MP44014 – BOUNDARY MODE PFC CONTROLLER

MP44014 Rev. 1.01

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11

11/10/2015

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Boundary Conduction Mode

When the current of the boost inductor reaches

zero, the voltage on the inductor is reversed.

ZCS then generates the turn-on signal of the

MOSFET by sensing the falling edge of the

voltage on the auxiliary winding coupled with the

inductor. If the ZCS voltage rises above 2.1V, the

comparator waits until the voltage falls below

1.6V. Once the voltage falls below 1.6V, the

MP44014 turns on the MOSFET. The 7.8V high

clamp and 0.55V low clamp protect ZCS. The

internal 175µs timer generates a signal to turn on

the MOSFET if the driver signal has been low for

more than 175µs. This also allows the MOSFET

to turn on during the start-up period since no

signal is generated from ZCD during start-up.

Zero-Crossing Compensation

The MP44014 offers 30mV voltage offset for the

multiplier output near the zero crossing of the line

voltage (which can force the circuit to process

more energy at the bottom of the line voltage).

With this function, the THD of the current is

reduced.

To prevent redundant energy, this offset is

reduced as the instantaneous line voltage

increases. Therefore the offset will be negligible

near the top of the line voltage.

Power Factor Correction

The MP44014 senses the inductor current

through the current sense pin and compares it

to the sinusoidal-shaped signal, which is

generated from the output of the multiplier. When

the external power MOSFET turns on, the

inductor current rises linearly. When the peak

current hits the sinusoidal-shaped signal, the

external power MOSFET begins to turn off, and

the diode turns on. Also, the inductor current

begins to fall. When the inductor current reaches

zero, the power MOSFET begins to turn on again,

which causes the inductor current to start rising

again. The power circuit works in boundary

conduction mode, and the envelope of the

inductor current is sinusoidal shaped. The

average input current is half of the peak current,

so the average input current is also sinusoidal

shaped. A high power factor can be achieved

through this control method (see Figure 4).

Multiplier output

Inductor current

Input average current

Figure 4: Inductor Current Waveform

The control flow chart of the MP44014 is shown

in Figure 5.

Figure 5: Control Flow Chart