it depend on... in fact, it depend on the requirments,such as cost ,topology.in china, we often use 230V line voltage, so half-bridge is much more popular. if you want to use push-pull, the swiching transistors must have a abilty of high reverse Vce.so it is not so good as half-bridge.the flowing is more often seen in china:
using half-bridge, general speaking under the case of line voltage 230V, the ballast at most can handle 3 lamps. if the line voltage is 120V, we would like to use push-pull and the ballast can drive more lamps than half bridge. this point is often seen in us model ballast.
