In voltage regulator, the following three types of capacitor
is usually used as the input voltage and output bypass capacitors: multilayer ceramic capacitors, solid tantalum electrolytic capacitor and aluminum electrolytic capacitors.
Designers in selecting bypass capacitors and film capacitor is used to filter, integrator, sequential circuits, and the actual capacitance value is very important to other applications, all these factors must be considered.
If choose undeserved, may cause the circuit is not stable, noise and power consumption is too large, the product life cycle is shortened, and the circuit of unpredictable behavior.
1 film capacitor selection requirements.
Rated voltage of capacitor: refers to the rated temperature range can be continuously applied to the highest dc capacitor voltage or pulse voltage peak.
Considering the reliability derating use requirement, usually requires actual operating voltage should be less than 80% of the rated voltage value.
The working voltage of capacitor selection: by pulse capacitor voltage and the resistance to voltage, because film capacitor loss, when used under the condition of high frequency and high pulse, if there is a bigger by the capacitor current would make film capacitor itself fever, serious when there will be thermal breakdown, etc. (
Also in danger, so use is limited by a capacitor rated current.
When using must ensure that both the voltage within the scope of the permit.
If you cannot determine the actual working voltage (
Waveform, can use to determine the temperature of condenser work themselves, usually for polyester capacitor, allowing their temperature rise under the condition of less than 10 c use.
For polypropylene capacitors, allowing in their temperature rise under the condition of less than 5 ℃.
Actual measurement should be in condenser end wire welding parts surface testing)
Capacitor capacity and lead span choice: 1)
Capacity selection must conform to the E24 series value range: 1.
0 and 1.
1 and 1.
2, and 6.
8 and 7.
Level 1, a total of 24, including the following picture for the E12 at 11:45 series value of the horizontal line, for optimizing series values.
Capacity scope shall comply with all kinds of capacitor capacity range: given in the general specification for different manufacturers provide the specifications of the book, on its capacity, lower limit range may be slightly different, but if the capacity selection of value has significantly below the lower limit of the class, should be selected in the ceramic capacitor, whereas value is higher than the upper limit of the class, such as capacity should be selected in the electrolytic capacitor.
Selection of wire forming pin pitch: different types of different specifications of the film capacitor, the conventional lead spacing of P in the manufacturer specification has a certain value, but in actual use, in accordance with the requirements of PCB assembly, molding can ask manufacturer supply, forming the size of the back foot from F requirements are presented.
Film capacitor to incorrect selection of common problem A rated voltage improper selection rated voltage states now is the most resonant circuit part (
Developers should according to the amount of power equipment, the input voltage, the circuit topology, inverter control mode, load material, magnetic load rate, after the circuit parameters such as the Q value as a comprehensive consideration for preliminary calculation.
Finally through the equipment in full power aging test, measure the temperature of a condenser F, according to the rise of temperature of the capacitor to allow proper parameters to determine the selection of the capacitor.
Current measurement and temperature rise to comprehensive evaluation)
C according to the improper line connection mode is undeserved, mainly appears in be used more than capacitor in parallel.
Due to the connection mode, mixed - line distance
Factor, such as to cause each parallel capacitor in the circuit of the shunt is inconsistent.
Finally reflected in more than parallel capacitor, the temperature rise of each only differ -
Individual position of condenser temperature rise too high, state is destroyed.
Therefore, micro for capacitor in parallel with reasonable wiring and connection, as far as possible to do both flow, improve the service life of the capacitor.
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