JPH07244098A - In-circuit testing method for capacitor - Google Patents

Abstract

PURPOSE:To effectively inspect whether a capacitor having smaller electrostatic capacitance is electrically connected or not. CONSTITUTION:A ceramic capacitor 3 connected in parallel with an electrolytic capacitor 2 has smaller electrostatic capacitance than a tolerance of that of the capacitor 2. In the case of executing an in-circuit testing method, a frequency (10MHz) at the time when an impedance of the capacitor 3 becomes smaller (substantially zero) than that of the capacitor 2, is decided, and a voltage of a half waveform having its frequency is input to an electric circuit 1. A voltage to be output from the circuit 1 is measured, and an absolute value of its output voltage is compared with a judging value. The judging value is smaller than the output voltage of the circuit 1 when only the capacitor 2 is electrically connected. It is judging that the capacitor 3 is connected only when the absolute value of the output voltage is the judged value or less.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an electric circuit in which two capacitors having greatly different electrostatic capacities are connected in parallel, and is for inspecting whether or not the capacitor having the smaller electrostatic capacity is electrically connected. It relates to the in-circuit test method of the capacitor of.

[0002]

2. Description of the Related Art Conventionally, in an automobile, for example, an electronic control unit (E
lectronic Control Unit, hereinafter simply referred to as "ECU")
Will be installed. A capacitor is usually used in the input circuit of the ECU to improve noise resistance, but it is necessary to inspect whether or not the connection is properly made. Therefore, conventionally, in a manufacturing process of an ECU, a so-called in-circuit test method has been performed in which it is inspected whether or not an electric characteristic value (electrostatic capacity) of a capacitor or the like on an electric circuit matches a designed value. There is. This is a method in which a constant current source supplies a current to a capacitor for a certain period of time, the voltage across the capacitor is measured, and the capacitance is obtained based on the voltage value.

[0003]

However, when another capacitor is connected in parallel to the capacitor to be measured, the above method requires the combined capacitance of the two capacitors. Therefore, when the electrostatic capacities of the two capacitors are significantly different from each other, there is a problem in that the capacitor having the larger electrostatic capacity can be inspected but the capacitor having the smaller electrostatic capacity cannot be inspected.

For example, an electrolytic capacitor using aluminum as a metal electrode and a ceramic capacitor may be connected in parallel to the input circuit of the ECU. The capacitance of this electrolytic capacitor is 10 to 100 μF, while the capacitance of the ceramic capacitor is 0.01 μF.
It is about 0.1 μF. The capacitance of this ceramic capacitor is smaller than the tolerance of the capacitance of the electrolytic capacitor. Therefore, although the capacitance of the electrolytic capacitor can be measured, even if the ceramic capacitor is not erroneously connected, it is not possible to confirm the presence or absence of the connection.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide a test signal applied to a capacitor in an in-circuit test of an electric circuit in which two capacitors having different electrostatic capacities are connected in parallel. Is a half-wave waveform signal with a frequency set according to the characteristics of the capacitor with the small capacitance, and it is possible to reliably check whether the capacitor with the smaller capacitance is connected to the electric circuit. It is to provide an in-circuit test method of a capacitor that can perform.

[0006]

In order to achieve the above object, a first invention according to a first aspect of the invention is to provide a first capacitor and a capacitor in parallel with the first capacitor, Second having a capacitance smaller than the tolerance of capacitance
And a half-wave waveform of a voltage having a frequency when the impedance of the second capacitor becomes smaller than the impedance of the first capacitor, the half-wave waveform being input to the electric circuit. And a second step of measuring the voltage output from the electric circuit according to the voltage input in the first step, and the absolute value of the output voltage measured in the second step. When,
By the comparison between the third step of comparing the judgment value set to be smaller than the absolute value of the output voltage of the electric circuit when only the first capacitor is electrically connected, and the comparison in the third step. And a fourth step of determining that the second capacitor is electrically connected to the electric circuit only when the absolute value of the output voltage is less than or equal to the determination value.

A second invention according to claim 2 is the first invention.
In addition to the configuration of the invention described above, the frequency of the half-wave waveform is the frequency when the impedance of the second capacitor is the smallest.

[0008]

In the first aspect of the invention, first, in the first step, the half-wave waveform is input to the electric circuit. The frequency of this half-wave waveform is the frequency when the impedance of the second capacitor becomes smaller than the impedance of the first capacitor.

Next, in the second step, the voltage output from the electric circuit is measured according to the voltage input in the first step. Here, when the second capacitor is connected to the electric circuit, since the impedance of the second capacitor is smaller than the impedance of the first capacitor, at least a part of the input frequency component is the second capacitor. It flows to the ground side through the capacitor of. That much
The frequency components output from the electric circuit are reduced.

On the other hand, when the second capacitor is not connected on the electric circuit, the input frequency component is hard to flow to the ground side. At this time, since the half-wave waveform is input to the electric circuit, the half-wave is smoothed by the first capacitor and a DC voltage is generated. Therefore, the second
The measured output voltage is different with and without the capacitor.

In the third step, the second step
The absolute value of the output voltage measured in the step of (3) and the preset determination value are compared. The judgment value is set smaller than the absolute value of the output voltage of the electric circuit when only the first capacitor is electrically connected.

In the fourth step, as a result of the comparison in the third step, when the absolute value of the output voltage is less than the judgment value, it is judged that the second capacitor is electrically connected to the electric circuit. To be done. When the output voltage is larger than the determination value, it is determined that the second capacitor is not electrically connected to the electric circuit.

As described above, according to the first aspect of the invention, even if the capacitance of the second capacitor is smaller than the tolerance of the capacitance of the first capacitor, it is inspected whether the second capacitor is electrically connected or not. It

In the second aspect of the invention, in the first step, a half-wave waveform having a frequency at which the impedance of the second capacitor is minimized is input to the electric circuit. Therefore, when the second capacitor is connected to the electric circuit, most of the input frequency components flow to the ground side through the second capacitor. As a result, the frequency component output from the electric circuit becomes small. Therefore, the output voltage measured in the second step is greatly different between the case where the second capacitor is connected and the case where the second capacitor is not connected. Therefore, it is possible to improve the accuracy of the determination in the fourth step by setting the determination value in consideration of the impedance variation of both capacitors.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment embodying the first and second inventions will be described below with reference to FIGS.

The electric circuit 1 of FIG. 1 is, for example, an electronic control unit (ECU) for controlling fuel injection of an automobile engine.
3 shows a part of the input circuit of. On this electric circuit 1, an electrolytic capacitor 2 as a first capacitor and a ceramic capacitor 3 as a second capacitor, which have greatly different electrostatic capacitances, are provided in parallel. That is, the ceramic capacitor 3 is provided between the input terminal 4 of the electric circuit 1 and the ground 5. Input terminal 4
The electrolytic capacitor 2 is provided between the ground 5 and the connection point a between the positive terminals of the ceramic capacitor 3. The output terminal 6 is connected to the connection point a and the connection point b between the plus side terminals of the electrolytic capacitor 2.

The electrolytic capacitor 2 is a capacitor in which a metal oxide film produced by electrolysis is used as a dielectric between the electrode plates, and has a characteristic that it is small in size and has a large capacity because the film is thin. In this embodiment, aluminum is used as the electrode metal of this electrolytic capacitor 2. The ceramic capacitor 3 is a capacitor using a ceramic having a large dielectric constant as a dielectric. The capacitance of the electrolytic capacitor 2 is 10 to 100 μF, while the capacitance of the ceramic capacitor 3 is about 0.01 to 0.1 μF. The capacitance of the ceramic capacitor 3 is the tolerance of the capacitance of the electrolytic capacitor 2 (± 10 to 20%).
Smaller than.

As shown in FIG. 2, the electrolytic capacitor 2 and the ceramic capacitor 3 have greatly different impedance (capacitance reactance) characteristics with respect to frequency. That is, with respect to the electrolytic capacitor 2, the impedance decreases as the frequency increases in the frequency range lower than about 100 KHz. The impedance becomes the smallest near 100 KHz. In the frequency range higher than about 100 KHz, the impedance increases as the frequency increases. On the other hand, regarding the ceramic capacitor 3, about 10
In the frequency range lower than MHz, the impedance decreases as the frequency increases. The impedance becomes the smallest value (nearly zero) near 10MHz. In the frequency range higher than about 10 MHz, the impedance increases as the frequency increases.

Therefore, when the frequency is 10 MHz, the impedance of the ceramic capacitor 3 has a minimum value, while the impedance of the electrolytic capacitor 2 has a relatively large value. In this embodiment, the phenomenon that the impedances of the electrolytic capacitor 2 and the ceramic capacitor 3 are greatly different at a predetermined frequency (10 MHz in this case) is used for the inspection of the presence or absence of the connection of the ceramic capacitor 3.

Here, in the in-circuit test method of this embodiment, the presence or absence of the ceramic capacitor 3 is inspected.
In other words, just check if you are out of stock,
It does not measure up to the value of its capacitance. This is because the capacitors 2 and 3 are mounted on the electronic board by the automatic mounting machine in the manufacturing process of the ECU, so it is more likely that the capacitors 2 and 3 having different electrostatic capacities are mounted by mistake during mounting. Also, there is a higher possibility that the product will be out of stock due to the subsequent missing.

The tester used for carrying out the in-circuit test method is a relatively small and lightweight general-purpose measuring instrument usually called an in-circuit tester, and is specially designed for the method of this embodiment. Not a thing. This tester has a function of rectifying a high-frequency sine waveform into a half-wave waveform and a function of measuring a DC voltage.

Next, the in-circuit test method performed by using the tester will be described step by step. First
Prior to the execution of the step (1), the frequency when the impedance of the ceramic capacitor 3 is the smallest and the impedance of the electrolytic capacitor 2 is large is determined. This frequency is 10 MHz at which the impedance of the ceramic capacitor 3 becomes almost zero, as described above.

First, in the first step, a tester is connected to the input terminal 4 and the output terminal 6 of the electric circuit 1. As shown in FIG. 3A, a high frequency voltage having the frequency (10 MHz) is rectified in a tester to generate a half-wave voltage on the positive side, which is supplied to the input terminal 4 of the electric circuit 1. To do.

Then, in the second step, the DC voltage (output voltage VO) output from the electric circuit 1 is measured according to the voltage (input voltage VI) input in the first step. This output voltage VO is shown in FIG. 3 when the ceramic capacitor 3 is electrically connected and when it is not electrically connected.
Different as shown in (b). First, when the ceramic capacitor 3 is connected, since the impedance of the capacitor 3 is substantially zero for this frequency signal, the frequency component input from the input terminal 4 passes through the ceramic capacitor 3 and is connected to the ground 5 side. The frequency component is not output to the output terminal 6. Therefore, the output terminal 6
The output voltage VO taken out from the output is approximately zero volts as shown by the chain double-dashed line in FIG. 3 (b).

On the other hand, when the ceramic capacitor 3 is not connected to the electric circuit 1, the frequency component input from the input terminal 4 may flow to the earth 5 side because the impedance of the electrolytic capacitor 2 is high. Absent.
At this time, if the input waveform is a sine wave, the output voltage VO will be zero volts. However, in this embodiment, since the positive half-wave waveform is input to the input terminal 4, the electrolytic capacitor 2
As a result, the half wave is smoothed to generate a positive DC voltage as shown by the solid line in FIG.

Next, in the third step, the absolute value of the output voltage VO measured in the second step is compared with a preset judgment value α. The determination value α is set to be smaller than the absolute value of the output voltage VO of the electric circuit 1 when only the electrolytic capacitor 2 is electrically connected. In this embodiment, a value slightly larger than zero volt is used as the determination value α in consideration of the variation in the impedances of the capacitors 2 and 3.

In the fourth step, as a result of the comparison in the third step, when the absolute value of the output voltage VO is less than the judgment value α, it is determined that the ceramic capacitor 3 is electrically connected to the electric circuit 1. judge. The output voltage VO is the judgment value α
If it is larger than the above, it is determined that the ceramic capacitor 3 is not connected.

As described above, in this embodiment, the voltage of the half-wave waveform is input to the electric circuit 1 and the output voltage VO from the electric circuit 1 is measured, and only when the absolute value is less than the judgment value α. , It is determined that the ceramic capacitor 3 is electrically connected. Therefore, the electrolytic capacitor 2
On the other hand, even if the ceramic capacitor 3 is connected in parallel and the capacitance of the ceramic capacitor 3 is smaller than the tolerance of the capacitance of the electrolytic capacitor 2, the presence or absence of electrical connection of the capacitor 3 can be surely inspected. You can

In this embodiment, the frequency of the half wave waveform is
The frequency is set so that the impedance of the ceramic capacitor 3 becomes the smallest. Therefore, when the ceramic capacitor 3 is connected to the electric circuit 1, most of the input frequency components flow through the capacitor 3 to the ground 5 side. As a result, the frequency component output from the electric circuit 1 becomes small. Therefore, as compared with the case where the frequency of the half-wave waveform is set to a value other than the above frequency (the frequency when the impedance becomes the smallest), the output voltage VO when the ceramic capacitor 3 is connected, The difference from the output voltage VO when not connected becomes large. Therefore, even if the impedances of the capacitors 2 and 3 vary, by setting the determination value α in consideration of the variation, highly accurate determination can be performed in the fourth step.

Particularly, in the present embodiment using the ceramic capacitor 3 as the second capacitor, the half-wave waveform of the frequency (10 MHz) when the impedance of the capacitor 3 becomes almost zero in the first step is an electric circuit. Input to 1. Therefore, the difference between the output power VO when the ceramic capacitor 3 is connected and the output voltage VO when the ceramic capacitor 3 is not connected is the largest. Therefore, the accuracy of the determination in the fourth step can be maximized.

Further, in this embodiment, the 10 MHz sine waveform is rectified inside the tester to generate a positive half-wave waveform. Therefore, it is not necessary to use complicated and expensive high frequency measurement technology. Further, since the DC output voltage VO is measured by utilizing the function that the tester has conventionally provided, it is possible to inspect whether or not the ceramic capacitor 3 is connected without newly using a dedicated tester.

The present invention can be embodied in the following other embodiments. (1) In the above embodiment, in order to obtain a half-wave waveform, the sine waveform of the frequency (10 MHz) when the impedance of the ceramic capacitor 3 is the smallest is rectified, but sine waveforms of other frequencies are rectified. You may
However, the frequency in this case needs to be selected from a frequency range in which the impedance of the ceramic capacitor 3 becomes smaller than the impedance of the electrolytic capacitor 2.

(2) A negative half-wave waveform may be input to the electric circuit 1. In this case, since the output voltage VO of the electric circuit 1 also becomes negative, the absolute value of this output voltage VO is used for comparison with the determination value α in the second step.

(3) The present invention can be applied to an electric circuit using a capacitor other than the electrolytic capacitor 2 as the first capacitor and a capacitor other than the ceramic capacitor 3 as the second capacitor. For example, a film capacitor can be used as the first capacitor,
For example, a tantalum capacitor can be used as the second capacitor.

(4) Instead of the sine wave in the above embodiment, a square wave, a sawtooth wave, a triangular wave, a pulse wave or the like may be rectified to obtain a half-wave waveform.

[0036]

As described above in detail, in the first invention, the half-wave waveform of the voltage having the frequency when the impedance of the second capacitor becomes smaller than the impedance of the first capacitor is input to the electric circuit. . Measure the output voltage from the electrical circuit. The determination value set to be smaller than the absolute value of the output voltage of the electric circuit when only the first capacitor is electrically connected is compared with the absolute value of the output voltage. Then, only when the absolute value of the output voltage is less than or equal to the determination value, it is determined that the second capacitor is electrically connected to the electric circuit. Therefore, in the electric circuit in which the first and second capacitors having different electrostatic capacities are connected in parallel, it is ensured whether or not the second capacitor having the smaller electrostatic capacity is connected on the electric circuit. Can be inspected.

In the second invention, the frequency of the half-wave waveform is set to the frequency at which the impedance of the second capacitor becomes the smallest. Therefore, in addition to the effect of the first invention, the accuracy of the determination in the fourth step can be improved.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a part of an input circuit of an ECU to which an in-circuit test method of an embodiment embodying the first and second inventions is applied.

FIG. 2 is a graph showing electrical characteristics (relationship of impedance to frequency) of an electrolytic capacitor and a ceramic capacitor of an example.

FIG. 3A is a waveform diagram showing a half-wave waveform input to an electric circuit in one embodiment, and FIG. 3B is a waveform diagram showing an output voltage output from the electric circuit.

[Explanation of symbols]

1 ... Electric circuit, 2 ... Electrolytic capacitor as first capacitor, 3 ... Ceramic capacitor as second capacitor, VO ... Output voltage, α ... Judgment value.

Claims (2)

[Claims] 1. An electric circuit comprising: a first capacitor; and a second capacitor provided in parallel with the first capacitor and having a capacitance smaller than a tolerance of the capacitance thereof. A first step of inputting to the electric circuit a half-wave waveform of a voltage having a frequency at which the impedance of the second capacitor becomes smaller than the impedance of the first capacitor. The second step of measuring the voltage output from the electric circuit according to the voltage input in the step of; and the absolute value of the output voltage measured in the second step;
Output from the third step of comparing the judgment value set to be smaller than the absolute value of the output voltage of the electric circuit when only the capacitor of (3) is electrically connected, and the comparison in the third step. And a fourth step of determining that the second capacitor is electrically connected to the electric circuit only when the absolute value of the voltage is less than or equal to the determination value. 2. The capacitor in-circuit test method according to claim 1, wherein the frequency of the half-wave waveform is a frequency at which the impedance of the second capacitor is minimized.