An auxiliary circuit in a circuitry comprising C-MOS integrated circuit components

Abstract

 Detection of failures in an electronic circuit (x), comprising one or more integrated-circuit components of the C-MOS type. For this detection-method an auxiliary circuit (Tr, Th) is provided, which is appropriate for monitoring the current-collection (I₁) by the circuit and generating a failure-signal, as soon as the monitored current-collection exceeds a pre-adjusted thresholdlevel.

Description

[0001] The invention relates to a circuit comprising one or more IC-components of the C-MOS type, means being provided to detect failures in the components of the circuit.

[0002] Such circuits are generally used in control-circuits of (control) processes of various nature. As an example, reference may be made to a control circuit for an electronic burner-ignition device.

[0003] The so-called double 'fail-safe'-principle may be used as a provision for detecting failures in the components of the circuit. This principle means that two identical circuits must be provided, connected in parallel, in which the outputs of the corresponding sections of the circuits are compared by a comparator and in which a signal, unequal to zero, is considered as a failure. One of the parallel connected circuits may be considered as the proper control-circuit, while the other performs the function of a comparing-circuit. A disadvantage of this principle is, that the failure-chance is doubled, while both circuits are to be adjusted precisely one with respect to the other. In addition, this detection principle involves substantial increase of the cost price in comparison with a single circuit.

[0004] The invention aims at overcoming the above-mentioned disadvantage and for this purpuse it makes use of the property, that the IC's of the C-MOS type, applied in the circuit, have a low and controlled current-collection and that a failure of such an IC is expressed in a significant increase of the current-collection.

[0005] The "fail safe"-circuit proposed by the invention is characterized by auxiliary circuit for detecting failures, which is adapted to monitor the current-collection by the circuit, and to generate a failure-signal, as soon as the monitored current-collection exceeds a pre-adjusted threshold- level.

[0006] The said auxiliary circuit may be realised in a simple and inexpensive way. In a practical embodiment, the auxiliary circuit includes a voltage- regulator, having its control-input connected to a thyristor, by which the voltage-regulator may be switched on and off respectively; a transistor with an adjustment-circuit, adapted to make the transistor issue a signal,as soon as the current-collection by the circuit exceeds a pre-adjusted threshold- level, resulting in the voltage-regulator and the power-supply of the circuit being switched off.

[0007] Prefarebly, the components of the auxiliary circuit are selected and connected in such a way, that in the event of a failure in one of the components of the auxiliary circuit, the power-supply of the circuit will be switched off in the same way, as described above with reference to the main circuit.

[0008] The invention will be hereinafter further described with reference to the drawing, in which a practical embodiment of the auxiliary circuit is shown.

[0009] The circuit shown in the drawing is supplied by a supply-voltage V₀, which in praxis may have a value between 15 and 24V. The voltage V₀ is transferred to a fixed voltage of 12V by the voltage-regulator IC₁ and the resistors R_I and R₄. The resistors R₁ and R₄ are selected in such a way, that there will be a voltage V₂ of 10,8V across the resistor R₁. Upon the supply-voltage V₀ being switched on, the capacitor C₃ will cause the volt_age V₁ to increase slowly to a value of 12V. The voltage V₁ is supplied to a 12V failure-relay, so as to energize the latter. The voltage V₁ is also connected to the positive supply-terminal of the circuit X, via resistor R₅. The circuit X comprises logic IC's of the C-MOS type. The negative supply-terminal of the circuit X is connected to the zero voltage of the power-supply. Under normal conditions, i.e. without failures in the components, the current-flow I₁ received by the circuit X will be very small. The voltage difference V_E-V_B between the emitter and base of the transistor Tr will than be much smaller than 1V, due to which the transistor Tr will be in its blockingstate. There will be no collectorcurrent I_C tlowing. The diode D₂ (in this example used as a zener of 0,7V) is applied to get a better adjustment of the voltage V_E and of the threshold-level, at which the transistor Tr begins to conduct. The gate-current I_G to the thyristor Th received from circuit X through the resistors R₂ and R₃ is below the threshold-level, at which the thyristor begins to conduct, sothat the thyristor Th is blocked.

[0010] As soon as a failure appears in the circuit X the current-flow I₁ will increase to a value far above 1000 A. The voltage-drop across resistor R₅ will increase to such an extent, that the base-voltage V_B of the transistor will become at least 0,6V below the emitter-voltage V_E, sothat the transistor Tr will get in the conduction-state. As a result of this a current I_C begins to flow, which controls the thyristor Th, via the current-divider achieved by the resistors R₃ and R₂. The current-divider R₃, R₂ ensures that the inputcurrent of the thyristor Th, which is applied via transistor Tr from the 12V power-supply, will not become too high. The gate-current I_G will now have a value above the threshold-level, at which the thyristor gets in the conduction-state; thus the thysristor Th begins to conduct. The capacitor C₁ ensures that the transistor Tr will put enough energy into the gate of Th, sothat the thyristor Th will get into conduction immediately and without oscillation-phenomena. The resistor R₁ is now short circuited by the thyristor Th, due to which the output-voltage V₁ of the voltageregulator decreases rapidly to 1,2V. The power-supply of the circuit X is thereby interrupted. The decrease of V causes the failure-relay (12V),fed by the voltage V₁, to drop, and this may control a secundairy circuit, indicating a failure in the circuit X, for example by means of a sound-or lightsignal.

[0011] The auxiliary circuit further comprises a zenerdiode D₁ of 15V and a capacitor C₂. The capacitor C₂ provides that the currentpulses caused by switching-actions in the circuit X will not cause the transistor Tr to come into conduction, sothat false control-signals to the thyristor Th are avoided. The zenerdiode D₁ contributes a protection against a too high value of the supply-voltage V₁. When the voltage V₁ becomes too high, the diode D₁ controls the thyristor Th, due to which the latter Th gets into conduction and the supply-voltage will be interrupted. Upon removal of the failure in the circuit X the thyristor may be reset into the blocking-state by depressing a reset-button, which will short circuit the thyristor, whereafter the voltage V_I may rise again to 12v, as soon as the reset-button is released.

[0012] It is an advantage of the above auxiliary circuit that in case of failures in the components of the auxiliary circuit itself(appearing as an interruption or short-circuiting), a similar effect will occur, as described above with reference to failures in the components of the circuit X. The supply-voltage of the circuit X will then also be interrupted.

[0013] It may be understood, that the auxiliary circuit according to the invention is applicable in circuits for various purposes and that the values of the components of the implementation shown are used for illustration only.

Claims

1.Circuit comprising one or more integrated-circuit components of the C-MOS type, characterized by an auxiliary circuit for the detection of failures, which is adapted to monitor the current-collection by the circuit and to generate a failure-signal, as soon as the monitored currant- collection exceeds a pre-adjusted threshold-level.

2. Circuit according to claim 1, characterized in that the auxiliary circuit includes a voltage-regulator, having its control-input connected to a thyristor, by which the voltage-regulator may be switched on and off respectively; a transistor with an adjustment-circuit, adapted to make the transistor issue a signal, as soon as the current-collection by the circuit exceeds a pre-adjusted threshold-level, resulting in tne voltage- regulator and the supply-voltage of the circuit being switched off.

3. Circuit according to claims I and 2, characterized in that the components of the auxiliary circuit are selected and connected in such a way, that, in the event of a failure in one of the components of the auxiliary circuit, the power-supply of the circuit will be switched off in the same way, as described above with reference to the circuit itself.

Drawing