MH2501SC datasheet(7/33 Pages) SHINDENGEN

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SHINDENGEN

ELECTRIC MFG.CO.,LTD

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Operating principles

2.1

Operating principles of current-critical PFC with ON range control

Fig. 4 Critical operation

Fig. 5 Waveform of a single switching cycle

This IC employs a current-critical system. As shown in Fig. 4, the choke current IL forms triangle

waves, starting and ending at 0 A repeatedly. The IC also uses an ON range control system. The

ON range Ton is determined by the load and is fixed. The OFF range Toff varies with the input

voltage Vin at every switching. The switching period varies.

The following formulas give the currents:

Ton and L are fixed. The peak value of IL, IL(peak), is proportional to Vin. Since Vin is sinusoidal,

IL(peak) is sinusoidal. (Formula 1)

]

[

)

(

peak

in 



...(1)

The switching frequency is significantly higher than the AC commercial frequency. Vin is

considered constant during a single switching cycle (Fig. 5).

The input current Iin equals IL(ave), which is IL with its high frequency component removed by the

capacitor Cin and averaged. Since IL is a triangle wave, IL(ave) is half of IL(peak). (Formula 2)

]

[

)

(

)

(

peak

ave



...(2)

We substitute Formula 1 into Formula 2.

]

[

)

(

)

(

peak

ave





...(3)

As Formula 3 shows, Iin is proportional to Vin due to the ON range control of this IC. The power

factor is improved. Fig. 6 shows waveform examples on the circuit.

Fig. 6 Waveform examples on the circuit

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