Method for detecting pulsating current of switching power supply capacitor and overcurrent protection

Abstract

The present application belongs to the field of electrical power supply, and is particularly suitable for power supply or electrolytic capacitor manufacturers to test the actual maximum allowed AC component of pulsating DC. It can simulate poor plug contact, and can freely control the on / off power grid frequency rectification charging circuit several to tens of times per second. The duration of each on / off rectification charging circuit is adjustable, and the actual maximum allowed AC component of pulsating DC of high-voltage electrolytic capacitor after grid frequency rectification can be tested. The present application can also directly add poor plug contact or grid undervoltage overload protection function, and can also add automatic input voltage increase function when the grid is in a super-wide undervoltage fluctuation state, which is equivalent to adding high-voltage electrolytic capacitor capacity in disguise, reducing the pulsating AC component of high-voltage electrolytic capacitor, and at the same time, can achieve the protection of national power grid and user equipment, especially the service life of high-voltage electrolytic capacitor.

Description

Technical Field

[0001] This invention belongs to the field of electrical power supply and is particularly suitable for switching power supply related circuits and products; it is also the best circuit device for electrolytic capacitor manufacturers to measure the maximum value of long-term pulse AC component of each capacitor. Background Technology

[0002] Electrolytic capacitors are essential components of switching power supplies. Because they are polarized, they can only be used with constant-direction steady or pulsed DC current. Any pulsating (or pulsed) DC current can be equivalently decomposed into a combination of pure steady DC current and multi-frequency pure sinusoidal AC current. The DC resistance of an electrolytic capacitor itself is very small and negligible, and the leakage current caused by insulation resistance during normal operation is also very small and negligible. The ratio of the AC component to the pure DC component in the pulsating DC current, also known as the "pulsation coefficient," is a key factor affecting the temperature rise of the electrolytic capacitor. This involves the ratio of the RC discharge circuit time constant between the capacitor and the load to the RC charging time constant of the capacitor's rectifier circuit. The capacitor industry commonly uses the concept of "ripple current" to describe this. Therefore, it is desirable for the product of the capacitor capacitance and the discharge circuit resistance to be as large as possible; this minimizes the difference between the peak voltage at full charge and the trough voltage at full discharge. Since the RC charging time constant of the capacitor's own rectifier circuit is very small, even adding a series current-limiting resistor to the rectifier circuit has little impact on the circuit. The main factor affecting the capacitor's temperature rise is the capacitor's discharge time constant, which is involved in energy transfer. After direct rectification from the power grid's AC frequency, the capacitor's withstand voltage requirement is very high, typically requiring high-voltage electrolytic capacitors of 400V or 450V or higher. This results in high costs. Many manufacturers' designers, under the same power requirement, reduce the required margin of high-voltage electrolytic capacitors to lower costs, unaware of the potential dangers. This is because the main characteristics of modern switching power supplies are: they often use transformer-type switching power supplies. [Based on whether there is a short-circuit loss in the DC component flowing through the switching power supply's regulating transistor? Switching power supplies are divided into two main categories: series [adjustable inductive reactance (i.e., inductive-capacitive LC combination) step-down switching power supplies] and transformer-type [commonly known as parallel (further subdivided: step-up / isolation and step-up)] switching power supplies]. A comparison reveals that: under AC 150V~ grid conditions, the maximum peak current flowing through the regulating transistor of a transformer-type switching power supply is 2.9 times that of a series-type switching power supply; under 90V~ grid conditions, the maximum peak current flowing through the regulating transistor of a transformer-type switching power supply is more than 5 times that of a series-type switching power supply. The DC component loss in this type of transformer-type switching power supply regulating transistor is inversely proportional to the input (mains) voltage. This effectively reduces the RC discharge time constant of the high-voltage capacitor, causing an increase in the AC / DC component ratio of the high-voltage electrolytic capacitor. This leads to overheating, aging, and even premature capacitor failure or short circuits. When power supply manufacturers reduce the main capacitor capacity, capacitor manufacturers need to provide better aluminum foil and manufacturing processes. Otherwise, the failure rate will be higher. Capacitor manufacturers often have to use higher voltage-resistant aluminum foil and higher temperature-resistant electrolytes to meet the power supply manufacturers' requirements for reduced high-voltage capacitor capacity.

[0003] If transformer-type switching power supply chip manufacturers don't add current limiting control, the input voltage fluctuation can easily adapt to fluctuations from 70V to 260V and still maintain normal voltage regulation. (This is because, in the principle of transformer-type switching power supplies, even if the input voltage is lower than the output voltage regulation value, they would rather burn out the switching transistor than not be able to regulate the voltage), so the potential danger is not apparent. Current limiting control by power supply chip manufacturers only provides protection within a general range. For example, small and medium power switching power supplies are allowed to tolerate mains voltage fluctuations of approximately 90V, while variable frequency air conditioner PFC (which belongs to the boost transformer-type switching power supply) is allowed to tolerate mains voltage fluctuations of at least 160V. However:

[0004] When encountering poor contact at the user's power supply plug, it's equivalent to an undervoltage fluctuation at the input power supply. This makes it more prone to short-circuit losses and a significant increase in current through the DC component of the regulating transistor in the transformer-type switching power supply. It also increases the likelihood of overheating and damage to the high-voltage electrolytic capacitors due to the accumulation of instantaneous overcurrent. For PFC power supplies, after startup or when the PFC stops working due to overload, the high-voltage electrolytic capacitors either haven't accumulated voltage or the accumulated 380V DC voltage drops to the normal power frequency grid's direct rectification and filtering state. If the main load is still operating or frequently starting, the pulsating AC component is even greater.

[0005] Existing capacitor manufacturers' ripple current detection technology uses only a simple sine wave superimposed on a DC power supply, which cannot reflect the impact of the current flowing through the power regulator of the switching power supply on the capacitor. Electrolytic capacitors are no longer used for decoupling, filtering, and AC-blocking coupling; they are now commonly used in the charging and discharging energy transfer of each stage of the rectifier circuit in switching power supplies. The most important characteristic is that when the mains frequency sinusoidal AC rectifier circuit is fully charged to its peak voltage, it forms a self-sufficient negative bias, causing the rectifier tube to be reverse-biased and cut off for a long time. It only conducts briefly when the peak voltage approaches in the next cycle, resulting in a very small conduction angle (current conduction period / cycle ratio) for the mains rectifier tube (only about 2 to 3 milliseconds of conduction in a 10-millisecond half-cycle), but a very large pulse current. The greater the voltage drop at the trough of the discharge circuit, the larger the amplitude of the next reciprocating charge-discharge current, the greater the AC component, and the more easily the capacitor heats up. Furthermore, for example, consider a power supply that drops from a full charge of 10V to a discharge voltage of 5V, versus one that drops from a full charge of 310V to a discharge voltage of 305V. Although both involve a 5V difference in voltage, the energy released differs significantly. The latter's energy release ratio for a 5V difference in high voltage is 41 times that of a 5V difference in low voltage. Therefore, for switching power supplies, under the minimum allowable undervoltage input voltage (e.g., 90V~), maximum output power, and highest temperature conditions, the difference between the peak voltage (90V~ × 1.4) and the deepest voltage trough of the discharge voltage drop after weekly charging of the high-voltage electrolytic capacitor should be measured. This is crucial for accurately determining the maximum allowable ripple current and capacitance. Given the difficulty of measuring and comparing the AC / DC component ratio of various capacitors using existing technology, and the inability to determine whether capacitor damage is caused by poor user plug contact, which is detrimental to the switching power supply, especially the high-voltage electrolytic capacitor, the following measures are taken: Summary of the Invention

[0006] The purpose of this invention is to help power supply and capacitor manufacturers design a destructive circuit testing device that can simulate poor plug contact, used to compare the adaptive maximum AC / DC component ratio of various electrolytic capacitors. This also helps users prevent hazards caused by poor mains plug contact when using transformer-type switching power supplies and provides a warning.

[0007] The basic principle and method of implementing this scheme are as follows: A voltage comparator or monostable multivibrator with hysteresis voltage difference characteristic (5) is designed. Through the resistor-capacitor R72 and C72 integration circuit (8), a near-sawtooth wave is formed. After being fed back to the hysteresis voltage difference (VH, VL) characteristic voltage comparator (5) through the pre-amplifier signal source matching circuit (6), a rectangular pulse wave oscillator is directly formed. Then, through the electronic relay circuit (2), it is used as an electronic switch connected in series in the power frequency grid rectifier charging circuit (i.e., forming a pulse current generator). It is used to simulate the frequent on / off function of the power grid rectification, which can represent the harm of poor plug contact (equivalent to the unstable undervoltage fluctuation of the power grid). When the plug makes poor contact, the mains rectifier charging circuit is interrupted. However, because the high-voltage electrolytic capacitor Z continues to operate in the discharge circuit, the DC component flowing through the transformer switching power supply regulating tube V suffers a large short-circuit loss. In particular, the peak current flowing through the switching power supply regulating tube V is extremely large. As a result, the AC component of the high-voltage electrolytic capacitor Z will increase significantly due to the next cycle of charging and discharging, and it will generate significant heat. If the cyclic simulation has poor contact, the high-voltage electrolytic capacitor will overheat and be damaged.

[0008] Existing technologies allow for easy testing of capacitors for withstand voltage and temperature variations, including destructive testing, particularly for high-voltage electrolytic capacitors. However, comparing the current withstand capabilities of different products is extremely difficult with current testing. This is because current testing requires a closed-loop circuit; however, most electrolytic capacitor failures outside of capacitor manufacturing processes and abnormal loads are due to poor plug contact (or equivalently, undervoltage fluctuations / frequent power grid switching), causing the transformer-type switching power supply to continue operating at excessive current. Even with frequent plugging and unplugging of the main switch by power supply designers, high-voltage electrolytic capacitors are unlikely to be damaged because the frequency is too low to achieve the desired current testing effect. Furthermore, modern transformer-type switching power supply manufacturers use self-excited power chip control. If the chip detects overcurrent, it will prematurely shut down the power supply's regulating transistor instead of shutting down the high-voltage electrolytic capacitor's rectifier charging circuit, making it impossible to continue simulated destructive capacitor overcurrent testing. Therefore, to simulate the current withstand capability of a capacitor, it is necessary to switch it on and off rapidly and frequently. To simulate poor plug contact = test under the condition of power grid undervoltage fluctuation: the current draw capability of the switching power supply regulating tube V from the high voltage electrolytic capacitor, the current pulse generator of this invention is required. For example, it can be switched on and off several or even more than ten times within 1 second. If the test is repeated frequently, the temperature rise of the capacitor can be felt to be obvious and the test results of the maximum pulsating current can be achieved in a destructive simulation.

[0009] Therefore, this invention is the first in the capacitor industry to develop a testing device for the actual current withstand capability of electrolytic capacitors. Advantages: Because a voltage rectangular wave generator (5) is designed and together with the electronic relay circuit (2) forms a current rectangular wave generator, it can simulate the frequent switching of the power grid several or more times within 1 second, allowing the originally working switching power supply to continue working for a moment, generating a large pull-down current, causing the high voltage electrolytic capacitor to have the largest difference between being fully charged and discharging to the lowest voltage every week. In this way, the maximum AC component withstand capability of the test capacitor can be artificially simulated when it is not damaged. [The accurate current parameters can be calculated from the voltage drop generated by the detection resistor RF using an oscilloscope], and at the same time, this invention directly adds protection for power supply manufacturers against overload shutdown circuits caused by poor plug contact or undervoltage of the power grid. Figure 4 [Example], to protect the power supply and, in particular, to protect the high-voltage electrolytic capacitors from damage. Attached Figure Description

[0010] This manual contains 10 illustrations across 3 pages. The illustrations on pages 1 and 2 show the following: when the detected signal source is below VL, the pulse transistor VKA is forced to turn off, resulting in a high-level output (1); when the detected signal source is above VH, the pulse transistor VKA is forced to saturate and conduct, resulting in a low-level output (0). These illustrations are suitable for capacitor and power supply manufacturers to simulate high-frequency contact defects in connectors for capacitor overcurrent protection testing. The illustration on page 3 shows the following: when the detected signal source is below VL, the pulse transistor VKA is forced to saturate and conduct, resulting in a low-level output (0); when the detected signal source is above VH, the pulse transistor VKA is forced to turn off, resulting in a high-level output (1). This is suitable for power supply manufacturers using circuits lacking comprehensive overcurrent protection functions such as mains power detection. All illustrations only describe the essential substantive features related to the innovative technology. The illustrations are derived from the schematic diagrams of printed circuit boards (PCBs) actually implemented by the inventor. Descriptions are progressively detailed, using necessary local magnification for specific descriptions. The functional name, component reference number, component parameters, or substitution range of each component in the circuit diagram are clearly indicated using different fonts for easy identification. For circuits consisting of multiple components forming a specific functional unit, large Arabic numerals are used within a dashed box in the diagram for easier reference to the instruction manual. Component reference numbers are in medium-sized boldface, and parameter specifications are in small-sized Song typeface. An asterisk (*) indicates adjustable parameters for non-inductor coils. "NC", ":", and other symbols are also used. "etc." indicates a removable, modifiable, or detachable terminal. "[" indicates that the component can be removed and short-circuited. When the primary winding of the pulse transformer is conducting, the primary and secondary induction polarity terminals of the same name are all indicated by a black dot. Items not annotated in the manual and drawings (especially components and their reference numbers) shall be interpreted according to legal or industry practice. Since the circuit components, parameters, and their reference numbers only represent the BOM parameters of the reference numbers and related attributes of the components in the printed circuit board (PCB) corresponding to the schematic diagram of the complete product, they are not marked specifically for this manual, but serve as a reference for specific products implementing the preferred embodiment of this innovation. Except for VCC, which generally refers to any high-potential power supply terminal, those with the same reference number or port marking in the drawings all refer to the same object and can be connected or substituted. In this manual, (especially in the same drawing), the same circuit number or component reference number indicates that the unit circuit or component has similar different schemes, and any one of them can be selected for substitution. The common terminal "ground" is divided into "cold ground" ⊥, which is not connected to the power grid, i.e. The low-potential common terminal of the "hot ground" connected to the power grid is available. Right now: Identification; In circuit diagrams, components that are in a switching state are indicated by pulse waveform symbols. Identification. The common terminal "⊥" can be connected to "cold ground" if the power supply manufacturer uses its own switching power supply for plug contact protection (or grid undervoltage protection). Moreover, the two switching power supply transformers T and T1 in the attached diagram can be combined. If the capacitor manufacturer and the power supply manufacturer simulate high frequency of plug contact problems, when making capacitor overcurrent protection test equipment, especially if a zero-crossing AND gate detection circuit (7) is required, ⊥ can be connected.

[0011] A brief description of each attached image is as follows: Figure 1 [This is the circuit diagram for this innovative general-purpose solution;] Figure 2 [It is replaceable] Figure 1 Another complete circuit diagram of the embodiment is the connection relationship between the optocoupler N2 and the four different sampling source integration circuits (8), matching circuits (6), and voltage comparator circuits (5) after removing the optocoupler N2; [ Figure 3 Example: Another complete schematic diagram suitable for overcurrent protection circuits; Figure 1-1 ]、[ Figure 3-1 ]: These are respectively Figure 1 , Figure 3 The required waveform description of the hysteresis characteristic is specified in the text. Figure 1-2 ]、[ Figure 3-2 ]: These are respectively Figure 1 , Figure 3 When the voltage enters undervoltage VL, the equivalent circuit of the positive feedback resistor R7 branch flips; Figure 1-3 ]、[ Figure 3-3 ]: These are respectively Figure 1 , Figure 3When the voltage VH is exceeded, the equivalent circuit of the positive feedback resistor R7 branch flips. Figure 4 Example: Add a circuit for power supply manufacturers to automatically shut down or standby the power supply in case of poor contact of user plug or power failure (9). Detailed Implementation

[0012] The best mode of implementing the present invention will be described in detail below with reference to the accompanying drawings, which have already been described above and will not be repeated here. Figure 1 , Figure 2 The innovative electronic relay circuit (2) is connected in series from the power grid AC direct rectification charging circuit (1), and then passes through the main characteristic circuit (3) of the switching power supply and its voltage regulation control circuit (4) to form a switching power supply circuit. The voltage regulation control circuit (4) is described in other patents or other existing technologies of the inventor. A high-frequency capacitor CP is connected in parallel with the high-voltage electrolytic capacitor and a diode UK2 is connected in reverse parallel to protect the high-voltage electrolytic capacitor from reverse charging.

[0013] The electronic relay circuit (2) described above functions the same as the "solid-state electronic relay" on the market. After the grid rectification and filtering at the low potential end of the return current, the lowest potential common terminal... and adjacent higher potential Between them, there is the electronic switching power transistor VKZ, which functions to connect / disconnect the power grid rectifier circuit; at the high potential end of the electronic switching power transistor VKZ... With the low potential terminal of the power regulator transistor V in the switching power supply To form a circuit, a total current sensing source resistor [which also serves as an overcurrent shutdown sampling resistor and a fuse resistor (RF)] can be connected in series (by adding or removing the short circuit).

[0014] The aforementioned on / off power grid rectifier charging circuit electronic relay circuit (2) can use a voltage-input type field-effect high-power device such as an IGBT as the electronic switching power transistor VKZ, and the low potential terminal of the electronic switching power transistor VKZ of the power grid rectifier circuit function is connected to the circuit. To the adjacent high potential end A diode UK needs to be connected in parallel (the actual IGBT has already integrated this transistor). During startup, the field-effect power switch VKZ is regulated by the start-up resistor R1 and the Zener diode WKZ, which can immediately and quickly bring the power switch VKZ to the normal saturation conduction state. This can form the subsequent switching power supply (3) to work normally. The present invention uses an electronic relay circuit (2) with the function of switching on / off the power grid rectifier circuit. Its main advantage is that it can simulate the disconnection of the power grid rectifier circuit several to more than ten times within 1 second. However, if a mechanical relay is used to frequently switch on and off the power grid, the time interval is at least 1 second. It cannot be used to simulate the limit pulse current limit test of electrolytic capacitors.

[0015] The electronic relay circuit (2) can be connected to the preamplifier transistor VKA and its comparator circuit (5) via an optocoupler N2. [Page 2] Figure 2 [Example]: Optocoupler N2 can also be removed. However, if optocoupler N2 is removed, it is necessary to add diode N2D, Zener diode or ordinary diode N2W, and diode V7 for reverse bias isolation to prevent the voltage signal at the input terminal of the switching power transistor VKZ from being clamped by the current. Otherwise, the rectifier charging circuit cannot enter the normal conduction state.

[0016] The instruction manual states that the electronic relay circuit (2) is powered by the starting resistor R1, which can be taken from the low potential terminal of the high voltage electrolytic capacitor Z. Or through the lower potential terminal of the current sensing resistor RF All of these can automatically disconnect the starting resistor after the switching power supply (3) is working, resulting in greater power saving. When the switching power supply is working, the secondary winding S4 of the switching power supply transformer T is rectified by diode U5 (which is opposite to the on / off state of the primary coil P), filtered by capacitor C5, and then passes through switching diode U52 to form an independent voltage source for the normal conduction of the electronic switching transistor VKZ. Because when the switching transistor VKZ is saturated and conducting, the original starting resistor R1 loses its starting function. The function of switching diode U52 is to prevent the gate voltage of the starting resistor R1 from being clamped and absorbed when starting the power transistor VKZ. Of course, the high potential end of the starting resistor R1 can be taken from the high potential end of the high voltage electrolytic capacitor Z. In this way, there is no need for winding reverse polarity rectification U5, capacitor C5, diode U52, resistor R11, etc. On the upper left of the attached diagram on page 3, you can also add independent power frequency full-wave rectifier diodes DS1 and DS2, resistors R12 and R13, and accelerating capacitor CP34 to form a zero-crossing AND gate that can only conduct.

[0017] The voltage comparator (5) with hysteresis voltage difference characteristics is also a composite transistor composed of a pulse transistor VKA and its pre-amplifier PNP transistor V5. Between the emitter-base junction of the pre-amplifier V5 and the collector-base junction of the rear transistor VKA, a positive feedback network is formed by the resistor R7 branch, generating a rectangular wave, which has the advantage of pulse-type fast switching. This reduces the time the pulse transistor VKA travels through the amplification region during the on / off switching process. (Here, the pulse transistor VKA can be directly connected to the mechanical relay coil and can be directly used in other mechanical relay circuits that do not require high-speed switching, such as […] Figure 3 Example] Power grid power supply mode switching); if a high-speed switching electronic relay circuit (2) is required, the tube VKA only drives the power electronic relay circuit (2) to the required switching state.

[0018] Hysteresis voltage comparators, also known as hysteresis comparators, have the following advantages: they preserve the original state and prevent it from being triggered to flip when the input signal changes between VL and VH (VN); they only trigger the flip when the value is below VL or above VH; and they ensure that frequent erroneous switching does not occur when hovering around the switching threshold.

[0019] The hysteresis voltage difference comparator described above uses a front-end input detection signal that is rectified and filtered from the secondary winding of the switching power supply transformer T, or the secondary winding of another power supply transformer T2, or rectified by the grid independent full-wave diodes DS1 and DS2. This signal is then integrated by the resistor R72 and capacitor C72 circuit (8) to form a sawtooth wave. [This technology may also include (see attached diagram, page 2)] Figure 2 Example) Resistor R722 and capacitor C722 form a dual-integral circuit, generating a signal that changes from below VL to above VH. Through the matching circuit (6), the signal is fed to the hysteresis voltage difference comparator (5). After passing through the positive feedback resistor R7 branch, a rectangular pulse wave in the required switching state is generated. This drives the power transistor VKZ to be in the required state. Adjusting the parameters of the sawtooth wave circuit, such as capacitor C72, resistor R72, R722, resistor R55B, Zener diode D7 (D7H), and resistor R7, can control the required rectangular wave's on-time, off-time, and frequency changes.

[0020] To enhance the reliability of the power switch VKZ and reduce noise, the optimal approach is to ensure that the normally conducting power switch VKZ switches to the off state synchronously when the instantaneous voltage of the mains AC frequency is at a trough. Therefore, this invention adds a switching circuit (7) that requires an AND gate logic to turn off only at zero voltage crossing: This circuit uses the same polarity envelope of the secondary winding of the switching transformer for power frequency detection. [See attached diagram, page 3] Figure 3 [(Diode U61, Capacitor C61) After passing through the DC blocking and AC passing clamping circuit (10), or [Figure 1 and 2] the power frequency full-wave rectifier diodes DS1 and DS2 are connected in series with the current limiting resistor RSb1 and the varistor switch device (such as Zener diode) WS (normal conduction, zero-crossing shutdown), driving the switch VS to be in the normal saturation conduction state, and at the same time controlling the short-circuit of the input terminal base-emitter junction of the subsequent pulse tube VKA to be in the normal cut-off state; only when the instantaneous value of the power grid is near zero voltage, the varistor switch device Zener diode WS changes from the conduction state to the cut-off state and the switch VS is locked, unlocking the pulse generator circuit (5) and the pulse tube VKA can be output by the voltage comparator, so that the normally conducting power switch can only be cut off near the power frequency zero voltage. When the pulse tube VKA starts control (during conduction), the diode DS3 pulls the input terminal of the switch tube VS to a low potential of 0, so that the switching circuit (7) that can only be turned off by the AND gate logic at zero voltage loses its control function.

[0021] The same polarity detector diode U61 is switched on and off in the same way as the primary coil. The difference between the envelope detector and the ordinary peak rectifier filter circuit is that the envelope detector only filters the high-frequency components of the switching power supply, but maintains the change of the power frequency envelope amplitude. Therefore, if the capacitor C61 is used for envelope detection, its capacitance is only about 10nF, but if it is used for filtering, its capacitance reaches more than 10uF. The clamping circuit (10) is based on the principle and circuit of the existing technology of synchronous clamping separation circuit in black and white televisions.

[0022] The accompanying diagram shows comparator circuits (5) for matching different detection signal sources. Regarding the function of diodes VD5 and V7 in the positive feedback resistor R7 branch, they are only added to prevent reverse bias breakdown of the PNP transistor V5 emitter-base junction circuit. Since there is no possibility of breakdown, they can be removed or short-circuited. However, if the optocoupler N2 scheme is removed, diode V7 must be added to prevent the normally conducting power transistor VKZ input signal from being bypassed. If a series capacitor C7 is added to the positive feedback resistor R7 branch, a monostable multivibrator will be formed, which will automatically disconnect after triggering. Both monostable multivibrators and hysteresis voltage comparators can be used to form rectangular wave signal oscillators. The difference is that even without RC integration or other hysteresis voltage difference changes, the monostable input waveform can still rotate at regular intervals, even if it is a rectangular wave. If a monostable multivibrator is not desired, the timing capacitor C7 can be removed or disconnected. The attached diagram on page 3 shows that if the PNP transistor is powered by 5V, the Zener diode VD7 can be uncircuited, and the resistor or diode R55 can be removed or disconnected.

[0023] The hysteresis voltage comparator or monostable multivibrator constitutes a rectangular wave pulse oscillator (5), a detection source RC integrator (8), and a matching circuit (6). This can be constructed within an integrated circuit (IC) with a similar hysteresis comparator (Schmitt trigger or 555 timer, etc.). The voltage-sensitive switching device (such as a Zener diode) D7 and voltage divider resistors R61A and R61B are directly matched to the IC's custom terminal OPT. The integrated circuit then drives the pulse transistor VKA or directly drives the power switch VKZ to the required state.

[0024] [ Figure 1-1 Examples [3-1] and [3-1]: Hysteresis characteristic description. The pulse transistor VKA triggers a flip-flop output characteristic when the voltage is below VL or above VH, respectively. Between VH and VL (VN), it exhibits a hysteresis characteristic that maintains the original state. Figure 1-2 ]and[ Figure 3-2 Example: The equivalent circuit of the positive feedback resistor R7 branch changes when VL is entered undervoltage. Figure 1-3 ]and[ Figure 3-3 Example: When the voltage VH is exceeded, the equivalent circuit of the positive feedback resistor R7 branch flips. (The above circuit analysis does not include isolation diodes V7 and VD5, etc.).

[0025] [Page 2] Figure 2 [Example]: After removing optocoupler N2, the electronic relay circuit (2) is connected to four different sampling source integration circuits (8), matching circuits (6), and voltage comparator circuits (5) respectively. Example on the upper left: The source is from other independent DC power supplies from 5V to 12V to form a dual integration circuit (8): the integration circuit of resistor R72 and capacitor C72 is set to VH value, and the integration circuit of resistor R722 and capacitor C722 constitutes the discharge circuit power supply after the control tube V5 is turned on, which is set to VL value. In this way, the conduction period and cutoff period of the pulse tube VKA can be freely and conveniently adjusted. The VH signal integration circuit of the lower left circuit is sourced from the grid after direct independent full-wave rectification (DS1 and DS2), and the VL signal is sourced from other DC power supplies from 5V to 12V. The integration circuit of resistor R722 and C722. The entire signal control circuit (5), (6), (7), and (8) on the lower right are all formed after direct independent full-wave rectification (DS1 and DS2) of the grid. The upper right signal source is an example of the negative voltage value of the power frequency detector enveloped by the same polarity rectifier U61 capacitor C61. Figure 1 After the trigger pulse transistor VKA is turned on, it can share an integrating capacitor C72 through the diode V74 and resistor R722 branch to accelerate the sawtooth wave discharge.

[0026] Page 3 Figure 4 Example] The power supply manufacturer adds an automatic shutdown or standby circuit (9) for poor user plug contact or power failure. The power supply is rectified independently by the switching power supply or by another power source, and then connected in parallel with the emitter-base junction of transistor A44 via diode V44. This causes transistor A44 to be reverse-biased and cut off after being energized, and to charge the large-capacity capacitor C44. When the plug has poor contact, the voltage of each winding of the switching power supply drops, causing the previously reverse-biased transistor to become conductive, triggering the overload shutdown circuit to protect the components of the switching power supply from damage due to undervoltage. The overload shutdown circuit device can be found in other patents of the inventor. [Page 3] Figure 3 Example] Comparison circuit (5) is mainly used for ultra-wide grid fluctuation power supply mode switching circuit. Tested: When the grid voltage drops to 130V, the rectified pulsating peak voltage of 182V is boosted to 308V peak voltage. When the grid voltage is low, it can automatically increase the voltage by 308 / 182 = 1.69 times: 1. It effectively reduces the maximum peak current flowing through the transformer-type switching power supply regulating tube V (inversely proportional to the input voltage), reduces the conduction period / cycle ratio, reduces the short-circuit loss of the DC component flowing through the switching power supply regulating tube V, improves power supply efficiency, and also reduces the pulsating AC component pulsation coefficient of the high-voltage electrolytic capacitor; reduces the harmonic current hazard. According to W = 1 / 2C↓U 2↑, If the voltage is increased by 2 times, under the same energy transmission conditions, the required capacitor capacity is reduced to 1 / 4 of the original technology. This indirectly increases the capacity of high-voltage electrolytic capacitors when the power grid is undervoltage. This is obviously beneficial to the State Grid, power users and capacitor manufacturers. Therefore, the comparator circuit (5) pulse tube VKA can directly use the mechanical relay KA, which can be a single-pole o3 single-throw switch relay or a double-pole (o1 and o2) double-throw switch relay. Since frequent switching is not required, a rectangular wave oscillator is not needed. It needs to be equipped with an integral sawtooth wave circuit (8) to form oscillation parameters.

[0027] For PFC circuits with active technology (increasing the conduction angle of the mains rectification), existing technologies all belong to the boost switching power supply category within transformer-type switching power supplies. This is similar to isolated transformer-type (i.e., step-up / step-down) power supplies: both suffer from the disadvantage of complete short-circuit loss of the DC component flowing through the regulating transistor, and the increased loss due to undervoltage fluctuations at the input mains. However, in a boost switching power supply (PFC), after normal operation, during the off-state (OFF / T) period of the switching transistor, the voltage of the high-voltage electrolytic capacitor is rectified by a boost freewheeling diode in the opposite polarity to the switching transistor and the primary coil of the switching transformer. This ensures the voltage reaches a stable value of approximately 380V, higher than the voltage directly rectified from the mains frequency at the input. If the boost switching power supply (PFC) stops working, it will always continue to supply power to the downstream main load through direct rectification from the mains and then connected in series with the freewheeling diode (boost diode). This is similar to ordinary direct mains rectification. When encountering poor contact at the user's plug (especially common with inverter air conditioners), the boost switching power supply (PFC) will trigger overload protection and stop operating. The PFC output to the high-voltage electrolytic capacitor at 380V will automatically switch to a state where it is directly rectified and filtered by the power grid. Many variable frequency air conditioner manufacturers set the motor to stop working when it is continuously at about AC160V. However, is the sampling source circuit sampling from the high-voltage electrolytic capacitor after the PFC stage or from the direct rectification of the power grid? The effect is different. If the sampling is directly rectified from the power grid, the motor will start frequently when there is poor contact with the plug, which will seriously damage the high-voltage electrolytic capacitor. Therefore, it is recommended that power supply manufacturers with PFC circuits must add a circuit to prevent poor plug contact (9) to force automatic standby for a certain period of time, or add the comparator circuit (5) of this invention to form a monostable trigger, so that when there is poor plug contact, the motor with PFC circuit can only be restarted after at least a few seconds. This is the only way to protect the high-voltage electrolytic capacitor from damage.

[0028] The innovative circuit described in this manual can be applied to other circuit device fields.

Claims

1. A circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply, comprising a switching power supply, a high-voltage electrolytic capacitor, and related circuitry, characterized in that: The charging circuit of the power supply input terminal is frequently switched on and off to measure the maximum allowable AC component parameter of the actual withstand voltage pulsation of the high voltage electrolytic capacitor; a voltage comparator or monostable trigger (5) with hysteresis voltage difference characteristic is used, and a sawtooth wave is formed through the RC integration circuit (8). After being fed back to the voltage comparator (5) with hysteresis voltage difference characteristic through the matching circuit (6) for comparison, a rectangular pulse wave oscillator is directly formed. Then, through the electronic relay circuit (2), as an electronic relay switch connected in series in the power frequency grid rectifier charging circuit, it is used to simulate the frequent on / off function of the grid rectifier. It can be switched on and off several times or more than ten times per second, which can represent the harm of poor plug contact or the undervoltage fluctuation of the grid. When the plug contact is poor, the grid rectifier charging circuit is interrupted. However, because the high voltage electrolytic capacitor Z is still working in the discharge circuit, the DC component flowing through the transformer switching power supply regulating tube has a large short circuit loss. In particular, the peak current flowing through the switching power supply regulating tube is extremely large. The AC component of the high voltage electrolytic capacitor will increase significantly and heat up significantly due to the next cycle of charging and discharging. If the poor contact is simulated in the cycle, the high voltage electrolytic capacitor will heat up and be damaged or even destroyed.

2. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of high-voltage electrolytic capacitors in switching power supplies according to claim 1, characterized in that: The electronic relay circuit (2), after the grid rectification and filtering at the low potential end of the grid return current, has a lowest potential common terminal. GND1” and adjacent higher potentials Between GND2, connect the electronic switching power transistor VKZ, which enables the switching on / off of the mains rectifier circuit; at the high potential terminal of the electronic switching power transistor VKZ. GND2 is connected to the low potential terminal of the power regulator transistor V of the switching power supply. Between them, the short-circuit series total current detection source resistor can be added or removed, which also serves as the overcurrent shutdown sampling resistor and the fuse resistor (RF), forming a circuit; The purpose of the electronic relay circuit (2) for switching on / off the power grid rectifier charging circuit is to simulate cutting off the power grid rectifier circuit several to more than ten times within 1 second; it uses a voltage-input type field-effect high-power device as the electronic switch power transistor VKZ; when the machine is started, the field-effect power switch transistor VKZ is regulated by the start-up resistor R1 and the Zener diode WKZ, which can immediately and quickly put the power switch transistor VKZ into the normal saturated conduction state; it can form a subsequent switching power supply (3) that can work normally.

3. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of high-voltage electrolytic capacitors in switching power supplies according to claim 1, characterized in that: The electronic relay circuit (2) can be connected to the preamplifier transistor VKA and its comparator circuit (5) through the optocoupler N2; or the optocoupler N2 can be removed. However, if the optocoupler N2 is removed, it is necessary to add a diode N2D, a Zener diode or a common diode N2W, and a diode V7 for reverse bias isolation to prevent the voltage signal at the input terminal of the switching power transistor VKZ from being clamped. Otherwise, the rectifier charging circuit cannot enter the normal conduction state.

4. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of high-voltage electrolytic capacitors in switching power supplies according to claim 1, characterized in that: The voltage comparator (5) with hysteresis voltage difference characteristic, after passing through the self-adjustable detection source and matching circuit (6), when the detection voltage is between the two set comparison values ​​VH and VL, the pulse tube VKA remains in its original state and is not triggered to flip; when the detection voltage is higher than the set VH or lower than VL, the pulse tube VKA is forced to immediately trigger to flip.

5. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply according to claim 1, characterized in that: The voltage comparator (5) with hysteresis voltage difference characteristics is also a heterogeneous composite tube composed of pulse tube VKA and its pre-amplifier PNP tube V5. Between the emitter-base junction of the pre-amplifier tube V5 and the collector-base junction of the rear tube VKA, a positive feedback network is formed by the resistor R7 branch to generate a rectangular wave, which has the advantage of pulse-type fast switching and reduces the time of the pulse tube VKA in the amplification region during the switching process of conduction / turn-off. Between the positive feedback resistor R7 branch, a series timing capacitor C7 can be added to form a monostable trigger. The timing capacitor C7 can be removed and shorted, and it functions as a voltage comparator with hysteresis characteristics. It will only trigger the flip-over of the original state when the voltage is below VL or above VH. This ensures that there will be no frequent erroneous switching when hovering around the switching critical point.

6. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of high-voltage electrolytic capacitors in switching power supplies according to claim 1, characterized in that: To enhance the reliability of the power switch VKZ and reduce noise, the power switch VKZ, which is normally conducting, should be switched synchronously when it is at the trough of the AC power frequency of the power grid and at zero voltage. To this end, a switching circuit (7) that can only be turned off by an AND gate logic at zero voltage is added: the power frequency detector with the same polarity envelope of the secondary side of the switching transformer is passed through a clamping circuit (10) that blocks DC and passes AC, or the power frequency full-wave rectifier diodes DS1 and DS2 are connected in series with a current-limiting resistor RSb1, and the voltage regulator WS, which is normally conducting and turns off at zero voltage, drives the switch VS to be in the normal saturation conduction state. After the short circuit of the control stage, the base-emitter junction of the input terminal of the pulse tube VKA is in the normal cut-off state; only when the instantaneous value of the power grid is near zero voltage, the voltage regulator WS of the varistor switch device changes from the conducting state to the cut-off state and the interlock switch VS is in the cut-off state, the pulse generator circuit (5) can be unlocked and the pulse tube VKA can be output by the voltage comparator, so that the normally conducting power switch can only be cut off near the zero voltage of the power frequency; when the pulse tube VKA starts to conduct, the diode DS3 pulls the input terminal of the switch VS to a low potential of 0, so that the switching circuit (7) that can only be turned off when the AND gate logic crosses zero voltage loses its control function.

7. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply according to claim 1, characterized in that: The hysteresis voltage comparator or monostable trigger constitutes a rectangular wave pulse oscillation generator (5), a detection source RC integrator (8), and a matching circuit (6). It can be constructed from an integrated circuit IC, which has a Schmitt trigger or a 555 timer circuit with a similar hysteresis comparator. The voltage regulator D7 and the voltage divider resistors R61A and R61B are directly matched to the custom terminal OPT of the integrated circuit, and then the pulse tube VKA is driven by the integrated circuit or the power switch VKZ is directly driven to the required state.

8. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply according to claim 1, characterized in that: The integrator circuit (8) can be a dual integrator circuit (8): the integrator circuit of resistor R72 and capacitor C72 is set to the charging VH value, and the integrator circuit of resistor R722 and capacitor C722 forms the discharge circuit power supply after the control tube V5 is turned on, and is set to the discharge VL value; in this way, the conduction period and cutoff period of the pulse tube VKA can be freely and conveniently adjusted; the dual integrator circuit (8) can share an integrator capacitor C72 through the diode V74 and resistor R722 branch to accelerate the sawtooth wave discharge.

9. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply according to claim 1, characterized in that: The power supply circuit should be equipped with a forced overload shutdown circuit (9) for poor plug contact or undervoltage fluctuation of the power grid. The circuit is rectified independently by the switching power supply or other power sources, and the diode V44 is connected in parallel to the emitter-base junction of the transistor A44. After the transistor A44 is energized, it is reverse biased and cut off, and charges the large-capacity capacitor C44. When the plug contact is poor, the voltage of each winding of the switching power supply drops, causing the transistor that was originally reverse biased and cut off to be in the conducting state, triggering the overload shutdown circuit to operate, thereby protecting the components of the switching power supply from damage due to undervoltage.

10. The circuit device for testing the maximum permissible AC component of pulse current withstand capability of a high-voltage electrolytic capacitor in a switching power supply according to claim 1, characterized in that: A high-frequency capacitor CP is connected in parallel with the high-voltage electrolytic capacitor, and a diode UK2 is connected in reverse parallel to protect the high-voltage electrolytic capacitor from being reverse charged.

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