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is from a low of a few watts to 200W,
with a maximum voltage about 60V
volts and a maximum current of 4A. The
larger the driver, the more likely it is to
be of higher efficiency.
For larger drivers, efficiencies quoted
in engineering articles are in the high 80%
range. Figures are not readily available for
the low end, but common sense indicates
that with magnetising current forming
a much larger part of small transformer
input current the efficiencies will be 10
percentage points lower.
From an overall lighting efficiency
aspect, the superior luminous efficiency
of LEDs makes up for loss of efficiency
in drivers. However, the AC to DC
conversion, if eliminated, can lift the
overall power conversion efficiency
spread from 65-80% to 80-90% (This
relates to power available to LEDs
compared with input power. Luminous
efficiency is not included.)
With the increase in rooftop photo-
voltaic installations, the drop in feed-in
tariffs, and the rising sales of battery
storage systems, can DC input power for
LED lighting be far off?
Is there any sense in supplying
the nightly load of lighting by
inverter-generated AC only to convert
it back to DC? One efficient DC-DC
converter for the home would take
care of business.
Vin
Vref
Vref
Q3
Rs3
Rs4
Coomp
+
A
B
V-
V
+
V-
V
+
Coomp
Roomp
Roomp
Q4
+
Figure 8: Individual string current control.