Half bridge or Full bridge

[bunalmis]

Full bridge driver need four MOS. Half bridge need only two MOS but this drivers need symetric voltage source and also MOS VDS voltage higher (min x2) then full bridge MOS.

All popular motor drivers are full bridge. I dont see simple half bridge driver.

Are there orher factors why we dont see half bridge motor driver?

[keebler303]

I think you mentioned the biggest reason. A bipolar power supply, of a size suitable for driving steppers or servos, is a lot more expensive than the extra 2 FETs to make it run on a single supply.

Matt

[bunalmis]

Power supply no problem. We can use 2 secondery (middle point) transformator and only extra one big capacitor.

If we use 3 motor. We need 12 mos and 6 mos driver for the full bridge.

Half brifge has advantages. Only 6 mos and 3 mos driver.

[Mariss Freimanis]

1) The half-bridge drive needs MOSFETs with twice the rated voltage as what a full-bridge drive requires. MOSFET Rds increases with the square of Vds. In other words, a 200V rated MOSFET will have 4-times the on resistance of a 100V rated MOSFET for the same silicon die size. The 200V MOSFET needs a 4 times bigger silicon die to have the same on resistance as the 100V MOSFET. This makes it cost 4 times as much.

2) Only one polarity supply can be used at any given time. This means a 50% utilization of the supplies. A full-bridge supply can enjoy 100% utilization. This means your power supply is twice as big and costs twice as much as would be need for a full-bridge drive.

Mariss