JPH0459592B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a deterioration detection circuit for an electrolytic capacitor used in a smoothing circuit in a power supply device configured to rectify alternating current voltage to obtain direct current voltage.

[Conventional technology]

Generally, a stabilized power supply circuit converts AC voltage to DC voltage, or converts DC input voltage to AC, transforms it to an arbitrary voltage, and then rectifies it to obtain DC output voltage.
In switching regulators and the like equipped with DC-DC converters, electrolytic capacitors, which are inexpensive and have a large capacity, are used to smooth DC output.

In a stabilized power supply configured in this manner, the electrolytic capacitor undergoes chemical changes and cannot avoid deterioration over time. This deterioration state of the capacitor manifests itself as an increase in dielectric loss tangent (tanδ), equivalent series resistance (ESR), or leakage current as the capacitance decreases over time, resulting in the risk of the capacitor overheating and being damaged. be.

From this point of view, the conventional means of detecting the deterioration state of this type of capacitor is to detect the heat generated by the increase in internal loss of the capacitor and the accompanying mechanical deformation of the internal mechanism or exterior body of the capacitor. Accordingly, various protection methods have been proposed that detect in advance a dangerous state in which the capacitor deteriorates and is damaged, and performs circuit safety operations.

However, the conventional deterioration detection method described above detects the heating state of the capacitor and the deformation of the capacitor components, so the deterioration state of the capacitor has progressed considerably, and during this time the electrical characteristics of the capacitor deteriorate significantly. Therefore, the negative impact on highly reliable power supply circuits is extremely large.

Therefore, the applicant first proposed a smoothing capacitor life detection device that monitors the ripple current or ripple voltage of the smoothing electrolytic capacitor and detects changes therein to determine the deterioration of the capacitor while it is in operation. A patent application was filed. FIG. 3 is a circuit diagram showing an example of the configuration of the lifespan detection device according to the above-mentioned patent application. In FIG. 2, reference numeral 10 indicates a transformer, and the AC voltage generated on the secondary side of the transformer 10 is rectified by diode rectifiers 12 and 14, and the resulting DC voltage is applied to the smoothing coil 16 and It is smoothed by a smoothing capacitor 18 to generate the required constant DC voltage. Further, a current detector 20 is provided to extract the ripple current flowing through the smoothing capacitor 18, and the ripple current detected by the current detector 20 is converted into a voltage signal by a current-voltage conversion circuit including an operational amplifier 22. This signal is input to an average value detection circuit consisting of operational amplifiers 24 and 26, and a DC voltage proportional to the ripple current amplitude of the capacitor 18 is extracted. This voltage is configured to be input to one input terminal of the comparator 32 as a required voltage level via the resistor _R1 . Further, a reference power supply 34 is provided to set a voltage level based on the ripple current when a normal smoothing capacitor is used, and this reference power supply voltage is applied to the other side of the comparator 32 via appropriate voltage dividing resistors R ₂ and R ₃ . The configuration is such that it is input as a reference voltage level to the input terminal of. Therefore, the comparator 32 compares the reference voltage level with the voltage level that decreases due to a decrease in ripple current due to deterioration of the smoothing capacitor 18, and when the deviation exceeds the allowable level, Set to output a predetermined output signal.
As a result, the output signal of the comparator 32 can energize the switching element 36 or the alarm 38 as appropriate.

[Problem that the invention seeks to solve]

In the smoothing capacitor life detection device described above, the capacitor 18
ripple current or ripple voltage may vary. Therefore, it is necessary to provide a compensation circuit that adjusts the reference voltage level input to the comparator 32 in accordance with changes in load current or changes in ambient temperature.

Therefore, an object of the present invention is to compensate for fluctuations in ripple current caused by fluctuations in load current or changes in ambient temperature, and to detect the deterioration state of a smoothing electrolytic capacitor properly at all times to generate an output signal. To provide a detection circuit.

[Means for solving problems]

In the electrolytic capacitor deterioration detection circuit according to the present invention, a DC voltage including a ripple component obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing electrolytic capacitor, and the smoothed voltage is supplied to a load. In a power supply circuit configured to do so, a detection signal corresponding to the ripple of the current flowing through the smoothing electrolytic capacitor is input, and this detection signal is compared with a predetermined reference signal to determine whether the smoothing electrolytic capacitor has deteriorated. A comparison circuit is provided to make the judgment, and a resistor is connected to the output line of the power supply circuit for this comparison circuit, and the output signal of an amplifier that converts the terminal voltage of this resistor into an appropriate voltage signal is used as the reference of the previous comparison circuit. compensation means for fluctuations in the load current of the power supply circuit configured to add the output signal to the reference signal of the comparison circuit; The present invention is characterized by adding compensation means for changes in the ambient temperature of the circuit.

[Effect]

According to the electrolytic capacitor deterioration detection circuit according to the present invention, a DC voltage including a ripple component obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing electrolytic capacitor, and the smoothed voltage is output. In a power supply circuit configured to supply a load, the ripple portion of the current flowing through the smoothing electrolytic capacitor is compared with a predetermined reference value to determine the deterioration state of the smoothing electrolytic capacitor, and the load current of the power supply circuit and By adjusting the reference value according to fluctuations in ambient temperature, it is possible to effectively distinguish between changes in ripple due to deterioration of the capacitor and changes in ripple due to fluctuations in the load current of the power supply circuit or ambient temperature. The deterioration state of the capacitor can be appropriately and reliably determined.

[Example] Next, an example of the deterioration detection 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. Components that are the same as those in the circuit shown in FIG. 2 are given the same reference numerals and detailed explanations thereof will be omitted. That is, in FIG. 1, a stabilized power supply circuit is constructed by connecting a rectifier circuit consisting of diode rectifiers 12 and 14 and a smoothing circuit consisting of a smoothing coil 16 and a smoothing capacitor 18 to the secondary side of the transformer 10. This is similar to the circuit shown in FIG.

Therefore, in this embodiment, a current detector 40 is connected in series with the smoothing capacitor 18, and both output ends of the current detector 40 are connected to both ends of the sliding resistor 42. Further, the intermediate connection terminal of this sliding resistor 42 is connected to one input terminal of a comparator 44. Further, a resistor _R14 is connected to the (-) side output line of the stabilized power supply circuit, and the power supply output side connection end of this resistor _R14 is connected to the (+) side input terminal of the amplifier 46, The other connection end of resistor R ₁₄ is connected to one connection line of the sliding resistor 42 . As this connection line GND line, the (-) side input terminal of the amplifier 46 is connected to a resistor.
Connect with GND line via _R15 . Additionally, a power supply 48 and resistors R ₁₇ and R ₁₈ for setting the reference voltage
are connected in series to the GND line, and the connection point between resistors _R17 and _R18 is connected to the (+) side input terminal of the comparator 44. Further, the output line of the amplifier 46 and the signal line from the temperature detector 50 are connected to the (+) side input terminal of the comparator 44. Furthermore, a resistor is connected to the output terminal of the comparator 44.
An alarm device 54 is connected to R ₂₀ via a switching element 52 and a resistor R ₂₁ .

In the stabilized power supply circuit of this embodiment configured as described above, the AC voltage generated across the secondary winding of the transformer 10 is transferred to the diode rectifiers 12 and 14.
After being rectified by a smoothing coil 16 and a smoothing capacitor 18, a constant DC voltage is generated. Here, the ripple current flowing through the capacitor 18 is transmitted to the sliding resistor 42 via the current detector 40, and the current detection voltage level (detection signal) generated in the sliding resistor 42 is transmitted to the comparator 4.
It is input to the (-) side input terminal of 4. This comparator 4
A power supply 48 and a resistor are connected to the (+) side input terminal of 4.
A predetermined reference voltage level generated by R ₁₇ and R ₁₈ is input, and the comparator 44 compares these input voltage levels to determine the detection voltage level input to the (-) side terminal (+) side terminal. A high-level output signal is generated when the voltage level becomes lower than the reference voltage level input to the input terminal. This high-level output signal energizes the switching element 52 and activates the alarm device 54, which includes a light emitting element or the like.

Here, the ripple current flowing through the capacitor 18 changes as the load current of the circuit changes even when the capacitor 18 is in a normal state. Therefore, in this embodiment, the potential drop occurring across the resistor _R14 is amplified by the amplifier 46, thereby converting the load current value to an appropriate voltage level. moreover,
This voltage level is input to the (+) side terminal of the comparator 44 to adjust the reference voltage level and compensate for variations in load current.

Furthermore, the ripple current flowing through the capacitor 18 also changes due to changes in ambient temperature. Therefore, in this embodiment, the temperature detector 50 detects the ambient temperature, converts it to an appropriate voltage level, and inputs this to the (+) side terminal of the comparator 44 to adjust the reference voltage level. temperature compensation.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, a DC voltage including ripples obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing electrolytic capacitor, and is smoothed. In a power supply circuit configured to supply a voltage to a load, the ripple component of the voltage or current across the smoothing electrolytic capacitor is monitored, and changes in the ripple component due to deterioration of the capacitor, load fluctuations in the power supply circuit, and ambient temperature are monitored. It is possible to distinguish between increases and decreases in ripple due to changes, and it is possible to appropriately and reliably determine the deterioration state of the smoothing electrolytic capacitor. Furthermore, since this can be achieved with the smoothing electrolytic capacitor in its operating state, there is no need for the troublesome work of predictive component replacement as in the past, making this type of stabilizing power supply circuit economical and efficient. Can drive.

Although the preferred embodiments of the present invention have been described above, it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a stabilized power supply circuit diagram showing an embodiment of the electrolytic capacitor deterioration detection circuit according to the present invention, and FIG.
The figure is a stabilized power supply circuit diagram showing an example of the configuration of a smoothing capacitor life detection device. 10...Transformer, 12, 14, 28, 30...
Diode rectifier, 16...Smoothing coil, 18
... Smoothing capacitor, 20 ... Current detector, 2
2, 24, 26, 46... operational amplifier, 32, 4
4... operational amplifier, 34, 48... power supply, 36,
52...Switching element, 38, 54...Alarm device, 40...Current detector, 42...Sliding resistor, 50...Temperature detector, _R14 ...Resistor.

Claims (1)

[Claims] 1. A power supply configured to supply a DC voltage including ripple obtained by rectifying an AC voltage or a pulse voltage to a smoothing circuit including a smoothing electrolytic capacitor, and supply the smoothed voltage to a load. In the circuit, a comparison circuit inputs a detection signal corresponding to a ripple portion of the current flowing through the smoothing electrolytic capacitor, and compares the detection signal with a predetermined reference signal to determine deterioration of the smoothing electrolytic capacitor. A resistor is connected to the output line of the power supply circuit for this comparison circuit, and the output signal of an amplifier that converts the terminal voltage of this resistor into an appropriate voltage signal is added to the reference signal of the previous comparison circuit. compensation means for variations in the load current of the power supply circuit configured to compensate for fluctuations in the load current of the power supply circuit; What is claimed is: 1. A deterioration detection circuit for an electrolytic capacitor, characterized in that a means for compensating for changes is added.