The full bridge converter is similar to the push pull converter, but a centre tapped primary is not required. The reversal of the magnetic field is achieved by reversing the direction of the primary winding current flow. This type of converter is found in high power applications.
For the full bridge converter, the output voltage Vout equals the average of the waveform applied to the LC filter
Vout = Vin x (n2/n1) x f x (Ton,q1 + Ton,q2)
whereVout=Output Voltage - Volts
Vin=Input Voltage - Volts
n2=0.5 x secondary turns
n1=primary turns
f = operating frequency - Hertz
Ton,q1 = Q1 conduction time - Seconds
Ton,q2 = Q2 conduction time - Seconds
Diagonal pairs of transistors will alternately conduct, thus achieving current reversal in the transformer primary. This can be illustrated as follows - with Q1 and Q4 conducting, current flow will be 'downwards' through the transformer primary, and with Q2 and Q3 conducting, current flow will be 'upwards' through the transformer primary.
The control circuit monitors Vout and controls the duty cycle of the drive waveform to Q1, Q2, Q3 and Q4.
The control circuit operates in the same manner as for the push-pull converter and half-bridge converter, except that four transistors are being driven rather than two.
