WO2018024036A1 - 一种带有源功率因数校正的开关电源 - Google Patents

一种带有源功率因数校正的开关电源 Download PDF

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Publication number
WO2018024036A1
WO2018024036A1 PCT/CN2017/088001 CN2017088001W WO2018024036A1 WO 2018024036 A1 WO2018024036 A1 WO 2018024036A1 CN 2017088001 W CN2017088001 W CN 2017088001W WO 2018024036 A1 WO2018024036 A1 WO 2018024036A1
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network
circuit
capacitor
parallel
series
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PCT/CN2017/088001
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English (en)
French (fr)
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王保均
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广州金升阳科技有限公司
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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
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • 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

Definitions

  • the invention relates to the field of switching power supplies, in particular to a high-reliability switching power supply with alternating current or direct current conversion to direct current with source power factor correction.
  • the switching power supply is widely used.
  • the flyback (Fly-back) switching power supply is dominant.
  • the flyback (Fly-back) switching power supply is dominant.
  • the power factor correction circuit is simply referred to as PFC circuit and is an abbreviation of Power Factor Correction.
  • a low-cost way is to connect an inductor in series between the rectifier bridge and the filter capacitor. Because it is a passive device, it is still called passive power factor correction.
  • Active power factor correction is the Chinese name of “Active Power Factor Correction”, referred to as APFC. It is usually defined as: a DC-DC switching converter is connected between the rectifier and the load, and current feedback technology is applied to make the input current i i Waveform Tracking AC input sinusoidal voltage waveforms make i i close to a sine wave. Thus, the total harmonic distortion THD of the input current is less than 5%.
  • the power factor can be increased to 0.99 or higher. Since active devices are used in this scheme, it is called active power factor correction. Generally, the PF value is 0.9 or more, which can meet the standards of many countries. If the load is a switching power supply, then the system has the source power factor.
  • the corrected switching power supply also called the two-stage switching type switching power supply, is used as the second-stage switching power supply of the first-stage PFC load, and is generally called the main power stage converter, which is simply referred to as the main power stage.
  • the power factor correction inductor is serially connected to the rectifier bridge, which is still passive power factor correction, not active power factor correction.
  • Figure 1 shows a mainstream Boost APFC circuit, generally written as a Boost PFC circuit. This is because the Boost circuit must be an active power factor correction circuit.
  • Vo Connected to other power stage DC-DC converters, the main power stage, is the standard switching power supply with source power factor correction.
  • Flyback converters, half-bridge converters, LLC converters, asymmetric half-bridges, and single-switch forward circuits can all be the main power stages.
  • the rectifier bridge Z101 is generally composed of four rectifier diodes.
  • Figures 4-1, 4-2, and 4-3 of the authorized invention specification of Application No. 201210056555.9 give several known drawings of the rectifier bridge.
  • C101 in Fig. 1 is a filter capacitor of the PFC, which is generally an electrolytic capacitor, hereinafter referred to as electrolysis.
  • the BOOST power factor correction circuit needs to use the electrolysis with the withstand voltage up to the peak of the input AC. For the 220VAC mains in China, consider the occasional voltage will rise to 264VAC, the peak value is 373V, and the electrolysis with the withstand voltage above 400V should be used as the BOOST power factor correction circuit.
  • the output filter capacitor in order to obtain a good power factor, the output voltage of the BOOST power factor correction circuit is generally set at about 400V, the electrolysis used is generally 450V withstand voltage, and some manufacturers cooperate to introduce 420V withstand voltage electrolysis. Since the output voltage of the BOOST power factor correction circuit is already 400V high, it brings trouble to the subsequent second-level main power level topology selection, such as the computer output voltage is 12V, 5V and 3.3V, which is reduced from 400V to such low. For the voltage, a MOS tube with high withstand voltage, high current, and low internal resistance is required as the switching tube. Because of this, the world's research on buck power factor correction circuits is increasing.
  • buck PFC circuit is also a buck power factor correction circuit, also uses electrolysis as a filter capacitor of PFC.
  • capacitor C101 is often 400V to 450V withstand voltage electrolysis, while electrolysis with a pressure greater than 250V, its low temperature can only work to -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 switching 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 switching power supply with source power factor correction is simply divided into three parts: power factor correction circuit, filter circuit, and main power stage.
  • the rectifier bridges Z101 and L101, the diode D101 and the switch transistor Q101, and the PWM control circuit constitute a power factor correction circuit;
  • the electrolytic C101 for filtering which is originally a power factor correction circuit is independent. It is regarded as a filter circuit.
  • the filter circuit can be an electrolysis, or it can be a parallel connection of electrolysis and high-voltage chip capacitors. It can also be a parallel connection between electrolysis and CBB-type film capacitors. It can also be a ⁇ -type filter circuit or low-voltage electrolysis. Connected in series with other high voltage capacitors in series; At the output Vo of the circuit of Figure 1, the other power stage DC-DC converters connected are the main power stages. Note that the power stage is not shown in Figure 1.
  • FIG. 2 of the prior patent A is cited as FIG. 2 of the present application, and number adjustment is performed: the C1 of the prior patent A is adjusted to the CA1 in FIG. 2 of the present application.
  • the C2 of the prior patent A is adjusted to CA2 in FIG. 2 of the present application, that is, CA1 in FIG. 2 of the present application represents C1 of the prior patent A, and CA2 in FIG. 2 of the present application represents C2 of the prior patent A.
  • the excitation current of the main power stage does not substantially appear in the inductor L, and the LED does not emit light;
  • the ESR of the electrolysis CA2 rises, the main When the excitation current of the power stage appears in L, and the power tube in the main power stage is turned off, the excitation current flowing through L cannot be abruptly changed, and the LED is continuously flowed through the illuminator, and the LED is driven to emit light, thereby reminding the user:
  • the ESR of the electrolytic CA2 of the switching power supply has risen, and there is a risk of failure, avoiding the loss, and having the characteristics of low cost, constant efficiency, and easy implementation.
  • the existing patent A uses the inductance L, and increases the capacitance CA1 to form a ⁇ -type filter circuit, in order to provide an indication before the filter electrolysis completely fails, and informs before the switching power supply completely fails. Since CA1 is subjected to the high-frequency ripple of the PFC circuit, the maximum ripple current of CA1 is required to be large, and the ESR of CA1 is required to be low, and the capacity of CA1 is not too low, and the cost of CA1 is high. At the same time, the circuit should be connected in series between the PFC circuit and the filter electrolytic capacitor, and the original circuit should be modified.
  • the capacitors CA1 and CA2 independently absorb higher harmonics in the switching power supply PFC circuit and the higher harmonics of the main power stage, which is not conducive to the improvement of electromagnetic compatibility (EMC) performance.
  • EMC electromagnetic compatibility
  • the present invention solves the deficiencies of the existing switching power supply with source power factor correction, and provides a switching power supply with source power factor correction, which provides an indication before the filter electrolytic capacitor completely fails, and does not With the ⁇ -type filter circuit, there is no inductor L and capacitor CA1 that affect the EMC performance, and the pre-notification before the switching power supply is completely failed is realized at a lower cost.
  • a switching power supply with source power factor correction comprising a power factor correction circuit, a filter circuit, a main power stage, an indicating circuit having two terminals, and an AC input via a power factor correction circuit
  • the filter circuit is connected, and 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 having two terminals, the third network is characterized in that the second diode and the first light emitting diode are in the same direction; and the third network is connected in anti-parallel with the first diode to form a second terminal a four network, the fourth network is connected in series with the first capacitor, and forms 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 terminals
  • the cost is lower than the prior art using the ⁇ -type filter circuit, there is no inductance L that affects the EMC performance, and the capacitor CA1 is not stored, the cost is low, and the volume is small, and the same is realized: before the electrolytic capacitor fails, the indicator light-emitting diode emits light or The light-emitting diodes in the optocoupler have current flowing through them, and the optocouplers output an isolated signal to alert the user or other circuits.
  • FIG. 1 is a schematic diagram of a PFC portion of a conventional active power factor corrected switching power supply
  • FIG. 2 is a schematic diagram of a switching power supply with source power factor correction of the prior patent A;
  • FIG. 3 is a schematic diagram of a switching power supply with source power factor correction according to a first embodiment of the present invention
  • 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 PFC to electrolytic charging and the exciting current i M of the main power stage in the first embodiment
  • FIG. 6 is an equivalent circuit diagram of high frequency charging and discharging currents of 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 switching power supply with source power factor correction according to a second embodiment of the present invention.
  • 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.
  • Figure 9 is a schematic diagram of a switching power supply with source power factor correction in accordance with a third embodiment of the present invention.
  • FIG. 3 shows a first embodiment of the present invention, which is a schematic diagram of a switching power supply with source power factor correction, including a power factor correction circuit PFC, a filter circuit 200, a main power stage 300, and an indicating circuit having two terminals.
  • the AC input IN is connected to the filter circuit 200 via a power factor correction circuit PFC
  • the filter circuit 200 is connected in parallel with the main power stage 300.
  • the filter circuit includes at least one electrolytic capacitor CA2 connected in parallel with the main power stage, and the feature is:
  • the indicating circuit 400 is connected in parallel with the electrolytic capacitor CA2.
  • the indicating circuit 400 includes at least a first resistor R1, a first capacitor C1, a first diode D1, and a first LED.
  • 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 switching power supply with source power factor correction 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 333/630V chip capacitor
  • the nominal capacity is 0.033uF
  • the D1 is 1N4148
  • the R1 is 12K patch.
  • the switching power supply with source power factor correction is used.
  • the 120W power supply is used.
  • the model is LI120-10B12.
  • the main control chip is TEA1716
  • the electrolytic CA2 for filtering is 150uF/400V. It is a domestic high-quality capacitor, PFC.
  • the working frequency is 60-100KHz
  • the main power level is LLC circuit
  • the working frequency is 100-120KHz.
  • the indicating circuit 400 in Figure 3 is directly connected to the electrolytic CA2 in the switching power supply.
  • the forward parallel or reverse parallel connection can be used, and the parallel connection is positive: the terminal 1 is connected to the positive electrode of the filter electrolysis, and the terminal 2 is connected to the negative of the filter electrolysis. Pole; or reverse parallel: terminal 1 is connected to the negative electrode of the filter electrolysis, and terminal 2 is connected to the positive electrode of the filter electrolysis.
  • the various indicators of the power source are measured, which are the same as before, especially the conversion efficiency, and there is no observable drop, which remains at 93.7%, and the LED of the LED Does not shine.
  • 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. 3 emits light, and the average value of the operating current is actually measured to be 1.9 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.
  • a current for charging the electrolytic CA2, from the PFC circuit, the PFC operating frequency is 60-100 KHz, that is, the frequency of the charging current is in the range of 60-100 KHz; the second is the discharging of the main power stage 300 by the electrolytic CA2, the discharging current
  • the excitation current of the main power stage 300 has an operating frequency of 100-120 KHz, that is, charging and discharging are high-frequency ripple currents; and a third type: at both ends of CA2, according to the existing theory of PFC, there is also a PFC circuit.
  • the output low-frequency ripple has a frequency twice the mains frequency of the input IN and is a standard sine wave, called 2 times the power-frequency large ripple.
  • the PFC circuit requires the input current to be in phase with the voltage. That is, the output power of the PFC circuit is the product of voltage and current. The product of two sines is a cosine of 2 times. The last constant, the constant is the DC amount.
  • the excitation current i M of the main power stage is shown in Figure 4, where Ugs is the driving voltage of the gate and source of the upper tube of the switching tube in the main power stage.
  • the path of the exciting current i M is shown in Figure 5, and the charging current is also high.
  • C1 has a small capacity of 0.033uF, compared with 150uF of CA2, the charging and discharging current in C1 is only two ten thousandth of CA2, and the charging and discharging current of CA2 is about 0.34A, then charging through C1 The discharge current is only 0.07 mA. At this time, the LED does not emit light because of the presence of R1.
  • the capacitive reactance of electrolytic CA2 at the switching frequency of 60KHz is 1/(2 ⁇ fC), which is calculated to be 17.7m ⁇ , which is much smaller than its ESR.
  • ESR plays a major role; the waveform shown in Figure 4 is not a sine wave, its base The wave is a sine wave, and its harmonic frequency is higher than 60KHz, so this is only an estimate.
  • C1 is 0.033uF, its capacity is small, but its capacitance is 80.4 ⁇ at 60KHz frequency, it can provide enough 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 C1 is small, C1 has the function of passing high frequency and blocking low frequency; at both ends of CA2, according to the existing theory of PFC, there is also a low frequency ripple outputted by a PFC circuit,
  • the frequency is twice the mains frequency of the input IN, and it is a standard sine wave, which is called 2 times power frequency large ripple.
  • the current of the 2 times power frequency large ripple caused by the PFC circuit passes through C1 is very small, and it is on the resistor R1.
  • the resulting voltage drop is not enough to illuminate the LED, and as the ESR of the electrolytic CA2 rises, the high-frequency excitation current of the power stage 300 and the high-frequency charging current of the PFC rise in synchronization with the voltage drop generated on the ESR, and the formed high-frequency pattern
  • the wave voltage rises with the aging of the electrolytic CA2.
  • C1 has a high-frequency effect. 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 valve. The magnitude of the value, that is, the voltage generated by the high-frequency ripple voltage across the capacitor C1 across R1 is lowered by the turn-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 CA2 has risen to the point of interest so that the user can decide the next step.
  • the load on the switching power supply with source power factor correction is reduced to 30%, the LED is still illuminated, and the operating current is reduced to 0.45 mA.
  • the use of high-brightness LEDs is still very noticeable.
  • the electrolytic capacitor can still work, but the excitation current of the main power stage has a large amount of heat in the ESR, in this case 0.24W, the electrolytic capacitor is already under high heat, which is already accelerating aging, in general 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 function is the same after the position is interchanged. Therefore, the scheme 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.
  • the circuit of 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. 3, and can be normally operated.
  • the six 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. 2, and 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 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 power stage 300 is changed from the LLC circuit to the power level of the ordinary notebook computer power adapter, which is roughly: power 65W, the main control chip is NCP1234, flyback topology, output voltage is 19V, 3.42A, and its rectification filter is removed. Circuit, only the power stage is reserved.
  • the adjustment R1 is 22K, and the invention shown in Fig. 3, that is, a switching power supply with source power factor correction, achieves the object of the invention.
  • the power stage can also be replaced with a half-bridge conversion circuit. Or a single-tube forward circuit, or a full-bridge circuit, the measured circuit can achieve the purpose of the invention; the PFC circuit is replaced with a buck PFC circuit, and the circuit can also work normally.
  • the current flowing through the LED of the LED is not DC, but a complex high-frequency superimposed current of the same frequency as the PFC and the power stage 300.
  • the lead of the LED is long, the electromagnetic radiation cannot be ignored;
  • the LED is replaced with an illuminator in the 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 shows a first embodiment of the present invention, which is a schematic diagram of a switching power supply with source power factor correction, including a power factor correction circuit PFC, a filter circuit 200, and a main power stage 300.
  • An indicating circuit 400 having two terminals, the AC input IN is connected to the filter circuit 200 via a power factor correction circuit PFC, and the filter circuit 200 is connected in parallel with the main power stage 300.
  • the filter circuit includes at least one electrolytic capacitor CA2 connected in parallel with the main power stage.
  • the indication circuit 400 is connected in parallel with the electrolytic capacitor CA2.
  • 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 For the first network 21 having two terminals, the indicating circuit 400 of FIG. 8 is separated for simplicity. 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 terminals.
  • Second network 22, second network 22 and then The second diode D2 is connected in series to form a third network 23 having two terminals.
  • the third network 23 is characterized in that the second diode D2 and the first LED are in the same direction; the third network 23 and the first two
  • the pole tube D1 is connected in anti-parallel to form a fourth network 24 having two terminals.
  • the fourth network 24 is further connected in series with the first capacitor C1 and forms a two-terminal network in series, which is an indicating circuit 400, and the two terminals in series
  • the network 400 is simply referred to as a series network.
  • the two terminals of the series network 400 are respectively a first terminal 1 and a second terminal 2.
  • the series network 400 is also a functional body of the switching power supply with source power factor correction of the present invention.
  • the main power stage 300 employs a flyback circuit topology.
  • 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.
  • the electrolytic CA2 when the electrolytic CA2 is normal, it is 68uF/400V, its ESR is about 0.5 ⁇ , and there are three kinds of ripple currents at the two ends of the electrolytic CA2.
  • the first one is the high-frequency current of the PFC circuit charging the electrolytic CA2.
  • the frequency is 60-100KHz;
  • the second is the high-frequency current of the electrolytic CA2 discharging to the main power stage 300, the frequency is 65KHz;
  • the third is the low-frequency ripple of the first high-frequency ripple current filtered by CA2, Standard sine wave, 2 times power frequency and large ripple.
  • C1 has a small capacity. At the low frequency of 2 times power frequency and large ripple, it is 100Hz or 120Hz. The capacitive reactance of C1 is large, and the current flowing through C1 is extremely small. After D2 rectification, C2 is filtered, and at both ends of R1. The voltage formed is not sufficient to illuminate the LED.
  • the ESR of the electrolytic CA2 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 CA2, 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.
  • the component parameters are: CA2 is 68uF/400V, C1 is 473/630V chip capacitor, the nominal capacity is 0.047uF, C2 is 104/16V chip capacitor, D1 and D2 are 1N4148, R2 is 1K, R1 For 10K, the LED is 3AR2UD.
  • the power stage 300 is the power level of the ordinary notebook computer power adapter, generally: power 65W, the main control chip is NCP1234, flyback topology, output voltage is 19V, 3.42A, and its rectifier filter circuit is removed, only the power level is reserved.
  • 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.
  • 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 all of them can work normally. It can be seen that the eight modes of the circuit of the second embodiment can achieve the purpose 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 switching power supply with source power factor correction according to a third embodiment of the present invention, including a power factor correction circuit PFC, a filter circuit 200, a main power stage 300, and one having two
  • the terminal indicating circuit 400 the AC input IN is connected to the filter circuit 200 via the power factor correction circuit PFC, and the filter circuit 200 is connected in parallel with the main power stage 300.
  • the filter circuit includes at least one electrolytic capacitor CA2 connected in parallel with the main power stage.
  • the indicating circuit 400 is connected in parallel with the electrolytic capacitor CA2, 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 switching power supply with source power factor correction 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 stage 300 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 capacitors CA21 and CA22 of the same capacity in series, and the connection point is connected to the half bridge.
  • the voltage equalizing resistor in parallel with the electrolytic capacitor is not shown in the figure;
  • 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 CA2, and the electrolytic CA2 is formed by connecting the electrolytic capacitors CA21 and CA22 in series. 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

一种带有源功率因数校正的开关电源，包括功率因数校正电路PFC，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CA2并联，C1的容量小，PFC引起的工频倍频正弦纹波，通过C1的电流极小，在R1上产生的压降不足以点亮LED；随着CA2的ESR上升，高频充放电电流在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，调节R1的阻值可以调节阀值的大小。从而提醒使用者电解CA2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

一种带有源功率因数校正的开关电源 技术领域
本发明涉及开关电源领域，特别涉及带有源功率因数校正的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，Power Factor，也称功率因素)不作要求的场合，反激式(Fly-back)开关电源占主流。对于输入功率大于75W的电源，甚至是很多照明用的开关电源式驱动器，尽管功率在75W以下，国家标准对其功率因数有要求。
目前已有采用功率因数校正电路解决这一问题，功率因数校正电路简称为PFC电路，是Power Factor Correction的缩写。一种低成本的方式是：在整流桥和滤波电容之间串联一只电感，由于都是无源器件，仍称为无源功率因数校正。有源功率因数校正是“Active Power Factor Correction”的中文名称,简称APFC，通常的定义为：在整流器和负载之间接入一个DC-DC开关变换器，应用电流反馈技术，使输入端电流ii波形跟踪交流输入正弦电压波形，可以使ii接近正弦波。从而使输入端电流的总谐波失真THD小于5％。而功率因数可以提高到0.99或更高。由于这个方案中使用了有源器件，故称为有源功率因数校正，一般PF值做到0.9以上，就可以满足很多国家的标准，若负载为开关电源，那么，系统就是带有源功率因数校正的开关电源，又叫两级变换式开关电源，作为第一级PFC负载的第二级开关电源，通常称为主功率级变换器，简称主功率级。
整流桥中串入功率因数校正电感，仍属无源功率因数校正，不是有源功率因数校正。我们把整流后直接滤波的开关电源，以及整流桥串入功率因数校正电感，再滤波的开关电源，因为只有一级功率变换电路，都定义为：直接滤波式开关电源。
图1示出了一种主流的Boost APFC电路，一般都写为Boost PFC电路，这是因为，带有Boost电路的，一定是有源功率因数校正电路，在图1的电路的输出端Vo，再接上其它的功率级DC-DC变换器，即主功率级，就是标准的带有源功率因数校正的开关电源。反激变换器、半桥变换器、LLC变换器，不对称半桥，单管正激电路都可以成为主功率级。
整流桥Z101一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。
传统的BOOST功率因数校正电路，其工作原理可以参见电子工业出版社的《开关电源的原理与设计》第190页、191页，该书ISBN号7-121-00211-6。
因电解电容单位体积的电容量非常大，所以在带有源功率因数校正的开关电源中，也使用了电解电容，图1中的C101是PFC的滤波电容，一般为电解电容，以下简称电解。BOOST功率因数校正电路需要使用耐压高达输入交流电峰值以上的电解，对于我国的220VAC市电，考虑偶尔电压会升至264VAC，峰值为373V，需使用耐压400V以上的电解作为BOOST功率因数校正电路的输出滤波电容；为了获得良好功率因数，BOOST功率因数校正电路的输出电压一般定在400V左右，使用的电解一般为450V耐压，有的厂商配合地推出420V耐压的电解。由于BOOST功率因数校正电路的输出电压已经为400V之高，给后续的第二级的主功率级拓扑选择带来麻烦，如计算机输出电压为12V、5V以及3.3V，从400V降到这么低的电压，需要用高耐压、大电流、低内阻的MOS管作为开关管。正因为如此，全球对降压式功率因数校正电路研究日益加强。
如美国专利公开号US 2010123448的《CONTROLIED ON-TIME BUCK PFC》美国专利公开说明书示出了一种降压式PFC电路，按其公开的技术方案，使用了BUCK电路，PWM方式控制BUCK电路中的开关。
再如中国已授权的申请号为201210271808.4的《一种降压式PFC电路》也是一种降压式功率因数校正电路，同样使用电解作为PFC的滤波电容。
随着工业领域中智能化系统的推广，使用电解作为PFC的滤波电容的不足之处也随之体现出来，见图1，因为使用了电解C101，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C101经常为400V至450V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、成本过高。
对于使用降压式功率因数校正电路的开关电源，由于降压式PFC输出电压低，其滤波用的PFC电解要承受的纹波电流更大，其使用寿命也不容忽视。
当然，还有一种功率因数校正电路，使用BUCK-BOOST作为功率因数校正电路的主拓扑，可以降压，也可以升压，但控制复杂，目前并没有普及。
为了方便，带有源功率因数校正的开关电源，我们简单地分为三个部分：功率因数校正电路，滤波电路，主功率级。如图1中，整流桥Z101、L101、二极管D101和开关管Q101以及PWM控制电路组成了功率因数校正电路；本申请为了描述方便，把本来属于功率因数校正电路的滤波用的电解C101独立出来，看作是滤波电路，滤波电路可以是一只电解，也可以是电解和高压贴片电容的并联，也可以是电解和CBB类的薄膜电容并联，也可以是π型滤波电路，也可是低压电解串联后再和其它高压电容并联； 在图1的电路的输出端Vo，连接的其它的功率级DC-DC变换器，就是所述的主功率级，注，图1中并未画出功率级。
设计一台开关电源时，经常面临电解C101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。成本太高，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％以上是由滤波的电解先行失效引起的。
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。在发明人的申请号为201610040059.2的现有专利申请《一种带有源功率因数校正的开关电源》中，给出一种解决方案，为了方便，该专利申请201610040059.2以下称为现有专利A。
参见现有专利A的图2，为了方便，引用了现有专利A的图2作为本申请的图2，并进行了编号调整：现有专利A的C1调整为本申请图2中的CA1，现有专利A的C2调整为本申请图2中的CA2，即本申请图2中的CA1表示现有专利A的C1，本申请图2中的CA2表示现有专利A的C2。
现有专利A的解决方案描述：在电解C101的PFC供电回路中串入指示电路，并增加电容CA1，指示电路由发光单元和电感L并联组成，确保PFC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，电解C101也就成了CA2，当电解CA2正常时，主功率级的激磁电流基本上不出现在电感L中，LED不发光；电解CA2的ESR上升较大时，主功率级的激磁电流出现在L中，且主功率级内的功率管关断时，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CA2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。
现有专利A使用了电感L，并增加电容CA1构成了π型滤波电路，才能实现在滤波电解完全失效前提供指示，在开关电源完全失效前预先告知。由于CA1要承受PFC电路的高频纹波，要求CA1的最大纹波电流大，要求CA1的ESR很低，CA1的容量就不会太低，CA1的成本就会很高。同时该电路要串联于PFC电路与滤波电解电容之间，对原有的电路要进行改动。
另外，因为使用了电感L，在开关电源PFC电路以及主功率级的高次谐波下，使得电容CA1和CA2独立吸收高次谐波，不利于电磁兼容(EMC)性能的提高。
发明内容
有鉴于此，本发明要解决现有的带有源功率因数校正的开关电源存在的不足，提供一种带有源功率因数校正的开关电源，实现在滤波电解电容完全失效前提供指示，同时不使用π型滤波电路，不存在影响EMC性能的电感L和电容CA1，以更低成本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，一种带有源功率因数校正的开关电源，包括功率因数校正电路，滤波电路，主功率级，一个具有两个端子的指示电路，交流输入经功率因数校正电路连接滤波电路，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，进行详细的阐述。
本发明的有益效果为：
成本比使用π型滤波电路的现有技术低，不存在影响EMC性能的电感L，也不存电容CA1，成本低，体积小，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为现有的有源功率因数校正的开关电源的PFC部份的原理图；
图2为现有专利A的带有源功率因数校正的开关电源的原理图；
图3为本发明第一实施例的带有源功率因数校正的开关电源的原理图；
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PFC对电解充电、主功率级的激磁电流iM的路径示意图；
图6为图5主功率级的高频充、放电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为本发明第二实施例的带有源功率因数校正的开关电源的原理图；
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为本发明第三实施例的带有源功率因数校正的开关电源的原理图。
具体实施方式
第一实施例
图3示出了本发明第一实施例，为带有源功率因数校正的开关电源的原理图，包括功率因数校正电路PFC，滤波电路200，主功率级300，一个具有两个端子的指示电路400，交流输入IN经功率因数校正电路PFC连接滤波电路200，滤波电路200和主功率级300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CA2，其特征是： 指示电路400与电解电容CA2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也是本发明的带有源功率因数校正的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333/630V的贴片电容，标称容量为0.033uF，D1为1N4148，R1为12K的贴片电阻，按图3组成带有源功率因数校正的开关电源，使用了120W电源，型号为LI120-10B12，其主控芯片采用TEA1716，其滤波用电解CA2为150uF/400V，为国产优质电容，PFC工作频率为60-100KHz，其主功率级为LLC电路，工作频率为100-120KHz。
要注意是的：图3中指示电路400直接与开关电源中电解CA2并联，正向并联或反向并联都可以，正向并联：即端子1连接滤波电解的正极，端子2连接滤波电解的负 极；或反向并联：端子1连接滤波电解的负极，端子2连接滤波电解的正极。下文会专门讲解。
当第一实施例以正向并联方式焊入，实测该电源的各方面指标，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，仍保持在93.7％，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5.1Ω时，相当于150uF/400V的电解电容的ESR从良品时的0.4Ω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3中的发光管LED发光，且工作电流的平均值实测为1.9mA。
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0.4Ω，滤波用电解CA2两端的纹波电流有三种，以开关电源满载工作时为例说明。
一种为对电解CA2充电的电流，来自PFC电路，PFC工作频率为60-100KHz，即充电的电流的频率在60-100KHz区间；第二种为电解CA2对主功率级300放电，放电的电流为主功率级300的激磁电流，其工作频率为100-120KHz，即充放电均为高频纹波电流；第三种：在CA2的两端，按PFC现有的理论，还存在一个PFC电路输出的低频纹波，其频率为输入IN的市电频率2倍，且是标准的正弦波，称为2倍工频大纹波，事实上为第一种的包络,即第一种的高频纹波电流被CA2滤波后的低频纹波，PFC电路要求输入的电流与电压同相，即PFC电路的输出功率为电压与电流的乘积，两个正弦的乘积为一个2倍频的余弦加上一个常数，常数即为直流份量。
主功率级的激磁电流iM如图4所示，其中，Ugs为主功率级中开关管上管的栅极与源极的驱动电压，激磁电流iM的路径见图5,充电电流也是高频电流：从PFC到CA2形成环路。
由于C1容量较小，为0.033uF，相比CA2的150uF，C1中的充电、放电电流仅为CA2的万分之二，CA2的充电、放电电流约为0.34A，那么，流过C1的充电、放电电流仅为0.07mA，这时，LED因为存在R1而不发光。
电解CA2在60KHz的开关频率下的容抗为1/(2πfC)，计算出来为17.7mΩ，远小于其ESR，在60KHz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60KHz要高，所以这里只是估算。
对CA2充电和放电电流，总称为iALL，这个电流在CA2的ESR上形成的压降，参见图6，为U＝IR＝0.34×0.4＝0.136V。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，这是放电波形，事实上，还存在充电波形，远比图4中的波形复杂，显然0.136V的平均值不足以让LED导通而发光。
当电解CA2的ESR从良品时的0.4Ω左右已上升至5.5Ω，即电解CA2已接近失效边缘。这个充、放电电流在CA2的ESR上形成的压降，以放电电流为例，参见图6，为U＝IR＝0.34×5.5＝1.87V。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1.87V为平均值，峰值约为其1.4至2倍，约为3.2V，这个电压经过C1后，足以让LED导通而发光。
C1为0.033uF，其容量较小，但在60KHz的频率下，其容抗为80.4Ω，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；在CA2的两端，按PFC现有的理论，还存在一个PFC电路输出的低频纹波，其频率为输入IN的市电频率2倍，且是标准的正弦波，称为2倍工频大纹波，PFC电路引起的2倍工频大纹波通过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CA2的ESR上升，功率级300的高频激磁电流和PFC的高频充电电流在ESR上产生的压降同步升高，形成的高频纹波电压随着电解CA2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电容CA2的183.3分之一以下即可。如CA2为150uF，那么C1应在(150uF/183.3)＝0.818uF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0.82uF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CA2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，把带有源功率因数校正的开关电源的负载降至30％，LED仍发光，工作电流降至0.45mA，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0.24W，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，所以指示电路的方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3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3中指示电路400，都可以正常工作，可见，第一实施例的六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，通过电容C1a和C1b的漏电流容易控制在限定值以下来实现安规达标。
同样，把功率级300由LLC电路换为普通笔记本电脑电源适配器的功率级，大体为：功率65W，主控芯片为NCP1234，反激拓扑，输出电压为19V，3.42A，并去了其整流滤波电路，只保留功率级。调节R1为22K，图3示出的本发明，即带有源功率因数校正的开关电源一样实现发明目的。图3中，功率级也可以更换为半桥变换电路， 或单管正激电路，或全桥电路，实测电路都是可以实现发明目的；PFC电路更换为降压式PFC电路，电路也是可以正常工作的。
其实第一实施例的内容中，包括了多种实施方式，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PFC、功率级300同频的、复杂的高频叠加电流，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示出了本发明第一实施例，为带有源功率因数校正的开关电源的原理图，包括功率因数校正电路PFC，滤波电路200，主功率级300，一个具有两个端子的指示电路400，交流输入IN经功率因数校正电路PFC连接滤波电路200，滤波电路200和主功率级300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CA2，其特征是：指示电路400与电解电容CA2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，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也是本发明带有源功率因数校正的开关电源的功能主体。
主功率级300采用了反激电路拓扑。
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CA2正常时，为68uF/400V，其ESR约为0.5Ω，电解CA2两端的纹波电流有三种，第一种为PFC电路对电解CA2充电的高频电流，频率为60-100KHz；第二种为电解CA2对主功率级300放电的高频电流，频率为65KHz；第三种为第一种的高频纹波电流被CA2滤波后的低频纹波,为标准的正弦波，2倍工频大纹波。
C1容量较小，在2倍工频大纹波的低频下，为100Hz或120Hz，C1的容抗大，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CA2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CA2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：CA2正为68uF/400V，C1为473/630V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。功率级300为普通笔记本电脑电源适配器的功率级，大体为：功率65W，主控芯片为NCP1234，反激拓扑，输出电压为19V，3.42A，并去了其整流滤波电路，只保留功率级。
开关电源的负载为100％时，电解CL的ESR上升至5Ω时，LED中的电流为1.2mA；把带有源功率因数校正的开关电源的负载降至30％，LED仍发光，工作电流降至0.32mA，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CA2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，可见，第二实施例的8种方式的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
请见参见图9，图9示出了本发明第三实施例的带有源功率因数校正的开关电源的原理图，包括功率因数校正电路PFC，滤波电路200，主功率级300，一个具有两个端子的指示电路400，交流输入IN经功率因数校正电路PFC连接滤波电路200，滤波电路200和主功率级300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CA2，其特征是：指示电路400与电解电容CA2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也是本发明带有源功率因数校正的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300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电容CA21、CA22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CA2并联，电解CA2为电解电容CA21、CA22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. 一种带有源功率因数校正的开关电源，包括功率因数校正电路，滤波电路，主功率级，一个具有两个端子的指示电路，交流输入经功率因数校正电路连接滤波电路，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，其特征在于：指示电路与电解电容并联。
  2. 根据权利要求1所述的带有源功率因数校正的开关电源，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所述的带有源功率因数校正的开关电源，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所述的带有源功率因数校正的开关电源，其特征在于：指示电路包括第一电阻、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所述的带有源功率因数校正的开关电源，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所述的带有源功率因数校正的开关电源，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任一项所述的带有源功率因数校正的开关电源，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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