Re: pic output port

"Meindert Sprang" <[EMAIL PROTECTED]> wrote in message
news:[EMAIL PROTECTED]
> "CBarn24050" <[EMAIL PROTECTED]> wrote in message
> news:[EMAIL PROTECTED]
> > Hi, you need a base resistor, 470R will do.
>
> That is waaay too low. 4k7 to 22k is much better.

I guess that depends on the beta of the transistor and the
resistance/impedance of the load, no? I would think that a transistor with a
beta of fifty, for example, couldn't drive much of a load with a 22k
resistor.

How does one calculate the base current required to saturate an NPN
transistor, such as in the subject circuit?

> I had a client who changed a 4k7 on one of my boards to 1k. The OC output
> couldn't be driven low anymore.

Before or after?

Mike