WO2018024037A1 - 一种直接滤波式开关电源 - Google Patents

一种直接滤波式开关电源 Download PDF

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Publication number
WO2018024037A1
WO2018024037A1 PCT/CN2017/088005 CN2017088005W WO2018024037A1 WO 2018024037 A1 WO2018024037 A1 WO 2018024037A1 CN 2017088005 W CN2017088005 W CN 2017088005W WO 2018024037 A1 WO2018024037 A1 WO 2018024037A1
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Prior art keywords
network
capacitor
parallel
circuit
series
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PCT/CN2017/088005
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English (en)
French (fr)
Inventor
王保均
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广州金升阳科技有限公司
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Publication of WO2018024037A1 publication Critical patent/WO2018024037A1/zh

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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • H02M1/143—Arrangements for reducing ripples from dc input or output using compensating arrangements
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33507—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters
    • H02M3/33523—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only with automatic control of the output voltage or current, e.g. flyback converters with galvanic isolation between input and output of both the power stage and the feedback loop
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only

Definitions

  • the invention relates to the field of switching power supplies, in particular to a switching power supply with high reliability alternating current or direct current conversion to direct current.
  • the rectifier bridge 101, the filter circuit 200, and the basic flyback topology unit circuit 300 are also referred to as the main power stage.
  • the practical circuit is also provided with a varistor, an NTC thermistor, and an EMI (Electromagnetic Interference) in front of the rectifier bridge. ) Protect the circuit to ensure that the electromagnetic compatibility of the flyback power supply meets the requirements for use.
  • the rectifier bridge 101 is generally composed of four rectifier diodes.
  • Figure 4-1, Figure 4-2, and Figure 4-3 of the authorized invention specification of the application No. 201210056555.9 show several well-known drawing methods of the rectifier bridge;
  • the filter circuit 200 generally It is composed of electrolytic CL.
  • the "electrolytic capacitor” is hereinafter referred to as “electrolysis” for short; for better EMI performance, a high-voltage small-capacity capacitor with high-frequency characteristics is usually connected in parallel at both ends of the electrolytic CL; main power level 300 Including many devices, here only power transformer B, main power switch V, generally MOS tube, output rectifier diode D, output filter capacitor C, power transformer B in flyback topology is actually energy storage inductor, main power
  • the stage 300 actually includes many circuits, such as a DCR circuit for absorbing the anti-peak voltage of the MOS tube, a PWM control circuit, an optocoupler feedback circuit, and even an active clamp circuit, and the main topology is not limited to the flyback circuit, and may be double Tube flyback circuit, half bridge converter, etc.
  • the main power stage is more than 300 positive.
  • the two-tube forward is a popular saying in the industry, actually a half-bridge converter; the rectifier bridge 101 does not even have a power factor correction inductor, that is, after rectification and filtering, power is supplied to the half-bridge converter.
  • the main power stage 300 is also implemented using a single-tube forward and asymmetric half-bridge.
  • the power factor correction inductor is serially connected to the rectifier bridge 101, and is still passive filter power factor correction, not active power factor correction.
  • the filter circuit 200 is generally composed of an electrolytic capacitor CL.
  • electrolytic CL electrolytic capacitor
  • the use of switching power supplies, the life of electrolysis at high temperatures and low temperatures has been a problem in the industry.
  • the capacitance CL is often 400V withstand voltage electrolysis, while the withstand voltage is greater than 250V electrolysis, its low temperature can only work to -25 °C.
  • the capacity per unit volume of electrolysis 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 phone charging. Instruments, laptop adapters, power supplies for various color TVs, desktop computer power supplies, standby power supplies for air conditioners, etc., all use switching power supplies, and also use electrolysis.
  • a directing indicating circuit is formed in the DC power supply circuit of the electrolytic CL, and the indicating circuit is composed of a light emitting unit and an inductor. L is composed in parallel to ensure that the current direction of the DC power supply through the inductor L is opposite to the conduction direction of the light-emitting unit.
  • the existing patent A uses an inductor L which is subjected to a peak voltage of an alternating current or a direct current input at the time of starting, and a large charging current for the first several charges of the filtered electrolytic CL, that is, the withstand voltage of the inductor is high and withstand The impact current is very demanding, and its cost is relatively low.
  • 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.
  • the present invention solves the shortcomings of the prior art direct-filtering switching power supply using electrolytic capacitor filtering, and provides a direct-filtering switching power supply, which does not use an inductor with high withstand voltage and large current, and does not change the original
  • the circuit provides an indication before the filter electrolytic capacitor completely fails, and realizes the advance notice before the switching power supply completely fails.
  • a direct filter switching power supply for a DC input including pulsating direct current including a filter circuit, a main power stage, and an indicating circuit having two terminals, a DC input connection filter circuit
  • the filter circuit is connected in parallel with the main power stage.
  • the filter circuit includes at least one electrolytic capacitor connected in parallel with the main power stage, and the characteristic is that the indicating circuit is connected in parallel with the electrolytic capacitor.
  • the indication circuit scheme 1 comprises a first resistor, a first capacitor, a first diode and a first light emitting diode, wherein the first resistor and the first diode and the first LED are connected in parallel, wherein the first The LED and the first diode are connected in anti-parallel.
  • the two-terminal network formed in parallel is referred to as a parallel network.
  • the terminals of the parallel network are distinguished by the anode of the first diode and the cathode of the first diode.
  • the two capacitors are connected in series with the first capacitor 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 respectively a first terminal and a second terminal.
  • the indication circuit scheme 2 includes a first resistor, a second resistor, a first capacitor, a second capacitor, a first diode and a second diode, and a first LED; the connection relationship is: a second resistor Connected in series with the first light emitting diode to form a first network having two terminals, the first network and the second capacitor are simultaneously connected in parallel with the first resistor to form a second network having two terminals, and the second network is connected in series with the second diode Forming a third network with 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 is connected in anti-parallel with the first diode to form a fourth network having two terminals, and the fourth network is further connected to the first capacitor In series, 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 respectively a first
  • the cost is lower than the prior art using the inductor, the added indicating circuit has low loss, and has little influence on the conversion efficiency of the original converter.
  • the wiring is simple, the volume is small, and the use is convenient, and the same is realized: before the electrolytic capacitor fails, the The LEDs of the LEDs are illuminated or the LEDs in the optocoupler have current flowing through them. The optocoupler outputs an isolated signal to alert the user or other circuitry.
  • FIG. 1 is a schematic diagram of a conventional flyback switching power supply for alternating current to direct current
  • FIG. 2 is a schematic diagram of a direct filter type switching power supply using a first embodiment of the indication circuit scheme 1, and is also a schematic diagram of the second embodiment;
  • FIG. 3 is a schematic diagram of a path of a charging current generated by a U DC direct current input to an electrolytic capacitor in the first embodiment
  • FIG. 4 is a timing chart of driving voltage and exciting current of a main power stage switching tube in the first embodiment
  • FIG. 5 is a schematic diagram showing the path of the exciting current i M of the main power stage when the electrolytic capacitor is normal in the first embodiment
  • FIG. 6 is an equivalent circuit diagram of the excitation current related to the main power stage of FIG. 5;
  • 7-1 is a schematic diagram of a first embodiment of the indication circuit of the present invention.
  • FIG. 7-2 is a schematic diagram of Embodiment 2 of a corresponding embodiment of the indication circuit of the present invention.
  • 7-3 is a schematic diagram of an embodiment of a first embodiment of the indication circuit of the present invention.
  • 7-4 is a schematic diagram of an embodiment of a first embodiment of the indication circuit of the present invention.
  • 7-5 is a schematic diagram of an implementation manner of a first embodiment of the indication circuit of the present invention.
  • FIGS. 7-6 are schematic diagrams of Embodiment 6 of a corresponding embodiment of the indication circuit of the present invention.
  • FIG. 8 is a schematic diagram of a direct filter type switching power supply using a second embodiment of the indication circuit scheme 2;
  • 8-1 is a schematic diagram of a first embodiment of the indication circuit scheme 2 of the present invention.
  • Embodiment 8-2 is a schematic diagram of Embodiment 2 of the second embodiment of the indication circuit of the present invention.
  • 8-3 is a schematic diagram of an embodiment of a second embodiment of the indication circuit of the present invention.
  • 8-4 is a schematic diagram of an embodiment of a second embodiment of the indication circuit of the present invention.
  • Fig. 9 is a schematic diagram of a direct filter type switching power supply of the third embodiment.
  • FIG. 2 is a schematic diagram of a direct filter switching power supply of a first embodiment of the present invention for a DC input including pulsating direct current, the DC input being shown as U DC , including a filter circuit 200, a main power stage 300, and including An indicating circuit 400 having two terminals, a DC input U DC is connected to the filter circuit 200, and the filter circuit 200 is connected in parallel with the main power stage 300.
  • the filter circuit 200 includes at least one electrolytic CL connected in parallel with the main power stage, and is characterized by:
  • the indicating circuit 400 is connected in parallel with the electrolytic circuit CL, and the indicating circuit 400 includes at least a first resistor R1, a first capacitor C1, a first diode D1, and a first LED.
  • Pulsating DC See Figure 1. After the AC power passes through the rectifier bridge 101, if there is no filter circuit, then the pulsed DC power with twice the frequency is obtained.
  • the application number 201210056555.9 is described in detail.
  • the first scheme of the indicating circuit the first resistor R1, the first capacitor C1, the first diode D1 and the first LED, the first resistor R1 and the first diode D1 and the first LED Parallel, wherein the first LED and the first diode D1 are connected in anti-parallel, and the two-terminal network formed after the parallel connection is simply referred to as the parallel network 24, and the terminal of the parallel network 24 is the anode of the first diode D1, the first two The cathode of the pole tube D1 is distinguished, and the parallel network 24 is connected in series with the first capacitor C1, and forms a two-terminal network in series.
  • serial network is simply referred to as a serial network, which is the indicating circuit 400, the serial network 400
  • the two terminals are a first terminal 1 and a second terminal 2, respectively, and the series network 400 is also a functional body of the direct filter type switching power supply of the present invention.
  • 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.
  • the LED is ⁇ 3mm red highlighted.
  • the LED is simply referred to as the LED
  • the model is 3AR2UD
  • the capacitor C1 is 333/500V chip capacitor
  • the nominal capacity is 0.033uF
  • the D1 is 1N4148
  • the R1 is 22K patch.
  • the direct-filtering switching power supply is used.
  • the switching power supply uses a 25W flyback power supply.
  • the model is the LH25-10B12 unfilled semi-finished product of the applicant company.
  • the filter electrolysis is 47uF/400V, which is a domestic high-quality capacitor.
  • the rectifier bridge is composed of four 1N4007s with an operating frequency of 65KHz. At 220VAC input, the maximum duty cycle of full load is 0.24.
  • Figure 2 indicates that the circuit 400 is directly connected in parallel with the electrolytic CL in the switching power supply.
  • the forward parallel or the reverse parallel connection can be forward parallel: that is, the terminal 1 is connected to the positive electrode of the filter electrolytic capacitor, and the terminal 2 is connected to the filter electrolytic capacitor.
  • Negative pole; 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.
  • an adjustable resistor is connected in series to simulate an electrolytic capacitor whose performance has been lowered.
  • the adjustable range of the adjustable resistor is 0-39 ⁇ .
  • the LED of FIG. 2 emits light, and the average value of the operating current is actually measured to be 1.6 mA.
  • 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.
  • 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.
  • the conduction voltage drop of the white light-emitting tube is about 3.0V
  • the red color is different from the green color
  • the illuminator conduction voltage drop inside the photocoupler is about 1.1V.
  • the four diodes in the rectifier bridge 101 at the front end of the U DC only turn on the two diodes inside the rectifier bridge when the input alternating current is close to the peak, and supplement the electric energy to the electrolysis CL, and the rectifier bridge 101 generates
  • the path of the charging current is shown in Figure 3.
  • the charging current is twice the frequency of the mains, 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 For the seven-thousandth of the CL, the peak value of the charging current of the CL is 2.39A, then the charging current flowing through the D1 is only 1.67 mA. At this time, the LED does not emit light due to the reverse bias.
  • the CL 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.
  • 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. If the U DC is continuous DC, then the problem of low frequency ripple illuminating the LED will not exist.
  • the capacitance of 0.033uF is about 48K ⁇ for the AC low frequency ripple of 100Hz, 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 0.40 mA, the R1 is 22K, and the voltage drop should be 8.8V. In fact, the LED does not emit light.
  • Reason Referring to Figure 3, when the mains charges the CL, a synchronous charging current flows through D1.
  • 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. If terminal 1 is connected to the negative pole of the filter electrolytic capacitor, terminal 2 is connected to the positive pole of the filter electrolytic capacitor, and when rectifier bridge 101 charges CL, the LED will emit light, the circuit is unsuccessful, and the value of R1 should be adjusted.
  • the electrolytic capacitors as described above 47uF / 400V the ESR is 0.5 [Omega at 65KHz, i.e., when V is working properly switch the main power stage of the exciting current i M 4, 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. 5 .
  • 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.
  • 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/(2 ⁇ fC), which is calculated to be 52m ⁇ , which is much smaller than its ESR.
  • ESR plays a major role; the waveform shown in Figure 4 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 stage 300 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 300 is about 408 mA when the switching transistor V is turned on, and the peak value is about 816 mA.
  • C1 is 0.033uF, its capacity is small, but its capacitance is 73.8 ⁇ at 65KHz frequency, it can provide sufficient working current for LED to emit light, and it can regulate current and can get different working current. .
  • 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.
  • the ESR of the electrolytic CL rises, the voltage drop generated by the high-frequency excitation current of the switching power supply of the present invention rises synchronously on the ESR, and the formed high-frequency ripple voltage rises as the electrolytic capacitor ages.
  • C1 has a high frequency effect, ESR When the high-frequency ripple voltage 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 is formed across the R1 through the current of the capacitor C1. The voltage is lowered by the on-voltage of the LED, the LED is not turned on, and the LED cannot be shunted for R1 to emit light.
  • 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.
  • the load of the direct-filtering 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 conspicuous.
  • 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.
  • C1 and parallel network 24 are connected in series.
  • C1 and parallel network 24 are connected in series. Because it is a series circuit, the functions are the same after the interchange of positions. Therefore, the circuit of the indication circuit includes multiple types of series, but the functions are the same, as follows:
  • the only effective connection method is only the above (a) of FIG. 7-1 and (b) of FIG. 7-2.
  • the capacitor C1 and the network 24 are connected in series. Since the series circuit is used, the functions of the device are the same after the position is interchanged.
  • the method of (b) of Fig. 7-2 is to interchange the position C1 of the mode (a) of Fig. 7-1 with the network 24, that is, essentially, (a) and Fig. 7-2 of Fig. 7-1.
  • the way (b) is equivalent. That is, the first scheme of the indication circuit includes the above four connection methods.
  • the capacitor C1 can be obtained by connecting two capacitors in series. Then, the capacitor C1 of FIG. 7-1 is replaced by the capacitors C1a and C1b in series, and the embodiment of FIG. 7-5 is obtained, and the circuit of FIG. 7-1 and FIG. 7- The circuit of 5 is equivalent. As described above, the series circuit, after the device interchanges the position, functions the same. Further, by swapping the capacitance C1b with the network 24, the embodiment shown in Figures 7-6 is obtained.
  • FIG. 7-2, the circuit of FIG. 7-3, the circuit of FIG. 7-4, the circuit of FIG. 7-5, and the circuit of FIG. 7-6 are replaced with the indicating circuit 400 of FIG. 2, which can work normally, FIG. 7
  • the resistance of R1 in -3 and Figure 7-4 should be small. Otherwise, the charging current generated by rectifier bridge 101 when the AC 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.
  • the circuit of FIG. 7-6 replaces the embodiment obtained by the indicating circuit 400 of FIG.
  • the capacitors C1a and C1b are respectively on the upper side and the lower side, and the capacity is small, and the light emitting diode can be realized. Electrical isolation from the switching power supply, because the frequency of the mains is low, the leakage current through the capacitors C1a and C1b is easily controlled below the limit value to achieve safety compliance.
  • the current flowing through the LED of the LED is not DC, but a high-frequency current of the same frequency as the power stage 300.
  • the LED of the LED is replaced by an optocoupler.
  • 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.
  • FIG. 8 is a schematic diagram showing a direct filter type switching power supply according to a second embodiment of the present invention, for a DC input including a pulsating direct current, the DC input being shown as U DC , including a filter circuit 200.
  • the main power stage 300 further comprising an indicating circuit having two terminals 400, DC input connector U DC filter circuit 200, filter circuit 200 and the main power stage 300 in parallel to the filter circuit 200 includes at least one power stage connected in parallel with the main
  • the electrolysis CL is characterized in that the indicating circuit 400 is connected in parallel with the electrolysis CL, and the indicating circuit 400 includes at least a first resistor R1, a first capacitor C1, a first diode D1 and a first LED.
  • the indicating circuit adopts the second scheme: the indicating circuit 400 further includes a second resistor R2, a second capacitor C2, and a second diode D2; if described together, the indicating circuit 400 includes a first resistor R1 and a second resistor R2. a first capacitor C1, a second capacitor C2, a first 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
  • the first network 21 has two terminals.
  • the indicating circuit 400 in FIG. 8 is separated. Referring to FIG. 8-1, the first network 21 and the second capacitor C2 are simultaneously connected in parallel with the first resistor R1 to form two.
  • the second network 22 of the terminal, 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 being characterized by a second diode D2 and a first light emitting diode The LEDs 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 is connected in series with the first capacitor C1 to form a two-terminal network in series.
  • the series two-terminal network 4 00 is abbreviated as a series network, and the two terminals of the series network 400 are respectively a first terminal 1 and a second terminal 2, and the series network 400 is also a functional main body of the direct filter type 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.
  • 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. .
  • the ESR of the electrolytic CL rises, the voltage drop generated by the high-frequency excitation current of the power stage 300 rises synchronously on the ESR, and the formed high-frequency ripple voltage rises with the aging of the electrolytic CL, and the C1 has a high-frequency.
  • the role of 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.
  • the current flowing through the LED of the LED is pure DC, and its electromagnetic radiation is directly reduced to zero.
  • the output current of the optocoupler is also an extremely stable DC signal.
  • 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.
  • connection modes of R2 and LED in series in the network 21 There are also various embodiments of the second embodiment, which constitute a series of embodiments.
  • 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.
  • network 22 is connected in series with diode D2.
  • capacitor C2 is equivalent to an open circuit for direct current
  • 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:
  • the fourth network 24 is in series with the first capacitor C1, and there are also two ways:
  • each series has two modes, a total of two 3 powers, and a total of eight connection modes, which are equivalent.
  • resistor R1 is connected in parallel with C2 as shown in Figure 8-4, and is connected in parallel with D1.
  • R1 can also adjust the threshold value. The technical solution is no longer used here to protect the rights.
  • the circuit of FIG. 8-2, the circuit of FIG. 8-3, and the circuit of FIG. 8-4 are replaced with the indicating circuit 400 of FIG. 8, and the normal operation can be performed. Since C2 can absorb the peak current, 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 present invention can solve the problems in the prior art, and obtain desired benefits with smaller components and costs.
  • the third embodiment shows that both the power stage 300 and the filter circuit 200 are replaced with other embodiments.
  • FIG. 9 is a schematic diagram of a direct filter type switching power supply according to a third embodiment of the present invention, which is used for a DC input including a pulsating direct current
  • the DC input is shown by U DC , and includes a filter circuit 200, a main power stage. 300, further comprising an indicating circuit having two terminals 400, DC input connector electrolytic CL U DC filter circuit 200, filter circuit 200 and the main power stage 300 in parallel to the filter circuit 200 includes at least one power stage connected in parallel with the primary,
  • the characteristic is that the indicating circuit 400 is connected in parallel with the electrolytic circuit CL, and the indicating circuit 400 includes at least a first resistor R1, a first capacitor C1, a first diode D1 and a first LED.
  • the indication circuit adopts the first scheme: the indication circuit includes a first resistor R1, a first capacitor C1, a first diode D1 and a first LED, the first resistor R1 and the first diode D1 and the first LED
  • the three devices are connected in parallel, wherein the first LED and the first diode D1 are connected in anti-parallel.
  • the two-terminal network formed after the parallel connection is simply referred to as the parallel network 24, and the terminal of the parallel network 24 is the anode of the first diode D1,
  • the cathode of the first diode D1 is distinguished, 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, which is an indication circuit 400, which is connected in series.
  • the two terminals of the network 400 are a first terminal 1 and a second terminal 2, respectively, and the series network 400 is also a functional body of the direct filter type switching power supply of the present invention.
  • the filter circuit 200 is connected in parallel with the main power stage 300. When paralleling, be careful not to reverse the connection, and ensure that the main power level is not reversed. This is a basic skill for those skilled in the art.
  • the main power stage 300 is a half bridge circuit.
  • the filter circuit 200 is formed by connecting two low-voltage electrolytic electrodes CL1 and CL2 of the same capacity in series, and the connection point is connected to the half bridge circuit.
  • the figure does not show a voltage equalizing resistor in parallel with the electrolytic capacitor; C31 is a coupling capacitor for improving the biasing performance, and the other side of the transformer B is a general-purpose output rectifier circuit.
  • the indicating circuit 400 is connected in parallel with the electrolytic CL, and the electrolytic CL is a series connection of the electrolytic electrodes CL1 and CL2. Based on the working principle of the first embodiment, the third embodiment also achieves the object of the invention.
  • circuit of Fig. 7-2, the circuit of Fig. 7-3, the circuit of Fig. 7-4, the circuit of Fig. 7-5, the circuit of Fig. 7-6, the circuit of Fig. 8-1, and the circuit of Fig. 8-2 The circuit, the circuit of Figure 8-3, and the circuit of Figure 8-4 replace the indicator circuit 400 of Figure 9 and all operate normally.

Abstract

一种直接滤波式开关电源，用于包括脉动直流电的场合，包括滤波电路200，主功率级300，以及指示电路400，400包括端子1、2、电阻R1、电容C1、二极管D1和发光二极管LED，LED和D1反向并联后再与R1并联，再与C1串联；400与滤波电解CL并联，C1的容量小，整流引起的工频倍频大纹波，通过C1的电流极小，在R1上产生的压降不足以点亮LED；随着CL的ESR上升，高频激磁电流在ESR上产生的压降同步升高，形成的高频纹波电压随之升高，C1具有通高频的作用，ESR上的高频纹波电压到达一定的阀值时，点亮LED而发光，调节R1的阻值可以调节阀值的大小。从而提醒使用者电解CL的ESR已上升，开关电源已存在失效风险，该电路成本低、实施容易，不使用电感检测。

Description

一种直接滤波式开关电源 技术领域
本发明涉及开关电源领域，特别涉及高可靠性的交流或直流变换为直流的开关电源。
背景技术
目前，开关电源应用很广，对于输入功率在75W以下，对功率因数(PF，PowerFactor，也称功率因素)不作要求的场合，反激式(Fly-back)开关电源具有迷人的优势：电路拓扑简单，输入电压范围宽。由于元件少，电路的可靠性相对就高，所以应用很广。为了方便，很多文献也称为反激开关电源、反激电源，日本和台湾地区又称返驰式变换器。常见的拓扑如图1所示，该图原型来自张兴柱博士所著的书号为ISBN978-7-5083-9015-4的《开关电源功率变换器拓扑与设计》第60页，该书在本文中简称为：参考文献1。由整流桥101、滤波电路200、以及基本反激拓扑单元电路300组成，300也简称为主功率级，实用的电路在整流桥前还加有压敏电阻、NTC热敏电阻、EMI(Electromagnetic Interference)等保护电路，以确保反激电源的电磁兼容性达到使用要求。
整流桥101一般由四个整流二极管组成，申请号201210056555.9的授权发明说明书中的图4-1、图4-2、图4-3给出了整流桥的几种公知画法；滤波电路200一般由电解CL构成，为了方便，“电解电容”以下都简称为“电解”；为了EMI性能更出色，一般在电解CL两端还会并联一个高频特性好的高压小容量电容；主功率级300包括很多器件，这里只列出功率变压器B，主功率开关管V，一般为MOS管，输出整流二极管D，输出滤波电容C，反激拓扑中的功率变压器B事实上是储能电感，主功率级300其实还包括很多电路，如用于吸收MOS管反峰电压的DCR电路，PWM控制电路，光耦反馈电路，甚至有源钳位电路，其主拓扑不局限于反激电路，可以是双管反激电路、半桥变换器等。
随着直流供电的兴起，如太阳能、风力发电设备普及，高压直流供电也开始普及，也出现了采用反激电源作为系统的待机电源等，图1的基本拓扑中，去了整流桥101，即可实现直流供电，也有人喜欢直接从整流桥101的前端采用直流供电，这样效率略低，但可实现交直流两用，且不用区分直流供电时的正负极。
国内很多厂家并没有认真执行国家标准，一些输入功率超过75W的应用领域，如台式电脑的供电电源，功率为150W以上，也是采用类似图1的拓扑，主功率级300多采用双管正激，双管正激为业界通俗说法，实际上为半桥变换器；整流桥101中甚至没有串入功率因数校正电感，即整流滤波后，给半桥变换器供电。主功率级300也有采用单管正激、不对称半桥来实现的。
整流桥101中串入功率因数校正电感，仍属无源滤波式功率因数校正，不是有源功率因数校正。我们把整流后滤波的开关电源，以及整流桥串入功率因数校正电感，再滤波的开关电源都定义为：直接滤波式开关电源。
滤波电路200一般由电解电容CL构成，随着工业领域中智能化系统的推广，使用电解的开关电源的不足之处也随之体现出来，因为使用了电解CL，而该电解的特性也因此限制了开关电源的用途，电解在高温和低温下的寿命一直是业界难题，众所周知，电容CL经常为400V耐压的电解，而耐压大于250V的电解，其低温一般只能工作到-25℃。即在-40℃的环境下，如东北三省、新疆、以及高纬度的国家与地区，开关电源的使用变得棘手，当然，可以使用如CBB薄膜电容来滤波，但体积过大，且成本过高。
电解单位体积的电容量非常大，所以在包括反激电源的开关电源中，特别是交流输入的领域，目前仍是低成本的解决方案，在各种电源中应用极多，如各种手机充电器、笔记本电脑适配器、各种彩电的电源、台式电脑电源、空调的待机电源等，都要用到开关电源，同时也使用了电解。
设计一台开关电源时，经常面临电解CL的寿命问题，在实际使用中，很多开关电源达不到使用寿命，其主因就是滤波用的电解提前失效。很多要求较高的场合，采用了冗余设计，使用两个开关电源互为备份，坏了一个，还可以正常工作。成本较高，且仍然不知道其中开关电源是什么时间失效，也不方便准备备品。
常见的非冗余设计场合，一旦开关电源失效，将会引起很多连带失效，从而使得损失被扩大，据统计，合格设计的开关电源发生失效，97％以上由滤波的电解先行失效引起。
现有的大部份使用电解的开关电源，尚不能对电解的失效进行有效的预先告知。在发明人的申请号201610040060.5的现有专利申请《一种直接滤波式开关电源》中，给出一种解决方案：在电解CL的直流供电回路中串入指示电路，指示电路由发光单元和电感L并联组成，确保直流供电通过电感L的电流方向与发光单元的导通方向相反，当电 解CL正常时，开关管V的激磁电流基本上不出现在电感L中，LED不发光；电容CL的ESR上升较大时，V的激磁电流出现在L中，且V关断时，流过L的激磁电流无法突变，经过发光器LED续流，同时驱动LED发光，这样来提醒使用者：开关电源的电解CL的ESR已上升，已存在失效的风险，避免损失的扩大，具有低成本、效率不变、实施容易的特点。为了方便，该专利申请201610040060.5以下称为现有专利A。
现有专利A使用了电感L，该电感L在启机时要承受交流电或直流输入的峰值电压，以及对滤波电解CL的前几次充电的大充电电流，即该电感的耐压高、承受的冲击工作电流要求很大，其成本相对来说，不算低。
同时该电路要串联于滤波电解电容的工频充电回路中，对原有的电路要进行改动。
发明内容
有鉴于此，本发明要解决现有的使用电解电容滤波的直接滤波式开关电源存在的不足，提供一种直接滤波式开关电源，不使用耐压高、电流大的电感，不改动原有的电路，在滤波电解电容完全失效前，提供指示，实现在开关电源完全失效前的预先告知。
本发明的目的是这样实现的，一种直接滤波式开关电源，用于包括脉动直流电的直流输入，包括滤波电路，主功率级，还包括一个具有两个端子的指示电路，直流输入连接滤波电路，滤波电路和主功率级并联，滤波电路中至少包括一只与主功率级并联的电解电容，其特征是：指示电路与电解电容并联。
优选地，指示电路方案一包括第一电阻、第一电容、第一二极管和第一发光二极管，第一电阻和第一二极管和第一发光二极管这个三个器件并联，其中第一发光二极管和第一二极管反向并联，并联后形成的两端子网络简称为并联网络，并联网络的端子以第一二极管的阳极、第一二极管的阴极进行区分，并联网络再与第一电容串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，串联网络的两个端子分别为第一端子、第二端子。
优选地，指示电路方案二包括第一电阻、第二电阻；第一电容、第二电容；第一二极管和第二二极管、以及第一发光二极管；其连接关系为：第二电阻与第一发光二极管串联，形成具有两端子的第一网络，第一网络与第二电容与第一电阻同时并联，形成具有两端子的第二网络，第二网络再与第二二极管串联，形成具有两端子的第三网络，第 三网络的特征是，第二二极管和第一发光二极管为同向；第三网络与第一二极管反向并联，形成具有两端子的第四网络，第四网络再与第一电容串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，串联网络的两个端子分别为第一端子、第二端子。
工作原理将结合实施例，进行详细地阐述。
本发明的有益效果为：
成本比使用电感的现有技术低，增设的指示电路损耗低，对原变换器的正常工作的变换效率几乎没有影响，接线简单、体积小、使用方便，同样实现：当电解电容失效前，该指示灯发光二极管发光或光耦中的发光二极管有电流流过，光耦输出一个隔离的信号以提示使用者或其它电路。
附图说明
图1为现有的反激式开关电源用于交流变直流的原理图；
图2为使用指示电路方案一的第一实施例的直接滤波式开关电源的原理图，也是第二实施例的原理图；
图3为第一实施例中UDC直流输入对电解电容产生的充电电流的路径示意图；
图4为第一实施例中主功率级开关管驱动电压与激磁电流时序图；
图5为第一实施例中电解电容正常时主功率级的激磁电流iM的路径示意图；
图6为图5主功率级的激磁电流相关的等效电路图；
图7-1为本发明指示电路方案一对应的实施方式一原理图；
图7-2为本发明指示电路方案一对应的实施方式二原理图；
图7-3为本发明指示电路方案一对应的实施方式三原理图；
图7-4为本发明指示电路方案一对应的实施方式四原理图；
图7-5为本发明指示电路方案一对应的实施方式五原理图；
图7-6为本发明指示电路方案一对应的实施方式六原理图；
图8为使用指示电路方案二的第二实施例的直接滤波式开关电源的原理图；
图8-1为本发明指示电路方案二对应的实施方式一原理图；
图8-2为本发明指示电路方案二对应的实施方式二原理图；
图8-3为本发明指示电路方案二对应的实施方式三原理图；
图8-4为本发明指示电路方案二对应的实施方式四原理图；
图9为第三实施例的直接滤波式开关电源的原理图。
具体实施方式
第一实施例
图2示出了本发明第一实施例的直接滤波式开关电源的原理图，用于包括脉动直流电的直流输入，直流输入以UDC示出，包括滤波电路200，主功率级300，还包括一个具有两个端子的指示电路400，直流输入UDC连接滤波电路200，滤波电路200和主功率级300并联，滤波电路200中至少包括一只与主功率级并联的电解CL，其特征是：指示电路400与电解CL并联，指示电路400至少包括第一电阻R1、第一电容C1、第一二极管D1和第一发光二极管LED。
脉动直流电：见图1，交流电经过整流桥101后，若没有滤波电路，那么，就会得到频率是交流电二倍的脉动直流电，背景技术中，申请号201210056555.9有详细介绍。
指示电路的方案一：第一电阻R1、第一电容C1、第一二极管D1和第一发光二极管LED，第一电阻R1和第一二极管D1和第一发光二极管LED这个三个器件并联，其中第一发光二极管LED和第一二极管D1反向并联，并联后形成的两端子网络简称为并联网络24，并联网络24的端子以第一二极管D1的阳极、第一二极管D1的阴极进行区分，并联网络24再与第一电容C1串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，就是指示电路400，串联网络400的两个端子分别为第一端子1、第二端子2，该串联网络400也是本发明的直接滤波式开关电源的功能主体。
第一电容C1以下简称为C1，第一电阻R1以下简称为R1，第一发光二极管LED以下简称为LED，其它器件相似。
LED采用Φ3mm红色高亮的，为了方便，发光二极管简称为发光管，型号为3AR2UD，电容C1为333/500V的贴片电容，标称容量为0.033uF，D1为1N4148，R1为22K的贴片电阻，按图2组成直接滤波式开关电源，开关电源使用了25W反激电源，型号为申请人公司的LH25-10B12未灌封的半成品，其滤波用电解为47uF/400V，为国产优质电容，整流桥为四只1N4007组成，工作频率为65KHz，在220VAC输入下，满载最大占空比为0.24。
要注意的是：图2指示电路400直接与开关电源中电解CL并联，正向并联或反向并联都可以，正向并联：即端子1连接滤波电解电容的正极，端子2连接滤波电解电容的负极；或反向并联：端子1连接滤波电解电容的负极，端子2连接滤波电解电容的正极。下文会专门讲解。
当第一实施例以正向并联方式焊入，实测反激电源的各方面指标，均和之前的相同，特别是变换效率，没有出现可以观察到的下降，且发光管LED不发光。
为了验证本发明是可以工作的，发明人采用了之前首创的方法来测试第一实施例：
由于失效的电解电容难以觅得，在上述的滤波用电解电容中，串入可调电阻，来模拟性能已经下降的电解电容，可调电阻在这里的可调范围是0-39Ω，当把可调电阻的阻值调到5Ω时，相当于47uF/400V的电解电容的ESR从良品时的0.5Ω左右已上升至5.5Ω，电解电容的性能已接近不能使用的边缘。
此时，图2中的发光管LED发光，且工作电流的平均值实测为1.6mA。
通过选取不同容量的电容C1，初步调节指示的灵敏度，电容C1的容量小，灵敏度低；电容C1的容量大，灵敏度高。由于发光管在发光时，存在1.6V至2.2V的正向压降，可以在发光管LED两端并联电阻R1来调节灵敏度，如本例中，R1若采用1.6K的电阻，那么，1mA以下的峰值电流在R1两端产生的电压在1.6V以下，这时发光管LED不发光。
注：白光发光管的导通压降为3.0V左右，红色的与绿色的也不同，而光耦内部的发光器导通压降为1.1V左右。
工作原理：参见图3，当电解电容正常时，那么其ESR为0.5Ω，滤波用电解CL两端的纹波电压有两种，以开关电源满载工作时为例说明。
当电解CL正常时，UDC前端的整流桥101中的四只二极管，只有当输入的交流电接近顶峰时才同时导通整流桥内部的两只二极管，对电解CL补充电能，整流桥101产生的充电电流的路径见图3，这个过程中，充电电流的频率为市电的2倍，为100Hz或120Hz，由于C1容量较小，为0.033uF，相比CL的47uF，C1中的充电电流仅为CL的万分之七，CL的充电电流的峰值为2.39A，那么，流过D1的充电电流仅为1.67mA，这时，LED因为反偏而不发光。
在下一个充电周期到来之前，CL一直要对主功率级放电，CL端电压一直在下降，直到10mS或8.33mS后再一次充电，这样CL的两端形成一个为市电频率的2倍的低频纹波，其峰-峰值在20V左右。当C1的容量足够大时，这个低频纹波可以在C1中形成足够的电流来点亮LED，所以，要确保低频纹波在C1中形成的电流，在电阻R1的两端形成的压降小于LED的导通压降。若UDC为持续直流，那么，低频纹波点亮LED这一问题将不存在。
0.033uF的电容对100Hz的交流低频纹波，其阻抗大约是48KΩ，峰-峰值在20V左右的低频三角纹波的有效值约为10V，那么，流过C1的低频纹波电流约为0.20mA，峰值为0.40mA，R1为22K，其压降应为8.8V，事实上，LED也没有发光，原因：参见图3，市电对CL充电时，有一个同步的充电电流流过D1，而当CL的端电压下降时，C1对CL放电，形成放电电流，充电时间短，放电时间却很长，充电一般在1mS内完成，而放电时间接近一个充电周期，接近(10mS-1mS)＝9mS，由于持续时间长，这个时间内的峰值电流极低。C1对CL放电，途径为：C1的上端→CL的正极→CL的负极→D1的阴极、即R1的下端→R1的上端、即D1的阳极→C1的下端；C1对CL放电的积分和等于市电对C1充电的积分，而放电的时间长，电流几乎恒定，所以其电流小，这个电流经过R1的两端，产生的压降很低。
R1阻值的选取，要确保低频纹波电流通过C1时，LED不发光，这里还有一个小技巧：整流桥101对CL充电时，这个充电电流直接流过D1，而不要流过LED，确保LED不发光。若端子1连接滤波电解电容的负极，端子2连接滤波电解电容的正极，整流桥101对CL充电时，LED就会发光，电路是不成功的，R1的取值要进行调整才可以。
当电解CL正常时，如上述的47uF/400V的电解电容，其在65KHz下的ESR为0.5Ω,即开关管V正常工作时，主功率级的激磁电流iM如图4所示，其中，Ugs为开关管V的栅极与源极的驱动电压，激磁电流iM的路径见图5。
当整流桥101不导通时，电解CL和C1对主功率级的放电电流完全等于主功率级的激磁电流iM。注，C1因为容量小对主功率级的放电电流太小，这里可以忽略。电解CL在65KHz的开关频率下的容抗为1/(2πfC)，计算出来为52mΩ，远小于其ESR，在65KHz下，ESR起主要作用；图4示出的波形不是正弦波，其基波是正弦波，其谐波频率都比65KHz要高，所以这里只是估算。
25W反激功率级300的工作频率为65KHz，在220VAC输入下，满载最大占空比为0.24。主功率级300的激磁电流iM在开关管V导通时的平均值约为408mA，峰值约为816mA，这个电流在CL的ESR上形成的压降，参见图6，为U＝IR＝0.816×0.5＝0.408V。即在图6中，端子1和2之间存在一个波动的高频纹波，其波形形状同图4中iM的波形，显然0.408V的峰值不足以让LED导通而发光。
当电解CL的ESR从良品时的0.5Ω左右已上升至5.5Ω，即电解CL已接近失效边缘。iM如在开关管V导通时峰值约为816mA，这个电流在CL的ESR上形成的压降，参见图6，为U＝IR＝0.816×5.5＝4.48V。即在图6中，端子1和2之间存在一个波动的高频纹波，其波形形状同图4中iM的波形，显然4.48V的峰值足以让LED导通而发光。
C1为0.033uF，其容量较小，但在65KHz的频率下，其容抗为73.8Ω，可以为LED提供足够的工作电流而发光，并起限流作用，调节其容量可以得到不同的工作电流。
本发明的工作原理不算复杂，C1的容量小，C1具有通高频、阻低频的作用；整流电路引起的工频大纹波通过C1的电流极小，在电阻R1上产生的压降不足以点亮LED，而随着电解CL的ESR上升，本发明开关电源的高频激磁电流在ESR上产生的压降同步升高，形成的高频纹波电压随着电解电容的老化而升高，C1具有通高频的作用，ESR 上的高频纹波电压到达一定的阀值时，会点亮LED而发光，调节R1的阻值可以调节阀值的大小，即高频纹波电压通过电容C1的电流在R1两端形成的压降低于LED的导通电压，LED不导通，LED也无法为R1分流从而不发光。
C1的取值方法：市电的工频2倍最高为120Hz，目前开关电源的工作频率一般在可听音频之外，为22KHz，那么，频率的比值为(22000/120)＝183.3倍，C1的取值在被监视的电解CL的183.3分之一以下即可。如CL为47uF，那么C1应在(47uF/183.3)＝0.256uF以下，由于电容的标称值是按E-3、E-6、E-12等系列取值的，这里可以取0.24uF以下。
这样驱动发光管LED发光来实现发明目的，提醒使用者：该电解CL的ESR已上升至关注点，以便使用者决定下一步的措施。本例中，把直接滤波式开关电源的负载降至30％，LED仍发光，工作电流降至0.36mA，使用高亮度的发光管仍然很醒目。
此时，电解电容仍能工作，但由于主功率级的激磁电流在ESR上存在较大发热量，本例中为0.22W，该电解电容已处于高发热量下，已在加速衰老中，一般情况下，会在几十小时至几百小时中，ESR快速上升，引起发热进一步加大，直至失效，容量丧失，从而引起如开关管炸毁等一系列失效。
C1和并联网络24串联说明：C1和并联网络24串联，由于是串联回路，互换位置后功能相同，所以指示电路的案一包括的串联方式有多种，但功能都相同，如下述：
(a)D1的阴极向下，C1在上边，如图2中400、或独立出来的图7-1所示，D1的阳极连接C1的一端，C1的另一端为指示电路的第一端子1，D1的阴极为指示电路的第一端子2；
(b)D1的阴极向下，C1在下边，如图7-2所示，D1的阴极连接C1的一端，D1的阳极为指示电路的第一端子1，C1的另一端为指示电路的第二端子2；
(c)D1的阴极向上，C1在上边，如图7-3所示，D1的阴极连接C1的一端，C1的另一端为指示电路的端子1；D1的阳极为指示电路的端子2；事实上，这与上述(b)的图7-2的方式是完全相同的，(b)方式的端子1等于(c)的端子2，(b)方式的端子2等于(c)的端子1，即把图7-3的端子1和2互换一下，完全与图7-2的(b)相同；
(d)D1的阴极向上，C1在下边，如图7-4所示，D1的阳极连接C1的一端，C1的另一端为指示电路的端子2；D1的阴极为指示电路的端子1；事实上，这与上述的图7-1的(a)方式是完全相同的，(a)方式的端子1等于(d)的端子2，(a)方式的端子2等于(d)的端子1，即把(d)方式的1和2互换一下，完全与图7-1的(a)相同。
即真正有效的连接方式只有上述的图7-1的(a)和图7-2的(b)方式，电容C1和网络24串联，由于是串联回路，器件互换位置后功能相同，这是公知技术，图7-2的(b)方式就是把图7-1的(a)方式的C1和网络24互换位置而已，即本质上，图7-1的(a)和图7-2的(b)方式是等效的。即指示电路的方案一包括了上述的四种连接方式。
另外，电容C1可用两只电容串联得到，那么，把图7-1的电容C1，用电容C1a和C1b串联替代，就得到图7-5的实施方式，图7-1的电路和图7-5的电路是等效的。正如前文所述，串联回路，器件互换位置后功能是相同的，进一步地，把电容C1b和网络24互换位置，就得到图7-6示出的实施方式。
把图7-2的电路、图7-3的电路、图7-4的电路、图7-5的电路、图7-6的电路替换图2中指示电路400，都可以正常工作，图7-3和图7-4中的R1的阻值要取小，否则，整流桥101在交流电达峰值时产生的充电电流会点亮LED。可见，第一实施例的四个电路可以实现发明目的。图7-6的电路替换图2中指示电路400得到的实施方式，有其优点：当电源的开关频率比较高时，电容C1a和C1b分别在上边和下边，且容量很小，可以实现发光二极管和开关电源的电气隔离，因为市电的频率低，透过电容C1a和C1b的漏电流容易控制在限定值以下来实现安规达标。
其实第一实施例的内容中，包括了6种实施方式，为了节约篇幅，仅以一个总的“第一实施例”来概括，其实是一个系列实施例。第一实施例中流过发光管LED的电流不是直流电，而是与功率级300同频的高频电流，当LED的引线较长时，其电磁辐射不容忽视；把发光管LED换成光耦中的发光器时，光耦的输出电流也是周期性出现，不是一个稳定的信号，这会给后续的电路造成麻烦。第二实施例示出了解决方案。
第二实施例
第二实施例参见图8，图8示出了本发明第二实施例的直接滤波式开关电源的原理图，用于包括脉动直流电的直流输入，直流输入以UDC示出，包括滤波电路200，主功 率级300，还包括一个具有两个端子的指示电路400，直流输入UDC连接滤波电路200，滤波电路200和主功率级300并联，滤波电路200中至少包括一只与主功率级并联的电解CL，其特征是：指示电路400与电解CL并联，指示电路400至少包括第一电阻R1、第一电容C1、第一二极管D1和第一发光二极管LED。
指示电路采用方案二：指示电路400还包括第二电阻R2、第二电容C2、第二二极管D2；若放到一起描述，即为：指示电路400包括第一电阻R1、第二电阻R2；第一电容C1、第二电容C2；第一二极管D1和第二二极管D2、以及第一发光二极管LED；其连接关系为：第二电阻R2与第一发光二极管LED串联，形成具有两端子的第一网络21，为了简洁，把图8中的指示电路400独立出来，参见图8-1中，第一网络21与第二电容C2与第一电阻R1同时并联，形成具有两端子的第二网络22，第二网络22再与第二二极管D2串联，形成具有两端子的第三网络23，第三网络23的特征是，第二二极管D2和第一发光二极管LED为同向；第三网络23与第一二极管D1反向并联，形成具有两端子的第四网络24，第四网络24再与第一电容C1串联，并形成一个串联的两端子网络，就是指示电路400，所述的串联的两端子网络400简称为串联网络，串联网络400的两个端子分别为第一端子1、第二端子2，该串联网络400也是本发明的直接滤波式开关电源的功能主体。
第二二极管D2和第一发光二极管LED为同向：第三网络23中，假设R1开路，电容C2对于直流来说，相当于开路，那么，从第三网络23下端流入的电流，经过LED后，再经过D2，从第三网络23上端流出，D2和LED都处于正向导通状态，这种串联方式，叫同向。D2和LED都处于正向导通状态，相当于压降更大的一个二极管，它的阴极就是第三网络23的阴极，直流电流可以从网络的阴极向外流出，它的阳极就是第三网络23的阳极，直流电流可以从网络的阳极向内流入。
第三网络23与第一二极管D1反向并联，就是指：第三网络23阴极连接D1的阳极，第三网络23的阳极连接D1的阴极。
工作原理：参见图8，当电解CL正常时，其ESR为0.5Ω，电解CL两端的纹波电压有两种：一个为市电频率的2倍的低频纹波，另一个为开关电源的高频激磁电流在ESR上产生的高频纹波。
C1容量较小，在市电频率的2倍的低频下，容抗大，流过C1的电流极小，经过D2整流后，C2滤波后，在R1的两端形成的电压不足以点亮LED。
而随着电解CL的ESR上升，功率级300的高频激磁电流在ESR上产生的压降同步升高，形成的高频纹波电压随着电解CL的老化而升高，C1具有通高频的作用，ESR上的高频纹波电压到达一定的阀值时，经过D2整流，C2滤波后，在R1的两端形成的电压足以点亮LED，R2起到限流作用。
这样，流过发光管LED的电流是纯净的直流电，其电磁辐射直接降为零，把发光管LED换成光耦中的发光器时，光耦的输出电流也是极为稳定的直流信号，这会给后续的电路带来便利。
元件参数为：C1为473/500V的贴片电容，标称容量为0.047uF，C2为104/16V的贴片电容，D1和D2均为1N4148，R2为1K，R1为10K，LED为3AR2UD。
开关电源的负载为100％时，电解CL的ESR上升至5.5Ω时，LED中的电流为0.9mA；把直接滤波式开关电源的负载降至30％，LED仍发光，工作电流降至0.33mA，使用高亮度的发光管仍然很醒目。这样驱动发光管LED发光来实现发明目的，提醒使用者：该电解CL的ESR已上升至关注点，以便使用者决定下一步的措施。
第二实施例也有多种实施方式，构成系列实施方式，网络21中的R2与LED串联存在两种连接方式：
(a)LED的阴极与R2的一端相连接，参见图8-1中的网络21中所示；
(b)LED的阳极与R2的一端相连接，参见图8-2中所示；
这两种是等效的。网络21与C2与R1同时并联，形成具有两端子的网络22，网络22再与二极管D2串联，网络22中，假设R1开路，电容C2对于直流来说，相当于开路，那么网络22相当于一只二极管，具有单向导电性能，LED的阴极所在一侧就是第二网络22的阴极，直流电流可以从网络的阴极向外流出，LED的阳极所在一侧就是第三网络23的阳极，直流电流可以从网络的阳极向内流入。由于限定为同向串联，网络22与D2也存在两种方式：
(a)网络22的阴极与D2的阳相连接，参见图8-1所示；
(b)网络22的阳极与D2的阴相连接，参见图8-3所示；
第四网络24再与第一电容C1串联，也存在两种方式：
(a)网络24的D1阳极与C1一端相连，参见图8-1所示；
(b)网络24的D1阴极与C1一端相连，参见图8-2所示；
第二实施例中，指示电路400中3个独立的串联，每个串联都有两种方式，共2的3次方，共8种连接方式，它们是等效的。
事实上，把电阻R1像图8-4那样，从原来的与C2并联，改为与D1并联，同样实现发明目的，R1同样可以调节阀值的大小，由于在方案一已给出技术启示，这里不再用技术方案来进行权利保护。
把图8-2的电路、图8-3的电路、图8-4的电路替换图8中指示电路400，都可以正常工作，由于存在C2可以吸收尖峰电流，整流桥101在交流电达峰值时产生的充电电流不会点亮LED。电路的性能进一步提高。可见，第二实施例的8种方式的四个电路可以实现发明目的。
可见，本发明确实可以解决现有技术中的问题，以较小的元件、成本获得想要的有益效果。
第三实施例示出的，是同时把功率级300和滤波电路200都换成其它实施方式。
第三实施例
参见图9，图9示出了本发明第三实施例的直接滤波式开关电源的原理图，用于包括脉动直流电的直流输入，直流输入以UDC示出，包括滤波电路200，主功率级300，还包括一个具有两个端子的指示电路400，直流输入UDC连接滤波电路200，滤波电路200和主功率级300并联，滤波电路200中至少包括一只与主功率级并联的电解CL，其特征是：指示电路400与电解CL并联，指示电路400至少包括第一电阻R1、第一电容C1、第一二极管D1和第一发光二极管LED。
指示电路采用方案一：指示电路包括第一电阻R1、第一电容C1、第一二极管D1和第一发光二极管LED，第一电阻R1和第一二极管D1和第一发光二极管LED这个三个器件并联，其中第一发光二极管LED和第一二极管D1反向并联，并联后形成的两端子网络简称为并联网络24，并联网络24的端子以第一二极管D1的阳极、第一二极管D1的阴极进行区分，并联网络24再与第一电容C1串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，就是指示电路400，串联网络400的两个端子分别为第一端子1、第二端子2，该串联网络400也是本发明的直接滤波式开关电源的功能主体。
滤波电路200和主功率级300并联，并联时注意不要接反，确保主功率级没有接反，这对于本技术领域的人来说，是基本技能。
本实施例主功率级300为半桥电路，为了适应半桥电路的连接方式，滤波电路200由两只容量相同的较低耐压的电解CL1、CL2串联而成，连接点连接到半桥电路上，图中没有画出与电解电容并联的均压电阻；C31为改善偏磁性能的耦合电容，变压器B的另一边为通用的输出整流电路。
指示电路400与电解CL并联，电解CL为电解CL1、CL2串联而成，基于第一实施例的工作原理，第三实施例同样实现发明目的。
同样，把图7-2的电路、图7-3的电路、图7-4的电路、图7-5的电路、图7-6的电路、图8-1的电路、图8-2的电路、图8-3的电路、图8-4的电路替换图9中指示电路400，都可以正常工作。
以上仅是本发明的优选实施方式，应当指出的是，上述优选实施方式不应视为对本发明的限制。对于本技术领域的普通技术人员来说，在不脱离本发明的精神和范围内，还可以做出若干改进和润饰，如将光耦中的发光器，即光耦中的发光二极管作为第一发光二极管；在第一二极管中也串入电阻，这些改进和润饰也应视为本发明的保护范围，这里不再用实施例赘述，本发明的保护范围应当以权利要求所限定的范围为准。

Claims (7)

  1. 一种直接滤波式开关电源，用于包括脉动直流电的直流输入，包括滤波电路，主功率级，还包括一个具有两个端子的指示电路，直流输入连接滤波电路，滤波电路和主功率级并联，滤波电路中至少包括一只与主功率级并联的电解电容，其特征是：指示电路与电解电容并联。
  2. 根据权利要求1所述的直接滤波式开关电源，其特征在于：指示电路包括第一电阻、第一电容、第一二极管和第一发光二极管，第一电阻和第一二极管和第一发光二极管这个三个器件并联，其中第一发光二极管和第一二极管反向并联，并联后形成的两端子网络简称为并联网络，并联网络的端子以第一二极管的阳极、第一二极管的阴极进行区分，并联网络再与第一电容串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，串联网络的两个端子分别为第一端子、第二端子。
  3. 根据权利要求2所述的直接滤波式开关电源，其特征在于：还包括另一电容，另一电容也与并联网络串联，并且另一电容和第一电容分别与串联网络的两个端子相连接。
  4. 根据权利要求1所述的直接滤波式开关电源，其特征在于：指示电路方案二包括第一电阻、第二电阻；第一电容、第二电容；第一二极管和第二二极管、以及第一发光二极管；其连接关系为：第二电阻与第一发光二极管串联，形成具有两端子的第一网络，第一网络与第二电容与第一电阻同时并联，形成具有两端子的第二网络，第二网络再与第二二极管串联，形成具有两端子的第三网络，第三网络的特征是，第二二极管和第一发光二极管为同向；第三网络与第一二极管反向并联，形成具有两端子的第四网络，第四网络再与第一电容串联，并形成一个串联的两端子网络，所述的串联的两端子网络简称为串联网络，串联网络的两个端子分别为第一端子、第二端子。
  5. 根据权利要求4所述的直接滤波式开关电源，其特征在于：将第一电阻改为和第一二极管并联。
  6. 根据权利要求4所述的直接滤波式开关电源，其特征在于：还包括另一电容，另一电容也与第四网络串联，并且另一电容和第一电容分别与串联网络的两个端子相连接。
  7. 根据权利要求2-6任一项所述的直接滤波式开关电源，其特征在于：第一发光二极管为光耦中的发光器，即光耦中的发光二极管。
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