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Film capacitor of industrial equipment power supply

1, in the switching power supply, do not use polystyrene capacitors, because polystyrene capacitors are relatively poor heat resistance.

2, surface temperature <85 ° C, over 85 ° C withstand voltage according to the following figure derating. The voltage here refers to the DC voltage superimposed AC peak voltage.

3, polyester capacitor self-temperature rise <8 ° C or defined by the specification, whichever is lower 4, polypropylene capacitor self-temperature rise <5 ° C or defined by the specification, whichever is lower.

5, the life of the film capacitor depends on the voltage value and the rate of rise of the voltage pulse. The number of pulses allowed and the relationship between the voltage value and the pulse slope, where: Npulse is the total number of pulses: Vr, max maximum rated DC voltage Vapplied Actual peak-to-peak voltage (dv/dt) max maximum rated pulse slope (dv/dt) applied actual Using pulse slope

Industrial control equipment power supply resistance

Resistance can be divided into three categories: fixed linear resistance, fixed nonlinear resistance, variable resistance

Fixed linear resistors include: carbon film, metal film, metal oxide film, metal glaze, carbon and other resistance and winding resistance.

Fixed nonlinear resistors include: NTC, PTC

The reliability of the resistor is mainly determined by the temperature of the resistor, and the temperature is the effect of the superposition of the ambient temperature and the self-power loss.

Both power and voltage impose limitations on the choice and use of resistors:

For resistors whose resistance is lower than the critical resistance, the use is limited by power, and for resistors above the critical resistance, the use is limited by withstand voltage.

The power limit for a single pulse depends on the shape of the pulse. At the same time, the peak voltage of the pulse must not exceed the rated limit.

Derating of resistors using rules:

1. Use enamel resistor 2 in a circuit with instantaneous high-voltage pulse, and use wirewound resistor in case of large inrush current.

3, continuous power <50% × rated power 4, do not use >1MΩ carbon film resistor, because long-term stability is too poor

5, high resistance long-term stability of the good resistance should use metal glaze resistance 6. After the thermal shock test, the resistance of the resistance must be within ± 5% of the rated range.

7, fusible resistors, such as fuse resistors, do not rely too close to the PCB to avoid overheating the PCB

8, try not to use rectangular chip resistors in the ESD protection circuit, because the sharp corners of the rectangle are easy to discharge

9. When using voltage and current sampling, if using chip resistors, try to use a size of more than 1206.

10, the pressure drop derating use:

For carbon film, metal film, metal oxide film resistance: R>100K, VRMS<50%× rated maximum continuous working voltage. When R≤100K, VRMS<90%×rated maximum continuous working voltage or 90%×(P×R)0.5, whichever is lower.

For carbon resistance, glaze resistance and wirewound resistance: VRMS < 90% × rated maximum continuous operating voltage or 90% × (P × R) 0.5, whichever is lower.

11. The instantaneous power when there is an inrush current in the circuit can be calculated according to the following empirical formula:

P = I2 × R × t / 4, where t is the time when the current drops to a maximum of 38%.

Magnetic components of industrial equipment power supply

The AWG wire gauge can be converted to mm unit wire diameter according to this formula: d=25.4×0.005×92 ((36-AWG)/39)

The enameled wire has a lifespan acceleration factor of approximately 2.5 per 10 °C.

The temperature derating of the line package states:

CLASS B: 95°C～110°C Note: The rated temperature is 130°C CLASS F: 110°C～125°C Note: The rated temperature is 155°C

CLASS H: 125 ° C ~ 150 ° C Note: The rated temperature is 180 ° C

Derating of the core: Bmax < 80% × Bsat under any conditions. Bsat is the saturation magnetic induction of the core. TCORE<70%×Tcurie-10°C Tcurie is the core Curie point temperature.

The metal oxide varistor MOV Tcase of the industrial equipment power supply is ≤85 °C. Under any conditions, the specific selection is recommended as:

AC120V/127V selects 150Vrms AC220V and selects 275Vrms (this is still controversial)

AC277V selects 320Vrms AC347V selects 420Vrms

Industrial control equipment power supply printed circuit board

PCB material and highest usable surface temperature: FR2: 75°C FR3: 90°C FR4: 125°C CEM1:125°C CEM3: 125°C

In addition, there are some rules: You can use vias to help dissipate heat through each via. The current does not exceed 2A. The relationship between the wiring and the voltage. The thermal conductivity of UL935 FR1 is twice that of FR4, but FR1 is not suitable for double. surface

Industrial equipment power supply fuse

The derating of the fuse is a compromise between circuit protection reliability and fuse life.

Derating the fuses does not directly lead to an increase in product reliability. Ambient temperature and current are the main factors affecting the life of the fuse.

At 25 ° C, the fuse current should be derated by 25%. When the ambient temperature rises, the slow-blow fuse should be derated by 0.5%/°C. The fast-blow fuses are derated by 0.1%/°C.

Industrial control equipment power optocoupler

Maximum working voltage <70%~90%×rated voltage Maximum operating current <25%～90%×rated current

Current transfer ratio, 20% margin is retained according to product life time. Junction temperature <85°C～100°C