ENMODS™

Rev 3.3

vicorpower.com

Page 8 of 13

06/2017

800 927.9474

EN1xxx

Application Note (Cont.)

Off-Line Power Supply Configuration

The ENMod system maintains the DC output bus voltage between

compatible with all Vicor 300V input converters. Autoranging

automatically switches to the proper bridge or doubler mode at

startup depending on the input voltage, eliminating the possibility

of damage due to improper line connection. The ENMod system

is rated at 575W output power. These modules can serve as the

AC front-end for any number and combination of compatible

converters as long as the maximum power rating is not exceeded.

FARM3 Module Pin Descriptions (see Figures 1a, 18a and 18b)

Strap (ST) Pin: In addition to input and output power pin

connections, it is necessary to connect the Strap pin to the center

junction of the series hold-up capacitors (C1, C2) for proper

(autoranging) operation. Varistors V1 and V2 provide capacitor

protection. The bleeder resistors (R1, R2) discharge the hold-up

capacitors when power is switched off. Capacitors C7 and C8 are

recommended if the hold-up capacitors are located more than 3

inches (75mm) from the output pins.

Enable (EN) Pin: The Enable pin must be connected to the PC

or Gate-In pin of all converter modules to disable the converters

during power-up. Otherwise, the converters would attempt to

start while the hold-up capacitors are being charged through

the current limiting thermistor, preventing the bus voltage from

reaching the thermistor bypass threshold, thus disabling the

power supply. The Enable output (the drain of an N channel

MOSFET) is internally pulled up to 15V through a 150kΩ resistor.

(see Figure 11)

A signal diode should be placed close to and in series with the

PC or (Gate-In) pin of each converter to eliminate the possibility of

control interference between converters. The Enable pin switches

to the high state (15V) with respect to the SR pin to turn on the

converters after the power-up inrush is over. The Enable function

also provides input overvoltage protection for the converters by

The thermistor bypass switch opens if this condition occurs,

placing the thermistor in series with the input voltage, reducing

the bus voltage to a safe level while limiting input current in case

the varistors conduct. The thermistor bypass switch also opens if

(see Figure 9).

CAUTION: There is no input to output isolation in the ENMods, hence

the –Out of the ENMods and thus the –In of the downstream DC-DC

converter(s) are at a high potential. If it is necessary to provide an external

enable / disable function by controlling the DC-DC converter’s PC pin

(referenced to the –In) of the converter an opto-isolator or isolated relay

should be employed.

Bus-OK (BOK) Pin: (see Figure 12) The Bus-OK pin is intended

to provide early-warning power fail information and is also

referenced to the SR pin.

CAUTION: There is no input to output isolation in the ENMods. It is

necessary to monitor Bus-OK via an optoisolator if it is to be used on the

secondary (output) side of the converters. A line isolation transformer

should be used when performing scope measurements. Scope probes

should never be applied simultaneously to the input and output as this will

destroy the unit.

L, N Pins: Line and neutral input.

+, – Pins: Positive and negative outputs.

SR Pin: Signal return for BOK and EN outputs.

MiniHAM Module Pin (see Figures 1a, 18a, and 18b)

Filter (see Figure 1b)

The input EMI filter consists of differential and common mode

chokes, Y-rated capacitors (line-ground) and X-rated capacitors

(line-line). This filter configuration provides sufficient common

mode and differential mode insertion loss in the frequency

range between 100kHz and 30MHz to comply with the Level B

conducted emissions limit, as illustrated in Figures 8a thru 8c.