses until the switching means in the pulse
generator 2 have become fully conductive, to prevent power loss
across the switching means.
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The pulses applied to tha pulse transformer 4 have characteristic
pulse lengths of about 1 ~s, characteristic peak voltages of about
400 V and characteristic peak currents of about 8000 A.
The pulse transformer 4 transforms these low-voltage pulses to
high-voltage pulses with characteris~ic peak voltages of 80 kV ant
peak currents of 40 A. The achieved transformation ratio ~s thus
1 : 200 in this case, which is considerably higher than customary
for pulse transformers. The high-voltage pulses are subsequently
applied to a radar transmitter 5, provided with ia high power tube,
such as a magnetron or klystron, which on the basis of the applied
pulses generates microwave pulses with corresponding pulse lengths.
Finally, the microwave pulses are emitted by an antenna 6.
An embodiment of the pulse transformer according to the invention,
illustrated in Fig. 2, comprises a transformcr core 7, primary
windings B and secondary windings 9. The transformer core 7, for
which conventional material is used, is built up from two tightly
~ Joined U-shaped parts forming a magnetic circuit, on two facing
`~ ~ parts of which the windings 8 iand 9 have been mounted. The core may
also be E-shaped, however, with a primary and secondary winding
- ~ wound around all three core legs, or ~-shaped with a primary and ~ -
secondary winding on only one leg. The principal point is that
`~; ~ primary winding 8 ~hould enclose the secondary winding as tightly as
possible, to achieve a proper couping.
To this end the primary winding 8, vhich in this case i8 in the
,form of a foil, is clamped through connections 13, 14, 15 to a
~;~ support frame consisting of three part~ 10, 11 and 12. The parts 10,
11 and 12 of the s~pport frame are made from electrically conducting
material, the part 12 being electrically insulated from the parts 10
` and 11 b~ an insulating layer 16. Part 12 makes electrical contact
with a part of the electrically conducting side of the primary
winding 8, which part is clamped by the connection 14. The side of
the primary winding 8 adJoining the transformer core 7 is not
provided with an insulating layer.
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The parts 10 and 11 make electrlcal contact with the leats of the
primary winding 8 which are clamped by the connections 13 and 15.
The parts 10 and 11 are subsequently connected electrically, through
connections 17, to a conducting plate 18. The part 12 protrutes
through an opening of the plate 18, and is clamped on the opposite
site of it through connections 19 and 20. Between the part 12 and
the plate 18 a foil 21 is inserted, with two conductive sides which
; are separated b~ an insulation layer. The foil 21 is connected to
the pulse generator 2 via the saturable coil 3. The primary current
path then runs via the side of the foil 21 which makes contsct with
the part 12, the part 12 proper, the primary winding 8, the parts 10
and 11, the plate 18 and tha side of the foil 21 which makes contact
with plate 18. Between the plate 18 and part 12 there is further the
- coil 3.
The primary winding 8 i8 prefsrably a foil w~th on one side a
contuct~ng layer. The advantage is that the potential differences
between the layers remain limitet to, in this csse, 400 V per layer.
Consequently little space is needed for inter-layer insulation and
the arrangement can be quite compact, ~hich has a favourable effect
on the leakage inductance and the coupling. The parts of the
~ secondary ~inding 9 which are nearest to the primary winding 8 and
¦ ~; those which are nearest to the transformer core 7 are providad with
low-voltage leads 22 and high-voltage leads 23, respectively, such
that tbey are e~ternally connectable. The high-voltage leads 23 are
electrically linked to the transformer core 7 through a
~ core-surrounding clamping ring 24. The secondary winding 9 is wound
-Y~ on a coil former (not shown in the figure), which freely surrounds
-~ the transformer core 7. One of the high-voltage leads 23 i8
connected to the core 7 by way of an AC coupling in the form of
capacitor 25, which forms a low impedance to the generated pulses
but, conversely, a high one to a low-frequency AC voltage, applied
in the customary manner across the secondary w~nding 9, to power the
filament of a high power tube, when connected.
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It should ba noted that there are tifferent ways in which the core 7
can be elactrically linked with the secondary winding. In an
alternative embodiment, for instance, part of the secondary winding
9 is wound directly on the core 7, no coil former being used in this
case.
In yet another embodiment, the secontary winding 9 may take the form
of a wire winding, but then more space will be needed for
insulation.
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Flg. 3 is a side view of the pulse transformer according to the line
A-A in Fig. 2. The low-voltage leads 22 are kept as far as possible
removed from the transformer core 7. The ratio between the width of
the primary winding 8 and the width of the secontary winting 9
determines the transformer characteristics to 8 consiterable estent.
Preferably, the secondary winding 9 i8 mad~ wider than the primary
w~nding 8.
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