JPH082141B2 - Deterioration detection circuit for electrolytic capacitors - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a deterioration detecting circuit for an electrolytic capacitor used in a smoothing circuit in a power supply device configured to rectify an AC voltage to obtain a DC voltage.

[Conventional technology]

Generally, in a switching regulator or the like equipped with a DC-DC converter that stabilizes a power supply circuit that converts an AC voltage to a DC voltage and that converts a DC input voltage to an AC and transforms it to an arbitrary voltage and then rectifies it to obtain a DC output voltage, In order to smooth the DC output, an inexpensive and large-capacity electrolytic capacitor is used.

In the stabilized power supply configured as described above, the electrolytic capacitor undergoes a chemical change, so that deterioration over time cannot be avoided. The deterioration state of this capacitor appears as an increase characteristic of dielectric loss tangent (tan δ) and equivalent series resistance (ESR) or delay current as the capacitance decreases with time, and as a result, there is a risk of the capacitor generating heat and being damaged. is there.

From this point of view, conventionally, as a means for detecting the deterioration state of this type of capacitor, by detecting the heat generation caused by the increase of the internal loss of the capacitor and the mechanical deformation of the internal mechanism of the capacitor or the external body accompanying it Various protection schemes have been proposed in which a dangerous state leading to deterioration and damage of a capacitor is detected in advance to perform a circuit safety operation.

However, the above-mentioned conventional deterioration detection method detects the overheated state of the capacitor, the deformation of the component members of the capacitor, etc., and therefore the deteriorated state of the capacitor has progressed considerably, during which the electrical characteristics of the capacitor are extremely deteriorated. Therefore, the adverse effect on the highly reliable power supply circuit is extremely large.

Therefore, the applicant first detects the ripple current in the smoothing electrolytic capacitor and compares the extracted ripple current with a reference value set based on the ripple current value in the normal state to determine the deterioration state of the capacitor. We have proposed a device for detecting the life of a capacitor and applied for a patent. FIG. 2 is a circuit diagram showing a configuration example of the life detecting device according to the above-mentioned patent application. In FIG. 2, reference numeral 10 indicates a transformer, the AC voltage generated on the secondary side of the transformer 10 is rectified by diode rectifiers 12 and 14, and the obtained DC voltage is smoothed by a smoothing coil 16 and a smoothing coil. It is smoothed by the capacitor 18 and a required DC constant voltage is generated. further,
A current detector 20 for extracting the ripple current flowing through the smoothing capacitor 18 is provided, and the ripple current detected by the current detector 20 is converted into a voltage signal by the current-voltage conversion circuit by the operational amplifier 22. This signal is input to an average value detection circuit composed of operational amplifiers 24 and 26, and a DC voltage proportional to the ripple current amplitude of the capacitor 18 is taken out. This voltage is applied to the resistor R ₁
A desired voltage level is input to one input terminal of the comparator 32 via the. Further, a reference power supply 34 for setting a voltage level based on a ripple current when a normal smoothing capacitor is used is provided, and the reference power supply voltage is appropriately supplied to the other side of the comparator 32 via voltage dividing resistors R ₂ and R _3. The reference voltage level is input to the input terminal of. Therefore,
In the comparator 32, the reference voltage level is compared with a voltage level that is reduced due to a decrease in ripple current due to deterioration of the smoothing capacitor 18, and a predetermined output signal is output when the deviation exceeds a permissible level. Is set to be output. As a result, the switching element 36 or the alarm device 38 can be appropriately activated by the output signal of the comparator 32.

[Problems to be solved by the invention]

In the smoothing capacitor life detecting device described above,
When the load of the power supply circuit fluctuates instantaneously, the ripple current flowing through the smoothing capacitor 18 changes accordingly, and the comparator 32 may output an output signal in response to this. Further, when the current is detected by the current detector 20, a ripple may be generated due to a change in the input voltage and a change in the AC component (pulsation) of the input voltage, and accordingly, the ripple is input to the comparator 32. There is a risk that the detection voltage level slightly changes, resulting in malfunction of the comparator 32 or output hunting.

Therefore, an object of the present invention is to discriminate a change in ripple current due to deterioration of a smoothing electrolytic capacitor and a change in ripple current due to a load change of a power supply circuit to prevent malfunction of a comparison circuit and to prevent deterioration of a smoothing electrolytic capacitor. Another object of the present invention is to provide a deterioration detection circuit for an electrolytic capacitor, which can always determine the state properly.

[Means for solving problems]

The deterioration detecting circuit for an electrolytic capacitor according to the present invention supplies a DC voltage including a ripple component obtained by rectifying an AC voltage or a pulse voltage to a smoothing circuit including a smoothing electrolytic capacitor to smooth a voltage. It consists of a power supply circuit configured to supply to the load, takes the ripple current flowing through the smoothing electrolytic capacitor, and the ripple current value is
In a deterioration detection circuit for an electrolytic capacitor configured to detect the deterioration state of the smoothing electrolytic capacitor by comparing it with a reference value consisting of the ripple current value of a normal smoothing electrolytic capacitor, In addition to connecting a current transformer to the current transformer, a current detection circuit consisting of a rectifier circuit is connected and arranged on the output side of this current transformer, and the output terminal of this current detection circuit and the set output terminal for setting the reference voltage level are respectively set. A comparison circuit connected to the comparison input terminal is provided, and a time constant circuit that delays the comparison output for a predetermined time is provided for the comparison circuit, and the detection voltage level detected by the current detection circuit is lower than the reference voltage level. Switch circuit for generating a predetermined deterioration detection signal after delaying a high level output signal for a predetermined time in the comparison circuit. Characterized in that it comprises a circuit.

[Action]

According to the deterioration detecting circuit of the electrolytic capacitor of the present invention, in the power supply circuit configured to smooth the DC voltage including the ripple component obtained by rectifying the AC voltage etc. through the smoothing electrolytic capacitor and supply the load. , The ripple current flowing through the smoothing electrolytic capacitor is detected, and the detected value is input to a comparison circuit and compared with a predetermined reference value, so that the detected ripple current value is significantly reduced. Deterioration of the electrolytic capacitor can be discriminated, and by giving a predetermined time constant and hysteresis to the comparison circuit, the ripple current change due to the deterioration of the smoothing electrolytic capacitor and the load fluctuation of the power supply circuit can be prevented. A malfunction of the comparison circuit can be prevented by discriminating the accompanying change in the ripple current.

〔Example〕

Next, an embodiment of a deterioration detecting circuit for an electrolytic capacitor according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a DC stabilized power supply circuit diagram showing an embodiment of the deterioration detection circuit of the present invention. The same components as those of the power supply circuit shown in FIG. 2 are designated by the same reference numerals, and detailed description thereof will be omitted. That is, in FIG. 1, a rectifier circuit composed of diode rectifiers 12 and 14 and a smoothing circuit composed of a smoothing coil 16 and a smoothing capacitor 18 using an electrolytic capacitor are connected and arranged on the output side of the transformer 10 for stability. The configuration of the digitalized power supply circuit is similar to that of the circuit shown in FIG. Therefore, in this embodiment, a current transformer 40 is connected in series to the smoothing capacitor 18, and a rectifier composed of a diode rectifier 42, a resistor R ₁₄ and a capacitor C ₂ is provided on the output side of the current transformer 40. The circuits are connected and arranged to form a current detection circuit, and the output terminal of the current detection circuit is connected to the (−) side input terminal of the comparator 44. Further, the comparator circuit is configured so that a reference voltage level obtained by dividing the output voltage of the stabilized power supply circuit into a predetermined value by resistors R ₁₅ and R ₁₆ is input to the (+) side input terminal of the comparator 44. .
The (+) side input terminal and output terminal of the comparator 44 are connected via a resistor R ₁₇ to set a predetermined hysteresis. Further, a diode rectifier is provided on the output side of the comparator 44.
46, a resistor R ₁₈ and a capacitor C ₃ are connected in series, and a diode rectifier 48 reverse-biased to the diode rectifier 46 is connected in parallel to the diode rectifier 46 and the resistor R ₁₈ to form a time constant circuit. To do. Further, a switching element 52 is connected to the output end of this time constant circuit via a Zener diode 50, and a Zener diode 54 is connected to the output end of this switching element 52 to generate a predetermined deterioration detection signal at the connection end. The switching circuit thus configured is configured.

In the stabilized power supply circuit of this embodiment configured as above, the ripple current flowing through the capacitor 18 is detected by the current transformer 40, and the obtained ripple current is diode rectifier.
The DC voltage is smoothed by a rectifier circuit composed of 40, the resistor R ₁₄ and the capacitor C ₂ and the resistor R ₁₄ and the capacitor C ₂
A DC voltage corresponding to the ripple current flowing through the capacitor 18 is generated between the terminals of the above, and this current voltage is input to the (-) side terminal of the comparator 44 as a detection voltage level. The comparator 44 compares the detected voltage level with the reference voltage level input to the (+) side terminal, and generates a high level output signal when the detected voltage level becomes lower than the reference voltage level. This high level output signal is delayed by a time constant circuit composed of a resistor R ₁₈ and a capacitor C _{3 for a} predetermined time and then transmitted to a switching element 52, which results in a switching element 52.
Is activated to generate a predetermined deterioration detection signal.

In the stabilized power supply circuit of the present embodiment that performs the above-described operation, the ripple current flowing through the capacitor 18 fluctuates instantaneously with the load fluctuation of the power supply, and the comparator 44 responds to this by generating a high level output signal. In this case, this instantaneous high-level output signal is consumed as the charging voltage of the capacitor C ₃ , so that the switching element is not activated. In addition, even when a ripple occurs when the current is detected by the current transformer 40 and the detected voltage level input to the (−) side terminal of the comparator 44 slightly changes, the hysteresis of the hysteresis set by the resistor R ₁₈ By the action, malfunction of the comparator 44 and hunting of the output can be prevented.

〔The invention's effect〕

As is apparent from the above-described embodiment, according to the present invention, the DC voltage including the ripple component obtained by rectifying the AC voltage or the pulse voltage is supplied to the smoothing circuit including the smoothing electrolytic capacitor and smoothed. In a power supply circuit configured to supply a voltage to a load, a ripple current flowing in a smoothing electrolytic capacitor is detected and compared with a predetermined reference value,
The deterioration of the smoothing electrolytic capacitor can be easily and easily determined by the marked decrease in the value of the detected ripple current, and a predetermined value is provided to the comparison circuit that compares the detected value of the ripple current with the reference value. By giving the time constant of, it is possible to prevent the malfunction of the comparison circuit due to the instantaneous load fluctuation of the power supply circuit. Further, by giving a predetermined hysteresis to the comparison circuit, it is possible to prevent malfunction of the comparison circuit or hunting of the output when a slight variation occurs in the detected value of the ripple current, and to smooth the electrolytic capacitor. It is possible to effectively and properly determine the deterioration state of the power supply circuit while it is in the operating state, and it is possible to improve the reliability of this kind of power supply circuit and to realize it at low cost.

[Brief description of drawings]

FIG. 1 is a stabilized power supply circuit diagram showing one embodiment of a deterioration detection circuit for an electrolytic capacitor according to the present invention, and FIG. 2 is a stabilized power supply circuit diagram showing one configuration example of a smoothing capacitor life detection device. . 10 …… Transformer 12,14,28,30,42,46,48 …… Diode rectifier 16 …… Smoothing coil, 18 …… Smoothing capacitor 20 …… Current detector, 22,24,26 …… Calculation Amplifier 32,44 …… Comparator, 34 …… Power supply 36,52 …… Switching element, 38 …… Alarm device 40 …… Current transformer, 50,54 …… Zener diode

Claims (1)

[Claims] 1. A structure in which a direct current voltage including a ripple component obtained by rectifying an alternating current voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing electrolytic capacitor to supply a smoothed voltage to a load. The ripple current flowing through the smoothing electrolytic capacitor is taken out, and this ripple current value is compared with a reference value consisting of the ripple current value of a normal smoothing electrolytic capacitor to deteriorate the smoothing electrolytic capacitor. In an electrolytic capacitor deterioration detection circuit configured to detect the state, connect a current transformer in series with a smoothing electrolytic capacitor, and connect a current detection circuit consisting of a rectifier circuit to the output side of this current transformer. And a comparison circuit in which the output terminal of the current detection circuit and the setting output terminal for setting the reference voltage level are respectively connected to the comparison input terminals. In addition, a time constant circuit that delays the comparison output for a predetermined time is provided for this comparison circuit, and when the detection voltage level detected by the current detection circuit becomes lower than the reference voltage level, the comparison circuit outputs a high voltage. A deterioration detection circuit for an electrolytic capacitor, comprising a switching circuit for generating a predetermined deterioration detection signal after delaying a level output signal for a predetermined time.