18-01-2013, 03:02 PM
Half-bridge and full-bridge converters
[attachment=47544]
Half-bridge converter
is a circuit diagram of a half-bridge converter. Two capacitors C1 and C2 have half
of d.c. input voltage across of each. The voltage, 0.5 V1 is switched across the primary winding
by MOSFET T1 and T2 alternately. The switch that is off will have the full d.c. voltage across
it. The output voltage Vo is:-
Vo = V1 x D x (Ns/Np)
Figure 12 - Half bridge converter
Some of advantages of half bridge converters are:
Small magnetic cores.
No magnetic path gap therefore low stray magnetic field.
Frequency seen by secondary circuits is double the basic switching frequency - small
filter components (L and C) in secondary circuits.
Low output ripple and noise.
Multiple output configurations easily implemented.
Relatively low radiated noise, especially if the secondary inductors are toroidal cores.
A disadvantage is because they are working at half the supply voltage the switching
transistors are working at twice the collector current compared with the basic push pull
circuit.
Full bridge converter
this is a full-bridge converter circuit diagram. T1 and T3 is a pair, they are
switched on simultaneously, while T2 and T3 is followed simultaneously. At least two of the
Half-bridge and Full-bridge converters
bridge transistors require gate isolation circuits. The output voltage, Vo is twice that of the
half-bridge:
Vo = 2 x V1 x D x (Ns/Np)
Figure 13 - Full bridge converter
The much simpler and lower power gate drive circuits required by MOSFETS when compared
with complex base drive requirements of bipolar transistors switches greatly favours their
use in high power full bridge circuits.
MOSFETS gives considerable size advantages in the transformer core and in filter
components. This is well illustrated by referring to the Power Ten range of high power rack
mounted units.
[attachment=47544]
Half-bridge converter
is a circuit diagram of a half-bridge converter. Two capacitors C1 and C2 have half
of d.c. input voltage across of each. The voltage, 0.5 V1 is switched across the primary winding
by MOSFET T1 and T2 alternately. The switch that is off will have the full d.c. voltage across
it. The output voltage Vo is:-
Vo = V1 x D x (Ns/Np)
Figure 12 - Half bridge converter
Some of advantages of half bridge converters are:
Small magnetic cores.
No magnetic path gap therefore low stray magnetic field.
Frequency seen by secondary circuits is double the basic switching frequency - small
filter components (L and C) in secondary circuits.
Low output ripple and noise.
Multiple output configurations easily implemented.
Relatively low radiated noise, especially if the secondary inductors are toroidal cores.
A disadvantage is because they are working at half the supply voltage the switching
transistors are working at twice the collector current compared with the basic push pull
circuit.
Full bridge converter
this is a full-bridge converter circuit diagram. T1 and T3 is a pair, they are
switched on simultaneously, while T2 and T3 is followed simultaneously. At least two of the
Half-bridge and Full-bridge converters
bridge transistors require gate isolation circuits. The output voltage, Vo is twice that of the
half-bridge:
Vo = 2 x V1 x D x (Ns/Np)
Figure 13 - Full bridge converter
The much simpler and lower power gate drive circuits required by MOSFETS when compared
with complex base drive requirements of bipolar transistors switches greatly favours their
use in high power full bridge circuits.
MOSFETS gives considerable size advantages in the transformer core and in filter
components. This is well illustrated by referring to the Power Ten range of high power rack
mounted units.