These changes dropped the temperature of the casing adjacent to the synchronous rectifier
MOSFET by 10[degrees]C.
In this topology the synchronous rectifier of the buck (Q2) is the same as the control switch of the boost part and thus they are sharing their dead time circuit.
To find the optimal dead time for Q2 the switch-on energy loss for the buck synchronous rectifier was estimated as well as the boost body diode energy loss.
Also, as was discussed in detail in an International Rectifier paper presented at APEC 2004, some synchronous rectifier MOSFETs can turn on for a short time after they have been switched off.
Because there was a short time during which both the series switch and the synchronous rectifier MOSFETs were conducting, efficiency was reduced.
The new LM5114 drives GaN FETs and MOSFETs in low-side applications, such as synchronous rectifiers
and power factor converters.
MOSFET synchronous rectifiers
for isolated, board-mounted DCDC converters.
are employed instead of Schottky diodes to reduce the conduction loss in the secondary side.
Designers also can substitute MOSFETs for diodes to create synchronous rectifiers
. "A diode will typically drop IV across it, so at higher currents that drop can create a lot of heat," said Spaziani.
The company's approach is to use synchronous rectifiers
in a resonant topology.
Advanced processor-based primary- and secondary-side control techniques are combined with precision timing of the synchronous rectifiers
for maximum efficiency.
Designed to provide a compact and efficient solution for fixed telecom applications requiring power supplies in the range of 50W to 150W, the half-bridge (Si9122, So9123) and push/pull (Si9124) devices operate over a 12- to 72- input voltage range, drive both primary-side MOSFETs, and provide timing for the secondary synchronous rectifiers
. Each device incorporates a secondary-side FET drive signal for synchronous rectification and a direct primary MOS drive (1A maximum) on the high- and low-side.