Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
  • G01R1/00—Details of instruments or arrangements of the types included in groups G01R5/00 - G01R13/00 and G01R31/00
  • G01R1/36—Overload-protection arrangements or circuits for electric measuring instruments
• • G—PHYSICS
  • G08—SIGNALLING
  • G08C—TRANSMISSION SYSTEMS FOR MEASURED VALUES, CONTROL OR SIMILAR SIGNALS
  • G08C15/00—Arrangements characterised by the use of multiplexing for the transmission of a plurality of signals over a common path

Definitions

• the present invention relates to analog measurement gates 5 protected against very high voltages.
• analog doors allowing either the copying at their output of a given input voltage, or the isolation of the output with respect to this input, according to the polarity of a command. K.
• These analog gates can select one input from among several and are then called analog multiplexers.
• Most of the analog doors currently available have a fairly reduced dynamic input voltage, beyond which there is a risk of destruction of the door. It is then very often necessary to protect their inputs with a clipping network capable of limiting the input signal to acceptable levels. This is the case, for example, with the measurement of the working voltage of high-voltage semiconductor switches, these switches being able to generate considerable breaking voltages.
• the number, the cost and the surface occupied by all of the elements of the doors and of their protection networks can be considered excessive in certain applications, especially if the reliability of the system is penalized.
• FIG. 1 represents an analog multiplexer with N inputs r 35 produced according to the invention, protected against substantially positive input overvoltages.
• FIG. 2 shows a variant of the multiplexer according to the invention protected against essentially negative input overvoltages.
• FIG 1 the various elements of an analog multiplexer according to the invention, capable of accepting bipolar input signals but particularly protected against high positive input overvoltages.
• the outputs of the N modules are combined at a common point A which is connected to the output Vs, in a first variant of the invention, by a section of zero resistance in which a negative current generator 8 circulates a current equal to the half of a reference current 1 (a negative current generator must be understood as a constant current source flowing towards a point with more negative potential than the point of application, whereas a positive current generator provides its constant current from a more positive potential than the point of application).
• Each gate 20-N contains a positive current generator 1 supplying a current of value 1 to an application point B. From this point leave at least three branches, the first branch leading to a negative or zero potential 9 through a switch 2, the second and third branches leading to the input VN and to point A respectively, through the rectifiers 4 and 3 and the resistors 5 and 7 respectively.
• the first branch isolates door 20-N, by closing switch 2 with a KN command. All the current I is then short-circuited to the potential 9 and cannot flow in the two other branches; the rectifier 3 being found in reverse, the door is therefore isolated. It will be noted that the assembly makes it possible to isolate input signals more negative than the potential 9, but that the input current is then limited only by the resistor 5.
• the door is in copy mode when switch 2 is open.
• the current generator 8 imposing a current 1/2 in the third branch, the current of the second branch becomes approximately equal to it, with the precision close to the ratio of the currents of the generators 1 and 8. Therefore the voltage drops in these two branches make up for feels exactly, because the values of the components of these branches are identical. Better still, the variations in temperature of the threshold of the rectifier 4 can be exactly compensated by that of the rectifier 3. The point A therefore "copies" the voltage VN of the input which has been selected.
• the mounting supports without serious consequence that several inputs are selected simultaneously. In this case, it is the most positive voltage which appears at the outlet, the other inputs being naturally isolated by the rectifier 3 reverse biased.
• the assembly can withstand large po ⁇ sitive input overvoltages, which will be isolated by the rectifier 4. This will, if necessary, be carried out with several diodes in series, so as to increase its breakdown voltage breakdown .
• Resistor 5 is mainly used to limit the instantaneous current passing through this rectifier when it is in reverse recovery phase. It may be necessary to reinforce this protection by connecting at point B a clipping diode 6 to a positive potential 10 which will limit the voltage at this point to acceptable values. If on the contrary the re ⁇ blocker 4 is particularly fast, the resistors 5 and 7 may be replaced by short-circuits. There are many known ways of making current generators 1 and 8, which will not be detailed here. In a less modular approach, the operation of the assembly remains unchanged by replacing the ⁇ resistors 7 by a single resistor of the same value located between point A and Vs, which represents an advantageous gain in components.
• the invention is particularly applicable to circuits for measuring voltages having to accept high input overvoltages, for example for controlling the voltage in the on state of power semiconductor switches.

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Emergency Protection Circuit Devices (AREA)
• Protection Of Static Devices (AREA)

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Citations (3)

• 1992
  • 1992-01-23 FR FR9200715A patent/FR2686700A1/fr active Granted
• 1993
  • 1993-01-18 AU AU35027/93A patent/AU3502793A/en not_active Abandoned
  • 1993-01-18 WO PCT/FR1993/000044 patent/WO1993015540A1/fr active Application Filing

Patent Citations (3)

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