WO2018024035A1 - Indicating circuit for switching power supply, and using method therefor - Google Patents

Abstract

An indicating circuit for a switching power supply, and a using method therefor. The indicating circuit for a switching power supply comprises a terminal 1, 2, a resistor R1, a capacitor C1, a diode D1, and a light-emitting diode (LED). The LED and the D1 are reversely connected in parallel, then are connected in parallel to the R1, and then are serially connected to the C1. In the method, the indicating circuit is directly connected in parallel to a filter electrolytic capacitor CL in the switching power supply; the capacity of the C1 is small, a current of the great power frequency ripple caused by rectification and passing through the C1 is very small, and a voltage drop generated on the R1 is insufficient to light the LED; as the ESR of the CL increases, a voltage drop generated on the ESR by a high-frequency excitation current synchronously increases, and accordingly a formed high-frequency ripple voltage increases; the C1 has the high-frequency switching-on effect, and when the high-frequency ripple voltage on the ESR reaches a threshold, the LED is lit and emits light, and the threshold can be adjusted by adjusting the resistance of the R1. In this way, a user is reminded that the ESR of the filter capacitor has increased, and the switching power supply has the risk of ineffectiveness. The circuit has low costs and is easy to implement.

Description

Indication circuit for switching power supply and method of using same Technical field

The invention relates to an indication circuit and a method of using the same, and particularly relates to an indication circuit and a method of using the same at the end of the life of an electrolytic capacitor in a switching power supply.

Background technique

Switching power supplies are widely used. For applications where the input power is below 75W and the power factor (PF, Power Factor) is not required, the flyback power supply has a fascinating advantage: the circuit topology is simple. The input voltage range is wide. Many documents are also known as flyback switching power supplies and flyback power supplies. Japan and Taiwan are also known as flyback converters. Since the flyback power supply has few components, the reliability of the circuit is relatively high, and the application is wide. The common topology is shown in Figure 1. The prototype is from the "Switching Power Supply Converter Topology and Design", booked by Dr. Zhang Xingzhu, ISBN 978-7-5083-9015-4. The rectifier bridge 101, the filter circuit 200, and the basic flyback topology unit circuit 300 are generally referred to as a main power stage. The practical circuit is further provided with a varistor, an NTC thermistor, a fuse, and an X capacitor in front of the rectifier bridge. Protection circuits such as EMI (Electromagnetic Interference) to ensure that the electromagnetic compatibility of the flyback power supply meets the requirements for use.

The filter circuit 200 is generally constituted by an electrolytic capacitor CL or the like, and the electrolytic capacitor CL is hereinafter simply referred to as electrolytic CL. With the promotion of intelligent systems in the industrial field, low-power flyback power supplies penetrate into various fields, and their shortcomings are also manifested, because the use of electrolytic CL limits the use of the flyback power supply of Figure 1, electrolytic capacitors The life at high temperature and low temperature has always been a problem in the industry. As we all know, the capacitor CL is often a 400V withstand voltage electrolytic capacitor, while the electrolytic capacitor with a withstand voltage greater than 250V can only work at -25 °C. That is, in the environment of -40 ° C, such as the three provinces of Northeast China, Xinjiang, and countries and regions at high latitudes, the use of low-power flyback power supplies has become tricky. Of course, filters such as CBB film capacitors can be used, but the volume is too large. And the cost is too high.

The capacity of electrolytic capacitors per unit volume is very large, so in the field of switching power supplies including flyback power supplies, especially in the field of AC input, it is still a low-cost solution, which is widely used in various power sources, such as various mobile phones. Charging Devices, laptop adapters, power supplies for various color TVs, power supplies for desktop computers, standby power supplies for air conditioners, etc., all use switching power supplies, and also use electrolytic capacitors.

When the electrolytic capacitor is used as an input rectifying filter capacitor in the flyback power supply, the ripple current is: charging is a low frequency ripple DC current, the discharge is a high frequency ripple current discharge, and the high frequency ripple current is derived from the excitation current of the main power stage. .

When designing a switching power supply, it often faces the life of electrolytic CL, and its life is generally based on withstand voltage, equivalent series resistance (ESR, which is the abbreviation of Equivalent Series Resistance), ripple current (Ripple current), loss angle ( Determined by factors such as tgδ), especially the maximum ripple current, also known as the maximum allowable ripple current, ie the rated ripple current (IRAC), which is defined as the maximum AC ripple that the capacitor can withstand at the highest operating temperature. Wave current rms value. And the specified ripple current is the absolute value of the sine wave of the standard frequency (typically 100Hz-120Hz).

In actual use, many flyback power supplies do not reach the service life. The main reason is that the electrolytic capacitors used for filtering fail in advance. In many occasions with high requirements, redundant design is adopted, and two switching power supplies are used for backup. One, it can work normally, but the cost is high, and still do not know when the switching power supply is bad.

Even in other applications, such as high-power switching power supply with PFC function, first rise from BOOST circuit to 380V, charge the electrolytic capacitor for filtering, get smooth DC, and then double-tube forward or LLC converter Power supply, too, the failure of the electrolytic capacitor can not be early warning.

Common non-redundant design occasions, once the switching power supply fails, will cause a lot of associated failure, so that the loss is expanded. According to statistics, the switching power supply fails, more than 97% is caused by the first failure of the filtered electrolytic capacitor.

In the application number 201610040378.3 "A switching power supply indicating circuit and its use method", an indicating circuit is provided. When the filtering electrolytic capacitor in the switching power supply fails, an indication is provided to solve the problem, and the problem is solved. The LED is connected in parallel with the inductor L. When the ESR of the electrolytic capacitor rises greatly, the exciting current of the main power stage appears in the inductor L, and when the switching tube is turned off in the switching power supply, the exciting current flowing through the inductor L cannot be changed. After the LED is continuously flowed, the LED is illuminated at the same time. The circuit is simple, but the inductor L is used. The inductor is subjected to the peak voltage of the alternating current at the start of the machine, and the charging current of the first several times of charging the electrolytic capacitor, that is, the withstand voltage of the inductor is high, the operating current is large, and the cost is high. Relatively speaking, it is not low.

At the same time, the circuit should be connected in series with the power frequency charging circuit of the filter electrolytic capacitor, and the original circuit should be modified.

Summary of the invention

In view of this, the present invention provides an indicating circuit and a method for using the same, which does not use an inductor with high withstand voltage and large current, and provides an indication before the filter electrolytic capacitor fails in the switching power supply, and the original switching power supply is less modified.

The first aspect of the invention provides a first circuit, comprising a first terminal, a second terminal, a first resistor, a first capacitor, a first diode and a first LED, a first resistor and a first diode and The first component of the first LED is connected in parallel, wherein the first LED and the first diode are connected in anti-parallel. The two-terminal network formed in parallel is referred to as a parallel network, and the terminal of the parallel network is an anode of the first diode. The cathode of the first diode is distinguished, and the parallel network is connected in series with the first capacitor to form a two-terminal network in series. The two-terminal network in series is simply referred to as a series network, and the two terminals of the series network are respectively One terminal and two terminals.

The invention further provides a second embodiment of the indication circuit, comprising: a first terminal, a second terminal, a first resistor, a second resistor; a first capacitor, a second capacitor; a first diode and a second diode, And a first light emitting diode; the connection relationship is: the second resistor is connected in series with the first light emitting diode to form a first network having two terminals, and the first network and the second capacitor are simultaneously connected in parallel with the first resistor to form a second terminal a second network, the second network is further connected in series with the second diode to form a third network having two terminals, the third network is characterized in that the second diode and the first light emitting diode are in the same direction; the third network and the third A diode is connected in anti-parallel to form a fourth network having two terminals. The fourth network is connected in series with the first capacitor and forms a two-terminal network in series. The serial two-terminal network is simply referred to as a series network, and is connected in series. The two terminals of the network are a first terminal and a second terminal, respectively.

Preferably, the first scheme and the second scheme are characterized in that: the first light emitting diode is an illuminator in the optocoupler, that is, the light emitting diode in the optocoupler.

The invention also provides a method for using the above-mentioned scheme 1, scheme 2, and preferred scheme, which is used in the following manner: the indication circuit is directly connected in parallel with the filter electrolytic capacitor in the switching power supply.

The working principle will be explained in detail in combination with the embodiment.

The beneficial effects of the invention are:

The cost is extremely low, the insertion loss is low, and the efficiency of the original switching power supply is hardly affected. The wiring is simpler, the volume is smaller, and the use is convenient; the indication function is also provided: the indicator LED emits light before the electrolytic capacitor fails. Or the light-emitting diode in the optocoupler has a current flowing through, and the optocoupler outputs an isolated signal to prompt the user or the circuit to replace the electrolytic capacitor for filtering or replace the switching power supply before the switching power supply fails, thereby allowing the system to work normally. .

DRAWINGS

Figure 1 is a common topology of a flyback switching power supply in the prior art;

2-1 is a schematic diagram of a first embodiment of a first embodiment of the present invention;

2-2 is a schematic diagram showing an equivalent implementation of the first embodiment of the first embodiment of the present invention;

2-3 is a schematic diagram of an equivalent implementation of the first embodiment of the first embodiment of the present invention;

2-4 is a schematic diagram of an equivalent implementation of the first embodiment of the first embodiment of the present invention;

2-5 are schematic diagrams showing an equivalent implementation of the first embodiment of the first embodiment of the present invention;

2-6 are schematic diagrams showing an equivalent implementation of the first embodiment of the first embodiment of the present invention;

3-1 is a schematic diagram of a second embodiment corresponding to the second embodiment of the present invention;

3-2 is a schematic diagram of an equivalent implementation of the second embodiment corresponding to the second embodiment of the present invention;

3-3 is a schematic diagram of an equivalent implementation of the first embodiment corresponding to the second embodiment of the present invention;

3-4 is a schematic diagram of an equivalent implementation of the first embodiment corresponding to the second embodiment of the present invention;

4 is a schematic diagram of a method for using the first and second aspects of the present invention;

5 is a schematic diagram of a path of a charging current generated by the rectifier bridge 101;

6 is a timing diagram of a switching transistor driving voltage and an exciting current i _{M in a} main power stage of a flyback power supply;

7 is a schematic diagram of a path of an exciting current i _M in a main power stage of a flyback power supply;

Figure 8 is a schematic diagram of the excitation current i _M producing high frequency ripple on the ESR of the electrolytic CL.

detailed description

First embodiment

Referring to FIG. 2-1, corresponding to the first scheme, an indicating circuit includes a first terminal 1, a second terminal 2, a first resistor R1, a first capacitor C1, a first diode D1, and a first LED. The first resistor R1 is connected in parallel with the first diode D1 and the first LED, wherein the first LED and the first diode D1 are connected in anti-parallel, and the two-terminal network formed in parallel is referred to as parallel connection. The network 24, the terminals of the parallel network 24 are distinguished by the anode of the first diode D1 and the cathode of the first diode D1, and the parallel network 24 is connected in series with the first capacitor C1 to form a two-terminal network in series. The two-terminal network in series is simply referred to as a series network, and the two terminals of the series network are the first terminal 1 and the second terminal 2, respectively, and the series network is also the main body of the indication circuit for the switching power supply of the present invention.

In anti-parallel connection, it is meant that the anode of the first diode D1 is connected to the cathode of the first LED, while the cathode of the first diode D1 is connected to the anode of the first LED.

The first capacitor C1 is hereinafter referred to as C1, and the first resistor R1 is hereinafter referred to as R1. The first LED is hereinafter referred to as LED, and other devices are similar.

C1 and the parallel network 24 are connected in series. Since they are series circuits, the functions are the same after the positions are interchanged. Therefore, the scheme 1 includes a plurality of series, but the functions are the same, as follows:

(a) The cathode of D1 is downward, C1 is on the upper side, as shown in Figure 2-1, the anode of D1 is connected to one end of C1, the other end of C1 is the first terminal 1 of the indicating circuit, and the cathode of D1 is the indicating circuit. One terminal 2;

(b) The cathode of D1 is downward, C1 is below, as shown in Figure 2-2, the cathode of D1 is connected to one end of C1, the anode of D1 is the first terminal 1 of the indicating circuit, and the other end of C1 is the indicating circuit. Two terminals 2;

(c) the cathode of D1 is upward, C1 is on the upper side, as shown in Figure 2-3, the cathode of D1 is connected to one end of C1, the other end of C1 is terminal 1 of the indicating circuit; the anode of D1 is terminal 2 of the indicating circuit; This is exactly the same as the method of Figure 2-2 of (b) above, the terminal 1 of the (b) mode is equal to the terminal 2 of (c), the terminal 2 of the (b) mode is equal to the terminal 1 of (c), That is, the terminals 1 and 2 of Fig. 2-3 are interchanged, which is completely the same as (b) of Fig. 2-2;

(d) the cathode of D1 is up, C1 is below, as shown in Figure 2-4, the anode of D1 is connected to one end of C1, the other end of C1 is terminal 2 of the indicating circuit; the cathode of D1 is terminal 1 of the indicating circuit; This is exactly the same as the above-mentioned (a) of FIG. 2-1. The terminal 1 of the (a) mode is equal to the terminal 2 of (d), and the terminal 2 of the (a) mode is equal to the terminal 1 of (d). That is, the 1 and 2 of the (d) mode are interchanged, and are completely the same as (a) of FIG. 2-1.

That is, the only effective connection method is only the above (a) of FIG. 2-1 and (b) of FIG. 2-1. The capacitor C1 and the network 24 are connected in series. Since the circuit is a series circuit, the functions of the device are the same after the position is interchanged. In the well-known technique, the method of (b) of Fig. 2-2 is to interchange the position C1 of the mode (a) of Fig. 2-1 with the network 24, that is, essentially, (a) and Fig. 2-1 of Fig. 2-1. The way (b) is equivalent. That is, the technical solution 1 includes the above four connection methods.

In addition, the capacitor C1 can be obtained by connecting two capacitors in series. Then, the capacitor C1 of FIG. 2-1 is replaced by a capacitor C1a and C1b in series, and the embodiment of FIG. 2-5 is obtained, and the circuit of FIG. 2-1 and FIG. 2 The circuit of 5 is equivalent. As described above, the series loops have the same function after the device interchanges the position. Further, the capacitor C1b and the network 24 are interchanged to obtain the embodiment shown in Figs. 2-6.

The LED is Φ3mm red highlighted. For convenience, the LED is referred to as the LED, the model is 3AR2UD, the capacitor C1 is 333/500V chip capacitor, the nominal capacity is 0.033uF, D1 is 1N4148, R1 is 22K chip resistor, according to Figure 2-1 constitutes the switching power supply indicating circuit, its use method is: Figure 2-1 indicates that the circuit is directly connected with the filter electrolytic capacitor in the switching power supply, forward parallel or reverse parallel Yes, forward parallel: that is, terminal 1 is connected to the positive pole of the filter electrolytic capacitor, terminal 2 is connected to the negative pole of the filter electrolytic capacitor; or reverse parallel: terminal 1 is connected to the negative pole of the filter electrolytic capacitor, and terminal 2 is connected to the positive pole of the filter electrolytic capacitor.

The switching power supply uses a 25W flyback power supply. The filter electrolytic capacitor is 47uF/400V, which is a domestic high-quality capacitor. The rectifier bridge is composed of four 1N4007. The working frequency is 65KHz. Under 220VAC input, the maximum duty cycle of full load is 0.24.

When the first embodiment is soldered into the flyback power supply in a forward parallel manner, all aspects of the measured flyback power supply are the same as before, especially the conversion efficiency, no observed drop, and the LED of the LED is not Glowing.

In order to verify that the invention is operational, the inventors have used the previously pioneered method to test the first embodiment:

Since the failed electrolytic capacitor is difficult to obtain, in the above-mentioned filter electrolytic capacitor, an adjustable resistor is connected in series to simulate an electrolytic capacitor whose performance has been lowered. The adjustable range of the adjustable resistor here is 0-39 Ω. When the resistance of the adjustable resistor is adjusted to 5 Ω, the ESR of the electrolytic capacitor equivalent to 47uF/400V has risen to about 5.5 Ω from 0.5 Ω at the time of good product, and the performance of the electrolytic capacitor is close to the edge that cannot be used.

At this time, the LED of FIG. 2-1 emits light, and the average value of the operating current is actually measured to be 1.6 mA.

By selecting capacitors C1 of different capacities, the sensitivity of the indication is initially adjusted, the capacity of the capacitor C1 is small, and the sensitivity is low; the capacity of the capacitor C1 is large and the sensitivity is high. Since the light-emitting tube emits light with a forward voltage drop of 1.6V to 2.2V, the resistance R1 can be connected in parallel with the LED of the LED to adjust the sensitivity. In this example, if R1 uses a resistance of 1.6K, then 1mA or less. The peak current produces a voltage of less than 1.6V across R1, at which point the LEDs do not illuminate.

Note: The conduction voltage drop of the white light-emitting tube is about 3.0V, the red color is different from the green color, and the illuminator conduction voltage drop inside the photocoupler is about 1.1V.

Working principle: Referring to Figure 4, when the electrolytic capacitor is normal, then its ESR is 0.5Ω, and there are two kinds of ripple voltages at both ends of the filtering electrolytic CL, as an example when the switching power supply is fully loaded.

When the electrolysis CL is normal, the four diodes in the rectifier bridge 101 only turn on the two diodes inside the rectifier bridge when the input AC power is close to the peak, and supplement the electric energy to the electrolysis CL. This rectification method is in the authorization bulletin number CN102594175B. The background art is described in detail, especially in the introduction of paragraph 0010.

The path of the charging current generated by the rectifier bridge 101 is shown in Fig. 5. One end of the AC input terminal passes through one end of the rectifier bridge 101, to the output + of the rectifier bridge 101, to the positive terminal of the electrolytic CL and the first terminal of the indicating circuit, from the negative electrode of the electrolytic CL. And the second terminal of the indicating circuit flows out, and the output to the rectifier bridge 101 flows out from the other terminal of the rectifier bridge 101 to the other end of the AC input terminal.

In this process, the charging current frequency is twice that of the commercial power, 100Hz or 120Hz. Since the C1 capacity is small, it is 0.033uF. Compared with the 47uF of CL, the charging current in C1 is only 7/7 of the CL. The peak value of the charging current of CL is 2.39A, then the charging current flowing through D1 is only 1.67 mA. At this time, the LED does not emit light due to the reverse bias.

Before the next charging cycle, the CL always discharges the main power stage, and the voltage at the CL terminal is always falling until 10mS or 8.33mS, so that the two ends of the CL form a low frequency pattern twice the mains frequency. The wave has a peak-to-peak value of around 20V. When the capacity of C1 is large enough, this low frequency ripple can form enough current in C1 to illuminate the LED. Therefore, to ensure the current formed by the low frequency ripple in C1, the voltage drop formed across the resistor R1 is less than The conduction voltage drop of the LED.

The capacitance of 0.033uF is about 48KΩ for the 100Hz AC ripple, and the effective value of the low-frequency triangular ripple with peak-to-peak value of about 20V is about 10V. Then, the low-frequency ripple current flowing through C1 is about 0.20mA. The peak value is 0.40mA, R1 is 22K, and the voltage drop should be 8.8V. In fact, the LED also does not emit light. See Figure 4. When the mains charges the CL, there is a synchronous charging current flowing through D1, and when CL When the terminal voltage drops, C1 discharges to CL, forming a discharge current, the charging time is short, the discharge time is very long, the charging is generally completed within 1 mS, and the discharge time is close to one charging cycle, close to (10mS-1mS)=9mS, due to continuous The time is long and the peak current during this time is extremely low. C1 discharges to CL by the upper end of C1 → the positive electrode of CL → the negative electrode of CL → the cathode of D1, that is, the lower end of R1 → the upper end of R1, that is, the anode of D1 → the lower end of C1; the integral sum of C1 to CL discharge is equal to The mains charges the C1 charge, and the discharge time is long, the current is almost constant, so the current is small, and this current passes through the two ends of R1, resulting in a low voltage drop.

R1 resistance value selection, to ensure that the low-frequency ripple current through C1, the LED does not emit light, there is a small trick here: when the rectifier bridge 101 charges the CL, this charging current flows directly through D1, not through the LED, to ensure The LED does not emit light.

When the electrolytic CL is normal, as described above, the 47uF/400V electrolytic capacitor has an ESR of 0.5 Ω at 65 kHz, that is, when the switching transistor V operates normally, the exciting current i _{M of the} main power stage is as shown in FIG. 6 , wherein Ugs is the driving voltage of the gate and source of the switching transistor V, and the path of the exciting current i _{M is shown} in FIG. 7 .

When the rectifier bridge 101 is not conducting, the discharge currents of the electrolysis CL and C1 to the main power stage are exactly equal to the excitation current i _{M of the} main power stage. Note that C1 is too small for the discharge current of the main power stage, which can be ignored here. The capacitive reactance of electrolytic CL at the switching frequency of 65KHz is 1/(2πfC), which is calculated to be 52mΩ, which is much smaller than its ESR. At 65KHz, ESR plays a major role; the waveform shown in Figure 6 is not a sine wave, its fundamental wave It is a sine wave, and its harmonic frequency is higher than 65KHz, so here is only an estimate.

The 25W flyback power supply operates at 65KHz and has a maximum duty cycle of 0.24 at 220VAC input. The excitation current i _{M of the} main power stage is about 408 mA when the switching transistor V is turned on, and the peak value is about 816 mA. The voltage drop formed by this current on the ESR of the CL, see FIG. 8, is U=IR=0.816× 0.5 = 0.408V. That is, in Fig. 8, there is a fluctuating high-frequency ripple between the terminals 1 and 2, and the waveform shape is the same as the waveform of i _M in Fig. 6, and it is apparent that the peak of 0.408 V is insufficient for the LED to be turned on to emit light.

When the ESR of the electrolytic CL has risen to about 5.5 Ω from about 0.5 Ω, that is, the electrolytic CL has approached the failure edge. If the peak value of i _M is about 816mA when the switching transistor V is turned on, the voltage drop formed by this current on the ESR of the CL, see FIG. 8, is U=IR=0.816×5.5=4.48V. That is, in Fig. 8, there is a fluctuating high-frequency ripple between the terminals 1 and 2, and the waveform shape is the same as the waveform of i _M in Fig. 6, and it is apparent that the peak of 4.48 V is sufficient for the LED to be turned on to emit light.

C1 is 0.033uF, which has a small capacity, but its capacitance is 73.8Ω at a frequency of 65KHz, which can provide sufficient operating current for the LED to emit light.

The working principle of the invention is not complicated, the capacity of the C1 is small, the C1 has the function of passing high frequency and blocking low frequency; the current of the power frequency large ripple caused by the rectifier circuit is extremely small through the C1, and the voltage drop generated on the resistor R1 is insufficient. In order to illuminate the LED, and as the ESR of the electrolytic CL rises, the voltage drop generated by the high-frequency excitation current of the switching power supply on the ESR rises synchronously, and the formed high-frequency ripple voltage rises as the electrolytic capacitor ages, C1 With the function of high frequency, when the high frequency ripple voltage on the ESR reaches a certain threshold, it will illuminate the LED and emit light. Adjusting the resistance of R1 can adjust the threshold value, that is, the high frequency ripple voltage passes through the capacitor C1. The current formed at the ends of R1 is lowered by the conduction voltage of the LED, the LED is not turned on, and the LED cannot be shunted for R1 to emit light.

The value of C1: The power frequency of the mains is 2 times up to 120Hz. At present, the working frequency of the switching power supply is generally 22KHz outside the audible audio. Then, the ratio of the frequency is (22000/120)=183.3 times, C1. Value in One or more than 183.3 minutes of the electrolytic capacitor CL to be monitored may be used. If CL is 47uF, then C1 should be below (47uF/183.3)=0.256uF. Since the nominal value of the capacitor is in the series of E-3, E-6, E-12, etc., it can be taken below 0.24uF. .

In this way, the LED of the LED is driven to achieve the purpose of the invention, and the user is reminded that the ESR of the electrolysis CL has risen to the point of interest so that the user can decide the next step. In this example, the load on the switching power supply is reduced to 30%, the LED is still illuminated, and the operating current is reduced to 0.36 mA. The use of high-brightness LEDs is still very conspicuous.

At this point, the electrolytic capacitor can still work, but because the excitation current of the main power stage has a large heat generation on the ESR, in this case 0.22W, the electrolytic capacitor is already under high heat, which is already accelerating aging, general situation Under the tens of hours to hundreds of hours, the ESR rises rapidly, causing the heat to further increase until the failure, the capacity is lost, causing a series of failures such as the explosion of the switch tube.

The circuit of FIG. 2-2, the circuit of FIG. 2-3, and the circuit of FIG. 2-4 are replaced by the indicating circuit 12 of FIG. 4, and the resistance of R1 in FIG. 2-3 and FIG. 2-4 is required. Take small, otherwise, the charging current generated by the rectifier bridge 101 when the alternating current reaches a peak will illuminate the LED. It can be seen that the four circuits of the first embodiment can achieve the object of the invention.

As mentioned above, capacitor C1 can be obtained by connecting two capacitors in series. The circuit of Figure 2-1 is equivalent to the circuit of Figure 2-5. Capacitor C1 of Figure 2-1 is replaced by series capacitors C1a and C1b. In the embodiment of Figures 2-5, the capacitor C1b and the network 24 are interchanged to provide the embodiment illustrated in Figures 2-6. The embodiment shown in FIG. 2-6 has the advantages that when the switching frequency of the power source is relatively high, the capacitors C1a and C1b are respectively on the upper side and the lower side, and the capacity is small, and the electrical isolation between the light emitting diode and the switching power supply can be realized. The frequency of electricity is low, and the leakage current through the capacitors C1a and C1b is easily controlled below the limit value.

In fact, in the content of the first embodiment, six implementation modes are included, and in order to save space, only one general "first embodiment" is summarized. In the first embodiment, the current flowing through the LED of the light-emitting tube is not a direct current, but a high-frequency current of the same frequency as the switching power supply. When the lead of the LED is long, the electromagnetic radiation cannot be ignored; the LED of the light-emitting tube is replaced by an optical coupler. In the case of an illuminator, the output current of the optocoupler also appears periodically, not a stable signal, which causes trouble for subsequent circuits. The second embodiment shows a solution.

Second embodiment

Referring to FIG. 3-1, corresponding to the foregoing solution 2, an indication circuit includes a first terminal 1, a second terminal 2, a first resistor R1, and a second resistor R2; a first capacitor C1 and a second capacitor C2; a diode D1 and a second diode D2, and a first LED; the connection relationship is: the second resistor R2 is connected in series with the first LED, forming a first network 21 having two terminals, the first network 21 Simultaneously parallel with the second capacitor C2 and the first resistor R1 to form a second network 22 having two terminals, the second network 22 is further connected in series with the second diode D2 to form a third network 23 having two terminals, the third network 23 is characterized in that the second diode D2 and the first light emitting diode LED are in the same direction; the third network 23 is connected in anti-parallel with the first diode D1 to form a fourth network 24 having two terminals, and the fourth network 24 Then connected in series with the first capacitor C1, and form a two-terminal network in series. The two-terminal network in series is simply referred to as a series network, and the two terminals of the serial network are the first terminal 1 and the second terminal 2, respectively. The network is also the main body of the indicating circuit for the switching power supply of the present invention.

The second diode D2 and the first LED are in the same direction: in the third network 23, assuming that R1 is open, and capacitor C2 is equivalent to an open circuit for DC, then the current flowing from the lower end of the third network 23 passes through After the LED, it passes through D2 and flows out from the upper end of the third network 23. D2 and the LED are both in a forward conduction state, and this serial connection is called the same direction. Both D2 and LED are in a forward conduction state, which is equivalent to a diode with a larger voltage drop. Its cathode is the cathode of the third network 23. The direct current can flow out from the cathode of the network, and its anode is the third network. The anode, DC current can flow inward from the anode of the network.

The third network 23 is connected in anti-parallel with the first diode D1, that is, the third network 23 is connected to the anode of D1, and the anode of the third network 23 is connected to the cathode of D1.

In the second technical solution mentioned above, a plurality of connection relationships are included, as described below.

There are two connection methods for R2 and LED in series in network 21:

(a) the cathode of the LED is connected to one end of R2, as shown in network 21 in Figure 3-1;

(b) the anode of the LED is connected to one end of R2, as shown in network 21 in Figure 3-2;

These two are equivalent. Network 21 and C2 and R1 are simultaneously connected in parallel to form a network 22 having two terminals, and network 22 is connected in series with diode D2. In network 22, assuming that R1 is open, capacitor C2 is equivalent to an open circuit for direct current, then network 22 is equivalent to one. Only the diode has unidirectional conductivity. The side of the cathode of the LED is the cathode of the second network 22. The direct current can flow out from the cathode of the network. The anode on the side of the LED is the anode of the third network 23, and the DC current. It can flow inward from the anode of the network. Since it is limited to the same direction, there are two ways for network 22 and D2:

(a) the cathode of network 22 is connected to the anode of D2, see Figure 3-1;

(b) the anode of network 22 is connected to the cathode of D2, see Figure 3-3;

The fourth network 24 is in series with the first capacitor C1, and there are also two ways:

(a) The D1 anode of network 24 is connected to one end of C1, as shown in Figure 3-1;

(b) The D1 cathode of network 24 is connected to one end of C1, as shown in Figure 3-2;

As in the first embodiment, in the second embodiment, three independent series, each of which has two modes, a total of two to the third power, a total of eight connection modes, in fact, they are equivalent.

Working principle: Referring to Figure 3-1, and Figure 4, the indicating circuit 12 of Figure 4 is replaced by Figure 3-1. When the electrolytic capacitor CL is normal, then the ESR is 0.5Ω, and the ripple at both ends of the filter is used. There are two kinds of voltages: one is the low frequency ripple of twice the mains frequency, and the other is the high frequency ripple generated by the high frequency excitation current of the switching power supply on the ESR.

C1 has a small capacity. At a low frequency twice the mains frequency, the capacitive reactance is large, and the current flowing through C1 is extremely small. After D2 rectification, after C2 filtering, the voltage formed at both ends of R1 is insufficient to illuminate the LED.

As the ESR of the electrolytic CL rises, the voltage drop generated by the high-frequency excitation current of the switching power supply rises synchronously on the ESR, and the formed high-frequency ripple voltage rises with the aging of the electrolytic capacitor, and C1 has a high-frequency pass. Function, when the high-frequency ripple voltage on the ESR reaches a certain threshold, after D2 rectification, after C2 filtering, the voltage formed at both ends of R1 is enough to illuminate the LED, and R2 acts as a current limiting function.

In this way, the current flowing through the LED of the LED is pure DC, and its electromagnetic radiation is directly reduced to zero. When the LED is replaced by an illuminator in the optocoupler, the output current of the optocoupler is also an extremely stable DC signal. Facilitate the subsequent circuits.

The component parameters are: C1 is 473/500V chip capacitor, nominal capacity is 0.047uF, C2 is 104/16V chip capacitor, D1 and D2 are 1N4148, R2 is 1K, R1 is 10K, LED is 3AR2UD.

When the load of the switching power supply is 100%, when the ESR of the electrolytic CL rises to 5.5Ω, the current in the LED is 0.9mA; the load of the switching power supply is reduced to 30%, the LED still emits light, and the operating current is reduced to 0.33mA. The brightness of the tube is still very eye-catching. In this way, the LED of the LED is driven to achieve the purpose of the invention, and the user is reminded that the ESR of the electrolysis CL has risen to the point of interest so that the user can decide the next step.

In fact, the resistor R1 is connected in parallel with C2 as shown in Figure 3-4, and is connected in parallel with D1. The same purpose is achieved. R1 can also adjust the threshold value. The technical solution is no longer used here to protect the rights.

The circuit of FIG. 3-2, the circuit of FIG. 3-3, and the circuit of FIG. 3-4 can be replaced by the indicating circuit 12 of FIG. 4, and the peak current can be absorbed by C2, and the rectifier bridge 101 reaches the peak when the alternating current reaches the peak. The generated charging current does not illuminate the LED. The performance of the circuit is further improved. It can be seen that the four circuits of the eight modes of the second embodiment can achieve the object of the invention.

The above is only a preferred embodiment of the present invention, and it should be noted that the above preferred embodiments are not to be construed as limiting the invention. It will be apparent to those skilled in the art that a number of modifications and refinements can be made without departing from the spirit and scope of the invention, such as stringing resistors in the first diode. These improvements and finishes should also be The scope of protection of the present invention is not to be construed as being limited to the scope of the present invention. The scope of the present invention should be determined by the scope defined by the appended claims.

Claims (6)

An indicating circuit for a switching power supply, comprising: a first terminal, a second terminal, a first resistor, a first capacitor, a first diode and a first light emitting diode, a first resistor and a first diode and The first component of the first LED is connected in parallel, wherein the first LED and the first diode are connected in anti-parallel. The two-terminal network formed in parallel is referred to as a parallel network, and the terminal of the parallel network is an anode of the first diode. The cathode of the first diode is distinguished, and the parallel network is connected in series with the first capacitor to form a two-terminal network in series. The two-terminal network in series is simply referred to as a series network, and the two terminals of the series network are respectively One terminal and two terminals. The indicating circuit for a switching power supply according to claim 1, wherein the first light emitting diode is an illuminator in the optocoupler, that is, a light emitting diode in the optocoupler. An indication circuit for a switching power supply, comprising: a first terminal, a second terminal, a first resistor, a second resistor; a first capacitor and a second capacitor; a first diode and a second diode; a first light emitting diode; the connection relationship is: the second resistor is connected in series with the first light emitting diode to form a first network having two terminals, and the first network and the second capacitor are simultaneously connected in parallel with the first resistor to form a second terminal having two terminals a network, the second network is further connected in series with the second diode to form a third network having two terminals, the third network is characterized in that the second diode and the first light emitting diode are in the same direction; the third network and the first The diodes are connected in anti-parallel to form a fourth network having two terminals, and the fourth network is connected in series with the first capacitor, and forms a two-terminal network in series. The serial two-terminal network is simply referred to as a series network, a serial network. The two terminals are respectively a first terminal and a second terminal. The indicating circuit for a switching power supply according to claim 3, wherein the first resistor is changed in parallel with the first diode. The indicating circuit for a switching power supply according to claim 3, wherein the first light emitting diode is an illuminator in the optocoupler, that is, a light emitting diode in the optocoupler. The method of using a indicating circuit for a switching power supply according to any one of claims 1 to 5, characterized in that the indicating circuit is directly connected in parallel with the filtering electrolytic capacitor in the switching power supply.

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