Vicor PFC Micro Power Factor Corrected AC-DC Switcher - Manual (Page 5)

03-000048 rev A Vicor 800-735-6200 Westcor Division 408-522-5280 Applications Engineering 800-927-9474 Pg. 5
Technical Description
The PFC Micro consists of an off-line single phase, power-factor-corrected front end, EMI filter, cooling fan, cus-
tomer interface, power supply control circuit, associated housekeeping circuits, and a selection of Vicor’s 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 Vicor’s 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 emis-
sion and high efficiencies.
At initial power-up, the PFC Micro outputs are disabled to limit the inrush current and to allow the DC bus poten-
tial 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 Vcc comes up within 1 s 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 250 ms later.
An output Enable/Disable function is provided to control Vicor’s 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 9-12 ms. The General Shutdown function controls all outputs
simultaneously and works in a similar manner.
PFC Micro Design Guide
Figure 1. PFC Micro Architecture
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