D
Dan
Guest
I'm trying to wrap my head around a simple H-bridge circuit, such as
shown here http://www.dprg.org/tutorials/1998-04a/ Simply two PNP's
at the top, and two NPN's at the bottom - and you get direction
control.
The NPN is simple - you apply a voltage to the base that is .7 volts
higher than the emitter (ground in this case) and it opens the
"switch".
However, where I'm getting lost is the PNP part. From what all I
read, you supply a voltage .7 volts lower than what is on the emitter
(12v in the diagram, so 11.3volts or less) to allow voltage to flow
out the collector.
What I think is confusing me and is left of the diagram is what turns
those PNP's on and off. They show a logic table of 0 and 1 for the
state of each swich, but I am trying to figure out what you would do
to put a PNP in the 0/Off state. Sure - you could put 12V on the
base, but isn't the idea that you are using a smaller voltage to
control a larger voltage.
If you had an IC that was putting out 0V for off, and 5V for on,
wouldn't the 0V be less than 11.3V and turn it on as well? So what am
I missing in the middle?
Thanks - this has been confusing me for a while trying to get into all
this.
-Dan
shown here http://www.dprg.org/tutorials/1998-04a/ Simply two PNP's
at the top, and two NPN's at the bottom - and you get direction
control.
The NPN is simple - you apply a voltage to the base that is .7 volts
higher than the emitter (ground in this case) and it opens the
"switch".
However, where I'm getting lost is the PNP part. From what all I
read, you supply a voltage .7 volts lower than what is on the emitter
(12v in the diagram, so 11.3volts or less) to allow voltage to flow
out the collector.
What I think is confusing me and is left of the diagram is what turns
those PNP's on and off. They show a logic table of 0 and 1 for the
state of each swich, but I am trying to figure out what you would do
to put a PNP in the 0/Off state. Sure - you could put 12V on the
base, but isn't the idea that you are using a smaller voltage to
control a larger voltage.
If you had an IC that was putting out 0V for off, and 5V for on,
wouldn't the 0V be less than 11.3V and turn it on as well? So what am
I missing in the middle?
Thanks - this has been confusing me for a while trying to get into all
this.
-Dan