Download SMPS: ISOLATED FORWARD CONVERTER "Non

SMPS: ISOLATED FORWARD CONVERTER
Vds
"Non-isolated SINGLE ENDED STEP-DOWN FORWARD (direct) CONVERTER"
Vind
Ids
Irect
Ei n
Iind Iout
L
ind
Vrect
Vgs
fsw
Iout
IC
C
R
Vout
Irect


limitations of the basic converter:
x single input  single output
x no isolation: single ended or common input -output connection
x fixed output voltage polarity : dependent upon topology
x output voltage relative to the input limited to duty cycle control
x 0<D<1;
D0 limited by transistor switching time


solution:
x transformer coupled (isolated) derivations of the basic converter


problem:
x suggests the need for a dc-dc transformer!!!!!
problem:
x suggests the need for a dc-dc transformer!!!!!
solution:
concept:
x introduce the 'concept' of a DC transformer

AC-AC
DC-DC
practice:
E
in(dc)
Vout(dc)
x primary side switching

pulsating input current
x secondary side rectification
 F-W in some topologies
sync
x 1-T (1-transistor switch) 

low& medium power stages
switch
x 2-T (2-transistor switch)
 half off-state voltage per
topologies:
x the 'dc-dc transformer' insertion point in the basic circuit results
in different topology converters
x the need for additional switches and rectifiers depends on the
topology as it is sometimes possible to use the existing basic
circuit elements in a dual role.

EET 423 POWER ELECTRONICS 2nr : np : ns 1
D1
Isolated v Non- Isolated Forward Converter
r ind
Iout
L =10A
Prof R T Kennedy
2006-2007
isolated converter advantages:
x multiple outputs possible
x isolation: no common input -output connection
 'indirect converter'
x output voltage polarity choice: dependent upon winding polarity
x output voltage can now be varied dependent upon turns ratio
and duty cycle  greater design flexibility in range of duty cycle..control
isolated converter disadvantages:
x extra
{
cost
{
size
weight
{
xlosses
xleakage inductance
{
winding resistance
{
core
{
{
overlap  reduced output voltage
transient voltages
x core saturation (possible)
x core reset requirements
EET 423 POWER ELECTRONICS 2
Isolated v Non- Isolated Forward Converter
2
Prof R T Kennedy
2006-2007