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Technical Description
The PFC Micro™ consists of an off-line single-phase, power-factor-corrected front end, EMI filter,
cooling fan, customer interface, power supply control circuit, associated housekeeping circuits and a
selection of Vicor VI-200™/VI-J00™ and/or Maxi DC-DC converters.
Input AC mains voltage is applied to input connector MB1J1. The input current is passed through an
EMI filter designed to meet conducted noise limit "A" specifications of FCC Part 15.
At start up, inrush current is limited by a PTC thermistor. The PTC is shunted out shortly after initial
power up by a DC bus voltage sense circuit driving a relay. After rectification, the input voltage is put
through a boost converter that keeps the AC input current sinusoidal and synchronized with the input
AC voltage (in compliance with EN61000). The boost converter delivers a regulated input to the hold-up
capacitors and a high-voltage backplane. The backplane supplies power to the DC-DC converters that
provide the desired low voltage regulated outputs.
Output voltage conversion is achieved by the Vicor family of Zero-Current Switching (ZCS) DC-DC
converters. These are forward converters in which the main switching element switches at zero current.
This patented topology has a number of unique attributes: low switching losses; high-frequency
operation, resulting in reduced size for magnetics and capacitors; excellent line and load regulation;
wide adjustment range for output; low EMI/RFI emission and high efficiencies.
At initial power up, the PFC Micro outputs are disabled to limit the inrush current and to allow the
DC bus potential to settle out to the correct operating level. A low-power flyback converter converts
the high-voltage DC bus into regulated low voltage to power the internal housekeeping circuits and
DC cooling fan.
The internal housekeeping V
CC
comes up within 1s after the application of input power. Once the
high-voltage bus is within operating limits, the AC Power OK signal asserts to a TTL "1," indicating the
input power is OK, and the power outputs will come up 250ms later.
An output enable / disable function is provided to control Vicor DC-DC converters. If the Enable/Disable
control pin is pulled low, the modules output is disabled. The nominal delay associated for an output to
come up when measured from release of the Enable/Disable pin is 9 – 12ms. The General Shut Down
function controls all outputs simultaneously and works in a similar manner.
Line Filter
Bridge
Rectifier
Soft Start
Circuit
Boost Converter
PFC Control
Power Supply
Control
Output Card #1
Output Card #2
Fan
Isolated
Housekeeping
Power Supply
Customer
Interface
Power
Output
Power
Output
Input
Enable/Disable -Power Good Read
Figure 1
PFC Micro architecture
