Application Note
The VI-ARM Autoranging Rectifier Module (ARM) provides
an effective solution for the AC front end of a power supply
built with Vicor DC-DC converters. This high performance
power system building block satisfies a broad spectrum of
requirements and agency standards.
If the bus voltage is less than 200V as the slope nears
zero, the voltage doubler is activated, and the bus voltage
climbs exponentially to twice the peak line voltage.
If the bus voltage is greater than 200V, the doubler is
not activated.
2.1
3.1
If the bus voltage is greater than 235V as the slope
approaches zero, the inrush limiting thermistor is
bypassed. Below 235V, the thermistor is not bypassed.
The ARM contains all of the power switching and control
circuitry necessary for autoranging rectification, inrush current
limiting, and overvoltage protection. This module also provides
converter enable and status functions for orderly power
up/down control or sequencing. To complete the AC front end
configuration, the user needs only to add holdup capacitors and
a suitable input filter with transient protection.
The converters are enabled 50 milliseconds after the
thermistor bypass switch is closed.
4.1
5.1
Bus-OK is asserted after an additional 50 millisecond
delay to allow the converter outputs to settle within
specification.
Functional Description
The switch that bypasses the inrush limiting PTC (positive
temperature coefficient) thermistor is open when power is
applied, as is the switch that engages the strap for voltage
doubling. (See Fig. 6). In addition, the converter modules are
disabled via the Enable (EN) line, and Bus-OK (B OK) is high.
Power-Down Sequence. (See Fig. 7). When input power is
turned off or fails, the following sequence occurs as the bus
voltage decays:
Bus-OK is deasserted when the bus voltage falls below
205Vdc (Typ.).
1.2
Power-Up Sequence. (See Fig. 7).:
Upon application of input power, the output bus capacitors
begin to charge. The thermistor limits the charge current,
and the exponential time constant is determined by the
holdup capacitor value and the thermistor cold resistance.
The slope (dv/dt) of the capacitor voltage approaches
zero as the capacitors become charged to the peak of the
AC line voltage.
The converters are disabled when the bus voltage falls
below 200Vdc. If power is reapplied after the converters
are disabled, the entire power-up sequence is repeated. If
a momentary power interruption occurs and power is
reestablished before the bus reaches the disable threshold,
the power-up sequence is not repeated.
1.1
2.2
Power
Up
Power
Down
+Out
90–132V
AC Line
PTC
Thermistor
Strap
400
L
Strap
–Out
300
200
100
0
Output
Bus
1.1
(Vdc)
2.1
Strap
N
PTC
3.1
Thermistor
Bypass
EN
4.1
Converter
Enable
Bus OK
2.2
Microcontroller
50ms
BOK
5.1
1.2
50ms
Figure 6—Functional block diagram
Figure 7—Timing diagram: power up/down sequence
Vicor Corp. Tel: 800-735-6200, 978-470-2900 Fax: 978-475-6715
ARM, Autoranging Rectifier Module
Rev. 2.4
Page 5 of 12
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