h-bridgeinverter
(of course replacing the motor with the load..)
Why most inverter circuits use the classical four switches not any other variation as this one as example? i just want to reduce the number of signals to control the bridge. The classical one needs 4 signals (people refuse to connect the gates of similar states together but i don't know why..)
also, Is there any reason to prefer h bridge over push pull configuration?
Yes, you can definitely parallel the two outputs of an L293D. I made a few stepper drivers based on L293D with parallel outputs and had no problems.
As this application note from ST Microelectronics (APPLICATIONS OF MONOLITHIC BRIDGE DRIVERS) states:
Higher output currents can be obtained by paralleling the outputs of both bridges. For example, the outputs of an L298N can be connected in parallel to make a single 3.5 A bridge. To ensure that the current is fairly divided between the bridges they must be connected as shown in figure 2. In other words, channel one should be paralleled with channel four and channel two paralleled with channel three. Apart from this rule the connection is very straightforward - the inputs, enables, outputs and emitters are simply connected together. The outputs of an L293 or L293E can also be paralleled - in this case too, channel 1 must be paralleled with channel 4 and channel 2 with channel 3.
But you should be aware that the total current capability of the parallel outputs would be less than the sum of the two channels (< 1200 mA).
EDIT: The only differences between the L293/L293E and the L293D are that:
the L239D has internal clamp diodes included
the L293/L293E has higher output current capabilities.
I would suggest starting with a smaller H-bridge project first. The control of MOSFETs seems simple, but there are some subtleties which can easily bite you if you are not careful. When designing a smaller H-bridge project, it's not too hard to protect a circuit in such fashion that even if something goes horribly wrong it won't do much damage (and may very well not do any, though whatever caused the problem will need to be fixed in any case). This is useful not only from the standpoint of reducing the amount of time spent replacing blown components, but also from the standpoint of being able to figure out what happened. If something goes wrong in a 12V 30A H-bridge controller, it's likely to cause enough destruction quickly enough that it will be hard to analyze the pile of cinders and determine what failed first.
Beyond that, the reason companies make H-bridge controllers is that other companies buy them, and the reason that other companies buy them is that a surprising number of discrete components are required to safely and optimally control a MOSFET. If one is trying to control a MOSFET whose Absolute Maximum Vgs is 15 volts, and an inductive transient causes Vgs to reach 30 volts even for a microsecond, the part may easily be destroyed (the voltage required to destroy the part would most likely be around 20 volts, but one shouldn't rely upon it being above 15.01). Keeping Vgs below 15 volts may not sound hard, but factors like parasitic gate-drain capacitance can lead to some unpleasant surprises.
Best Answer
This does not look like a good idea. The problem is that both top transistors can be on for a while at switch-over. Remember that the motor make a connection too. Think of replacing the motor with a resistor and you can see that both top transistors are initially driven on when one of the bottom transistors goes on. Also consider that it takes a little while for each top transistor to turn off after its base voltage is raised.