EN1C11_15 Datasheet, PDF (9/13 Pages) Vicor Corporation – Component Power Front-end System for EN Compliance

APPLICATION NOTE (CONT.)
Hold-up Capacitors
Hold-up capacitor values should be determined according to
output bus voltage ripple, power fail hold-up time, and
ride-through time (see Figure 15). Many applications require
the power supply to maintain output regulation during a
momentary power failure of specified duration, i.e., the
converters must hold-up or ride through such an event while
maintaining undisturbed output voltage regulation. Similarly,
many of these same systems require notification of an
impending power failure in order to allow time to perform an
orderly shutdown.
The energy stored on a capacitor which has been charged to
voltage V is:
ε = 1/2(CV²)
(1)
Where: ε = stored energy
C = capacitance
V = voltage across the capacitor
EN1xxx
Energy is given up by the capacitors as they are discharged by
the converters. The energy expended (the power-time product)
is:
ε = PΔt = C(V₁₂–V₂₂) / 2
(2)
Where:
P = operating power
Δt = discharge interval
V₁ = capacitor voltage at the beginning of Δt
V₂ = capacitor voltage at the end of Δt
Rearranging Equation 2 to solve for the required capacitance:
C = 2PΔt / (V₁₂–V₂₂)
(3)
N
EMI GND
+
15 Vdc
150 k
B OK
ST
SR
EN
Micro-
controller
L
–
FARM3
250 Ω
+In
PC (Gate In)
Vicor DC-DC
Converter
PR (Gate Out)
–In
N
15 Vdc
EMI GND
27 kΩ
SR
Micro-
controller
L
+
BOK
ST
EN
–
FARM3
+5 Vdc
Secondary
referenced
Figure 11 — Enable (EN) function
40
35
30
25
20
15
10
5
0
250
1,300 μF
1,100 μF
1,600 μF
2,200 μF
* ^{820 μF}
680 μF
*
500
Operating Power (W)
Figure 13 — Power fail warning time vs. operating power and
total bus capacitance, series combination of C1, C2 (see
Figure 1a)
ENMODS™
Page 9 of 13
Rev 3.1
06/2015
Figure 12 — Bus OK (BOK) isolated power status indicator
100
90
80
70
60
50
40
90 Vac
115 Vac
30
20
10
0
250
500
Operating Power (W)
Figure 14 — Ride-through time vs. operating power
vicorpower.com
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