Delta Electronics Series 240W - Manual (Page 8)

DS_E48SB9R625_05222008 8
DESIGN CONSIDERATIONS
Current Sharing
The modules are capable of operating in parallel without
any external current sharing circuitry.
For a normal parallel operation, the following
precautions must be observed:
1. The current sharing accuracy calculation equation is:
Current sharing accuracy=((I
load
/n)-I)*100%)/I
rated
Where, I
load
=Total load current;
I= Output current of per converter;
I
rated
=Converter’s rated output current at different Vin;
n=the numberous of parallel modules
2. The maximum load current for N converters is
I
max
=(1-X%)*N*I
rated
.
Where, X% is current sharing load accuracy.
I
rated
is 100% load for different Vin
This unit has been tested with up to 2 units in
parallel.
3. To ensure a better steady current sharing accuracy,
below design guideline should be followed:
a) The inputs of the converters must be connected to the
same voltage source
b) The PCB trace resistance from Input voltage source to
Vin+ and Vin- of each converter should be as equalize as
possible.
c) The PCB trace resistance from each converter’s
output to the load should be equalized as much as
possible.
4. To ensure a better transient current sharing, and the
monotonic startup of the parallel module
a) The ON/OFF pin of the converters should be
connected together to keep the parallel modules start up
at the approximately same time.
b) The under voltage lockout point will slightly vary from
unit to unit. The dv/dt of the rising edge of the input
source voltage must be greater than 1V/ms to ensure
that the parallel can start up at the approximately same
time.