Vicor Micro Family of DC-DC Converter - Manual (Page 44)

Design Guide & Applications Manual
For Maxi, Mini, Micro Family DC-DC Converters and Configurable Power Supplies
Maxi, Mini, Micro Design Guide Rev 4.9 vicorpower.com
Page 43 of 88
Apps. Eng. 800 927.9474 800 735.6200
9. Modular AC Front-end System (ENMod)
POWER-UP SEQUENCE (Figure 9–4)
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.
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 ms after the
thermistor bypass switch is closed.
5.1 Bus OK is asserted after an additional ~150 ms delay
to allow the converter outputs to settle within
specification.
POWER-DOWN SEQUENCE (Figure 9–4)
When input power is turned off or fails, the following
sequence occurs as the bus voltage decays:
1.2 Bus OK is de-asserted 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.
Figure 9–7 — Power down from 120 Vac
Figure 9–8 — Power down from 240 Vac
Figure 9–9 — Output overvoltage protection 240 Vac range
I ac input @2A / mV
I ac input @2A / mV
Vdc output
Enable
Bus OK
Vdc output
Enable
Bus OK
Vdc output
Enable
Bus OK