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System for diagnosing impedances and having accurate current source and accurate voltage level-shift

A voltage level, current source technology, applied in the measurement of resistance/reactance/impedance, capacitance measurement, transportation and packaging, etc., can solve the problems of large circuit area, resistor occupation, etc., to reduce damage and improve safety. Effect

Inactive Publication Date: 2010-02-03
NXP BV
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

The first problem with such a circuit is that the voltage level drift across a resistor is not constant but relative to the voltage across the capacitor
However, in order to provide a resistor with a sufficiently high resistance, the resistor occupies a considerable circuit area

Method used

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  • System for diagnosing impedances and having accurate current source and accurate voltage level-shift
  • System for diagnosing impedances and having accurate current source and accurate voltage level-shift
  • System for diagnosing impedances and having accurate current source and accurate voltage level-shift

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Embodiment Construction

[0029] In the following description, various embodiments of the invention are explained in connection with capacitor measurements. All circuits can be extended to impedance measurements of other electronic components, as will be apparent to those of ordinary skill in the art.

[0030] In an airbag safety system, for example, a capacitor is used to store the energy required to ignite the airbag squib. In order to ensure the reliable operation of these safety systems, these capacitors are diagnosed. For example, use the circuit shown in Figure 1a to measure the capacitance of a capacitor. Taking the current I from the capacitor C causes the voltage to decrease with time, as shown in Figure 1b. By measuring the time interval Δt of a fixed voltage drop, or by measuring the voltage drop ΔV over a fixed time interval Δt, the capacitance can be determined as:

[0031] C=IΔt / ΔV (1)

[0032] Since capacitance is voltage dependent, it needs to be measured at operating voltage, which...

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PUM

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Abstract

The present invention relates to a system for measuring a capacitor (C). A current source (I2) is connected in parallel to the capacitor (C) between a supply plane (Vc) and ground (VGND) for providinga current to the capacitor (C). A voltage level-shift is connected between the supply plane(Vc)and the ground (VGND) in parallel to the capacitor (C) and in parallel to the current source (I2). The voltage level-shift device detects the voltage between two ends of the capacitor (C), provides the relative level-shifted output voltage Vout. The voltage level-shift device includes a resistor R1, theresistor R1 is connected with the current source I1 in series; a output port arranged between the resistor R1 and the current source I1. The current sources I1 and I2 have opposite temperature coefficients, thereby the current provided for the electronic unit is constant.

Description

technical field [0001] The present invention relates to air bag safety systems, and more particularly, to a circuit for diagnosing capacitors used in igniting air bag detonators. Background technique [0002] Air bags are commonplace in motor vehicles to enhance passenger safety in a crash. In fact, air bags are now standard equipment in many, if not most, newer motor vehicles. Airbags are usually placed in vital parts, such as the steering wheel of a motor vehicle, to reduce the damage to occupants in the event of an accident. In the event of an accident, the airbag system must be reliably triggered. For this purpose, at least one storage capacitor is provided for storing the energy required for igniting the airbag squib. To ensure reliable operation of these safety systems, diagnostics of this storage capacitor are performed, for example, before starting the motor vehicle or when the ignition key is turned at predetermined time intervals. [0003] Systems for monitorin...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G01R27/26B60R21/01
CPCG01R27/2605B60R21/0173G01R27/20
Inventor 克拉斯-扬·德朗根约翰·维特
Owner NXP BV