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Detection of the supply state of a load supplied by a variable voltage

a technology of variable voltage and supply state, applied in the direction of electric variable regulation, ac network voltage adjustment, instruments, etc., can solve the problems of measurement circuit, inability to have a perfect stability, and limited detection time window

Inactive Publication Date: 2006-03-02
STMICROELECTRONICS SRL
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Benefits of technology

[0033] The present invention also aims at providing a s

Problems solved by technology

A problem of conventional circuits for supervising the state of a load and of its switches is linked to the tolerances of the different components and mainly to the possible variations of the voltage reference of converter 5 which is provided by voltage Vdc, likely not to have a perfect stability.
If voltage Van is constantly between thresholds THH and Vdc or smaller than threshold THL, this indicates a defect of the measurement circuit.
Indeed, the A.C. shape of the measured signal Van and the possible variation ranges of these shapes result in that, in practice, a possible detection time window is limited to each halfwave in the vicinity of the maximum of this halfwave.
A disadvantage is that there are significant risks of false detection in case of a loss of synchronism of the measurement or in case of a distortion of voltage Vac (wrong shape factor).
Another disadvantage is that the possibility of performing a single measurement per half period slows down the detection.
Another disadvantage is that a circuit of supervision of the load state is not transposable without modifications to a mains voltage of different frequency or amplitude.

Method used

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  • Detection of the supply state of a load supplied by a variable voltage
  • Detection of the supply state of a load supplied by a variable voltage
  • Detection of the supply state of a load supplied by a variable voltage

Examples

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first embodiment

[0064] not shown, resistor R1 between terminals 3 and 2, and a resistor RIN connected to an input terminal IN of a measurement circuit 20 can be found.

[0065] According to a second shown embodiment, resistor R1 is placed in parallel only with the load and resistor RIN connects load 3 to input terminal IN of measurement circuit 20. The difference on the detected states will be discussed in relation with FIG. 6.

[0066] Resistor R1 corresponds to the resistor which, for the application of the present invention, conditions the relatively low impedance of the load. In fact, load Q must have, in normal operation, an impedance smaller than resistor R1.

[0067] Unlike the conventional case, resistors R1 and RIN are different from each other. Resistor R1 preferably is of high value with respect to resistor RIN. Further, resistor RIN preferably is of same value as resistor RREF, which connects terminal 2 to a reference input REF of circuit 20.

[0068] In the example of FIG. 5, the difference ca...

second embodiment

[0083] According to the present invention which will be described hereafter in relation with FIG. 7, voltage RVout is compared in parallel with the different thresholds to directly provide digital information about the operating state of the system.

[0084] In FIG. 7, voltage RVout is applied to an average value calculation circuit 30 for the case of a periodic voltage Vac. In fact, the average value of absolute value RVout of the difference between the voltage across the load and the supply voltage is considered, voltage RVout being provided, for example, by the circuit of FIG. 5. For example, averager 30 is formed of an RC cell having its time constant selected to approximately correspond to the period of voltage Vac. The output of circuit 30 is sent to first respective inputs of four comparators 31, 32, 33, and 34 having their respective second inputs receiving reference levels MMED, MREFIH, MREFH, and MTHH determined according to thresholds MED, REFIH, REFH, and THH. To simplify t...

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Abstract

A method and a circuit for detecting the state of supply of a load by a variable voltage, including measuring the difference between values representative of the variable supply voltage and of a voltage across the load.

Description

BACKGROUND OF THE INVENTION [0001] 1. Field of the Invention [0002] The present invention generally relates to the detection of the supply state of a load supplied by a variable voltage (A.C. or unipolar) and more specifically the supervision of the state of this load and of one or several switches controlling it. [0003] The present invention more specifically applies to the detection of possible failures of the load or of switches in series with this load. [0004] 2. Discussion of the Related Art [0005]FIG. 1 shows a conventional example of an assembly of supervision of the state of a load Q supplied by an A.C. voltage Vac under control of two switches T and SW. This example relates to the control of the motor (load Q) of a washing machine under the action of a first switch formed of a triac T receiving a control signal CT from a programmer (not shown). A second switch SW symbolizes a door-opening detection contact of the machine to interrupt the motor supply in case of an opening (...

Claims

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Application Information

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IPC IPC(8): G05F1/10H02J3/12G01R19/165H02J13/00
CPCG01R19/10H02P4/00G01R31/343G01R19/16538
Inventor MOINDRON, LAURENT
Owner STMICROELECTRONICS SRL