MOSFET circuit question

[AnalogKid]

Depends. Typically, an open collector output is negative-true. That is, it would go low when the output relay is on. That is the opposite logic polarity from previous posts.

ak

 

[earckens]

Depends. Typically, an open collector output is negative-true. That is, it would go low when the output relay is on. That is the opposite logic polarity from previous posts.

ak

Hi ak, how can we keep have positive true on open collector with Q1 as pnp? Or does an open collector require the negative-true logic?

 

[AnalogKid]

Hi ak, how can we keep have positive true on open collector with Q1 as pnp? Or does an open collector require the negative-true logic?

It doesn't require negative-true, but that is the traditional mode because the only active element pulls down. There is nothing preventing an NPN open collector output being positive-true, but you will have to make sure the pull up resistor is somewhere. Note that the pull up resistor can be to any voltage the transistor can withstand; it is not limited to the Vcc value of the driving circuit.

ak

 

[AnalogKid]

Try this.

ak

 

[earckens]

Try this.

ak
View attachment 106205

Analogkid, I had been chewing on a decent answer to your post #63 and you send me #64: a big thank you! Yes, that will do it. I have learned a lot during this thread.

Meanwhile I have been mulling on another circuit, for LDR sensors but that is part of another topic.

Grts
Erik