This article mainly introduces some common fault diagnosis and repair methods of the frequency converter, and briefly describes the causes and prevention measures of the fault. Need to understand the inverter repair knowledge, you can start from the following five aspects.

First, understand the difference between analog and digital

The difference between analog and digital

Many people just entering the electronics industry, the automation industry on the analog electronic circuits and digital electronic circuits, there are some doubts, by the people who just entered the line is even more unclear, of course, in contact with the inverter repair and maintenance must be familiar with.

The so-called analog electronic circuit is actually relative to digital electronic circuit.

Dielectric: Generally refers to the frequency below hundreds of megabytes HZ below the analog voltage signal within the dozens of volts and the signal analysis / processing and the use of related devices. Fast HZ signal belongs to the category of high-frequency electronic circuits. More than 100 volts signal belongs to the category of strong electricity or high voltage.

Digital electricity: Generally refers to the digital logic and calculation to analyze and process signals, digital logic circuit structure and use.

The input and output of digital electricity are generally made up of the dielectrics. The basic logic elements that make up the digital electricity are the saturation characteristics and the cutoff characteristics of the three tubes in the dielectrics.

Because digital can be large-scale integration, complex mathematical operations, temperature, interference, aging and other parameters are not sensitive, it is the future direction of development. However, in the real world, the information is analog information (light, radio, heat, cold, etc.). Modification is impossible to eliminate, but the power consumption of a system may be reduced. The ideal composition is: analog input – AD sampling (digital) – digital processing – DA conversion – analog output.

Second, the difference between op amp and comparator

Operational amplifier and dedicated comparator in the inverter control board circuit more common

1, op amp can be connected to become more output, the comparator is compared.

2, the comparator output is generally OC for level conversion; comparator no frequency compensation, SLEW RATE than the same stage op amp, but then into the amplifier easy to self-excited.

The open-loop gain of the comparator is much higher than the average amplifier, so the small difference between the positive and the negative of the comparator causes the output to change.

3, the frequency response is on the one hand, the other op amp output when the comparator is not stable, may not be able to meet the requirements of the logic circuit.

4, the comparator is open-collector output, easy to output TTL level, while the op amp has a saturated voltage drop, the use of inconvenience.

5, the comparator flip speed, about NS orders of magnitude, while the op amp flip speed is generally the order of magnitude (except for special high-speed op amp)

6, the op amp can enter the negative feedback circuit, and the comparator can not use the negative feedback, although the comparator also has two inverting and inverting input, then because of its internal phase compensation circuit, if the input negative feedback, the circuit can not be stable, There is no internal phase compensation circuit, which is why the comparator is faster than the op amp.

7, the op amp input primary generally push-pull circuit, bipolar output, and most of the comparator output is very collector-level open-circuit structure, so the need for pull-up resistor, unipolar output, easy and digital circuit connection.

Third, Schottky diodes and fast recovery diode What is the difference

Fast recovery diode refers to the reverse recovery time is very short diode (5us the following), the process of using more gold-doped measures, the structure has a PN junction structure, and some use of improved PIN structure. The forward voltage drop is higher than the normal diode (1-2V), reverse voltage more than 1200V. From the performance can be divided into fast recovery and ultra-fast recovery of two levels. The former reverse recovery time is hundreds of nanoseconds or longer, the latter is below 100 nanoseconds.

Schottky diodes are based on a barrier formed by the contact of metals and semiconductors, referred to as Schottky Barrier Diodes, with low forward voltage drop (0.4-0.5 V) and short reverse recovery time (10) -40 nanoseconds), and the larger reverse leakage current, low voltage, generally lower than 150V, used for low voltage occasions.

These two tubes are commonly used for switching power supplies.

Schottky diode and fast recovery diode difference: the former recovery time is about a hundred times smaller than the latter, the former reverse recovery time is about a few nanoseconds ~!

The former advantages are low power consumption, high current, high speed ~! Of course, are the electrical characteristics of the diode Ah ~!

Fast recovery diodes in the manufacturing process using gold-doped, simple diffusion process, access to higher switching speed, but also get higher withstand voltage.At present, fast recovery diodes are mainly used in inverter power rectifier components.

Schottky diode: Reverse breakdown voltage is lower 40V-50V, on-state voltage drop 0.3-0.6V, less than 10nS reverse recovery time. It is a Schottky-featured “metal-semiconductor junction” diode. Its positive start voltage is lower. The metal layer in addition to materials, but also can be used gold, molybdenum, nickel, titanium and other materials. The semiconductor material using silicon or gallium arsenide, mostly N-type semiconductor. The device is conductive by majority carriers, so its reverse saturation current is much larger than the PN carriers that conduct minority carriers. Due to the small storage effect of minority carriers in Schottky diodes, the frequency response is limited only by the RC time constant, making it ideal for high frequency and fast switching. Its operating frequency up to 100GHz. Also, MIS (Metal-Insulator-Semiconductor) Schottky diodes can be used to fabricate solar cells or light-emitting diodes.

Fast recovery diode: a 0.8-1.1V forward voltage drop, 35-85nS reverse recovery time, the rapid switch between turn-on and turn-off, improve the frequency of use of the device and improve the waveform. Fast recovery diodes in the manufacturing process using gold-doped, simple diffusion process, access to higher switching speed, but also get higher withstand voltage.At present, fast recovery diodes are mainly used in inverter power rectifier components.

Fourth, the inverter – electrolytic capacitors in the role of the circuit

1, the filter effect, in the power circuit, the rectifier circuit will be AC ​​into a pulsating DC, and access to the rectifier circuit in a larger capacity electrolytic capacitor, the use of its charge-discharge characteristics, so that the pulsating DC voltage rectifier into a Relatively stable DC voltage. In practice, in order to prevent the various parts of the power supply voltage changes due to load changes, so the output of the power supply and the load power input terminals generally receive tens to hundreds of micro-law electrolytic capacitors. As large-capacity electrolytic capacitors generally have a certain inductance, the high-frequency and pulse interference signals can not be effectively filtered, so at both ends in parallel with a capacity of 0.001–0.lpF capacitor to filter out high-frequency And pulse interference.

2, the coupling effect: In the process of transmission and amplification of low-frequency signals, in order to prevent the static operating point before and after the two circuits affect each other, often using capacitive coupling. In order to prevent the signal rhyme low frequency component loss is too large, the general use of larger capacity electrolytic capacitors.

Second, the electrolytic capacitor to determine the method

Electrolytic capacitor common fault, capacity reduction, capacity loss, breakdown short circuit and leakage, of which capacity change is due to the use of electrolytic capacitors or placed in the process of its internal electrolyte gradually dried up, and the breakdown and leakage are generally added The voltage is too high or caused by poor quality. Judge the power capacitor is generally good or bad resistance meter multimeter to measure. The specific method is: the two short-circuit capacitor to discharge, with a black meter pen multimeter positive electrolytic capacitor. Red pen then negative (on the pointer multimeter, with a digital multimeter test pen intermodulation), the normal time table

Needle should be the direction of small resistance swing, and then gradually returned until infinity. The greater the swing amplitude of the hands or the slower the speed of return, indicating that the greater the capacity of the capacitor, the other hand, the smaller the capacity of the capacitor. If the index finger in the middle no longer change, indicating that the capacitance leakage, such as resistance indication is small or zero, it indicates that this capacitor has been breakdown short circuit. Because the voltage of the battery used by the multimeter is generally very low, it is more accurate when measuring the capacitor with lower withstand voltage. When the capacitor with higher withstand voltage, although the measurement is normal at the time of the blowout, leakage or blowout may occur with high voltage Wear phenomenon.

Third, the use of electrolytic capacitors precautions

1, electrolytic capacitor due to the positive and negative polarity, so when used in the circuit can not reverse the connection. In the power circuit, when the positive voltage is output, the positive electrode of the electrolytic capacitor is connected to the power output end, and the negative electrode is grounded. When the negative voltage is output, the negative electrode is connected to the output end and the positive electrode is grounded. When the polarity of the filter capacitor in the power circuit is reversed, the filtering effect of the capacitor is greatly reduced, causing the fluctuation of the output voltage of the power supply on the one hand and heating of the electrolytic capacitor corresponding to a resistor at this time due to the reverse powering. When the reverse voltage exceeds a certain value, the capacitance of the reverse leakage resistance will become very small, so energized work soon, you can make the capacitor due to overheating and blasting damage.

2. Plus the voltage across the electrolytic capacitor can not exceed the allowable operating voltage in the design of the actual circuit should be based on the specific circumstances leave some margin in the design of the power supply filter capacitor, if the AC power supply voltage is 220 ~ Level rectifier voltage up to 22V, select the electrolytic capacitor voltage is 25V generally meet the requirements. However, if the AC power supply voltage fluctuations and may rise to 250V or more, the best choice of voltage 30V electrolytic capacitors.

3, electrolytic capacitors in the circuit should not be close to high-power heating elements, to prevent accelerated heating and drying of the electrolyte.

4, for positive and negative signal filtering, two electrolytic capacitors can be taken in the same polarity series, as a non-polar capacitor.

Five, inverter – varistor basic knowledge

1, what is “varistor”

“Varistor is a term in mainland China, which means” the resistance value changes with the voltage in a certain current and voltage range “or” the resistance value is voltage-sensitive. “The corresponding English name is” Voltage Dependent Resistor “Is shortened to” VDR “.

Varistor resistor material is a semiconductor, so it is a variety of semiconductor resistors. Nowadays, ZnO varistors, which are widely used, are composed of divalent element (Zn) and hexavalent elemental oxygen (O). So from a material point of view, zinc oxide varistor is a “Ⅱ-Ⅵ oxide semiconductor.”

In Taiwan, China, varistors are named for their use, called “surge absorbers.” Varistors are sometimes referred to as “shock (surges) suppressors (absorbers)” depending on their purpose.

2, varistor circuit “safety valve” role

Varistor what is the use? The most prominent feature of a varistor is that when the voltage applied to it is lower than its threshold “UN”, the current flowing through it is extremely small, which is equivalent to a shut-off valve. When the voltage exceeds UN, it flows through Its current surge, equivalent to the valve open. With this function, you can suppress abnormal over-voltage often appear in the circuit to protect the circuit from over-voltage damage.

3, the type of application

Different occasions, the purpose of the application of varistor, the role of varistor voltage / current stress is not the same, so the varistor requirements are not the same, pay attention to distinguish this difference, for the correct use is very important of.

4, circuit function with varistor

Varistor is mainly used in transient overvoltage protection, but its volt-ampere characteristics similar to the semiconductor regulator, it also has a variety of circuit element functions, for example, can be used as:

(1) DC high-voltage small current regulator components, the stable voltage up to several thousand volts or more, which is silicon regulator can not be achieved.

(2) voltage fluctuation detection element.

(3) DC battery displacement components.

(4) equalizing components.

(5) Fluorescent start device

5, the basic performance of the protection varistor

(1) Protection characteristics: The varistor voltage limit shall not exceed the surge withstand voltage (Urp) of the protected object when the impulse source impact (or the impulse current Isp = Usp / Zs) does not exceed the specified value. .

(2) Impact resistance, that is, the varistor itself should be able to withstand the specified inrush current, impact energy, and the average power when multiple impacts occur one after the other.

(3) There are two life characteristics, one is the continuous working voltage life, which means that the varistor should work reliably for a specified time (hours) under the specified ambient temperature and system voltage conditions. Second, the impact life expectancy, which can reliably withstand the provisions of the impact of the number.

(4) After the varistor is inserted into the system, it will bring some additional influences besides the protection function of “safety valve”. This is called “secondary effect”, and it should not reduce the normal working performance of the system. At this time to consider the three main factors, one varistor itself capacitance (tens to tens of thousands of PF), the second is the system voltage leakage current, the third is the varistor non-linear current through the source impedance The effect of coupling on other circuits.

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