Full Bridge Converter

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Full Bridge Converter

Full Bridge Converter are two Half bridge Converters, but the output of each powered stage are inverted in polarity, driving the transformer harder like in H mode load
Fig 1 show the basic circuit, note that transformer are connected between the two half bridge outputs in order to utilize both polarities of magnetic flux of the transformer, with no capacitors dividers like in Half bridge
Diodes  D2 rectifier the forwarded energy from the four MOSFETS.
R3 sense the voltage output and it is compared with voltage reference Vref. photo isolated transistor then feedback the PWM signal required to regulate the voltage according to the value of Diode Zener Vref.+ Photo diode Vf (Vf = voltage forward of photo diode)
The size of the inductor and capacitor determinate the switching frequency and the power output
Advantages/Applications:
It is used for:
 Provide high output power and efficient designs
 Optimize transformer utilization
 Advantages
 Provides same advantages as HB
 Only one 60cps bulk cap.
 Provides 2 times the output power of the HB with the same Switch MOSFETS
 Disadvantages
 It requires 4 MOSFETS and 4 drivers
 Power circuit has 2 pole
 It can be used in current mode PWM control
 MOSFET selection
 Vds > 1.1 Vin(max)
 Ids(max) >  Po/(n*Vin(min))
 Diodes Selection
 Ifmax >= Io(max), If(avg)=0.5Io(max)
 D01 should be fast (20-100nS)

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