H-Bridge - should a maximum of 5 V appear across the load?

[adilmahsan]

H-Bridge

I wanted to know a little about h-bridge... lets say i made one using 4 npn transistors... the switching voltage at the base of each transistor is 5 V and 50 volts are at the collectors of the upper transistors

Now, as the upper two are in emitter follower configurations, shouldnt a maximum of 5 V appear across the load?

 

[FvM]

H-Bridge

Yes, it would be the case, if you assume a ground referenced control voltage for the high side switches.
But a H-bridge doesn't work this way. It involves some kind of level shifter or isolated driver.

 

[elrayes]

Re: H-Bridge

you can use darligton pairs in driving or optocouplers to drive transistor to isolate input control signal from the high side.
if you are building a small H-bridge circuit you might not need an isolation system but remember to add a current limiting resistor on the transistors base.
also i recommend you L298 IC, it is a dual H-bridge with maximum current up to 2A for the IC.
good luck