EP0567877A1 - Schaltung zur Zustandsmeldung eines elektrischen Schalters zum Beispiel zur Fehlermeldung des schliessen einer Fahrzeugtür - Google Patents

Schaltung zur Zustandsmeldung eines elektrischen Schalters zum Beispiel zur Fehlermeldung des schliessen einer Fahrzeugtür Download PDF

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Publication number
EP0567877A1
EP0567877A1 EP93106288A EP93106288A EP0567877A1 EP 0567877 A1 EP0567877 A1 EP 0567877A1 EP 93106288 A EP93106288 A EP 93106288A EP 93106288 A EP93106288 A EP 93106288A EP 0567877 A1 EP0567877 A1 EP 0567877A1
Authority
EP
European Patent Office
Prior art keywords
transistor
fact
circuit according
switch
electrical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP93106288A
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English (en)
French (fr)
Inventor
Vittorio Di Nunzio
Gianni Sterza
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fiat Auto SpA
Original Assignee
Fiat Auto SpA
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Fiat Auto SpA filed Critical Fiat Auto SpA
Publication of EP0567877A1 publication Critical patent/EP0567877A1/de
Withdrawn legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B23/00—Alarms responsive to unspecified undesired or abnormal conditions

Definitions

  • the present invention relates in general to devices for signalling the state of an electric switch, for example, for optical signalling of the functioning state (open/closed) of the switch.
  • the invention can be used, for example, for signalling by indicator lights, on board a vehicle of the open or closure state of electrical switches disposed at various points around the vehicle for the purpose of providing information useful to the driver.
  • indicators visible and audible
  • said signals are provided by small incandescent lamps which provide back lighting to specific areas of the instrument on which specific symbols are reproduced (for example by printing). Some times such indicators are also fitted to control panels and other controls.
  • Some light signalling functions are implemented directly by switches which operate in series with the associated indicator lamps. This is the case with the indication of some liquid level indicators, and also with indicators for the state of opening of the doors, boot lid or the like.
  • the necessary signals are provided by electrical switches mounted on the door jambs or within the locks and are actuated mechanically upon opening or closure of the door. Similar applications arise for indicating if a liquid level is low, for example, to indicate the level of the engine coolant liquid.
  • the switch is constituted by a reed relay which detects the position of a float carrying a magnet, by means of which the relay contact is actuated when the level falls below a predetermined value.
  • the switch I when in the closure state, closes the circuit between the battery voltage Vb and the earth M thereby activating the LED D.
  • the LED forms part of an on-board instrument and must be illuminated only when the switch I is closed, it can happen that the LED is illuminated more or less weakly because of moisture, dust or whatever else causing a current leakage through the switch I (resistance Rp very low).
  • the switch I acts via a decoupling diode D1 the presence of which has no relevance on what is discussed here, on a network of three resistors R1, R2 and R3 which set the biasing of the base of the transistor T.
  • the transistor T acts specifically as a current amplifier which allows a transition between light and dark of the LED for a very much narrower range of leakage resistance Rp than the circuit of Figure 1.
  • the curve which represents the current through the diode D as a function of the leakage resistance Rp has a hyperbolic shape.
  • the curve of the current intercepts this value at rather higher values of Rp, in the region of several KOhms.
  • the curve of the current as a function of resistance Rp has a pronounced commutation knee; the current curve intercepts the threshold value for resistance values Rp very much lower than in the case of the circuit of Figure 1.
  • a further inprovement could be obtained by inserting in the Figure 2 circuit a zener diode (for example, with a threshold voltage of 4.7 volts) in series with a resistor R2, without however, achieving the desired objective.
  • a zener diode for example, with a threshold voltage of 4.7 volts
  • the present invention is based on the principle of associating with the electrical warning element D sensing means Dz,Q,R4 for detecting the state of the electrical switch I connected to the indicator element D in current subtraction relationship so that when the switch I is in a first operating state the sensing means Dz,Q,R4 drain current from the indicator D which is therefore disactivated, and when the switch I is in a second operating state, the sensing means Dz,Q,R4 allow a certain passage of current through the indicator element D which is thus activated.
  • the LED diode D has the cathode connected to the emitter of an NPN transistor Q and the anode connected to the collector of the transistor Q.
  • the emitter of the transistor Q is in turn connected to earth M whilst the collector is connected via the resistor R to the battery voltage Vb, which is understood to be positive.
  • the base of the transistor Q is connected to the anode of a Zener diode Dz.
  • the cathode of the zener diode Dz is connected, via resistor R4, to the battery voltage Vb and is further connected to the anode of the diode D1.
  • the cathode of the diode D1 is connected to one of the terminals of the switch I, the other terminal of the switch I being connected to earth.
  • the values of the resistors R and R4 can, for example, be equal to 820 Ohms and 1KOhm respectively.
  • the switch I When the switch I is closed the resistance across its terminals is practically zero so that the cathode of the zener diode Dz is at a voltage close to the ground voltage.
  • the diode Dz is therefore switched off preventing the passage of current to the base of the transistor Q, which is therefore switched off permitting all the current to pass to the diode D which in this way is activated.
  • the diagram of Figure 4 illustrates, with reference to the circuit of Figure 3, the variation of the current through the diode D (along the ordinate) as a function of the resistance Rp of the switch I (along the abscissa).
  • This in particular relates to the possibility of replacing the bipolar transistor Q described with reference to Figure 3, with a component (for example, a field effect transistor FET) capable of performing a selective current subtraction operation with respect to the indicator element (LED D in the illustrated example).
  • a component for example, a field effect transistor FET capable of performing a selective current subtraction operation with respect to the indicator element (LED D in the illustrated example).

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  • Business, Economics & Management (AREA)
  • Emergency Management (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Dc Digital Transmission (AREA)
  • Audible And Visible Signals (AREA)
EP93106288A 1992-04-27 1993-04-19 Schaltung zur Zustandsmeldung eines elektrischen Schalters zum Beispiel zur Fehlermeldung des schliessen einer Fahrzeugtür Withdrawn EP0567877A1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
ITTO920361A IT1259558B (it) 1992-04-27 1992-04-27 Circuito per segnalare lo stato di un interruttore elettrico, ad esempio per segnalare la mancata chiusura della portiera di un veicolo
ITTO920361 1992-04-27

Publications (1)

Publication Number Publication Date
EP0567877A1 true EP0567877A1 (de) 1993-11-03

Family

ID=11410423

Family Applications (1)

Application Number Title Priority Date Filing Date
EP93106288A Withdrawn EP0567877A1 (de) 1992-04-27 1993-04-19 Schaltung zur Zustandsmeldung eines elektrischen Schalters zum Beispiel zur Fehlermeldung des schliessen einer Fahrzeugtür

Country Status (2)

Country Link
EP (1) EP0567877A1 (de)
IT (1) IT1259558B (de)

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4017847A (en) * 1975-11-14 1977-04-12 Bell Telephone Laboratories, Incorporated Luminous indicator with zero standby power
EP0271267A2 (de) * 1986-12-10 1988-06-15 U.S. Capacitors Inc. Piezo-elektrische Meldevorrichtung

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4017847A (en) * 1975-11-14 1977-04-12 Bell Telephone Laboratories, Incorporated Luminous indicator with zero standby power
EP0271267A2 (de) * 1986-12-10 1988-06-15 U.S. Capacitors Inc. Piezo-elektrische Meldevorrichtung

Also Published As

Publication number Publication date
IT1259558B (it) 1996-03-20
ITTO920361A1 (it) 1993-10-28
ITTO920361A0 (it) 1992-04-27

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