MPFC-U-390-QP

Product # MPFC-U-390-QP

Phone 1-888-567-9596

www.synqor.com

Doc.# 005-0006726 Rev. B

03/30/2016

Page 8

BasicOperation&Features

The MPFCQor power factor correction module is an

essential building block of an overall high power AC-DC

power supply. As shown in Fig. A, a typical power supply

would be comprised of a SynQor MCOTS AC Line Filter,

a SynQor MPFCQor module, an energy storage hold-up

capacitor and one or more SynQor MCOTS DC-DC

converters, depending on how many output voltages are

required. Fuses are needed in various places to meet safety

requirements.

The primary purpose of the MPFCQor is to shape the input

current that is drawn from a single-phase sinusoidal AC source

into a nearly perfect sinusoidal waveform so that the AC-DC

power supply will present a very high power factor load (PF >

0.99) to this source. In doing this wave-shaping, the MPFCQor

ensures that the harmonic components of the AC current

waveform are below the levels called for in MIL-STD-1399. The

total harmonic distortion of the AC current waveform is less than

8%.

The MPFCQor accomplishes its wave-shaping task by first

rectifying the filtered AC source voltage, and then processing the

input power through a non-isolated, high-efficiency, high-

frequency “boost converter” that both gives the input AC current

its sinusoidal shape and provides a regulated DC voltage across

the hold-up capacitor.

The hold-up capacitor handles the cyclic imbalance between

the flow of energy drawn from the AC source and the flow of

energy delivered to the DC-DC converters.

This energy

imbalance has a cyclic frequency twice that of the AC source

voltage (e.g. 120Hz for a 60Hz input). This relatively low

frequency makes the hold-up capacitor relatively large. Another

purpose of the hold-up capacitor is to be a source of energy so

that the DC-DC converters can continue to deliver load power

during a temporary brownout or dropout of the AC source. A

typical power supply will have sufficient hold-up capacitor to

give a “hold-up time” in the 20ms range, but longer times can be

achieved with yet more hold-up capacitance.

Besides shaping the AC current waveform, the MPFCQor

performs several other important functions. At start-up it controls

the level of inrush current drawn from the AC source to charge the

hold-up capacitor. It limits the DC current that can be drawn from

its output and it will shut-down if a short circuit appears across the

output. It will also shut-down if the AC input voltage is out of its

range (either too high or too low) for too long, or if the temperature

of the module is too high.

In addition, the MPFCQor has input and output control signals

that include PFC_ENABLE, and LOAD_ENABLE, (which doubles

as a POWER_OUT_GOOD signal). Both signals are described in

more detail below. There is also an auxiliary bias supply that can

be used to power a low power control circuit at the output of the

MPFCQor .

StartUp Sequence

When the AC source voltage is first applied, regardless of

whether the MPFCQor is enabled or disabled through its

PFC_ENABLE

pin, the MPFCQor will pre-charge the

output hold-up capacitor with a current limited to

approximately 50mA. This pre-charging continues until

the output voltage is within approximately 10V of the peak

voltage of the AC source. If, at this time, the PFC_ENABLE

input is logically high, and the MPFCQor is therefore

disabled, the MPFCQor will remain in this pre-charged

state indefinitely.

NOTE: During both this pre-charging time and for

whatever time afterwards that the MPFCQor remains disabled

it is essential that all the load converters connected to the

output of the MPFCQor be disabled so that the total load

current seen by the MPFCQor is only a small fraction of the

50mA charging current. To help facilitate this requirement,

the MPFCQor’s LOAD_ENABLE output can be used to

disable the load converters.

When the PFC_ENABLE input pin is pulled low, and after

the pre-charging is completed if it is not already, the boost

converter within the MPFCQor will start operating and the

MPFCQor ’s output voltage will be increased to its nominal

regulated value.

After this regulated voltage level is achieved, the MPFCQor

will provide a logical low signal on its LOAD_ENABLE output

pin. This signal should be used to enable the load converters so

that they can begin to draw power from the MPFCQor .

If the PFC_ENABLE input is de-asserted (pulled high or

allowed to float), the boost converter in the MPFCQor will shut

down and the LOAD_ENABLE output pin will return to a logic

high. This will then disable the load converters.

NOTE: The voltage across the hold-up capacitor will remain in

a charged state after the MPFCQor is disabled as long as the AC

source voltage is present.

Application Section