Fuse, thermistor, rectifier bridge design power component calculation

fuse

1 role:

Security. In case of abnormal power supply, the core device is protected from damage.

2 technical parameters:

Rated voltage V, rated current I, and fuse time I^2RT.

3 classification:

Quick break, slow break, regular

1, 0.6 is the power factor estimation without power factor correction

2, Po output power

3, η efficiency (designed evaluation value)

4, Vinmin minimum input voltage

5 and 2 are empirical values. In practical applications, the value range of the fuse is 1.5 to 3 times the theoretical value.

6, 0.98 PF value

Thermistor

The role of NTC

NTC is a fine semiconductor electronic ceramic component made of manganese oxide or the like as a main raw material. The resistance value changes nonlinearly with temperature, and the resistance value decreases as the temperature increases. Using this characteristic, a negative temperature coefficient thermistor is connected in series with the input of the circuit to increase the impedance of the line, so that the surge current generated by the surge voltage generated at the time of starting can be effectively suppressed. When the circuit enters steady state operation, the NTC heat caused by the continuous operating current in the line makes the resistance value of the resistor become small, and the influence on the line can be completely ignored.

Explain the above formula as follows:

1. Rt is the resistance of the thermistor at T1 temperature;

2. Rn is the nominal resistance of the thermistor at normal temperature Tn;

3. B is the material parameter; (common range 2000K~6000K)

4. exp is the index based on the natural number e (e = 2.71828);

5. Here T1 and Tn refer to K degree, ie Kelvin temperature, K degree = 273.15 (absolute temperature) + degrees Celsius.

Rectifier bridge

Calculation of rectifier bridge (bridge stack)

Voltage withstand selection of rectifier bridge

Vinmax is the highest input voltage (such as 88~264V input power supply, Vinmax=264).

Current resistance selection of rectifier bridge

Po is the power output power

η is the efficiency of the whole machine

Vinmin is the lowest input voltage (such as 88~264V input power supply, Vinminx=88).

2 is a multiple of the input current rms value, the empirical value.

Power loss calculation for the selected rectifier bridge

Vf is the forward voltage drop of the rectifier bridge.

note

Select the fuse and rectifier bridge, but also pay attention to its instantaneous flow resistance

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