JPH04161057A - Power supply provided with service life indicating function - Google Patents

Abstract

PURPOSE:To detect service life through a simple constitution with low cost by providing a constant voltage power supply circuit comprising a capacitor for smoothing a rectified output and a service life indicating circuit connected in parallel with a constant voltage power supply circuit. CONSTITUTION:AC voltage is fed from an input AC power supply 1 through a noise filter 2 to rectifying circuits 3, 43 thence to smoothing capacitors 4, 44. A constant voltage power supply circuit X comprising the smoothing capacitor 4 feeds a constant output voltage to a load 33 through output terminals 32A, 32 irrespective of the fluctuation of the input voltage. An output voltage V0 is applied through a brightness regulating resistor 34 onto an operation indicating LED 34 which then emits light with a predetermined brightness thus indicating the operation of the constant voltage power supply circuit X.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a power supply device with a lifespan display function that detects the lifespan of a power supply circuit that has the function of keeping an output voltage constant.

<Prior Art and Problems> Conventionally, there is a power supply device of this type as shown in FIG. 3. In the figure, 1 is an AC input, 2 is a noise filter (
NF), 3 is a rectifier circuit such as a bridge rectifier circuit, and 4 is a smoothing capacitor. 5 is a transformer, and a switching transistor 6 as a switching element is connected in series to an input winding 5a of the transformer. Reference numeral 7 represents a starting resistor for the switching transistor 6, and reference numeral 8 represents a resistor connected in series with the switching transistor 6.

A control circuit 9 is connected to the control winding 5b of the transformer 5 and controls the ON-OFF time ratio of the switching transistor 6 in accordance with the detection output of an output voltage detection circuit, which will be described later. For example, a limiting resistor 10 connected to the base of the switching transistor 6
A diode 11 is inserted between the resistor 10 and the control winding 5b, a speed-up capacitor 12 is connected in parallel to the diode 11, and a control transistor 1 is connected to the base of the switching transistor 6.
3. A capacitor 17 forming a series body connected in parallel to the control winding 5b with the resistors 14, 15 and the diode 16, and between the connection point of the diode 16 and the capacitor 17 and the resistor 15. The phototransistor 18 is inserted into the phototransistor 18.

19 is a rectifying diode connected to the output winding 5C of the transformer 5, and 20 is a smoothing capacitor. Reference numeral 21 denotes an output voltage detection circuit connected in parallel to the smoothing capacitor 20, which includes a voltage dividing circuit 22 and a detection comparison circuit 23. The voltage dividing circuit 22 includes a resistor 24 and a variable resistor 26.
It consists of a series body of . The detection comparison circuit 23 includes a resistor 27 and the phototransistor 18, and the photocoupler 2
A series body consisting of a light emitting diode 29 constituting 8 and a shunt regulator 30 that compares the internal reference voltage and the divided voltage of the voltage dividing circuit 22, and the shunt regulator 3.
0 and a capacitor 31 connected between the cathode and the reference. 32A and 32B are a pair of output terminals, and 33 is a load connected between the output terminals 32A and 32B. The above output terminal 32A.

A series body of a current limiting resistor 34 and an operation display light emitting element 35 is connected in parallel between 32B.

Next, the operation of the above configuration will be explained.

When the AC input voltage is converted to DC by the rectifier circuit 3 and the smoothing capacitor 4, and the base current flows into the switching transistor 6 through the starting resistor 7, this transistor 6 becomes ONL, and the input winding of the transformer 5 is first turned on. The wire 5a is energized, and from the control winding 5b, a speed-up capacitor 12, a diode 11, and a limiting resistor 10 are connected.
through which a larger current is supplied to the base of the switching transistor 6, which turns on the transistor 6.
become a state. The speed-up capacitor 12 is for supplying a steep current to the base of the switching transistor 6 in order to speed up the turn-on of the switching transistor 6, and has the effect of reducing the loss of the transistor 6 during switching operation.

When the switching transistor 6 is turned on, the collector current of the switching transistor 6 increases with a characteristic determined by the inductance of the input winding 5a of the transformer 5, but the voltage across the resistor 8 also increases, and the control voltage is passed through the resistor 14. Since the base current is supplied to the transistor 13, the transistor 13 is turned on. Therefore, the base current of the switching transistor 6 stops flowing, and the transistor 6 is turned off. By repeating the ON/OFF switching operation of the switching transistor 6, the DC voltage is converted into an AC voltage and output to the output winding 5c of the transformer 5. The alternating current voltage Vnl output to the output winding 5C is converted to direct current by the rectifying diode 19 and the smoothing capacitor 20, and the output voltage
0, which is supplied to the load 33 as the output current IO.

In the output voltage detection circuit 21, the shunt regulator 30 compares the voltage dividing point potential of the voltage dividing circuit 22 with an internal reference voltage, and a comparison difference signal is applied to the base of the control transistor 13 via the photocoupler 28. By this,
The switching operation of switching transistor 6 is controlled. That is, when the divided voltage becomes higher than the internal reference voltage of the shunt regulator 30, the shunt regulator 30 becomes conductive, the light emitting diode 29 emits light, and the phototransistor 18 becomes conductive. This reduces the ON time of the switching transistor 6 and keeps the output voltage vO constant.

Conversely, when the divided voltage is about to become lower than the internal reference voltage, the shunt regulator 30 is non-conductive and the light emitting diode 29 does not emit light, so the phototransistor 18 is also not conductive and the ON time of the switching transistor 6 is shortened. The output voltage vO is kept constant.

However, it is generally said that the lifespan of this type of power supply is determined by the degree of deterioration of the aluminum electrolytic capacitor built in as the smoothing capacitor 4, that is, the decrease in capacitance, and the output value is determined by the end of its lifespan. There is a possibility that a situation where the function as a power supply device cannot be performed due to the decrease may occur.

Additionally, the rate of deterioration of aluminum electrolytic capacitors is greatly influenced by the environmental temperature and humidity of the surrounding environment in which they are used.
It is extremely difficult to predict or visually recognize its deterioration state, as its speed does not change suddenly or its appearance changes. must be built-in, which is expensive.

<Object of the invention> This invention was made to solve the above problems,
It is an object of the present invention to provide a power supply device with a lifespan display function that has a simple configuration and can detect the lifespan at low cost.

<Configuration and Effects of the Invention> The power supply device according to the present invention includes a constant voltage power supply circuit having a smoothing capacitor for smoothing the rectified output obtained by rectifying alternating current with a rectifier circuit, and a constant voltage power supply circuit connected in parallel to the constant voltage power supply circuit. This lifespan display circuit comprises the above-mentioned alternating current rectifier circuit, a lifespan detection smoothing capacitor that smoothes the rectified output thereof and has characteristics equivalent to the above-mentioned smoothing capacitor, and this lifespan detection smoothing capacitor. The present invention includes a voltage detection circuit that detects that the smoothed voltage is below a predetermined reference voltage, and a lifespan display light emitting element whose brightness is variably controlled in accordance with the detected voltage of the voltage detection circuit. Features.

In the above configuration, it can be determined that the constant voltage power supply circuit has reached the end of its lifespan by visually recognizing a change in the brightness of the lifespan indicating light emitting element.

According to the above configuration, the lifespan of the constant voltage power supply circuit can be easily confirmed by the brightness of the light emitting element, and a decrease in the output of the power supply circuit due to the end of the lifespan of the smoothing capacitor can be easily and accurately detected. Furthermore, the measurement is simple and inexpensive.

<Explanation of Examples> Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an electric circuit diagram showing an example of a power supply device with a life display function according to the present invention, and this power supply device is composed of a constant voltage power supply circuit X and its life display circuit Y. Since this is the same as that shown in the conventional example, the same parts as in FIG.

That is, to the output terminal of the noise filter 2, a rectifier circuit 3 constituting the constant voltage power supply circuit X and a rectifier circuit 43 constituting the life display circuit Y are connected in parallel. Smoothing capacitor 44 made of an aluminum electrolytic capacitor with characteristics equivalent to capacitor 4
are connected in parallel.

The smoothing capacitor 44 includes a reference voltage generating circuit 47 consisting of a resistor 45 and a constant voltage element such as a Zener diode 46 in series, and a voltage dividing circuit 50 consisting of a series resistor 48 and 49. A voltage detection circuit 56 is constituted by a comparator circuit 51 connected in parallel and to which the divided potential V2 and the reference potential 3 are applied.

The comparison difference signal from the comparison circuit 51 is applied to the base of the control transistor 53 via the resistor 52, thereby controlling the switching operation of the switching transistor 53. A life display light emitting element 54 made of a light emitting diode is connected in series to the switching transistor 53 via a current limiting resistor 55, and this series body is connected in parallel to the smoothing capacitor 44.

Next, the operation of the above configuration will be explained.

The AC input voltage from the AC input power supply 1 is supplied to the rectifier circuit 3.43 via the noise filter 2 for removing noise, and converted to DC by the smoothing capacitor 4.44. The constant voltage power supply circuit X including the smoothing capacitor 4 operates in the same manner as that described in the conventional example, so that a constant output voltage is maintained at the output terminals 32A and 3 without being affected by fluctuations in the input terminal.
2 to the load 33, and its output voltage 0 is applied to the operation display light emitting element 34 via the brightness adjustment resistor 34, and by causing the light emitting element 34 to emit light at a predetermined brightness, the above-mentioned This indicates that the constant voltage power supply circuit X is in operation.

On the other hand, after the AC input voltage is full-wave rectified by the rectifier circuit 43, the output voltage v1 is smoothed by the smoothing capacitor 43.
When the waveform is as shown by the solid line in FIG. 2, the waveform of the divided potential v2 of the voltage dividing circuit 50 connected in parallel therewith becomes the attenuated waveform of the output voltage V1. Further, the divided potential (2) is compared with the reference potential V3 of the reference voltage generation circuit 47 in the comparator circuit 51, and at this time, V2>V3
Therefore, the output voltage v4 of the comparison circuit 51 is held at L level, and the control transistor 53 is held non-conductive. Therefore, the life display light emitting element 54 is in an off state.

On the other hand, as the smoothing capacitor 44 deteriorates due to surrounding environmental conditions, its initial capacitance Aμ
As F sequentially decreases, the waveforms of the output voltage V1 and the divided potential v2 become attenuated waveforms as shown by the virtual lines in FIG. 2, and when V2 < V3, the comparator circuit 51
The output voltage v4 of becomes H level, and each time the output voltage v4 becomes H level, the control transistor 5
3 repeats conduction (ON) and non-conduction (OFF), and the life display light emitting element 54 enters a blinking state.

However, in this blinking state, as the deterioration of the smoothing capacitor 44 progresses, the period (2)<V3 becomes progressively longer, and the period T4 during which the output voltage v4 of the comparison circuit 51 is at the H level also becomes longer. The above-mentioned light emitting element 5 for displaying the lifespan
Since the blinking period of 4 is too) lx or 120) 1z, which is twice that of the commercial power supply, the blinking state cannot be visually recognized, and the length of the lighting time of the light emitting element 54 is displayed as a change in brightness. be done. That is, as the deterioration of the smoothing capacitor 44 progresses, the brightness of the light emitting element 54 shifts to become brighter.

However, in this state, it only indicates that the smoothing capacitor 44 has deteriorated, and the constant voltage power supply circuit
It does not mean that it indicates the lifespan of the product. Therefore, how to match the above two will be explained below.

First, the initial capacitance of the aluminum electrolytic capacitor 4, which is the most important for the constant voltage power supply circuit X to exhibit the specified performance, is A.
μF and the terminal capacitance of the aluminum electrolytic capacitor 4 when the constant voltage power supply circuit The time T required for Kt to change from AμF to BμF can be calculated using Arrhenius' law.

Similarly, if the initial capacitance of the aluminum electrolytic capacitor 44 for life detection is CμF, then 1 at the ambient temperature Kt.
The capacitance DμF after a certain period of time can be calculated using Arrhenius' law.

Furthermore, the waveform of the divided potential V2 when the capacitance of the aluminum electrolytic capacitor 44 for life detection becomes CμF can be easily obtained by calculation or actual measurement, and the capacitance Cμ
F itself indicates the end of the life of the power supply circuit X.

Therefore, in order for the light emitting element 54 to have a predetermined brightness ELux when the capacitance CAtF is reached, the blinking period is adjusted by the reference potential v3 of the reference voltage generation circuit 47, and the current value is adjusted. When the brightness of the light emitting element 54 reaches ELux as determined by adjustment by the current limiting resistor 55, the end of the life of the power supply circuit X is displayed. The lifespan of the constant voltage power supply circuit X can be easily confirmed.

As is clear from the above, the lifespan of the constant voltage power supply circuit It is possible to easily and accurately detect a decrease in the output of the constant voltage power supply circuit X due to the end of its life, and the measurement is simple and inexpensive.

In particular, if the two capacitors 4 and 44 are set close to each other, the usage environmental conditions such as temperature and humidity will be the same, and even if the usage environmental conditions of the power supply vary, the aluminum electrolytic capacitor 4 will have a capacitance of AμF. The time required for deterioration from to BμF and the life of aluminum electrolytic capacitor 44
The time required for the capacitance C/, to deteriorate from 1F to DμF is always the same according to Arrhenius law, and the measurement accuracy can be maintained well.

Although the above embodiment describes the case where an aluminum electrolytic capacitor is used as the smoothing capacitor 4, the lifespan of the constant voltage power supply circuit Needless to say, the present invention is also applicable to detecting breaks.

[Brief explanation of drawings]

Fig. 1 is an electric circuit diagram showing an example of a constant voltage power supply circuit according to the present invention, Fig. 2 is a voltage waveform diagram for explaining the life display operation of the same circuit, and Fig. 3 is a configuration of a conventional constant voltage power supply circuit. FIG. 3.43... Rectifier circuit, 4... Smoothing capacitor, 4
4... Smoothing capacitor for life detection, 54... Light emitting element for life display, 56... Voltage detection circuit, X... Constant voltage power supply circuit, Y... Life display circuit, vl... Smoothing Voltage, v4...Detection voltage.

Claims (1)

[Claims] (1) Equipped with a constant voltage power supply circuit having a smoothing capacitor that smoothes the rectified output obtained by rectifying alternating current with a rectifier circuit, and a lifespan display circuit connected in parallel to this constant voltage power supply circuit, and this lifespan display circuit. The circuit consists of the above AC rectifier circuit, a life detection smoothing capacitor that smoothes the rectified output and has characteristics equivalent to the above smoothing capacitor, and a voltage smoothed by the life detection smoothing capacitor that is equal to or less than a predetermined reference voltage. It is equipped with a voltage detection circuit that detects a certain state, and a lifespan display light emitting element whose brightness is variably controlled according to the detected voltage of this voltage detection circuit, and the above constant voltage is controlled by changes in the brightness of this lifespan display light emitting element. A power supply device with a lifespan display function, characterized in that it is configured to determine the lifespan of a power supply circuit.