A series voltage equalization detection circuit for electrolytic capacitors

Abstract

The present application discloses a series voltage equalization detection circuit for electrolytic capacitors, which includes N electrolytic capacitors, a differential operational amplifier unit, and a comparator unit. The N electrolytic capacitors are connected in series across the power supply to form a closed loop, and a voltage equalization resistor is connected in parallel with each electrolytic capacitor. In this embodiment, the electrolytic capacitors all refer to electrolytic capacitors. The voltage equalization detection circuit in this embodiment collects the voltage value between the positive electrode of each electrolytic capacitor and the negative electrode of the power supply and inputs it into the differential operational amplifier unit. After being amplified by the differential operational amplifier unit, it is input into the comparator unit together with the reference voltage. The comparator unit then outputs a protection signal according to the magnitude of the signal at the input end. The power supply terminal of the comparator is connected to the low-voltage power supply through a pull-up resistor. The voltage equalization detection circuit disclosed in the present application can monitor in real time whether the voltage across the series electrolytic capacitors is abnormal, greatly improving the system safety. The voltage detection adopts a differential method, with strong anti-interference ability, and can be applied in a complex electromagnetic environment.

Description

Technical Field

[0001] This application relates to the field of detection and protection of electrolytic capacitors, and specifically relates to a series voltage equalization detection circuit for electrolytic capacitors. Background Art

[0002] An electrolytic capacitor is an electronic component composed of two conductors sandwiching an insulator. As one of the three basic components, its main functions are energy storage and filtering. Additionally, it also has functions such as blocking DC, bypassing, coupling, rectifying, tuning, and energy conversion. An electrolytic capacitor usually has a metal foil (aluminum / tantalum) as the positive electrode, the insulating oxide layer of the metal foil (aluminum oxide / tantalum pentoxide) as the dielectric, and an electrolyte as the negative electrode.

[0003] The electrolytic capacitance per unit volume of an electrolytic capacitor is very large, and the rated capacitance can easily reach tens of thousands of μF or even several F, which is dozens to hundreds of times larger than other types of electrolytic capacitors. Moreover, since the constituent materials of electrolytic capacitors are all ordinary industrial materials, such as aluminum, etc., and the equipment for manufacturing electrolytic capacitors is also ordinary industrial equipment, they can be mass-produced, and the cost of electrolytic capacitors is relatively low, having an overwhelming advantage over other types of electrolytic capacitors. However, the disadvantages of electrolytic capacitors are also obvious, with low stability and insufficient voltage resistance. When the voltage resistance is increased in series, with the loss of the electrolyte or electrolyte, it is very easy to have a problem of insufficient voltage equalization, which can easily lead to the damage of the electrolytic capacitor, and more seriously, it can lead to an explosion; and given the relatively low cost of the electrolytic capacitor itself, when designing the voltage equalization detection or protection circuit, stability and cost factors are the factors that need to be considered emphatically. Summary of the Invention

[0004] This application provides a voltage equalization detection circuit for electrolytic capacitors, which can timely detect the abnormal voltage equalization of series-connected electrolytic capacitors and greatly improve the system safety.

[0005] This application discloses a series voltage equalization detection circuit for electrolytic capacitors, including N electrolytic capacitors, a differential operational amplifier unit, and a comparator unit; the N electrolytic capacitors are connected in series across the power supply; the voltage between the positive electrode of each electrolytic capacitor and the negative electrode of the power supply is collected and input into the differential operational amplifier unit, and after being amplified by the differential operational amplifier unit, it is input into the comparator unit together with the reference voltage; the comparator unit outputs a protection signal according to the magnitude of the signal at the input end.

[0006] Further, the differential operational amplifier unit includes a first differential operational amplifier group and a second differential operational amplifier group. The first differential operational amplifier group includes N differential operational amplifiers. Each differential operational amplifier corresponds to an electrolytic capacitor. The negative input terminal of each differential operational amplifier is connected to the positive electrode of the corresponding electrolytic capacitor, and the positive input terminal of the differential operational amplifier is connected to the negative electrode of the last electrolytic capacitor. The second differential operational amplifier group includes N - 1 differential operational amplifiers. The two input terminals of each differential operational amplifier in the second differential operational amplifier group are respectively connected to the output terminals of two adjacent differential operational amplifiers in the first differential operational amplifier group; the second differential operational amplifier group outputs N - 1 amplified signals.

[0007] Further, the comparator unit includes N - 1 comparators. The output terminal of each differential operational amplifier in the second differential operational amplifier group is connected to the positive input terminal of a corresponding comparator in the comparator unit, and the negative input terminal of the comparator is connected to a reference voltage.

[0008] Further, the power supply terminal of the comparator is connected to a low - voltage power supply through a pull - up resistor.

[0009] Further, a voltage - equalizing resistor is connected in parallel to each of the electrolytic capacitors.

[0010] Further, the reference voltage is obtained by stabilizing the voltage through a reference voltage chip.

[0011] Beneficial effects: The voltage - equalizing detection circuit disclosed in this application can monitor in real time whether the voltage across the series - connected electrolytic capacitors is abnormal, greatly improving the system safety. The voltage detection adopts a differential method, with strong anti - interference ability, and can be applied in a complex electromagnetic environment. As long as one of the series - connected electrolytic capacitors is damaged, the voltage - equalizing detection circuit will generate voltage imbalance, and the comparator unit will output a protection signal in time. Other auxiliary circuits connected to the voltage - equalizing detection circuit will take defensive measures in time to prevent further damage to other electrolytic capacitors, and at the same time reduce the harm caused by the damage of the electrolytic capacitors. Moreover, the components used in the detection circuit are all common components, making the total cost of the entire circuit low, matching the price advantage of the electrolytic capacitors, and suitable for actual production selection. Through voltage - equalizing detection and bus voltage detection, various situations that may occur in the capacitor system are basically covered, greatly increasing the system safety. For different voltage levels and voltage protection ranges, it can be conveniently matched by adjusting individual resistance values. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a schematic diagram of the series voltage - equalizing detection circuit;

[0013] Figure 2 is a schematic circuit diagram (1) of voltage - equalizing protection for three series - connected electrolytic capacitors;

[0014] Figure 3Schematic circuit (2) for voltage equalization protection of three electrolytic capacitors connected in series;

[0015] Figure 4 A circuit for detecting whether the bus is normal.

[0016] Specific real-time manner

[0017] The following further describes the specific embodiments of the present invention in conjunction with the accompanying drawings of the specification, making the technical solutions and their beneficial effects of the present invention clearer and more definite. The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] A series voltage equalization detection circuit for electrolytic capacitors includes N electrolytic capacitors, a differential operational amplifier unit, and a comparator unit. The N electrolytic capacitors are connected in series across the power supply to form a closed loop, and a voltage equalization resistor is connected in parallel with each electrolytic capacitor. In this embodiment, the electrolytic capacitors all refer to electrolytic capacitors. The voltage equalization detection circuit in this embodiment collects the voltage value between the positive electrode of each electrolytic capacitor and the negative electrode of the power supply and inputs it into the differential operational amplifier unit. After being amplified by the differential operational amplifier unit, it is input into the comparator unit together with the reference voltage. The comparator unit then outputs a protection signal according to the magnitude of the input signal at the input end. The power supply terminal of the comparator is connected to the low-voltage power supply through a pull-up resistor.

[0019] Among them, the differential operational amplifier unit includes a first differential operational amplifier group and a second differential operational amplifier group. The first differential operational amplifier group includes N differential operational amplifiers, each differential operational amplifier corresponding to an electrolytic capacitor. The negative input terminal of the differential operational amplifier is connected to the positive electrode of the corresponding electrolytic capacitor, and the positive input terminal of the differential operational amplifier is grounded; the second differential operational amplifier group includes N - 1 differential operational amplifiers. The two input terminals of each differential operational amplifier in the second differential operational amplifier group are respectively connected to the output terminals of two adjacent differential operational amplifiers in the first differential operational amplifier group; the second differential operational amplifier group outputs N - 1 amplified signals. The output terminal of each differential operational amplifier in the second differential operational amplifier group is connected to the positive input terminal of a corresponding comparator in the comparator unit, and the negative input terminal of the comparator is connected to the reference voltage.

[0020] Such as Figure 1As shown, electrolytic capacitors C1, C2, C3 up to Cn are connected in series, where n represents the number of series connections and can be selected as needed. A voltage-sharing resistor is connected in parallel with each electrolytic capacitor. Differential operational amplifier 1-1 takes the voltage between the positive busbar P (i.e., the positive electrode of electrolytic capacitor C1) and the negative busbar N. Differential operational amplifier 1-2 takes the voltage between the positive electrode of electrolytic capacitor C2 and the negative busbar N. Differential operational amplifier 1-3 takes the voltage between the positive electrode of electrolytic capacitor C3 and the negative busbar N. Differential operational amplifier 1-n takes the voltage between the positive electrode of electrolytic capacitor Cn and the negative busbar N. The output terminal of differential operational amplifier 1-1 and the output terminal of differential operational amplifier 1-2 are respectively connected to the negative electrode and the positive electrode of differential operational amplifier 2-1, and are connected according to this rule. The output terminal of each second-stage differential operational amplifier is connected to the input terminal of a comparator. The other input terminal of the comparator is connected to the reference voltage VR. By comparison, the comparator outputs a high-level signal or a low-level signal. According to the level of the signal output by the comparator, it can be judged whether each electrolytic capacitor is in the voltage-sharing state currently. Taking three electrolytic capacitors connected in series as an example, the specific voltage-sharing detection circuit is as Figure 2 , 3 shown. Figure 2 In, the double diodes Q1, Q2, Q3, Q4, Q5, Q6 are double diodes, which can clamp the voltage of the differential sampling input and protect the operational amplifier.

[0021] In addition to detecting whether the voltage across each capacitor is normal, the invention can also detect whether the busbar voltage is within a reasonable range. When the busbar voltage is too high, it will cause the power electronic switch at the later stage to bear too high a voltage and be damaged. When the busbar voltage is too low, the energy received by the load end is insufficient, which will affect the normal operation of the system. By designing the threshold comparison of the busbar voltage, it can be judged whether the busbar voltage is within the normal range according to the level signal output by the comparator. The specific detection circuit is as Figure 4 shown. In Figure 3 and Figure 4 , a positive feedback circuit composed of a resistor and a diode is added to the positive input terminal of the comparator, which has a hysteresis effect, avoiding multiple flips at the critical point and improving the stability. Taking the U8A comparator in Figure 4 as an example, under normal circumstances, the input value at pin 2 is less than the reference voltage at pin 3, and the comparator outputs a high level at pin 1; when a surge voltage appears on the busbar and the input at pin 2 suddenly increases and is higher than the reference voltage at pin 3, the comparator outputs a low level at pin 1 and an alarm occurs. At this time, diode Q10 conducts and pulls down the voltage value at pin 3; when the alarm is restored, the voltage value at pin 2 needs to drop to a greater extent, thus avoiding the impact of the repeated fluctuations of the voltage busbar at the critical point on the entire circuit.

[0022] The reference voltage VR is obtained by stabilizing the voltage through a reference voltage chip, with relatively high accuracy and not easily affected by the voltage fluctuation at the front end. As Figure 4As shown, by adjusting the closed-loop amplification factor of U9B (i.e., adjusting the resistance value of R88 or R94), the voltage value of its output reference voltage VR can be conveniently adjusted.

[0023] Through the description of the above structure and principle, those skilled in the art should understand that the present invention is not limited to the above specific embodiments. Improvements and substitutions using well-known technologies in the art based on the present invention fall within the protection scope of the present invention. The protection scope of the present invention shall be defined by each claim item and its equivalents. Parts not described in the specific embodiments are all prior art or common general knowledge.

Claims

1. A series voltage equalization detection circuit for electrolytic capacitors, characterized in that, It includes N electrolytic capacitors, a differential operational amplifier unit, and a comparator unit; the N electrolytic capacitors are connected in series across the power supply; the voltage between the positive electrode of each electrolytic capacitor and the negative electrode of the power supply is collected and input into the differential operational amplifier unit, and after being amplified by the differential operational amplifier unit, it is input into the comparator unit together with the reference voltage; the comparator unit outputs a protection signal according to the magnitude of the input signal at the input end; The differential operational amplifier unit includes a first differential operational amplifier group and a second differential operational amplifier group. The first differential operational amplifier group includes N differential operational amplifiers. Each differential operational amplifier corresponds to an electrolytic capacitor. The negative input terminal of each differential operational amplifier is connected to the positive electrode of the corresponding electrolytic capacitor, and the positive input terminal of the differential operational amplifier is connected to the negative electrode of the last electrolytic capacitor; The second differential operational amplifier group includes N - 1 differential operational amplifiers. The two input terminals of each differential operational amplifier in the second differential operational amplifier group are respectively connected to the output terminals of two adjacent differential operational amplifiers in the first differential operational amplifier group; The second differential operational amplifier group outputs N - 1 amplified signals; the comparator unit includes N - 1 comparators. The output terminal of each differential operational amplifier in the second differential operational amplifier group is connected to the positive input terminal of a corresponding comparator in the comparator unit, and the negative input terminal of the comparator is connected to the reference voltage.

2. The series voltage equalization detection circuit of an electrolytic capacitor according to claim 1, wherein The power supply terminal of the comparator is connected to the low-voltage power supply through a pull-up resistor.

3. The series voltage equalization detection circuit for electrolytic capacitors according to claim 1, wherein, A voltage equalizing resistor is connected in parallel across each electrolytic capacitor.

4. The series voltage equalization detection circuit of an electrolytic capacitor according to claim 1, wherein, The reference voltage is obtained by stabilizing the voltage through a reference voltage chip.

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