FR2678771A1 - REGULATED PASSIVE CIRCUIT SUPPLY DEVICE, PARTICULARLY FOR TUBE WITH PROGRESSIVE WAVES. - Google Patents

Abstract

The regulated power supply device comprises regulation means (MR), comprising an inductive circuit (L) and a resistive circuit (R) connected in parallel, connected between an input (BE1) intended to be connected to a high voltage source substantially continuous (SO), and an output (BS) suitable for supplying voltage to the cathode (K) of a microwave tube (TOP) capable of emission by pulses by generating corresponding pulsed currents. The level of the input voltage at low or zero current and the characteristics of the regulation means are adapted, taking into account the temporal characteristics of the pulses, to deliver, in the presence of said inrushes of current, a regulated output voltage of substantially constant level and equal to a nominal level chosen as a function of the characteristics of the tube and authorizing the emission of said pulses.

Description

Regulated supply device with passive circuit. especially for traveling wave tubes.

The invention relates to voltage regulation.

It applies in particular to the supply of voltage to charges liable to impulse current calls, and more particularly to microwave tubes, such as traveling wave tubes, capable of emission by pulse.

Traveling wave tubes are an essential element in the radar systems that use them. By their construction, they directly influence the phase of the waves emitted.

Indeed, the phase transfer of such a tube is sensitive to its bias voltages, and in particular to the cathode voltage.

However, during transmission pulses, the cathode voltage drops by several tens of volts causing a parasitic phase modulation of the transmitted signal, which is particularly troublesome in certain applications requiring good spectral purity and non-degraded radar coherence. from recurrence to recurrence.

To date, there is no solution that is both simple and satisfactory to this problem.

The main object of the invention is to provide such a solution.

To this end, the invention proposes a regulated supply device with a simple and original structure.

Another object of the invention is to offer a device compatible with the complex structure and operation of microwave tubes.

Another object of the invention is to propose a device which largely avoids structural modifications to the feeding of the tube.

According to a general characteristic of the invention, the regulated supply device comprises regulation means, comprising an inductive circuit and a resistive circuit connected in parallel, connected between an input intended to be connected to a substantially continuous high voltage source, and an output suitable for supplying voltage to the cathode of a microwave tube capable of emission by pulses by generating corresponding impulse current calls; in addition, the level of the input voltage at low or zero current (that is to say outside the impulse current calls from the tube) and the characteristics of the regulation means are adapted, taking account of the temporal characteristics of the pulses. , to deliver, in the presence of said current calls, a regulated output voltage of substantially constant level and equal to a nominal level chosen according to the characteristics of the tube and authorizing the emission of said pulses.

According to one embodiment, the level of the input voltage at low or zero current is higher than said nominal level chosen by a level deviation at least equal to the voltage drop in the source, caused during the call of tube current; the value of the resistive circuit is greater than a predetermined threshold depending on this level difference and on the corresponding current level in the cathode; the value of the inductive circuit depends directly on the value of the resistive circuit and the duration of the pulses.

The regulation means may further comprise an additional capacitive resistive circuit connected across the terminals of the inductive and resistive circuits, the characteristics of which are chosen as a function of those of the inductive and resistive circuits and of the duration of the pulses.

According to another embodiment, the inductive value of the inductive circuit decreases substantially linearly as a function of the current flowing through it. To this end, the inductive circuit can comprise at least two saturable inductances at different saturation thresholds. The level of the input voltage at low or zero current is then advantageously greater than said nominal level chosen by a level deviation at least substantially equal to the voltage drop in the source caused during the current draw from the tube, taking into account the residual voltage across the saturated inductive circuit.

Other advantages and characteristics of the invention will appear on examining the detailed description below and the appended drawings in which - FIG. 1 illustrates an embodiment of the device according to the invention, - FIGS. 2A to 2C illustrate the operation of the device of Figure 1, - Figure 3 illustrates another embodiment of the device according to the invention, - Figures 3A and 3B relate to the operation of the device of Figure 3, and - Figure 4 illustrates an application of the invention to another microwave tube.

The drawings essentially contain elements of a certain character. As such, they form an integral part of the description and can not only serve to better understand the detailed description below but also contribute, if necessary, to the definition of the invention.

In FIG. 1, the reference SO designates a substantially continuous high-voltage power source, such as that described in French Patent No 87 10922 in the name of the Applicant.

This source SO delivers, between the terminals BE1 and BE2 (in principle connected to ground), a nominal voltage level, the value of which will be specified below.

In addition to the two supply terminals BE1 and BE2, there are provided one or more other supply terminals BE3, ..., BE4 delivering intermediate voltage levels intended for the polarization of one or more collectors CO1, ... , C02 depending on the type of TOP traveling wave tube used.

The helix H of this tube is connected to the power supply terminal BE2 while the cathode K is suitable for being connected to the power supply terminal BE1.

The TOP tube is capable of microwave emission by pulses according to a predetermined recurrence frequency. During each emission pulse, the tube takes energy from the source
SO, which causes a drop in the cathode voltage of several tens of volts, causing parasitic phase modulation of the transmitted signal.

Those skilled in the art will understand that this voltage drop leads in particular to two major drawbacks which consist - of an ascent of the secondary lobes of the compressed pulse with degradation of the radar performance of the system incorporating such a tube, and - of a degradation of the phase coherence in the pulse and a fortiori, from recurrence to recurrence (from one pulse to another).

One solution to this problem could be to increase the value of the power source filter capacitors.

However, this increase would lead to reaching very large amounts of stored energy, dangerous for the safety of a traveling wave tube. Furthermore, the volume of the capacitors which would then be used would make such equipment incompatible with its use in certain applications where the constraints of weight and volume are significant.

The solution provided by the Applicant is both original and simple and also has the advantage of not significantly modifying the structure of the power source.

It is thus planned to insert by floating between the supply terminal BE1 and the cathode K of the tube, regulation means MR comprising an inductive circuit L and a resistive circuit R connected in parallel.

Furthermore, the level of the input voltage delivered at terminal BE1, at low or zero current (that is to say outside the impulse current calls from the tube) and the characteristics of these regulation means are adapted. , taking into account the temporal characteristics of the pulses (duration and frequency of recurrence) for delivering at the output terminal BS connected to the cathode K, in the presence of these current calls, a regulated output voltage VK of substantially constant level and equal to a nominal level chosen according to the characteristics of the tube and authorizing the emission of pulses.

The floating mounting of the regulation means thus makes it possible not to use components capable of withstanding a very high voltage.

In general, and as a first approximation, the level of the input voltage VBE1 at low or zero current is greater than the nominal level chosen for the emission of the pulses, by a level deviation AVK at least substantially equal to the voltage drop in the source caused when the tube draws current.

Furthermore, the value R of the resistive circuit is greater than or equal to a predetermined threshold S depending on this difference in level AVK and on the corresponding current level IK in the cathode.

More precisely, the value R is greater than or equal to the ratio AVK / IK.

The value of the inductive circuit L depends directly on the value of the resistive circuit R and on the predetermined maximum duration of the pulses of the tube At. More precisely, the value L is taken equal to R.At.

Such a resistive inductive circuit allows, during impulse current calls from the tube, to deliver to the output terminal
BS, and therefore at the cathode K of the tube, an output voltage of a substantially constant level.

The level of the output voltage results from the compensation of two phenomena, namely a linear voltage drop from the source SO and an exponential charge of reverse slope in the resistive inductive circuit.

However, those skilled in the art will understand that the compensation of a linear phenomenon and an exponential phenomenon does not in principle make it possible to obtain a perfectly constant output voltage level.

Also, a solution to improve the level of constancy would then consist in increasing the time constant of the circuit
LR. However, increasing it would lead to a loss of efficiency, an increase in resistance R, and therefore an increase in the power dissipated in the regulation means.

The Applicant then observed that it was preferable to have an additional resistive / capacitive circuit at the terminals of the resistor R and of the inductor L. This additional circuit thus comprises an additional resistor RA arranged in series with an additional capacitor CA. The characteristics of this additional resistance and this additional capacitance are chosen as a function of those of the inductive L and resistive R circuits as well as the maximum duration of the pulses At.

More specifically, it was observed that it was preferable to take a time constant RA.CA of the additional circuit directly proportional to the duration of the pulses, for example of the order of 0.7At.

Tests have been carried out with an inductance L of 320 micro
Henry, a resistor R of 150 ohms, an additional resistor
RA of 155 ohms and an additional AC capacity of 22 nanofarads.

The cathode voltage VK chosen for the emission of the pulses is here -10,800 volts, taking into account the characteristics of the tube. The duration of the pulses is here of the order of 6 microseconds with a form factor of 2%. The voltage drop caused during current calls is of the order of 75 volts.

Also, the level of the low or zero current input voltage which could have been taken in theory equal to -10,875 volts has been taken here equal to -10,900 volts.

The operation of the device is illustrated in Figures 2A to 2C.

During the current call IK (here equal to 1.5 A) from the tube (Figure 2A), the voltage VBE1 (Figure 2B) decreases linearly from 10900 volts to approximately -10800 volts.

At the start of the current draw, the voltage at the cathode (VK) (Figure 2c) drops very quickly to around -10,800 volts, the current passing almost exclusively through resistance R.

At the same time, the inductance L is charged and, as the pulse progresses, the current passing through the inductance L becomes more and more important, consequently reducing the current in the resistance R and minimizing the fall Of voltage. As a result, the voltage level of the cathode
VK remains practically constant at a level of the order of -10,800 volts, to within +1 volt.

The RA CA network is traversed by an exponentially decreasing current opposite to the exponentially increasing current flowing in the inductor L. The respective potentials at the terminals of these two networks deliver laws which compensate each other.

After the pulse, the level VBE1 of the input voltage gradually reaches the nominal level of -10900 volts while the inductor L discharges. For this purpose, it is preferable to choose a discharge time constant of this inductance at most equal to one fifth of the pulse recurrence period, which then limits the form factor of the tube to around 20%.

In addition to the means already described, a protection resistor RP is provided, limiting the current in the event of a short short-circuit possibly initiating in the traveling wave tube. The value of this resistance depends on the characteristics of this tube.

Of course, the value of this resistance RP must also be taken into account when determining the input voltage VBE1. For example, for a resistance of 50 ohms leading to a voltage drop of 75 volts under 1.5 Amps, the level of the input voltage should be further increased by the value of 75 volts. So the actual evolution of the tension
VK is not modified compared to that illustrated in FIG. 2C, but it is offset by -75 volts.

In addition, it is planned to place at the terminals of the inductance
L the overvoltage protection means of the regulation means. These protective means are for example a varistor
ZnO zinc oxide VR limiting the voltage to a value of 400 volts.

FIG. 3 illustrates another embodiment of the regulation means. In this figure, the elements analogous or having functions analogous to those of FIG. 1 have references assigned a suffix v with respect to those they had in this figure 1. Only the differences between these two figures will be described below. -after.

The Applicants have observed that the constant level of the output voltage can also be obtained by an inductive circuit
Lv whose inductive value decreases appreciably linearly according to the current which crosses it. In other words, the law L (i) is substantially of the form A-Bi.

In practice, this variable inductance is obtained from at least two saturable inductors, at different saturation thresholds.

In this embodiment, the level of the input voltage at low or zero current is greater than the nominal level chosen for the cathode voltage, by a level difference substantially equal to the voltage drop in the source caused during the current draw of the tube, also taking into account the residual voltage across the saturated inductive circuit. Indeed, when the magnetic core is saturated, there remains at the terminals of the inductance a residual voltage corresponding to the residual inductance of this inductance in air.

In other words, the level of the input voltage VBE1 must be increased by the voltage drop caused in the tube during current calls as well as by this residual voltage.

In the example described here, the inductive circuit L-V comprises four inductors L1-v, L2-v, L3-v and L4-v connected in series, it being noted that at least some of these inductors could also be connected in parallel.

The respective values of these inductors L1-v, L2-v, L3-v and
L4-v are equal to 1.2 millihenry. The value of the resistance Rv is taken equal to 90 ohms. The residual voltage of the inductive circuit is here of the order of ten percent compared to the voltage drop of 75 volts caused by the current draw from the tube. Also, the level of the input voltage at low or zero current is still taken here equal to -10,900 volts.

The inductive value of the inductive circuit L follows the evolution represented in FIG. 3A and can be approximated to a law of the form L = 5-0.74I where L is expressed in millihenry and I in
Ampere.

The voltage VK (FIG. 3B) is then substantially constant to a value of the order of -10,800 volts to within +/- 2 volts.

Such an embodiment avoids the use of an additional resistive capacitive compensation circuit. It also makes it possible to achieve form factors of the order of 30%.

Of course, the characteristics of the regulation means in the two embodiments described above take into account the inherent impedance of the traveling wave tube which can be compared to a pure resistance of the order of 8000 ohms.

The invention also applies to the supply of magnetrons which have a structure different from that of traveling wave tubes. Thus, as illustrated in FIG. 4, the regulation means MR are inserted between the supply terminal BE1 of the source SO and the cathode K of the magnetron while the anode of the latter is connected to the second terminal BE2 from this power source.

One advantage of the device according to the invention lies in its great simplicity, its efficiency, its low yield and its very low cost. It is also very robust because of the passive nature of the constituent components.

The invention is not limited to the embodiment described above but embraces all the variants contained within the scope of the claims below.

Of course, some of the means described above can be omitted in the variants where they are not used.

Claims (10)

Claims. 1. Regulated supply device, characterized in that it comprises regulation means (MR), comprising an inductive circuit (L) and a resistive circuit (R) connected in parallel, connected between an input (BE1) intended for be connected to a substantially continuous high voltage source (SO), and an output (BS) suitable for supplying voltage to the cathode (K) of a microwave tube (TOP) capable of emission by pulses by generating current calls corresponding pulses, and in that the level of the input voltage at low or zero current and the characteristics of the regulation means are adapted, taking into account the temporal characteristics of the pulses, to deliver, in the presence of said current calls, a voltage regulated output level substantially constant and equal to a nominal level chosen according to the characteristics of the tube and authorizing the emission of said pulses. 2. Device according to claim 1, characterized in that the microwave tube is a traveling wave tube (TOP), comprising at least one collector, and in that the high voltage source comprises a first supply terminal (BE1) connected at said input for supplying the cathode (K) of the tube via said output (BS) and regulating means (MR) mounted floating between the input and the output, a second supply terminal ( BE2) connected to the propeller (H) of the tube, and one (or more) terminal (s) of polarization-collector (BE3, BE4), located (s) between the first and second supply terminals and connected (s) respectively to (x) collector (s) (CO1, C02) of the tube. 3. Device according to claim 1, characterized in that the microwave tube is a magnetron (MGN), and in that the high voltage source (SO) has two supply terminals (BE1, BE2), a first terminal power supply (BE1) being connected to said input for supplying the cathode (K) of the magnetron via said output and regulating means mounted floating between the input and the output, while a second terminal d power (BE2) is connected to the anode (A) of the magnetron. 4. Device according to one of the preceding claims, characterized in that the level of the input voltage at low or zero current is greater than said nominal level chosen by a level deviation at least substantially equal to the voltage drop in the source caused when the tube draws current, while the value of the resistive circuit is greater than a predetermined threshold depending on this level difference and the corresponding current level in the cathode, and that the value of the inductive circuit depends directly from the value of the resistive circuit and the duration of the pulses. 5. Device according to one of the preceding claims, characterized in that the regulation means (MR) further comprise an additional resistive circuit (RA) capacitive (CA) connected to the terminals of the inductive (L) and resistive (R) circuits. , the characteristics of which are chosen as a function of those of the inductive and resistive circuits and of the duration of the pulses. 6. Device according to claim 5, characterized in that the time constant of the additional circuit is directly proportional to the duration of the pulses. 7. Device according to one of claims 1 to 3, characterized in that the inductive value of the inductive circuit decreases substantially linearly as a function of the current flowing through it. 8. Device according to claim 7, characterized in that the inductive circuit comprises at least two saturable inductors (L1-v, L2-v, L3-v, L4-v) at different saturation thresholds. 9. Device according to claim 7 or 8, characterized in that the level of the input voltage at low or zero current is greater than said nominal level chosen by a level deviation at least substantially equal to the voltage drop in the source caused when the tube draws current, taking into account the voltage residual across the saturated inductive circuit. 10. Device according to one of the preceding claims, characterized in that it further comprises over-voltage protection means (VR) of the regulation means.