Vicor MegaMod DC-DC Converter Family User Manual
Page 4
Fusing.
Safety agency conditions of acceptability require
module input fusing. The fuse should be inserted in the +Input
lead, not the –Input lead, since opening the –Input lead will
cause the gate terminals to rise to the voltage of the +Input lead,
which may damage connected modules or devices. Consult the
Vicor Applica tion Engineering Department for proper fuse values.
Grounding.
If the converter baseplate is accessible to the
operator, ground the baseplate to earth/chassis ground. Use the
same wire gauge as that specified for your converter’s input
wire, below.
Input Wire Gauge.
Calculate the input current for MegaMods
and MegaMod Jr.’s as follows and use the recommended input
wire gauge.
■
I
IN
= P
OUT
/ (
η x V
LL
)
P
OUT
= output power
η = efficiency = 0.8
V
LL
= low line voltage
■
Example:
I
IN
= 300 / (0.8 x 42) = 8.93A
Use a #16 input wire.
Input Source Impedance.
The converter should be connected
to an input source that exhibits low AC impedance. If source
impedance is questionable, mount a small electrolytic capacitor
close to the module voltage input pins. This will restore low AC
impedance while avoiding the potential resonance associated
with “high-Q” film capacitors. The minimum value of the
capacitor, in microfarads, should be C(μF) = 400 ÷ V
IN
mini mum.
Example: V
IN
minimum for a VI-260-CV module is 200 V.
The minimum capacitance would be 400 ÷ 200 = 2 μF.
Installation and Application Notes
Input
Input Wire
Current
Gauge
16.5 A–26.1 A
#12
10.4 A–16.4 A
#14
6.6 A–10.3 A
#16
4.1 A–6.5 A
#18
2.6 A–4.0 A
#20
0 A–2.6 A
#22
(continued on page 6)
3