There are three possible power scenarios:
- Single or three-phase power available:
- The converter supplies
all voltages and charges the supercapacitors in a variable time between
1 minute and 21 seconds as first charge, and 36 seconds as successive
recharges.
- The switching waveform
present on the secondary side winding is peak-rectified and is used to
disable the inverting buck-boost.
- At the same time, as the
voltage on the supercapacitors is in the range 4.3 V–7.8 V, the boost
converter is active and delivers 11.5 V. This voltage level, slightly
lower than 12 V, is on purpose to avoid delivering current when mains is
present. Keeping the boost converter active eliminates the delay due to
the device soft start.
- When the supercapacitors
are charged, a voltage supervisor TL7705A is enabling the flag “EOC”
(end of charge, useful for a digital output to uC) and turning an LED
on.
- Power unavailable:
- Since the boost converter
with TPS55330 is always active, the 12-Vp bus droops from 12 V to 11.5
V, keeping all rails alive.
- At the same time, both ±
14-V outputs from the flyback converter go to zero and the peak
rectified voltage used for the signal Disable goes to zero.
- Then the inverting
buck-boost starts and supplies ±14 V, which are connected by ORing
diodes to the input of the dual LDO, supplying ± 12 V.
- The power is delivered
until the supercapacitors are discharged below boost UVLO (4.3 V). At
this point all rails are off.
- 12-V bench supply on:
- Here the supercapacitors
are not recharged because there is no voltage on auxiliary winding of
the flyback.
- The 12 V from bench power
is supplying all the rails normally. The inverting buck-boost is also
supplying ±14 V for dual LDO.