juan manuel garofalo wrote:

>                 +24 v
>         |               |
>         |               |
>       fet_1           fet_3
>         |               |
>      (a)|-----motor-----|
>         |               |
>         |               |
>       fet_4           fet_2
>         |               |
>         |               |
>
> Hi there,
>
> Suppose that the bridge depicted is used to only to reverse the motor, not
> using PWM.
>
> Is it true that, when fet_1 & fet_2 are on, point (a) is not at ~zero volts,
> and therefore you need a gate bias higher than 24v to turn fet_1 on ? I read
> this is the case but i really don't get it why it's so. Anybody care to
> explain it to me ?

If you use P Channel FETs for FET1&3, you have a easier time driving them on.

There is no "therefore", the FETs are not perfect switches,
they have a voltage burden when they conduct current.
An N-Channel FET requires that the gate be a higher voltage than the source.
SO if FET1 is an N-Channel and the drain is 24 volts, you need to drive the gate

greater than 27 volts to turn the FET on hard.

> Does Using PWM make any diference regarding bias for the fets ?

No

> Thanks a lot!

Your welcome.

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