EN1C11_15 Datasheet, PDF (7/13 Pages) Vicor Corporation – Component Power Front-end System for EN Compliance

APPLICATION NOTE
The ENMod component power front-end system for
EN compliance provides an effective solution for an AC
front end of a power supply enabled with Vicor DC-DC
converters. The ENMod system’s basic building blocks are
the MiniHAM passive harmonic attenuation module, the
FARM3 autoranging AC-DC front-end module (Figure 9) and
a discrete EMI filter.
The ENMod system provides transient/surge immunity,
harmonic current attenuation and EMI filtering, in addition to
all of the power switching and control circuitry necessary for
autoranging rectification, inrush current limiting, and
overvoltage protection. Converter enable and status functions
for orderly power up/down control or sequencing are also
provided. To complete the AC front-end configuration, the user
only needs to add hold-up capacitors, a simple EMI filter, and
a few discrete components (see Fig. 1a).
Functional Description (FARM3, see Figures 9 & 10)
Power-Up Sequence.
1.1 Upon application of input power, the hold-up capacitors
begin to charge. The thermistor limits the charge
current, and the exponential time constant is determined
by the hold-up capacitor value and the thermistor cold
resistance. The slope (dV/dt) of the capacitor voltage
versus time approaches zero as the capacitors become
charged to the peak of the AC line voltage.
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. In addition, the converter
modules are disabled via the Enable (EN) line, and Bus-
OK (BOK) is high.
+OUT
PTC
Thermistor
Strap
L
Strap
EMI
Filter
N
Microcontroller
–OUT
SR
EN
BOK
EMI GND
Figure 9 — Functional block diagram: FARM3 module
ENMODS™
Page 7 of 13
Rev 3.1
06/2015
EN1xxx
2.1 ^{If the bus voltage is less than 200 V 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 200 V, the
doubler is not activated.
3.1 If the bus voltage is greater than 235 V as the slope
approaches zero, the inrush limiting thermistor is
bypassed. Below 235 V, it is not bypassed.
4.1 The converters are enabled ~150 milliseconds after the
thermistor bypass switch is closed.
5.1 Bus-OK is asserted after an additional ~150 millisecond
delay to allow the converter outputs to settle within
specification.
Power-Down Sequence. When input power is turned off
or fails, the following sequence occurs as the bus voltage
decays:
1.2 Bus-OK is deasserted when the bus voltage falls below
210 Vdc.
2.2 The converters are disabled when the bus voltage falls
below 190 Vdc. 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,
i.e., the power conversion system “rides through”
the momentary interruption.
Power
Up
Power
Down
90–132 V
AC Line
Output
Bus
(Vdc)
400
300
200
100
0 ^1.1
2.1
Strap
PTC
Thermistor
Bypass
Converter
Enable
Bus OK
3.1
4.1
~150 ms
5.1
~150 ms
2.2
1.2
Figure 10 — Timing diagram: power-up/down sequence
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