Re: Updated website

Wayne,

I got it now. The circuit shown has a number of problems, the biggest
being it will self-destruct at motor power supply voltages above
+5VDC. Contact me off list for needed corrections to it.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "waynegramlich" <Yahoo@G...> wrote:
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
>
> > Here's what the diodes do. Let's say the "upper left" and "lower
> > right" transistors are on, the current in the coil builds up and
the
> > direction of current will be left to right. The coil has
inductance
> > and inductance does not like current to change abruptly.
> >
> > Now the previously on transistors turn off and the opposite
> > pair turn n (lower left and upper right). The current direction
> > in the coil will still be left to right. Here's where things
> > get interesting.
> >
> > That condition would require current to flow out of the
> > "lower left" collector and into the emitter of the "upper
> > right" transistors. You can't do that. Because you can't,
> > it would rupture both transistors; the coil inductance
> > would generate whatever voltage it took to do that.
> >
> > This is where the diodes come in. They provide the path
> > for this current to flow while it decays. The transistors
> > don't carry any current until the coil decays to zero
> > current. Then the direction of current can reverse and
> > build in the opposite direction, now supplied by the
> > transistors again.
>
> Mariss:
>
> I'm not sure we are talking about the same circuit.
> The one I am talking about has the following URL:
>
> http://www.pilotltd.net/hbridge.gif
>
> This is FET H-bridge, not a transistor H-bridge.
>
> In addition, the diodes I am talking about (D2-D9)
> are attached to the gates of the FETS, not the
> sources or drains. While it is quite clear to me
> that the voltages from the motor will vary between
> Vs +.5 volts to -.5 volts, I just do not see how
> the voltage from motor can get through the FET
> gates. Maybe this is a mental block of mine about
> FETs, but my understanding is that there is on
> conductive path from the source/drain to the gate.
>
> I'm still confused, and any further illumination
> would be greatly appreciated.
>
> Thanks,
>
> -Wayne