EP0165640B1 - Device for the galvanic insulation between a pulse generator and a load - Google Patents

Description

The present invention relates to a device for carrying out galvanic isolation between a pulse generator and a load, comprising a primary circuit and a secondary circuit coupled by mutual inductance, at least one circuit for eliminating the magnetizing current connected to the secondary circuit and a unidirectional transmission circuit connected to the primary circuit.

A device of this type is known from the German document DE-B-1 236 566 filed by PHILIPS on February 9, 1965 and gives complete satisfaction when the pulse generator has a high impedance cyclically, in particular, like that presented at the output of a transistor in switching regime. When the generator transmits a series of pulses of the same sign (for example positive), the magnetizing current tends to increase by a phenomenon of accumulation in time, if one does not manage to flow it quickly enough. The characteristics of the transformer then deteriorate as the magnetizing current increases, the material of the core goes into saturation and the transformer no longer transmits the pulses. By connecting a magnetization current elimination circuit to the transformer secondary and in parallel with the load, the drawbacks due to saturation are avoided.

However, if the pulse generator continuously has a low impedance as is the case for example for an operational amplifier, another fault appears. The transformer primary then chooses the shortest and least resistance path to flow the magnetizing current, which then returns to the generator, thus causing disturbances or even destruction. This second type of drawback can be avoided by using a unidirectional transmission circuit, such as that proposed in GB-A-836 027, which has a very low impedance in one direction for passing the pulses and a very high impedance in the Another way to avoid the return of demagnetization currents.

However, these types of devices are not intended to be connected to a generator delivering bipolar signals, signals commonly used.

The invention provides a device combining the advantages of these known devices and which can be directly connected to the output of a generator supplying bipolar signals.

For this, the device for carrying out the galvanic isolation between a pulse generator and a load of the type mentioned in the preamble is remarkable in that to be directly connected to a generator supplying pulses of bipolar type, on the one hand the primary circuit consists of two windings each admitting a polarity of the pulses, said pulses being switched by means of unidirectional transmission circuits each consisting of a diode connected in series with the primary circuit to allow the pulses to pass and force in cooperation with circuits elimination of the magnetizing current the magnetizing currents to flow quickly and only through the secondary circuit while for each of the polarities is also provided a circuit for attenuation of the transient phenomena due to the switching consisting of a zener diode connected in series with corresponding unidirectional transmission circuit to clip parasitic voltage fluctuations, and on the other hand the secondary circuit has two windings to transmit each, according to the polarity of the pulses, said pulses to the load.

Thus the diode of each unidirectional transmission circuit allows the pulses to pass to the primary circuit and has a high impedance for the magnetizing current wishing to return to the generator having a continuously low impedance, it thus masks the low impedance of the latter. In addition, the pulse generator is subjected to frequent transitions during the transmission of a message (message coded in “return to zero” RZ, for example), with each transition are generated fluctuations or parasitic noises called phenomena transient. The zener diode therefore clips these parasitic noises, advantageously attenuates the transient phenomena due to switching and immunizes the transmission of the signals.

• La figure 1 montre un dispositif complet combinant les dispositifs connus pour un générateur fournissant des impulsions unipolaires.
• La figure 2 présente un dispositif conforme à l'invention, pour un générateur fournissant des impulsions bipolaires.
• La figure 3 représente l'allure de quelques signaux dans le dispositif montré à la figure 2.

The following description with reference to the accompanying drawings, given by way of example, will make it clear how the invention can be implemented.

• Figure 1 shows a complete device combining the known devices for a generator providing unipolar pulses.
• FIG. 2 shows a device according to the invention, for a generator supplying bipolar pulses.
• FIG. 3 represents the appearance of a few signals in the device shown in FIG. 2.

In FIG. 1, the device consists of a transformer 1 formed of a primary circuit 2 comprising a single winding 3 and of a secondary circuit 4 also comprising a single winding 5, the primary circuit 2 and the secondary circuit 4 being coupled by mutual induction M. The winding 5 of the secondary circuit 4 and the winding 3 of the primary circuit 2 are wound so that the pulses returning with a determined polarity (positive for example) on the winding 3, come out with the same polarity of the winding 5. The transformer 1 performs galvanic isolation and transmits the signal from the generator E, connected to the input between terminals 6 and 7, supplying pulses of positive polarity, to the load CH connected between the points 8 and 9. At terminals 10 and 11 of secondary circuit 4 is connected a series circuit 12, known as the magnetizing current elimination circuit, composed of a diode 13 and a resistor 14. One side of the resistor 14 is connected on the one hand to the terminal 11 of the circuit secondary 4 and secondly at point 9, thus connecting it to one side of the load CH. The other side of the resistor 14 is connected to the anode of the diode 13. The cathode of the diode 13 is connected on the one hand to the terminal 10 of the secondary circuit 4 and on the other hand to the point 8, thus connected to the other side of the CH load. The diode 13 conducts the magnetizing current which therefore flows in the resistor 14, this if the pulse generator E has during this time a high impedance. Connected between the pulse generator E and the primary circuit 2, a unidirectional transmission circuit 15 allows the pulses to pass and force in cooperation with the magnetizing current elimination circuit 12, said magnetizing current to flow quickly and only by the secondary circuit 4. The unidirectional transmission circuit 15 preferably consists of a diode 16, connected in series with the primary circuit 2 of the transformer 1. The cathode of the diode 16 is connected to the primary circuit 2 at terminal 17.

Upstream of the unidirectional transmission circuit 15 and in series with it, there is a circuit for attenuation of the transient phenomena due to switching 18, which preferably consists of a zener diode 19. The anode of the diode zener 19 is connected to the anode of the diode 16. The cathode of the zener diode 19 is connected to the input terminal 6 and thus connected at a point of the pulse generator E. The terminal 20 of the primary circuit 2 is directly connected to the second input terminal 7, itself connected to the pulse generator E at its second point.

The diode 16 allows the pulses of positive polarity to pass and prevents the return of the magnetizing current since it has a high impedance in reverse, it thus forces the magnetizing current to flow through the secondary circuit 4 in the current elimination circuit. magnetizer 12, specially provided for this purpose.

On the other hand, the pulse generator E is subjected to frequent transitions and therefore is disturbed by transient phenomena due to switching. The role of the zener diode 19 is to advantageously attenuate the influence of the transient phenomena due to the switching, it clips the parasitic fluctuations and immunizes the transmission of the signals.

FIG. 2 shows a device according to the invention, for which the pulse generator E supplies pulses of bipolar type, such as those proposed in FIG. 3a.

The primary circuit 2 here comprises two windings 3 'and 3 "each admitting a polarity of the pulses, similarly the secondary circuit 4 comprises two windings 5' and 5" transmitting the pulses to a load CH. The winding 5 'of the secondary circuit 4 and the winding 3' of the primary circuit 2 are wound so that the pulses returning with a determined polarity (positive for example) on the winding 3 ', come out with the same polarity of winding 5 '. On the contrary, the winding 5 "of the secondary circuit 4 and the winding 3" of the primary circuit 2 are wound so that the pulses returning with a determined polarity (negative for example) on the winding 3 ", come out of the 5 "winding with opposite polarity (positive).

The pulses of positive polarity are routed through the unidirectional transmission circuit 15 'and transmitted to the winding 3' of the primary circuit 2. The pulses of negative polarity are routed through the unidirectional transmission circuit 15 "to the 3 "winding of the primary circuit 2. The circuits for attenuating transient phenomena due to switching 18 'and 18" are connected in series, respectively with the unidirectional transmission circuits 15' and 15 ".

The unidirectional transmission and attenuation circuits for transient phenomena due to switching are each adapted to the polarities of the pulses.

The operation of the device shown is based on that described for the device of FIG. 1, except that in the unidirectional transmission circuit 15 "and the circuit for attenuation of the transient switching phenomena 18", the diode 16 "and the zener diode 19 "are connected in reverse relative to the connections of the diode 16 and the zener diode 19, this in order to direct and to let pass only the pulses of negative polarity.

The diode 16 'placed in series with the winding 3' of the primary circuit 2 allows only the pulses of positive polarity to pass while the diode 16 "placed in series with the winding 3" of the primary circuit 2 allows only the pulses of negative polarity. The diodes 16 'and 16 "prevent the magnetizing current from returning to the pulse generator E.

The zener diode 19 'is connected in series with the diode 16' while the zener diode 19 "is connected in series with the diode 16". The zener diodes 19 'and 19 "protect the pulse generator E by clipping parasitic fluctuations, thus attenuating the transient phenomena due to switching.

The diodes 16 'and 19' are connected in the same way as the diodes 16 and 19 of the device of FIG. 1, since they all receive pulses of positive polarity.

The cathodes of the 16 "and 19" diodes are interconnected. The anode of diode 16 "is connected to point 17" of the primary circuit 2. The anode of diode 19 "is connected to the input at terminal 6, connected at one point to pulse generator E. The primary circuit 2 is connected by its terminal 20 "to the second point of the pulse generator E via terminal 7.

The 12 'and 12 "circuits for eliminating the magnetizing current are in total identity with the circuit 12 of Figure 1 as to the operation and arrangement of the elements.

At points 8 'and 9' on the one hand, a load CH 'is connected, the voltage V ₊ is the voltage across the terminals of this load, at points 8 "and 9" on the other hand, an equivalent load CH "is connected, the voltage V_ is the voltage at the terminals of this second load. The voltage V ₊ is applied to the inverting input of a voltage comparator circuit 21 ′, it is compared to a reference voltage REF, which is a fraction of the value of the amplitude of the input voltage, thus the transitions of V ₊ are detected. At the output of the voltage comparator 21 ′ is the output voltage V _{s +} (see FIG. 3b). The voltage V_ is applied to l inverting input of a second voltage comparator circuit 21 ", it is also compared to the reference voltage REF, in order to detect the transitions of V_. At the output of the voltage comparator 21" the output voltage V _s _ ( see figure 3c).

Obtaining these two voltages V _{s +} and V _s _ advantageously makes it possible on the one hand to reconstruct the starting clock using a NAND logic circuit 22, the two inputs of which receive V _{s +} and V _{s― respectively} , and on the other hand to transform the coded message into "return to zero" RZ into a coded message into "non return to zero" NRZ, by means of a flip-flop 23, of the RS flip-flop type for example, obtained from two NAND logic circuits. The reconstituted clock HR and the transformed message IR, are reproduced respectively in FIGS. 3d and 3e.

Such a device is of great interest as to its use in receiving data, it gives the possibility of strictly complying with the ARINC 429-2 standard.

Claims (1)

1. An arrangement for providing the d. c. insulation between a pulse generator (E) and a load (CH', CH") comprising a primary circuit (2) and a secondary circuit (4) coupled to each other by mutual inductance, at least one circuit (12) for eliminating the magnetizing current connected to the secondary circuit and a unidirectional transmission circuit (15) connected to the primary circuit, characterized in that, in order to be directly connected to a generator supplying pulses of the bipolar type, on the one hand the primary circuit is constituted by two windings (3', 3") each admitting one polarity of the pulses, the said pulses being routed by means of the unidirectional transmission circuits (15', 15") each constituted by a diode (16', 16") connected in series with the primary circuit (2) to cause the pulses to pass and to force in cooperation with circuits (12', 12") for eliminating the magnetizing current the magnetizing currents to flow rapidly and solely through the secondary circuit (4), while moreover there is provided for each of the polarities a circuit for attenuating the transient phenomena due to the commutation (18', 18") constituted by a Zener diode (19', 19") connected in series with the corresponding unidirectional transmission circuit to smooth the parasitic voltage fluctuations, and on the other hand the secondary circuit (4) comprises two windings (5', 5") each for transmitting, in accordance with the polarity of the pulses, the said pulses to the load (CH', CH").

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