JPH0541950B2 - - Google Patents

Description

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

[Conventional technology]

Generally, when configuring a power supply circuit that converts an alternating current voltage to a direct current voltage, a chiyoke coil or a capacitor is used to smooth the direct current output voltage.
In this case, the capacitor is required to have a large capacity, and an electrolytic capacitor is usually used.

In addition, as a stabilized power supply, it is possible to downsize the device and reduce loss when controlling the output voltage, so a switching regulator that controls the output voltage by turning on and off the DC voltage is used. It is widespread. This switching regulator generally includes a DC-DC converter that converts a DC input voltage into AC, transforms it to an arbitrary voltage, and then rectifies it to obtain a DC output voltage. In a switching regulator constructed in this way, an inexpensive electrolytic capacitor with a large capacity is used to smooth the DC output.

As described above, the reliability of today's stabilized power supplies, as typified by switching regulators, has improved, but on the other hand, electrolytic capacitors still undergo chemical changes and are subject to deterioration over time. There is an inconvenience in that it cannot be avoided and must be replaced periodically over its lifespan.

Generally, it is known that the deterioration state of a capacitor appears as an increase in dielectric loss tangent (tan δ), equivalent series resistance (ESR), or leakage current as the capacitance decreases over time. However, in order to detect these deterioration characteristics of a capacitor, it is necessary to remove the capacitor from the circuit and measure each capacitor individually, which not only requires a lot of effort and time, but also requires the circuit operation to be temporarily stopped. There is this inconvenience.

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. Therefore, various protection methods have been proposed that detect in advance a dangerous condition that could lead to deterioration or damage of a capacitor and perform safety operations such as cutting off the circuit (for example, Japanese Patent Application Laid-Open No. 57-9226; 59
-89521).

[Problem to be solved by the invention]

The conventional deterioration detection method for capacitors described above detects overheating of the capacitor and deformation of the capacitor components, so the deterioration of the capacitor has progressed considerably, and during this time the electrical characteristics of the capacitor are extremely affected. The situation is getting worse, and the negative impact on highly reliable power supply circuits is extremely large.

Therefore, the inventors of the present invention focused on the fact that the equivalent series resistance of an electrolytic capacitor increases as it deteriorates, and as a result of extensive research, the inventors found that a DC voltage containing ripple obtained by rectifying an AC voltage or a pulse voltage In a power supply device configured to supply smoothed DC voltage to a load via a smoothing circuit consisting of a coil and a capacitor, load current when normal and deteriorated capacitors are used in the smoothing circuit. When we measured the changes in the ripple current in the coil and the ripple current in the capacitor with respect to changes in , we found that there was almost no change in the ripple current in the coil. It was found that the value decreases significantly as the load current increases. In other words, deterioration of a capacitor can be detected by detecting a drop in the ripple current of the capacitor using a pick-up coil, etc., thereby appropriately determining the state of deterioration of the capacitor's electrical characteristics and easily detecting its lifespan during circuit operation. It turns out that it is possible.

Therefore, an object of the present invention is to provide a smoothing capacitor that can easily determine the deterioration of a capacitor in an operating state by monitoring the ripple current of the smoothing capacitor and smoothing coil and detecting its changes. To provide a lifespan detection method.

[Means to solve the problem]

In the smoothing capacitor life detection method according to the present invention, a DC voltage including ripple obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing capacitor, and the smoothed voltage is applied to a load. In a power supply circuit configured to supply an inductance element to the smoothing circuit, a ripple current (ΔI _L ) flowing through the inductance element, a ripple current (ΔI _C ) flowing through the smoothing capacitor, and the ripple current flowing through the smoothing capacitor are supplied to the load. detecting the load current (I _O ) caused by the inductance element, and detecting the difference (ΔI _L −ΔI _C ) between the ripple current (ΔI _L ) flowing through the inductance element and the ripple current (ΔI _C ) flowing through the smoothing capacitor; From the load current (I _O ), the output ripple coefficient (γ = (ΔI _L
−ΔI _C )/I _O ) is calculated, and the output ripple coefficient (γ ^* ) of the normal smoothing capacitor set for the value of the load current (I _O ) is calculated.
and the value of the output ripple coefficient (γ) obtained by measurement, and the deterioration state of the smoothing capacitor is determined from the correlation.

[Effect]

According to the method for detecting the life of a smoothing capacitor according to the present invention, when a DC voltage including ripples obtained by rectifying an AC voltage etc. is smoothed and supplied to a load via a smoothing capacitor, the inductance By constantly monitoring the ripple current flowing through the element and smoothing capacitor by detecting it with a current detector installed so as not to affect the circuit, as the deterioration of the smoothing capacitor progresses, the normal smoothing Since the ripple current value gradually decreases compared to that of a smoothing capacitor, by electrically determining this state, it is possible to achieve appropriate life detection of the smoothing capacitor while it is in its used state.

In this case, by using the ripple current flowing through the inductance element as a reference value and comparing it with the ripple current of the smoothing capacitor, it is possible to improve the accuracy of electrically determining the deterioration state of the smoothing capacitor.

〔Example〕

Next, an embodiment of the method for detecting the life of a smoothing capacitor according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 shows a typical circuit configuration of a switching regulator that implements the method for detecting the life of a smoothing capacitor according to the present invention. That is, in FIG. 1, reference numeral 10 indicates a DC power supply;
12 is a voltage transformer, 14 is a switching element, 1
6, 18, and 20 are diodes, 22 is a smoothing coil, 24 is a smoothing capacitor, and 26 is a load, which is configured as a forward converter. The switching regulator configured in this way obtains a pulse voltage from the DC voltage Ei supplied by the DC power supply 10 through the switching element 14, and converts this pulse voltage into a predetermined voltage value via the transformer 12. This pulse voltage is then rectified by diodes 18 and 20, and smoothing coil 22 and smoothing capacitor 2
4 to smooth the signal and supply it to the load 26.

Therefore, in the present invention, in the power supply circuit having the above configuration, current detectors 28 and 30 each consisting of a pick-up coil or the like are provided for the smoothing capacitor 24 and the smoothing coil 22 to detect the ripple current flowing individually. establish. In this case, in the circuit shown in FIG. 1, equivalent circuits when the switching element 14 is in the on state and off state are as shown in FIGS. 2 and 3. The contents of each element in FIGS. 2 and 3 are as follows.

Ei: Input voltage E _O : Output voltage C: Capacitance of smoothing capacitor 24 L: Inductance of smoothing coil 22 R _L : Load resistance V _D2 : Forward equivalent voltage source of diode 18 V _D3 : Forward equivalent of diode 20 Voltage source r ₁ : Sum of internal resistance of input power supply 10, on-state resistance of switching element 14, and primary winding resistance of transformer 12 r ₂ : Internal resistance of diode 18, winding resistance of coil 22, and transformation Sum of the secondary winding resistances of the capacitor 12 r ₃ : Sum of the internal resistance of the diode 20 and the winding resistance of the coil 22 r _C : Equivalent series resistance (ESR) of the smoothing capacitor 24 I _L : The sum of the internal resistance of the diode 20 and the winding resistance of the coil 22 Average flowing current I _O : Average current value of the load ΔI _L : Ripple current of the smoothing coil 22 ΔI _C : Ripple current of the smoothing capacitor 24 Therefore, in the circuit configuration described above, the capacitance of the smoothing capacitor 24 is 441.2 μF. ,ESR108.5m
Smoothing coil 2 for load current I _O for a normal product with Ω and a deteriorated product with a capacity of 345.7 μF and an ESR of 996.3 mΩ.
As a result of measuring the ripple currents ΔI _L and ΔI _C of the smoothing capacitor 2 and the smoothing capacitor 24, the characteristics shown in FIG. 4 (normal product) and FIG. 5 (deteriorated product) were obtained. From these measurement results, smoothing capacitor 2
Regarding the deteriorated product No. 4, almost no change was observed in the ripple current ΔI _L of the smoothing coil 22, but a remarkable change was observed in the ripple current ΔI _C of the smoothing capacitor 24. In addition, the characteristic curves shown by solid lines in FIGS. 4 and 5 are as follows.
This is based on calculated values calculated based on the equivalent circuits shown in FIGS. 2 and 3. Also, the fourth
Although the characteristic curves shown in FIG. 5 and FIG. 5 are for a forward type converter, it has been confirmed that similar characteristic curves can be obtained when feedback is applied.

Here, the difference between the ripple current ΔI _L of the smoothing coil 22 detected by the circuit shown in FIG. 1 and the ripple current ΔI _C of the smoothing capacitor 24, that is, the output ripple current, is taken, and γ=(ΔI _L −
If a dimensionless quantity (referred to as an output ripple coefficient) defined by ΔI _C )/I _O is obtained, the degree of ESR can be determined with almost no influence from the load. Therefore, if we show the γ vs. I _O characteristic in this case,
As shown in FIG. In other words, as is clear from Fig. 6, when the load current I _O = 3A, γ is 0.8% for the normal product, while γ is 0.8% for the deteriorated product.
= about 6%, and the deterioration state of the smoothing capacitor can be sufficiently determined.

Based on the above-described life detection method of the present invention, the output ripple coefficient characteristics (γ vs. This can be easily achieved by setting the I/ _O characteristics) and comparing this set value with the detected value of the actual circuit state. In this case, the load current can be easily detected using a known instrument current transformer or the like.

FIG. 7 shows the ripple current ΔI C of the smoothing capacitor 24 detected by the current detector 28 and the ripple current ΔI _C of the smoothing capacitor 24 detected by the current detector 28, and
_The output ripple coefficient γ _{= ( ΔI L}
−ΔI _C )/I _O is calculated by the calculator OP, and this output ripple coefficient γ is input to the comparator COMP, which determines the set value γ ^* of the output ripple coefficient of a normal smoothing capacitor based on the load current I _O. , the set value γ ^* of the output ripple coefficient is compared with the detected value γ of the output ripple coefficient, and when a deviation of a predetermined value or more occurs, an alarm output signal S _A is output.

〔Effect of the invention〕

As is clear from the embodiments described above, according to the present invention, the deterioration of the smoothing capacitor over time is constantly monitored by a current detector that does not affect the circuit by monitoring the ripple current flowing through the smoothing capacitor and the smoothing coil. By using the ripple current flowing through the smoothing coil as a reference value and determining the output ripple coefficient in relation to the ripple current flowing through the smoothing capacitor, the deterioration state of the smoothing capacitor can be easily and reliably determined, and the required It can be configured to take an alarm action.

In this way, according to the present invention, it is possible to properly detect the deterioration of the smoothing capacitor in its operating state without performing any special processing on the smoothing capacitor. Deterioration determination and parts replacement can be performed economically and efficiently without the need for complicated parts replacement.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Not only can it be widely applied as a lifespan detection method for determining the deterioration state of a smoothing capacitor in a power supply circuit configured to smooth with a chiyo-impact type smoothing circuit, but also can be applied within the scope of the spirit of the present invention. Of course, various design changes can be made.

[Brief explanation of the drawing]

FIG. 1 is a basic circuit diagram of a switching regulator showing an embodiment of the method for detecting the life of a smoothing capacitor according to the present invention, and FIGS.・Equivalent circuit diagram in off-operation, Figure 4 is a characteristic curve diagram showing the relationship between ripple current and load current when a normal product is used as the smoothing capacitor in the circuit shown in Figure 1, and Figure 5 is A characteristic curve diagram similar to Figure 4 when a deteriorated smoothing capacitor is used. Figure 6 shows the relationship between output ripple coefficient and load current when a normal and deteriorated smoothing capacitor is used. The characteristic curve diagram, FIG. 7, is a block circuit diagram for detecting the life span based on the output ripple coefficient based on the ripple current detection value of the smoothing capacitor and the smoothing coil and the set output ripple coefficient. 10...DC power supply, 12...Voltage transformer, 14
... Switching element, 16, 18, 20 ... Diode, 22 ... Smoothing coil, 24 ... Smoothing capacitor, 26 ... Load, 28 ... Current detector, 30 ... Current detector, COMP ... comparator,
OP...Arithmetic unit, S _A ...Alarm output signal.

Claims (1)

[Scope of Claims] 1. A power source configured such that a DC voltage including ripple obtained by rectifying an AC voltage or a pulse voltage is supplied to a smoothing circuit including a smoothing capacitor, and the smoothed voltage is supplied to a load. In the circuit, an inductance element is provided in the smoothing circuit, and a ripple current (ΔI _L ) flowing through the inductance element, a ripple current (ΔI _C ) flowing through the smoothing capacitor, and a load current (I _O ) is detected, and the difference (ΔI _L −ΔI _C ) between the ripple current (ΔI _L ) flowing through the inductance element and the ripple current (ΔI _C ) flowing through the smoothing capacitor, and the load current (I _O ) are detected. and the output ripple coefficient (γ=(ΔI _L −
Calculate ΔI _C )/I _O ) and find the output ripple coefficient (γ ^* ) of a normal smoothing capacitor set for the value of the load current (I _O ).
and the value of the output ripple coefficient (γ) obtained by measurement, and the deterioration state of the smoothing capacitor is determined from the correlation thereof.